GLOSSARY(brief)

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.

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 10BASE-T.

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.

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 (OSI) -- 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 station 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.

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.

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).

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 10BASE5 coaxial cable or cascading them using twisted pair between individual ports on each hub.

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 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 OSI model. Token Ring networks can be run at two different data rates, 4 Mbps or 16 Mbps.

10BASE-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.

10BASE5 -- An Ethernet specification that uses a thick coaxial cable. 10BASE5 is seldom installed in new Ethernet networks today.

10BASE2 -- An Ethernet specification that uses a thin coaxial cable medium. 10BASE2 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.