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Characteristic of a transmission technology that affords greater bandwidth in one direction than in the other directions

asymmetrical DSL

A variation of DSL that offers more throughput when data travels downstream, than when it travels upstream


a communications method in which nodes do not have to conform to any predetermined schemes that specify the timing of data transmissions

Asynchronous Transfer Mode

A data link layer technology originally conceived in the early 1980s at Bell Labs and standardized by the ITU in the mid-1990s. Relies on fixed packets, that consist of 48 bytes of data plus a 5 byte header


The server compares credentials with those in its database

B channel

the "bearer" channel, employing circuit-switching techniques to carry voice, video, audio, and other types of data over the ISDN connection

Basic rate interface

uses two B channels and one D channel


the process of combining more than one bearer channel of an ISDN line to increase throughput

broadband cable

A method of connecting to the Internet over a cable network

bus topology WAN

A WAN in which each site is directly connected to no more than two other sites in a serial fashion

cable drop

The fiber-optic or coaxial cable that connects a neighborhood cable node to a customer's house

cable modem

a device that modulates and demodulates signals for transmission and reception via cable wiring


A packet of a fixed size

central office

the place where a telephone company terminates lines and switches calls between different locations

Channel service unit

a device that provides termination for the digital signal and ensures connection integrity through error correction and line monitoring

Channel service unit/Data Service unit

the connection point for a T1 line at the customers site

committed information rate

A minimum amount of bandwidth that the service provider guarantees


a user name and password

D channel

the "data" channel, employing packet-switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, and call forwarding, and conference calling signals

Data Service unit

a device that converts the T-carrier frames into frames the LAN can interpret and vice versa

dedicated lines

continuously available communications channels from a telecommunications provider, such as a local telephone company or ISP

dial up

connection in which a user connects her computer, via a modem, to a distant network and stays connected for a finite period of time

Dial up networking

The process of dialing into a remote access server to connect with a network

digital signal, level 0

equivalent of one data or voice channel

digital subscriber line

A dedicated WAN technology that uses advanced data modulation techniques at the Physical Layer to achieve extraordinary throughput over regular phone lines


refers to data traveling from the carrier's switching facility to the customer

DSL access multiplexer

a device that aggregates multiple DSL subscriber lines and connects them to the carriers CO

DSL modem

a device that demodulates incoming DSL signal, extracting the information and passing it to the data equipment and modulates outgoing DSL signals


A digital carrier standard used in Europe that offers 30 channels and a maximum of 2.048 Mbps


A digital carrier standard used in Europe that offers 480 channels and a maximum of 34.368 Mbps

fiber to the home

a carriers provision of fiber-optic connections to residential end users for dramatically increased throughput and a better range of services

fractional T1

allows organizations to use only some of the channels on a T1 line and be charged according to the number of channels they use

frame relay

An updated, digital version of X.25 that also relies on packet switching

full mesh WAN

The type of mesh topology in which every WAN site is directly connected to every other site

head end

a cable company's central office, which connects cable wiring to many nodes before it reaches customer sites

hybrid fiber-coax

a link that consists of fiber cable connecting the cable company's offices to a node location near the customer and coaxial cable connecting the node to the customer's house

Independent Computing Architecture client

The software from Citrix Systems INC, that when installed on a client, enables the client to connect with a host computer and exchange keystrokes, mouse clicks, and screen updates.

Integrated Services Digital Network

an international standard, originally established by the ITU in 1984, for transmitting digital data over the PSTN


A digital carrier standard used in Japan that offers 24 channels and 1.544 Mbps


A digital carrier standard used in Japan that offers 480 channels and 32.064 Mbps

Layer 2 Tunneling Protocol

A protocol that encapsulates PPP data, for use on VPNs.

LAN Emulation

encapsulates incoming Ethernet or token ring frames, then converts them into ATM cells for transmission over an ATM network

local loop

the portion of the PSTN that connects any residence or business to the nearest CO

mesh topology WAN

every site is interconnected, data can travel directly from its origin to its destination

network interface unit

the point at which PSTN-owned lines terminate at a customers premises

network service providers

A carrier that provides long-distance connectivity between major data-switching centers across the Internet

Network Termination 1

device that connects the twisted pair wiring at the customer's building with the ISDN terminal equipment via RJ-11 or RJ-45

Network Termination 2

an additional connection device required on PRI To handle the multiple ISDN lines between the customer's network termination connection and the local phone company's wires

open source

the term for software that is developed and packaged by individuals and made available to anyone for free

Optical Carrier

a rating that is internationally recognized by networking professionals and standards organizations

partial mesh WAN

type of mesh topology in which only critical WAN sites are directly interconnected and secondary sites are connected through star or ring topologies

permanent virtual circuits

a point to point connection over which data may follow any number of different paths, as opposed to a dedicated line that follows a predifned path

plain old telephone service

another name for Public switched telephone network

Point to Point protocol

a communications protocol that enables a workstation to connect to a server using a serial connection

PPP over Ethernet

PPP running over an Ethernet network

Primary Rate Interface

uses 23 B channels and one 64-Kbps D channel

Public Switched Telephone Network

the network of lines and carrier equipment that provides telephone service to most homes and businesses

Remote Access Service

The dial-up networking software provided with Microsoft Windows client operating sytems.

Remote Access

a method for connecting and logging on to a LAN from a workstation that is remote, or not physically connected, to the LAN

Remote Desktop

a feature of Windows operating systems that allows a computer to act as a remote host and be controlled from a client running another Windows OS

Remote Desktop Protocol

an Application layer protocol that uses TCP/IP to transmit graphics and text quickly

ring topology WAN

each site is connected to two other sites so that the entire WAN forms a ring pattern

Routing and Remote Access Service

Microsofts software that enables a server to act as a router, firewall, and remote access server


A characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed

Serial Line Internet Protocol

A communications protocol that enables a workstation to connect to a server using a serial connection

signal level

An ANSI standard for T-carrier technology that refers to its Physical layer electrical signaling characteristics

smart jack

A termination for T-carrier wire pairs that is located at the customer demark and which functions as a connection protection and a monitoring point

star topology WAN

A single site acts as the central connection point for several other points

switched virtual circuits

a logical, point to point connection that relies on switches to determine the optimal path between sender and receiver


provides equal capacity for data traveling both upstream and downstream

symmetrical DSL

a variation of DSL that provides equal throughput both upstream and downstream between the customer and the carrier

Synchronous Digital Hierarchy

the international equivalent of SONET

Synchronous optical network

a high-bandwidth WAN signaling technique developed by Bell Communications Research in 1980s, and later standardized by ANSI and ITU. It specifies framing and multiplexing techniques at the physical layer.


data being transmitted and received by nodes must conform to a timing scheme.


carry the equivalent of 24 voice or data channels, giving a maximum data throughput of 1.544 Mbps


carry the equivalent of 672 voice or data channels, giving a maximum data throughput of 44.736 Mbps


the term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s

terminal adapter

device that converts digital signals into analog signals for use with ISDN phones and other analog devices

terminal equipment

the end nodes served by the same connection

tiered topology WAN

sites connected in star or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings


a secured, virtual connection between two nodes on a VPN


the process of encapsulating one type of protocol in another


refers to data traveling from the customer to the carrier's switching facility

Virtual circuits

connections between network nodes that, although based on potentially disparate physical links, logically appear to be direct, dedicated links between those nodes

virtual network computing

an open source system designed to allows one workstation to remotely manipulate and receive screen updates from another workstation

virtual private networks

a logically constructed WAN that uses existing public transmission systems

WAN link

a point to point connection between two nodes on a WAN


an analog, packet-switched technology designed for long-distance data transmission and standardized by the ITU in the mid-1970s


the term used to refer to all varieties of DSL

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