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B2B

Stands for business-to-business and refers to e-commerce between different companies that have some sort of partnering arrangement, in contrast to B2C, or business-to-consumer, relationships in which individuals or companies purchase the products or services of another company.

Overview

Companies traditionally negotiate special business relationships with other companies that can provide them with the raw materials, tools, and services that they need for the success of their businesses. Such relationships are known as a value chain, which typically includes activities such as obtaining raw materials, processing these materials into finished products, shipping products to distributors, servicing customers, and marketing. To support a value chain, several business activities are essential, including procurement, research and development, manufacturing, and managing of human resources, operations, finances, and customer needs.

B2B is basically the use of the Internet to streamline and automate these business processes to enhance the value chain. This can result in streamlined business- cycle processes that are faster-to-market and in substantial cost savings by eliminating traditional paper-based invoicing and communications used in procurement channels. B2B can benefit companies in many different scenarios, including corporate purchasing, supply chain trading, and direct marketing.

Architecture

The technologies at the heart of B2B are the Internet, virtual private networks (VPNs) and Extensible Markup Language (XML). The Internet now provides a ubiquitous communications infrastructure that allows companies anywhere to connect with each other for exchange of business information. This can be accomplished through a variety of means, including leased lines, xDSL, dial-up modem connections, and wireless satellite links. Just as the existing public switched telephone network (PSTN) catalyzed the explosive growth of fax technology after it was introduced, the Internet is revolutionizing the way business partners communicate to buy and sell goods and services.

VPNs are a popular technology that is widely used to secure communications over the Internet. Without the Internet itself, business partners would have to purchase costly leased lines for secure, reliable electronic communications between them, and many companies still use leased lines to support their Electronic Data Interchange (EDI) platforms. Using VPNs, however, companies can send these communications securely over the public Internet, allowing them to reduce costs by eliminating leased lines in favor of better-positioned technologies such as xDSL.

XML is a third component of most emerging B2B solutions platforms, as it provides a standardized way of encoding business communications for transmission over the Internet.

In addition to these technologies, other elements of successful B2B relationships include establishing credit relationships between companies and building B2B technology into legacy systems.

An emerging standard that may help promote B2B overall is an initiative from Ariba, Microsoft, and IBM called Universal Description, Discovery, and Integration (UDDI). UDDI is a proposed directory service that will make it easier for companies to find business partners that offer specific types of goods and services.

Implementation

You can implement B2B in three basic ways: build a custom solution, buy a packaged solution, or lease services from an online marketplace.

Building a custom B2B solution in conjunction with business partners is an approach that is often taken by large companies that require custom solutions that are integrated deeply into their existing legacy business systems and that have pockets deep enough to implement this type of solution. The disadvantage is the longer time-to-market period required for realizing benefits from this solution, and with the rapidly changing Internet economy this is a concern that needs to be seriously addressed by enterprise e-implementers. B2B solution providers pursuing this market segment are basically pursuing a vertical market in which they will handle a small number of large clients with extensive integration needs.

Buying an off-the-shelf B2B solution is another approach that can take several forms, from purchasing and deploying a software platform for developing B2B solutions such as Microsoft BizTalk Server to hiring a B2B consulting company to implement its own off-the- shelf solution. This approach is often taken by mid- sized companies with reduced capital availability and limited IT (information technology) resources, and especially so by dot-com startups seeking rapid time-to- market. A startup company might outsource all of their procurement needs to a B2B consulting service that will implement a packaged Web-based system for procurement and supply-chain management for them.

Leasing services from an existing B2B exchange is a third solution. Numerous online marketplaces supply B2B services for narrowly targeted market segments such as the food industry and the plastics industry. These B2B exchanges (or online marketplaces) provide packaged B2B solutions that include online catalog publishing services, secure transactions, direct marketing, and related services. An example is the food industry, where a B2B exchange can help grocery store chains manage procurement and speedy delivery of perishable goods.

A B2B exchange with a specific industry focus such as this is often called an Industry-Sponsored Marketplace (ISM), and a B2B solution provider with a more general focus of providing packaged B2B solutions for small-sized or mid-sized companies is generally referred to as a "pure player." These providers are competing in a horizontal market-that is, trying to gain as many customers as they can-and most first-generation B2B marketplaces took this approach to growing their ventures. Many of them provide B2B services on a transaction-fee basis, though there's movement away from this model toward flat-rate pricing that makes B2B costs more predictable for clients.

B2B exchanges come in all flavors, from online shopping portals such as the healthcare industry portal PointStore, to industry-partnered ventures in which several companies form a cooperative exchange such as Hyatt International Corporation and Marriott International's Avendra marketplace for the hospitality industry, to pure-play independent B2B exchanges such as Chemdex for the chemical industry built on B2B software from Commerce One and Ariba. Of these different approaches, the most successful ventures are generally the cooperatives in which the narrow industry focus and high alignment with partner needs generate the best results.

Marketplace

Commerce One and Ariba are two major players in the B2B marketplace arena, and between them they have more than 500 corporate customers. Ariba has partnered with IBM and i2 Technologies to provide software and services, and Commerce One has done the same with SAP AG.

Some of the bigger players in the ISM market include

Companies that provide full-featured packaged B2B platforms include Ironside Technologies, Yantra Corporation, and many others.

Prospects

The future of the emerging B2B market overall is probably bright despite the shakeout of many startups that occurred in 2001. Many early proponents followed the horizontal market strategy of building one-size-fits-all B2B exchanges and then trying to attract customers along the "build it and they will come" paradigm. Unfortunately, most larger companies have legacy business systems that require a great deal of customization to participate effectively in B2B, and, as a result, most public B2B exchanges attracted only small and mid-sized companies whose resources were limited.

The main issues that tend to make many companies slow to jump on the bandwagon of public B2B exchanges are the unpredictable costs of transaction-based fees for involvement in these marketplaces, the complexity of integrating B2B solutions into existing supply chain systems (especially for companies that have progressed little in developing Web-based intranet and extranet solutions for their businesses), and issues relating to branding and customer loyalty that make suppliers reluctant to offer their wares at cut-rate prices in the new online marketplaces. As a result, successful B2B exchanges tend to be those that can build community-that is, a group of buyers and sellers loyal to one another. Private exchanges (those built upon preexisting business relationships) thus tend to fare well but offer few avenues for market growth for suppliers involved, and public exchanges offer a way of helping suppliers find new markets and new customers.

Another issue that has restrained many from the wholesale plunge into B2B is the snake-oil syndrome: new technologies breed startups that offer end-to-end solutions that are ready to implement "yesterday." Due diligence is required of companies contemplating aligning themselves with a B2B solution or platform, and decision-makers should obtain financials and customer testimonials to avoid getting caught in the web of fly-by-night operations that are here today and gone tomorrow.

With the failure of numerous public B2B marketplaces, companies that were early adopters are taking a more cautious view of further involvement, so that while recognizing the need to pursue B2B solutions in order to compete in the future economy, they are now more effectively taking care in investigating the financial viability of exchanges before jumping on board again. Nevertheless, while getting your company involved with a specific B2B provider is a tactical solution that requires good thought and due diligence, getting your company involved generally in B2B solutions is a strategic requirement for any company that hopes to survive in the Internet economy that is here and yet to come.

Notes

Microsoft Corporation has its own internal B2B solution called the Microsoft Market, which allows employees to quickly and easily procure goods and services from a wide variety of partner businesses. Microsoft Market has enabled Microsoft to lower average procurement costs by more than 90 percent.

Many B2B marketplaces provide procurement services based on either forward (sell-side) auctions which benefit suppliers or reverse (buy-side) auctions in which buyers submit a Request for Quotation (RFQ) and wait for the lowest bid to come in from suppliers. These services have not been as successful as anticipated, however, mainly because companies generally negotiate trusted long-term contractual business relationships with partners rather than just bid for the best-priced solution.

See Also BizTalk Server 2000 ,Commerce Server 2000 ,Digital Subscriber Line (DSL) ,electronic data interchange (EDI) ,Microsoft Market ,Universal Description,Discovery,and Integration (UDDI),virtual private network (VPN)

B2C

Stands for business-to-consumer, relationships in which individuals or companies purchase the products or services of another company.

See Also B2B

backbone

The portion of a network that ties different departmental networks into a single whole.

Overview

Backbones are primarily used in medium to large networks, such as those occupying a building or a group of buildings on a campus. The backbone carries the bulk of the network traffic and must be designed accordingly. Backbone designs generally fall into two basic categories:

Distributed backbones generally have a greater degree of fault tolerance than collapsed ones, because the collapsed backbone unit forms a single point of failure. However, collapsed backbones usually have better traffic flow than distributed backbones because of the underlying star topology. Collapsed backbones generally offer better performance because of the reduced number of hops that traffic must make when passing between departmental LANs. Collapsed backbones are also easier to manage because they bring all the backbone switching and routing equipment into a single room or building. Collapsed backbones are used frequently for connecting departmental LANs within a single building, but less often for connecting building LANs across a campus network because of the increased distances and cabling costs.

Backbone cabling should have the highest bandwidth of any cabling in your network, since backbones are used to join together hubs, switches, and routers, linking departmental LANs or subnetworks into building-wide or campus-wide internetworks. In buildings, backbone cabling often refers to the vertical cabling running through the risers or elevator shafts that connects the hubs and switches in each floor's wiring closet. Depending on performance requirements, anticipated growth, and cost, any of the following might be suitable for backbone cabling:

Notes

The term backbone is also used to refer to the collection of networking components (cabling, hubs, switches, and routers) that form the supporting network into which workgroup and departmental LANs are connected. A mesh topology is often used for network backbones to provide fault tolerance for critical high-speed data paths.

You should put considerable thought and planning into the design and implementation of your network's backbone, because the overall performance of networking services is largely dependent on the backbone's bandwidth and reliability. Design your backbone with network expansion in mind. Planning for growth is especially important if the cost of cable reinstallation is high. Fiber-optic cabling is preferred for most network backbones because of its high bandwidth, security, and resistance to electromagnetic interference.

See Also collapsed backbone

backboning

Sending messages between similar messaging systems by using an intermediate messaging system of a different type.

Overview

A simple backboning example is the connecting of two or more Lotus cc:Mail postoffices using a Microsoft Exchange Server organization as the messaging backbone. By installing the cc:Mail Connector on Exchange Server, messaging connectivity can be established with connected cc:Mail postoffices. Messages can then be routed from one postoffice through the Exchange organization to other postoffices on the network.

Another example of backboning is connecting different sites in an Exchange Server organization using a public or private messaging network. Here are two possible scenarios:

Backboning. Connecting similar messaging systems by backboning over a different messaging system.

When using a public messaging backbone (or a private one owned by a different company) for connecting your Exchange sites, you should consider the following:

For very large Exchange organizations, use a hub and spoke topology instead of a mesh topology. Hub and spoke topologies have less redundancy and fault tolerance, but mesh topologies have routing tables that grow exponentially with the number of sites involved. Mesh topologies for large organizations can lead to routing tables that are so large they degrade the performance of the message transfer agents, even on high-performance servers.

Notes

The term backboning is sometimes used to describe the core messaging paths set up for a large Exchange organization, regardless of whether messaging systems other than Exchange are involved.

See Also Exchange Server

background

A context for running applications or services on a computer.

Overview

A program that runs in the background is unnoticed while the user performs another task on a different program in the foreground. For example, a spreadsheet that calculates data could be hidden and running in the background while the user types a letter using a word processor program running in the foreground. If the user switches from the letter to the spreadsheet, the roles of the two programs become reversed.

Operating systems usually assign fewer CPU resources to background programs than to foreground ones. In Microsoft Windows 2000, Windows XP, and Windows .NET Server, the System utility in Control Panel offers you several Performance options on the Advanced tab for optimizing performance between background and foreground tasks:

In addition, you can tune or enhance performance by modifying the total paging file size on all drives.

BackOffice

A suite of integrated server products from Microsoft Corporation.

Overview

The Microsoft BackOffice suite of server products is built upon the foundation of the Microsoft Windows 2000 Server and Advanced Server platform and provides a scalable, reliable solution for the needs of departments, branch offices, and medium-sized businesses. BackOffice is provided in an integrated package called BackOffice Server 2000, which provides tools for building directory, networking, messaging, Web services, database, proxy and firewall services, and Systems Network Architecture (SNA) host integration infrastructures.

BackOffice Server 2000 includes the following Microsoft server products:

In addition, BackOffice Server 2000 offers a host of additional tools for deploying and managing BackOffice components such as BackOffice Server management consoles, various wizards, reporting tools, and Microsoft FrontPage and Microsoft Outlook client software. For additional information on each of the server applications listed above, see their respective articles elsewhere in this book.

For More Information

Visit the BackOffice site at www.microsoft.com/backoffice.

See Also Small Business Server

BackOffice Server

A suite of integrated server products from Microsoft Corporation.

See Also BackOffice

Back Orifice

A remote administration tool for Microsoft Windows developed by the hacker group Cult of the Dead Cow.

Overview

Back Orifice was first released for the Microsoft Windows NT platform in 1997 by Cult of the Dead Cow (CDC), a professed hacker group. Although the tool is basically a form of Trojan horse that can be used to gain control of a target machine, it is also a full-featured remote administration system for computers that run Windows NT and Windows 2000.

Back Orifice consists of two parts:

Back Orifice is a powerful remote administration tool, but because of its stealth features it is also a serious threat to systems running Windows NT and Windows 2000. Administrators who are concerned about this threat should consult article Q237280 in the Knowledge Base on Microsoft TechNet, which explains how to detect when the server component of Back Orifice is present on a system and how to remove it.

For More Information

You can find Back Orifice 2000 at www. cultdeadcow.comMicrosoft TechNet can be found at www.microsoft.com/technet.

See Also virus

backup

The process of making reliable copies of important data so that the data can be recovered in the event of a disaster.

Overview

Performing regular backups is perhaps the system or network administrator's least glamorous but most important task. Data loss on a corporate network can occur for various reasons, including

In each of these scenarios, having reliable backups of your company data is essential to recover from the disaster and continue normal business functioning.

Backup. Network and LAN-free backup scenarios in the enterprise.

At the enterprise level, backups can be performed using a variety of technologies, each of which have their own advantages. These technologies are a blend of backup device hardware and how these devices are implemented. The next section of this article looks at a few common scenarios. First, backup solutions can be characterized by the devices used to store the backed-up data. These devices can include

Besides these different backup devices, there are also various ways of implementing them for backing up data from network servers:

Finally, a third component of a backup system is the backup software itself. Some of the more popular backup software products used in the enterprise include

Implementation

Instituting a regular backup plan is one of the main components of a company's disaster recovery policy (see the article "disaster recovery" elsewhere in this book for more information), and the importance of doing so cannot be stressed enough. To guard against these unexpected losses of data-or rather, to prepare for them, since they are, to a certain extent, inevitable-establish a disaster recovery policy that includes a reliable backup plan. In today's business world, where data is the lifeblood of the enterprise, a comprehensive plan is essential. The following steps are recommended when creating such a plan:

Notes

To enable administrators to perform regular backups, Microsoft Corporation includes backup utilities with all versions of Microsoft Windows, such as the Backup tool in Windows XP.

See Also backup strategy ,backup type storage over IP, storage service provider (SSP), tape drive, tape format, tape library

backup agent

A service that can be installed on a computer to allow files and folders stored on the computer to be backed up remotely over the network.

Overview

Backup agents enable backups to be performed across an entire network from a centralized location. In networks that utilize this type of storage retention architecture, where a backup agent is installed on each server, files are backed up over the network to a central storage location, which in enterprise environments is usually a tape library or some type of Network Attached Storage (NAS). This approach to backups makes it easier to manage enterprise storage requirements even for large scale corporate networks and Internet service providers (ISPs).

Backup agents are specific to the type of backup software being used and are usually supplied with that software when you purchase it from a vendor. Once an agent is installed on a computer, you can back it up over the network as easily as if a tape drive were connected directly to the computer.

See Also backup

backup browser

A Windows 2000, Windows XP, and Windows .NET Server computer that participates in the Computer Browser service.

Overview

A backup browser is a computer that obtains a copy of the browse list from the master browser. The browse list contains information about which shared resources are available to client machines on the network and about which domains are on the network. Backup browsers automatically contact the master browser every 12 minutes to request a copy of the browse list. If the contact is successful, the master browser issues the list to the backup browser. If the backup browser cannot contact the master browser, it starts a browser election to force a new master browser to be selected.

Once the backup browser has obtained the browse list, it caches the list and distributes it to any client that requests it. To request the browse list from a backup browser, a client calls the NetServerEnum application programming interface (API) on the backup browser.

Backup browser. How a client obtains the browse list from a backup browser.

Notes

There will be one backup browser for every 32 systems in a given domain or workgroup on the network. The Computer Browser service determines the number of backup browsers necessary to ensure that clients can have efficient access to network resources.

See Also Computer Browser service ,domain master browser ,master browser

backup catalog

A representation of the results of performing a backup of servers on a network.

Overview

Backup software, such as the Backup tool in Microsoft Windows 2000, Windows XP, and Windows .NET Server, creates catalogs so that the location and properties of backed-up files are documented and can be found easily when a restore needs to be performed. Windows 2000, Windows XP, and Windows .NET Server Backup stores its catalogs on the backup storage media themselves. These catalogs are then loaded into memory when the program is run. Catalogs can also be saved to disk and printed for documentation purposes.

Windows 2000, Windows XP, and Windows .NET Server Backup creates two different types of backup catalogs:

See Also backup set

backup domain controller (BDC)

A Microsoft Windows NT domain controller containing a read-only copy of the Security Accounts Manager (SAM) database.

Overview

On the Windows NT platform, the only writable copy of the SAM database is located on the primary domain controller (PDC). In addition to this PDC, a Windows NT domain can have zero or more backup domain controllers (BDCs) as well. These BDCs are used to provide load balancing and redundancy for network authentication. These BDCs periodically undergo directory synchronization with the PDC by retrieving a copy of the directory database from the PDC.

Backup domain controller (BDC). Different ways to deploy a BDC over a WAN link.

Every Windows NT network should have at least one BDC for fault tolerance. If the PDC fails, the BDC can be promoted to take its place. One BDC can support approximately 2000 users on a network, but many factors can affect this figure.

Note that a BDC can perform logon validation and authentication as a PDC can, but it cannot manage accounts-for example, it cannot change user passwords.

Implementation

The placement of BDCs in wide area networks (WANs) that are based on Windows NT is an important issue. In a master domain model scenario, user accounts are centralized in a master domain located at company headquarters, but users and shared network resources are distributed in resource domains located at branch offices in different locations. The users in this scenario must log on to the master domain in order to access resources in the enterprise. There are two ways of facilitating this:

See Also domain controller ,primary domain controller (PDC)

Backup Operator

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a user who is assigned the responsibility of backing up and restoring servers on a network.

Overview

To make an individual a Backup Operator, simply make him a member of the Backup Operators group. Backup Operators can exist on Windows NT domain controllers, on member servers, and on workstations. In Windows 2000, Windows XP, and Windows .NET Server, Backup Operators are members who have a similar function and belong to the built-in group called the Backup Operators built-in group.

Backup Operators have the preassigned right to log on locally to a computer and to back up and restore files and directories on the system. Backup Operators also have the right to shut down the system. Backup Operators do not need permissions assigned to them in order to back up a particular file or directory-they have a broad system right to do so.

Notes

Backup Operators should be assigned only in enterprise-level networking environments. In small to medium-sized networking environments, backing up and restoring servers is usually the responsibility of the administrator.

See Also Backup Operators built-in group ,built-in group

Backup Operators built-in group

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a built-in group for containing users who need privileges to back up servers on the network.

Overview

Backup Operators is a built-in group existing on all Windows 2000-, Windows XP-, and Windows .NET Server-based servers and workstations. The Backup Operators built-in group is a local group with the following preassigned rights:

Notes

If you want a user to be able to back up files and directories on any domain controller in a domain, place the user in the Backup Operators group on any domain controller. Since all domain controllers share the same directory database, the user will be a member of the Backup Operators built-in group for all domain controllers. However, if you want a user to be able to back up a member server, place the user in the Backup Operators built-in group that is a local group on that particular member server.

See Also built-in group

backup set

A collection of files and folders on a backup media that were saved in a single Microsoft Windows 2000, Windows XP, and Windows .NET Server Backup operation.

Overview

There are several options for creating backup sets in Windows 2000, Windows XP, and Windows .NET Server:

Windows 2000, Windows XP, and Windows .NET Server Backup creates a backup set catalog for each backup set. This catalog lists the various files and directories that have been backed up, and you can use it for restoring individual files or directories or print it for documentation purposes. The backup set catalog is saved at the end of each backup set on the tape. A backup set map at the end of the tape locates all backup sets on the tape.

Notes

A copy of the local system's registry can also be included in the backup set for a Windows 2000, Windows XP, and Windows .NET Server system. Backup sets are described with friendly names that can be up to 32 characters long.

See Also backup catalog

backup strategy

A plan for performing backups to ensure against data loss.

Overview

Successful backup strategies take the following issues into account:

There's no one right way to implement a backup strategy for resources on a network of computers. To select the best backup strategy for your network, you must consider each of the items in the preceding list and balance them against one another. Your strategy should be simple, efficient, and reliable. The following table shows some examples of backup strategies:

Possible Backup Strategies

Backup Strategy

Advantages

Disadvantages

Normal backups Monday through Friday.

Most secure-every tape contains all backed up files

Longest time to back up

Normal backup Monday; differential backups Tuesday through Friday.

Less time to restore

More time to back up

Normal backup Monday; incremental backups Tuesday through Friday.

Less time to back up

More time to restore

Use a separate tape for each weekday and archive Monday's full backup tape weekly or monthly.

Less chance of data loss

Higher cost, since more tapes are needed

Use the same tape for each weekday and archive the tape each week or month.

Cheaper- only one tape required per week or month

Greater chance of data loss, since using only one tape

See Also backup ,backup type

backup type

A particular method for performing a backup of files and directories.

Overview

Each type of backup has a different function in an overall backup plan. Most network backup software (such as Microsoft Windows 2000, Windows XP, and Windows .NET Server Backup) supports five backup methods:

Notes

Different types of backup operations have different effects on the archive attributes of the files and directories they back up. A backup operation marks the archive attribute by clearing it to indicate that the file has been backed up. If the file is later modified in some way, its archive attribute is set (unmarked). The following table shows what each type of backup operation does to the archive attribute.

Effects of Backup Operations on the Archive Attribute

Backup Type

Archive Attribute

Normal

Cleared

Copy

No effect

Incremental

Cleared

Differential

No effect

Daily copy

No effect

See Also backup ,backup strategy

Backup Wizard

A wizard that is part of the Microsoft Windows 2000, Windows XP, and Windows .NET Server Backup tool.

Overview

You can use the Backup Wizard to configure, schedule, and execute a backup. The Backup Wizard starts by letting you choose among the following:

The wizard then leads you through the process of specifying a backup location and other advanced backup options, such as verification, compression, and remote storage. You can also schedule a backup job to run unattended at a later time when users have stopped working and all files are closed.

See Also backup

BACP

Stands for Bandwidth Allocation Control Protocol, an enhanced version of Bandwidth Allocation Protocol (BAP), a protocol that manages bandwidth for Multilink Point-to-Point Protocol (MPPP) connections.

See Also Bandwidth Allocation Control Protocol (BACP)

balanced line

An electrical cable consisting of pairs of conductors that have identical electrical characteristics with respect to each other and with respect to ground.

Overview

In a balanced line, both of the two wires are carrying current at any given instant. However, at any particular moment, the directions of the current in the wires are opposite each other. This condition is also described by saying that the currents in the wires are 180 degrees out of phase with each other at any given moment.

Both wires have voltages that are above ground potential, but the potentials of the wires are different with respect to ground, resulting in a flow of current. The wire pair is twisted in order to ensure that the electromagnetic radiation produced by both wires is effectively canceled out, reducing the overall electromagnetic interference (EMI) produced by the wires and reducing their sensitivity to induced currents from external sources of EMI.

The most common example in computer networking is the twisted-pair cabling used in 10BaseT Ethernet networks.

Notes

A balun can be used to connect a balanced line to an unbalanced line.

See Also balun ,unbalanced line

balun

Stands for balanced unbalanced, a device used to connect balanced lines and unbalanced lines.

Overview

Balanced and unbalanced lines have different electrical characteristics that prevent them from simply being connected to each other. A balun matches these different characteristics by providing impedance transformation between the two different lines.

Balun. An example of a coxial-to-twisted-pair balun.

Baluns can be used for various types of connections between different wiring systems:

See Also balanced line ,unbalanced line

bandwidth

The information-carrying capacity of a signal or technology.

Overview

By definition, bandwidth equals the difference between the highest and lowest frequencies in a given range of frequencies. For example, if the lowest and highest frequencies a telephone line can carry are 300 hertz (Hz) and 3300 Hz, the bandwidth of the telephone line is 3300 - 300 = 3000 Hz, or 3 kilohertz (kHz).

The above definition of bandwidth applies to any signaling system, analog or digital. With digital systems such as computer data networks, the term bandwidth is often used to describe the capacity of a communication channel for carrying signals. The greater the bandwidth, the more data can be transferred in a given time. Since bandwidth is here synonymous with information, and digital information is conveyed in bits (1=on and 0=off), bandwidth for such systems is usually expressed in bits per second (bps) or some multiple thereof (including Kbps, Mbps, Gbps, and Tbps). This rate of flow of information in bits per second is more properly termed "throughput," but bandwidth is the usual expression used in popular literature.

Shannon's Law can be used to determine the information-carrying capacity of a transmission channel as follows:

(Throughput in bps) = (Bandwidth in Hz) x log2 [1 + R]

where

R = (Signal power in Watts) / (Noise power in Watts)

This formula is only approximate since it does not take into account the medium's transmission properties and other considerations. The significant thing to notice, however, is that as noise (due to crosstalk, interference, or some other source) increases, the channel's capacity to carry information decreases.

For fiber-optic cabling, the bandwidth is usually expressed in units of MHz-km. For example, a cable rated at 500 MHz-km could carry 500 Mbps of data a distance of 1 kilometer (km), 250 Mbps of data a distance of 2 kilometers, 100 Mbps of data a distance of 5 kilometers, and so on. A similar explanation holds for measurements in units of MHz-miles.

Notes

Adequate bandwidth is a prerequisite for reliable communications, and ensuring sufficient bandwidth in today's Internet economy often drives upgrades for enterprise networks. When a new bandwidth need arises, such as deployment of streaming media across a network, the obvious solution may seem to be to "throw bandwidth at the problem," that is, to spend money on upgrading the network infrastructure from Ethernet to Fast Ethernet to Gigabit Ethernet (GbE) and beyond. This is really only one solution-another, sometimes better, approach is to implement Quality of Service (QoS) mechanisms to prioritize traffic so that certain forms of traffic receive preferential transport over less important forms. QoS is an elegant solution that sidesteps the brute-force approach of simply adding more bandwidth, but QoS can be difficult to configure and manage. Although Asynchronous Transport Mode (ATM) networks have the advantage of having QoS built into their operational fabric, the far more common Ethernet networks require new protocols such as DiffServ and Resource Reservation Setup Protocol (RSVP) to be implemented to support even rudimentary QoS features. And with the rapidly dropping prices of GbE switching gear and the appearance of 10 GbE on the horizon, simply adding more bandwidth when it is needed is still the most common solution for most large companies.

See Also quality of service (QoS) ,signaling

Bandwidth Allocation Control Protocol (BACP)

An enhanced version of Bandwidth Allocation Protocol (BAP), a protocol that manages bandwidth for Multilink Point-to-Point Protocol (MPPP) connections.

Overview

Although BAP dynamically controls how bandwidth can be allocated for Multilink Point-to-Point Protocol (MPPP) connections, a condition can sometimes occur in which both hosts at the two ends of a MPPP connection try to add or remove an additional link at the same time. The Bandwidth Allocation Control Protocol (BACP) is an enhanced version of BAP that is designed to handle such a scenario. It does this by establishing ahead of time which MPPP host is the favored peer, that is, the one whose BAP request will be honored in case of a collision of two requests.

See Also Bandwidth Allocation Protocol (BAP) ,Multilink Point-to-Point Protocol (MPPP)

Bandwidth Allocation Protocol (BAP)

An offshoot of Multilink Point-to-Point Protocol (MPPP) that allows new links to be added or removed dynamically when needed.

Overview

The Bandwidth Allocation Protocol (BAP) dynamically controls how bandwidth can be allocated for multilink connections using the Point-to-Point Protocol (PPP). BAP makes multilink remote access (RAS) connections more efficient by allocating lines only as required, thus eliminating wasted bandwidth. This can be especially useful if the telecommunications carrier provisioning the PPP connection charges by the amount of bandwidth being utilized by the customer.

BAP allows the administrator to configure the PPP server to specify which particular MPPP lines can be added or dropped. The administrator also specifies which bandwidth thresholds must be crossed before additional lines are added or existing ones are dropped. BAP is especially useful over Integrated Services Digital Network (ISDN) connections, because these dial-up services can almost instantly add or drop lines.

Notes

BAP is included in Microsoft Windows 2000 and Windows .NET Server as an enhancement to the Routing and Remote Access Service (RRAS) of Windows NT 4. BAP is outlined in detail in RFC 2125.

See Also Bandwidth Allocation Protocol (BAP) ,Multilink Point-to-Point Protocol (MPPP)

bandwidth on demand

Any networking or telecommunications technology that provides both a permanent, dedicated connection and the capability of quickly increasing bandwidth when needed by users.

Overview

Many telecommunications devices incorporate bandwidth-on-demand features of various types. For example, some Integrated Services Digital Network (ISDN) devices used for Basic Rate Interface ISDN (BRI-ISDN) can be configured to use the second ISDN B channel only when the utilization of the first channel exceeds a certain threshold. If this threshold is exceeded for a specified period of time, the second B channel automatically opens up to facilitate and speed data transfer. Once the data rate has dropped below the threshold, the second B channel shuts down until it is needed again. The ISDN technology for accomplishing this combining of channels is called bonding. Many Asynchronous Transfer Mode (ATM) products also support various bandwidth-on-demand features.

Bandwidth-on-demand technologies are typically used in bursty networking situations in which high transmission speeds and capacities are required for transporting video, voice, and data on common networking circuits. Bandwidth-on-demand configurations often involve a mix of leased-line services and circuit-switched telecommunications services, and they can save users money by opening additional circuits only on an as-needed basis. Networks that make use of bandwidth on demand can be designed to supply additional bandwidth under conditions such as

See Also Asynchronous Transfer Mode (ATM), bandwidth, Integrated Services Digital Network (ISDN)

bandwidth throttling

Generally, any networking technology that controls the amount of network bandwidth used by servers, applications, or network communication paths.

Overview

In the context of Microsoft Internet Information Services (IIS), for example, bandwidth throttling is a technique for controlling the amount of network bandwidth used by individual Web sites hosted on the server. You can use bandwidth throttling to prevent hits on a popular site from overwhelming the server and preventing other sites hosted on the server from being accessed by clients.

For example, if five Web sites are being hosted on a single machine running IIS but one of them is extremely popular, the other sites might get starved for bandwidth and users might have difficulty connecting to them. In order to rectify this situation, a specific maximum bandwidth level can be allocated to the popular site with the Internet Services Manager snap-in used for administering IIS using the Microsoft Management Console (MMC). If this maximum bandwidth is exceeded, no further connections to that site are allowed until the bandwidth utilization level drops below the threshold. This allows the unallocated bandwidth to be shared among the remaining less popular sites so that users can connect to them.

See Also bandwidth ,Internet Information Services (IIS)

Banyan VINES

Stands for Banyan Virtual Integrated Network Service (VINES), a legacy network operating system (NOS) for building enterprise-level networks.

Overview

VINES was originally based on a proprietary family of protocols that was derived from the Xerox Network Systems (XNS) protocol. VINES uses a client/server distributed networking architecture for allowing clients to access network resources on servers over the network. VINES includes such features as

VINES includes clients for MS-DOS, OS/2, Microsoft Windows, and Macintosh platforms as well as optional applications for integrating Windows NT, AppleTalk, Novell, and UNIX networks into existing VINES-based networks.

VINES is built on a client/server model in which clients can make requests for services from servers on the network. The VINES protocol stack consists of five basic layers that map to the seven-layer Open Systems Interconnection (OSI) reference model as follows:

Notes

When connecting Windows 95 or Windows 98 clients to a VINES-based network, use the 32-bit client for Windows that comes with VINES instead of the 16-bit VINES client included with Windows 95 and Windows 98.

For More Information

Visit the Banyan home page at www.banyan.com

BAP

Stands for Bandwidth Allocation Protocol, an offshoot of Multilink Point to Point Protocol (MPPP) that allows new links to be added or removed dynamically when needed.

See Also Bandwidth Allocation Protocol (BAP)

baseband transmission

A signaling technology that sends digital signals over a single frequency as discrete electrical pulses.

Overview

The entire bandwidth of a baseband system carries only one data signal and is generally less than the amount of bandwidth available on a broadband transmission system. The baseband signal is bidirectional so that a baseband system can transmit and receive signals simultaneously.

Baseband signals can be regenerated using repeaters in order to travel longer distances before weakening and becoming unusable because of attenuation. Baseband transmission technologies do not use modulation but often use time-division multiplexing (TDM) to accommodate multiple channels over a single baseband transmission line.

Common local area network (LAN) networking technologies such as Ethernet use baseband transmission technology. All stations on a baseband network share the same transmission medium, and they use the entire bandwidth of that medium for transmission. As a result, only one device on a baseband network can transmit at a given instant, resulting in the need for a media access control method to handle contention.

See Also broadband transmission ,Ethernet

baseline

A set of data that indicates normal usage of monitored network resources.

Overview

You can use the Microsoft Windows 2000, Windows XP, or Windows .NET Server Performance console to collect data for the present performance of your network to establish a baseline. Then, if you upgrade hardware or add new users, you can measure the network's performance again and compared it with the baseline to determine trends, identify bottlenecks, and measure capacity.

Creating a baseline for server and network activity begins with the process of identifying which server and network resources should be systematically measured. Generally, you always want to measure at least the following four resources: memory, processor, disk, and network subsystems. Using the Performance console, you should collect data for the objects shown in the following table.

Resources and Corresponding Performance Objects to Monitor Performance

Resource

Objects to Collect

Memory

Memory, cache

Processor

Processor, system, server work queues

Disk

Logical disk, physical disk

Network

Server, network interface, network segment

These performance objects should be regularly captured for a period of time in order to collect the data needed to establish the baseline. Generally, you should append each log file collected to a master log file using relogging. Focus on periods of peak server and network activity and collect at least a week of measurements to establish your baseline.

Notes

If you want to collect disk subsystem data, first enable disk objects using the Diskperf command. Make sure you use a computer that is not being monitored to create your measurement baseline log files so that the activity of the computer doing the monitoring will not affect the data being collected.

Basic authentication

Also called cleartext or plaintext authentication, an authentication scheme that passes a user's credentials over a network in unencrypted form.

Overview

Basic authentication is defined as part of the Hypertext Transfer Protocol (HTTP) version 1 specification in RFC2617. It is not a secure authentication scheme, since anyone who can intercept network traffic and read it using a protocol analyzer can obtain the user's credentials. Although it is sometimes called cleartext authentication, Basic authentication actually encodes a user's credentials using a well-known public encoding algorithm known as Uuencoding or Base64. Because the algorithm for this encoding method is so well known, however, it is easy to decode encoded text and extract a user's credentials from a Basic authentication session.

Implementation

Basic authentication is one of several authentication schemes available on Microsoft Internet Information Services (IIS) for the Microsoft Windows 2000, Windows XP, and Windows .NET Server platforms. When a user tries to access content on a Web site hosted on IIS and the site implements Basic authentication, a dialog box appears on the user's browser asking for the user's credentials (username and password). The credentials are passed to IIS in the headers of the HTTP GET request, and are compared either to credentials in Active Directory directory service (if implemented) or to the Security Accounts Manager (SAM) database (on a workgroup server). If Active Directory is used, the user's User Principal Name (UPN) can be utilized for authentication purposes. Users who need to be able to access IIS using Basic authentication require the Log On Locally system right (although this can be changed using Active Directory Services Interface, abbreviated ADSI).

The problem with employing Basic authentication is that it is inherently insecure because of the cleartext transmission of the user's password. However, IIS does allow Basic authentication to be implemented with Secure Sockets Layer (SSL) encryption, in which case an encrypted session is first established for the user after which the user's credentials are passed to IIS in encrypted form.

The plus side of Basic authentication is that it can be performed through a firewall or proxy server (Integrated Windows authentication or Windows NTLM cannot work in this case).

Notes

Basic authentication is often used in a UNIX environment for authenticating remote HTTP users.

If you employ Basic authentication with IIS, make sure you also use the NTFS file system (NTFS) to secure access to files on your system.

See Also authentication protocol

basic disk

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a physical disk that can contain primary partitions, extended partitions, and logical drives.

Overview

Basic disks can be accessed by MS-DOS and legacy Windows platforms and are backward-compatible with these platforms for multiboot systems. Basic disks can also contain volumes created using Windows NT version 4 or earlier, such as spanned volumes (volume sets), striped volumes (stripe sets), mirrored volumes (mirror sets), and RAID 5 volumes (stripe sets with parity).

Basic disks are the default type of disk in Windows 2000 and Windows XP. All disks are basic disks unless you convert them to dynamic disks. Basic disks can have two kinds of partitions:

Notes

You can create only basic volumes on basic disks. You cannot create new simple, spanned, striped, mirrored, or RAID 5 volumes on basic disks.

See Also basic volume ,dynamic disk

Basic Rate Interface ISDN (BRI-ISDN)

The slower version of Integrated Services Digital Network (ISDN) communications (the faster being Primary Rate Interface ISDN, abbreviated as PRI-ISDN).

Overview

Basic Rate Interface ISDN (BRI-ISDN, or simply BRI) communications links consist of two B channels and one D channel. The B channels carry the voice or data between the customer premises and the telco central office (CO), and the D channel (control channel) is used for establishing connections and signaling various conditions. BRI is often referred to as 2B+D because of the channels that it employs.

Since the bandwidth of each B channel is 64 kilobits per second (Kbps), the total bandwidth of BRI is twice that, or 128 Kbps. This bandwidth can be used as two separate communication links of 64 Kbps each (for example one for voice and the other for data), or it can be combined into a single 128-Kbps communication link using a technique called bonding. The bandwidth of the D channel is 16 Kbps.

Implementation

BRI connections at customer premises can be connected directly to a switch at the CO, an ISDN call controller that is linked to the CO, an ISDN Private Branch Exchange (PBX), or some other signaling and communication equipment.

If you plan to order a router or access server that supports BRI, make sure you find out from your telco of what kind of ISDN interface is used at your customer premises. The two most common interfaces are the U interface and the S/T interface, and they physically appear the same. Many ISDN access devices support both kinds of interfaces, but check to make sure first.

See Also bonding ,Integrated Services Digital Network (ISDN) ,Primary Rate Interface ISDN (PRI-ISDN)

basic volume

A type of volume in Microsoft Windows 2000, Windows XP, and Windows .NET Server that is compatible with earlier Windows operating systems.

Overview

A basic volume can be created only on a basic disk and can be

See Also basic disk ,dynamic volume

bastion host

A network server that is hardened against attack from the outside world.

Overview

Bastion hosts are servers exposed to the outside world and fortified to protect them from attack by hackers. Bastion hosts usually reside on the edge of your corporate network where it connects to the Internet, and often within a specific area called the perimeter network, also known as the DMZ (demilitarized zone), which forms a kind of transition network between your corporate network and the public Internet.

There are many different kinds of bastion hosts:

Managing a bastion host involves several activities:

Finally, it is essential to accept the fact that bastion hosts are likely to be compromised as new operating system and application bugs are reported and fixes issued by vendors. As a result, never put anything on a bastion host that you would mind losing or which is not available somewhere else. Accept the worst-your host will be compromised someday.

Notes

Some additional tips on deploying bastion hosts:

See Also firewall ,network security

batch commands

A special set of commands generally found only in batch files.

Overview

Although batch files can essentially contain any commands that can be executed at the command line, a special set of batch commands enable special actions to be performed such as jumps, terminal echoing, and conditional processing.

The table on the following page lists special batch commands that are found only in batch files. These commands are all supported by Microsoft Windows 2000, Windows XP, and Windows .NET Server, but earlier versions of Windows might support only a subset of them.

Batch File Commands

Command

Description

Call

Calls one batch program from another while allowing the calling program to continue running

Echo

Toggles command-echoing on or off

Endlocal

Restores environment variables set by a Setlocal command

For

Used to run a specified command for each file in a set of files

Goto

Jumps to a specific line that is labeled in a batch file

If

Used to perform conditional processing of commands

Pause

Suspends processing of the batch file and waits for the user to respond

Rem

Used to insert remarks (comments) in a batch file for documentation purposes

Setlocal

Initiates localization of environment variables in a batch file

Shift

Used to change the position of replaceable parameters in a batch file

See Also batch file ,Windows commands

batch file

Also called a batch program, an ASCII file containing a series of commands.

Overview

The commands within a batch file are executed sequentially when the file is invoked. Generally, any command that can be entered at the command line can be used within a batch file as well. You can execute batch files either at the command prompt, by associating a shortcut with them and double-clicking on the shortcut, or by invoking them in a logon script or through some other script or program.

Batch files are traditionally identified using the extension .bat or .cmd. Batch files trace their origins back to MS-DOS, with the Autoexec.bat file being the best- known example. While batch files are still used by many administrators for logon scripts, the advent of the Windows Script Host (WSH) in Microsoft Windows 98, Windows NT Option Pack, Windows 2000, Windows XP, and Windows .NET Server allows more powerful administrative scripts to now be written using higher- level scripting languages such as Microsoft Visual Basic Scripting Edition (VBScript) and JavaScript. As a consequence of the WSH, the old paradigm of batch files may finally be about to disappear.

Examples

Batch files are used primarily to simplify the execution of routine or repetitive administrative tasks such as mapping drives, synchronizing system clocks, or performing backups. For example, on a Windows NT-based network, to control the rate at which directory information is replicated between a backup domain controller (BDC) and a primary domain controller (PDC), you can create a batch file that will change the value of the ReplicationGovernor parameter on the BDC. To do this, first create a script that has the full path to this parameter in the registry along with the value you want to assign to it and then create the following simple batch file:

regini <Script_Name> net stop netlogon net start netlogon

Two different scripts and batch files can be created for different times of the day, and the At command can be used to schedule the execution of each batch file at the appropriate time. This illustration is especially useful if directory replication must occur over a slow wide area network (WAN) link, and you can use it to ensure that most replication traffic occurs during off hours.

See Also batch commands ,scripting ,Windows Script Host (WSH)

bCentral

An initiative from Microsoft Corporation to help small businesses get online by providing them with subscription-based services, tips and advice, technology consultants, and other aids.

Overview

Microsoft bCentral is designed to help small businesses get online so they can increase sales, improve their market share, and provide better services to customers. The bCentral initiative is an integral part of Microsoft's .NET strategy of providing software as a service to consumers and businesses.

Services available from bCentral include

In addition, bCentral services are available to any computer having a Web browser and an Internet connection, so you can manage your online business from anywhere using a laptop computer. Partnerships with companies such as Office Depot provide value-added services such as purchasing office equipment and supplies over the Internet from any location. Many bCentral services have free 30-day trial periods that allow businesses to test these services. Finally, bCentral helps you sell your company's products and services at MSN eShop and through an online auction site developed by Microsoft Corporation and FairMarket.

For More Information

You can find bCentral at www.bcentral.com

B channel

Stands for Bearer channel, a circuit-switched channel for carrying voice or data in Integrated Services Digital Network (ISDN) services.

Overview

Such channels are called Bearer channels because they "bear," or carry, the actual information being communicated between the customer premises and the telco's central office (CO). B channels are standard, bidirectional, digital telephone channels that can carry digital information at a rate of 64 kilobits per second (Kbps). Users with greater bandwidth needs can combine several B channels into larger data-carrying pipes. The two most common configurations are

Notes

B channels carry voice or data only, not signaling information. D channels carry information for establishment and control of ISDN connections.

See Also 802.10 ,Integrated Services Digital Network (ISDN)

BDC

Stands for backup domain controller, a Microsoft Windows NT domain controller containing a read- only copy of the Security Accounts Manager (SAM) database.

See Also backup domain controller (BDC)

beaconing

A technique used on token-passing networks for monitoring the status of the token-passing process.

Overview

Beaconing is used in Token Ring and Fiber Distributed Data Interface (FDDI) networks to ensure that token passing is functioning properly. On a token-passing network such as FDDI, every station is responsible for monitoring the status of the token-passing process. If a station detects that a fault has occurred, it starts placing beacons onto the ring. When the next station on the ring detects a beacon, it in turn starts placing beacons on the ring and the first station stops transmitting them. This process will continue until the station immediately upstream of the fault location is the only station sending beacons.

Beaconing enables administrators to quickly locate the fault and repair it. Once the fault is fixed, the station emitting the beacon detects its own beacon returning to it after traveling around the ring, and the station stops beaconing.

See Also Fiber Distributed Data Interface (FDDI) ,Token Ring

BEEP

Stands for Blocks Extensible Exchange Protocol, an emerging framework to replace Hypertext Transfer Protocol (HTTP) for transport of Extensible Markup Language (XML)-based information over the Internet.

See Also Blocks Extensible Exchange Protocol (BEEP)

benchmarking

Any systematic method for performing comparative measurements of computer hardware, operating systems, and their components and subsystems.

Overview

Benchmarking began as system attempts to compare the speed and power of hardware, operating systems, and applications that had similar functions. For example, an early comparison between Microsoft Word and Corel WordPerfect might have been to compare how quickly both applications could spell-check the same 100-page document. In the early days, vendors themselves often performed benchmarking to highlight the superior performance of their products in the marketplace.

To elevate benchmarking to something more consistent and reliable, independent nonprofit organizations have been formed to benchmark certain aspects of system and application behavior. Two of these organizations have achieved a high degree of credibility in the industry, namely Standard Performance Evaluation Corporation (SPEC) and the Transaction Processing Performance Council (TPC).

SPEC's goal is to establish a suite of standardized benchmarks for comparing the performance of computer systems. SPEC licenses its tools for use by vendors, who can publish and report the results on SPEC's Web site. An example is the SPEC CPU2000 benchmark for comparing performance of CPU subsystems, which replaces the popular, but now retired, SPEC CPU95 benchmark.

TPC's goal is to develop standard benchmarking tools and procedures for comparing transactional processing between different database products. A transaction is a form of business action performed by a computer system-for example, an online purchase or sale. Database transactions include inventory control, books, account updates, and similar procedures. TPC benchmarks such as TPC-C for Online Transactional Processing (OLTP) and TCP-W for Web-based e-commerce transactions attempt to mirror real-world transaction processing to compare the performance of database systems from different vendors.

Another popular set of benchmarks are those of media company ZDNet, which has developed its set of Winbench and Winstone benchmarks for compar- ison of business and consumer computer systems and peripherals.

The main difficulty with most benchmarking systems is interpreting them. While trying to mirror real-world effects, benchmarks nevertheless operate under idealized conditions in which certain variables are controlled and others are changed to study the results. The challenge continues to be to develop reliable independent benchmarks that will test significant components of complex real-world systems while maintaining fairness and vendor-neutrality.

For More Information

You can find SPEC at www.spec.orgTPC can be found at www.tpc.orgZDNet can be found at www.zdnet.com

BeOS

Stands for Be Operating System, an operating system especially developed as a high-performance platform for multimedia applications.

Overview

BeOS was developed by Be, a company founded in 1991 by Jean-Louis Gass e, a former president of Apple Computer's product division. The first version of BeOS became available in 1995, and the current release is version 5.

BeOS is a preemptive multitasking operating system that incorporates pervasive multithreading in which every application has at least two threads, one for application logic and one for the user interface. BeOS also supports eight-way symmetric multiprocessing (SMP). BeOS also includes a 64-bit journaling file system that supports 18 petabytes of direct storage, protected memory, and a Portable Operating System Interface for UNIX (POSIX)-compliant subsystem.

BeOS has an object-oriented set of application programming interfaces (APIs) that are optimized for real-time digital multimedia and communication functions. Because of this, BeOS is sometimes called a "media OS" to emphasize its high-performance multimedia capabilities.

BeOS runs on Intel-based platforms and certain PowerPC-based hardware, and it includes basic Transmission Control Protocol/Internet Protocol (TCP/IP) support and services. On a PowerPC, you can even run the MacOS as a shell within the BeOS desktop interface.

A lightweight version of BeOS called BeIA (Be Internet Appliance) is also being developed for Internet appliances and similar devices.

For More Information

Visit the Be home page at www.be.com

BER

Stands for Bit Error Rate, a measurement of the reliability of a networking architecture or device.

See Also Bit Error Rate (BER)

Berkeley Internet Name Domain (BIND)

A popular software tool for administering and maintaining the Domain Name System (DNS) on UNIX platforms.

Overview

Berkeley Internet Name Domain (BIND) was originally written for 4.3BSD UNIX and replaced an earlier domain naming system called JEEVES. BIND is now maintained by the Internet Software Consortium (ISC) and its current major version is BIND 9.

Because most versions of UNIX include some sort of BIND with their distributions and a majority of Internet Service Providers (ISPs) still use the UNIX platform for much of their operations, BIND is still the most popular DNS server on the Internet. BIND is also freely distributed by the ISC and is available for AIX, HP-UX, Irix, Solaris, SunOS, and other operating systems such as Linux and Windows NT.

Notes

The DNS Server services of Microsoft Windows 2000 and Windows .NET Server are Request for Comments (RFC)-compliant implementations of DNS and are fully compatible with BIND. Active Directory directory service can also use BIND as its DNS naming service, provided BIND 8.1.2 or later is used. If you choose to use BIND with Active Directory, make sure you disable name checking on your BIND server because Active Directory uses the underscore character in its SRV records and BIND name checking flags this character as an illegal character.

For More Information

Visit the Internet Software Consortium at www.isc.org

See Also Active Directory ,Domain Name System (DNS) ,Internet ,UNIX

BERT

Stands for Bit/Block Error Rate Tester, a device used to troubleshoot serial lines.

See Also Bit/Block Error Rate Tester (BERT)

best effort

Used to describe network communications in which delivery of data is not guaranteed.

Overview

Routable internetworking protocols such as Internet Protocol (IP) and Internetwork Packet Exchange (IPX) use best effort delivery based on datagrams. In other words, delivery of data by these protocols is not guaranteed. The reason is that these protocols are connectionless in operation, and acknowledgements are not returned as they pass from one hop to the next across a routed internetwork.

An example where communications may fail is what is called a "black hole." In this situation, a failed router drops packets it is supposed to forward, and the station from which the packets originated is unaware that these packets never reached their destination.

See Also black hole ,Internet Protocol (IP) ,routing

BGP

Stands for Border Gateway Protocol, an exterior routing protocol used on the Internet to provide loop-free routing between different autonomous systems (ASs).

See Also Border Gateway Protocol (BGP)

Binary Runtime Environment for Wireless (BREW)

A platform from QUALCOMM for developing applications for cellular communications systems.

Overview

Binary Runtime Environment for Wireless (BREW) was developed by QUALCOMM as an alternative to Java 2 Micro Edition (J2ME) from Sun Microsystems. Although both platforms enable downloading of applications over wireless phones, BREW has been designed from the ground up to work effectively in the cellular environment and J2ME is a general-purpose developer environment for small devices. BREW's main disadvantage is that it was designed with QUALCOMM's Code Division Multiple Access (CDMA) cellular technology in mind, but J2ME is device- and technology-independent.

A number of companies have committed to building products and services that use BREW, including Wireless Knowledge and Visto Corp.

For More Information

Find out more about BREW at QUALCOMM's Web site at www.qualcomm.com/brew.

See Also cellular communications

Binary Tulloch Transport Protocol (BTTP)

A draft specification for a routing protocol to save the Internet from its projected meltdown on or around April 1, 2003.

Overview

Because of the proliferation of Autonomous System Numbers (ASNs) used to identify internetworks connected to the Internet and due to the limited pool of possible ASNs, which is quickly drying up, analysts predict that no more ASNs will be available on or around April 1, 2003. At that point the Internet is expected to collapse.

A proposed solution soon to be presented to the Internet Engineering Task Force (IETF) is the Binary Tulloch Transport Protocol (BTTP). BTTP addresses the underlying issue of ASNs running out by assigning a binary flag (1=on and 0=off) to each ASN, allowing half the ASNs connected to the Internet to be temporarily revoked while the other half remain available at any given time. The protocol switches ASNs between these two states at a frequency of 1000 times per second; in other words, autonomous systems are online one millisecond and off the next, effectively reducing the size of the Internet by half at any given moment and thus giving room for several more years of expansion and growth of the Internet before the problem becomes critical again. Since the average latency for establishing Internet connections is around 20 milliseconds for wired connections (and several hundred milliseconds for satellite links), this is clearly sufficient time for connections to be established with Internet hosts whose networks are rapidly switching on and off.

For More Information

You can find out more about BTTP and its creator, Mitch Tulloch, at www.mtit.com

BIND

Stands for Berkeley Internet Name Domain, a popular software tool for administering and maintaining the Domain Name System (DNS) on UNIX platforms.

See Also Berkeley Internet Name Domain (BIND)

bindery

In Novell's NetWare version 3.x and earlier networking operating systems, the database containing network security information (such as users, groups, and rights) for a particular server.

Overview

Each NetWare 3.x server has its own bindery for controlling access to that server's file and print resources. In version 4.x and later, the bindery is replaced by the Novell Directory Services (NDS), although 4.x servers are also capable of running in bindery emulation mode.

Microsoft's optional Microsoft Windows 2000 Server service Gateway Services for NetWare (GSNW) can be used to implement gateways to resources located on NetWare file and print servers that are using bindery security. This allows Windows users to access volumes, directories, and print queues on NetWare servers without requiring NetWare client software to be installed on them. Client Services for NetWare (CSNW) can also be installed on client machines running Windows 2000 Professional and Windows XP to enable them to directly access bindery-based NetWare 2.x , 3.x , or 4.x servers that are running in bindery emulation mode.

See Also Client Services for NetWare (CSNW) ,Gateway Service for NetWare (GSNW) ,Novell Directory Services (NDS)

bindings

A mechanism for linking the various components of an operating system that make network communications possible.

Overview

Bindings link together network interface card (NIC) drivers, network protocols (such as Transmission Control Protocol/Internet Protocol [TCP/IP]), and networking services (such as Workstation service). Microsoft Windows 2000, Windows XP, and Windows .NET Server let you optimize network communication by selectively enabling, disabling, and modifying the order of the bindings between these different networking components. Windows 2000, Windows XP, and Windows .NET Server support Network Driver Interface Specification (NDIS) version 5, which allows multiple protocols to be independently bound to multiple NICs.

Binding. Configuring bindings in Windows 2000.

To configure bindings for Windows 2000, choose Advanced Settings from the Advanced menu of the Network And Dial-Up Connections window, which is accessed from Control Panel. In this way bindings can be easily enabled, disabled, or reordered. To optimize network performance, disable any unnecessary bindings on your workstations.

See Also network driver interface specification (NDIS)

biometric authentication

Any authentication scheme that uses an aspect of a person's physical body or behavior to verify that person's identity.

Overview

Biometric authentication (or biometric identification) has been employed for years for entry-access control of high-security environments such as military compounds and virology laboratories, but only recently have commercial products become available for securing computer networks. Biometric authentication mechanisms take many forms, including

Some biometric authentication systems measure behavior patterns instead of physical features. An example is BioPassword from Net Nanny Software International, which requires a user to enter a password on a keyboard and then compares the way the user typed the password with information stored in a database.

Biometric authentication systems must be designed carefully in order for them to be truly secure. For example, a simple voice-print authentication system could be fooled by using a tape recording of the user's voice. To guard against this, these systems commonly ask the user to speak a randomly generated series of words into the microphone, which renders such tape recordings useless.

Biometrics will probably soon make their way into the wireless arena as well. Cellular communications vendor Nokia has prototyped a biometric-enabled cell phone, which would make stealing such a phone useless. The main barrier against this development is cost-cell phones are mass-produced cheaply and even a biometric component costing $10 per phone could break the cost model.

Another general barrier to all forms of biometric authentication systems are privacy issues regarding having digital information about your physical makeup stored on a device that could be stolen or misused. Despite these concerns, the biometrics market in 1999 was $166 million and is rising rapidly.

Notes

When implementing biometric authentication systems, be sure to consider fallback authentication options should the biometric device fail. Costs of purchasing and deploying such systems across an enterprise may also be considerable, and help desk departments might find it more time-consuming to troubleshoot a faulty sound card of a voice-print authentication system than simply resetting a user's traditional text-based password.

See Also network security

B-ISDN

Stands for broadband ISDN, the broadband transmission counterpart of Integrated Services Digital Network (ISDN).

See Also broadband ISDN (B-ISDN)

Bit/Block Error Rate Tester (BERT)

A device used to troubleshoot serial lines.

Overview

A Bit/Block Error Rate Tester (BERT) is a kind of cable tester specially designed for testing serial lines. BERTs can be connected to serial ports on PCs, routers, and other devices to provide a visual indication of the condition of the serial interface.

A typical BERT is a small box with a 25-pin serial connector and 25 light-emitting diodes (LEDs), one for each lead of the interface. A quick visual inspection can provide information about whether data is being reliably transmitted across the interface. You can also use jumpers to make or break specific leads to see the effect-this simulates the effect of crossed wires and can be used to detect such wires in miswired serial cables or connectors.

See Also test equipment

Bit Error Rate (BER)

A measurement of the reliability of a networking architecture or device.

Overview

Bit Error Rate (BER) is expressed in terms of probability of a bit of data being lost while being transported over a network or processed by a device. As an example, standard (10 megabits per second [Mbps]) Ethernet over copper specifies a maximum BER of 10-8 , which means only 1 out of every 100,000,000 (100 million) bits transported can be allowed to be lost. This is actually a worst-case scenario, however, as actual Ethernet networks generally have a BER of 10-11 or better, meaning that only 1 out of every 100,000,000,000 (100 billion) bits is lost. Fast Ethernet and Gigabit Ethernet (GbE) have BERs an order of magnitude smaller.

An associated measure for Ethernet reliability is Frame Loss Rate (FLR), which for Ethernet networks is typically 10-7 , or 1 frame lost in every 10,000,000 (10 million) frames transported. Lost frames are handled by higher-level layers of the Open Systems Interconnection (OSI) model and are ignored by the Data Link Layer.

See Also Ethernet

bits per second (bps)

A unit used for measuring the speed of transmission of data on a network of computers.

Overview

Bits per second, or bps, represents the rate at which information is being sent or received. A bit is a single unit of digital information, represented by either a 1 or a 0. The total number of bits per second that can be transmitted over a network link describes the bandwidth or throughput of that link.

Because most network communication takes place at thousands or millions of bits per second, the following related units are commonly used:

See Also bandwidth

BizTalk

An initiative from Microsoft Corporation to standardize the exchange of electronic documents between businesses.

Overview

Businesses exchange information for various reasons:

BizTalk is designed to standardize these processes using Extensible Markup Language (XML) as a foundation for creating a standard "electronic envelope" for exchanging electronic documents between businesses.

BizTalk actually consists of four interlocking facets:

For More Information

Visit the BizTalk resource site at www.biztalk.org

See Also B2B ,BizTalk Framework ,BizTalk Server 2000 XML

BizTalk Framework

A specification describing the architecture of BizTalk messages.

Overview

BizTalk Framework is part of the BizTalk initiative from Microsoft Corporation to facilitate the exchange of electronic documents and orchestration of business processes between trading partners, supply-chain partners, and other business partners. BizTalk Framework is designed to be the underlying document standard for B2B e-commerce and is based on the standard Extensible Markup Language (XML) specification.

Architecture

When two businesses in a B2B relationship need to exchange information electronically, the first step is to decide on a common XML schema to use that both can understand. A schema defines the type of content being transmitted and the structure of the document containing it. Microsoft has established the site www.biztalk.org as a resource site for businesses to develop and publish BizTalk schemas for their industry sectors.

BizTalk Framework. Format for a BizTalk Message.

A BizTalk message consists of two parts: the Transport Envelope and the BizTalk Document.

The Transport Envelope specifies the transport protocol used to deliver the message. BizTalk Server 2000, Microsoft's own implementation of a platform for building BizTalk solutions, supports a number of different transports, including

The other portion of a BizTalk message, the BizTalk Document itself, consists of the following parts:

See Also BizTalk ,BizTalk Server 2000 XML

BizTalk Server 2000

Microsoft Corporation's platform for exchange of business documents and orchestration of business processes using the BizTalk Framework.

Overview

BizTalk Server 2000 is one of the new Microsoft Windows 2000 Server applications. BizTalk Server 2000 is used for building B2B e-commerce through using Extensible Markup Language (XML) to deliver business documents such as sales orders, invoices, and service requests. BizTalk Server 2000 can transmit both XML and Simple Object Access Protocol (SOAP)-based messages. It can use a variety of transports for accomplishing this, including Hypertext Transport Protocol (HTTP), Simple Mail Transfer Protocol (SMTP), File Transfer Protocol (FTP), and others.

For More Information

Find out more about BizTalk Server 2000 at www.microsoft.com/biztalk.

See Also BizTalk ,BizTalk Framework XML

Blackcomb

Microsoft Corporation's code name for its upcoming successor to the Windows .NET Server family of operating system platforms.

Overview

"Blackcomb" is planned for release sometime after the release of Windows .NET Server, which had the code name "Whistler." "Blackcomb" will be the first fully .NET version of Microsoft Windows and will be an integral platform for developing and deploying Microsoft's .NET vision of software-as-services.

At this point, little is known about "Blackcomb," but at the Windows Hardware Engineering Conference (WinHEC) in March 2001, Microsoft unveiled some of its intended features, including

Notes

Whistler and Blackcomb are two ski resorts in British Columbia, Canada, only a few hours away from Microsoft's headquarters at Redmond, Washington.

For More Information

Find out about the latest developments with the Microsoft Windows series of operating system platforms at www.microsoft.com/windows.

See Also Microsoft Windows

black hole

A network condition in routed internetworks where packets are dropped without any explanation to the transmitting host.

Overview

A black hole is generally caused by a router that goes down and whose absence from the network is not detected by other routers. Packets that are forwarded to the black hole are dropped-that is, they never reach their destination and give no indication to the stations sending them of the situation-therefore, the data is lost. Normally, a router will issue an "ICMP Destination Unreachable" message when it cannot forward a packet. However, with a black hole, these messages are not generated, so the transmitting host does not know that data is being permanently lost.

If static routing is being used, a black hole persists until the affected router is brought back on line or until other static routers have their routing tables reconfigured to take the downed router into account. If dynamic routing is used, other routers soon detect the presence of the black hole and adjust their routing tables accordingly to favor other paths.

Black holes can also originate when routers that are active nevertheless drop certain packets for specific reasons. An example is when the Path Maximum Transmit Unit (PMTU) is configured for a router so that it discards Internet Protocol (IP) packets that need to be fragmented in order to be forwarded. If a PMTU router is not configured to also forward indications of dropped packets to transmitting hosts (and by default they are not so configured), then the network problems they produce can be difficult to detect since some (smaller) packets get through successfully while other (larger) packets mysteriously disappear.

The reason, of course, why this condition is known as a "black hole" is its parallel with black holes in Einstein's theory of General Relativity. Einstein's black holes are collapsed stars that swallow everything and from which not even light can return.

See Also routing

BLEC

Stands for Building-centric Local Exchange Carriers, a telecommunications carrier focused on the Multitenant Unit (MTU) market.

See Also Building-centric Local Exchange Carrier (BLEC)

block coding

An encoding scheme whereby groups of data bits are encoded into a larger number of code bits.

Overview

A variety of block codes are used for encoding transmissions for networking and telecommunications systems. Examples of some common ones include

The reasons for making the "code space" larger than the "bit space" in these encoding schemes are to allow for additional data characteristics to be included in transmissions and to make room for control signals to manage the flow of data or check for error conditions.

See Also line coding

Blocks Extensible Exchange Protocol (BEEP)

An emerging framework to replace Hypertext Transport Protocol (HTTP) for transport of Extensible Markup Language (XML)-based information over the Internet.

Overview

Blocks Extensible Exchange Protocol (BEEP) is a proposed framework for a protocol that would run on top of Transmission Control Protocol (TCP) as an alternative to HTTP. It is designed to facilitate the exchange of XML-framed information for a variety of uses, including file transfer, instant messaging (IM), and network management.

BEEP has been proposed because HTTP was not originally intended for XML data transport and performs poorly when performing this function. BEEP uses a peer-to-peer (P2P) architecture instead of the client- server one used by HTTP. In a typical scenario, BEEP first establishes a connection between two hosts on a network. The hosts alternate between client and server roles to allow two-way communications between them over a channel. Hosts can choose either to push or pull data between themselves. An advantage of BEEP is that unlike HTTP, a single BEEP connection can open multiple channels for exchange of XML data, which means, for instance, that files could be transferred through one channel while an IM chat session occurs on another.

The BEEP framework also includes a toolkit for rapid development of custom application protocols that would run on top of BEEP to efficiently handle specific types of communications tasks. In effect, BEEP would provide reusable code that would greatly facilitate the development of such special-purpose protocols.

BEEP is being presented as a draft standard to the Internet Engineering Task Force (IETF) for consideration, and the framework is outlined by RFCs 3080 and 3081. BEEP's development has been spearheaded by the company Invisible Worlds.

Notes

BEEP was formerly known by the acronym BXXP.

For More Information

Visit Invisible Worlds at www.invisibleworlds.com

See Also Hypertext Transfer Protocol (HTTP) ,XML

blue screen

In Microsoft Windows platforms, a blue screen on a user's monitor indicates that something has gone seriously wrong with the system.

Overview

In Windows 2000, Windows XP, and Windows .NET Server, blue screens are normally called stop screens. A stop screen contains complex information that qualified support technicians can use to diagnose the problem. A reboot might get the system going again, but the stop screen might reappear if the problem is not resolved. The problem causing the stop screen to appear can be either hardware-related or software-related, but the stop screen itself is generated by the operating system in response to the underlying problem.

In Windows 95 and Windows 98, the blue-colored screen normally appears when parity errors or memory violations occur. Parity errors can indicate that your system random access memory (RAM) has mismatched single inline memory modules (SIMMs) on your motherboard-for example, RAM with different speeds or a mix of parity and nonparity RAM. Also, systems from some manufacturers require special proprietary RAM in order to function. You should consult the documentation from your computer's manufacturer or your RAM's manufacturer to ensure that you have the correct type of RAM in each slot. The Windows 98 blue screen requests that you either shut down the offending application or restart your system using Ctrl+Alt+Delete.

Bluetooth

An evolving specification for short-range wireless transmission between small portable devices in a Personal Area Network (PAN).

Overview

Bluetooth is a wireless networking technology that promises to provide a simple, low-cost method of linking together cellular phones with headsets, Personal Digital Assistants (PDAs) with printers, and similar ad hoc associations between devices in a PAN. A PAN is essentially a network of portable devices carried by a user or devices within which a user comes into close proximity by movement. The vision of Bluetooth actually extends beyond personal data networking to a nirvana world of wireless devices that includes milk containers that signal refrigerators when they are almost empty, whereupon the refrigerator orders more milk using an Internet connection. Needless to say, not everyone expects (or even wants) this brave new world to happen!

Original work on the Bluetooth specification dates back to 1994 when cellular phone manufacturer Ericsson first outlined the technology. The original intention was to provide a way to connect wireless headsets with cellular phones, but the Bluetooth specification has evolved far past this initial goal. In 1998 a consortium called the Bluetooth Special Interest Group (SIG) was created, and it published its first specification in 1999. The original members included Ericsson, its rival Nokia, and other industry leaders such as IBM, Intel Corporation, and Toshiba Corporation. This consortium has grown to include over 2000 different vendors, and the current Bluetooth specification is version 1.1.

The success of the Bluetooth SIG is based largely on the fact that companies that join must grant a royalty-free license to all other members of the alliance for any Bluetooth-related technology they develop. The SIG's main purpose is to develop specifications for real-world interoperable Bluetooth products-it is not a standards body, and the intention is that any specifications developed by the SIG will be passed on to the Institute of Electrical and Electronics Engineers (IEEE) for final standardization.

Because of the original vision of Bluetooth for small handheld devices, a consistent goal of the Bluetooth SIG has been to develop Bluetooth technology that can be implemented on a single chip. Much success has been achieved in that respect, with chip prices in large lots coming down to the $4 range.

Architecture

Bluetooth is based on baseband FM transmission using frequencies between 2.4 and 2.4835 gigahertz (GHz) within the unlicensed 2.4-GHz Industrial, Scientific, and Medical (ISM) band. Bluetooth divides this band of frequencies into 79 separate channels, and transmission uses a frequency-hopping scheme to hop between channels randomly at a rate of 1,600 hops per second. The result is that a different frequency is used to transmit each packet of a Bluetooth transmission. The advantage of such aggressive frequency-hopping is to provide smooth operation by minimizing the effects of fading due to reflecting obstacles and overcoming noise due to electromagnetic interference (EMI) generated by microwave ovens and other devices. Bluetooth also uses short packets and fast acknowledgments to increase reliability and employs forward error correction to reduce the effects of random noise.

Bluetooth's data transmission rate is 1 megabit per second (Mbps), but with protocol overhead the resultant practical maximum transmission rate is more like 780 kilobits per second (Kbps) or lower. Bluetooth uses a shared-media transmission scheme similar to Ethernet in which only one device in a group of connected devices can transmit at any one time, and duplex transmission is simulated through time-division multiplexing of simplex transmissions. The result is that a PAN with many Bluetooth devices will perform more poorly than one with only a few devices, but this is not considered a serious disadvantage since the specification was designed to be a lightweight one from the beginning.

Given its aim of supporting devices in PANs, Bluetooth is a low-power technology with a maximum range of transmission of 33 feet (10 meters). Bluetooth's automatic power adaptation adjusts transmission power to the minimum needed for reliable transmission in any given situation to enhance battery life in portable devices.

The Bluetooth protocol suite is centralized around the Logical Link Control and Adaptation Protocol (L2CAP). This protocol supports two data transmission modes:

The Application Layer of the Bluetooth protocol suite is implemented as a series of "profiles" representing operating parameters for different kinds of uses of Bluetooth. Currently, 13 different application layer profiles have been developed under the specification, and Bluetooth systems are required only to implement a core subset of these together with other profiles needed for their operation.

Other Bluetooth protocols include the Link Manager Protocol (LMP), which manages device authentication for forming new connections, and the Service Discovery Protocol (SDP), which maintains the browse list of accessible devices.

Security is built into Bluetooth at the data-link level and provides the following services:

Implementation

Bluetooth supports concurrent connections among up to eight devices, forming what is called a piconet. Each device in a piconet is temporarily assigned a unique 3-bit MAC address for the duration of the connection. A master/slave relationship exists between one device and all other devices in the piconet for the duration of the connection. The purpose of this is for establishing clocking to synchronize devices for using the hopping sequence. In all other respects, the devices operate as peers during a connection.

Unconnected Bluetooth devices are always on in a standby mode where they listen for connection attempts every 1.28 seconds on each of 32 preassigned hopping frequencies. Once a compatible device is found, link setup and authentication is then performed using the Link Manager Protocol (LMP), which uses the link controller services built into the Bluetooth chip. Connections between Bluetooth devices can be either point-to-point or point-to-multipoint, and groups of piconets can be joined together into larger associations called scatternets, with each piconet within a scatternet having a uniquely different hopping sequence.

Marketplace

The Bluetooth marketplace is still in its infancy, but some of the highlights are as follows:

The Bluetooth SIG holds a yearly conference called Unplugfest where old and new vendors of Bluetooth products meet to test interoperability between their different implementations of the specifications. Because of the specification's evolving nature, early-to-market products based on the 1.0 specification may have compatibility issues with products based upon the newer 1.1 standard.

Issues

Using the ISM band for Bluetooth communications has been problematic. The ISM band is supposedly reserved worldwide for unlicensed communications, but governments in some countries and regions have licensed portions of this band for specific uses. The problem is of special concern in Spain and France, which have only a narrow portion of the band available, and the Bluetooth specifications have been massaged to produce a special version of the specification technically able to function under these restrictions, but legal restrictions prohibit its use in these two countries to prevent the jamming of other services. The reason this is such an issue is that, due to the multiplication of different specifications, Bluetooth cellular phones will not be able to easily function throughout Europe as originally envisioned by Ericsson.

Another issue is that not only is the ISM band also used by other wireless networking technologies such as 802.11b and HomeRF, but it is also used for non- networking applications such as garage door openers, microwave ovens, cordless telephones, telco local loop systems, baby monitors, medical scanners, and various other business and consumer devices. By using an aggressive frequency-hopping scheme, Bluetooth is fairly resistant to interference from these different systems, but that very fact means that Bluetooth easily interferes with the operation of these other systems. Tests have shown, in fact, that communications over 802.11b wireless networks can be degraded and even disrupted by nearby Bluetooth devices. The result has been that large companies that rely heavily on 802.11b wireless networks have instituted policies to ban Bluetooth devices from the premises.

Besides the threat to 802.11b local area networks (LANs), Bluetooth poses dilemmas for other industries as well. The airline industry has voiced particular concern that Bluetooth devices carried by different passengers might detect each other during a flight, turn themselves on, and generate transmissions that could disrupt an aircraft's sensitive navigation equipment. The Bluetooth SIG is attempting to allay these concerns through further refinement of the specifications.

Prospects

Despite issues relating to interference with 802.11b wireless local area networks (WLANs) and whether ad hoc always-on wireless networking is desirable or even safe, Bluetooth has a great deal of momentum from industry and products are likely to be widely available soon. In addition to consumer-oriented applications for PANs and wireless public access kiosks, Bluetooth may also find some place in the enterprise as a cable- replacement technology.

Only time will tell, however, whether a Bluetooth- enabled can of beer will someday communicate with a similarly enabled refrigerator to ask it to lower the temperature for just the right taste.

Notes

The goals of Bluetooth and 802.11b are different: although 802.11b was specifically developed mainly for laptop computers as a wireless replacement for wired Ethernet LANs, Bluetooth is optimized for forming short-range ad hoc networks for connecting smaller portable devices such as cell phones and PDAs. The implementations of these technologies, although confined to the same ISM frequency band, are also different: Bluetooth uses frequency-hopping, but 802.11b uses spread-spectrum transmission.

The interesting name "Bluetooth" comes from Harald Bluetooth, the Viking who in the 10th century unified Norway and Denmark.

Bluetooth also supports voice transmission that use up to three concurrent synchronous 64-Kbps voice-only channels or one channel that simultaneously supports both asynchronous data and synchronous voice transmission. The voice channels use the continuous variable-slope delta modulation-coding scheme.

A competing technology for PANs besides Bluetooth is the Infrared Data Association (IrDA) protocol, but while IrDA devices require line-of-site communication, Bluetooth devices overcome this restriction. IrDA does have certain advantages however, including much greater data transmission rates.

For More Information

You can find the Bluetooth SIG at www.bluetooth.com

See Also 802.11b ,802.15 ,Infrared Data Association (IrDA) ,Personal Area Network (PAN) ,piconet ,wireless networking

BNC connector

A group of connectors used for joining thinnet cable segments together and for connecting thinnet cabling to 10Base2 network cards.

Overview

BNC connectors are used on 10Base2 (thinnet) Ethernet networks and use a twist-and-lock mechanism that provides a secure connection between network cabling and components. The male connector has a center pin with a rotating ring with projections that mate with the female connector.

The various types of BNC connectors include the following:

Notes

Several possibilities are usually suggested as to the origin of the term BNC :

For situations where large mechanical loads may affect cabling, a threaded form of the connector is available called TNC.

See Also connector (device) ,terminator

B-node

A NetBIOS name resolution method used by Microsoft Windows NT in which broadcast messages are used for name registration and resolution.

Overview

Name resolution is the process of converting the name of a host on the network into a network address (such as an Internet Protocol [IP] address). Name resolution must be performed in order to establish communication over a Windows NT network. B-node is one of four basic methods supported by Windows NT for resolving NetBIOS host names-that is, computer names-into IP addresses.

If a computer running Windows NT is configured as a B-node machine, it always uses broadcasts to resolve names of other hosts on the network. For example, if a B-node machine wants to communicate with another machine with the NetBIOS name SERVER7 (for example, if it wants to connect to a shared resource on SERVER7), the B-node machine broadcasts a packet containing a NetBIOS name query request. If SERVER7 receives the packet, it responds by returning a frame containing its IP address. If SERVER7 is off line or fails to return a response, the B-node client will be unable to establish a connection with SERVER7.

As a name resolution method, B-node is flawed in two ways:

A better approach to NetBIOS name resolution on Windows NT networks is to configure clients as H-node machines and use a Windows Internet Naming Service (WINS) server. H-node is a NetBIOS name resolution method that combines B-node and P-node.

Notes

On Windows 2000 and Windows .NET Server networks, the Domain Name System (DNS) is the preferred name resolution scheme, and NETBIOS can be disabled when there are no longer any downlevel Windows NT machines left after an upgrade is complete. Note, however, that Windows 2000, Windows XP, and Windows .NET Server systems based on the Active Directory directory service must be configured with the IP address of a WINS server in order to communicate with any Windows-based systems that are not Active Directory-based, including other Windows 2000, Windows XP, and Windows .NET Server systems.

See Also H-node ,M-node ,NetBIOS name resolution ,P-node

bonding

A term used to describe a variety of different technologies for aggregating multiple wide area network (WAN) links together to form a single fatter pipe.

Overview

In Integrated Services Digital Network (ISDN) and T-carrier transmission technologies, bonding provides a way of combining multiple DS0 channels from different circuits into a single, faster data transmission channel. This is accomplished using inverse multiplexing technologies together with special techniques for resolving the timing differences found among groups of different circuits.

ISDN Bonding is typically found in Basic Rate Interface ISDN (BRI-ISDN) where it is used to combine the two 64-kilobits-per-second (Kbps) B channels into a single 128-Kbps data transmission channel. Several different bonding protocols can be implemented for BRI-ISDN services, a common one being Multilink PPP (MPPP), which is used for asynchronous bonding.

Bonding must be supported by the ISDN devices at both ends of the ISDN link. Typically, one of the B channels is designated as responsible for initiating the bonding process. Many ISDN terminal adapters can override bonding when the user wants to place a regular Plain Old Telephone Service (POTS) phone call. For example, you might be using ISDN for high-speed Internet access with both B channels bonded to give you 128-Kbps (or 14-kilobyte-per-second [KBps]) access. Then, if you suddenly pick up a phone connected to the terminal adapter's POTS jack, bonding stops and the second B channel is freed up for the phone call. Once the call is complete, bonding will resume.

Another WAN technology that uses bonding is digital subscriber line (DSL). By configuring the DSL Access Multiplexer (DSLAM) at the service provider's central office (CO), hardware bonding can be implemented to link multiple DSL connections into a single high- bandwidth pipe.

An alternative to hardware bonding for DSL is customer premises equipment (CPE) bonding in which Multilink PPP is used to aggregate multiple DSL circuits at the customer premises instead of the DSLAM. This newer form of bonding has the advantage of being easier to deploy and configure than hardware bonding, which often requires costly upgrades of DSLAMs. A market example is Netopia, a DSL service provider that offers bonding of up to four Internet Digital Subscriber Line (IDSL) lines.

DSL bonding has several advantages:

See Also Digital Subscriber Line (DSL) ,Integrated Services Digital Network (ISDN) ,Multilink Point-to-Point Protocol (MPPP)

boot

A term used to refer to the process of starting a computer, as in the phrase, "Please boot the computer."

Overview

The term boot also refers specifically to the series of steps by which a computer locates and loads the operating system once the power is turned on. This series of steps is usually referred to as the boot sequence or boot process, and it depends on both the type of operating system installed on the machine and the type of hardware platform (for example, x86 platform or Alpha platform).

The term warm boot refers to resetting the system or rebooting using Ctrl+Alt+Delete. The power to the system is not interrupted during a warm boot, but the boot process starts again from the beginning using the system basic input/output system (BIOS).

The term cold boot refers to shutting down a computer and actually turning off the power source and then turning it back on. Cold boots are sometimes necessary after installing or configuring some legacy hardware devices to ensure that the devices are properly initialized. For example, if you change the configuration parameters of an internal modem, you sometimes need to cold boot your system for these changes to take effect.

See Also boot files ,boot process

boot files

Files needed to boot an operating system on a computer.

Overview

Every operating system has its own set of boot files needed to locate, load, and initialize the operating system during the boot sequence. For example, MS-DOS and Windows 3.x use the hidden files Io.sys and Msdos.sys and the file Command.com. Configuration information stored in the text files Config.sys and Autoexec.bat is also used during the process.

On Windows 95, Windows 98, and Windows Millennium Edition (Me), the files used for booting are Io.sys, Msdos.sys, and Win.com, with the files Config.sys and Autoexec.bat used optionally to support legacy hardware.

The files needed to boot Windows NT vary depending on whether the x86 or Alpha processor platform is used.

The files needed to boot Windows 2000, Windows XP, and Windows .NET Server (and Windows NT on x86) include the following:

The Windows 2000, Windows XP, and Windows .NET Server boot process also makes use of other files, including device drivers and the system hive.

See Also boot ,boot process

Boot.ini

A file used to create the boot loader menu in Windows 2000, Windows XP, and Windows .NET Server.

Overview

Boot.ini is a hidden, read-only text file on the root of the system partition of a Microsoft Windows 2000, Windows XP, or Windows .NET Server machine. The boot loader menu is used on dual-boot and multiboot systems to select which operating system (Windows 2000 or some other operating system) to boot. The Boot.ini file creates this menu, which normally is only displayed if more than one operating system is installed on the machine.

Examples

A typical Boot.ini file for a default Windows 2000 installation might look like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\ WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\ WINNT="Microsoft Windows 2000 Professional" /fastdetect

You can see a close correspondence between the appearance of the Boot.ini file and the boot loader menu, which the Ntldr program creates during the Windows NT boot sequence.

A Boot.ini file for a dual-boot system configured to boot to either Windows 2000 or Windows 98 usually looks like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\ WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\ WINNT="Microsoft Windows 2000 Professional" /fastdetect C:\="Microsoft Windows"

The last line of the file is the same for booting to any MS-DOS-based operating system, including Windows 95, Windows 98, and Windows Millennium Edition (Me).

See Also boot ,boot files ,boot loader menu

boot loader menu

A menu that appears when you boot a Microsoft Windows 2000, Windows XP, or Windows .NET Server computer configured for dual-boot or multiboot operation with other operating systems.

Overview

The boot loader menu appears during the boot loader phase of Windows NT startup, and it is displayed by the Windows 2000, Windows XP, and Windows .NET Server loader program called Ntldr. The boot loader menu allows you to select the particular operating system you want to run on a dual-boot or multiboot system and to use optional boot-time switches for booting Windows 2000, Windows XP, and Windows .NET Server in various enhanced ways or for troubleshooting purposes. The table summarizes some of the more commonly used boot-time switches used in Boot.ini.

Some Common Boot-Time Switches Used in Boot.ini

Switch

Description

/3GB

Used only with Windows 2000 Advanced Server to increase user address space from 2 gigabytes (GB) to 3 GB

/basevideo

Starts Windows 2000 using generic Video Graphics Adapter (VGA) video

/bootlog

Creates a log, called Ntbtlog.txt, of steps in the boot process

/fastdetect

Skips enumeration of serial and parallel devices during the boot process (included by default)

/numproc=

Specifies the number of CPUs to use on a symmetric multiprocessing (SMP) system

/sos

Lists the device drivers marked to load at boot time and displays other information

Notes

The boot loader menu is created by the Boot.ini file. This file can be edited using a text editor such as Notepad, but this should be done with care as mistakes could render your system unbootable.

See Also boot ,boot files ,Boot.ini

BOOTP

Stands for bootstrap protocol, a Transmission Control Protocol/Internet Protocol (TCP/IP) protocol and service that allows diskless workstations to obtain their IP address, other TCP/IP configuration information, and their boot image file from a bootstrap protocol (BOOTP) server.

See Also bootstrap protocol (BOOTP)

boot partition

The partition of a disk on which Microsoft Windows 2000, Windows XP, or Windows .NET Server installs its core operating system files.

Overview

The core operating system files for Windows 2000, Windows XP, and Windows .NET Server are typically stored in \Winnt and its subdirectories. The \Winnt directory and its system files are located on what is referred to as the boot partition (by a strange choice of terminology, the boot files in Windows 2000, Windows XP, and Windows .NET Server are stored on the system partition).

The choice of which partition is to be the boot partition is made during installation of Windows 2000, Windows XP, and Windows .NET Server and cannot be changed afterward. An important consideration when installing Windows 2000, Windows XP, and Windows .NET Server is designating a boot partition that has sufficient free space to contain the various operating system files together with all the optional and future components such as device drivers.

Notes

The boot partition can be the same as or different from the system partition.

See Also boot process ,system partition

boot process

The series of steps that occurs when an operating system boots on a machine.

Overview

Each operating system has its own particular boot sequence and uses its own specific set of boot files. Knowledge of the boot sequence for a particular operating system can aid in troubleshooting problems booting a machine on which that operating system is installed. For example, from messages displayed during the boot process, a technician can often determine whether a particular boot file is missing or corrupt.

The following is a brief summary of the boot sequence for the Microsoft Windows 2000 operating system (the Windows XP and Windows .NET Server boot sequences are similar). Note that the actual boot process involves more than 100 different steps and that this description gives only an overview of the process.

See Also boot ,boot files

Bootsect.dos

A boot file in Microsoft Windows 2000, Windows XP, and Windows .NET Server used to support dual-boot scenarios with MS-DOS-based operating systems such as Windows Millennium Edition (Me).

Overview

When the boot loader menu appears during the boot process on a dual-boot Windows 2000, Windows XP, or Windows .NET Server machine, the user selects the operating system to boot. If an MS-DOS-based operating system such as Windows 95, Windows 98, or Windows Me is selected, the Ntldr program immediately switches the processor back to 16-bit real mode and then loads Bootsect.dos and turns control of the boot process over to it. Bootsect.dos then continues with an MS-DOS-specific boot process leading to initialization of the selected operating system.

Bootsect.dos contains the location of the partition boot sector that existed on the partition prior to the installation of Windows 2000, Windows XP, or Windows .NET Server. Thus, Bootsect.dos enables the system to locate and load the alternate operating system. Bootsect.dos is not loaded during a normal boot of the Windows 2000, Windows XP, or Windows .NET Server operating system.

See Also boot files ,boot process

bootstrap protocol (BOOTP)

A Transmission Control Protocol/Internet Protocol (TCP/IP) protocol and service that allows diskless workstations to obtain their IP address, other TCP/IP configuration information, and their boot image file from a bootstrap protocol (BOOTP) server.

Overview

The network interface card (NIC) on these diskless workstations contains a programmable read-only memory (PROM) chip containing code necessary to initialize the client.

When a bootstrap protocol (BOOTP) client is started, it has no IP address, so it broadcasts a message containing its MAC address onto the network. This message is called a "BOOTP request," and it is picked up by the BOOTP server, which replies to the client with the following information that the client needs:

When the client receives this information from the BOOTP server, it configures and initializes its TCP/IP protocol stack, and then connects to the server on which the boot image is shared. The client loads the boot image and uses this information to load and start its operating system.

BOOTP is defined in RFCs 951 and 1084. The Dynamic Host Configuration Protocol (DHCP) was developed as an extension of BOOTP.

Notes

The term bootstrap protocol (or boot protocol ) comes from the idea of lifting yourself up by your own bootstraps-something that is obviously difficult to do. In other words, how does a client machine start up when it initially has neither an IP address nor an operating system? BOOTP makes this difficult task possible.

Most UNIX servers support diskless workstations using the BOOTP protocol. BOOTP is implemented on UNIX servers using the bootpd daemon. Certain aspects of BOOTP are supported by Microsoft Windows 2000, Windows XP, and Windows .NET Server, but the protocol is rarely used in Windows networks.

See Also Dynamic Host Configuration Protocol (DHCP)

boot volume

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, the volume that has the operating system files.

Overview

The boot volume can be the same as or different from the system volume, and it can be formatted in either NTFS file system (NTFS) or file allocation table (FAT). The term volume indicates that we are referring here to dynamic storage, which enables volumes to be created and managed. By contrast, basic storage enables the creation and management of partitions instead.

See Also boot partition

Border Gateway Protocol (BGP)

An exterior gateway protocol (EGP) used on the Internet to provide loop-free routing between different autonomous systems (ASs).

Overview

The Internet consists of large, independently administered networks called ASs connected by routers to form a single, enormous internetwork. ASs themselves are smaller internetworks and contain routers that exchange routing information with each other using various interior gateway protocols (IGPs) such as Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP). These IGPs do not scale well enough to handle exchange of routing information between the border routers that join various ASs together, however, and for such purposes exterior gateway protocols (EGPs) are used, the de facto standard EGP for the Internet being the Border Gateway Protocol (BGP).

Like RIP and IGRP, BGP is based on the distance vector routing algorithm (or more specifically on a variant called path-vector), which enables groups of routers to share their routing information in a highly efficient and scalable manner. The routing information BGP exchanges between boundary routers is called Network Layer Reachability Information (NLRI), and specifies which other AS's data can be forwarded to from the local AS and the most efficient routes (best path) for doing this. BGP also can ensure against routing loops occurring.

BGP was developed in 1982 as the successor to EGP and was formalized in RFCs 827 and 904. Since then it has gone through several versions, with the current version being BGP 4, specified by RFC 1771. BGP 4 includes a number of enhancements over earlier versions, including support for

Architecture

BGP is a connection-oriented protocol that runs on top of Transmission Control Protocol (TCP) to provide reliable transport of routing updates. TCP port 179 is used for forming connections between BGP-enabled routers, and incremental updates to routing tables only are transmitted, which makes BGP efficient in terms of bandwidth utilization (other distance-vector routing protocols exchange entire routing tables at regular intervals, which makes them scale poorly to internetworks the size of the Internet).

To use BGP, your internetwork must first be assigned an Autonomous System Number (ASN). You can get one by contacting your regional Internet registry, such as the American Registry for Internet Numbers (ARIN) for North and South America, Reseaux IP Europ ens (RIPE) for Europe, or the Asian-Pacific Network Information Center (APNIC) for Asia. ASNs for public internetworks are assigned from the range 1 through 64511.

BGP-speaking routers within an AS establish peering relationships with each other to form a loop-free routing mesh. The first update between two peers includes all known routes on the network, while succeeding updates are incremental.

Implementation

BGP needs to be implemented only in very large internetworks. When smaller internetworks using IGRP grow to the point that IGRP performs poorly, BGP can be used to partition the internetwork into two autonomous systems for better routing performance.

Another situation where you might implement BGP is if your corporate internetwork is multihomed, that is, has several dedicated connections to the Internet using different Internet service providers (ISPs). In this case, you can use BGP to balance the load between the Internet connections and provide redundancy.

Finally, if your corporate internetwork is being used as a transit network to connect other networks to the Internet, you need to employ BGP.

If you plan to implement BGP, make sure your router is powerful enough to handle it, especially if your internetwork will be directly connected to a regional ISP's network.

Notes

There are actually two flavors of BGP, though this distinction is not widely used in the literature:

See Also autonomous system (AS) ,exterior gateway protocol (EGP) ,routing protocol

border router

A router that connects two different autonomous systems (ASs).

Overview

The Internet consists of a collection of thousands of different independently administered large internetworks called ASs. Border routers are high-speed backbone routers that connect these different internetworks.

Border router. Using a border router to connect two autonomous systems.

Border routers use the Border Gateway Protocol (BGP) as the routing protocol for exchanging route information between them. Since the routing tables for border routers are large and rapidly growing as the Internet itself expands and evolves, border routers need to be high-performance, with at least 64 kilobytes (KB) of memory to hold these routing tables. Without these border routers and BGP, the Internet would be limited to a much smaller size than it is.

See Also autonomous system (AS), Border Gateway Protocol (BGP), Internet, router

bottleneck

A situation that occurs when computer and network systems and components are unable to meet the demand placed upon them by real-world situations.

Overview

A bottleneck is essentially the particular network component or server subsystem that is causing the problem. For example, if users on a Microsoft Windows 2000-based network are complaining that it takes too long to log on when they arrive at the office in the morning, the bottleneck and its potential resolution might be

The etymological reason for describing each of the above situations as a "bottleneck" is that a bottle's thinnest point is its neck and hence the neck controls the flow of liquid should the bottle be inverted. In the same way, the performance of an application running on a computer system can be limited by the amount of physical memory, read/write speed of the disk subsystem, throughput of the network interface card, speed of the CPU, and other parameters-any of these components (or several of them) could be a bottleneck that prevents the application from performing as desired. Or more generally, the performance of a browser accessing Web content on a corporate Intranet could be affected by overworked name servers for Domain Name System (DNS) name resolution, an insufficient number of domain controllers to handle authentication requests, slow or faulty routers joining subnets within an internetwork, misconfigured firewalls, and a host of other issues that could represent bottlenecks.

Notes

Troubleshooting bottlenecks is the science (sometimes the art) of identifying, isolating, and correcting issues that limit application performance. Valuable tools for ferreting out bottlenecks in Windows 2000-, Windows XP-, and Windows .NET Server-based networks are the Performance console, one of the administrative tools in Windows 2000, Windows XP, and Windows .NET Server, and Task Manager. For system performance, there are four main types of bottlenecks:

bounce

An effect that happens to signals on a bus topology network when the ends of the bus are improperly terminated or unterminated.

Overview

A signal that is placed on a bus that is unterminated will continue to reflect from the end of the bus until that signal is attenuated by the impedance of the cable. Another situation that can cause signals to bounce is a break in the cable, which essentially creates two unterminated ends for the two segments.

The effect of signal bounce on baseband networks such as Ethernet is serious, since the transceivers on the network interface cards (NICs) attached to the bus interpret the problem as a collision and stop transmitting. This collision occurs because the signal is colliding with its own reflection. Once the proper termination is applied to the bus, network communication can resume.

See Also terminator

bps

Stands for bits per second, a unit used for measuring the speed of transmission of data on a network of computers.

See Also bits per second (bps)

breakout box

A troubleshooting tool used to determine the wiring of an RS-232 interface on a networking device or computer.

Overview

A breakout box can be inserted between two RS-232 devices to determine which wires are active. Breakout boxes are useful in troubleshooting RS-232 connection problems resulting from a manufacturer's device not using standard pinning.

Breakout boxes are specific examples of a more general category of network testing equipment called "status monitors." Status monitors are available for testing a variety of serial interfaces, including RS-232, RS-449, V.35, and X.21. They generally come with a variety of connectors and are quick and easy to use for isolating problems with serial transmission connections in networking, telecommunications, and industrial settings.

See Also serial transmission

BREW

Stands for Binary Runtime Environment for Wireless, a platform from QUALCOMM for developing applications for cellular communications systems.

See Also Binary Runtime Environment for Wireless (BREW)

bridge

A networking component used either to extend or to segment networks.

Overview

Bridges work at the data-link layer of the Open Systems Interconnection (OSI) model of networking. They can be used to

Bridges regenerate signals but do not perform any protocol conversion, so the same networking protocol (such as Transmission Control Protocol/Internet Protocol [TCP/IP]) must be running on both network segments connected to the bridge. Bridges can also support Simple Network Management Protocol (SNMP), and they can have other diagnostic features.

Bridges come in three basic types:

Architecture

Bridges operate by sensing the source MAC addresses of the transmitting nodes on the network and automatically building an internal routing table. This table is used to determine which connected segment to route packets to, and it provides the filtering capability that bridges are known for.

If the bridge knows which segment a packet is intended for, it forwards the packet directly to that segment. If the bridge does not recognize the packet's destination address, it forwards the packet to all connected segments except the one it originated on. And if the destination address is in the same segment as the source address, the bridge drops the packet.

Bridges also forward broadcast packets to all segments except the originating one.

Advantages and Disadvantages

Bridges are less expensive than routers and can easily be used to add more stations to a network. They are transparent to high-level protocols and can even be used with nonroutable protocols that routers cannot handle.

Bridges have the disadvantages, however, of increasing the chance of broadcast storms occurring on a network and are not as efficient in larger networks as routers are.

Implementation

Use bridges to reduce network congestion and improve performance by segmenting busy Ethernet networks into smaller collision domains. You can also use bridges to connect segments more efficiently than repeaters and to join dissimilar networks such as Ethernet and Token Ring. Remote bridges can be used to create WAN links.

A poorly placed bridge can actually worsen network performance. For example, if you use a bridge to divide users who belong to the same department and frequently communicate with one another over the network, this might actually slow down communication among users by creating a bottleneck. It is better to use bridges to join together separate departmental LANs on which intradepartmental traffic is greater than interdepartmental traffic.

When using bridges to connect networks, make sure that only one path leads to any destination node on the network; otherwise, frames could become locked in loops and circle the network endlessly, causing a network storm.

Notes

Switches and bridges function similarly, but although switches can have many ports, bridges only have two.

See Also remote bridge ,wireless networking

bridgehead server

A server that acts as an endpoint of communications with another site.

Overview

In Microsoft terminology, bridgehead servers occur in several contexts. For example, in Microsoft Exchange Server, a bridgehead server in one site is responsible for routing messages through a connector to a similar server in a different site. More generally, in Microsoft Windows 2000 and Windows .NET Server, a bridgehead server is a domain controller that replicates Active Directory directory service information with domain controllers in other sites. The first domain controller in each site assumes the role of Inter-Site Topology Generator and determines which domain controllers in the site will be selected as bridgehead servers.

BRI-ISDN

Stands for Basic Rate Interface ISDN, the slower version of Integrated Services Digital Network (ISDN) communications (the faster being Primary Rate Interface [PRI]-ISDN).

See Also Basic Rate Interface ISDN (BRI-ISDN)

broadband

A signaling technology that sends signals simultaneously over a range of different frequencies as electromagnetic waves. The opposite of baseband.

See Also broadband transmission

broadband Internet access

Generally refers to various technologies such as digital subscriber line (DSL) and cable modems that provide high-speed Internet access for residential and business customers.

Overview

The growth and evolution of the Internet and World Wide Web over the last 10 years has seen simple text-based Web pages become replaced with media-rich content that includes graphic files, sound clips, Shockwave animations, and streaming media. In addition text-based Simple Mail Transfer Protocol (SMTP) e-mail has become heavy with large attachments including Microsoft Word files, spreadsheets, images, and other content. These changes in content forms require high-bandwidth Internet connections, and traditional dial-up modem connections (even 56K) feel inadequate to many users.

As a result, the broadband Internet access market has taken off in the last couple of years, with widespread deployment of cable modem and DSL connections now in the millions. In addition, for remote locations, companies such as StarBand Communications and Digistar provide satellite-based broadband Internet access with download speeds in the 2-megabit-per-second (Mbps) range (for more on satellite-based broadband, see the article "broadband wireless communications" elsewhere in this chapter).

The two most commonly deployed broadband Internet access solutions are cable modems and variants of DSL. Cable modems are a low-cost solution that is easier to deploy than DSL, but they are generally only available in residential markets where the cabling infrastructure has already been widely deployed. DSL is a more complex solution offered by telcos but has the advantage that connections are dedicated rather than shared: a DSL connection offers guaranteed bandwidth, while the effective bandwidth for a cable modem connection depends on the number of users to which it is deployed in a given area (cable modem users are essentially connected in a LAN and so share the available bandwidth of the LAN).

Speed is the main benefit of various broadband Internet access technologies, and a comparison is useful:

Uses

In addition to providing the ability to surf the Web at high speeds or send Christmas card images through e-mail, broadband Internet access is seen by increasing numbers of companies as an idea solution for supporting the remote workforce of home-based telecommuters. By using a cable modem or DSL connection and setting up a Virtual Private Network (VPN) connection using Microsoft Windows 2000, Windows XP, and Windows .NET Server, or some other platform, employees can work from home across secure connections to their company intranet.

Large companies that choose DSL or other broadband solutions as replacements for or backups to existing leased-line wide area network (WAN) links need to consider things such as service level agreements (SLAs), Quality of Service (QoS) guarantees (usually nonexistent for DSL), the number of Internet Protocol (IP) addresses that can be provided with the connection (usually under 150 for DSL), deployment times (usually weeks, but sometimes months), and business pricing (which is significantly more than residential pricing).

Advantages and Disadvantages

One important limitation of DSL as a broadband Internet access solution is that it is only viable within a small distance from the telco's central office (CO). This distance is typically about 18,000 feet (5500 meters) for the most popular implementation of DSL; that is, ADSL. Cable modem provisioning does not suffer from this distance limitation, but its deployment is limited to areas where the necessary cabling infrastructure is already present, which excludes most business and industrial parks.

Cable modems also have the additional advantage of being simpler to implement than DSL, which often requires professional installation services. On the other hand, DSL is intrinsically more secure than cable modems since DSL connections are dedicated-it is just your customer premises and the DSL provider on the network. With cable modems, all users in a given service area are on a shared LAN, and if your connection is not secured using a firewall, then other users in your neighborhood may be able to view and access shared files on your system.

Marketplace

Copper DSL is available from most telcos and carriers, including Sprint Corporation, Covad Communications Company, the various "baby Bells," and many others. Fiber DSL is being piloted by Pacific Bell Telephone Company and others.

Most cable companies provide cable modem access now, with AT&T being a major player in this market.

Prospects

While broadband Internet access services are becoming more and more widely deployed in the United States, the marketplace tends to be fractured, and solutions and equipment from one vendor often have interoperability issues with those from other vendors. This is especially the case with broadband wireless technologies.

One country that is taking a more aggressive approach to broadband is Japan. While the Japanese economy largely missed out on the narrowband Internet and PC revolution of the 1990s, the country is making strong efforts to become the world leader in implementing broadband Internet technologies, with companies such as Sony taking the lead.

See Also broadband transmission ,broadband wireless communications cable modem, Digital Subscriber Line (DSL), Internet access, xDSL

broadband ISDN (B-ISDN)

The broadband transmission counterpart of Integrated Services Digital Network (ISDN).

Overview

Broadband ISDN (B-ISDN) encompasses a set of International Telecommunication Union (ITU) standards and services designed to provide an integrated digital network for audio, video, and data transmission. Instead of using the copper media used in ordinary ISDN, broadband ISDN uses fiber-optic and radio media.

Broadband ISDN is designed to use the cell-switching transport technology of Asynchronous Transfer Mode (ATM) together with the underlying physical transport mechanisms of Synchronous Optical Network (SONET). Broadband ISDN standards and technologies were intended to provide high-speed digital connectivity for homes and businesses, but the technology was never widely deployed and has been superseded by Digital Subscriber Line (DSL) and other high-speed telco services.

See Also Digital Subscriber Line (DSL)

broadband transmission

A signaling technology that sends signals simultaneously over a range of different frequencies as electromagnetic waves. The opposite of baseband transmission.

Overview

Broadband transmissions are divided into multiple bands or channels by multiplexers using a multiplexing scheme such as frequency-division multiplexing (FDM). Each channel has a carrier frequency that is modulated to carry the signal from a given source. At the receiving station, multiplexers separate the various signals. Guard bands are used to prevent interference among channels.

Broadband signals are unidirectional-traveling in only one direction at a time-so a broadband system can generally either transmit or receive but cannot do both simultaneously. Broadband signals can be regenerated using amplifiers in order to travel longer distances before becoming attenuated.

Uses

Broadband transmission is typically used for environments in which video, audio, and data need to be transmitted simultaneously. Cable television systems are based on broadband transmission technologies, as are satellite-based television services. Examples of broadband services in the computer networking arena include T-carrier services, Asynchronous Transfer Mode (ATM), and the various flavors of Digital Subscriber Line (DSL).

See Also Asynchronous Transfer Mode (ATM), baseband transmission, broadband Internet access, broadband wireless communications, Digital Subscriber Line (DSL), T-carrier

broadband wireless communications

Generally refers to high-speed wireless communications systems where data rates are approximately 1 megabit per second (Mbps) or higher.

Overview

Broadband wireless (or wireless broadband) is an emerging high-speed communications technology that is being largely driven by the Internet access market. Broadband wireless systems achieve data rates comparable to Digital Subscriber Line (DSL) or cable modems and can be used in environments where these technologies are unavailable or difficult to deploy, such as isolated rural areas. And like DSL and similar technologies, broadband wireless is an always-on solution that provides fast access to the Internet and can be used in other corporate wide area network (WAN) scenarios as well.

Broadband wireless basically comes in three forms: fixed wireless, mobile wireless, and satellite-based.

Fixed broadband wireless is a technology that is gaining significant market share at all levels, from small businesses to the enterprise. In a typical fixed wireless scenario, a business requiring high-speed Internet access or a WAN connection deploys a broadband radio transmitter/receiver with a fixed unidirectional dish or horn antenna pointed toward the service provider's antenna. A clear line of sight is required between the customer premises antenna and the provider's antenna, which generally means customers deploy their antenna on their rooftop and providers deploy antennas on high towers, skyscrapers, or nearby mountains. Fixed wireless broadband can be based on various different technologies including Local Multipoint Distribution System (LMDS), Multichannel Multipoint Distribution System (MMDS), and others. Fixed broadband wireless communications systems are based on spread-spectrum communications technologies and may use frequencies from the Industrial, Scientific, and Medical (ISM) band's 2.5 GHz range up to millimeter wavelengths in the 66 gigahertz (GHz) range. Dedicated point-to-point microwave links can offer data transmission speeds of 10 Mbps or higher, but speeds of 1 or 2 Mbps are more common.

Mobile broadband wireless solutions are still in planning stages in most countries and regions, with Europe and Asia in the lead with planned rollouts of 3G cellular technologies such as Wideband Code Division Multiple Access (WCDMA) and Universal Mobile Telecommunication System (UMTS). Nevertheless, widespread deployment of these technologies probably will not happen until 2005 or later.

Mobile broadband services are also expected to provide significantly slower speeds than fixed solutions. For example a WCDMA system that provides 2 Mbps for fixed transmission can only support 384 Kbps for mobile (walking) transmission when handoffs are required, and may go as low as 144 Kbps for highway travel.

Satellite-based broadband wireless solutions generally offer speeds of around 2 Mbps, are easy to deploy, and are rapidly becoming more widely available. An in- depth discussion of how this technology works can be found in the article "satellite networking" elsewhere in this book.

Uses

Companies may implement broadband wireless in a variety of scenarios:

Advantages and Disadvantages

A primary advantage of broadband wireless over competing wired broadband technologies such as DSL or cable modems is their ease of setup and the speed at which they can be deployed. Industry reports indicate that DSL services sometimes take weeks to set up, but fixed broadband wireless solutions typically take only a day or two. In the rapidly evolving Internet economy where time-to-market is critical for new startups, deployment speed is a factor that has influenced many new companies in adopting broadband wireless solutions. In addition, many large companies are turning to broadband wireless to replace or provide backup for expensive leased lines such as T1 or E1 at a fraction of the cost of these lines. Some broadband wireless carriers are also looking at providing value-added services such as Voice over IP (VoIP) in the near future as part of their integrated package of services. Broadband wireless systems are also relatively secure because most are based on spread-spectrum wireless communications technologies, which means that signals are scrambled across a large number of frequencies, making it difficult to eavesdrop (a firewall is nevertheless recommended when implementing broadband wireless as this is an always-on solution). Finally, broadband wireless is often the only solution for customers in remote areas requiring broadband Internet access or WAN links.

Besides the line-of-site limitation, broadband wireless does have other disadvantages that need to be considered before deployment. High-frequency broadband wireless platforms such as LMDS are more easily influenced by environmental factors such as weather than systems that use the low-frequency ISM or other low- frequency bands, and that can be a consideration in certain locations. Satellite-based broadband services have a latency on the order of several hundred milliseconds (compared with under 20 msec for most wired land- based systems), which is fine for corporate data transmission but annoying to users for Web browsing.

Marketplace

In the fixed wireless broadband marketplace, many carriers and service providers are starting to provision broadband wireless for business and enterprise customers. Sprint Broadband Direct provisions 2 Mbps MMDS services, typically in a matter of days. MCI WorldCom is also making significant inroads into the MMDS market. Players in the higher-frequency LMDS market include Teligent, NextLink Communications, WinStar Communications, and others. AT&T is, of course, also a major player in the fixed wireless broadband market.

In the mobile wireless broadband market, the emerging players are currently Ericsson and Nokia, with their pre-third generation (3G) broadband cellular initiatives known as 2.5G.

In the satellite-based broadband wireless market, major players include DirecPC and StarBand Communications, both of which offer nationwide coverage. Tachyon also provides 2 Mbps service across the United States.

Notes

The Institute of Electrical and Electronics Engineers (IEEE) is standardizing fixed broadband wireless technologies under the new 802.16 group of standards.

See Also 802.16, broadband transmission, Digital Subscriber Line (DSL), Internet access, Local Multipoint Distribution Service (LMDS), Multipoint Multichannel Distribution Service (MMDS)

broadcast domain

The collection of all stations on a network that can receive broadcast messages from any station among them.

Overview

Broadcast domains and collision domains are two different things:

Examples of broadcast domains include

Notes

Bridges used to segment Ethernet networks divide collision domains but do not divide broadcast domains.

See Also collision domain

broadcast frame

In Ethernet networks, a frame broadcast to every station on the network.

Overview

An Ethernet media access control (MAC)-layer broadcast frame has a hexadecimal MAC address of FF-FF- FF-FF-FF-FF. This hexadecimal address is equivalent to 48 binary "ones." The meaning of this address in Ethernet is simply that this frame is intended to be received and processed by every connected node on the network.

Broadcast frames are typically generated when network services make announcements of their presence and availability to other hosts on the network. Too many broadcast frames on a network can degrade communication between nodes on the network.

Notes

In routed internetworks, routers are usually configured not to forward broadcast frames to other subnets. The reason is to prevent broadcast storms in one subnet from overwhelming hosts in other connected subnets. As a result of this limitation, however, broadcast frames used as service announcements are usually limited in scope to the local subnet on which the host providing the services is located.

See Also broadcasting ,broadcast packet ,broadcast storm directed frame, frame

broadcasting

A network communications method in which a packet or frame is sent simultaneously to all stations on the network.

Overview

Broadcasts take place when broadcast frames (or packets) are sent out over the network. These frames contain a special address that instructs every station on the network to accept and process the frame's contents.

Broadcasts have various functions on a network, including

Examples of Internet Protocol (IP) services that employ broadcasts include

Broadcasts are usually not an efficient use of network bandwidth, since only one or a few network stations might actually be interested in the information being broadcast. For this reason, directed frames (or packets) are used for most network communication, which involves targeting a packet directly for the intended station. (All other stations ignore the directed packet.) Another alternative is multicasting, which involves a form of limited broadcast to a select group of hosts.

Notes

Certain network conditions, such as certain types of device failure, can generate large numbers of unwanted broadcasts. These broadcast storms can sometimes bring down a network if the condition is not resolved.

Applications that are poorly designed may sometimes employ unnecessary amounts of broadcasting, with resulting degradation of overall network services.

See Also broadcast frame ,broadcast packet multicasting, unicasting

broadcast packet

In Internet Protocol (IP) networks, an IP packet broadcast to every host on the network.

Overview

Broadcasts can be used in any type of IP network, including class A, B, C, D, and E networks. The actual broadcast address depends on the class of network under consideration. For example:

The general broadcast address 255.255.255.255 is called a local area network (LAN) broadcast and can be routed to every host on an internetwork if routers are allowed to forward broadcasts. A faulty device that produces excessive 255.255.255.255 packets is said to be "flooding" the internetwork with broadcasts, and this can lead to a condition called a "broadcast storm."

The common denominator in these examples is 255, which is the decimal representation of the binary octet 11111111. Thus, the LAN broadcast address 255.255.255.255 in binary notation is a series of 32 binary "ones."

See Also broadcasting ,broadcast frame ,broadcast storm directed packet, packet

broadcast storm

A network condition in which so many broadcasts are occurring that normal communication between hosts is disrupted.

Overview

Broadcast storms commonly occur on Ethernet networks where baseband transmission technologies allow only one station to transmit at a time. The presence of broadcast storms often indicates that a networking component is malfunctioning and is continually sending out broadcast messages. A typical situation might be a failed transceiver on a network interface card (NIC) that is continually sending out a stream of binary "ones."

During a broadcast storm, the wire is continually busy and no other station is able to transmit information over the network. As a result, a broadcast storm essentially brings down the network. Since routers often are not configured to forward broadcast frames between subnets, broadcast storms usually are confined to a single subnet (configuring routers to forward broadcasts is thus a bad idea as a broadcast storm in one subnet could bring down the entire internetwork).

Broadcast storms might also indicate that your network's bandwidth is nearly saturated and needs to be upgraded.

See Also broadcasting

brouter

Any network device having the capabilities of both a bridge and a router.

Overview

Usually, a brouter acts as a router for one protocol (for example, Transmission Control Protocol/Internet Protocol [TCP/IP]) and a bridge for all other protocols (for example, Internetwork Packet Exchange/Sequenced Packet Exchange [IPX/SPX]). Network services often send their announcements over every protocol on the network, which generates additional traffic and makes it generally disadvantageous to run more than one protocol on a single network.

Brouters are not common anymore, however, and the solution adopted by most network designers nowadays is to use a single protocol for all network communication on the main portion of the network, with gateways connecting to segments running other protocols. The protocol of choice for most internetworking today is TCP/IP.

See Also bridge ,router

browse list

The list of available shared network resources on a Microsoft Windows network.

Overview

The browse list is maintained and distributed by the Computer Browser service. The browse list contains a list of all available domains, workgroups, and servers on the network. This list is then distributed to clients who desire to connect to shared resources on the network so that they can locate and connect to these resources.

Essentially, when you are browsing Network Neighborhood in Windows NT or My Network Places in Windows 2000, Windows XP, or Windows .NET Server, you are looking at a representation of the browse list for your locally accessible network.

Notes

The browse list is maintained by the master browser computer, but clients that need it obtain it from backup browsers on the network.

If a server or domain is not heard from by the master browser after three announcement periods (amounting to approximately 45 minutes), the server or domain is removed from the browse list.

See Also Computer Browser service ,election

browser (Computer Browser service)

Any Microsoft Windows machine that is running the Computer Browser service and participates in updating and maintaining the browse list of shared resources available on the network.

See Also Computer Browser service

browser (Web browser)

A client application that supports Hypertext Transfer Protocol (HTTP), the language of the World Wide Web.

See Also Hypertext Transfer Protocol (HTTP) ,Web browser

browsing

Generally, the process of exploring the shared resources available on a network or the Web content available on the Internet.

Overview

You can browse for shared resources on a Microsoft Windows network using Windows Explorer, My Network Places, and other tools. Browsing a Windows network is made possible by the Computer Browser service, which keeps track of all shared resources on a Windows NT network and communicates this information to clients when they need to access a resource. The Computer Browser service is at the core of the ability to locate shared file and printer resources on a network and maintains the browse list, the list of available shared resources.

Regarding the Internet, the term browsing refers to the process of using a Web browser such as Microsoft Internet Explorer, Netscape Navigator, or Opera Software's Opera to view and download Web pages from the Internet. The origin of the term probably stems from the idea of reading magazines, in which you pick up one magazine and skim through its contents, then go to another magazine, and so on. On the Internet, it is even easier. You do not have to "pick up" anything; you simply keep clicking the links.

See Also Computer Browser service ,Web browser

BSD

Stands for Berkeley Software Distribution, a family of UNIX operating systems.

Overview

BSD UNIX was developed in the 1970s at the University of California at Berkeley, which licensed the UNIX operating system from AT&T and then made a number of modifications and enhancements, including many common UNIX features such as the vi editor, the C shell, and Transmission Control Protocol/Internet Protocol (TCP/IP) networking.

BSD UNIX and its offshoots constitute one of the two most popular families of UNIX in use today, the other family being UNIX System V and its offshoots. BSD UNIX formed the basis of the SunOS from Sun Microsystems, but Sun later combined features of both BSD and System V into their popular Solaris operating system. BSD UNIX is older than Linux but has not attracted as much attention as Linux has lately.

The major flavors of BSD UNIX popular today include

Notes

The commercial version BSDi is now known as iXsystems and is licensed by Wind River Systems.

For More Information

For a general overview of BSD flavors, see www.bsd.orgFreeBSD can be found at www.freebsd.orgOpenBSD can be downloaded from www.openbsd.orgNetBSD can be found at www.netbsd.org

See Also UNIX

BSP

Stands for business service provider, an application service provider (ASP) that offers a wide range of online business services that include not just Web hosting and e-commerce services typical of ASPs but also customer relations management, desktop maintenance support, system integration and consulting services, and other value-added business services.

See Also application service provider (ASP) ,xSP

building-block services

A component of Microsoft Corporation's .NET platform that provides core Extensible Markup Language (XML) Web services.

Overview

Building-block services provide consistency and ease of use across services and applications developed for the .NET platform. These services are used to move the control of data from applications to the users who use these applications and ensure that user content forms the basis of all transactions.

Microsoft is developing a number of different building-block services to empower developers for rapid development of .NET Web services. Examples of these include services for

While Microsoft is developing the core set of .NET services, third-party partners will develop additional services to build in enhanced functionality to .NET applications and services.

See Also .NET platform

Building-centric Local Exchange Carrier (BLEC)

A telecommunications carrier focused on the Multitenant Unit (MTU) market.

Overview

With the increasing deregulation of the U.S. telecommunications industry over the last decades, several different types of local exchange carriers (LECs) have emerged in the marketplace, including Incumbent Local Exchange Carriers (ILECs) and Competitive Local Exchange Carriers (CLECs). The latest of these is the Building-centric Local Exchange Carrier (BLEC), which represents a carrier focused on providing broadband telco services within multitenant units (MTUs). An MTU is essentially a building or group of buildings that primarily host small and medium-sized businesses with between 10 and 200 employees. Examples of business environments serviced by BLECs include office skyscrapers, industrial parks, and hotels. Some BLECs also target residential apartment blocks and malls as well. By targeting MTUs, BLECs are essentially focusing on a market that ILECs have generally neglected (ILECs have historically focused on the large-enterprise and individual consumer markets instead). The requirements of BLEC clients are usually diverse, and typically include Internet Protocol (IP) data, Web hosting, e-mail, and Internet access, which BLECs offer as value-added data services to traditional voice telephone connectivity.

BLECs can typically be grouped into two categories:

Implementation

Typically a single business client within an MTU cannot justify the cost of having a leased line such as T1 deployed to service its needs. That is where BLECs come in, however-they provision such services for all clients within a given MTU.

Building-centric Local Exchange Carrier (BLEC). How a BLEC provisions customers with broadband services.

Typically, a BLEC first has to provide new fiber to an MTU to provide clients with high-speed services brokered from larger LECs and IXCs. This first step is necessary because the majority of large office buildings in the United States do not currently have fiber-optic cabling deployed to them. Once fiber has been laid by the BLEC from the building to the central office (CO) of the LEC or IXC from which the BLEC obtains wholesale broadband provisioning, the BLEC then purchases T1 or T3 services from the LEC or IXC to run over the fiber. Switching gear (usually a DSLAM, an Asynchronous Transfer Mode [ATM] access switch, or some form of high-speed Ethernet switch) is then deployed by the BLEC in the basement of the MTU to provide broadband services to clients throughout the building. This arrangement is preferable to co-locating such equipment at LECs and IXCs and often give BLECs a competitive edge in the speed at which new services can be deployed and problems troubleshot.

Another technology option for BLECs is fixed broadband wireless, which bypasses the initial step of laying fiber to the building. This is often a method for cost- effective provisioning of broadband services for MTUs that is easy to implement rapidly and is often the only solution when the MTU is too far from a central office (CO) for DSL or T-carrier services to be effective.

To provision either of these scenarios, BLECs first have to negotiate right-of-way through revenue-sharing agreements with building owners to gain access to basement wiring closets or deploy rooftop antennas, and this is usually factored into the price for services offered by BLECs to tenants.

Marketplace

Some of the major players among BLECs include Broadband Office, which has right-of-way to a large portion of U.S. commercial office space; Comactive, which is an offshoot of Intermedia Communications; and many others.

Prospects

With increasing deregulation of the telecommunications industries, BLECs find themselves squeezed by rising customer expectations on the one hand, high levees from building owners for fiber and rooftop right-of-way on another hand, and direct competition from CLECs, ILECs, and IXCs higher up on the carrier feeding chain. Customers owning multiple MTUs desire simultaneous rollout regardless of the up-front costs to BLECs for servicing smaller premises. Some building owners (usually real estate companies) are also consider deploying their own broadband switching gear instead of partnering with BLECs to do so and thus bypass BLECs entirely by going to LECs and IXCs directly. Future rulings of the Federal Communications Commission (FCC) might also affect how this all works out in the marketplace.

Notes

Another common name for BLECs is Multitenant Broadband Service Providers (MBSPs).

See Also broadband Internet access ,broadband wireless communications carrier, inter-exchange carrier (IXC), local exchange carrier (LEC), multitenant unit (MTU)

built-in account

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a type of user account that is created during installation.

Overview

All computers running Windows 2000, Windows XP, and Windows .NET Server, have two built-in user accounts:

Depending on whether the computer is a domain controller, a member server, or a workstation, built-in accounts will be either local user accounts or global user accounts. A built-in account on a domain controller is a global user account that exists everywhere within the domain. Users can log on to any machine in the domain using such an account, which provides administrators with the capability of administering a Windows 2000-based network from anywhere on the network. On a member server or workstation, the Administrator and Guest accounts are local user accounts and exist only on those machines.

Notes

Rename the Administrator built-in user account to make it more secure.

See Also built-in group

built-in domain local group

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a domain local group created during installation that has preassigned rights and permissions. Built-in local groups are used to simplify the administrative task of assigning users and groups rights to perform system tasks and permissions to access network resources. Some of these groups include

See Also built-in global group

built-in global group

A type of global group created during installation of Active Directory directory service.

Overview

Built-in global groups are created in order to organize common groups of users for administrative purposes. These built-in global groups are created within either Active Directory (when implemented) or in the Security Accounts Manager (SAM) database (for stand-alone servers). The four types of built-in global groups are

See Also built-in group ,built-in domain local group

built-in group

In Microsoft Windows 2000 and Windows .NET Server, a type of group created during installation to simplify the delegation and assignment of common administrative tasks.

Overview

Built-in groups have preassigned sets of user rights, and some also have preassigned members.

Windows 2000 and Windows .NET Server contain three kinds of built-in groups:

Notes

You cannot rename or delete a built-in group, and you cannot change the membership of a built-in identity.

See Also built-in global group ,built-in domain local group

built-in identities

In Microsoft Windows 2000, Windows XP, and Windows .NET Server, a term used to refer to what were known in Windows NT as system groups.

Overview

Built-in identities can represent different subsets of users in different situations, and they do not have a specific membership that administrators can modify. However, you can assign built-in identities rights and permissions for accessing resources or performing system tasks. Examples of built-in identities include

See Also built-in group

burst

A condition in which network activity rises suddenly for a short period of time.

Overview

A burst is a transient elevation in network activity, and a network on which a lot of bursts occur is said to be bursty. Bursty networks have different bandwidth requirements than networks on which the traffic is steady, and they need to be designed accordingly. For example, a network on which large video files are frequently transmitted tends to be bursty in its traffic flow.

Bursts can be indicative of a sudden increase in demand for network resources, or they can indicate hardware or software problems. Some networking components are capable of briefly sending data at speeds greater than normal transmission speeds; this is referred to as "operating in burst mode."

A good first step in accommodating bursty conditions is to use Ethernet switches instead of hubs for concentrating your network connections.

bus

A linear circuit path that can be used to connect multiple devices for exchange of data.

Overview

The idea of a bus in computer networking technology is analogous to that of a bus as a means of transportation: a bus travels over a fixed route across a city, carrying people and stopping at various points for people to get on or off. In the same way, computers and networks use buses to transport data from one device to another. The point on a bus where a device can be connected is generally called a slot.

Buses generally fall in three categories: system buses, peripheral buses, and network buses (or bus topology networks).

System buses are internal to computer systems and are used to carry data between the processor, chipset, memory, disk subsystem, video subsystem, and peripheral cards such as network adapters and sound cards. Examples of different types of system buses include

When the term bus is used in conjunction with computer systems, it is commonly interpreted as meaning input/output (I/O) bus. The I/O bus has gone through many changes over the years, including the following:

Peripheral buses are buses whose primary use is for connecting peripherals to computer systems or network switches. Examples of this type include Small Computer System Interface (SCSI) and Fibre Channel.

Network buses (or bus topology networks) represent any form of network in which devices are connected together in linear fashion. Examples include 10Base2 and 10Base5 Ethernet and Token Bus networks, all three of which are obsolete. Most networks today are based on a star topology, which is easier to manage than bus topology because of its centralized nature.

Prospects

The state of system bus technology is currently in flux. Whereas previously networks could not keep up with their servers, now the server has become the bottleneck: a Peripheral Component Interface (PCI) local bus has a difficult time performing I/O fast enough to fully utilize a Gigabit Ethernet (GbE) network connection. The result has been various industry initiatives to speed up the I/O bus to match rapidly growing network capacity (10 GbE is now on the horizon). Another source of pressure has been the increasing need for modern servers to be able to rapidly access large amounts of database storage, sometimes in the terabyte range.

Some of the newer industry initiatives for evolving system buses include

Other proposals include using high-speed SCSI technologies (such as Ultra160 SCSI) and FiberChannel for internal system buses, but these initiatives have not gained much momentum.

Notes

A bus and a port are both similar in that they transport data between devices, but although a port can be used only to connect two devices, a bus can connect three or more devices.

See Also 10Base2 ,10Base5 ,Fibre Channel ,Infiniband (IB) ,Small Computer System Interface (SCSI)

business logic

That portion of an application that reflects the actual way the enterprise does business.

Overview

Business logic is a term used in writing applications for Microsoft Transaction Server (MTS) using reusable COM+ components. These components represent a combination of logon verifications, policies, database lookups, validation edits, and other processes that constitute how business is done in the enterprise. An application's business logic specifies how the component's programming logic reflects the actual way the enterprise does business. Business logic enables consistent and logical processing of business data.

A representation of a real-world component of the enterprise's business is called a "business object." Examples of business objects include customers, orders, products, invoices, and anything else that can be encapsulated in an application's business logic and manipulated by its users.

business-to-business

Also known as B2B, e-commerce between different companies that have a partnering arrangement.

See Also B2B

business-to-consumer

Also known as B2C, a relationship in which individuals or companies purchase the services of another company.

See Also B2B

bus topology

A networking topology that connects networking components along a single cable or that uses a series of cable segments that are connected linearly.

Overview

A network that uses a bus topology is referred to as a "bus network." Bus networks were the original form of Ethernet networks, using the 10Base5 cabling standard. Bus topology is used for

Bus topology is the cheapest way of connecting computers to form a workgroup or departmental LAN, but it has the disadvantage that a single loose connection or cable break can bring down the entire LAN.

Notes

A hub or concentrator on an Ethernet network is really a collapsed bus topology. Physically, the network appears to be wired in a star topology, but internally the hub contains a collapsed bus, creating a configuration called a star-wired bus. However, in this case, a failure in one of the cables does not affect the remaining network.

Communication problems on bus networks might indicate that the bus ends are improperly terminated. A break in the cable will produce a similar result, since the ends of the break are not terminated. Use a cable tester to determine the problem's nature and location.

See Also mesh topology ,ring topology ,star topology


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Microsoft Encyclopedia of Networking
Microsoft Encyclopedia of Networking
ISBN: 0735613788
EAN: 2147483647
Year: 2002
Pages: 36
Authors: Mitch Tulloch, Ingrid Tulloch
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