Network Plus 2005 In Depth

822 Glossary

Transport layer—The fourth layer of the OSI Model. In the Transport layer, protocols ensure that data are transferred from point A to point B reliably and without errors. Transport layer services include flow control, acknowledgment, error correction, segmentation, reassembly, and sequencing.

tree—A logical representation of multiple, hierarchical levels in a directory. It is called a tree because the whole structure shares a common starting point (the root), and from that point extends branches (or containers), which may extend additional branches, and so on.

tree object—In NetWare terminology, the object that represents the root of an eDirectory tree.

Triple DES (3DES)—The modern implementation of DES, which weaves a 56-bit key through data three times, each time using a different key.

Trivial File Transfer Protocol—See TFTP.

Trojan—See Trojan horse.

Trojan horse—A program that disguises itself as something useful, but actually harms your system.

trust relationship—The relationship between two domains on a Windows Server 2003 network that allows a domain controller from one domain to authenticate users from the other domain.

TTL (Time to Live)—A number that indicates the maximum time that a datagram or packet can remain on the network before it is discarded. Although this field was originally meant to represent units of time, on modern networks it represents the number of router hops a datagram has endured. The TTL for datagrams is variable and configurable, but is usually set at 32 or 64. Each time a datagram passes through a router, its TTL is reduced by 1. When a router receives a datagram with a TTL equal to 1, the router discards that datagram.

tunnel—A secured, virtual connection between two nodes on a VPN.

tunneling—The process of encapsulating one type of protocol in another. Tunneling is the way in which higher-layer data is transported over VPNs by Layer 2 protocols.

twinaxial cable—A type of cable that consists of two copper conductors at its center surrounded by an insulator, a braided metal shielding, called braiding, and an outer cover, called the sheath or jacket.

twist ratio—The number of twists per meter or foot in a twisted-pair cable.

twisted-pair—A type of cable similar to telephone wiring that consists of color-coded pairs of insulated copper wires, each with a diameter of 0.4 to 0.8 mm, twisted around each other and encased in plastic coating.

two-way transitive trust—The security relationship between domains in the same domain tree in which one domain grants every other domain in the tree access to its resources and, in turn, that domain can access other domains’ resources. When a new domain is added to a tree, it immediately shares a two-way trust with the other domains in the tree.

type 1 IBM connector—A type of Token Ring connector that uses interlocking tabs that snap into an identical connector when one is flipped upside-down, making for a secure connection. Type 1 IBM connectors are used on STP-based Token Ring networks.

typeful—A way of denoting an object’s context in which the organization and organizational unit designators (“O=“ and “OU=,” respectively) are included. For example, OU=Inv.OU=_Ops.OU=Corp. O=Sutkin.

Glossary 823

typeless—A way of denoting an object’s context in which the organization and organizational unit designators (“O=“ and “OU=,” respectively) are omitted. For example, Inv.Ops.Corp._Sutkin.

UDF (Universal Disk Format)—A file system used on CD-ROMs and DVD (digital video disc) media.

UDP (User Datagram Protocol)—A core protocol in the TCP/IP suite that sits in the Transport layer of the OSI Model. UDP is a connectionless transport service.

UFS—The primary file system used in the Solaris operating system.

unicast address—A type of IPv6 address that represents a single interface on a device. An IPv6 unicast address begins with either FFC0 or FF80.

uninterruptible power supply—See UPS.

Universal Disk Format—See UDF.

universal group—A group on a Windows Server 2003 network that allows members from one domain to access resources in multiple domains and forests.

unpopulated segment—A network segment that does not contain end nodes, such as workstations. Unpopulated segments are also called link segments.

unshielded twisted-pair—See UTP.

upgrade—A major change to the existing code in a software application, which may or may not be offered free from a vendor, and may or may not be comprehensive enough to substitute for the original application.

uplink—A connection from an earth-based transmitter to an orbiting satellite.

uplink port—A port on a connectivity device, such as a hub or switch, used to connect it to another connectivity device.

UPN (user principal name) suffix—The portion of a universal principal name (in Windows Server 2003 Active Directory’s naming conventions) that follows the @ sign.

UPN (user principal name)—The preferred Active Directory naming convention for objects when used in informal situations. This name looks like a familiar Internet address, including the positioning of the domain name after the @ sign. UPNs are typically used for e-mail and related Internet services.

UPS (uninterruptible power supply)—A battery-operated power source directly attached to one or more devices and to a power supply (such as a wall outlet), which prevents undesired features of the power source from harming the device or interrupting its services.

upstream—A term used to describe data traffic that flows from a customer’s site to a carrier’s facility. In asymmetrical communications, upstream throughput is usually much lower than downstream throughput. In symmetrical communications, upstream and downstream throughputs are equal.

USB (universal serial bus) port—A standard external bus that can be used to connect multiple types of peripherals, including modems, mice, and NICs, to a computer. Two USB standards exist: USB 1.1 and USB 2.0. Most modern computers support the USB 2.0 standard.

user—A person who uses a computer.

User Datagram Protocol—See UDP.

user principal name—See UPN.

824 Glossary

UTP (unshielded twisted-pair)—A type of cabling that consists of one or more insulated wire pairs encased in a plastic sheath. As its name implies, UTP does not contain additional shielding for the twisted pairs. As a result, UTP is both less expensive and less resistant to noise than STP.

vault—A large tape storage library.

virtual address—See network address.

virtual circuit—A connection between network nodes that, although based on potentially disparate physical links, logically appears to be a direct, dedicated link between those nodes.

virtual local area network—See VLAN.

virtual memory—The memory that is logically carved out of space on the hard disk and added to physical memory (RAM).

virtual private network—See VPN.

virus—A program that replicates itself to infect more computers, either through network connections or through floppy disks passed among users. Viruses may damage files or systems, or simply annoy users by flashing messages or pictures on the screen or by causing the keyboard to beep.

virus hoax—A rumor, or false alert, about a dangerous, new virus that could supposedly cause serious damage to your workstation.

VLAN (virtual local area network)—A network within a network that is logically defined by grouping its devices’ switch ports in the same broadcast domain. A VLAN can consist of any type of network node in any geographic location and can incorporate nodes connected to different switches.

Voice over IP (VoIP)—The provision of telephone service over a packet-switched network running the TCP/IP protocol suite. One form of VoIP (pronounced “voyp”) is Internet telephony, though VoIP is frequently used over private networks to circumvent long-distance toll charges.

VoIP – See voice over IP.

volt—The measurement used to describe the degree of pressure an electrical current exerts on a conductor.

voltage—The pressure (sometimes informally referred to as the strength) of an electrical current.

volt-amp (VA)—A measure of electrical power. A volt-amp is the product of the voltage and current (measured in amps) of the electricity on a line.

voltmeter—A device used to measure voltage (or electrical pressure) on an electrical _circuit.

VPN (virtual private network)—A logically constructed WAN that uses existing public transmission systems. VPNs can be created through the use of software or combined software and hardware solutions. This type of network allows an organization to carve out a private WAN through the Internet that serves only its offices, while keeping the data secure and isolated from other (public) traffic.

WAN (wide area network)—A network that spans a long distance and connects two or more LANs.

WAN link—A point-to-point connection between two nodes on a WAN.

WAP (wireless access point)—See AP.

war driving—The act of driving while running a laptop configured to detect and capture wireless data transmissions.

Glossary 825

warm site—A place where the computers, devices, and connectivity necessary to rebuild a network exist, though only some are appropriately configured, updated, or connected to match the network’s current state.

wavelength—The distance between corresponding points on a wave’s cycle. Wavelength is inversely proportional to frequency.

wavelength division multiplexing—See WDM.

WDM (wavelength division multiplexing)—A multiplexing technique in which each signal on a fiberoptic cable is assigned a different wavelength, which equates to its own subchannel. Each wavelength is modulated with a data signal. In this manner, multiple signals can be simultaneously transmitted in the same direction over a length of fiber.

Web portal—A secure, Web-based interface to an application or group of applications.

Web server—A computer that manages Web site services, such as supplying a Web page to multiple users on demand.

Webcasting—A broadcast transmission from one Internet-attached node to multiple other Internetattached nodes.

Well Known Ports—TCP/IP port numbers 0 to 1023, so named because they were long ago assigned by Internet authorities to popular services (for example, FTP and Telnet), and are therefore well known and frequently used.

WEP (Wired Equivalent Privacy)—A key encryption technique for wireless networks that uses keys both to authenticate network clients and to encrypt data in transit.

whois—The utility that allows you to query ICANN’s DNS registration database and find the information as a domain.

wide area network—See WAN.

Wi-Fi—See 802.11b.

Wi-Fi Alliance—An international, nonprofit organization dedicated to ensuring the interoperability of 802.11-capable devices.

Wi-Fi Protected Access—See WPA.

WiMAX—See 802.16a.

Windows Internet Naming Service—See WINS.

Windows Services for UNIX—A suite of applications designed to integrate Windows Server 2003 servers with UNIX-type of servers and clients. One application in this suite enables Windows and UNIX-type of servers to share directory information (when the UNIX-type of server has a directory installed). Another application enables UNIX-type of clients to view resources on a Windows Server 2003 server as if they were resources on a UNIX-type of server.

winipcfg—The TCP/IP configuration and management utility for use with Windows 9x and Me systems. Winipcfg differs from ipconfig in that it supplies a graphical user interface.

WINS (Windows Internet Naming Service)—A service that resolves NetBIOS names with IP addresses. WINS is used exclusively with systems that use NetBIOS—therefore, it is found on Win- dows-based systems.

826 Glossary

wire-bound—A type of signal that relies on a physical medium, such as a cable, for its transmission.

Wired Equivalent Privacy—See WEP.

wireless—The signals made of electromagnetic energy that travel through the atmosphere.

wireless access point—See WAP.

wireless broadband—The term used to describe the recently released standards for high-throughput, long-distance digital data exchange over wireless connections. WiMAX (IEEE 802.16a) is one example of a wireless broadband technology.

wireless LAN—See WLAN.

wireless personal area network—See WPAN.

wireless spectrum—A continuum of electromagnetic waves used for data and voice communication. The wireless spectrum (as defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300 GHz. Each type of wireless service can be associated with one area of the wireless spectrum.

WLAN (wireless LAN)—A LAN that uses wireless connections for some or all of its transmissions.

workgroup—A group of interconnected computers that share each others’ resources without relying on a central file server.

workgroup hub—See standalone hub.

Workgroup Manager—The application in Mac OS X Server that enables a network administrator to manage users and groups.

workstation—A computer that runs a desktop operating system and connects to a network.

Worldwide Interoperability for Microwave Access (WiMAX)—See 802.16a.

worm—An unwanted program that travels between computers and across networks. Although worms do not alter other programs as viruses do, they may carry viruses.

WPA (Wi-Fi Protected Access)—A wireless security method endorsed by the Wi-Fi Alliance that is considered a subset of the 802.11i standard. In WPA, authentication follows the same mechanism specified in 802.11i. The main difference between WPA and 802.11i is that WPA specifies RC4 encryption rather than AES.

WPA2—The name given to the 802.11i security standard by the Wi-Fi Alliance. The only difference between WPA2 and 802.11i is that WPA2 includes support for the older WPA security method.

WPAN (wireless personal area network)—A small office or home network in which devices such as mobile telephones, PDAs, laptops, and computers are connected via wireless transmission.

X Server—A NetWare 6.x server’s graphical desktop. X Server loads by default when the server starts.

X Window system—The GUI environment for UNIX-type of systems.

X.25—An analog, packet-switched WAN technology optimized for reliable, long-distance data transmission and standardized by the ITU in the mid-1970s. The X.25 standard specifies protocols at the Physical, Data Link, and Network layers of the OSI Model. It provides excellent flow control and ensures data reliability over long distances by verifying the transmission at every node. X.25 can support a maximum of only 2-Mbps throughput.

Glossary 827

xDSL—The term used to refer to all varieties of DSL.

XNU—The Mach-based kernel in Mac OS X.

Xserve—The enterprise-class of server computer by Apple Computer, which is based on the PowerPC processor and which runs Mac OS X Server.

Zeroconf (Zero Configuration)—A collection of protocols designed by the IETF to simplify the setup of nodes on a TCP/IP network. Zeroconf assigns a node an IP address, resolves the node’s host name and IP address without requiring a DNS server, and discovers services, such as print services, available to the node, also without requiring a DNS server.

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