See
See Internet Locator Service (ILS)
See Universal Mobile Telecommunications System (UMTS)
A procedure for installing software without user intervention. Many Microsoft products, such as Microsoft Windows 2000 and Microsoft BackOffice, support unattended installation. Unattended installation allows network administrators to perform simultaneous installations of operating system and application software on networked computers. For example, an administrator can install Windows 2000 Professional on several desktop client computers simultaneously without having to remain at each desktop during the installation process.
How It Works
Unattended installations typically make use of a distribution server, which is simply a file server on the network that has the source files for the software you want to install stored on one of its shared folders. Client software can connect to the share point on the distribution server, download the necessary files, and run the software setup program.
You can create a file to provide a fixed set of responses to prompts for information (such as the computer name, the network protocol to employ, and optional components to install). In the Microsoft Windows version of unattended installation, this file is called an answer file; you use it by appending the filename to the /u switch when you run Setup from the command prompt. The Windows NT and Windows 2000 compact discs contain a sample answer file called unattend.txt. You can customize this file with a text editor such as Notepad, and then you can use the file to perform unattended installations of Windows.
NOTE
Windows NT and Windows 2000 include several installation tools for simplifying the deployment of servers and desktop computers in the enterprise. For example, as an alternative to manually creating answer files by using a text editor, Windows NT and Windows 2000 provide a wizard called Setup Manager that you can use to easily create answer files for unattended installations.
Another way to set up multiple computers running Windows for deployment on a network is to use disk-image duplication (or disk cloning) software such as Symantec’s Ghost or PowerQuest’s DriveImage software. In order to use disk cloning as an installation method, however, the master and target systems must have identical hardware configurations. To create a clone, you install and configure the operating system and applications on the master machine, and then use the disk imaging software to capture an exact bit-image of the master machine’s hard drive, which you then duplicate to the hard drives on the other computers, producing exact clones of the master machine. When you use disk-image duplication software, you must be careful that incompatibilities do not result. For example, if you clone a computer running Windows 2000, the cloned version will have the same security identifier (SID) as the original, which means that the two computers cannot coexist on the same network. Makers of disk-image duplication software can provide utilities for modifying SIDs to work around this problem. Note also that the master and target computers must be stand-alone member servers and not part of a Windows 2000 domain.
Finally, Windows 2000 Server includes Remote Installation Services (RIS), which you can use to install Windows 2000 Professional on client computers from a network share. An image of the fully configured operating system with any locally installed applications that will be required is created and stored on the network share, and a RIS boot disk is used to boot the client computers, connect to the RIS server, download the image, and install the operating system on the client computers. If the client computers have ROM that supports PXE (Pre-Boot eXecution Environment) architecture and have remote boot–enabled network adapter cards, a remote boot disk is not required for each client.
Microsoft also supports disk-image duplication of Windows 98 systems when the Windows 98 Image Preparation Tool is used to prepare the master disk image.
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If you need to perform simultaneous installations of software on large numbers of networked computers, you might consider using systems management software such as Microsoft Systems Management Server (SMS). Unattended installation using answer files is practical only for smaller deployments and doesn’t offer the management and upgrade capabilities that systems management software does.
See also answer file
See answer file
An electrical cable in which the potential of the signal-carrying conductor is above ground while the return-path conductor is at ground potential. The two conductors thus have different electrical characteristics. This is different from a balanced line, in which both conductors carry a signal and have potentials that are equal in magnitude but 180 degrees out of phase.
In computer networking, an example of an unbalanced line is coaxial cabling, in which the electrical signal is carried solely by the central conductor while the ground path (the internal wire-braid or mesh shielding inside the cable jacket, which is connected to the earth at one termination point of the cable) provides the unbalanced signal return path. An example of a balanced line is twisted-pair cabling, which comes in the shielded twisted-pair (STP) or unshielded twisted-pair (UTP) variety. Because of its electrical characteristics, unbalanced coaxial cabling is more susceptible to electromagnetic interference (EMI) than balanced STP cabling, but coaxial cabling is capable of higher transmission rates over longer distances.
Graphic U-1. The return-path conductor of the unbalanced line is at ground potential. The return-path conductor of the balanced line carries a signal.
See also balanced line
See Universal Naming Convention (UNC)
Two-way, point-to-point communication between stations on a network. This is in contrast to broadcasting, which is multipoint in nature and directs information to all accessible hosts on the network, and multicasting, which directs information only to hosts that request it. For a unicast packet to arrive at its destination host on the network, it must be configured with the specific destination address of that host, usually in the form of a logical address such as an IP address and a physical address, or MAC address.
Most user-initiated network traffic is unicast or directed traffic, while broadcast traffic is mostly for clients and services to announce themselves on the network and multicast traffic is for streaming multimedia communication. In the TCP/IP protocol suite, both the connection-oriented Transmission Control Protocol (TCP) and the connectionless User Datagram Protocol (UDP) support unicast transmission of Internet Protocol (IP) packets.
Graphic U-2. Comparison with multicasting and broadcasting.
NOTE
Routers, which are network devices that can forward packets to other networks, are usually configured to forward unicast packets (packets directed to a specific host on a destination network) but not broadcast packets (packets directed to all users on a subnet, network, or internetwork). You can use a Microsoft Windows NT or Windows 2000 multihomed system for unicast IP routing by installing the Routing and Remote Access Service (RRAS), which turns the system into a dynamic router that supports both the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) Protocol.
In addition to supporting streaming multicast traffic, Microsoft NetShow supports unicasting to transmit streaming audio and video over the Internet and corporate intranets directly from a NetShow server to a specific NetShow client.
A character set that is capable of representing all written languages.
How It Works
The ANSI character set, which employs a single byte (8 bits) to represent each character, can represent up to 28 = 256 characters only. This is enough for Western languages, but it is insufficient for languages such as Chinese. In contrast, the Unicode character set employs two bytes (16 bits) per character, so it can represent a total of 216 = 65,536 characters—enough for every language in the world plus punctuation and standard mathematical symbols.
Unicode is the native character encoding for file and object names in Microsoft Windows NT and Windows 2000. The Win32 subsystem converts American National Standards Institute (ANSI) strings to Unicode before any string operations are performed on them. Filenames are represented in NTFS file system using Unicode.
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If you create a logon script in Windows NT by using Notepad, do not select the Save As Unicode check box when you save the logon script, or it will fail to execute properly.
On the Web
•
Unicode Consortium : http://www.unicode.org
See also ASCII
An addressing scheme that enables browsers such as Microsoft Internet Explorer and software such as File Transfer Protocol (FTP) clients to access various resources on the Internet. Uniform Resource Locators (URLs) are to the Internet what absolute paths are to file systems and what Universal Naming Convention (UNC) paths are to shared file and print resources on a Microsoft Windows network. In other words, URLs are a way of addressing resources on the Internet. By typing the URL of a resource into your browser, your browser can find and download the requested file at this address.
How It Works
A URL is a hierarchical, structured address based on the Domain Name System (DNS), although a URL can also use an IP address to locate its targets. A URL takes the following standard form:
[protocol:]//[domain or IP address][:port]/[path to target file]
The protocol is an optional address element that describes the application layer Internet protocol on the server that must be used in order for the client to access the resource. Examples are HTTP:, FTP:, and Telnet:.
The domain name or IP address, which represents the logical address of the server on which the resource resides, is required.
The port number is an optional element that represents the port on the server to which the client must connect in order to access the resource. If no port number is specified, the request is assumed to use the well-known port number for the protocol being used. For example, the well-known port number for Hypertext Transfer Protocol (HTTP) is port 80.
The path is required if the resource is not in the root of the server’s directory that is mapped to the specified domain name or IP address. This path is usually a virtual path that is mapped to a hierarchical series of directories on the server or on the server’s network.
The following are examples of URLs:
http://www.microsoft.com/train_cert/MCSE.htm
ftp://172.16.8.99:3355/usr/bin/frag.Z
http://b12.sales.expedia.com/Sales%20Department/Wigs/Colors/red.html
NOTE
The string “%20” in the third URL is an example of character encoding. Since certain ASCII characters (such as spaces) are not allowed in URLs, they must be encoded using the form %xx, in which xx is the hexadecimal code for the character using the International Organization for Standardization (ISO) Latin-1 character set. The string “%20” represents a space character.
A device that can temporarily provide power to key components of a network if a general power failure happens. Uninterruptible power supply (UPS) devices generally use rechargeable batteries and perform operations such as the following:
Notifying users that a shutdown is imminent and that they should save their work
Pausing services on servers to prevent new connections from being established
Providing enough power to perform a soft shutdown of servers and other key network components
Performing other actions as specified in a batch file that runs automatically
Providing power line conditioning and smoothing out spikes and dips in the power flow
UPS units for computer networking equipment are available in both stand-alone and rack-mountable versions. UPS devices are generally rated according to two values:
Volt-amperes (VA) or kilovolt-amperes (kVA), which represents the overall ability of the UPS unit to support connected equipment. The larger the kVA value, the greater the number and power requirements of the connected equipment it can support. UPS units range from 1 or 2 kVA units for computer network server rooms to cabinet-sized 500-kVA units for hospitals. UPS units can also be rated in watts (W): 1 VA = 1 W, and 1 kVA = 1 kW.
The amount of time that the unit can sustain maximum power generation. Typical times for network UPS units are 5 to 15 minutes. You can use additional battery packs with some devices to extend available uptime.
NOTE
To configure a UPS to work with Microsoft Windows NT 4, use the UPS utility in Control Panel. (To configure a UPS to work with Microsoft Windows 2000, use the Power Options utility in Control Panel.) A serial cable with special pinouts is usually required to connect servers running Windows NT or Windows 2000 to the UPS devices.
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Always test your UPS after installing it. Otherwise, you might be sorry when a power failure happens in your neighborhood!
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The larger the load attached to a UPS unit, the shorter the time interval the unit can continue powering attached devices during a power outage. Be sure that your UPS unit can support your power needs for the time needed to properly shut down your system.
A text file that supplements an answer file during unattended installations of Microsoft software such as Windows NT and Windows 2000. Uniqueness Database Files (UDFs) override the general answers that the answer file provides to prompts during unattended setup with information that is specific to a given computer or small group of computers.
How It Works
UDFs typically supply information such as computer name or username for each installed computer, while answer files specify more general setup options such as Typical setup or time zone, which are the same for all computers on the network. Thus, while you might need only one answer file for all the computers on which you are installing Windows NT in your local area network (LAN) or at your geographical locale, you need a separate UDF for each computer or small group of computers.
The UDF is merged into the answer file at the start of the graphical user interface (GUI) portion of setup, so you can use UDFs only to define setup parameters for the GUI portion of setup, not the text portion. During the text portion of setup, only the answer file can specify parameters to use in response to setup prompts.
See also answer file, unattended installation
See G.Lite
One of three types of groups in Microsoft Windows 2000. Universal groups can include members from any domain and can be granted permissions for resources in any domain in the current forest. They can contain user accounts, global groups, and universal groups from any domain in the current forest. They cannot contain domain local groups. Like global groups, all trusted domains have access to universal groups in order to grant them permission to access resources on the network.
NOTE
You can create universal groups only when the domain is running in native mode, not when it is in mixed mode. In other words, you cannot use universal groups in a network that has a mixture of Windows 2000 and Microsoft Windows NT domain controllers. You can use them only in a network whose domain controllers are running Windows 2000.
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You can use global groups nested inside universal groups to dramatically reduce network traffic due to global catalog replication in a Windows 2000–based network. Use universal groups only when their membership changes infrequently, since excessive replication traffic can occur in a domain tree if their membership changes frequently.
You can also use universal groups to grant users access to resources that are located in multiple domains. Simply add global groups from each domain to a universal group and assign permissions for the resource to the universal group. This use of universal groups is similar to that of domain local groups, except that you can use domain local groups only to assign permissions for resources in a single domain.
See also group
A standard from the European Telecommunications Standards Institute (ETSI) for 3G (third-generation) wireless communication networks. The Universal Mobile Telecommunications System (UMTS) is part of the International Mobile Telecommunications-2000 (IMT-2000) initiative from the International Telecommunication Union (ITU) and uses Wideband Code Division Multiple Access (W-CDMA) transmission technology to achieve higher transmission speeds than existing Code Division Multiple Access (CDMA) cellular telephone systems. UMTS uses a newly licensed portion of the 2-GHz band of the electromagnetic spectrum.
One cost involved in the UMTS upgrade process is that of replacing the circuit-switched core network that connects existing base stations with an IP-based backbone network, which can be used to interface between the wireless system and the Internet.
On the Web
•
UMTS Forum : http://www.umts-forum.org
A convention for naming shared network resources. The syntax for a Universal Naming Convention (UNC) path to a network resource is as follows:
\\server_name\share_name[\path]
where “share_name” is a shared folder, and “path” is the (optional) path to the file within the shared folder.
Example
The UNC path \\max\sales\1998\report.doc indicates that the document report.doc is located within the shared folder called sales on the file server called max. The document is in the 1998 subfolder of the sales shared folder.
A serial interface standard for connecting peripherals to computers. Serial cards with universal serial bus (USB) ports are included on most computers sold today, and USB peripherals are becoming popular, especially in the consumer market. USB provides higher speeds than traditional RS-232 serial ports and can allow multiple stations to connect to a single port by using USB hubs. USB also supports “hot plugging” of peripheral devices, which is similar to that supported by PCMCIA cards in notebook computers.
Graphic U-3. Universal serial bus (USB).
USB makes it easier to connect peripherals to computers and eliminates the need to configure interrupt request (IRQ) settings or dual inline package (DIP) switches. USB peripherals include keyboards, mouse devices, joysticks, scanners, printers, monitors, and digital cameras. USB brings plug and play functionality to external peripheral devices and is fully supported by Microsoft Windows 98 and Windows 2000.
How It Works
USB uses a tiered star topology to connect up to 127 USB devices to a single USB port on a host. (A USB system can have only one USB host—the computer that has the USB port.) To set up this topology, you can arrange USB hubs into star and tiered star arrangements. You can physically daisy-chain some USB devices that have built-in USB hubs. Some monitors have this capability for greater flexibility of configuration. This is not true daisy-chaining; it’s simply an extension of the tiered USB topology. Whatever the arrangement, USB devices can be no more than 5 meters apart or 5 meters from a hub. The entire cabling arrangement is collectively referred to as the USB bus, even if the actual topology itself does not appear bus-like.
The USB controller on the host (the computer with a built-in USB port or a USB serial card) manages communication between the connected USB devices by using a mechanism called transfer queuing, whereby devices make a request to the controller, which queues the request and responds to it in a first in, first out (FIFO) manner. Requests made by USB devices are typically one of the following:
Requests for or reports of status information
Requests for reading data to or writing data from another device on the bus
All USB requests are handled by the host controller, which obtains and sends the necessary control information or data to the device.
USB cabling is 4-wire cabling that typically uses a 28-gauge twisted pair for data transmission and a 20-gauge untwisted pair for carrying power to the devices. Cabling is available in both shielded and unshielded forms. The following table shows the pinning types for USB cabling. USB supports two speeds, which depend on the type of media used to connect peripherals:
1.5-Mbps transmission over unshielded USB cabling
12-Mbps transmission over shielded USB cabling
Most USB hubs and serial cards are autosensing and can determine which transmission speed to use from the attached cabling.
Pinning Types for USB Cabling
| Pin | Color | Function |
| 1 | Red | +5 V power |
| 2 | White | Data - |
| 3 | Green | Data + |
| 4 | Black | Ground |
NOTE
You can prevent loops in a USB cabling configuration by using only USB cables with a Type A (flat) connector at one end and a Type B (square) connector at the other. The flat connector plugs into the USB port on the computer or into the device ports on the hub.
The USB 2.0 standard extends USB to higher transmission speeds of up to 400 Mbps.
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When you use shielded USB cabling, connect the shield to ground only at the USB host (computer), not at the USB devices (peripherals).
You can connect an IEEE 1284–compliant printer that has a standard Centronics interface to a USB system by using a Centronics/USB adapter or patch cable.
A proposed standard from the Universal Wireless Communication Consortium (UWCC)—a consortium of more than 85 telecommunications carriers and wireless product vendors—for a 3G (third-generation) wireless communication system. Universal Wireless Communications (UWC-136) is part of the International Mobile Telecommunications-2000 (IMT-2000) initiative from the International Telecommunication Union (ITU). The UWCC promotes UWC-136 as a competing IMT-2000 standard.
UWC-136 is a pure Time Division Multiple Access (TDMA) technology that is designed to be backward compatible with the existing IS-136 TDMA digital cellular phone system defined by the ANSI-136 and IS-41 standards and still widely used in North America.
Implementation of UWC-136 is planned in phases by first upgrading existing IS-136 TDMA systems to IS-136+ to provide data rates of 43.2 Kbps over standard 30-kHz channels. Then IS-136+ will be upgraded to IS-136HS, which is the high-speed component of UWC-136. Eventually UWC-136 will provide packet-data services at speeds of up to 384 Kbps for wide-area coverage and up to 2 Mbps for in-building coverage. Voice communication on this system will be high-fidelity wireline quality, comparable to that of Integrated Services Digital Network (ISDN).
On the Web
•
UWCC home page: http://www.uwcc.org
See also Time Division Multiple Access (TDMA)
An operating system developed at AT&T Bell Laboratories in 1969 and widely deployed today in the enterprise networking environment. UNIX was the first operating system written entirely in the C programming language and consequently has close ties to C. UNIX was designed as a time-sharing environment, in contrast to the batch environment of most computing systems of the time. Using UNIX, multiple users could simultaneously access the system and run their programs, communicating interactively with the system using remote terminals. Users could thus collaborate in real time on computing projects by sharing files and resources.
UNIX became widely available around 1975 and established strong roots in academic computing environments, where it is still used and taught today. UNIX has the stability and robustness of an operating system that has evolved over 25 years, but it has a reputation for being difficult to learn and administer. UNIX has evolved into a number of different “flavors” as vendors have adapted it to their own hardware platforms. These flavors include the following:
System V: Evolved from versions of UNIX developed by UNIX Systems Laboratories and AT&T
BSD: Developed at the University of California, Berkeley; the basis of the SunOS from Sun Microsystems
AIX: Developed by IBM for its mid-range computer systems
HP/UX: Developed by Hewlett-Packard
Solaris: Developed by Sun Microsystems for its SPARC systems
IRIX: Developed by Silicon Graphics for its high-end workstations
The original source code for System V UNIX is owned by Santa Cruz Operation (SCO), which licenses the code to other UNIX vendors and offers its own version called SCO UNIX for various hardware platforms. The actual trademark “UNIX” is now owned by The Open Group, a consortium of software and hardware manufacturers. A variety of open versions of UNIX also exist. These are highly popular machine-independent implementations of UNIX that have been compiled to run on multiple hardware platforms. Their source code is available with few restrictions. An example is FreeBSD, which evolved from BSD UNIX. Another example is Linux, a UNIX-like operating system that is rapidly growing in popularity.
Several attempts have been made to standardize the UNIX operating system. AT&T created a written standard called the System V Interface Definition (SVID) for its UNIX System V Release 4 (SVR4). In addition, an industry consortium has created a standard called Portable Operating System Interface for UNIX (POSIX).
NOTE
Microsoft Windows NT and Windows 2000 support interoperability with UNIX platforms in heterogeneous enterprise environments through protocols, services, and utilities such as the following:
Common support for industry-standard protocols such as TCP/IP, Dynamic Host Configuration Protocol (DHCP), Domain Name System (DNS), and remote procedure call (RPC) functionality
Support for File Transfer Protocol (FTP) and Hypertext Transfer Protocol (HTTP) for cross-platform file sharing
Support for UNIX printing through Line Printer Daemon (LPD), Line Printer Queue (LPQ), and Line Printer Remote (LPR) utilities
Support for remote terminal emulation using Telnet
Support for cross-platform database access through open database connectivity (ODBC)
Support for industry-standard network management through Simple Network Management Protocol (SNMP) and Remote Network Monitoring (RMON)
Third-party companies also offer Windows-compatible interoperability solutions such as the following:
X Windows clients for Windows-based PCs
Server Message Block (SMB) to Network File System (NFS) protocol conversion for file sharing between platforms
See also POSIX, shell
Commands for administering various aspects of the UNIX operating system. Most of these commands can be used in batch files to perform complex administrative tasks from a single command. You can create batch files with a text editor such as ed or vi and schedule their execution by using the cron command. The following table describes some commonly used UNIX commands. (They are listed in alphabetical order, not according to function.) Some commands have a simple syntax, such as the cd command for changing the current directory. Others are more complex and include scripting engines and even programming compilers, such as cc, the UNIX C compiler.
Most versions of UNIX support these commands, but there are subtle differences from system to system. To see the syntax for any UNIX command, use the man command, which provides access to the UNIX online command reference on most UNIX systems. For example, to see the syntax for the cd command, type man cd.
Common UNIX Commands
| Command | Description |
| alias | Displays or sets aliases for long command strings |
| awk | Searches a file for a pattern and performs an action on the lines containing that pattern |
| bg | Moves a stopped process into the background and restarts it |
| cal | Displays a calendar |
| cat | Concatenates or displays files |
| cc | C language compiler |
| cd | Changes the current directory |
| chgrp | Changes group ownership of a file |
| chmod | Changes access permissions for a file |
| chown | Changes individual ownership of a file |
| chsh | Changes the default shell in a password file |
| clear | Clears the screen |
| cmp | Compares two files and returns the line numbers that differ |
| cp | Copies a file |
| csh | C shell command interpreter |
| date | Displays the date and time |
| df | Displays the amount of free disk space in a file system |
| diff | Displays differences between two files |
| du | Displays file system usage |
| echo | Echoes the text typed following the command to the screen; in a batch file, displays a line on the screen |
| ed | Text editor |
| elm | Text-based e-mail |
| emacs | Text editor |
| f77 | FORTRAN77 compiler |
| fg | Moves a stopped process to the foreground and restarts it |
| find | Finds a file with specified characteristics |
| ftp | File Transfer Protocol (FTP) client |
| grep | Searches a file for a text pattern |
| head | Displays the beginning of a file (by default, displays the first 10 lines) |
| help | Displays help |
| hostname | Displays the name of the current host system |
| kill | Ends a running process |
| ksh | Korn shell command interpreter |
| ln | Links files |
| lpq | Displays the print queue |
| lpr | Sends a print job to the spooler |
| ls | Lists files in a directory and displays the file statistics |
| | Sends e-mail |
| man | Accesses the online manual |
| mkdir | Creates a new directory |
| more | Displays a file one screen at a time |
| mv | Moves or renames a file |
| passwd | Changes your password |
| pico | Text editor |
| pine | Text-based e-mail program |
| ps | Displays the status of a process |
| pwd | Displays the name of the current directory |
| rm | Deletes a file |
| rmdir | Deletes a directory |
| sed | Stream line editor |
| sh | Bourne shell command interpreter |
| sleep | Pauses a process |
| sort | Sorts or merges files |
| split | Splits a file into multiple files |
| talk | Text-based chat |
| telnet | Terminal emulator |
| uucp | UNIX-to-UNIX system file copies |
| uudecode | Decodes a uuencoded file |
| uuencode | Encodes a binary file |
| vi | Text editor |
| who | Displays who else is logged on |
| whoami | Displays the name of the user currently logged on |
| whois | Finds remote users and sites |
| write | Sends a message to a user |
See also UNIX
Twisted-pair cabling with no internal shielding. The outer insulating jacket protects the cable from physical stress or damage but does not shield the cable from electromagnetic interference (EMI). Unshielded twisted-pair (UTP) cabling is the most common form of network cabling for workgroups and departmental local area networks (LANs) because of its low cost, flexibility, and good performance.
UTP cabling has an impedance of approximately 100 ohms and comes in various grades or categories based on data transmission capabilities, as shown in the following table. Category 5 cabling is the most popular form of UTP cabling in 10/100-Mbps Ethernet workgroup or departmental LANs. No agreed standards exist above category 5, but many manufacturers offer UTP cabling certified for transmission rates up to 350 MHz or higher.
UTP Cabling Categories
| Category | Use |
| Category 1 | Analog voice grade |
| Category 2 | Digital voice transmissions up to 4 Mbps |
| Category 3 | Digital transmissions up to 10 Mbps |
| Category 4 | Digital transmissions up to 16 Mbps |
| Category 5 | Digital transmissions up to 100 Mbps |
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To ensure that category 5 UTP cabling performs effectively, you should also use certified category 5 wall plates, connectors, and patch panels. The patch panel or wall plate connections should be untwisted no more than 0.5 inches; also try to keep cabling away from fluorescent lights, motors, and other sources of EMI. Do not bend the cable sharply—the radius of a bend should not be less than 10 times the diameter of the cable. Finally, avoid pulling cable wraps too tightly or crushing the cables in any way.
See also shielded twisted-pair (STP) cabling
A type of identifier for controlling directory replication in Microsoft BackOffice products such as Microsoft Exchange Server and in Microsoft Windows 2000.
How It Works
As an example, we will consider how update sequence numbers (USNs) are used in directory replication between Windows 2000 domain controllers. When an object is changed in Active Directory, that change must be replicated to all other domain controllers. To do this, Active Directory assigns a USN to each changed object, incrementing the values with time. Each domain controller uses a table to keep track of its own current USN and the highest USN it has received from each of the other domain controllers on the network.
Graphic U-4. Update sequence number (USN).
For example, if a domain controller called ABLE notifies a domain controller called BAKER of the updates it has for Active Directory, ABLE sends its own current USN number to BAKER, which compares the USN with the USN it recorded for ABLE in its internal table after the last directory update it received from ABLE. If the received USN is higher than the recorded USN, BAKER requests that ABLE send its updates for the directory. If the received USN is equal to or lower than the recorded one, BAKER knows that it has an up-to-date copy of ABLE’s directory and does not request any updates.
NOTE
USNs are more accurate than time stamps in controlling replication between domain controllers because time stamps depend on the clocks of domain controllers being exactly synchronized. However, time stamps are also employed if a tie-breaking mechanism is required for replication purposes. USNs also speed the recovery of Active Directory if a domain controller experiences a failure.
A port on a hub that is used to connect the hub to another hub on an Ethernet network. Uplink ports allow hubs to be cascaded to form larger networks by using ordinary unshielded twisted-pair (UTP) patch cables and not using up any of the station ports on the hub that are used to connect computers. If you do not have an uplink port on your hub, you can still connect a station port on the hub to a station port on another hub by using a crossover cable. Hubs are typically connected in a cascaded star topology.
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Be sure that the root or main hub of your cascaded star arrangement of hubs is a high-quality hub. Do not create collision domains larger than about 150 computers—network performance can seriously degrade due to too many collisions on the network. If hubs cannot meet your bandwidth requirements, consider replacing the main hub with an Ethernet switch.
See uninterruptible power supply (UPS)
See Uniform Resource Locator (URL)
A technology that allows companies to flexibly manage Web content by managing Hypertext Transfer Protocol (HTTP) request traffic based on the requested HTTP headers. URL switching is sometimes referred to as layer 7 content switching.
How It Works
URL switching allows HTTP requests from clients to be directed to Web servers and caches based on the value of substrings in the HTTP headers. For example, requests for static Web pages can be switched to a Web caching server, and requests for dynamic content can be switched to a Web application server. Other criteria that can be used to switch requests include the size of the file requested, whether the content is multimedia in form, and so on. Once the switch determines the best server to service the request, it binds the request to that server for the duration of the session. Cookies can also be used in Uniform Resource Locators (URLs) to switch requests to specific servers. URL switching also provides a way to load balance Web servers that is more flexible than the currently deployed Internet Protocol (IP) switching technologies. A leading vendor in URL switching devices is Alteon WebSystems.
A tool included with Microsoft Site Server and Microsoft Site Server Express for importing log files from a Web server. Usage Import can read various log file formats, which are Site Server, W3C Extended, Microsoft Internet Information Server (IIS), and NCSA Common. To use Usage Import, you select the desired log files and start the importing process. The importing process will import the log file data into the Site Server database. You can generate reports and analyze these imported logs by using Report Writer.
See universal serial bus (USB)
A global network of servers that supports approximately 50,000 newsgroups on every imaginable topic. These servers are called news servers. Thousands of them around the world collectively function as a global bulletin board. Usenet is part of the Internet’s family of protocols and services and is typically used by individuals for such purposes as
Asking questions or requesting assistance on a particular issue
Distributing free information, including binary files such as images, sound clips, and multimedia files
Advertising products and services
Discussing issues of general, regional, local, or topical interest
How It Works
The Usenet system is based on the Network News Transfer Protocol (NNTP), a standard Internet protocol defined in Request for Comments (RFC) 977 that has two components:
A client/server portion that allows users running client software such as Microsoft Outlook Express to interact with news servers by downloading a list of available Usenet newsgroups on the server, reading existing messages in the newsgroups, replying to existing messages, or posting new messages.
A server/server portion that allows news servers to communicate with each other, primarily for the purpose of replicating messages from newsgroups. An example of software that can function as a Usenet server is Microsoft Exchange Server, which fully supports NNTP.
Graphic U-5. Usenet.
Users typically gain access to the Usenet system by dialing in to their local Internet service provider (ISP) and accessing a news server running at the ISP. Users typically must have an account and a password to connect to their ISP’s news server, although a number of free Usenet servers are also available on the Internet. Users employ NNTP client software such as Outlook Express to access newsgroups on the ISP’s server and post new messages to them. Periodically, the ISP’s news server replicates its newsgroup messages by pushing or pulling newsfeeds together with nearby Usenet servers on the Internet. As a result, within about 24 hours the messages posted by users are available on virtually every Usenet server in the world. A message typically remains on a news server for a few weeks or until enough new messages have been posted to the newsgroup to bump the old messages off the list.
As mentioned earlier, Usenet currently consists of around 50,000 newsgroups, although new groups are constantly being created as old ones die off. Most news servers do not carry the complete range of Usenet newsgroups because of the multigigabyte size of a full newsfeed. Other news servers exclude certain categories of groups, such as adult newsgroups. Some newsgroups are moderated, which means that new postings to the group must be approved by a moderator before they can appear in the newsgroup. This minimizes the “noise” or extraneous messages (mostly advertising).
The Usenet system of newsgroups is hierarchical in nature, similar to the Domain Name System (DNS). At the top level, Usenet consists of a number of top-level news hierarchies that identify either a range of topics (such as .rec for recreational topics) or a geographical location (such as .mn for Minnesota). The following table shows some of the popular top-level categories. Newsgroups are created hierarchically under these top-level categories, as in these examples:
forsale.mn
computers.forsale.mn
macintosh.computers.forsale.mn
Top-Level Usenet Categories
| Category | Description |
| alt | Alternative, which is a collection of various topics |
| comp | Information on computer hardware, software, algorithms, and so on |
| misc | Miscellaneous information |
| news | Information about Usenet itself |
| rec | Recreational topics such as hobbies and travel |
| sci | Scientific issues |
| soc | Social issues |
| talk | General discussion topics such as politics and religion |
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If you don’t have an NNTP client program or if your company firewall will not allow you to access Usenet services using the well-known port number for NNTP (port 119), you can still access Usenet (if you can browse the Internet using a standard Web browser such as Microsoft Internet Explorer). Web sites such as Deja.com (www.deja.com) offer a Web interface for reading and posting to Usenet newsgroups. (Before you do this, make sure that your company does not have any policies forbidding employees to access Usenet.)
See user account
A type of account assigned to an individual user to allow that user to access network resources. These resources can include folders containing files, shared printers, mail services, or databases. The network administrator grants a user access to these resources by assigning the user a user account.
Two types of user accounts are available in Microsoft Windows NT and Windows 2000:
Domain user accounts: Created on domain controllers and exist domainwide on the network. You can log on to any computer on the network if you have a domain user account. Domain user accounts are often referred to simply as “user accounts.”
Local user accounts: Exist only within the directory database of a stand-alone member server or workstation that is not part of a domain. Users who have a local user account can log on only to the computer on which the account was created.
NOTE
A group account acts as a container for grouping user accounts. Group accounts simplify network administration by allowing multiple users to be granted or denied access to network resources in a single step—by granting or denying access for the group account to the resource.
See also account, domain user account, local user account
A TCP/IP transport layer protocol that supports unreliable, connectionless communication between hosts on a TCP/IP network.
How It Works
User Datagram Protocol (UDP) is a connectionless protocol that does not guarantee delivery of data packets between hosts. It differs from its companion transport layer protocol, the Transmission Control Protocol (TCP), which is a connection-oriented protocol for reliable packet delivery. UDP offers only “best-effort delivery” services and is used for both one-to-one and one-to-many communication in which small amounts of data are exchanged between hosts. UDP is used by applications and services that do not require acknowledgments. It can transmit only small portions of data at a time because it is not capable of segmenting and reassembling frames and does not implement sequence numbers.
UDP is typically used for services that perform broadcasts. These broadcasts can be directed to one of the following:
All hosts on the network—for example, to 255.255.255.255. All hosts will receive this packet unless they are prevented from doing so by a router along the way that is configured to drop such broadcasts instead of forwarding them.
Hosts on a specific (logical) network—for example, to 131.105.255.255 with subnet mask 255.255.0.0. All hosts with network ID 131.105 will receive this packet unless they are prevented from doing so by a router along the way.
Hosts on a specific (physical) subnet—for example, to 131.105.27.255 with subnet mask 255.255.255.0. All hosts on subnet 27 of network 131.105 will receive this packet.
UDP is used for the following services and functions in a Microsoft Windows networking environment:
NetBIOS name resolution using subnet UDP broadcasts sent to all hosts on a subnet or using unicast UDP packets sent directly to a Windows Internet Name Service (WINS) server
Domain Name System (DNS) host name resolution using UDP packets sent to name servers
Trivial File Transfer Protocol (TFTP) services
TIP
If a router is configured to allow 255.255.255.255 broadcasts, a broadcast storm can occur on the internetwork and bring network services to a halt. You should generally configure routers to allow only directed network traffic if possible.
A mode of security on computers running Microsoft Windows 95 and Windows 98 that protects shared folders and printers by requiring that users be authenticated by the network’s security provider. The security provider can be a Microsoft Windows NT or Windows 2000 domain controller or a Novell NetWare server, depending on which network client the computer running Windows 95 or Windows 98 has installed.
How It Works
Windows 95 and Windows 98 use pass-through authentication for granting client requests for shared resources on the computer:
A remote client attempts to access a share on the computer running Windows 95 or Windows 98, passing it the user’s credentials.
The computer forwards the user’s credentials to the network security provider.
The security provider verifies the credentials and informs the computer.
The computer grants the user the specified level of access to the share, depending on the user’s account and group memberships.
NOTE
Use the Network utility in Control Panel to enable user-level security on a computer running Windows 95 or Windows 98.
See also share-level security
See Internet Locator Service (ILS)
An administrative tool in Microsoft Windows NT for administering security on computers running Windows NT in a domain. You can use User Manager for Domains to
Create new users and groups
Edit the properties of users and groups
Set an account policy governing password restrictions
Set an audit policy for tracking resource usage
Configure trust relationships between domains
Assign rights to users and groups
Graphic U-6. User Manager for Domains.
NOTE
When Windows NT Server is installed as a member server, an administrator who logs on using a local user account can use the User Manager tool to administer the local security database on the computer. User Manager is the same tool as User Manager for Domains but has a different name on a member server or a computer running Windows NT Workstation.
When Microsoft Exchange Server is installed on a server running Windows NT, User Manager has a .dll extension and enables administrators to
Create an associated mailbox when they create a new user
View and modify the properties of a user’s mailbox
To create and manage users and groups in Microsoft Windows 2000, use Active Directory Users and Computers.
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If you need to make the same modification to a series of user accounts (for example, if you need to set new restrictions on logon hours), hold down the Ctrl key and select the accounts, and then choose Properties from the User menu and make the modification.
A restricted mode of operation for processes in Microsoft Windows NT and Windows 2000. User mode processes have lower priority and fewer privileges than kernel mode processes. User mode processes include components of the operating system that directly support user applications and the applications that use those subsystems.
Graphic U-7. User mode.
User mode subsystems include
Win32 subsystem, which supports Windows applications
OS/2 subsystem, which supports OS/2 applications
POSIX subsystem, which supports POSIX-compliant applications
Security subsystem, which handles logon validation
NOTE
User mode processes cannot access hardware directly in Windows NT; they must pass their access requests to the Windows NT executive.
See also kernel mode, Windows NT executive
A unique identifier that enables a user to log on to a computer or network. A typical example is “jsmith” or “jeffs” for a user named Jeff Smith. Usernames are part of a user’s credentials, which include the username, password, and domain name. Each user on the network must have a unique username so that his or her personal folders can be protected against unauthorized access and for administrative purposes such as auditing.
NOTE
When a user requires access to a Microsoft Windows NT network, the administrator or account operator must first use the tool User Manager for Domains to create a user account for the user, specifying the username, password, domain, group memberships, and account restrictions. On a Microsoft Windows 2000–based network, the administrator or the account operator can use Active Directory Users and Computers to create and manage user accounts, and account restrictions can be created and managed using group policies.
See also naming convention
In Microsoft Windows 2000, the logon name of a user on the network. The user principal name consists of the associated name of the User object in Active Directory that is associated with the user, followed by an ampersand (&), and then typically followed by the Domain Name System (DNS) name of the container in Active Directory in which the User object resides. The user principal name must be unique for every User object in Active Directory.
Example
If the User object in Active Directory for user Jeff Smith has the name jsmith and if this User object resides in the container whose DNS name is sales.microsoft.com, the default form of Jeff Smith’s user principal name is as follows:
jsmith@sales.microsoft.com
An alternative form of the user principal name for Jeff Smith is
jsmith@microsoft.com
In other words, the suffix for the user principal name of a user can be either the name of the tree or the name of the domain that resides above the object named in the tree. Note the similarity between the user principal name for Jeff Smith and what you might expect his Simple Mail Transfer Protocol (SMTP) e-mail address to be. The difference is that the user principal name is merely a property that is assigned to the user and can be set to any value.
NOTE
The user principal name is one of three types of names by which objects in Active Directory can be known. The others are the distinguished name and the relative distinguished name.
In Microsoft Windows 95, Windows 98, Windows NT, and Windows 2000, user-definable information about a user’s work environment, including desktop settings, network connections, printer connections, and Start menu items.
In Windows NT, when a user logs on to a workstation, his or her profile is saved locally in a personal subfolder of the %SystemRoot%\profiles folder. You can also store user profiles on a network share to allow users to access their work environment from any workstation.
How It Works
A user’s profile is stored in a folder named after the username and consists of a registry hive and a series of subfolders whose functions are listed in the following table. If additional software is installed on the computer (such as Microsoft Internet Explorer), additional subfolders might exist within the user’s profile folder.
NOTE
In Windows 95 and Windows 98, ntuser.dat and ntuser.dat.log are replaced by user.dat and user.da0, which make Windows 95 and Windows 98 user profiles incompatible with Windows NT and Windows 2000 user profiles.
User Profile Subfolders and Registry Hives
| Subfolder or hive | Contents |
| Application Data folder | Vendors’ application-specific data |
| Desktop folder | Files and shortcuts on the Desktop |
| Favorites folder | Favorite locations |
| NetHood folder | Shortcuts to Network Neighborhood items |
| Personal folder | Users’ personal documents |
| PrintHood folder | Shortcuts to Printer Folder items |
| Recent folder | Shortcuts to recently opened documents |
| SendTo folder | Shortcuts for the SendTo menu |
| Start Menu folder | Start menu shortcuts |
| Templates folder | Shortcuts to templates |
| ntuser.dat | Copy of the HKEY_CURRENT_USER hive |
| ntuser.dat.log | Transaction log for error recovery |
A built-in group in Microsoft Windows NT and Windows 2000. The Users group is a local group that exists on all servers and workstations running Windows NT. In Windows 2000, however, the Users group is a domain local group on domain controllers and a local group on member servers, stand-alone servers, and computers running Windows 2000 Professional. The initial membership of the Users group is the domain users global group (all ordinary users on the network). The Users group has no preassigned rights or permissions and should be assigned permissions to network resources that ordinary users will normally require.
See also built-in group
See update sequence number (USN)
See unshielded twisted-pair (UTP) cabling
Stands for UNIX-to-UNIX Copy, a UNIX protocol and utility for copying (sending) files between two UNIX computers on a network. UUCP was originally intended for transferring files over an asynchronous serial transmission interface such as RS-232. With UUCP, you can transfer files via a direct cable connection between serial ports on two computers by using a null modem cable or over telephone lines by using modems connected to the serial ports of each computer. A version of UUCP has been developed for transferring files over Ethernet as well. UUCP was also used for transferring electronic mail messages (e-mail) between hosts in the early days of the Internet. A UNIX host used UUCP to transfer mail to a remote host simply by executing the MAIL program on the remote UNIX host and having it run on the local message file to be delivered.
UUCP uses the well-known port number 117 for its path service and number 540 for the UUCP daemon called UUCPD. UUCP has been eclipsed by File Transfer Protocol (FTP) as a general protocol for moving files between hosts and by Simple Mail Transfer Protocol (SMTP) for transferring e-mail messages.
NOTE
Third-party vendors have created UUCP gateway connectors for Microsoft Exchange Server to enable Exchange to send and receive UUCP mail over the Internet.
A method of encoding binary files into 7-bit ASCII text that was originally developed for UNIX platforms. Uuencoding enables you to attach binary files to e-mail messages and transmit them over the Internet using Simple Mail Transfer Protocol (SMTP). The sending program first “uuencodes” the attachments and sends them with the e-mail message, which the receiving program “uudecodes” into its original binary format.
Although still popular on some platforms, uuencoding has been largely superseded by Multipurpose Internet Mail Extensions (MIME), a more sophisticated scheme for encoding multipart e-mail messages. Uuencoding is still used in one context in Microsoft Windows, namely for Basic Authentication on Internet Information Services (IIS). Basic Authentication transmits the user’s credentials between the Web browser client and the IIS computer in uuencoded form. This method is commonly referred to as clear-text transmission, although if you were to capture authentication traffic by using a network sniffer such as Microsoft Network Monitor, you would be unable to read the user’s credentials without uudecoding the information. Uuencoding is not considered a cryptographic algorithm because it is extremely simple to crack.
NOTE
An encoding method similar to uuencoding that is implemented on Apple Macintosh systems is called BinHex.
TIP
You can tell that a binary file has been uuencoded into an ASCII text file if the text of the file starts with “begin 644….”
See Universal Wireless Communications (UWC-136)
