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Voice over IP
Dictionary

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Q

queue- A prioritized list of items in a system that are waiting to be acted upon (such as files waiting to be output to a printer).

R

radio frequency (RF)- The frequency range (10 KHz-3000 GHz) in which radio signals are transmitted.

radio frequency interference (RFI)- Noise caused by devices producing electromagnetic radiation in the radio frequency range.

redundant array of inexpensive disks (RAID)- The use of several small disk drives to provide data integrity and redundancy.

Business Phone System

remote access- A user's ability to connect to a distant network through a modem.

remote monitoring- A network management technique which relieves the NMS of certain monitoring duties by using a monitor to observe a specific LAN segment and report back to the NMS.

repeater- Repeaters, which function at the Physical layer of the OSI Reference Model, extend and regenerate digital signals traveling from one cable segment to another.

response- A type of SNMP message which carries management information from the managed device back to the network management station (NMS).

Ring In/Ring Out (RI/RO)- Ports on a token ring MAU which allow connection to other MAUs.

ring of trees- An FDDI topology in which layers of concentrators (trees) cascade from concentrators connected to the trunk rings.

ring topology- 1. A physical topology in which network devices are arranged in a closed circle. 2. A logical topology in which packets travel sequentially through all devices around the ring. See also bus topology, logical topology , network topology , and star topology .

RJ-11- A 4-to-6 pin telephone-style connector used with UTP.

RJ-45- An 8-pin telephone-style connector used with UTP.

RMON- A specialized SNMP MIB for use with remote monitoring devices.

route- To direct a packet of data (or a message) along a path of intermediate nodes.

router- A device that connects multiple networks together and forwards packets between them. A router operates at Layer 3 of the OSI Reference Model. It is also called a network relay.

Routing Information field- An optional field in token ring and FDDI frames that carries source route bridging information.

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S

SC connector- A fiber-optic connector used with multimode fiber. SC stands for subscriber connector.

ScTP- Screened twisted-pair cable.

SDLC- See Synchronous Data Link Control (SDLC).

segment- 1. A portion of a LAN separated from the rest of the LAN by a bridge. 2. An uninterrupted length of Ethernet cable within a network.

Sequenced Packet Exchange (SPX)- Novell NetWare's transport-layer protocol.

server- A workstation which provides access to network resources, such as a printer or hard drive.

Session layer- Layer five of the OSI Reference Model, which defines standards and protocols for establishing a session between nodes on a network.

session- The connection time during which data is transmitted between two users, two devices, or a user and a computing device on a network.

Set- An SNMP message used to change or reconfigure a MIB variable.

ST connector- A fiber-optic connector used with multimode fiber. ST stands for straight tip.

shielded twisted pair (STP)- A twisted-pair cable with foil shielding around each pair.

shielding- Insulation using a grounded, metallic covering to protect a cable or wire against interference.

Simple Network Management Protocol (SNMP)- A network management protocol for TCP/IP-based networks.

simplex- Data transmission in one direction only. See also duplex and half duplex .

single-mode fiber- A very thin fiber-optic cable which allows only one mode (light ray) to pass through it. Single-mode fiber supports long transmission distances and high data rates.

Single-Mode Fiber-Physical Medium Dependent (SMF-PMD)- An FDDI Physical-layer protocol that specifies the use of 125µm fiber cable.

single attachment concentrator (SAC)- An FDDI concentrator that is connected to only one ring (usually the primary).

single attachment station (SAS)- An FDDI station that is connected to only one ring (usually the primary).

SMF-PMD- See Single-Mode Fiber-Physical Medium Dependent (SMF-PMD) .

SNA- See Systems Network Architecture (SNA) .

SNMP- See Simple Network Management Protocol (SNMP) .

soft error- A type of token ring error that does not completely disrupt the ring.

SONET- See Synchronous Optical Network (SONET) .

source address- The address (unique node identifier) of the location from which a packet is sent.

spread-spectrum- A wireless LAN transmission technique which spreads the original signal over a broad range of frequencies.

star topology- A network configuration in which all stations are individually connected to and all messages pass through a central node.

See also bus topology, logical topology, network topology, physical topology, ring topology, and physical star topology .

StarLAN- AT&Ts implementation of IEEE 802.3 1BASE-5. It pro

station- A network node such as a workstation, server, or bridge.

Station Management layer (SMT)- The FDDI protocol layer which is involved in managing and monitoring all other FDDI protocol layers.

structured wiring system- A plan for building cabling which is based on modular subsystems and which specifies consistent wiring practices and materials.

subnet- 1. A name sometimes applied to the lower levels of the network architecture, collectively responsible for moving the data round the network. It is also known as the transport layer. 2. (TCP/IP) The portion of an IP address which, though actually part of the host, is treated as part of a network number within the local network.

switch- 1. A multiport device which provides high-speed packet switching between ports. 2. In packet-switching networks, the device that directs packets, usually located at one of the nodes on the network's backbone. It is also known as data PABX.

Switched Multimegabit Data Service (SMDS)- A high-speed networking technology that provides data transmission at rates from 1.544 to 45 megabits per second.

switching hub- A high-performance hub which provides a high-speed backplane and semiconductor -based switching matrix technology to reduce bottlenecks allow full bandwidth to each port on the hub.

switching matrix- A component of switching hubs which rapidly switch packets from port to port by allocating memory. The switching matrix is based on application specific integrated circuits (ASIC).

Synchronous Data Link Control (SDLC)- The SNA data link protocol equivalent to the IEEE 802.2 Logical Link Control (LLC) sublayer protocol.

Synchronous Optical Network (SONET)- A standard for a high-speed (45-Mbps to 1.5 Gbps) optical transmission network.

Systems Network Architecture (SNA)- IBM's design for wide area networks in which data communications system functions are separated into three discrete areas: the Application layer, the Function Management layer, and the Transmission Subsystem layer. SNA is a de facto standard that includes a peer-to-peer protocol called Advanced Program to Program Communications (APPC), and is supported by many computer vendors.

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T

T-1- A high-speed transmission technology (1.544 Mbps) that transfers voice and data over long- distance leased lines.

TCP/IP- See Transmission Control Protocol/Internet Protocol (TCP/IP) .

telecommunications- The transmission of data, voice, or video using telephone, radio, or other communication channels.

Telnet- A TCP/IP application protocol that provides virtual terminal service, letting a user log in to another computer system and access a host computer if the user wants to directly communicate with the host.

terminal- A device (usually a display and keyboard combination) that can process both data input and output.

terminal emulation- The ability of a computer to initiate a terminal so that the computer can receive signals sent by another computer (such as a mainframe).

thick Ethernet cable- A 0.4-inch diameter cable or RG-8 with four shields cable. It requires an external transceiver cable or N-series to BNC series adapter. It is often called thick Ethernet cable. See also thin Ethernet cable .

thin Ethernet cable- A cable standard for Ethernet (IEEE 802.3), networks using RG-58 A/U or RG-58 C/U cable and BNC connectors. The coaxial cable is 0.2 inches in diameter, so it is more flexible than thick Ethernet. Thin Ethernet operates at the same frequency as thick Ethernet but over shorter distances, and it provides less insulation from interference than thick Ethernet.

throughput- The total of correctly transmitted information processed or communicated during a specified time period, expressed in bits per second or packets per second.

token- A bit pattern that travels continuously in a predetermined direction along the transmission line of a ring or bus network. It can indicate that the line is currently transmitting information or that it is clear for transmission for the next station that wants to transmit on the network.

token bus- A bus topology LAN that uses a token to signal network access by a particular station.

token passing- A communication medium access technique on a ring or bus network that circulates a token from node to node. When a node wants to transmit, it grabs the token and attaches an information packet to it. Only one message can be transmitted on one channel at a time, and only the node with control of the token can transmit.

token ring- A baseband industry standard (designed to the IEEE 802.5 standard and the OSI Reference Model) that comprises a token passing access method and a ring topology.

topology- The physical or logical layout of the nodes in a network.

See also bus topology, logical topology, physical topology, star topology, and ring topology .

TP-PMD- See Twisted-Pair Physical Medium Dependent (TP-PMD)

Transmission Control- Protocol/Internet Protocol (TCP/IP) A widely used set of communication protocols developed to conform to the Department of Defense ARPANET standard.

transmission medium- The physical medium over which data is transmitted, such as radio frequency satellite link, a telephone line, or a LAN cable.

transparent- Invisible to or unnoticed by the user. Examples include the topology of a network and location of a resource on a remote node.

Transport layer- Layer four of the OSI Reference Model. It provides reliable data transfer, sequencing, and flow control, and ensures errorfree, end-to-end delivery.

twisted pair- Refers to wiring like that commonly found in telephone systems, consisting of two insulated wires loosely twisted around each other to help cancel out induced noise. See also 10BASE-T .

Twisted-Pair Physical Medium Dependent (TP-PMD)- An FDDI Physical- layer protocol that provides for the use of twisted-pair cable.

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U

unshielded twisted pair (UTP)- A popular LAN cable consisting of two wires twisted around each other and surrounded by a plastic jacket. See also 10BASE-T .

unstructured wiring system- A network wiring system which has grown in an unplanned and/or inconsistent way.

user- A person who uses but does not administer network resources.

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V

virtual workgroup- A feature of port-switching hubs which allow the remote assignment of users to LAN segments regardless of their physical location. It is equivalent to an electronic patch panel. See also patch panel .

voice-grade cable- Cable that is adequate for telephone (voice) communication but not necessarily adequate for transmission of digital data.

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W

wide area network (WAN)- A network covering an area larger than a city or a metropolitan area.

workstation- 1. A single user computer, in many cases specialized for high performance. 2. Any personal computer or terminal.

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X

X.25- The CCITT recommendation governing interface between data terminal equipment (DTE) and data circuit terminating equipment (DCE) for terminals operating in the packet mode on public data networks.

X.400- The CCITT recommendation for a messaging and document distribution protocol to connect different electronic mail systems.

X.500- The CCITT recommendation for a directory standard that provides global naming to coordinate the dispersed file directories of different systems.

X Windows- UNIX-based graphical user interface (GUI)

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