Internet - Glossary of Terms

Alphabetic Index:
[A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] [X]

A

Analog -- A way of sending voice, video, or data that is "analogous" to the original signal. Analog transmission is associated with voice and data signals over conventional telephone lines. (Contrast with digital).

Access router -- An access device with built-in basic routing protocol support, specifically designed to allow remote LAN access to corporate backbone networks. Not designed to replace backbone routers or to build backbone networks.

AIM -- See Ascend Inverse Multiplexing protocol.

AMI -- Alternate Mark Inversion. A line encoding scheme for transmitting data bits over T1 transmission systems.

AppleTalk -- Apple Computer's proprietary local area network for linking Apple computers and peripherals.

Application -- Functional system made up of software, hardware, or combination of both that performs some useful task. Database managers, spreadsheets, word processors, videoconferencing systems, LANs, fax machines, etc., are examples of applications.

ARP -- Address Resolution Protocol. This portion of the TCP/IP protocol maps an IP address to the physical address (Ethernet Address) of the PC that it is on, helping to identify PCs on an Ethernet LAN.See also Ethernet and TCP/IP.

Ascend Inverse Multiplexing protocol (AIM) -- An in-band protocol used to manage the interconnection of two remotely located inverse multiplexers. AIM is a feature-rich, widely used inverse multiplexing protocol developed and supported by Ascend Communicat ions.

Ascend MAX -- See MAX.

Ascend Multiband -- See Multiband.

Ascend Pipeline -- See Pipeline.

Asynchronous Transfer Mode (ATM) -- A high bandwidth, controlled-delay fixed-size packet switching and transmission system. Uses fixed-size packets also known as "cells"; ATM is often referred to as "cell relay". ATM will provide the basis for future broad band ISDN standards.

ATM -- See Asynchronous Transfer Mode.

AUI -- Autonomous Unit Interface or Attachment Unit Interface. This refers to the 15-pin D connector and cables that connect single and multiple channel equipment in an Ethernet transceiver.

B

B8ZS -- Binary Eight Zero Suppression. An encoding scheme for transmitting data bits over T1 transmission systems.

Backbone -- The part of the communications network intended to and architectured to carry the bulk of traffic. Provides connectivity between subnetworks in an enterprise-wide network.

Backbone Router -- Routers designed to be used to construct backbone networks using leased lines. Typically do not have any built-in digitaldial-up WAN interfaces. Typical manufacturers include Cisco, Wellfleet, 3Com, CrossCom, etc.

Backup -- The process of creating a copy of computer data on an external storage medium, such as a floppy disk, tape, or external hard drive. If the external storage medium is remotely located, some form of data communications channel must be established b etween sites.

Bandwidth -- The range of electrical frequencies that a device can handle. The amount of bandwidth a channel is capable of carrying is equivalent to how much capacity is possible.

Bandwidth-on-demand -- A Pipeline 25 feature that reduces costs by automatically determining whether or not a second ISDN B-Channel is necessary during data transfer. For example, the Pipeline 25 evaluates the percent of usage on a single ISDN B-Channel (i n a data transfer). If the utilization exceeds 90% for a specified length of time, the Pipeline 25 automatically brings up the second B-channel to speed up the transfer. Then it reverts back to one B-channel when two are no longer necessary.

B-channel -- Bearer channel. A circuit-switched digital channel that sends and receives data, voice, or video signals at speeds up to 64 kbps.

Basic Rate Interface -- An ISDN subscriber line, consisting of two 64 kbit/s B channels, or "bearer" channels, and one 16 kbit/s D channel, used for both data and signaling purposes.

BERT -- See Bit Error Rate Test.

Bit Error Rate Test -- A test to determine the percentage of received bits in error compared to the total number of bits received. Usually expressed as a number to the power of 10.

Bit -- Contraction of the term "BInary digiT". The smallest unit of information a computer can process, representing one of two states (usually indicated by "1" and "0").

BONDING -- Bandwidth On Demand Interoperability Group. A consortium of over 40 datacommunications equipment vendors and service providers who joined together to create a standardized inverse multiplexing protocol so that inverse multiplexers from different vendors could interoperate. Also refers to the resultant specification, sometimes known as the BONDING specification.

Branch Office -- A smaller remotely located office separate from corporate headquarters facilities.

BRI -- Basic Rate Interface. One of two subscriber "interfaces" in ISDN. BRI has two bearer B-channels at 64 kbps and a data D- channel at 16 kbps. The B-channels are for voice, video, and data. The D- channel is for signalling between telephone company sw itches and for carrying ISDN user-network messages.

Bridge -- A device or setup that connects and passes data, voice, or video between two network segments, based on the destination field in the packet header. The Pipeline 25 is a learning bridge, because it passes all packets to the next network segment (t he ISDN line), and builds a table to identify the destination addresses that are local and remote. After learning the addresses on both sides of a network, the bridge passes only packets for the remote network. (Contrast with router).

Broadband -- A way of transmitting large amounts of data, voice, and video that is greater than standard voice grade transmission. In ISDN, broadband channels support rates above the primary rate (1.544 Mbps or 2.048 Mbps).

C

CAD/CAM -- Computer-Aided Design/Computer-Aided Manufacturing. A computer and its related software and terminals used to design and manufacture things. CAD terminals are often run over LANs and/or WANs.

Central Office -- A telephone company facility that joins subscriber telephone lines to switching equipment. This allows subscribers to connect to one another, through local and long distance connections.

Central Site -- A location which acts as a data collection point for remote and branch offices, as well as telecommuters and travelers.

Channel -- A transmission path between two points. It is usually the smallest subdivision of a transmission system by means of which a single type of communications service is provided.

Channel service unit -- A device used to connect a digital phone line coming in from the phone company to network access equipment located on the customer premises. A CSU may also be built into the network interface of the network access equipment.

CHAP -- Challenge Handshake Authentication Protocol. This security protocol allows access between data communications systems prior to and during data transmission. CHAP uses challenges to verify that a user has access to a system.

Codec -- COder-DECoder. In the videoconferencing world, a video codec converts analog video signals from a video camera to digital signals for transmission over digital circuits, and then converts the digital signals back to analog signals for display. In the audio world, an audio codec converts analog audio signals to digital signals for transmission over digital circuits, and then converts the digital signals back to analog signals for reproduction.

Control-lead dialing -- The initiation of a dialed call over the network using signals on leads within the interface cable between an application and the network access equipment. Thus, an application instructs the network access equipment to dial a call b y toggling one or more leads within the cable between the application and the network access equipment.

Crossover cable -- A cable with wires that "cross over," so the terminating ends of the cable have opposite wire assignments. (Contrast with straight-through cable).

CSU -- See Channel Service Unit.

Customer Premises Equipment (CPE) -- Terminal equipment located on the customer premises which connects to the telephone network.

D

D4 -- A T1 framing format.

DCE. Data Communications Equipment -- As defined in the RS-232 specification, equipment to which DTE (Data Terminal Equipment) is connected, often to enable access to network facilities. DCE refers to equipment such as network access equipment while DTE re fers to application equipment such as a videoconference terminal.

Digital -- A way of sending voice, video, or data that reconstructs the signals using binary codes (1s and 0s) Digital transmission offers faster speeds, better accuracy, and more flexibility than analog transmission. (Contrast with analog).

Digital Dial-Up Bandwidth -- Communications channels created by signaling to the network from the caller's site the intended destination of the connection. These channels may be terminated when the caller or called party chooses. The user pays for the band width only when it is used. Digital Dial-Up Bandwidth operates in a fashion similar to the dialed voice telephone network but the resultant connections are digital and of specified bandwidths.

Digital Modem -- A system component which allows communication over digital access facilities with a remotely located system connected to the public network over analog facilities. Converts incoming digital data stream containing PCM-encoded modem waveform into actual data contained in waveform at data rate transmtted by far-end modem; performs inverse function for outgoing data stream.

Disaster Recovery -- The use of alternative network circuits to re-establish communications channels in the event that the primary channels are disconnected or malfunctioning.

Drop and Insert -- A process of adding data (insert) to a T1 data stream, or terminating data (drop) from a T1 data stream to other devices connected to the drop and insert equipment.

DS0 -- A 64 kbit/s unit of transmission bandwidth. A worldwide standard speed for digitizing one voice conversation, and more recently, for data transmission. Twenty-four DS0's (24x64 kbit/s) equal one DS1.

DS1 -- A 1.544 Mbit/s unit of transmission bandwidth in North America, and a 2.048 Mbit/s unit of transmission elsewhere. A telephony term describing a 1.544 or 2.048 Mbit/s digital signal carried on a T1 facility.

DTE -- Data Terminal Equipment. As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, such as personal computers or data terminals. DTE refers to application equipment, such as a videoconference termin al or LAN bridge or router, while DCE refers to equipment such as network access equipment.

Dual 56 -- Two switched 56 calls made between videoconferencing equipment to allow data transfer at 112 kbit/s. The videoconferencing equipment performs a two-channel inverse-multiplexing procedure to assure channel alignment.

Dynamic Bandwidth Allocation -- The process of determining current traffic loads over a channel, and automatically increasing or decreasing the bandwidth of the channel to optimize overall utilization efficiency.

E

E1 -- A digital transmission link with a capacity of 2.048 Mbit/s, used outside of North America. Typically channelized into 30 DS0s, each capable of carrying a single voice conversation or data stream. Uses two pairs of twisted pair wires.

ESF -- Extended Super Frame. A T1 framing format.

Ethernet -- A local area network that connects devices like computers, printers, and terminals. Ethernet operates over twisted-pair or coaxial cable at speeds at 10 Mbps.

Ethernet transceiver -- An Ethernet device that connects workstations to standard thick or thin Ethernet-style cable. This device sends and receives information and often offers data packet collision detection.

F

Fractional T1 -- Service offering data rates between 64 kbit/s (DS0 rate) and 1.536 Mbit/s (DS1 rate), in specified intervals of 64 kbit/s.

Frame Relay -- A form of packet switching, but using smaller packets and less error checking than traditional forms of packet switching (such as X.25). Now a new international standard for efficiently handling high- speed, bursty data over wide area networ ks.

Frame -- A segment of a digital signal that has a repetitive characteristic in that corresponding elements of successive frames represent the same things. In a time-division multiplex system, a frame is a sequence of time slots, each containing a sample fr om one of the channels served by the multiplex system; the frame is repeated at the sampling rate, and each channel occupies the same sequence position in successive frames.

FT1 -- See Fractional T1

G

GloBanD -- The name given for a set of European network services which offer digital dial-up bandwidth on demand in 64 kbit/s increments, accessed from the customer premise over PRI lines. These services are offered under different names in each participat ing country.

H

H channel -- A transmission channel, defined in the CCITT ISDN standards, made up of multiple B channels. Currently defined H channels include H0 (384 kbit/s), H10 (1.472 Mbit/s), H11 (1.536 Mbit/s), and H12 (1.920 Mbit/s).

H.221 -- A CCITT standard describing a method of inverse multiplexing for videoconferencing terminals, to be used with Px64 videoconferencing.

H.261 -- A CCITT standard describing a protocol for digitally encoding and decoding video images to allow videoconferencing terminals from different manufacturers to interoperate.

H.320 -- A set of CCITT standards describing methods to allow videoconferencing terminals from different manufacturers to interoperate.

H0, ISDN H0 -- An H channel made up of 6 B channels to create a 384 kbit/s ISDN channel.

H10, ISDN H10 -- An H channel made up of 23 B channels to create a 1472 kbit/s ISDN channel.

H11, ISDN H11 -- An H channel made up of 24 B channels to create a 1536 kbit/s ISDN channel.

H12, ISDN H12 -- An H channel made up of 30 B channels to create a 1920 kbit/s ISDN channel.

Hybrid Private/Public networking -- The creation of a network using both private leased lines and public switched facilities (digital dial-up bandwidth). The goals of combining both networking technologies are increased performance and flexibility at reduc ed cost.

I

IEC. Inter Exchange Carrier -- Common carrier providing communications channels between local telephone companies (LECs, or Local Exchange Carriers). Also known as long distance carriers, such as AT&T, MCI, Sprint, WilTel, etc.

IEEE -- Institute of Electrical and Electronics Engineers. An organization that maintains the standards for 10BaseT and other communications standards.

In-band signaling -- Signaling made up of tones or defined bits which pass within the data transmission stream. Tones sent over digital circuits are encoded into digital PCM bursts and sent as digital data within the data channel.

Inverse multiplexing -- Several combined, lower-speed circuits that make up one circuit for greater bandwidth. Inverse multiplexing also pulls together and synchronizes multiple channels at the receiving end of data, voice, or video transmission.

IP address -- Internetwork Protocol Address or Internet Address. A unique number assigned by an Internet authority that identifies a computer on the Internet. The number is four groups of numbers separated by three periods (dots), each between 0 and 255. F or example, 195.112.56.75 is an IP address.See also IP subnet.

IP subnet -- Internet Protocol Subnet. An IP subnet or subnet mask is a way to subdivide a network into smaller networks, so you can have a greater number of computers on a network with a single IP address. The IP subnet is a number that you append to the IP address. For example, 195.112.56.75/14, 195.112.56.75/15, and 195.112.56.75/16 are all IP addresses with subnets of 14, 15, and 16.

IPX. Internet Packet eXchange -- NetWare's native LAN communications protocol, which can run over Ethernet or Token Ring LANs.

ISDN -- Integrated Services Digital Network. A system that provides simultaneous voice and high-speed data transmission through a single channel to the user's premises. ISDN is an international standard for end-to-end digital transmission of voice, data, a nd signaling.

ISDN Multirate -- A network-based ISDN service which allows users network access equipment to dial network channels of bandwidth in increments of 64 kbit/s, up to 1536 kbit/s. Access to ISDN Multirate service is obtained over ISDN PRI lines.

ISP -- Internet Service Provider. A company that offers their subscribers access to the Internet.

IXC -- Inter eXchange Carrier. See IEC.

L

LAN -- A network that interconnects devices over a geographically small area, typically in one building or a part of a building. The most popular LAN type is Ethernet, a 10 Mbps standard that works with 10BaseT, 10Base2, or 10Base5 cables. When you interco nnect a single computer to the Pipeline 25 with the crossover cable in your package, you are creating a two-node Ethernet network.

LAN Internetworking -- The reach of local area networks (LANs) to other networks, so users can get access to other applications. Bridges and routers are the devices which typically accomplish the task of joining LANs.

LDC -- Long Distance Carrier. See IEC.

Leased Lines -- A circuit rented for exclusive use twenty-four hours a day, seven days a week from a telephone company. The connection exists between two predetermined points and cannot be switched to other locations.

LEC -- Local Exchange Carrier. Local telephone company, providing connections between local points or to long distance carriers for extended connections. Examples are Pacific Bell in California, Illinois Bell in Illinois, GTE in Hawaii, etc.

Local Area Network -- A datacommunications network spanning a limited geographical area, usually within a single facility or campus. It provides communications between computers and peripherals.

Local Loopback -- Loopback performed between an application and network access equipment. The signal is sent from the application to the network access equipment and back to the application without being sent out over the network.

Loopback -- A diagnostic test or test state in which the transmitted signal is returned to the sending device after passing through a communications link or network.

LSU -- LAN Service Unit. See Multiband LSU.

M

MAX -- Media Access Exchange. The Ascend MAX is a system-level network access unit, with a cage and backplane into which Multiband or Pipeline cards can be inserted to configure it for various application requirements. It supports up to 32 host ports or di rect Ethernet connection and up to 8 Mbit/s to the network. It supports multiple applications, including remote LAN access, leased line backup and individual videoconferencing units, as well as connecting videoconference MCUs to the digital dial-up network .

MCU -- See Multipoint Control Unit.

MIB -- Management Information Base. A directory listing the logical names of all information resources residing in a network and pertinent to the network's management. A key element of SNMP management systems.

MPP -- Multichannel Point-to-Point protocol. A protocol similar to PPP (Point-to-Point Protocol) but operable over multiple network channels in an inverse multiplexed scenario. Developed by Ascend Communications.

Multiband LSU -- LAN Service Unit. The Ascend Multiband LSU is a member of the Ascend Multiband product family. It allows LAN bridges and routers to be interconnected, creating WANs, using a combination of dedicated leased circuits and digital dial-up circ uits. By creating such hybrid networks, users can match bandwidth to real-time traffic loads, saving money and maximizing performance.

Multiband Plus -- The Ascend Multiband Plus is a member of the Ascend Multiband product family. Like all members of the Multiband family, it provides application access to digital dial-up bandwidth on demand. It supports up to four simultaneous application s (video, LAN, backup, imaging, etc.) and up to 3 Mbit/s to the network.

Multiband RPM -- Remote Port Module. The Ascend Multiband RPM is a member of the Ascend Multiband product family. A device used to extend data, control, and management data ports from a Multiband to application equipment located elsewhere in a facility. An RPM might be thought of as a sophisticated repeater, converting high-speed data and control signals for transmission using simple unshielded twisted pair wiring over extended distances (typically up to 3400 feet).

Multiband VSU. Video Service Unit -- The Ascend Multiband VSU is a member of the Ascend Multiband product family. It allows videoconference users to initially purchase a VSU for use as a dual 56 (112 kbit/s) CSU/DSU, and then easily upgrade the VSU to a fu ll-fledged 384 kbit/s inverse multiplexer at a later date as requirements dictate. The upgrade process is performed by remotely downloading new software from Ascend Communications.

Multiband -- The name of a product family of network access equipment manufactured by Ascend Communications.

Multiplexing -- The process of combining a number of individual channels into a common frequency band or into a common bit stream for transmission. The converse equipment or process for separating a multiplexed stream into individual channels is called dem ultiplexer.

Multipoint Control Unit (MCU) -- Videoconferencing equipment which allows multiple individual videoconference units to connect together to form a multi-party videoconference session.

MUX. Multiplex or Multiplexer -- A device that performs multiplexing.

N

NFAS. Non Facilities-Associated Signaling -- Allows a D- channel on one ISDN PRI to control channels located on other PRIs.

NT1 -- An ISDN BRI line terminating device at the subscriber's location that provides line maintenance access, timing, and echo cancellation. NT1s may be built into other pieces of equipment or stand alone.

O

Octet -- Eight data bits.

Out-of-band signaling -- Signaling that is separated from the channel carrying the information and sent over an independent ("out of band") channel.

Overflow -- The process of dialing additional bandwidth to accommodate peak traffic loads, and reducing the total bandwidth during times of reduced traffic loads.

P

PAP -- Password Authentication Protocol. A security protocol that uses password protection to allow access to a network or host.

PBX -- See Private Branch Exchange.

Pipeline -- The name of an Ascend product family of network access equipment with integrated remote LAN access capabilities. Pipeline allows remotely located branch offices, telecommuters, or traveling computer users to access corporate backbone LAN resour ces.

PPP -- Point-to-Point Protocol. A protocol that allows single nodes to access a LAN backbone network constructed of leased lines and routers. Often used for dial-up remote LAN access.

PRI, ISDN PRI -- See Primary Rate Interface.

Primary Rate Interface An ISDN subscriber line, consisting of twenty-three 64 kbit/s B channels in North America (thirty 64 kbit/s channels elsewhere) and one 64 kbit/s D channel, used for signaling purposes.

Private Branch Exchange (PBX) -- A private switching system, usually serving an organization, such as a business or a government agency, and usually located on the customer's premises.

Private Network -- A network, usually operated by a single corporate entity, made up of dedicated lines leased from the carriers, and switching equipment located on the corporate premises.

PSDN. Public Switched Digital Network -- Term used to describe the set of digital dial-up services offered by carriers (IECs and LECs).

Public Network -- A network operated by the carriers (IECs and LECs) which includes network-based services and network-based switching.

Px64 -- Common reference to the CCITT standards (H.261 et. al.) which describe methods to allow for videoconferencing system interoperability.

R

Remote Access -- See Remote LAN Access.

Remote LAN Access -- The process of allowing branch offices, telecommuters, and traveling computer users to access the corporate LAN backbone over dedicated or dialed, digital or analog lines.

Remote Loopback -- Loopback performed between an application and remotely located access equipment or application. The signal is sent from the application over the network to the remote access equipment or application, from where it is looped back to the o riginating equipment.

Router -- An interconnection device that can connect individual LANs. Unlike bridges, which logically connect at OSI layer 2, routers provide logical paths at OSI layer 3. Like bridges, remote sites can be connected using routers over dedicated or switched lines to create WANs.

Routing -- A device or setup that finds the best route between any two networks, even if there are several networks to traverse. (Contrast with bridge).

RPM -- Remote Port Module. See Multiband RPM.

RS-232 -- A set of EIA standards specifying various electrical and mechanical characteristics for interfaces between DTE and DCE data communications devices. The standard applies to both synchronous and asynchronous binary data transmission at rates below 64 kbit/s.

RS-366 -- An EIA standard for providing dialing commands to network access equipment. Uses RS-232 electrical specifications but different connector pinouts and signal functions.

RS-442 -- An EIA standard describing electrical characteristics for balanced-voltage digital interface circuits. Typically used for high-speed and synchronous data connections between DTE and DCE data communications devices.

RS-443 -- An EIA standard describing electrical characteristics for unbalanced-voltage digital interface circuits. Typically used for high-speed synchronous data connections between DTE and DCE data communications devices.

RS-449 -- An EIA standard for a 37-pin data communications connector, usually used with RS-422 or RS-423 electrical specifications.

Rubber Bandwidth -- A term used to describe a communications channel whose bandwidth can be increased or decreased without terminating and re-establishing the channel. Typically used with inverse multiplexing.

S

S interface -- n. See S/T interface.

S-interface -- adj. See S/T interface.

S/T interface -- n. The electrical interface between a network terminator (NT1) device and one or more ISDN communications devices that do not contain their own NT1s.

S/T-interface -- adj. Specifies an ISDN communications device that connects to an external network terminator (NT1).

SDSAF -- See Switched Digital Services Applications Forum.

SMDR -- Station Management Detail Recording. The ability of network access equipment to output call statistics and performance information for tabulation and analysis.

SMDS -- Switched Multimegabit Data Service. A packet-based network service allowing the creation of high-speed data networks (up to 45 Mbit/s). Now in the testing and initial implementation phases.

SNMP -- Simple Network Management Protocol. A protocol governing network management and monitoring of network devices and their functions. Originally developed in the TCP/IP environment.

SPID -- Service Profile Identifier. Your ISDN service provider (telephone company) uses this number at the Central Office switch to identify services on your ISDN line. This number is derived from a telephone number. See also Central Office and ISDN.

Straight-through cable -- A cable with wires that have terminating ends with the same wire assignments.

SW56 -- See Switched 56.

Switched 56 -- A dial-up network-based service providing a data channel operating at a rate of 56 kbit/s. Also a type of network access line, used to provide access to switched 56 network services.

Switched 64 -- A dial-up network-based service providing a data channel operating at a rate of 64 kbit/s.

Switched 384 -- A dial-up network-based service providing a data channel operating at a rate of 384 kbit/s.

Switched 1536 -- A dial-up network-based service providing a data channel operating at a rate of 1536 kbit/s.

Switched Digital Services Applications Forum (SDSAF) -- A consortium of equipment vendors, service vendors, and users, with the goal of advancing the state of switched digital services.

T

T1 -- A digital transmission link with a capacity of 1.544 Mbit/s, used in North America. Typically channelized into 24 DS0s, each capable of carrying a single voice conversation or data stream. Uses two pairs of twisted pair wires.

T3 -- A digital transmission link with a capacity of 45 Mbit/s, or 28 T1 lines.

Tariff -- Documents filed by a regulated telephone company with a state public utility commission or the Federal Communications Commission. Document details services, equipment, and pricing publicly offered by the telephone company.

TCP/IP -- Transmission Control Protocol/Internet Protocol. A set of protocols that link dissimilar computers across networks. TCP/IP is popular because you can connect computers and networking equipment to a variety of other systems and protocols.

10BaseT -- An IEEE standard (802.3) for operating 10 Mbps Ethernet networks with twisted-pair cabling and a wiring hub.

Telecommuter -- A work-at-home computer user who connects to the corporate LAN backbone using remote access technologies (i.e., using a modem over analog lines, ISDN TA over ISDN lines, or CSU/DSU over switched 56 lines).

TELNET -- Terminal-to-remote host protocol developed for ARPAnet. It is the TCP/IP protocol governing the exchange of character- oriented terminal data.

Thick Ethernet -- A term that describes a type of Ethernet cable. Thick Ethernet, or thicknet, is .4" diameter coaxial cable for Ethernet networks.

Thin Ethernet -- A term that describes a type of Ethernet cable. Thin Ethernet, or thinnet, is .2" diameter coaxial cable for Ethernet networks.

U

U interface -- n. The electrical interface between an ISDN telephone line and a network terminator (NT1) device.

U-interface -- adj. Specifies an ISDN communications device that connects directly to an ISDN telephone line. A U-interface device contains its own network terminator (NT1).

UTP cable -- Unshielded Twisted Pair cable. Two paired wires with wire twisted two or more times per inch to help cancel out noise.

V

V.25 bis -- An automatic calling and answering command set for use between DTE and DCE which includes both in-band and out-of-band signaling.

V.35 -- Commonly used to describe electrical characteristics and connector characteristics for a high speed synchronous interface between DTE and DCE. Originally V.35 described a 48 kbit/s group band modem interface with electrical characteristics defined in an appendix. Although V.35 is considered obsolete and no longer published by the CCITT, its legacy lives on in the data communications world in the form of the electrical characteristics originally described in the appendix.

Videoconferencing -- The use of digital video transmission systems to communicate between sites using video and voice. Digital video transmission systems typically consist of camera, codec (coder-decoder), network access equipment, network, and audio syste m.

VSU -- Video Service Unit. See Multiband VSU.

VT-100 -- An ASCII character data terminal, consisting of screen and keyboard. Manufactured by Digital Equipment Corporation (DEC), the VT-100 has become an industry standard data terminal. VT-100 emulation software allows a standard PC to act as a VT-100 terminal.

W

WAN -- See Wide Area Network

Wide Area Network. -- A data network typically extending a LAN outside a building or beyond a campus, over IXC or LEC lines to link to other LANs at remote sites. Typically created by using bridges or routers to connect geographically separated LANs.

X

X.21 -- A set of CCITT specifications for an interface between DTE and DCE for synchronous operation on public data networks. Includes connector, electrical, and dialing specifications.