Table of Contents




ITU-T electrical and mechanical specifications for connections between telephone company equipment and DTE using BNC connectors and operating at E1 data rates.


Describes the 64-kbps PCM voice coding technique. In G.711, encoded voice is already in the correct format for digital voice delivery in the PSTN or through PBXs. Described in the ITU-T standard in its G-series recommendations.


Describes a compression technique that can be used for compressing speech or audio signal components at a very low bit rate as part of the H.324 family of standards. This CODEC has two bit rates associated with it: 5.3 and 6.3 kbps. The higher bit rate is based on ML-MLQ technology and provides a somewhat higher quality of sound. The lower bit rate is based on CELP and provides system designers with additional flexibility. Described in the ITU-T standard in its G-series recommendations.


Describes ADPCM coding at 40, 32, 24, and 16 kbps. ADPCM-encoded voice can be interchanged between packet voice, PSTN, and PBX networks if the PBX networks are configured to support ADPCM. Described in the ITU-T standard in its G-series recommendations.


Describes a 16-kbps low-delay variation of CELP voice compression. CELP voice coding must be translated into a public telephony format for delivery to or through the PSTN. Described in the ITU-T standard in its G-series recommendations.


Describes CELP compression where voice is coded into 8-kbps streams. There are two variations of this standard (G.729 and G.729 Annex A) that differ mainly in computational complexity; both provide speech quality similar to 32-kbps ADPCM. Described in the ITU-T standard in its G-series recommendations.


ITU-T framing standard that defines the mapping of ATM cells into the physical medium.


1. Component of an H.323 conferencing system that performs call address resolution, admission control, and subnet bandwidth management.

2. Telecommunications: H.323 entity on a LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper can provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways. A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup and request admission to a call from the gatekeeper.


In the IP community, an older term referring to a routing device. Today, the term router is used to describe nodes that perform this function, and gateway refers to a special-purpose device that performs an application layer conversion of information from one protocol stack to another. Compare with router.

Gateway Discovery Protocol

See GDP in the "Cisco Systems Terms and Acronyms" section.

gateway host

In SNA, a host node that contains a gateway SSCP.

gateway NCP

NCP that connects two or more SNA networks and performs address translation to allow cross-network session traffic.

Gateway-to-Gateway Protocol

See GGP.


gigabyte. Approximately 1,000,000,000 bytes.


gigabytes per second.


gigabit. Approximately 1,000,000,000 bits.


gigabits per second.


generic connection admission control. In ATM, a PNNI algorithm designed for CBR and VBR connections. Any node can use GCAC to calculate the expected CAC behavior of another node given than node's advertised link metrics and the QoS of a connection setup request. See also CAC.


generic cell rate algorithm. In ATM, an algorithm that defines conformance with respect to the traffic contract of the connection. For each cell arrival, the GCRA determines whether the cell conforms to the traffic contract.


See GDP (Gateway Discovery Protocol) in the "Cisco Systems Terms and Acronyms" section.

generic connection admission control


generic routing encapsulation

See GRE in the "Cisco Systems Terms and Acronyms" section.

Get Nearest Server

See GNS.


Gateway-to-Gateway Protocol. MILNET protocol specifying how core routers (gateways) should exchange reachability and routing information. GGP uses a distributed shortest-path algorithm.




Abbreviated Gb.

gigabits per second

Abbreviated Gbps.


Abbreviated GB.

gigabytes per second

Abbreviated GBps.


Abbreviated GHz.


Global Internet eXchange. Common routing exchange point which allows pairs of networks to implement agreed-upon routing policies. The GIX is intended to allow maximum connectivity to the Internet for networks all over the world. See CIX, FIX, and MAE.


Process by which a router automatically derives AARP table entries from incoming packets. Gleaning speeds up the process of populating the AARP table. See also AARP.


Get Nearest Server. Request packet sent by a client on an IPX network to locate the nearest active server of a particular type. An IPX network client issues a GNS request to solicit either a direct response from a connected server or a response from a router that tells it where on the internetwork the service can be located. GNS is part of the IPX SAP. See also IPX and SAP (Service Advertisement Protocol).


Generally referring to the measurement of actual data successfully transmitted from the sender(s) to receiver(s). This is often a more useful measurement than the number of ATM cells per second throughput of an ATM switch if that switch is experiencing cell loss that results in many incomplete, and therefore unusable, frames arriving at the recipient.


distributed document delivery system. The Internet Gopher allows a neophyte user to access various types of data residing on multiple hosts in a seamless fashion.


Government OSI Profile. U.S. government procurement specification for OSI protocols. Through GOSIP, the government mandates that all federal agencies standardize on OSI and implement OSI-based systems as they become commercially available.

Government OSI Profile


grade of service

Measure of telephone service quality based on the probability that a call will encounter a busy signal during the busiest hours of the day.

graphical user interface

See GUI.


See GRE (generic routing encapsulation) in the "Cisco Systems Terms and Acronyms" section.

ground station

Collection of communications equipment designed to receive signals from (and usually transmit signals to) satellites. Also called a downlink station.

Group 3

Standard created by the International Telecommunications Union Telecommunications (ITU-T) relating to fax devices. A Group 3 fax device is a digital machine containing a 14400 baud modem that can transmit an 8 1/2 by 11 inch page in approximately 20 seconds with a resolution of either 203 by 98 dots per inch (dpi) or 203 by 196 dpi (fine), using Huffman code to compress fax data. Group 3 faxes use a standard dial-up telephone line for transmission.

group address

See multicast address.

group delay

See distortion delay.


Generic Service State.

guard band

Unused frequency band between two communications channels that provides separation of the channels to prevent mutual interference.


graphical user interface. User environment that uses pictorial as well as textual representations of the input and output of applications and the hierarchical or other data structure in which information is stored. Conventions such as buttons, icons, and windows are typical, and many actions are performed using a pointing device (such as a mouse). Microsoft Windows and the Apple Macintosh are prominent examples of platforms using a GUI.

Posted: Tue Sep 21 15:27:31 PDT 1999
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