100Base-T The technical name for twisted-pair Ethernet operating at 100 megabits per second (Mbps).
DEC
Acoustic Coupler A device onto which a telephone handset is placed to connect a computer with a network;
might also contain a modem, or the modem could be a separate device.
WPD
Asynchronous (1) Pertaining to two or more processes that do not depend on the occurrence of specific
events such as common timing signals. (2) Without regular time relationship; unexpected or unpredictable with respect to the
execution of program instructions.
IBM
Baseband Characteristic of any network technology like Ethernet that uses a single carrier frequency and
requires all stations attached to the network to participate in every transmission.
DEC
Bit Rate The ratio of the number of bits transferred between devices in a specified amount of time,
typically one second. Bit rate is the same as data rate, data transfer rate, and bit time.
WPD
Bridge A computer that connects two or more networks and forwards packets among them. Bridges operate at
the physical network level, differing from repeaters by storing and forwarding complete packets, and differing from routers by
using physical addresses. DEC
Coaxial Antenna A variant of the dipole antenna, designed for use with an unbalanced feed line. One side
of the antenna element consists of a hollow conducting tube through which a coaxial cable passes. The shield of the cable is
connected to the end of the tube at the center of the radiating element. The center conductor of the cable is connected to the
other half of the radiating element. The element can be oriented in any fashion, although it is usually vertical.
WIS
Coaxial Cable A cable consisting of one conductor, usually a small copper tube or wire, within and
insulated from another conductor of larger diameter, usually copper tubing or copper braid.
IBM
CSU/DSU Channel Service Unit/Data Service Unit: An electronic device that connects a computer or router to
a digital circuit leased by the telephone company. Although the device fills two roles, it is usually a single piece of
equipment. DEC
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Data Encryption Standard DES, in computer security, a standard of the National Institute of Standards and
Technology (NIST), adopted by the U.S. government as Federal Information Processing Standard (FIPS) Publication 46, which
allows only hardware implementations of the data encryption algorithm. A symmetric-key encryption method using a 56-bit key,
developed in 1975 and standardized by ANSI in 1981 as ANSI X.3.92. IBM WPD
Dense Wavelength Division Multiplexing A technology that puts data from different sources together on an
optical fiber, with each signal carried on its own separate light wavelength. Using DWDM, up to 80 (and theoretically more)
separate wavelengths or channels of data can be multiplexed into a lightstream transmitted on a single optical fiber. In a
system with each channel carrying 2.5 gigabits per second (Gbps), up to 200 billion bits can be delivered per second by the
optical fiber. WIS
DS-CDMA Direct Sequence-Code Division Multiple Access, also known as Direct Sequence Spread Spectrum, is
one of two approaches to spread spectrum modulation for digital signal transmission over the airwaves. In direct sequence
spread spectrum, the stream of information to be transmitted is divided into small pieces, each of which is allocated to a
frequency channel across the spectrum.
UFL
Flow Control Control of the rate at which hosts or routers inject packets into a network or internet,
usually to avoid congestion. DEC
Frame Rate In motion pictures, television, and computer video displays, the number of frames or images
projected or displayed per second. Used in synchronizing audio and pictures, whether film, television, or video. In motion
pictures and television, frame rates are standardized by the Society of Motion Picture and Television Editors (SMPTE). WIS
Frame Relay (1) An interface standard describing the boundary between a user's equipment and a fast-packet
network. In frame-relay systems, flawed frames are discarded; recovery comes end-to-end rather than hop-by-hop. (2) A
technique derived from the integrated services digital network (ISDN) D-channel standard. It assumes that connections are
reliable and dispenses with the overhead of error detection and control within the network. IBM
High Availability High availability systems are defined as loosely coupled normal availability systems
with redundant hardware components managed by software that provides fault detection and correction procedures to maximize the
availability of the critical services and applications provided by that system. These systems require no manual, human
intervention to identify a failed component, execute a procedure to avert a system failure, and notice the averted failure.
DMI
High Speed Serial Interface A short-distance communications interface commonly used to interconnect
routing and switching devices on local area networks (LANs) with the higher-speed lines of a wide area network (WAN). HSSI is
used between devices that are within fifty feet of each other and achieves data rates up to 52 Mbps. Typically, HSSI is used
to connect a LAN router to a T-3 line. HSSI can be used to interconnect devices on Token Ring and Ethernet LANs with devices
that operate at Synchronous Optical Network (SONET) OC-1 speeds or on T-3 lines. WIS
Infrastructure The physical hardware used to interconnect computers and users. Infrastructure includes the
transmission media, including telephone lines, cable television lines, and satellites and antennas, and also the routers,
aggregators, repeaters, and other devices that control transmission paths. Infrastructure also includes the software used to
send, receive, and manage the signals transmitted.
WIS
Jabber (1) An error in which a faulty device (usually a NIC ) continuously transmits corrupted or
meaningless data onto a network. This may halt the entire network from transmitting data because other devices will perceive
the network as busy. (2) A sent data packet greater than the maximum 1,518 bytes specified in IEEE 802.3. To prevent this,
jabber control should be added to the hardware to make the circuitry incapable of sending information for more than 150
milliseconds (approximately 1500 bytes). WPD
LAN Local Area Network: Any physical network technology designed to span short distances (up to a few
thousand meters). Usually, LANs operate at tens of megabits per second through several gigabits per second. Examples include
Ethernet and FDDI.
DEC
Layer 3 In the Open Systems Interconnection seven-layer model, this layer provides switching and routing
technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and
forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control, and packet
sequencing. WPD
Loopback Test A test in which signals from a tester are looped at a modem or other network element back to
the tester for measurements that determine or verify the quality of the communications path. IBM
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MAC Address Media Access Control Address: A hardware address that uniquely identifies each node of a
network. In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI Reference Model is divided into two sublayers: the
Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The MAC layer interfaces directly with the network
media. Consequently, each different type of network media requires a different MAC layer. WPD
MAN Metropolitan Area Network: A network formed by the interconnection of two or more networks that may
operate at higher speed than those networks, may cross administrative boundaries, and may use multiple access methods.
Contrast with Local Area Network (LAN) and Wide Area Network (WAN). IBM
Modem Error-Correcting Protocols The protocols that modems agree on and use for checking and correcting
transmission errors. These have evolved toward accuracy, speed, and efficiency since 1978 when the Xmodem protocol became a de
facto standard. To briefly summarize: in all protocols data is chunked into "blocks" of a certain byte size and sent to the
destination modem which checks each block for errors and, depending on the results and the protocol, returns a positive (ACK)
or negative (NAK) acknowledgement, the latter usually resulting in a retransmission. The type of checking (checksum or cyclic
redundancy check) and the frequency at which a response is sent vary by protocol. Today, new modems use a V.42 protocol, but
the earlier protocols are still in use for older modems. WIS
MTU Maximum Transfer Unit or Maximum Transmission Unit: The largest amount of data that can be transferred
across a given physical network. The MTU is determined by the network hardware. DEC Mux Multiplexer: A device that combines
data from several sources into a single stream in such a way that it can be separated again later. Multiplexing occurs at many
levels. DEC
Null Modem A cable specially designed to allow direct connection of two computers by their communications
(RS-232) ports. Null modems are particularly useful with portable computers in allowing exchange of data with a larger system.
WPD
Optical Wireless An optical wireless (OW) system is similar to a microwave wireless system except that the
information is carried on optical or infrared rather than a microwave carrier. OW systems generally have higher capacities,
smaller antennas, and smaller beam widths. They are also referred to as Free Space Optical (FSO) or Infrared (IR)
communications systems. OW transmitters use light-emitting diodes (LEDs) or lasers. RFV
Packet Switching The process of routing and transferring data by means of addressed packets so that a
channel is occupied only during transmission of a packet. On completion of the transmission, the channel is made available for
transfer of other packets. IBM
Path Control Also called pathing, a networking approach used to address the specific needs of storage
networks (as compared to ordinary message networks) by changing the way communication paths are managed and organized.
Connection failures in message networks generally just mean that the connection must be retried; in storage networks, however,
a failure is more likely to cause a system crash. Also, the margin for error is smaller for storage networks; whereas error
recovery within minutes is acceptable for message networks, for storage networks it should be within seconds, and preferably
milliseconds. Because of these differences, storage network routing must include redundant, well-defined paths, enable fast
path changes, and have the altered topology information updated rapidly.
WIS
PVC Permanent Virtual Circuit: In asynchronous transfer mode (ATM), a predefined connection between two
users that is similar to a leased line. Call setup and disconnection are unnecessary for a PVC. Unlike a Switched Virtual
Circuit (SVC), a PVC lasts a long time (typically weeks or months). DEC IBM
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Remote Access Server A server dedicated to handling users who are not on a LAN but need remote access to
it. The remote access server allows users to gain access to files and print services on the LAN from a remote location. For
example, a user who dials into a network from home using an analog modem or an ISDN connection dials into a remote access
server. After authentication, the user can access shared drives and printers as if physically connected to the office LAN.
WPD
Ring (1) A network in which every node has exactly two branches connected to it and in which there are
exactly two paths between any two nodes. (2) A network configuration in which devices are connected by unidirectional
transmission links to form a closed path.
IBM
Router A special-purpose, dedicated computer that attaches to two or more networks and forwards packets
from one to the other. In particular, an IP router forwards IP datagrams among the networks to which it connects. A router
uses the destination address on a datagram to choose a next-hop to which it forwards the datagram.
DEC
RS-232C An Electronic Industries Alliance (EIA) standard that specifies the electrical characteristics of
slow-speed interconnections between terminals and computers or between two computers. DEC
Server Farm Also referred to as server cluster, computer farm, or ranch: a group of networked servers
housed in one location. A server farm streamlines internal processes by distributing the workload between the individual
components of the farm and expedites computing processes by harnessing the power of multiple servers. Farms rely on
load-balancing software that accomplishes such tasks as tracking demand for processing power from different machines,
prioritizing the tasks and scheduling, and rescheduling them depending on priority and demand that users put on the network.
When one server in the farm fails, another can step in as a backup. WPD
Sockets An endpoint provided by the transport service of a network for communication between processes or
application programs. IBM
T Interface In Integrated Services Digital Network (ISDN) service, the electrical interface between a
network terminating unit 1 (NT1) and a network terminating unit 2 (NT2) device, which typically is a private branch exchange
(PBX). Like the S interface, the T interface has four wires, allowing up to eight devices to be addressed. In Basic Rate
Interface (BRI) ISDN, the bits that flow from the central office through the NT1 are divided into two 64 Kbps channels (known
as B, or bearer, channels) and one 16 Kbps channel (the D, for data or delta, channel) for control signals. The control
signals allow a specific device to be addressed. WIS
Telephone Network Standards The V-Series recommendations from the ITU-T include the most commonly used
modem standards and other telephone network standards. Prior to the ITU-T standards, the American Telephone and Telegraph
Company and the Bell System offered its own standards (Bell 103 and Bell 212A) at very low transfer rates. Another set of
standards, the Microcom Networking Protocol, or MNP Class 1 through Class 10 (there is no Class 8), has gained some currency,
but the development of an international set of standards means these will most likely prevail and continue to be extended.
(Some modems offer both MNP and ITU-T standards.)
WIS
Thicknet Refers to the original thick coaxial cable used with 10Base5 Ethernet. DEC
Trivial File Transfer Protocol In the Internet suite of protocols, a protocol for file transfer that
requires low overhead and has little capability. TFTP uses the connectionless datagram delivery services of the User Datagram
Protocol (UDP), which allows hosts that have no disk storage to implement TFTP in read-only memory (ROM) and use it to boot
themselves. IBM
Twisted-Pair Cabling A type of cable that consists of two independently insulated wires twisted around one
another. One wire carries the signal while the other wire is grounded and absorbs signal interference. While twisted-pair
cable is used by older telephone networks and is the least expensive type of local area network (LAN) cable, most networks
contain some twisted-pair cabling at some point along the network. WPD
Wavelength Switching Also called Lambda Switching or Photonic Switching, the technology used in optical
networking to switch individual wavelengths of light onto separate paths for specific routing of information. In conjunction
with technologies such as dense wavelength division multiplexing (DWDM)-which enables 80 or more separate light wavelengths to
be transmitted on a single optical fiber-lambda switching enables a light path to behave like a virtual circuit. Although the
ability to redirect specific wavelengths intelligently is, in itself, a technological breakthrough, wavelength switching works
in much the same way as traditional routing and switching. Wavelength routers are positioned at network junction points. The
wavelength router takes in a single wavelength of light from a specific fiber optic strand and recombines it into another
strand that is set on a different path. BPL
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Footnotes
BPL BytePile.com, Inc. Definitions and Terms. <http://www.bytepile.com/definitions-l.php>
BytePile.com, Inc., 2002.
DEC Comer, Douglas E. Internetworking With TCP/IP: Principles, Protocols, and Architectures (4th
Edition). Prentice-Hall, Inc., 2000.
DMI DataMaster International, Inc. High Availability White Paper.
<http://www.dm-int.com/high_availability_whitepaper.htm>
IBM IBM Corporation. Glossary of Computing Terms.
<http://publib.boulder.ibm.com/infocenter/eserver/v1r3s/index.jsp?topic=/iphav/iphwglos.htm> IBM
Corporation, 1999.
RFV Red 5 USA, Inc. Frequently Asked Questions.
<http://www.red5usa.com/main_frame_optical_faq.htm>
UFL University of Florida, Office of Information Technology Network Services. Glossary.
<http://net-services.ufl.edu/~ns/provided_services/wireless/glossary.html>
WPD Webopedia. Jupiter Media Corporation, 2003.
WIS WhatIs. <http://whatis.techtarget.com> TechTarget.com, Inc., 2000.
