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100BaseT
Fast Ethernet is Ethernet that runs at 100Mbps as opposed to the standard 10Mbps. There are two primary standards that have been proposed: 100Base-T and 100VG-AnyLAN. 100Base-T is also referred to as the IEEE 802.3u standard. The 100VG-AnyLAN standard is in the hands of a new committee, the IEEE 802.12. Fast Ethernet and the 100Base-T standard are synonymous terms.

100BaseTX
100Base-TX is the specification that describes how to run 100Mbps Fast Ethernet over Category 5 UTP. Category 5 UTP is the most popular type of cabling used in LANs today.

100VGAnyLAN
100VG-AnyLAN is another 100Mbps Ethernet technology standard. It directly competes with 100Base-T Ethernet. The IEEE 802.12 committee is currently investigating it. The access method used by this standard is different than 10Mbps Ethernet and Fast Ethernet (CSMA/CD). The MAC frame however stays the same. The new access method is called "demand priority."

10Base2
10Base2 is the IEEE standard for 10Mbps baseband Ethernet over coaxial cable (RG-58). 185 meters is the maximum distance for this standard. 10Base2 is also referred to as "Thinnet," "Thinlan" and "Cheapernet." 10Base2 or Thinnet uses twist-on BNC connectors to attach to devices. Each device that attaches to the cable uses a T-connector to daisy chain to the next device. The final T-connector in the series must include a termination plug. In most 10Base2 implementations the Network Interface Card contains the transceiver functions.

10Base5
10Base5 is the IEEE standard for 10Mbps baseband Ethernet over coaxial cable. 500 meters is the maximum distance for this type of cable. Also called "Thicknet" and "Yellow Wire." This type of physical cable is typically used as the backbone media for Ethernet networks.

10BaseF
10BaseF is the Ethernet 10Mbps standard for star configuration Ethernet using fiber optic cable.

10Broad36
10Broad36 is the IEEE Standard for an 802.3 (Ethernet) network using broadband transmission with thick coax cable running at 10Mbps.

2B+D
This is the common way of stating ISDN's BRI interface. 2B is short for two bearer channels. D stands for a data channel. BRI is the Basic Rate Interface in ISDN. On ISDN circuit is composed of two 64Kbps bearer channels which may be used for voice or data, and one 16Kbps data channel. The data channel is also used for signaling.

23B+D
The ISDN Primary Rate Interface. It is a circuit consisting of 23 64Kbps channels for carrying voice, data, and video and a data channel used for carrying signaling information. It is similar to T1 signaling.

24x7
This term refers to 24 hours per day, 7 days per week, and is used to describe the system uptime and support hours

3172
A type of networking gateway (protocol converter) which allows LAN traffic such as Token Ring and Ethernet to attach to an IBM mainframe. It is also referred to as a LAN gateway.

3174
IBM cluster controllers or communications controllers. These devices are used to control communications between an IBM mainframe and a terminal device. The devices can be 3270s or ASCII terminals. The 3274 is the older type of cluster controller that the 3174 replaced.

3270
A type of IBM terminal or printer used in SNA networks. Other vendors also provide 3270 emulations for their terminals and printers.

3270 Gateway
A 3270 gateway is a computer that handles the communication path and conversion between a terminal device or PC and an IBM mainframe.

3274
IBM cluster controllers or communications controllers. These devices are used to control communications between an IBM mainframe and a terminal device. The devices can be 3270s or ASCII terminals.

3745
IBM front end processor (FEP) model number. Older versions included the 3725 and the 3705. These devices attach LANs and other devices such as cluster controllers to an IBM host. 3745s can also be attached to each other in cross-domain configurations.

5/4/3 Rule
This is a rule of thumb that applies to 10Base2 and 10Base5 Ethernet and associated repeaters. There can be a maximum of five segments connected by four repeaters with a maximum of three segments containing network nodes. Therefore, up to two Ethernet segments may be used as "link" segments (cable only, without network nodes) to extend the overall distance of an Ethernet network.

80/20 Rule
The 80/20 rule is a rule of thumb states that 80 percent of network traffic should stay in local subnets, and only 20 percent should cross the backbone to reach a remote subnet.

802.1
802.1 is the IEEE standard for overall architecture of LANs and internetworking.

802.1B
802.1B is the IEEE standard for network management.

802.1D
MAC layer standard for inter-LAN bridges. The 802.1D standard encompasses the interconnection of 802.3: 802.4 and 802.5 LANs.

802.2
802.2 is the standard for the upper Data Link Layer sublayer also known as the Logical Link Control layer. It is used with the 802.3, 802.4 and 802.5 standards (lower DL sublayers).

802.3
Standard for CSMA/CD (Carrier Sense Multiple Access with Collision Detection). Both Ethernet and Starlan follow this standard. It encompasses both the MAC and Physical Layer standards. At the Data Link Layer, it is one of three primary data link sublayers. The Physical Layer specifications depend on the type of media used (10Base T, 10Base 5, etc.). 10Mbps is the transmission rate for this standard.

802.4
Standard for the Data Link and Physical Layer for the Token Bus protocol. It is typically used with the Manufacturing Automation Protocol (MAP) developed by General Motors. 10Mbps is the typical transmission speed for this standard. See the LAN Architectures section of this document for further details on this subject.

802.5
Standard for the token-passing (Token Ring) access method of LAN protocols. It encompasses both the Data Link and Physical Layer standards. Transmission speeds include both 16Kbps and 4Kbps.

802.6
The 802.6 standard is the IEEE standard for Metropolitan Area Networks (MANs) also known as Distributed Queue Dual Bus (DQDB).

A and B Bit Signaling
These are the bits used in T1 transmission links that convey signaling information. These bits are used to carry dialing and control information such as off hook and dial tone for each voice conversation that is carried across a T1 link.

A to D Conversion
Analog to digital conversion is also called A to D conversion or ADC. It is the process of converting an analog waveform into binary format. The most common example of this is found in the codec (coder/decoder). This device takes the analog voice signal and converts it to digital (binary) format for transmission over a digital path such a T1.

AAL
The ATM adaption layer is an end-to-end process used only by the two communicating entities to insert and remove data from the ATM layer. At every point in the network, processing is done only on each ATM cell in isolation. At no point is it necessary to gather more information than is contained in a single cell header to complete the process. The network is not concerned with arrivals of groups of cells, sequencing or acknowledgment. The AAL enhances the service provided by the ATM layer to a level required by the next highest layer.

AARP
When using other Data Link Layer protocols below DDP, a fundamental problem exists of address matching. This problem arises because of the two different types of addresses (Link Layer and Network Layer) which must be resolved. The matching the Link Layer address to the Network Layer address is resolved by using the AppleTalk Address Resolution Protocol (AARP), which is similar to the Address Resolution Protocol (ARP) used in the TCP/IP protocol stack. AARP is used to resolve (or bind) Ethernet addresses to DDP. When Ethernet sends frames containing DDP, the DDP packet is encapsulated by the Ethernet frame. These services, together with the mechanisms used by the Ethernet data link, are referred to as ELAP.

AUI
AUI stands for Attachment Unit Interface. It is a connector that attaches Ethernet equipment such as a workstation or fan-out box to a transceiver. AAUI is the AppleTalk Attachment Unit Interface.

ABM
ABM stands for Asynchronous Balanced Mode. ABM is one of three types of data transfer modes in the HDLC family of protocols:

• Normal Response Mode (NRM). Used in the unbalanced configuration, secondary may only respond to a poll from the primary station.
• Asynchronous Balanced Mode (ABM). Either station may initiate transmission (balanced configuration).
• Asynchronous Response Mode (ARM). Either station may initiate transmission but one station has responsibility for line maintenance such as error recovery.

Abbreviated Dialing
Abbreviated dialing enables a caller to dial a frequently used number by using only a few of the digits instead of the entire telephone number. Abbreviated dialing is also referred to as speed dialing and short-code dialing.

Abstract Syntax Notation
ASN.1 stands for Abstract Syntax Notation One. It provides a standardized format for data transfer between nodes. Each node is only concerned with translating to and from ASN.1 and doesn't need to know anything about the format in which data are stored elsewhere on the network.

ACF
ACF stands for Advanced Communications Facility. It refers to IBM software products used to allow IBM products and compatibles to communicate.

ACF/NCP
ACF/NCP is IBM's control software that runs in a front end processor (FEP) and controls the data communications network in an SNA environment.

ACF/VTAM
ACF/VTAM stands for Advanced Communications Facility/Virtual Telecommunications Access Method. It is the data communications control software running on the host computer in an IBM network. It is used to control links and devices in an SNA network.

ACK
ACK is short for acknowledgment. In data communications a node will send an ACK to another node to indicate a transmitted frame or packet has been received. Connection-oriented protocols use acknowledgments.

Access Device
An access device is a network component used to gain access to network resources from a remote location, and vice versa. Common access devices are routers and modem pools. Modem pools are banks of modems that allow multiusers to dial in to an organization's local area network (LAN).

Active Loop
An active loop is two or more paths between a pair of devices on a bridged network. An active loop is formed when one node is inadvertently connected to more than one bridge.

Active Server Pages (ASP)
ASP is a Microsoft technology for dynamic Web pages. ASP pages contain blocks of VBScript or Jscript, which the Web server interprets to create a unique HTML page for each browser request.

ActiveX Control
ActiveX control is a broad category of software components that can be downloaded and run by a Web browser to add extra functionality to a Web page. ActiveX, developed by Microsoft, is an outgrowth of two technologies: OLE and COM.

Address
An address is a unique identifier that determines the originating location of data or the destination of data being transmitted across a communication link. There is a distinction between a station's link address, a station's network address, and an individual process running on a station.

Address Resolution Protocol (ARP)
ARP is the protocol used by Internet Protocol (IP) (as in Transmission Control Protocol [TCP]/IP) for address resolution. Address resolution refers to the ability of a station to resolve another station's media access control (MAC) (hardware) address given its IP address.

Address Resolution Protocol (ARP) Cache
An ARP cache is a host's internal list that maps IP (network) addresses to their corresponding hardware addresses.

Adapter
An adapter is a term used to identify the computer card that fits into the computer bus. One type of adapter is a network interface card (NIC). A NIC provides a connection (interface) to the networking media for sending information across a network.

Algorithm
An algorithm is a set of specific steps for solving a particular problem. These steps can be implemented in any natural or programming language.

American National Standards Institute (ANSI)
ANSI is a national voluntary organization that develops and publishes standards for data communications, programming languages, magnetic storage media, the OSI model, office systems, and encryption. It is a member of ISO. For the most part, ANSI standards are similar to ISO standards, differing only when unique aspects of North American systems need to be considered.

American Standard Code for Information Interchange (ASCII)
ASCII is one of the most widely used codes for representing information on a computer system. These codes represent characters, such as keyboard characters. ASCII uses 7 bits for the 128 elements it represents. For example, when the character "A" is pressed on the keyboard, the ASCII binary representation is 100 0001.

Analog
An analog signal, also referred to as an analog wave or carrier wave, is a continuous electrical signal on a communication circuit. An analog signal in its normal form does not have intelligence. Modulation is used to add intelligence to an analog wave.

AppleScript
AppleScript is a scripting language developed by Apple Computer that is integrated into the MacOS, starting with System 7.5.

Applet
An applet is a small executable program written in the Java programming language. Applets can be embedded in HTML pages to provide interactive features. Java applets are supported by any browser that supports Java.

AppleTalk Filing Protocol (AFP)
AFP is the protocol used in Apple Networks for retrieving and storing files across a network.

Application Programming Interface (API)
APIs are standard function calls embedded in software to call commonly used code. They are usually associated with specific programming languages. APIs are generally thought to be more efficient than CGI-based programs, which must be recompiled each time they are needed.

Application-Specific Integrated Circuit (ASIC)
ASIC refers to electronics technology that use customized chips to perform functions normally done in software. Switches that use ASIC hardware are much faster than switches that rely on slower software.

Architecture
Architecture is the design and method of construction of a particular entity. Within computer networks, common architectures were developed, or constructed, for a particular purpose. Examples are IBM's Systems Network Architecture (SNA) and Apple's AppleTalk.

Asynchronous Control Character Map (ACCM)
ACCM or async map is a 32-bit array that identifies characters that must be "escaped," or marked, to keep them from being misinterpreted as transmission control characters.

Assets
The computing infrastructure and supporting systems of a Web site, including hardware, software, knowledge, and content (databases, articles, and graphic elements) are referred to as assets.

Asynchronous Transfer Mode (ATM)
ATM is a technology used to pass information in "cells" (small frames) across a network. An ATM network consists of multiple ATM switches that forward each individual cell to its final destination. ATM can provide transport services for audio, data, and video.

Asynchronous Transfer Mode (ATM) Edge Switch
This is a switch at the "edge" of an ATM network. It is an ATM switch that connects the ATM network to non-ATM external networks.

Asymmetrical Digital Subscriber Line (ADSL)
See DSL.

Authentication
In networking, authentication is the process of accurately identifying a user of a network. This is usually done through passwords or some other method for identification purposes.

Autonomous System
An autonomous system is a private group of networks and routers. Each autonomous system is administered by a single organization. An ISP is one example of an autonomous system.

Availability
Availability refers to the amount (or percentage) of time that a given network or component in a network (such as a host or server) is available to carry out its intended task.

AWG
AWG stands for American Wire Gauge. It is a numbering system that specifies the thickness of the wire. As the thickness of the wire increases, the number referring to the wire decreases. Examples of common AWG gauges are listed below.

• RS-232: 22 AWG
• Ethernet Thinnet (10 Base2): 20 AWG
• Ethernet Thicknet (10 Base5): 12 AWG