Data Communications and Computer Networks Chapter 11

Plain Old Telephone Service, POTS
The basic telephone system.
Local Loop
The telephone line that leaves your house or business; it consists of either four or eight wires.
Central Office
Contains the equipment that generates a dial tone, interprets the telephone number dialed, checks for special services, and connects the incoming call to the next point.
Local Access Transport Area, LATA
A geographic area, such as a large metropolitan area or part of a larger state. Telephone calls that remain within a LATA are usually considered local telephone calls, while telephone calls that travel from one LATA to another are considered long-distance telephone calls.
Trunk
A telephone connection used by telephone companies that carries multiple telephone signals, is usually digital and high speed, and is not associated with a particulare telephone number.
Modified Final Judgment
A court ruling in 1984 that required the divestiture, or breakup , of AT&T.
Local Exchange Carriers, LEC’s
The name given to local telephone companies after the division of AT&T in 1984.
Interexchange Carriers, IEC’s or IXc’s
The name given to long-distance telephone companies after the division of AT&T in 1984.
Centrex, Central Office Exchange Serivce
A service from local telephone companies through which up-to-date telephone facilities at the telephone company’s central or local office are offered to business users so that they do not need to purchase their own facilities.
Private Branch Exchange, PBX
A large computerized telephone switch that sits in a telephone room on the company property.
Private Lines
A leased telephone line that requires no dialing.
Telecommunications Act of 1996
A major event in the history of the telecommunications industry that, among other things, opened the door for business other than local telephone companies to offer a local telephone service.
Competitive Local Exchange Carriers, CLEC’s
A new provider of local telephone services.
Incumbent local Exchange Carriers, ILEC’s
A local telephone company that existed before the Telecommunications Act of 1996.
V.90 Standard
A 56,000 bps dial-up modem standard approved by a standards-making organization rather than a single company; it is slightly incompatible with both x2 and K 56flex.
V.92 Standard
An improvement of the V.90 standard that provides a higher upstream data transfer rate and also provides a call waiting service, in which the user’s data connection is put on hold when someone calls the user’s telephone number.
Digital Subscriber Line, DSL
A technology that allows existing twisted pair telephone lines to transmit multimedia materials and high-speed data.
Symmetric Connection
A type of connection in which the transfer speeds in both directions are equivalent.
Asymmetric Connection
A connection in which data flows in one direction at a faster transmission rate than the data flowing in the opposite direction.
Spliterless DSL
A form of digital subscriber line in which there is no POTS signal accompanying the DSL signal, thus there is no need for a splitter.
xDSL
The generic name for the many forms of digital subscriber line, DSL.
Asymmetric Digital Subscriber Line, ADSL
A popular form of digital subscriber line that transmits the downstream data at a faster rate than the upstream data.
DSL Lite
A form of consumer DSL that has lower transmission speeds and thus lower consumer costs.
Very High Data Rate DSL, VDSL
A form of digital subscriber line that is very fast, between 51 and 55 Mbps, over very short distances, less than 300 meters.
Rate-Adaptive DSL, RADSL
A form of digital subcriber line in which the transfer rate can vary depending on noise levels within the telephones line’s local loop.
Cable Modem
A communications device that allows high-speed access to wide area networks, such as the Internet, via a cable television connection.
Frame Relay
A commercially availabel packet-switched network that was designed for transmitting data over fixed lines as opposed to dial-up lines.
Permanent Virtual Circut, PVC
A fixed connection between end points in a frame relay network. Unlike a telephone circuit, which is a physical circuit, a PVC is created with software routing tables, thus making it a virtual circuit.
Layer 2 Protocol
A prototcol that operates at the second layer, or data link layer, of the OSI seven-layer model.
Committed Information Rate, CIR
The data transfer rate that is agreed on by both the customer and the carrier in a frame relay network.
Service Level Agreement, SLA
A legally binding writtendocument that can include service parameters offered in a service set up between a communications provider and its customer.
Burst Rate
A rate agreed upon between a customer and a frame relay provider; this agreement allows the customer to exceed the committed information rate by a fixed amount for brief moments of time.
Asynchronous Transfer Mode, ATM
A high-speed packet-switched serivce, simular to frame relay, that supports various classes of service.
Virtual Channel Connection, VCC
Used in Asynchronous Transfer Mode; a logical connection that is created over a virtual path connection.
Virtual Path Connection, VPC
Used in Asynchronous Transfer Mode to support a bundle of virtual channel connections, VCCs, that have the same endpoints.
User-Network Interface
The connection between a user and the network in Asychronous Transfer Mode, ATM.
Network-Network Interface
One type of connection in Asynchronous Transfer Mode; a network-network interface is created by a network and used to transfer management and routing signals.
Class of Service
A definition of a type of traffic and the underlying technology that will support that type of traffic.
Constant Bit Rate, CBR
Used in Asynchronous Transfer Mode; an expensive service that is similar to a current telephone system leased line.
Variable Bit Rate, VBR
A class of service offered by ATM that is similar to frame relay service. VBR is used for real-time applications, such as sending compressed interactive video, and non-real-time applications, such as sending e-mail with large, multimedia attachments.
Available Bit Rate
A class of service supported by Asynchronous Transfer Mode that is used for traffic that may experience bursts of data, called “bursty” traffice, and whose bandwidth range is roughly knon
Unspecified Bit Rate, UBR
A class of service offered by ATM that is capable of transmitting traffic that may experience bursts of data, but does not make any promise about when the data may be sent.
Computer-Telephony Integration, CTI
New telephone services and systems that combine more traditional voice networks with modern computer networks.
Unified Messaging
A telecommunication service that allows users to utilize a single desktop application to send and receive e-mail, voice mail, and fax.
Interactive Voice Response
A system that enables a company to use a customer’s telephone number to extract the customer’s records from a corporate database when that customer calls the company.
Integrated Voice Recognition and Response
A system in which a user callining into a company telelephone system provides some form of data by speaking into the telephone, and a database query is performed using this spoken information.
Fax Processing
A computer-telephony integration application in which a fax image that is stored on a LAN server’s hard disk can be downloaded over a local area network, converted by a fax card, and sent out to a customer over a trunk line.
Fax-Back
A computer-telephony integration application in which a user can dial in to a fax server, retrieve a fax by keying in a number, and send that fax anywhere.
Text-to-Speech and Speech-toText Connection
Telephone system that can digitized human speach and store it as a tex file, and take a text files and convert it to human speach.
Third-Party Call Control
A telephone feature that allows users to control a call, without being part of the call.
PBX Graphic User Interface
An interface in which different icons on a computer screen represent common PBX functions such as call hold, call tranfer, and call conferencing, making the system easier for operators to use.
Call Filtering
A technology in which users can specify which telephone numbers are allowed to get through. All other calls will be routed to an attendant or voice mailbox.
Customized Menuing Systems
A menu system that can be created and/or changed dynamically according to a user’s profile or needs.
Unified Communications
The convergence of multiple forms of communications such as messaging, telephony, and video confrencing into a comsumer-friendly, unified interface.