AppleTalk
 
A communications protocol developed by Apple Computer to allow networking between Macintoshes. All Macintosh computers have a LocalTalk port, running AppleTalk over a 230K bps serial line. AppleTalk also runs over Ethernet (EtherTalk) and Token Ring (TokenTalk) network media. 
 

Auto-Negotiate
 
Clause 28 of the IEEE 802.3u standard specifies a MAC sublayer for the identification of the speed and duplex mode of connection being supported by a device. Support of this feature is optional for individual vendors. 
 

Auto-sense
 
Ability of a 10/100 Ethernet device to interpret the speed or duplex mode of the attached device and to adjust to that rate. Official term is Auto-Negotiation in Clause 28 of the IEEE 802.3u standard. 
 

AUI
 
Attachment Unit Interface. A 15-pin shielded, twisted pair Ethernet cable used (optionally) to connect between network devices and a MAU. 
 

Autobaud
 
Automatic determination and matching of transmission speed. 
 

AWG
 
American Wire Gauge. A system that specifies wire size. The gauge varies inversely with the wire diameter size. 
 

Backbone
 
The main cable in a network. 
 

Bandwidth on Demand
 
Feature that allows a remote access device to initiate a second connection to a particular site to increase the amount of data transferred to that site to increase the desired threshold. The network manager configuring the remote access server will specify a number of bits or a percentage of connection bandwidth threshold which will trigger the secondary connection. Multilink PPP is an emerging standard to allow this feature to be interoperable, but right now the only way to ensure correct operation is to use devices on both end from the same vendor. 
 

Baseband LAN
 
A LAN that uses a single carrier frequency over a single channel. Ethernet, Token Ring and Arcnet LANs use baseband transmission. 
 

Baud
 
Unit of signal frequency in signals per second. Not synonymous with bits per second since signals can represent more than one bit. Baud equals bits per second only when the signal represents a single bit. 
 

Binaries
 
Binary, machine readable forms of programs that have been compiled or assembled. As opposed to Source language forms of programs. 
 

Binary
 
Characteristic of having only two states, such as current on and current off. The binary number system uses only ones and zeros. 
 

Bitronics 
 
Specification for parallel printing which allows bidirectional communication on a Centronics-type interface. Pioneered by Hewlett-Packard, mainly used for postscript printers. 
 

Bit
 
The smallest unit of data processing information. A bit (or binary digit) assumes the value of either 1 or 0. 
 

BNC 

A standardized connector used with Thinnet and coaxial cable. 
 

BOOTP
 
A TCP/IP network protocol that lets network nodes request configuration information from a BOOTP "server" node. 
 

bps
 
Bits per second, units of transmission speed. 
 

Bridge
 
A networking device that connects two LANs and forwards or filters data packets between them, based on their destination addresses. Bridges operate at the data link level (or MAC-layer) of the OSI reference model, and are transparent to protocols and to higher level devices like routers. 
 

Broadband
 
A data transmission technique allowing multiple high-speed signals to share the bandwidth of a single cable via frequency division multiplexing. 
 

Broadband Network
 
A network that uses multiple carrier frequencies to transmit multiplexed signals on a single cable. Several networks may coexist on a single cable without interfering with one another.

 
Brouter
 
A device that routes specific protocols, such as TCP/IP and IPX, and bridges other protocols, thereby combining the functions of both routers and bridges. 
 

Bus
 
A LAN topology in which all the nodes are connected to a single cable. All nodes are considered equal and receive all transmissions on the medium.

 
Byte
 
A data unit of eight bits. 
 

Channel 

The data path between two nodes.

 
CHAP
 
(Challenge Handshake Authentication Protocol) Authentication scheme for PPP where the password not only is required to begin connection but also is required during the connection - failure to provide correct password during either login or challenge mode will result in disconnect. 
 

Coaxial Cable
 
An electrical cable with a solid wire conductor at its center surrounded by insulating materials and an outer metal screen conductor with an axis of curvature coinciding with the inner conductor - hence "coaxial." Examples are standard Ethernet cable and Thinwire Ethernet cable.

 
Collision
 
The result of two network nodes transmitting on the same channel at the same time. The transmitted data is not usable. 
 

Collision Detect
 
A signal indicating that one or more stations are contending with the local station's transmission. The signal is sent by the Physical layer to the Data Link layer on an Ethernet/IEEE 802.3 node. 
 

Communication Server
 
A dedicated, standalone system that manages communications activities for other computers. 
 

Console
 
The terminal used to configure network devices at boot (start-up) time. 
 

Crosstalk
 
Noise passed between communications cables or device elements.

 
Cut-through
 
Technique for examining incoming packets whereby an Ethernet switch looks only at the first few bytes of a packet before forwarding or filtering it. This process is faster than looking at the whole packet, but it also allows some bad packets to be forwarded. 
 

CSMA/CD
 
Carrier Sense Multiple Access with Collision Detection is the Ethernet media access method. All network devices contend equally for access to transmit. If a device detects another device's signal while it is transmitting, it aborts transmission and retries after a brief pause. 
 

Data Link
 
A logical connection between two nodes on the same circuit.

 
Data Link Layer
 
Layer 2 of the seven-layer OSI reference model for communication between computers on networks. This layer defines protocols for data packets and how they are transmitted to and from each network device. It is a medium-independent, link-level communications facility on top of the Physical layer, and is divided into two sublayers: medium-access control (MAC) and logical-link control (LLC). 
 

DECnetTM
 
Digital Equipment Corporation (DEC) proprietary network architecture, a system for networking computers. It runs on point-to-point, X.25 and Ethernet networks.

 
Dial on Demand
 
When a router detects the need to initiate a dial-up connection to a remote network, it does so automatically according to pre-defined parameters set by the network manager. 
 

Dialback
 
A security feature that ensures people do not log into modems that they shouldn't have access to. When a connection is requested, the system checks the user name for validity, then "dials back" the number associated with that user name. 
 

Distributed Processing
 
A system in which each computer or node in the network performs its own processing and manages some of its data while the network facilitates communications between the nodes. 
 

Domain Name
 
A domain name is a text name appended to a host name to form a unique host name across internets. 
 

Download
 
The transfer of a file or information from one network node to another. Generally refers to transferring a file from a "big" node, such as a computer, to a "small" node, such as a terminal server or printer.