Networking Glossary

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).

DECnet^TM

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.

End Node

A node such as a PC that can only send and receive information for its own use. It cannot route and forward information to another node.

Ethernet

The most popular LAN technology in use today. The IEEE standard 802.3 defines the rules for configuring an Ethernet network. It is a 10 Mbps, CSMA/CD baseband network that runs over thin coax, thick coax, twisted pair or fiber optic cable.

EtherTalk

Apple Computer's protocol for Ethernet transmissions.

FDDI

Fiberoptic Data Distribution Interface. A cable interface capable of transmitting data at 100 Mbps. Originally specified for fiber lines, FDDI can also operate over twisted-pair cable for short distances.

Fiber-Optic Cable

A transmission medium composed of a central glass optical fiber cable surrounded by cladding and an outer protective sheath. It transmits digital signals in the form of modulated light from a laser or LED (light-emitting diode).

File Server

A computer that stores data for network users and provides network access to that data.

Filtering

Process whereby an Ethernet switch or bridge reads the contents of a packet and then finds that the packet does not need to be forwarded, drops it. a filtering rate is the rate at which a device can receive packets and drop them without any loss of incoming packets or delay in processing.

Firmware

Alterable programs in semipermanent storage, e.g., some type of read-only or flash reprogrammable memory.

Forwarding

Process whereby an Ethernet switch or bridge reads the contents of a packet and then passes that packet on to the appropriate attached segment. A forwarding rate is the time that it takes the device to execute all of the steps.

Flash ROM

See ROM.

Framing

Dividing data for transmission into groups of bits, and adding a header and a check sequence to form a frame.

FTP

File Transfer Protocol, a TCP/IP protocol for file transfer.

Full-Duplex

Independent, simultaneous two-way transmission in both directions, as opposed to half-duplex transmission.

Gateway

A device for interconnecting two or more dissimilar networks. It can translate all protocol levels from the Physical layer up through the Applications layer of the OSI model, and can therefore interconnect entities that differ in all details.

Hardware Address

See Network Address.

Header

The initial part of a data packet or frame containing identifying information such as the source of the data, its destination, and length.

Heartbeat

Ethernet defined SQE signal quality test function.

Hertz (Hz)

A frequency unit equal to one cycle per second.

Host

Generally a node on a network that can be used interactively, i.e., logged into, like a computer.

Host Table

A list of TCP/IP hosts on the network along with their IP addresses.

IEEE 802.3

The IEEE (Institute of Electrical and Electronic Engineers) standard that defines the CSMA/CD media-access method and the physical and data link layer specifications of a local area network. Among others, it includes 10BASE2, 10BASE5, 10BASE-FL and 10BASE-T Ethernet implementations.

Internet

A series of interconnected local, regional, national and international networks, linked using TCP/IP. Internet links many government, university and research sites. It provides E-mail, remote login and file transfer services.

Internetworking

General term used to describe the industry composed of products and technologies used to link networks together.

IP Address

See Network Address.

IPX

Internetwork Packet eXchange, a NetWare protocol similar to IP (Internet Protocol).

ISDN

(Integrated Services Digital Network): All digital service provided by telephone companies. Provides 144K bps over a single phone line (divided in two 64K bps "B" channels and one 16K bps "D" channel).

ISO Layered Model

The International Standards Organization (ISO) sets standards for computers and communications. Its Open Systems Interconnection (OSI) reference model specifies how dissimilar computing devices such as Network Interface Cards (NICs), bridges and routers exchange data over a network. The model consists of seven layers. From lowest to highest, they are: Physical, Data Link, Network, Transport, Session, Presentation and Application. Each layer performs services for the layer above it.

Jabber

Network error caused by an interface card placing corrupted data on the network. Or, an error condition due to an Ethernet node transmitting longer packets than allowed.

Kbps

Kilobits per second.

Kermit

A popular file transfer and terminal emulation program.

LAN

Local Area Network, a data communications system consisting of a group of interconnected computers, sharing applications, data and peripherals. The geographical area is usually a building or group of buildings.

LAT

Local Area Transport, a Digital Equipment Corporation proprietary network communication protocol. The protocol is based on the idea of a relatively small, known number of hosts on a local network sending small network packets at regular intervals. LAT will not work on a wide area network scale, as TCP/IP does.

Latency

The delay incurred by a switching or bridging device between receiving the frame and forwarding the frame.

Layer

In networks, layers refer to software protocol levels comprising the architecture, with each layer performing functions for the layers above it.

Line Speed

Expressed in bps, the maximum rate at which data can reliably be transmitted over a line using given hardware.

Load Balancing

Shifting a user job from a more heavily loaded resource to a less loaded resource.

Local Network Interconnect (LNI)

A Port Multiplier, or concentrator supporting multiple active devices