AMI (Alternate Mark Inversion): A T1 line coding scheme that operates at 56 Kbps by reserving one bit out of eight as a control bit. AMI is an older standard, but is still used for transporting voice transmissions.
ATM (Asynchronous Transfer Mode): An international standard for high-speed transport over broadband packet switched networks. ATM is based upon all media (voice, video and data) being transformed into standardized-length (53-byte) cells. Transmission delays and errors are drastically reduced through the use of these fixed-length cells and the cell processing within the ATM hardware.
B8ZS (Bipolar Eight-Zero Substitution): A T1 line coding scheme, also known as Clear Channel, that operates at 64Kbps by sending a string of eight zeros with a deliberate bipolar violation which maintains line synchronization. Bandwidth: The relative range of frequencies that can be passed by a transmission medium without distortion. The greater the bandwidth, the greater the information-carrying capability of the transmission medium. Bandwidth, which is measured in Hertz, may also be expressed as the number of bits that can be transmitted per second.
CAP (Competitive Access Provider): A for-profit company that offers local access, transport and switching services in competition with similar services of the local telephone company.
Channel Bank: An interface device that multiplexes multiple channels onto an analog or digital carrier.
CIR (Committed Information Rate): The rate at which a Frame Relay network agrees to transfer information over a specific PVC. Measured in bits per second.
Circuit: A communications link between two or more points.
CLEC (Competitive Local Exchange Carrier): A common carrier that delivers local switched services to end-users in competition with a RBOC.
Clocking: See Synchronization.
CO (Central Office): A local telephone company office to where all local loops in a specific area terminate and in which circuit switching of subscriber lines occurs.
Common Carrier: A licensed, private utility company that provides communications services to the public at government-regulated rates.
CPE (Customer Premises Equipment): Any piece of telecommunications service terminating equipment, such as routers, CSU/DSUs, or phones, installed at a customer site.
CSU (Channel Service Unit): A digital interface device that directly connects end-user equipment to the local digital telephone loop. Often combined with a Data Service Unit to make CSU/DSU.
Demarc: Abbreviation for Demarcation Point, it is the terminating point on a customer premise where the LEC's responsibility for service ends and the customer's begins.
DS-0 (Digital Signal Level 0): A framing specification used in transmitting digital signals over a single channel of a T-1 facility at 64 Kbps.
DS-1 (Digital Signal Level 1): A framing specification used in transmitting digital signals at 1.544 Mbps over a T-1 facility (U.S.) or at 2.108 Mbps over an E-1 (Europe).
DS-3 (Digital Signal Level 3): A framing specification used in transmitting digital signals at 44.736 Mbps over a T-3 facility.
DSU (Data Service Unit): A digital interface device that converts the physical interface on any data terminal equipment to the digital transmission signal. Often combined with a Channel Service Unit to make CSU/DSU.
DSX-1 (Digital Signal Cross-connect, Level 1): A cross-connection point for DS-1 signals.
DWDM (Dense Wave Division Multiplexing): A method of multiplying the capacity of an optical fiber by simultaneously operating at more than one wavelength.
E1: The European standard equivalent of a DS-1 with the capacity to transmit information at speeds of up to 2.048 Mbps.
E3: The European standard equivalent of a DS-3 with the capacity to transmit information at speeds of up to 34.364 Mbps.
ESF (Extended Superframe Format): T-1 carrier framing format that provides 64kb clear channel capability, error checking, 16-state signaling, and other data transmission features.
Ethernet: A proprietary contention bus network, or LAN protocol, developed by Xerox, Digital Equipment Corporation and Intel that connects devices such as printers, computers and terminals.
Fast Ethernet: Based upon an extension to the IEEE 802.3 specification for Ethernet, which offers speeds ten times that of 10BaseT Ethernet.
FCC (Federal Communications Commission): The regulatory agency established in the United States for all interstate radio and electronic communications.
FDM (Frequency Division Multiplexing): The subdivision of a transmission circuit into two or more separate circuits by splitting the frequency range of the circuit into narrow frequency bands.
Firewall: A system or group of systems that enforces an access control policy between an organization's network and the Internet for purposes of security.
FRAD (Frame Relay Access Device): A concentration and network access device, usually a router, which provides protocol conversion into the frame relay format.
Frame Relay: A connection-oriented data communications service that transports frames of information across a network to one or more points.
FT-1 (Fractional T-1): The transmission of a fraction of a DS-1 facility based in 64Kbps increments but not less than 64Kbps total.
Gbps (Gigabits per second): A unit of data transmission speed measured in billions of bits per second.
Inter-LATA: A description of data or voice traffic that originates in one LATA and terminates in a different LATA.
Internet: A worldwide connectionless digital internetwork, which provides users with access to a vast number of databases, information sources and pornography.
Intra-LATA: A description of data or voice traffic that originates and terminates in the same LATA.
IP (Internet Protocol): Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and sercurity.
ISP (Internet Service Provider): Commercial organization that provides Internet access to individuals and organizations; for example, America Online and UUNet.
IXC (Inter-Exchange Carrier): A long-distance telephone company offering circuit-switched, leased-line, or packet switched service or some combination of these.
Kbps (Kilobits per second): A unit of data transmission speed measured in thousands of bits per second.
LAN (Local Area Network): A private data communications network linking various computing resources such as PCs, printers and servers within a relatively small geographic area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model.
LATA (Local Access and Transport Area): The geographic boundaries within which LECs are permitted to offer their services and handle call delivery.
Leased Line: A private line, leased from a common carrier, between two or more points.
LEC (Local Exchange Carrier): A common carrier that delivers local switched services to end-users.
Local Loop: A circuit between a LEC's central office and the customer's premise.
Mbps (Megabits per second): A unit of data transmission speed measured in millions of bits per second.
Multiplexing: The process of combining multiple signals into a single channel.
Network: A group of nodes interconnected by communication channels.
NPA (Numbering Plan Area): In the North American numbering system, the first three digits in the 10-digit addressing scheme also known as the area code.
NXX: In the North American numbering system, the second three digits in the 10-digit addressing scheme also known as the prefix or central office code.
OC (Optical Carrier): A dedicated fiber-based, point-to-point SONET service that can transport voice, video, or data between two sites at very high speeds.
POP (Point of Presence): The physical point at which a LEC interfaces with its customer or the physical point at which an IXC interconnects with the LEC.
PSTN (Public Switched Telephone Network): A generic term for the interconnected networks of operating telephone companies.
PVC (Permanent Virtual Circuit): A permanent logical connection established for a customer in a frame relay network connecting two points.
QoS (Quality of Service): A measure of performance for a transmission system that reflects its transmission quality and availability of service.
RBOC (Regional Bell Operating Company): One of the original seven LECs created from the break-up of AT&T in 1983. The seven were; Ameritech, NYNEX, Bell Atlantic, US West, Southwestern Bell, Bell South and Pac Tel.
Router: An active device linking two segments of a LAN or WAN through their physical, data link and network layers.
Smart Jack: A connector device that is installed by the LEC at the Demarc which provides the customer with the physical connection to their DS-1 service and provides the LEC the ability to perform diagnostic testing on the circuit.
SNA (Systems Network Architecture): An IBM data communications architecture that includes structure, formats, protocols and operating sequences.
SONET (Synchronous Optical NETwork): A fiber optic, dedicated transport service that allows high volumes of information to be transmitted between multiple sites in either a point-to-point configuration, OC-N Service, or between customer's locations and central offices creating a wide area network, Dedicated Ring Service.
Synchronization: A network function that keeps transmission interfaces and customer premise equipment in step with one another to prevent the loss of the signal. Channel Synchronization is created by the CSU/DSU at each end of the circuit. Network Synchronization is created by digital communications links within the service provider's network.
T1: An AT&T term for a digital carrier facility used to transmit a DS-1 formatted digital signal at 1.544 megabits per second.
T3: An AT&T term for a digital carrier facility used to transmit a DS-3 formatted digital signal at 44.736 megabits per second.
TCP/IP (Transmission Control Protocol over Internet Protocol): The combination of a network and transport protocol developed by ARPANET for internetworking IP-based networks like the Internet.
TDM (Time Division Multiplexing): The subdivision of a transmission circuit into two or more separate circuits by assigning a given circuit successively to several different users at different times.
Token Ring: A LAN protocol of allocating network access in which a terminal can send traffic only after it has acquired the network's token.
VPN (Virtual Private Network): Connection that has the appearance and many of the advantages of a dedicated link but occurs over a shared network.
WAN (Wide Area Network): A network that operates over a large geographic territory and commonly uses carrier facilities and services to connect customer locations.
WWW (World Wide Web): A distributed hypertext-based information system conceived at CERN to provide its user community an easy way to access global information.