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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. VPNs enjoy the security of a private network via access control and encryption, while taking advantage of the economies of scale and built-in management facilities of large public networks. |
| 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 | (1) 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. They are also used to tie two LANs of the same type together. Repeaters work at layer 1 of the OSI model. |
| 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. |
| Brouter | A communications device that provides the functions of a bridge and router. |
| Gateway | Gateways function at layer 4 and above in the OSI model. They perform complete conversions from one protocol to another rather than simply support one protocol from within another, such as IP tunneling. Sometimes routers can implement gateway functions. |
| 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 | Category 5 UTP wire in order to be able to run or upgrade to the faster network technologies that will require it. |
| 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. |
| Fiber Optic Cable | Fiber- optic communications networks have transformed the world. Barely starting in the late 1960s but gaining serious momentum in the 1980s, the phone companies began to replace their copper long distance trunks with fiber cable. Eventually, all transmission systems and networks are expected to become fiber based, even to the home. In time, the electronic circuits in computers may be partially or fully replaced with circuits of light, in which case fiber pathways would be used throughout the system. |
| 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).A network adapter is also commonly called a "NIC" (network interface card). Ethernet, Token Ring and Apple's LocalTalk are common network adapters. |
| 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 |
| 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. |
