Basic Networking Terms and Definitions

Basic Networking Terms and Definitions

Numeric
10BASE2
Ethernet running on thin coax network cable at 10 Mbps.

10BASE5
Ethernet running on thick wire network cable at 10 Mbps.

10BASE-T
Ethernet running on unshielded twisted pair (UTP) cable at 10 Mbps. Point-to-point network media, with one end of cable typically going to repeater/hub and other to network device.

100BASE-TX
Ethernet running on unshielded twisted pair (UTP) cable at 100 Mbps. Point-to-point network media, with one end of cable typically going to repeater/hub and other to network device.

A

AAL (ATM Adaptation Layer)

A collection of standard Asynchronous Transfer Mode (ATM) protocols that adapt user traffic to the cell format. AAL is subdivided into the convergence sub-layer (CS), and the Segmentation And Reassembly (SAR) sub-layer. There are several types of AALs -- AAL0, AAL1, AAL2, AAL3/4 and AAL5 -- to support the various AAL service classes.

AAL0 (AAL Type 0)
Null protocol. No cell adaptation occurs.

AAL1 (AAL Type 1)
Used for transporting time-dependent Constant Bit Rate (CBR) traffic, such as audio and video, and emulating Time Division Multiplexer (TDM)-based circuits, such as digital signal level 1 (DS1) and E1. Timing information must be exchanged between the source and the destination. AAL1 supports QoS Class A (defined under QoS in this glossary).

AAL2 (AAL Type 2)
Used for supporting time-dependent slow or Variable Bit Rate Real Time (VBR-RT) connection-oriented traffic (e.g., packetized and compressed audio and video). Timing information must be exchanged between the source and the destination. AAL2 supports QoS Class B (defined under QoS in this glossary).

AAL 3/4 (AAL Type 3 and 4)
Used for supporting both connectionless and connection-oriented Variable Bit Rate Non-Real Time (VBR-NRT) traffic. AAL3 supports quality of service (QoS) class C while AAL4 supports QoS class D. AAL3 and AAL4 are combined into one type. AAL3/4 also performs re-sequencing and cell identification operations. AAL3/4 services are suitable for supporting interworking with frame relay, SMDS and X.25.

AAL5 (AAL Type 5)
Used for supporting connection-oriented variable bit rate VBR-NRT data traffic and signaling messages. AAL5 supports quality of service (QoS) Class X. AAL5 services are suitable for supporting interworking with most data networking protocols, such as frame relay, SMDS, Ethernet and Internet Protocol (IP). AAL5 is more popular and easier to implement than AAL3/4.

ABR (Available Bit Rate)
One of five Asynchronous Transfer Mode (ATM) service categories. In this service type, the network attempts to pass the maximum number of cells but does not guarantee cell delivery. ABR supports Variable Bit Rate (VBR) data traffic with flow control, a minimum guaranteed data transmission rate, and specified performance parameters. In exchange for regulating user traffic flow, the network offers minimal cell loss of accepted traffic. Traffic parameters are Peak Cell Rate (PCR) and Maximum Cell Rate (MCR). Quality of Service (QoS) parameters are Cell Loss Ratio (CLR) and Cell Error Rate (CER).

Access Network
Portion of public switched network that connects access nodes to individual subscribers. Predominantly passive twisted pair copper wiring.

Access Nodes
Points on edge of the Access Network that concentrate individual access lines into smaller number of feeder lines. May also perform various forms of protocol conversion. Examples are Digital Loop Carrier systems concentrating individual voice lines to T1 lines, cellular antenna sites, PBXs, and Optical Network Units (ONUs).

ACK
Acknowledgement.
Address Prefix
String of 0 or more bits up to maximum of 152 bits that is lead portion of one or more ATM addresses.

Address Resolution
Procedure by which client associates LAN destination with ATM address of another client or the BUS.

Administrative Domain
Collection of managed entities grouped for administrative reasons.
ADPCM (Adaptive Differential Pulse Code Modulation)
(1) Reduced bit rate variant of PCM audio encoding. (See also PCM.) This algorithm encodes difference between actual audio sample amplitude and predicted amplitude and adapts resolution based on recent differential values. (2) Coding scheme standardized by CCITT (See CCITT) that allows analog voice to be carried on 32 kbps digital channel instead of standard 64 kbps PCM channel.

ADSI (Analog Display Services Interface)
Protocol that simplifies use of advanced features by displaying text messages, generated by a remote computer or central office switch, on a user's telephone display or television set.

ADSL (Asymmetric Digital Subscriber Line)
Modems attached to twisted pair copper wiring that transmit from 1.5 to 9 Mbps downstream (to subscriber) and from 16 to 800 kbps upstream, depending on line distance.

AIN (Advanced Intelligent Network)
Bellcore's switching concept that centralizes significant amount of intelligence rather than constantly placing more information in central office switch.

AMI (Alternate Mark Inversion)
Line coding format used on T1 facilities that transmits ones by alternate positive and negative pulses.

AMPS
Advanced Mobile Phone Service (US), the name applied to the original analog cellular system. Still the predominant cellular transmission scheme.

ANSI (American National Standards Institute)
U.S. body and standards-setting organization, not arm of the government. Accredits various other standards setting committees.

API (Application Programming Interface)
A set of calling conventions that define how a service is invoked through a software package.

AppleTalk
Communications protocol developed by Apple Computer to allow networking between Macintoshes. All Macintosh computers have LocalTalk port, running AppleTalk over 230K bps serial line. Also runs over Ethernet (EtherTalk) and Token Ring (TokenTalk) network media.

Application Layer

The top layer of the network protocol stack. The application layer is concerned with the semantics of work, such as formatting electronic mail messages. (The lower layers of the network address how to represent that data and how to reach the foreign node.)

Application-Level Firewall

Firewall system providing service by processes that maintain complete TCP connection state and sequencing. Often re-addresses traffic so outgoing traffic appears to have originated from firewall, rather than internal host.

APPN (Advanced Peer to Peer Network)
IBM network architecture for building dynamic routing across arbitrary network topologies. Intended as an eventual replacement for SNA, IBM's static routed, hierarchical network architecture.

ARP (Address Resolution Protocol)
Used to dynamically discover the low-level physical network hardware address that corresponds to the high-level Internet Protocol (IP) address for a given host. ARP is limited to physical network systems that support broadcast packets that can be heard by all hosts on the network.

ARP is defined in Request for Comments (RFC) 826.

ASCII (American Standard Code for Information Interchange)
A seven-level code (128 possible characters) used for data transfer.

ASP (Abstract Service Primitive)
Implementation-independent description of interaction between service-user and service-provider at particular service boundary, as defined by Open Systems Interconnection (OSI).

Asynchronous Time Division Multiplexing

Multiplexing technique in which transmission capability is organized in unassigned time slots that are assined to cells upon request of each application's instantaneous real need.

Asynchronous Transmission
A transmission method that sends units of data one character at a time. Characters are preceded by start bits and followed by stop bits, which provide synchronization at the receive terminal.

ATM (Asynchronous Transfer Mode)
A standard implementation of cell relay, a packet switching technique using packets of a fixed length, called cells. It is asynchronous because the recurrence of cells containing information from an individual user is not periodic.

ATM Address
Defined in UNI Specification as 3 formats, each having 20 bytes in length, including country, area and end-system identifiers.

ATM-ARP (ATM Address Resolution Protocol)
An address resolution protocol for mapping Asynchronous Transfer Mode (ATM) and Internet Protocol (IP) addresses. (Each host is assigned a unique IP address.) ATM-ARP can be used for discovering local area network (LAN) hosts attached to an ATM network or in classical IP over ATM.

ATM Layer Link
Section of an ATM Layer connection between two adjacent active ATM Layer entities (ATM-entities).

ATM Link
Virtual path link (VPL) or virtual channel link (VCL).
ATM Peer-to-Peer Connection
Virtual channel connection (VCC) or virtual path connection (VPC).

ATM Traffic Descriptor
Generic list of traffic parameters that can be used to capture the intrinsic traffic characteristics of requested ATM connection.

ATM User-User Connection
Association established by ATM Layer to support communication between two or more ATM service users (i.e., between two or more next higher entities or between two or more ATM-entities). Communications over an ATM Layer connection may be either bidirectional or unidirectional. Same Virtual Channel Identifier (VCI) issued for both directions of connection at interface.

ATM25
ATM Forum-defined 25.6Mbit/s cell-based user interface based on IBM token ring network.

ATU-C and ATU-R (ADSL Transmission Unit, Central or Remote)
Device at end of ADSL line that stands between line and first item of equipment in subscriber premises or telephone switch. May be integrated within access node.

AUI (Attachment Unit Interface)
15-pin shielded, twisted pair Ethernet cable used (optionally) to connect between network devices and MAU.

Authentication
Process of determining identity of user attempting to access system.

Authentication token
Portable device used for authenticating user. Operates by challenge/response, time-based code sequences or other techniques. May include paper-based lists of one-time passwords.

Authorization
Process of determining what types of activities are permitted. Usually, authorization in context of authentication.

Autobaud
Automatic determination and matching of transmission speed.

Auto-Negotiate
Clause 28 of the IEEE 802.3u standard specifies MAC sublayer for identification of speed and duplex mode of connection being supported by device. Support optional for individual vendors.

Auto-sense
Auto-Negotiation in Clause 28 of IEEE 802.3u standard. Ability of 10/100 Ethernet device to interpret speed or duplex mode of attached device and adjust to that rate.

AWG (American Wire Gauge)
System that specifies wire size. Gauge varies inversely with wire diameter size.