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| VPN | Virtual Private Network) A private network that is configured within a public network. For years, common carriers have built VPNs that appear as private national or international networks to the customer, but physically share backbone trunks with other customers. |
| DNS | Domain Name System) Name resolution software that lets users locate computers on a UNIX network or the Internet (TCP/IP network) by domain name. The DNS server maintains a database of domain names (host names) and their corresponding IP addresses. |
| hub | A central connecting device in a network that joins communications lines together in a star configuration. Passive hubs are just connecting units that add nothing to the data passing through them. Active hubs, also sometimes called "multiport repeaters," regenerate the data bits in order to maintain a strong signal, and intelligent hubs provide added functionality |
| repeater | A communications device that amplifies (analog) or regenerates (digital) the data signal in order to extend the transmission distance. Available for both electronic and optical signals, repeaters are used extensively in long distance transmission. |
| bridge | A device that connects two LAN segments together, which may be of similar or dissimilar types, such as Ethernet and Token Ring. A bridge is inserted into a network to segment it and keep traffic contained within the segments to improve performance. |
| router | A device that forwards data packets from one local area network (LAN) or wide area network (WAN) to another. Based on routing tables and routing protocols, routers read the network address in each transmitted frame and make a decision on how to send it based on the most expedient route (traffic load, line costs, speed, bad lines, etc.). Routers work at layer 3 in the protocol stack, whereas bridges and switches work at the layer 2. |
| gateway | A computer that performs protocol conversion between different types of networks or applications. For example, a gateway can convert a TCP/IP packet to a NetWare IPX packet and vice versa or from AppleTalk to DECnet, from SNA to AppleTalk and so on. |
| rj-45 | (Registered Jack-45) A telephone connector that holds up to eight wires. RJ-45 plugs and sockets are used in Ethernet and Token Ring Type 3 devices. |
| cat 5 | The following categories are based on their transmission capacity. The majority of new wiring installations use Category 5 UTP wire in order to be able to run or upgrade to the faster network technologies that will require it. Categories 1 through 5 are based on the EIA/TIA-568 standard. Levels 6 and 7 are enhanced Category 5 cables and are not yet standardized. |
| bnc connector | Bayonet Neill-Concelman or British Naval Connector) A commonly used plug and socket for audio, video and networking applications. BNCs connect two-wire coaxial cable (signal and ground) using a bayonet mount. After the plug is inserted, the bayonet mechanism causes the pins to be pinched into the locking groove when the plug is turned |
| fiber-optics cable | There are numerous types of plugs and sockets to connect optical fibers, using threaded, bayonet, push-pull and snap-lock connections. The first fiber-optic connector to be standardized was SMA, which were followed by the SC, ST and FC types. Since most optical transmissions require two cables (one to transmit and the other to receive), smaller form factors such as the snap-lock Fiber Jack are increasingly being developed to make installations as simple as plugging in a telephone |
| network adapter | A printed circuit board that plugs into both the clients (personal computers or workstations) and servers and controls the exchange of data between them. The network adapter provides services at the data link level of the network, which is also known as the "access method" (OSI layers 1 and 2). |
| half duplex | The transmission of data in both directions, but only one direction at a time. Two-way radio was the first to use half-duplex, for example, while one party spoke, the other party listened |
| full duplex | Transmitting and receiving simultaneously. In pure digital networks, this is achieved with two pairs of wires. In analog networks or in digital networks using carriers, it is achieved by dividing the bandwidth of the line into two frequencies, one for sending, the other for receiving. |
| tcp/ip | (Transmission Control Protocol/Internet Protocol) A communications protocol developed under contract from the U.S. Department of Defense to internetwork dissimilar systems. Invented by Vinton Cerf and Bob Kahn, this de facto UNIX standard is the protocol of the Internet and has become the global standard for communications. |
| ip address | Internet Protocol address) The address of a computer attached to a TCP/IP network. Every client and server station must have a unique IP address. Client workstations have either a permanent address or one that is dynamically assigned to them each dial-up session. IP addresses are written as four sets of numbers separated by periods; for example, 204.171.64.2. |
| ipx | Internetwork Packet EXchange) A NetWare communications protocol used to route messages from one node to another. IPX packets include network addresses and can be routed from one network to another. An IPX packet can occasionally get lost when crossing networks, thus IPX does not guarantee delivery of a complete message. Either the application has to provide that control or NetWare's SPX protocol must be used. |
| spx | Sequenced Packet EXchange) The NetWare communications protocol used to control the transport of messages across a network. SPX ensures that an entire message arrives intact and uses NetWare's IPX protocol as its delivery mechanism. Application programs use SPX to provide client/server and peer-to-peer interaction between network nodes. SPX provides services at layer 4 of the OSI model. |
| netbeui | NetBIOS Extended User Interface) Pronounced "net-booey." The transport layer for NetBIOS. NetBIOS and NetBEUI were originally part of a single protocol suite that was later separated. NetBIOS sessions can be transported over NetBEUI, TCP/IP and SPX/IPX protocols. |
