Glossary of Terms

asynchronous transfer mode (ATM) -- A type of switching technology in which the switches are small, fixed-length cells containing data.

backbone -- A segment of network that links several individual workgroup or department LANs together in a single building. It is also used to link several building LANs together in a campus environment.

bridges -- Devices that filter packets between LANs by making a simple forward/don’t forward decision on each packet they receive from any of the networks they are connected to.

bus topology -- The original coaxial cable-based LAN topology in which the medium forms a single bus to which all stations are attached. The bus topology is rarely used in LAN installations today because it is relatively difficult to add new users or more existing users from one location to another. It is also difficult to troubleshoot a bus-based LAN unless it is very small.

carrier sense multiple access with collision detection (CSMA/CD) -- An element defined by the IEEE 802.3 specification. ft is an access method that is used by stations connected to an Ethernet LAN. In this method, each station contends for access to the shared medium.

collision -- This occurs when two stations try to send packets at the same time. In Ethernet networks, collisions are considered normal events and the CSMA/CD access method is designed to quickly restore the network to normal activity after a collision occurs.

dedicated LAN -- Switch configurations in which a port supports a “dedicated” 10 Mbps Ethernet LAN connected to a single high-performance station such as a server, providing an uncontested 10 Mbps Ethernet link all to itself.

EMI -- Electromagnetic interference.

Ethernet -- The most widely used LAN technology, accounting for approximately 80 percent of all network connections. Standard Ethernet runs at 10 million bits per second (10 Mbps) and balances speed, price, ease of installation, and availability. The rules of Ethernet are defined by the IEEE 802.3 specification. The most popular form of Ethernet is 1OBASE-T.

Fast Ethernet -- An extension of 10 Mbps Ethernet, Fast Ethernet runs at 100 million bits per second (Mbps). The rules of Fast Ethernet are defined by the IEEE 802.3u specification. Because they use the same protocol, data can be moved between Ethernet and Fast Ethernet without protocol translation.

Fiber Distributed Data Interface (FDDI) -- LAN technology that runs at 100 Mbps, a much higher data rate than Ethernet or Token Ring. Originally, FDDI networks required fiber optic cable, but today they can also be run on UTP.

filtering -- Occurs when a data packet is examined on the network to determine its destination. By looking at a packet’s address, network hardware decides whether it should be retained in the local LAN or copied to another LAN. Filtering, which provides some control over internetwork traffic and security, is usually performed by bridges, switches, and routers.

header -- A message at the beginning of a data packet that carries special information used by the network to identify the destination station. It is similar to a trailer, which comes at the end of a packet.

IEEE 802.3 -- An Ethernet specification commonly defined by the Institute of Electrical and Electronics Engineers (IEEE). The 802.3 specification covers rules for configuring Ethernet LANs, the types of media that can be used, and how the elements of the network should interact.

IEEE 802.5 -- A Token Ring specification commonly defined by the Institute of Electrical and Electronics Engineers (IEEE). The 802.5 specification covers rules for configuring Token Ring LANs, the types of media that can be used, and how the elements of the network should interact.

intelligent hubs -- Wiring concentrators that can be monitored and managed by network operators.

interoperability -- The ability of software and hardware on multiple machines from multiple vendors to communicate.

interrepeater link -- One method of linking hubs. This type of connection simply repeats all of the packets from one hub to the other hub it is linked to, so that in effect the two hubs are part of the same LAN.

LAN internetwork -- Connecting disparate and geographically dispersed LANs together to form an enterprise system.

local area network (LAN) -- A high-speed communications system designed to link computers and other data processing devices together within a small geographic area such as a workgroup, department, or a single floor of a multistory building.

manageable hubs -- Another definition for intelligent hubs. Each of the ports on the managed hub can be configured, monitored, and enabled or disabled by a network operator from a hub management console.

modular hubs -- A hub that starts with a chassis, or card cage, with multiple card slots, each of which can accept a communications card, or module. Each module acts like a standalone hub; when the communications modules are placed in the card slots in the chassis, they connect to a high-speed communications backplane that links them together so that a station connected to a port on one module can easily communicate with a station on another module.

multistation access unit (MALT) -- A Token Ring wiring concentrator that connects each station in a Token Ring LAN.

network center -- A single, secure, fire-safe location where a company consolidates its network resources.

network interface card (NIC) -- The physical connection from the computer to the network is made by putting a NIC inside the computer and connecting it to the shared cable.

Open Systems Interconnect reference model (051) -- A communications model developed by the International Standards Organization (ISO) to define all of the services a LAN should provide. This model defines seven layers, each of which provides a subset of all of the LAN services. This layered approach allows small groups of related services to be implemented in a modular fashion that makes designing network software much more flexible.

packet -- In a shared media network, when one stations wishes to send a message to another station, it uses the network software to put the message in an “envelope.” This envelope is called a packet.

protocols -- Developed by international standards bodies, individual LAN equipment vendors, and ad hoc groups of interested parties to define how to implement a group of services in one or two layers of the OSI model.

repeaters -- Devices that amplify and regenerate signals so they can travel farther on a cable. The term “repeater” is often used to describe hubs.

ring topology -- A network whose nodes are connected in a continuous loop.

routers -- These are more complex internetworking devices that are also typically more expensive than bridges. They use Network Layer Protocol Information within each packet to route it from one LAN to another.

segmentation -- The act of improving network performance by dividing a single large network into multiple smaller, less congested LANs while maintaining connectivity between them. Switches offer an effective segmentation tool by providing each port with dedicated bandwith without requiring users to change any existing equipment such as NICs, hubs, wiring, or any routers or bridges that are currently in place. Switches can also support numerous transmissions simultaneously.

shared access -- Shared media technology means that all of the devices attached to the LAN share a single communications medium, usually a coaxial, twisted pair, or fiber optic cable.

shielded twisted pair (STP) -- Cable that has shielding around it to provide more protection against electromagnetic interference (EMI).

stackable hubs -- Hubs that look and act like standalone hubs except that several of them can be “stacked” or connected together, usually by short lengths of cable. When they are linked together they can be managed as a single unit.

standalone hubs -- Single box-level hubs with a number of ports. Standalone hubs usually include some method of linking them to other standalone hubs -- either by connecting them together with a length of 1 OBASE5 coaxial cable or cascading them using twisted pair between individual ports on each hub.

structured wiring architecture -- A wiring architecture that physically star-wires all network stations to intelligent hubs.

switches -- A device that links several separate LANs and provides packet filtering between them. A LAN switch is a device with multiple ports, each of which can support an entire Ethernet or Token Ring LAN.

token -- a signal used in a Token Ring network that coordinates the transmission of data among the nodes. The token travels around the network, and a node can transmit data only when it has a token.

token passing -- The access method used on Token Ring networks.

Token Ring -- A major LAN technology in use today. Token Ring rules are defined in the IEEE 802.5 specification. Like Ethernet, the Token Ring protocol provides services at the Physical and Data Link Layers of the 051 model. Token Ring networks can be run at two different data rates, 4 Mbps or 16 Mbps.

trailer -- A message a the end of a data packet that carries special information used by the network to identify the destination station. It is similar to a header, which comes at the beginning of a packet.

1OBASE-T -- The specification for running Ethernet on UTP. This stands for 10 Mbps, baseband signaling (the signaling method used by Ethernet networks), over twisted pair cable.

1OBASE5 -- An Ethernet specification that uses a thick coaxial cable. 1 OBASE5 is seldom installed in new Ethernet networks today.

1OBASE2 -- An Ethernet specification that uses a thin coaxial cable medium. 1 OBASE2 is only used in very small office networks.

unshielded twisted pair (UTP) -- UTP cable is similar to telephone cable but has somewhat more stringent specifications regarding its susceptibility to outside EMI than common telephone wire. UTP is used much more often than STP.