ADSL Technology Glossary

A packet delivery system in which a copy of a packet is given to all hosts attached to the network. Example: Ethernet.

See CAP.

Cisco Broadband Operating System. An operating system that users access to configure and operate Cisco products.

See CBOS.

See CCO.

Common Language Equipment Identifier.

A common way to describe network services and the user processes (programs) of those services. Examples include the name-server/name-resolver paradigm of the DNS and file-serve/file-client relationships such as NFS and diskless hosts.

Common Language Location Identifier.

Central office. A local telephone office where all local loops in an area connect and where switching of subscriber lines occurs.

See CLEI.

See CLLI.

The transport of a single datagram or packet of information from one network node to a destination node or multiple nodes without the establishing of a network connection.

The transport of packets of information from one network node to a destination node once a network connection is established.

Customer premises equipment. Terminating equipment, such as terminals, telephones, and modems, supplied by the telephone company. The equipment is installed at customer sites and connected to the telephone company network.

See CPE.

Lets computer users dial up a service provider's computer using a modem.

See DOH.

See DS3.

See DMT.

An approach that allows one application program to execute on multiple computers linked together by a network. The networked computers share the work between them.

Discrete Multi-Tone.

Discrete Multi-Tone Issue 2. Actually ANSI T1.413 specification.

Digital Off-Hook. A technology for enabling ADSL connections to be established when needed (dialed up). When connections are not established, the central office ADSL modem resources are made available to other CPE.

The line rate for return messages or data transfers from the network machine to the user's customer premises machine.

Dynamic random-access memory. A type of semiconductor memory in which the information is stored in capacitors on a metal oxide semiconductor integrated circuit.

Digital signal level 3. Framing specification used for transmitting digital signals at 44.736 Mbps on a T3 facility.

Digital subscriber line access multiplexer. Concentrates and multiplexes digital subscriber line signals at the telephone service provider location and transmits them to the broadband wide area network. Replaces ADSLAM.

See DRAM.

Electronic Industries Association. A standards group made up of electronics industry organizations. EIA is responsible for the RS-232C and RS-422 standards.

See EIA.

The technique used by layered protocols in which a layer adds header information to the protocol data unit (PDU) from the layer above.

A physical or logical system component that is represented in the Cisco 6100 SNMP agent.

A process used during file transfer to discover discrepancies between transmitted and received data. Some file transfer programs only detect errors; others detect errors and attempt to fix them (called error correction).

One of the most common local-area network (LAN) wiring schemes, Ethernet has a transmission rate of 10 Mbps; a newer standard called Fast Ethernet carries 100 Mbps.

A European standards body established in 1988 by a decision of the European Conference of Postal and Telecommunications Administrations (CEPT).

Federal Communications Commission. A U.S. government agency that regulates interstate and foreign communications. The FCC sets rates for communication services, determines standards for equipment, and controls broadcast licensing.

A method for protecting Internet-connected enterprise networks from break-ins by unauthorized persons outside the network.

A packet as it is transmitted over a serial line. The term derives from character oriented protocols where special start-of-frame and end-of-frame characters are added when packets are transmitted.

A system that performs translation from one native format to another. Examples include X.400 to/from RFC 822 electronic mail gateways. See router.

Part of the procedure to set up a data communications link. The handshake can be part of the protocol itself or an introductory process. The computers that are to talk to each other set out the conditions under which they can operate. Sometimes the handshake is just a warning that a communication is imminent.

High-Level Data Link Control. A bit-oriented, synchronous, link layer, data-framing, flow control, and error detection and correction protocol. Available subsets include

• 802.2 (logical link control for FDDI, Token Ring, and some Ethernet LANs)

• LAP (link access procedure balanced for X.25)

• LAPD (link access procedure for the ISDN D channel and frame relay)

• LAPM (link access procedure for modems specified as part of V.42)

See HDLC.

A measure of distance between two points on the Internet. It is equivalent to the number of gateways that separate the source and destination.

Internet Control Message Protocol. The protocol used to handle errors and control messages at the IP layer.

Institute of Electrical and Electronics Engineers. A U.S. publishing and standards organization responsible for many LAN standards.

See IEEE.

See ITU-T.

A collection of networks interconnected by a set of routers that allow them to function as a single, large virtual network.

An IP address assigned in blocks of numbers to user organizations accessing the Internet. The United States Department of Defense's Network Information Center (NIC) establishes these addresses. Duplicate addresses can cause major problems on the network, but the NIC trusts organizations to use individual addresses responsibly. Each address is a 32-bit address in the form of x.x.x.x where x is an eight- bit number from 0 to 255.

See ICMP.

See IP.

See ISP.

Internet Protocol. The network layer protocol for the Internet Protocol suite.

The 32-bit address assigned to hosts that want to participate in a TCP/IP Internet.

The fundamental unit of information passed across the Internet. It contains source and destination addresses, along with data and a number of fields that define such things as the length of the datagram, the header checksum, and flags to say whether the datagram can be or has been fragmented.

Internet service provider. A company that allows home and corporate users to connect to the Internet.

International Telecommunication Union Telecommunication Standardization Sector. ITU-T is the telecommunication standardization sector of ITU and is responsible for making technical recommendations about telephone and data (including fax) communications systems for service providers and suppliers.

Local-area network. A limited distance (typically under a few kilometers or a couple of miles) high-speed network (typically 4 to 100 Mbps) that supports many computers (typically two to thousands).

Line interface module. Provides concentration services for ADSL port.

See LCM.

A function performed by a type of multiplexer that combines multiple channels onto a single transmission medium in such a way that all the individual channels can be simultaneously active.

See LIM.

The speed by which data is transferred over a particular line type, expressed in bits per second (bps).

See LAN.

A logical entry to a server machine. Logical ports are mostly invisible to the user, though you may occasionally see a URL with a port number included in it. These ports do not refer to physical locations; they are set up by server administrators for network trafficking.

A diagnostic test that returns the transmitted signal to the sending device after it has passed through a network or across a particular link. The returned signal can then be compared to the transmitted one. The discrepancies between the two are used to trace the fault. When you are trying to locate a faulty piece of equipment, repeat loopbacks are used, eliminating satisfactory machines until the problem is found.

See MIB.

Multiplexer chassis.

Management Information Base. A collection of objects that can be accessed by a network management protocol, such as SNMP or CMIP (Common Management Information Protocol).

A printed circuit board that occupies a slot in a chassis.

See MMF.

A special form of broadcast in which copies of the packet are delivered to only a subset of all possible destinations. See broadcast.

A device that can combine several signals and send them over a single line. The signals are then separated by a similar device at the other end of the link. This can be done in a variety of ways (for example, time division multiplexing, frequency division multiplexing, and statistical multiplexing). Multiplexers are also becoming increasingly efficient in terms of data compression, error correction, transmission speed, and multi-drop capabilities.

A general term used to refer to a computer or related device; often used to refer to a networked computer or device.

The amount of noise tolerated by the ATU-C and ATU-R during training.

Optical Carrier Level 3. Physical protocol, defined for SONET optical signal transmissions.

A networking term that identifies eight bits. In TCP/IP, it is used instead of byte, because some systems have bytes that are not eight bits.

See OSI.

See OC-3.

Open System Interconnection. An international standardization program to facilitate communications among computers from different manufacturers. See ISO.

The unit of data sent across a packet-switching network.

Peripheral Component Interconnect. An industry local bus standard. Supports up to 16 physical slots but is electrically limited to typically three or four plug-in PCI cards in a PC. Has a typical sustained burst transfer rate of 80 Mbps---enough to handle 24-bit color at 30 frames per second (full-color, full-motion video).

See PCI.

See PVC.

Handles transmission of raw bits over a communication channel. The physical layer deals with mechanical, electrical, and procedural interfaces.

A physical grouping of chassis slots within the MC or LCC.

See POTS.

See PPP.

The abstraction used by Internet transport protocols to distinguish among multiple simultaneous connections to a single destination host. A single termination point on one of the multiport modules (POTS, LIM, or ATU-C).

Plain old telephone service.

See PSC.

A formal description of messages to be exchanged and rules to be followed for two or more systems to exchange information.

Permanent virtual circuit. A fixed virtual circuit between two users: the public data network equivalent of a leased line. No call setup or clearing procedures are needed.

Quality of service, a characteristic of data transmission that measures how accurately and how quickly a message or data is transferred from a source computer to a destination computer over a network.

See QoS.

Release Definition file. The file that contains all of the image information and part number information for a particular Cisco 6100 series release. This file is required for software downloads.

See RDF.

The IP address of a remote server.

See RADIUS.

A network computer that allows a user to log on to the network from a distant location.

See RFC.

Request For Comments. The document series, begun in 1969, which describes the Internet suite of protocols and related experiments. Not all RFCs describe Internet standards, but all Internet standards are written up as RFCs.

The path that network traffic takes from its source to its destination. The route a datagram may follow can include many gateways and many physical networks. In the Internet, each datagram is routed separately.

Information stored within a router pertaining to network path and status. The routing table is used to select the most appropriate route for information forwarding.

An EIA standard that specifies the most common way of linking data devices together.

A method of data transmission in which bits of data characters are sent sequentially over a single channel.

See SNR.

Single in-line memory module. A small circuit board or substrate, typically about 10 cm x 2 cm, with RAM integrated circuits or die on one or both sides and a single row of pins along one long edge.

See SNMP.

See SIMM.

A numbered location within a chassis capable of housing a module.

Signal-to-noise ratio. The usable signal being transmitted divided by the noise or undesired signal.

SDSL transmission unit---central office.

See address mask.

A logical entity with attributes identifying the customer that is receiving service on a particular LIM port.

Switched virtual circuit. A temporary virtual circuit between two users.

Equipment used to connect and distribute communications between a trunk line or backbone and individual nodes.

See SVC.

See SDSL.

A form of communication in which data is not sent in individual bytes, but as frames of large data blocks.

Transmission Control Protocol. The major transport protocol in the Internet suite of protocols. It provides reliable, connection-oriented, full-duplex streams.

The virtual terminal protocol in the Internet suite of protocols. It allows users of one host to log in to a remote host and act as normal terminal users of that host.

Trivial File Transfer Protocol. A simple file transfer protocol (a simplified version of FTP) that is often used to boot diskless workstations and other network devices such as routers over a network (typically a LAN). TFTP has no password security.

The procedure used by the ATU-C and ATU-R to establish an end-to-end ADSL connection.

See TCP.

See TFTP.

Two insulated copper wires twisted together with the twists or lays varied in length to reduce potential signal interference between the pairs.

User-Network Interface signaling for ATM communications.

The line rate for message or data transfer from the source machine to a destination machine on the network. See also downstream rate.

Virtual circuit. A logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). In ATM, a virtual circuit is called a virtual channel. Sometimes abbreviated VC.

Virtual channel connection. A logical circuit, made up of links, that carries data between two end points in an ATM network.

Virtual channel identifier. A 16-bit field in the header of an ATM cell. The VCI, together with the VPI, is used to identify the next destination of a cell as the cell moves through the network. Sometimes called virtual channel connection. See also VPI.

See VCC.

See VCI.

In ATM, a connection between end users that has a defined route and endpoints.

A logical grouping of virtual circuits that connect two sites.

See VPI.

See VPI and VCI.

Virtual path. One of two types of ATM circuits identified by a VPI. A virtual path is a bundle of virtual circuits, all of which are switched across a network based on a common VPI. See also VPI.

Virtual path identifier. An 8-bit field in the header of an ATM cell. The VPI, together with the VCI, is used to identify the next destination of a cell as it moves through the network. See also VCI.

Wide-area network. A data communications network that spans any distance and is usually provided by a public carrier (such as a telephone company or service provider).

See WAN.