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Voice over IP
Dictionary

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J

jabber- In a malfunctioning station, to send incessant transmissions of random data that can lock up the network.

jam signal- A signal used to reinforce collisions in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) LAN so that all transmitting stations are aware of the collision state.

jitter- An error condition caused by a signal being out of synchronization with other devices.

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K

Kilobit (Kb)- One thousand bits. Bit is the contraction of binary digit. A bit is the electrical equivalent of a value 0 or 1 that represents the basic unit of computer information.

Kilobyte (KB)- One thousand bytes. A byte is eight bits long and represents one character.

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L

LAN- See local area network (LAN) .

LAN segmentation- The process of dividing LAN bandwidth into multiple independent LANs to improve performance.

layer- A logically distinct module in the architecture of a network, responsible for particular data communications tasks. It is also called a level. See Open Systems Interconnection (OSI) Reference Model .

LCF-PMD- See Low Cost Fiber-Physical Medium Dependent (LCF-PMD) .

light emitting diode (LED)- A fiber-optic light source.

link- A physical or logical circuit between two points in a network.

line encoding- The process of creating a signal that is appropriate for the transmission medium.

load sharing- The use of two power supplies to protect from a power outage.

local area network (LAN)- A communications network within a limited physical area (up to about 6 miles or 10 kilometers) that provides high-speed (over 1-Mbps) data transmission. The three basic components of a LAN are the boards that plug into each computer to connect it to the network, cabling, and server hardware and software for network control.

LocalTalk- Apple Computer's original Physical-layer protocol for LAN connectivity which is built-in to every Macintosh.

Logical Link Control (LLC)- The IEEE 802.2 data link sublayer protocol which provides a common interface with higher protocol layers for Ethernet, token ring, and FDDI LANs.

logical topology- The logical and electronic relation between network devices.

loopback- A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through all of, or a portion of, a data communications link or network. A loopback test permits the comparison of a returned signal with the transmitted signal.

Low Cost Fiber-Physical Medium Dependent (LCF-PMD)- An FDDI Physical-layer protocol that allows the use of 50/125, 85/125, 100/ 140, and 200/230µm graded fiber.

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M

MAC entity- The circuitry in a network device capable of implementing

MAC-layer protocols. See Media Access Control (MAC)

Management Information Base (MIB)- A logical naming of all information sources residing in a network and pertinent to the network's management. Simple Network Management Protocol's (SNMP) management uses a set of standard MIBs known as MIB II and other standards MIBs for FDDI, Ethernet, and others. In addition, vendors write proprietary MIB extensions for SNMP management of particular devices. The MIB is also the database of configuration and performance data for network device.

MAU- See medium attachment unit (MAU) or multistation access unit (MAU) .

Media Access Control (MAC)- A method for controlling access to a transmission medium. An example is the Ethernet (CSMA/CD access method.

media filter- Converts output from a token ring network adapter to a signal appropriate to the LAN medium. Typically used for transition to UTP cable.

media interface connector (MIC)- 1. The term for the IBM standard connector used for STP in token ring LANs 2. The term for the connector used with the original fiber FDDI PMD.

medium attachment unit (MAU)- An Ethernet transceiver that connects the adapter card to the local network medium.

medium independent interface (MII)- The interface and protocol used to transition between the 100BASE-T network adapter and the varieties of 100BASE-T transceivers.

megabit (Mb)- One million binary bits (ones and zeroes). The term bit is the contraction of binary digit. It is the electrical equivalent of a value 0 or 1 and represents the basic units of computer information.

megabyte (MB)- One million bytes. (A byte is eight bits long and represents one character).

metropolitan area network (MAN)- A data communication network covering the geographic area of a city. FDDI can provide a private MAN while IEEE 802.6 can provide a public MAN.

MHz- Abbreviation for megahertz. One million cycles per second.

microsecond (µs)- One-millionth of a second (0.000001 second).

modem- Contraction for "modulate/demodulate." A modem converts the serial digital (binary) data from a transmitting terminal into a form suitable for retransmission over an analog telephone channel. A second modem reconverts this signal to binary data for acceptance by the receiving terminal.

MSB- Most significant bit; the leftmost bit in a byte.

multicast- A message sent simultaneously to a specific group of nodes on a network.

multicast address- An address that includes a specified group of devices on the network. Only devices in this group simultaneously receive messages sent to this address.

multimode fiber- a type of fiber-optic cable which allows multiple modes (light rays) to pass through it.

multiport repeater- See hub .

multistation access unit (MAU)- A hub in a IBM Token-Ring network. Each unit supports up to eight workstations an servers and can be connected to either hub to create large networks.

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N

nanosecond (ns)- One-billionth of a second (0.000000001 second).

near-end crosstalk (NEXT)- A measurement of crosstalk. See crosstalk .

NetWare Core Protocol (NCP)- The means by which NetWare clients transmit requests to servers to perform tasks such as read and write files, create queue jobs, login, and logout.

NetWare Loadable Modules (NLMs)- Native Novell and third-party applications that are loaded onto the Novell NetWare server to perform specialized tasks.

network adapter board- A circuit board inside each workstation or server on the network. It allows a device to listen and talk to other stations and nodes on the network. Also known as a network interface card (NIC).

network administrator- A person or program responsible for controlling the operation of all or part of a network. In the LAN Manager environment, this person is called the network administrator.

network analyzer- A device that simulates and tests a network.

network element- A network device managed by SNMP.

Network layer- Layer three of the OSI Reference Model, controlling communication links and data routing across one or more links. This layer receives data that has been framed by the Data Link layer below it, converts this data into packets, and passes the result to the Transport layer that directs the packets to their destination.

network management- Administrative services performed in managing a network, such as network topology and software configuration, downloading of software, monitoring network performance, maintaining network operations, and diagnosing and troubleshooting problems.

network management platform- Powerful network management software programs which provide a set of network management utilities and application program interfaces that enable software developers to write network management applications for specific devices.

network management station (NMS)- A station or server running SNMP manager software.

Network Operating System (NOS)- a set of operating system protocols which control the resources of a network.

network topology- The pattern of connection between points in a network.

node- A communication device attached to a network, such as an intelligent workstation, file server, or host computer.

noise- Undesirable signals on a communication channel that can interfere with or distort data signals.

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O

octet- A unit of information consisting of 8 bits.

Open Systems Interconnection (OSI) Reference Model- A sevenlayer reference model of data communications protocols, drafted by the International Standards Organization (ISO).

operating system (OS)- The fundamental software instructions controlling a local computer.

optical fiber cable- A thin cable with a glass or plastic core used in fiber-optic communications. The cable transmits light instead of electrical signals.

optical bypass switch (OBS)- A device used in FDDI networks that acts as a mirror, preventing a ring wrap in the event of a node power off.

out-of-band management- The use of a backup communication link in order to manage a severely errored network.

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P

packet- A block of data handled by a network in a well-defined format that includes a header and a data field. In this course it refers to the unit transmitted over the LAN medium.

pad- Provides filler octets to allow a packet to meet a minimum packet size or boundary requirement.

parallel tasking- A network adapter feature that allows frames to be rapidly processed.

parameter- 1. A variable assigned to a constant value for a specific purpose or process. 2. A measured value delimiting a process, such as the beginning and ending columns of fields that are being sorted.

patch cord- A short, connectorized cable for interconnecting devices.

patch panel- A connectorized cross-connect for interconnecting cables and devices.

PBX- An automated telephone switching system serving one company, located on the company's premises, and connecting to the public telephone network.

peer-to-peer architecture- A network architecture in which stations can share information and each other's resources without relying on a centralized server.

Physical layer- Layer 1 of the OSI Reference Model. It describes the electrical and physical connection standards between communication devices.

physical topology- The actual physical pattern in which devices are interconnected.

point-to-point topology- A network configuration that connects only wo communications facilities (one at each end).

port- A place where a physical connection is made between a computing device and cabling to a peripheral, a network, and others.

port density- The number of ports, physical and logical, per network device.

port-switching hub- A hub allowing the creating of virtual workgroups through remote configuration and relocation of users to LAN segments regardless of their physical location.

preamble- A sequence of encoded bits that is transmitted before each data frame to allow synchronization of clocks and other circuitry at other sites on the channel. In the Ethernet specification, the preamble is 64 bits.

Presentation layer- Layer 6 of the OSI Reference Model. It determines the format and visual presentation of displayed data.

propagation delay- The time it takes for the beginning of a frame to arrive at its destination.

protocol- 1. A strictly defined procedure and message format allowing two or more systems to communicate over a transmission medium. 2. A formalized set of rules that computers use to communicate. Because of the complexity of communications between systems and the need for different communications requirements, protocols have been divided into modular layers, in which each layer performs a specific function for the layer above.

protocol converter- A device for translating the data transmission code or protocol of one network or device to the corresponding code or protocol of another network or device, allowing equipment with different conventions to communicate with one another.

protocol data unit (PDU)- A unit of data equivalent to the frame which is passed between protocol layers.

protocol layers or levels- A hierarchical set of protocols in which each protocol layer obtains services from the layer below it and performs services for layer above it. See Open Systems Interconnection (OSI) Reference Model .

proxy agent- A type of SNMP agent software which enables the management of non-SNMP devices or devices using private enterprise MIBs.

punch-down block- A type of cross-connect for interconnecting twisted-pair wires.

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