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E-carrier

The digital telecommunications services backbone system of Europe, a format standardized by the International Telecommunication Union (ITU). E-carrier services were developed in the 1970s and became widely available in the 1980s. E-carrier services can be used for wide area network (WAN) connections, for high-speed Internet connections, for private videoconferencing services, and for public frame relay services. E-carrier services are generally available wherever the parallel T-carrier services are not.

E-carrier transmissions are graded E1, E2, and so on in order of increasing transmission speeds. These different service grades are multiples of the basic DS0 data transmission rate, similar to the T-carrier system of North American telecommunications carriers.

The E-carrier service rates are specified by the organization CEPT (Conférence Européenne des Administration des Postes et des Télécommunications, or European Conference of Postal and Telecommunications Administrations). The most popular of these services, E1, is also the slowest. E1 transmits data at speeds of up to 2.048 Mbps over two pairs of twisted wires. It consists of 31 separate 64-Kbps DS0 channels multiplexed together, each of which can carry either a voice conversation or a stream of data. E1 is sometimes referred to as 2-Meg.

graphic e-1. e-carrier.

Graphic E-1. E-carrier.

The E-series transmission rates are shown in the table included in the article on DS0 elsewhere in this work. E-carrier lines use 8 bits per channel for encoding signals and do not rob bits for control signals as T-carrier lines do.

NOTE

If the E1 service entering your customer premises needs to connect directly to a different building, you have two solutions. First, you could have the service provider extend the E1 line to the other building, thus moving the demarcation point (termination point) of the line. This could be costly, however. A simpler solution might be to connect the E1 line to a fiber-optic line driver, lay down a fiber-optic cable from the line driver to a similar driver in the other building, and then connect the remote line driver to your E1 equipment.

edbutil

A command-line tool for versions 4.0 and 5.0 of Microsoft Exchange Server. Edbutil can be used to defragment, repair, and check the integrity of the following Exchange Server databases:

Edbutil works at the Joint Engine Technology (Jet) level and attempts to find and repair inconsistencies. It can also be used to defragment these databases, resulting in a database size reduction.

NOTE

In Exchange Server version 5.5, the edbutil utility has been replaced by the newer tool eseutil.

TIP

Use this utility with caution, and make sure that you have backed up the information store and directory databases first! Microsoft recommends using this utility only when troubleshooting Exchange Server problems in consultation with Microsoft Technical Support.

EDGE

See Enhanced Data Rates for Global Evolution (EDGE)

edge router

A device in an Asynchronous Transfer Mode (ATM) network that routes data between an ATM backbone network and local area networks (LANs). Edge routers can be used to translate Ethernet or Token Ring data for transmission over ATM backbones. This allows ATM to be used as a backbone for connecting multiple LANs into a metropolitan area network (MAN) or wide area network (WAN). An alternative and more commonly used configuration is to connect LAN networking equipment directly to ATM backbone switches, which provide points of contact with an ATM provider’s backbone network. An edge router can function as an ATM switch and provide routing capabilities for LAN networking protocols—all in one hybrid device.

graphic e-2. edge router.

Graphic E-2. Edge router.

EDI

See electronic data interchange (EDI)

effective permissions

In Microsoft Windows NT and Windows 2000, the cumulative permissions a user has for accessing a resource based on his or her individual permissions, group permissions, and group membership. The effective permissions a user experiences trying to access a file or folder depend on the various permissions granted to the user expressly or by virtue of their membership in a particular group. When a permissions conflict exists between one group and another, or between the user and a group, rules are applied that resolve the issue.

How It Works

In networks based on Windows NT or Windows 2000, calculation of effective permissions can be determined using three simple rules:

First, if a user belongs to two (or more) groups, and these two groups have different NTFS standard file permissions on a given file, the user’s ability to access the file both locally and over the network is determined as follows:

Second, if a user belongs to two (or more) groups, and these two groups have different shared folder permissions on a given shared folder, the user’s ability to access the shared folder over the network is determined as follows:

Third, when a user attempts to access a folder or file over a network that has both NTFS permissions (the first example) and shared folder permissions (the second example) configured on it, the effective permission is the most restrictive (least permissive) permission. For example,

read (NTFS) + change (shared folder) = read (combined)

See also NTFS permissions (Windows 2000), NTFS permissions (Windows NT), shared folder permissions

EFS

See Encrypting File System (EFS)

EGP

See Exterior Gateway Protocol (EGP)

EIA

See Electronic Industries Alliance (EIA)

EIA/TIA wiring standards

Standards for commercial and telecommunications wiring developed by the Electronic Industries Alliance (EIA) and Telecommunications Industry Association (TIA). These standards are also supported by the American National Standards Institute (ANSI). The EIA/TIA wiring standards actually consist of a group of standards covering different aspects of premise cabling and other wiring practices. These standards include the following:

For more information, see the Web sites for the EIA and TIA listed in this entry.

TIP

When installing wiring for your network, be sure to follow the EIA/TIA standards, both for legal reasons and to ensure that your network will function as expected. Be sure also to follow any local or state building codes.

On the Web

•

Electronic Industries Alliance (EIA) : http://www.eia.org

•

Telecommunications Industry Association (TIA) : http://www.tiaonline.org

election

See browser election

electromagnetic interference (EMI)

Electrical noise induced in cabling by the presence of nearby electrical equipment such as motors, air conditioners, fluorescent lights, and power lines. Electromagnetic interference (EMI) can interfere with the transmission of signals.

EMI is only a problem with copper cabling. It’s caused when the changing electromagnetic fields generated by one cable induce extraneous currents or interference in adjacent or nearby cables. EMI in copper cabling can be reduced to acceptable levels by

EMI can be a greater concern in heavy industrial settings where high voltages and equipment, such as motors and generators, produce high levels of electrical noise. Using coaxial cabling in these settings affords greater resistance to the effects of EMI than using twisted-pair cabling. Fiber-optic cabling is an even better solution in heavy industrial settings because it is wholly resistant to EMI. (Changing electromagnetic fields have no effect on the light waves traveling along a glass fiber.)

electronic data interchange (EDI)

A standard format developed by the Data Interchange Standards Association (DISA) in which companies can exchange business data and financial transactions. Electronic data interchange (EDI) is defined in the American National Standards Institute (ANSI) standard called X.12.

How It Works

The basic unit of an EDI transmission is the message, which consists of a transaction set with a header and footer attached. A transaction set is roughly equivalent to a typical business form, such as a purchase order, and consists of a number of data segments, each containing various fields delimited by some character. These fields represent individual elements of the business transaction, such as company name, account number, quantity, and so on; they are formatted according to a standard code. This code is implemented as a map between your business application’s data fields and the type of EDI standard that is appropriate for the transaction being performed.

EDI data can originate from any computing level, from mainframe to local area network (LAN) server. Systems communicate through EDI translation software that formats the data into standard EDI encoding and exchange information—either through a direct dedicated link between business partners or through an external third-party value-added network (VAN) service provider that acts as a clearinghouse for EDI transactions. If a VAN is used, as it normally is, the VAN processes EDI messages and routes them to the appropriate electronic mailbox for the destination business partner, who can then retrieve the EDI messages from the mailbox and process the transactions using business applications.

On the Web

•

Data Interchange Standards Association (DISA) home page : http://www.disa.org

Electronic Industries Alliance (EIA)

The main trade organization representing the U.S. high-tech community. The Electronic Industries Alliance (EIA) was founded in 1924 as the Radio Manufacturers Association. It plays an important role in enabling U.S. electronics producers to be competitive by developing technical standards, hosting trade shows and seminars, performing market analysis, and facilitating relations with the government. The EIA represents a broad spectrum of U.S. electronics manufacturing interests.

The EIA is organized along the lines of specific electronic products and markets, with each sector, group, or division having its own board of directors and its own agenda for enhancing competitiveness. Major divisions include the components, consumer electronics, electronic information, industrial electronics, government, and telecommunications divisions.

An important computer networking function of the EIA is the series of standards for residential and commercial network cabling that are collectively known as the EIA/TIA wiring standards. Individuals and companies installing cabling for computer networks must follow these standards in order to comply with government legal and safety requirements.

On the Web

•

Electronic Industries Alliance (EIA) home page : http://www.eia.org

e-mail

Stands for electronic mail; any system for sending and receiving messages over a network. E-mail originated in the early 1970s with ARPANET and is now the primary method of business communication today.

Many vendors and organizations have developed electronic messaging standards and formats, including the IBM mainframe host-based PROFS and SNADS messaging systems, Microsoft Mail, Lotus cc:Mail, and Novell GroupWise. The two most popular messaging formats used today are the Internet Simple Mail Transfer Protocol (SMTP) and X.400 mail systems.

X.400 is a popular messaging format that is used throughout much of Europe, but SMTP mail, which was developed in the United States as part of the ARPANET project, enjoys worldwide popularity and acceptance. Both systems are based on a client/server architecture, with messaging clients sending e-mail to mail servers that act as message transfer agents by routing messages through a backbone of mail servers to their final destination. Microsoft Exchange Server is Microsoft’s premiere e-mail messaging server software, and combined with the Microsoft Outlook client, it makes a full-featured messaging and collaboration system. Microsoft Exchange Server supports interoperability with most existing messaging systems, including SMTP, X.400, Microsoft Mail, and Lotus cc:Mail.

e-mail address

Any of several types of addresses that ensure an e-mail message reaches its intended recipient. An e-mail address must contain sufficient information so that the message can be routed to its specific recipient. There are various kinds of e-mail address formats depending on the e-mail system in use. Address formats typically include at least two parts:

The following table shows some examples of e-mail address formats.

E-Mail Address Formats

Type of Address Example

SMTP (Internet)

BobS@Northwind.Microsoft.com

Microsoft Mail

Northwind/MICROSOFT/BOBS

Lotus cc:Mail

BobS at Northwind

X.400

C=US;a=SPRINT;p=Microsoft;o=Northwind;s=BobS

emergency repair disk (ERD)

A recovery tool for repairing missing or corrupt files or restoring the registry on a Microsoft Windows NT or Windows 2000 system. Having a current copy of the emergency repair disk for each server on your network is an important part of preparing for disaster recovery.

How It Works

An emergency repair disk (ERD) contains compressed versions of registry hive, default user profile, setup.log, and other system configuration files. An ERD can be created any time using the rdisk utility, and should always be created after installing new services or software or upgrading hardware or device drivers on a system.

An ERD cannot be used to boot a computer running Windows NT or Windows 2000. To perform a system recovery of a machine running Windows NT using an ERD, boot your system using the three boot floppies and select the Repair option from the appropriate menu. Then select the specific repair options you want to perform, namely

To perform a system recovery on a machine running Windows 2000, try booting to Safe Mode first by pressing the F8 function key during startup. If this fails or if the system cannot be repaired, boot the system using the four boot floppies, select the Repair option by pressing the R key when prompted, and then either use the ERD to attempt a repair or press C to open the Recovery Console. The Recovery Console is a powerful command-line interface to the operating system, designed for use by advanced administrators only.

TIP

If you can’t find your three Windows NT boot floppies, you can create a new set by running the command winnt32/ox from the Windows NT compact disc on a working computer running Windows NT. To create the four Windows 2000 boot floppies, insert the Windows 2000 compact disc and a blank floppy into any machine running MS-DOS or Windows, click Start, select Run, and enter the following path into the Run box:

 <cdrom_drive>\bootdisk\makeboot a:

emergency startup disk

A startup disk created during a Microsoft Windows 95 or Windows 98 setup that can be used to troubleshoot Windows 95 and Windows 98 boot problems. Having a current copy of the emergency startup disk for each machine running Windows 95 or Windows 98 on your network helps with disaster recovery if these machines fail to boot properly.

The emergency startup disk contains files necessary to load a command-line version of Windows 95 or Windows 98, plus other useful system-recovery utilities, including a real-mode registry editor. When you insert an emergency startup disk into your computer and reboot, the computer starts from the disk instead of from your hard drive.

TIP

You should create a new emergency startup disk whenever you make a configuration change to a machine running Windows 95 or Windows 98—for example, when you install new hardware or update device drivers.

EMI

See electromagnetic interference (EMI)

encapsulation

Generally, a process by which a lower-layer protocol receives data from a higher-layer protocol and then places the data into the data portion of its frame. Thus, encapsulation is the process of enclosing one type of packet using another type of packet. Encapsulation at the lowest levels of the Open Systems Interconnection (OSI) reference model is sometimes referred to as framing. Examples of encapsulation include the following:

The data-link layer (layer 2) of the OSI model for networking is responsible for encapsulation or framing of data for transmission over the physical medium. In local area network (LAN) technologies, this is usually Carrier Sense Multiple Access with Collision Detection (CSMA/CD) for Ethernet networks. For wide area network (WAN) technologies, the data-link protocols used depend on whether the communications are point-to-point or multipoint:

Encrypting File System (EFS)

A Microsoft Windows 2000 core technology for storing encrypted NTFS files on disk; designed to protect data on NTFS volumes from local access by unauthorized users.

How It Works

Encrypting File System (EFS) is a public key cryptography scheme based on the Data Encryption Standard (DES) that runs as a Windows 2000 system service and is transparent to the user. EFS is simple to use and automatically generates an encryption key pair for the user who is logged on if one does not already exist. The user’s private key, stored in Active Directory, is used for decrypting encrypted files and folders.

Each time EFS encrypts a file or folder, it generates a random encryption key. EFS encrypts this encryption key using the user’s public key. EFS stores encryption keys in the nonpaged pool of memory.

To access an encrypted NTFS file, the user must meet one of the following criteria:

You can encrypt or decrypt a file or folder on an NTFS volume with the Advanced button on the General page of that file or folder’s property sheet. You can also enable or disable encryption from the command prompt using the cipher command.

NOTE

EFS does not work on FAT volumes.

TIP

If you are working with applications that create temporary files, you might want to enable encryption at the folder level instead of the file level in order to guard against unauthorized access to your temporary files. With folder-level encryption, all files in the folder are encrypted.

encryption

The process of rendering a message (or data) unusable to all but the intended recipients, who have the ability to decrypt it. Cryptography is the science of creating workable procedures for encrypting and decrypting messages. The goal is to ensure that a message intercepted by a distrusted user cannot be decrypted in a feasible amount of time.

How It Works

Although there are many different approaches to encryption, the two most common are

For example, if user A wanted to send an encrypted message to user B, it would typically work like this:

  1. User A requests user B’s public key or obtains this key from a certificate authority (CA) that both users trust.

  2. User A encrypts his message using user B’s public key and sends the encrypted message to user B.

  3. User B receives the encrypted message from user A and decrypts it with user B’s private key.

    graphic e-3. the public key encryption method.

    Graphic E-3. The public key encryption method.

NOTE

The preceding approach outlines the steps used for encrypting and decrypting the actual message being transmitted during a secure communication session. A different approach, called a digital signature, is used to confirm the authenticity of the sender and the integrity of the message. Digital signatures are encrypted in a reverse fashion to the message itself. Specifically, if user A wants to send his digital signature to user B, then

  1. User A creates a hash of his message using a hashing algorithm. This hash forms the basis of the digital signature, which user A then encrypts using his own private key.

  2. User A appends the encrypted digital signature and his own public key to the message, which is then encrypted using user B’s public key.

  3. User B receives the message and attachments, decrypts its contents using her own private key, and uses user A’s public key to decrypt the digital signature that user A attached to the message. User B then generates a hash of the received message and compares this to the digital signature that user A sent. If the two are identical, it is unlikely that the message has been tampered with in transit.

See also public key cryptography

encryption algorithm

A mathematical procedure for encrypting data. Encryption algorithms form the basis by which encryption can take place and are fundamental to cryptography.

How It Works

Encryption algorithms generally use some kind of mathematical key (chosen from a large set of available keys) to transform plaintext (the data being encrypted) into ciphertext (the resulting encrypted data). An encryption algorithm must be reversible so that the recipient can use another mathematical key to decrypt the data in order to read it. A good encryption algorithm is difficult to decrypt if you don’t know the decrypting key. It might take massively parallel computers centuries (or aeons) of intense computing, trying all possible keys, to decrypt a typical message without knowing the specific decryption key.

Encryption algorithms typically perform their encryption process on multibyte segments of data instead of on one byte at a time. Such an algorithm is referred to as a block cipher. For example, the Data Encryption Standard (DES) algorithm, a 56-bit key algorithm used for many years by the U.S. government, encrypts data 8 bytes at a time.

End-User License Agreement (EULA)

A type of contract between a computer software publisher and the purchaser of the software that outlines the various rights granted to the purchaser for the legal use of the software. The End-User License Agreement (EULA) for a software product is usually found on a separate piece of paper accompanying the product, inside the front cover of the user manual, or on screen prior to installing the software. You should read and become familiar with the terms of your EULA for the software you purchase. Failure to follow the terms of the EULA might open you or your company to prosecution for software piracy.

TIP

You can access the EULA for Microsoft Windows 98 by opening the text file license.txt. It is located in the \Windows folder. In Windows 2000, the file is called eula.txt and is located in the \System32 folder.

On the Web

•

Microsoft antipiracy site : http://www.microsoft.com/piracy

enhanced category 5 cabling

Sometimes referred to as CAT5E, an informal cabling standard that some cable manufacturers use to refer to category 5 cabling that is capable of supporting transmission speeds faster that 100 Mbps. At present, there is no official standard for unshielded twisted-pair (UTP) cabling above category 5, although category 6 and category 7 specifications have been proposed. In other words, there is no standard or specification that has been agreed upon for defining category 6 or higher UTP cabling, although steps are being made to develop one.

How It Works

Enhanced category 5 cabling has certain electrical characteristics that make it the recommended type of cabling for most new networking installations. Supporting frequencies up to 350 MHz or higher, it is typically 4-pair solid conductor 24-gauge UTP cabling that has a low capacitance in the range of 13 to 14 pF/ft, as compared with regular category 5 cabling that has a capacitance of around 17 pF/ft. Its impedance is 100 ohms, the same as for regular category 5 cable. CAT5E cabling is suitable for Fast Ethernet installations, Integrated Services Digital Network (ISDN) wiring, 155-Mbps Asynchronous Transfer Mode (ATM) networks, and other present and proposed high-speed networking solutions such as 1000BaseT.

TIP

If you plan to use enhanced category 5 cabling in your network, you should make sure that all your other wiring components match these specifications. This means purchasing and installing enhanced category 5 patch panels, wall plates, and other components. Also, be sure to strictly follow wiring guidelines because improper installation of enhanced category 5 cabling will result in loss of potential bandwidth. The real key to operating a successful high-speed UTP wiring system is careful installation.

Enhanced Data Rates for Global Evolution (EDGE)

A proposed upgrade to the hardware for the General Packet Radio Service (GPRS) packet-switched wireless mobile data service. Enhanced Data Rates for Global Evolution (EDGE) is designed to provide mobile users with wireless roaming data services of up to 400 Kbps.

EDGE can be deployed by many Global System for Mobile Communications (GSM) providers as an upgrade for existing GSM systems within the GSM Phase 2+ initiative, which is planned for the years 2000–2001. GSM networks do not require new network elements to implement EDGE, although some hardware and software upgrades will be required. EDGE uses a different modulation technique called phase-shift keying that allows it to provide higher data rates than existing GSM systems over reduced areas of coverage.

EDGE can be deployed on both circuit-switched and packet-switched cellular services. In North America, EDGE can be deployed by Time Division Multiple Access (TDMA) cellular providers under the IS-136 standard. Initial test deployments are planned for the year 2000.

See also General Packet Radio Service (GPRS)

enterprise

A large company, geographically distributed with a large number of users. In this context, an enterprise-level network of computers refers to the network belonging to an enterprise; that is, a network that typically consists of thousands of computers distributed across several geographically remote locations and connected by WAN links.

Enterprise-level networks generally use the TCP/IP protocol and are divided into a number of smaller networks called subnets, which are joined using routers. Enterprise-level networks are often heterogeneous networks consisting of different protocols and operating systems such as Microsoft Windows NT and Windows 2000, Novell NetWare, and varieties of UNIX, all interoperating to various degrees. Enterprise-level networks can include legacy mainframe and minicomputer systems as well.

This mixture of systems and protocols can make it challenging to administer and manage an enterprise-level network and offers a good argument for upgrading legacy systems to newer, standardized ones. Companies can save considerable costs in the long run by upgrading their networks to secure, reliable, scalable network operating systems such as Windows NT and Windows 2000. The initial cost of upgrades and training are quickly recouped through lower maintenance and administration costs, the result of migrating an enterprise’s heterogeneous combination of systems and protocols to a homogeneous network consisting of computers running Windows NT or Windows 2000, and running TCP/IP.

Enterprise Admins

A built-in group for the Microsoft Windows 2000 operating system platform. Enterprise Admins is one of four predefined global groups that Windows 2000 creates by default to help administrators organize users in their network. The other three groups are Domain Users, Domain Guests, and Domain Admins. While Domain Admins are those users who can perform administrative tasks on any computer belonging to the domain, the Enterprise Admins group is intended to have an even larger scope. Enterprise Admins need to be able to perform administrative tasks on any computer in the enterprise. A Windows 2000–based enterprise can consist of a number of domains interconnected in a domain tree, or even several domain trees connected into a domain forest. Enterprise Admins can administer the entire network for the enterprise. Just as with the Domain Admins group, the Enterprise Admins group has one initial member: the Administrator user account that belongs to the local domain.

enterprise resource planning (ERP)

A general term describing the entirety of the business functions of an enterprise. Enterprise resource planning (ERP) includes tasks such as planning, purchasing, tracking orders, supplying customers, managing inventory, servicing customer requests, producing financial reports, and bookkeeping.

ERP software is modular software designed to integrate these various business functions and simplify their management. ERP software typically consists of an integrated suite of tools for performing standard line-of-business functions such as payroll, accounting, inventory management, and order entry. ERP software is used in transportation and automotive businesses, industrial environments, and other large industrial settings. ERP software lets these large businesses manage diverse business resources across the enterprise in order to plan more effectively for growth and expansion.

Because most business data is stored in databases, ERP software usually depends on the database-management program used. Microsoft SQL Server forms a robust and scalable foundation on which to build ERP software.

enterprise server

A designated server running Microsoft Windows NT or Windows 2000 in an enterprise, which is used as a central repository for software licensing information regarding Windows NT, Windows 2000, or Microsoft BackOffice. An enterprise server is typically a primary domain controller (PDC) but can also be a stand-alone server that is not part of any domain in the enterprise. All PDCs in the enterprise replicate their licensing information with the enterprise server, so the enterprise server contains a master database of this information. If there is only one domain in the enterprise, the PDC for that domain is the master licensing server. If there are several domains, each domain’s PDC keeps track of licenses for that domain, and all PDCs then replicate their licensing information to the specifically designated enterprise server. Stand-alone member servers that are not part of any domain also need to replicate their licensing information with the enterprise server.

NOTE

You can have more than one enterprise server in your enterprise, but it is simplest to have only one because enterprise servers cannot replicate with each other.

See also License Manager

environmental subsystems

Components of the Microsoft Windows NT or Windows 2000 operating system that support the running of applications from different operating system architectures. Environmental subsystems provide the necessary “environment” in which these applications can run. They are an essential part of the Windows NT operating system that enables cross-platform support for applications written for different operating systems. Windows NT and Windows 2000 include the following environmental subsystems:

NOTE

MS-DOS-based applications run on Windows NT in the context of a Win32 application called a Virtual DOS Machine (VDM) that emulates an MS-DOS environment.

environment variables

String variables containing information that an operating system uses to control services and applications. The PATH and TEMP variables used in the autoexec.bat file in MS-DOS were early examples of environment variables. Microsoft Windows NT and Windows 2000 offer a more extensive selection. For example, environment variables for Windows NT include the following:

You can view and specify environment variables in Windows NT and Windows 2000 by using the System utility in Control Panel. Environment variables may be used in logon scripts by enclosing them within percent symbols; for example, %USERNAME% contains the currently logged on user name.

NOTE

The System utility in Control Panel shows only a portion of the system environment variables defined on a system running Windows NT or Windows 2000.

ERD

See emergency repair disk (ERD)

ERP

See enterprise resource planning (ERP)

eseutil

A command-line tool for version 5.5 of Microsoft Exchange Server. Eseutil can be used to defragment, repair, and check the integrity of the following Exchange Server databases:

Eseutil works at the Joint Engine Technology (Jet) level and attempts to find and repair inconsistencies. You can also use eseutil to defragment these databases, resulting in a database size reduction.

NOTE

Eseutil replaces the earlier utility edbutil that was used with Exchange Server versions 4 and 5.

TIP

Use this utility with caution, and make sure that you have backed up the information store and directory databases first! Microsoft recommends using this utility only when troubleshooting Exchange Server problems in consultation with Microsoft Technical Support.

ESMTP

Stands for SMTP Service Extensions, an extension to the Simple Mail Transfer Protocol (SMTP) protocol that lets receiving SMTP hosts inform sending hosts of the extensions that it supports. ESMTP requires no modification of the SMTP configuration of either the client or the mail server.

How It Works

Instead of beginning the session with the helo command, the receiving host issues the ehlo command. If the sending host accepts this command, the receiving host then sends it a list of SMTP extensions it supports. The sending host then knows which SMTP extensions it can use to communicate with the receiving host.

NOTE

The Internet Mail Service for Microsoft Exchange Server version 5.5 supports ESMTP. The ESMTP standard is defined in Request for Comments (RFC) number 1869.

Ethernet

The most popular network architecture for local area networks (LANs). Ethernet was originally developed by Xerox in the 1970s and was proposed as a standard by Xerox, Digital Equipment Corporation (DEC), and Intel in 1980. A separate standardization process for Ethernet technologies was established in 1985 in the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard known as Project 802. The IEEE standard was then adopted by the International Organization for Standardization (ISO), making it a worldwide standard for networking. Because of its simplicity and reliability, Ethernet is by far the most popular networking architecture used today. It is available in three different speeds:

How It Works

Ethernet specifications define the functions that occur at the physical layer and data-link layer of the Open Systems Interconnection (OSI) reference model, and package data into frames for transmission on the wire. Ethernet is a baseband networking technology that sends its signals serially one bit at a time. It operates in half-duplex mode, in which a station can either transmit or receive, but cannot do both simultaneously.

Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) media access control method for determining which station can transmit at any given time over the shared medium. In an Ethernet network, each station (computer) listens to the network and transmits data only if no other stations are currently using the network. If the wire is free of signals, any station that wants to can contend (try to take control of) the network in order to transmit a signal. Ethernet networks are thus based on the concept of contention and operate on a first-come, first-served basis, rather than relying on a master station that controls when other stations can transmit. If two stations try to transmit data at the same time, a collision occurs, and both stations stop transmitting. They wait a random interval of time (measured in milliseconds) and then try again.

The more stations on an Ethernet network, the higher the number of collisions, and the worse the performance of the network. Typical performance of a 10-Mbps Ethernet network with around 100 stations will support a bandwidth of only about 40 to 60 percent of the expected value of 10 Mbps. One way of solving the problem of collisions is to use Ethernet switches to segment your Ethernet network into smaller collision domains.

Ethernet stations transmit their data over the wire in packages called frames. An Ethernet frame has a minimum size of 64 bytes and a maximum size of 1518 bytes. A total of 18 bytes are used for information such as source and destination addresses, network protocol being used, and other frame overhead. Thus, the maximum payload size (amount of data carried) for an Ethernet frame is 1500 bytes. There are four different Ethernet encapsulation methods by which Ethernet packages data into a frame:

Ethernet can use virtually any physical networking topology and cabling system (medium). Although a star topology (stations wired in a star-like fashion to a central hub) is often used from the physical point of view, all Ethernet networks are logical bus topology networks at heart. One station places a signal on the bus, and that signal travels to every other station on the bus.

Ethernet is available in three different speeds and can be further differentiated by media and other considerations, as shown in the following table.

Ethernet Speeds, Types, Standards, and Specs

Speed Type of Ethernet IEEE Standards IEEE Specs

10 Mbps

Ethernet

10Base2

10Base5

10BaseF

10BaseT

802.3

100 Mbps

Fast Ethernet

100BaseFX 100BaseT

100BaseT4

100BaseTX

802.3u

1000 Mbps or 1 Gbps

Gigabit Ethernet

1000BaseCX

1000BaseLX

1000BaseSX

1000BaseT

802.3z

NOTE

Ethernet media specifications such as 10BaseT look strange and obscure, but can be easily interpreted. For example, 10BaseT means 10 -Mbps baseband transmission over twisted-pair cabling media.

A new type of Ethernet technology that solves the problems of collisions and has twice the bandwidth of traditional Ethernet is called full-duplex Ethernet. Full-duplex Ethernet uses two pairs of wires with Ethernet switches to allow stations to simultaneously send and receive data without collisions. On a 10BaseT wired network, each full-duplex Ethernet station would have a transmission bandwidth of 20 Mbps.

graphic e-5. the ethernet ii frame format.

Graphic E-5. The Ethernet II frame format.

TIP

The various Ethernet framing formats are incompatible with each other, so if you have a heterogeneous Ethernet network, you need to specify the correct frame type in order for machines running Microsoft Windows NT to see your Novell NetWare servers. Windows NT allows you to select Auto Detect from the Frame Type drop-down list on the NWLink IPX/SPX-Compatible Transport protocol configuration property sheet if you don’t know what frame type your NetWare servers are using. (In Windows 2000, select the check box next to Auto Frame Type Detection in the NWLink IPX/SPX/NetBIOS-Compatible Transport protocol configuration property sheet.) You might also need to configure your routers for the proper frame type. Older Cisco routers running Internetwork Operating System (IOS) version 10 or earlier do not support Ethernet 802.3/802.2 with SNAP.

The following table shows some troubleshooting tips for Ethernet media problems.

Troubleshooting Tips for Ethernet Media Problems

Problem Suggestion

No link integrity

Check that you have not mismatched 10BaseT and 100BaseT (or 100BaseTX and 100BaseT4) cables, hubs, or network interface cards; make sure no crossover cables are used for station-to-hub cable connections.

Too much noise

Check for damaged cables; make sure you are using category 5 (CAT5) cabling (or enhanced category 5 cabling for 100BaseT) and that all your cabling interface components (patch panels, wall plates, terminal blocks, and so on) are CAT5 certified.

Too many collisions (greater than 0.1 percent of total frames on the network)

Check for unterminated cables using a time-domain reflectometer; use a protocol analyzer to look for a jabbering transceiver (a network interface card that is continually broadcasting); and make sure you don’t have any cables exceeding the maximum specified length.

On the Web

•

Charles Spurgeon’s Ethernet Web site : http://www.ots.utexas.edu/ethernet

See also 10Base2, 10Base5, 10BaseT, 100BaseT, Fast Ethernet, Gigabit Ethernet

Ethernet address

See MAC address

Ethernet switch

Sometimes simply called a switch (when referring to Ethernet networking hardware), a networking component used to connect workgroup hubs to form a larger network or to connect stations that have high bandwidth needs. Ethernet switches provide superior performance to hubs but are more expensive.

How It Works

In a hub, which basically functions as a multiport repeater, a packet entering one port is regenerated and passed to every other port. As a result, if you try to connect several workgroup local area networks (LANs) by uplinking their hubs to a main hub, the new larger network remains a single collision domain. With the increased number of nodes on the network, more collisions will occur, and network traffic congestion can result. If a 10-Mbps Ethernet hub has 10 ports, each port effectively gets one-tenth of the total bandwidth, or 1 Mbps.

A solution to this congestion problem is to use an Ethernet switch in place of the main hub. When a signal enters a port of the Ethernet switch, the switch looks at the destination address of the frame and internally establishes a logical connection with the port connected to the destination node. Other ports on the switch have no part in the connection. The result is that each port on the switch corresponds to an individual collision domain, and network congestion is avoided. Thus, if a 10-Mbps Ethernet switch has 10 ports, each port effectively gets the entire bandwidth of 10 Mbps—to the frame, the switch’s port appears to provide a dedicated connection to the destination node. Ethernet switches are capable of establishing multiple internal logical connections simultaneously, while routers generally process packets on a first-come, first-served basis (although this distinction is blurring in newer hardware).

There are two main types of Ethernet switches:

Some manufacturers also refer to their newest switches as layer-4 switches, but these are essentially an enhanced form of layer-3 switch that takes into account some higher-level protocol information in routing traffic.

The actual mechanism by which switching occurs divides Ethernet switches into two general device classes:

Ethernet switches are also distinguished in other ways, such as by the number of ports they have, whether they operate in half-duplex or full-duplex mode, their transmission speed (for example, 10 Mbps, 10/100 Mbps, or 100/1000 Mbps), ports for connectivity with high-speed Fiber Distributed Data Interface (FDDI) backbones, and so on. Advanced features can include Simple Network Management Protocol (SNMP), out-of-band management (OBM), and custom packet filtering.

Although Ethernet switches relieve traffic congestion by segmenting collision domains, they do have some disadvantages:

Here is a good rule of thumb for deciding whether to incorporate switches into your existing network: switches can improve your network’s performance if the current network utilization level is higher than 35 percent or if collisions are running at more than 10 percent. For starters, replace your main hub in a cascading hub topology network with an Ethernet switch and connect servers that are heavily utilized directly to the switch (see diagram).

graphic e-6. ethernet switch.

Graphic E-6. Ethernet switch.

TIP

If users in a department have high bandwidth needs, such as those running CAD or multimedia applications, consider replacing their workgroup hub with an Ethernet switch, or if the number of users is small, connect their stations directly to the main Ethernet switch.

Another use for Ethernet switches is to connect 100-Mbps Ethernet “islands” to an existing 10-Mbps Ethernet LAN. Simply use a 10/100-Mbps Ethernet switch with two ports to connect them.

You can also connect two LANs several kilometers apart by using two Ethernet switches, both having one 100BaseT port and one 100BaseFX port. Connect the switches to the LANs, and then connect a fiber-optic cable between the FX ports.

When purchasing Ethernet switches, make sure they have RMON agents built into each port, as this will considerably ease remote network troubleshooting.

EULA

See End-User License Agreement (EULA)

events

Types of occurrences that are logged by the Event Log service of Microsoft Windows NT or Windows 2000 and can be viewed using the administrative tool called Event Viewer. There are five basic types of events:

Event Viewer

A Microsoft Windows NT administrative tool used to monitor events on a server. Events are significant actions that take place on a server and include the following:

Event Viewer records events in three different logs:

The system and application logs should be monitored regularly for signs of problems with devices, services, or applications running on the server. When a problem occurs, Event Viewer is the first place you should check. If auditing is configured on the server, you can monitor the security log for signs of attempted unauthorized access (failure audits) or for an indication of resource usage (success audits).

graphic e-7. event viewer.

Graphic E-7. Event Viewer.

NOTE

In Windows 2000, Event Viewer is implemented as a snap-in for Microsoft Management Console (MMC) and appears as one of the administrative tools in Control Panel. The Windows 2000 Server version of Event Viewer includes additional logs such as the directory service log, the DNS server log, and the file replication service log. Windows 2000 Event Viewer is extensible, with additional logs present when new network services are installed on the machine.

TIP

Select View, and then select Filter Events to filter out unwanted events when the Event Viewer logs are large.

Everyone group

A system group existing on all Microsoft Windows NT and Windows 2000 servers and workstations. The Everyone group includes all local and remote users who have access to any computer running Windows NT on which the Everyone group is defined. This includes users from untrusted domains and non–Windows NT networks. By default, the Everyone system group has the sole preassigned system right “Access this computer from network.” Additional rights can be granted to this group if desired. You cannot modify the membership of system groups such as the Everyone group directly.

NOTE

The Everyone group is one of seven built-in system groups that are defined on networks based on the Windows 2000 operating system.

TIP

When you share a folder on a server running Windows NT, full control permission is initially assigned to the Everyone group. It is a good idea to remove this group and assign appropriate permissions to other groups, such as Administrators and Users.

Be careful about assigning additional permissions to the Everyone group. If you allow users who do not have valid user accounts to access the network using the Guest account, they will gain any permissions and rights that you have assigned to the Everyone group.

See also built-in group, special identity

Exchange Administrator

The primary tool for managing the sites, servers, services, and recipients in a Microsoft Exchange organization. The Exchange Administrator program can be installed on a computer running Microsoft Exchange Server during setup, or as a stand-alone administrative tool on a server or workstation running Microsoft Windows NT or Windows 2000, provided that the machine can establish a remote procedure call (RPC) connection with all Exchange servers it wants to administer.

The Exchange Administrator program provides a view of the Exchange directory hierarchy for the organization. Using the menus, toolbars, and property sheets for directory objects, administrators can configure all aspects of their Exchange sites, services, connectors, gateways, recipients, and other Exchange components. Exchange Administrator provides a two-pane view similar to Windows Explorer, including

Exchange directory service

One of the four core components of Microsoft Exchange Server. The Exchange directory service is responsible for maintaining the Exchange directory database of information concerning the organization’s sites, servers, services, and recipients. This directory is based on the X.500 directory recommendations of the International Telecommunication Union (ITU) and is essentially a Lightweight Directory Access Protocol (LDAP)–compliant directory.

To synchronize the information among all servers, the directory service also replicates the directory information among all Exchange Server computers in an Exchange organization through directory replication. This replication takes place automatically every five minutes among Exchange servers in the same site and when the administrator has scheduled it to occur between different sites. The Exchange directory service is implemented as a Microsoft Windows NT service and can be stopped, started, or paused like any other service. Errors that occur in the directory service are written to the application log on the Exchange server.

NOTE

The directory service agent for Windows 2000 can integrate information maintained by the Exchange directory service with Active Directory in Windows 2000.

Exchange event service

A Microsoft Windows NT service running on Microsoft Exchange Server version 5.5 computers. This service can be configured using Microsoft Outlook to monitor for occurrence of specific events in public folders. These events include timing events, message postings, and message deletions. The event service notifies users of specific actions that occur on public folders. This allows developers to write custom workflow applications that perform specific actions when a specific event occurs in a public folder. Developers can write scripts using the Exchange Scripting Agent to trigger responses to messages being posted in both public folders and users’ mailboxes.

TIP

When writing mailbox agents that use the event service, use high-level programming languages such as C or C++. If you write mailbox agents using an interpreted language such as Microsoft Visual Basic, Scripting Edition (VBScript), Exchange Server will slow to the speed of the interpreter whenever the script is called by a message being posted to the mailbox. This can cause a significant drop in performance.

Exchange permissions

Sets of rights assigned to users or groups to control access to directory objects in the organization of Microsoft Exchange Server. These rights are grouped into common roles, which are then assigned to users and groups.

Exchange permissions can be assigned to any object in the Exchange directory hierarchy and are inherited by other objects below that object, provided they are in the same context.

The following table shows the individual rights that can be granted to users and groups to control access to directory objects. Note that not all of these rights are available for any given directory object.

TIP

If you don’t see the Permissions property page for an Exchange directory object, use Options from the Tools menu of the Exchange Administrator program to make it visible. (The screen capture illustrates the property sheet for the Toronto site in an Exchange organization.)

graphic e-9. exchange permissions.

Graphic E-9. Exchange permissions.

Individual Rights

Right Type of Permission Granted

Add Child

Create objects within a container.

Modify User Attributes

Modify user-level attributes of an object.

Modify Admin Attributes

Modify administrator-level attributes of an object.

Modify Permissions

Modify the permissions on the existing object.

Delete

Delete the object.

Logon

Access the directory database (needed by Exchange service account).

Replication

Replicate directory information with other servers (needed by Exchange service account).

Mailbox Owner

Read and delete messages in the mailbox.

Search

View the contents of the container.

Send As

Send a message using the sender’s return address.

Exchange Scripting Agent

A tool for Microsoft Exchange Server that allows server-side scripts to be written that execute actions when specific events or conditions occur in public folders. These events include timing events, message postings, and message deletions. For example, an action could be triggered in response to generation of an Out-of-Office (OOF) message. Another example of such an event is the automatic generation of a reminder message when a user doesn’t read his or her e-mail for a specified number of days. A form that is submitted to a public folder could be validated by a script that determines whether it satisfies some specific criteria, such as a minimum order quantity. Scripts can be written in Microsoft Visual Basic, Scripting Edition (VBScript) or JScript using the Exchange Scripting Agent.

Exchange Server

See Microsoft Exchange Server

executive

See Windows NT executive

expand command

A Microsoft Windows NT and Windows 2000 command that can be used to uncompress files from the distribution files on the Windows NT compact disc. Use this command to perform a system recovery when a missing or corrupt Windows NT operating system file is preventing your system from booting. Expand is an MS-DOS–based utility.

Example

expand d:\i386\sol.ex_ c:\winnt\system32 installs Solitaire the hard way—off the Windows NT compact disc.

NOTE

The Windows NT Resource Kit includes a Windows NT–based expansion utility called expndw32.exe that can be accessed from the File Tools program group in the Start menu.

For the full syntax of this command, type expand /? at the command line.

export server

A Microsoft Windows NT or Windows 2000 server that exports directories and files to other computers using the Directory Replicator Service in Windows NT and Windows 2000. The export server contains the master copy of the directory tree that is being copied to the import servers by the Directory Replicator Service.

In Windows NT, configure your export server using the Replication button on Server Manager, which is accessed either from the Server icon in Control Panel or from the Start menu’s list of administrative tools. You must specify the following:

In Windows 2000, the directory replication functionality is integrated into Active Directory.

TIP

In Windows NT, if you add any domain or computer names to the To list box for directory replication, you are no longer automatically replicating to the local domain and must specify the name of the local domain (if desired).

See also Directory Replicator Service

extended partition

A physical disk partition on which a series of logical drives can be created. You can create an extended partition on a disk to overcome the limitation of having only four partitions per disk.

Information about the various partitions on a disk is stored in a structure called the partition table. The partition table is 64 bytes in size and is located on cylinder 0, head 0, sector 1 of your hard drive, in the same sector as the Master Boot Record. The partition table has the same format no matter what operating system is used on the disk. Up to four partitions can be created on a disk, but only one partition can be extended per disk. In Microsoft Windows NT, you can create an extended partition using Disk Administrator. For earlier Windows platforms, use the fdisk utility.

NOTE

In Windows 2000, extended partitions can be created only on basic disks.

See also partition of a disk

extender

A general name for a class of networking devices that extend the distances over which stations (computers) can typically be connected to concentrators such as hubs and switches.

An example is a 10BaseT extender for Ethernet networks. In 10BaseT networks, stations should be located no more than 100 meters from a hub, but by using an extender, you could increase this to about 183 meters. A 10BaseT extender can thus be used for connecting a remote station, such as a station located in a nearby building, to the network. Extenders are essentially a simplified form of bridge designed to support only a few remote stations. They need to be installed in pairs, one at the remote location and one at the main network. Some extenders can be used to carry network data over installed phone lines, connecting remote stations without installing additional network cabling.

graphic e-10. extender.

Graphic E-10. Extender.

Extenders are also available for increasing the maximum connection distance for other data transmission technologies such as the Small Computer System Interface (SCSI) bus. A normal SCSI bus is limited to about 6 meters, but a fiber-optic SCSI extender can increase this distance to a kilometer or more using duplex fiber-optic cable. You can use parallel extenders for directly connecting to printers located in a different building. You can use serial extenders to connect computers to remote RS-232 serial test equipment located in laboratories in different buildings.

extension cable

A cable used to extend a length of cabling. Extension cables come in all types with various connector devices and can be used to extend serial lines, parallel lines, network cables, power cables, and so on.

TIP

Extending a cable using an extension cable is not always a good idea because the additional interface introduced by the connection usually results in some signal loss. Furthermore, extending network cables can cause problems if the new, longer cable exceeds the maximum length of the specifications for that type of network. For example, extending unshielded twisted-pair (UTP) cabling beyond 100 meters in a 10BaseT Ethernet network can result in unreliable communication between hosts on the network.

Exterior Gateway Protocol (EGP)

A type of routing protocol used to distribute routing information between different autonomous systems in large internetworks based on the TCP/IP protocol. The Internet is one example of an Exterior Gateway Protocol (EGP). EGPs specify how networks within an autonomous system are advertised to routers outside the given autonomous system. EGPs thus facilitate the exchange of inter-autonomous-system routing information between different autonomous systems, independent of whether these autonomous systems employ the same Interior Gateway Protocols (IGPs) within their networks.

The EGP was the original routing protocol developed for communicating routing information between autonomous systems on the Internet. It is no longer used because of its poor support for multipath networking environments, and the Border Gateway Protocol (BGP) has replaced it. The term “Exterior Gateway Protocol” now refers both to the particular protocol itself and to the class of protocols it describes.

See also autonomous system (AS)

extract command

The Windows Cabinet Extraction tool for Microsoft Windows 95 and Windows 98 that is used to extract files and lists of files from Windows cabinet files. These cabinet files are found on the Windows CD. The extract command lets you extract one or more files from the cabinet files—for example, if a system file becomes corrupt and you want to replace it rather than rerun Setup.

Example

To display the contents of the cabinet file Win95_02.cab, type extract /d win95_02.cab at the command prompt.

extranet

In its simplest form, a private TCP/IP network that securely shares information using Hypertext Transfer Protocol (HTTP) and other Internet protocols with business partners such as vendors, suppliers, and wholesale customers. An extranet is thus a corporate intranet that is exposed over the Internet to certain specific groups that need access to it. Extranets built in this fashion follow the client/server paradigm, with Web servers such as Microsoft Internet Information Services (IIS) functioning as the server, and Web browsers such as Microsoft Internet Explorer functioning as the client. Other extranet models exist, however, such as a peer-to-peer business connection for electronic data interchange (EDI).

Extranets are a powerful tool because they let businesses share resources on their own private networks over the Internet with suppliers, vendors, business partners, or customers. Extranets are typically used for supporting real-time supply chains, for enabling business partners to work together, or to share information such as catalogs with customers. The power of the extranet is that it leverages the existing technology of the Internet to increase the power, flexibility, and competitiveness of businesses utilizing well-known and easily used tools such as Web servers and Web browsers. Extranets also save companies money by allowing them to establish business-to-business connectivity over the Internet instead of using expensive, dedicated leased lines. Extranets can also save money by reducing phone and fax costs.

How It Works

Peer-to-peer extranets between business partners typically use virtual private networks (VPNs) to establish secure, encrypted communication over the unsecured public Internet for the transmission of sensitive business information, such as EDI between partners, or between headquarters and branch offices. These extranets act as dedicated gateways between business partners and generally do not allow private access to individual users. Peer-to-peer extranets can use Internet Protocol Security (IPSec) with a public key infrastructure (PKI) to provide IP-based authentication and encrypted transmission of information.

Client/server extranets have different requirements, as individual users need to be authenticated before receiving secure, encrypted access to company resources. Instead of authenticating on the basis of IP addresses as in peer-to-peer extranets, users must be authenticated using user accounts or digital certificates mapped to accounts. Client/server extranets might support HTTP access only or might allow other client/server applications to run. Encryption for HTTP access is performed using the Secure Sockets Layer (SSL) protocol.


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Microsoft Encyclopedia of Networking
Microsoft Encyclopedia of Networking
ISBN: 0735613788
EAN: 2147483647
Year: 2000
Pages: 37
Authors: Mitch Tulloch, Ingrid Tulloch
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