AAL1 - AAL type 1 - Protocol standard used for the transport of time-dependent Constant Bit Rate (CBR) traffic (e.g. audio and video) and the emulation of TDM-based circuits (i.e. DS1, E1). Timing information is required to be exchanged between the source and the destination. AAL1 supports QoS Class A.

AAL2 - AAL type 2 - Protocol standard for supporting time-dependent slow or Variable Bit Rate (VBR-RT) connection-oriented traffic (e.g. packetized and compressed audio and video). Timing information is required to be exchanged between the source and the destination. AAL2 supports QoS Class B.

AAL 3/4 - AAL type 3 and 4 - Protocol standard for supporting both connectionless and connection-oriented Variable Bit Rate (VBR-NRT) traffic. AAL3 supports QoS class C while AAL4 supports QoS class D. They are currently combined into one type. AAL3/4 also performs resequencing and cell identification operations. AAL3/4 services are suitable for supporting interworking with Frame Relay, SMDS and X.25.

AAL5 - AAL type 5 - Protocol standard for supporting connection-oriented Variable Bit Rate (VBR-NRT) data traffic and signaling messages. AAL5 supports QoS Class X. AAL5 services are suitable for supporting interworking with most data networking protocols, such as Frame Relay, SMDS, Ethernet and IP.

2-Wire Analog Circuit - A telephone line or trunk that has just one current loop (one pair), most commonly FXS, FXO or E&M.

4-Wire Analog Circuit - A telephone circuit having two pairs, TX and RX. Provides higher quality signal than two-wire circuit, most commonly E&M.

4-Wire Circuit - A communications path consisting of two pairs of conductors (wires), one pair for transmitting and one pair for receiving.

AAL (ATM Adaptation Layer) - A collection of standardized protocols that adapt user traffic to the cell format. The AAL is subdivided into the Convergence Sublayer (CS) and the Segmentation and Reassembly (SAR) sublayer. There are several types of AALs (AAL1, AAL2, AAL3/4 and AAL5) to support the various AAL service classes.

ABCD Bit Manipulation - The signaling bits are used by telephone switches and PBXs for call answer and disconnect supervision. Flexibility in manipulating these bits simplifies installation and configuration when matching the voice system with the existing switches.

A-bis - This is a GSM term for an interface linking between the BTS (base transceiver station) and the BSC (base station controller). Other GSM interfaces are the A between the BSC and the MSC (mobile switching controller), and the E between the MSC and the PSTN.

ABR (Available Bit Rate) - One of five ATM Forum-defined service categories. In this service type, the network makes the best effort to pass the maximum number of cells but does not guarantee cell delivery. Supports variable bit rate 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 PCR and MCR. QoS parameters are CLR and CER.

Address - A coded representation of the origin or destination of data.

ADPCM (Adaptive Differential Pulse Code Modulation) - An ITU standard technique for encoding analog voice signals into a digital form at 32 kbps (half the standard PCM rate).

Agent - In SNMP, this refers to the managed system.

AIM (ATM Inverse Multiplexing) - See IMA.

AIS (Alarm Indication Signal) - One of the OAM function types used for fault management (see also CC, RDI).

Alternate Routing - In switching, alternate routing is the choice of the next-best path when the best path is blocked.

AMI (Alternate Mark Inversion) - A bipolar coding scheme in which successive 1s (marks) must alternate in polarity.

Analog - A continuous wave or signal (such as human voice).

Analog Loopback - A testing technique that isolates faults in transmission equipment by performing a loopback on the data at the analog (line) side of the modem.

Analog Transmission - The transmission of a continuously variable signal, as opposed to a discrete (digital) one.

ANSI - American National Standards Institute.

ARQ (Automatic Request for Repeat or Retransmission) - A communications feature where the receiver asks the transmitter to resend a block or frame because errors were detected by the receiver.

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

Async - See Asynchronous Transmission.

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. Also called start-stop transmission.

ATM (Asynchronous Transfer Mode) - A standard (ITU) implementation of cell relay, which is a packet switching technique using packets (cells) of a fixed length. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not periodic. ATM is used for transmission of integrated services, broadband switching and multiplexing with high-performance and cost-effectiveness under certain QoS guarantees.

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

Attenuation - Signal power loss through equipment, lines or other transmission devices. Measured in decibels.

Automatic Rate Fallback - Ensures that the logical channel remains open even if individual links fail, by automatically dropping to the next lower rate. When failed links are recovered, the original rate is restored.

AWG - The American Wire Gauge System, which specifies wire width.

Backhaul - Transporting traffic between distributed sites (typically access points) and more centralized points of presence. See Cellular Backhaul.

Balanced - A transmission line in which voltages on the two conductors are equal in magnitude, but opposite in polarity, with respect to ground.

Balanced Line - A circuit in which neither side of the line is grounded. This minimizes crosstalk or noise pickup between pairs in the same cable.

Bandwidth - The range of frequencies passing through a given circuit. The greater the bandwidth, the more information can be sent through the circuit in a given amount of time.

Baseband - Refers to transmission of a digital or analog signal at its original frequency, as an unmodulated signal.

Baud - Unit of signaling speed equivalent to the number of discrete conditions or events per second. If each signal event represents only one bit condition, baud rate equals bps (bits per second).

BERT (Bit Error Rate Test/Tester) - A device used to test the bit error rate of a communications circuit (i.e. the ratio of received erroneous bits to received bits, usually a number referenced to a power of 10).

Best effort - A QoS class in which no specific traffic parameters and no absolute guarantee are provided. Best effort includes UBR and ABR.

Bipolar - A signaling method (in T1/E1) represents a binary “1” by alternating positive and negative pulses, and a binary “0” by absence of pulses.

Bit - The smallest unit of information in a binary system. Represents either a one or zero (“1” or “0”).

Bit Interleaving/Multiplexing - A process used in time division multiplexing where individual bits from different lower speed channel sources are combined (one bit from one channel at a time) into one continuous higher speed bit stream.

BOD (Bandwidth on Demand) - A concept in digital communications that enables users to request additional network bandwidth as the application warrants, allowing them to pay for only the bandwidth they use.

bps (Bits Per Second) - A measure of data transmission rate in serial transmission.

Bridge - A device interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.

Bridging - Interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.

Broadband - Wideband technology capable of supporting voice, video and data, possibly using multiple channels.

BSC (Base Station Controller) - Provides the intelligence behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, and controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control is in part the responsibility of the anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilization) become reduced to a smaller number of connections towards the mobile switching center (MSC) with a high level of utilization.

BTS {Base Transceiver Station) - The equipment which facilitates the wireless communication between a user’s handset and the network. BTS can also be referred to as RBS (radio base station), Node B (in 3G networks) or simply BS (base station). Typically a BTS will have several transceivers (TRXs), which allow it to serve several different frequencies and different sectors of the cell. The BTS includes equipment for encrypting and decrypting communications with the base station controller (BSC).

Buffer - A storage device. Commonly used to compensate for differences in data rates or event timing when transmitting from one device to another. Also used to remove jitter.

Buffering - Used to compensate for differences in data rates or event timing when transmitting from one device to another. Also used to remove jitter.

Bus - A transmission path or channel. A bus is typically an electrical connection with one or more conductors, where all attached devices receive all transmissions at the same time.

Byte - A group of bits (normally 8 bits in length).

Carrier - A continuous signal at a fixed frequency that is capable of being modulated with a second (information carrying) signal.

Carrier Ethernet- Carrier Ethernet is a ubiquitous service based on standardized equipment and protocols providing seamless connectivity between high speed Ethernet-based LANs and WANs. Carrier Ethernet is characterized by industry-defined attributes for service level agreements, provisioning, system-wide management, and carrier-class OAM. Originally implemented in the core network, Carrier Ethernet is now being extended to the edge and access segment.

CAS (Channel Associated Signaling) - Voice signaling based on bits taken from voice timeslots, used by many PBXs.

CAT-3 (Category 3 UTP) - Unshielded Twisted Pair standard, commonly used with ATM for cell transmission at low speeds up to 25 or 51 Mbps at very short distances (few hundred meters).

CAT-5 (Category 5 UTP) - Unshielded Twisted Pair standard, commonly used with ATM interfaces for higher-speed cell transmission (more than 50 Mbps).

CBR (Constant Bit Rate) - One of the five ATM classes of service. CBR supports the transmission of a continuous bit-stream of information, such as voice and video traffic, which require a constant amount of bandwidth allocated to a connection for the duration of the transmission.

CC (Continuity Cell) - A cell used periodically to check whether a connection is idle or has failed. Continuity checking is one of the OAM function types for fault management.

CCS 7 (Common Channel Signaling Version 7) - Also known as Signaling System 7 (SS7), a network standard that transmits call-handling information for telecom calls over a separate channel than that taken by the calls.

CCS Compression (Common Channel Signaling Co) - Signaling information is transported out-of-band. CCS compression takes advantage of the idle flags between HDLC formatted messages to reduce signaling bandwidth required.

CCS Transparency - Passes the out-of-band signaling channel transparently with no compression or store-and-forward delay characteristics.

CD (Carrier Detect) - A modem interface signal indicating to an attached terminal that the local modem is receiving a signal from the remote modem.

CDP (Conditional Di-Phase) - A digital encoding technique that is a variant of Manchester encoding, and is not sensitive to polarity of wires (wires in a pair can be crossed).

CDR (Call Detail Recording) - A device and method used to record statistics about telephone calls such as the number dialed, cost of the call extension from which the call was made, duration of the call, and trunk or trunk group used to place the call.

CDV (Cell Delay Variation) - A QoS parameter that measures the difference between the transfer delay of a single cell (CTD) and the expected transfer delay. This parameter is important for time-sensitive virtual circuits such as CBR and VBR-RT.

CDVT (Cell Delay Variation Tolerance) - Used in CBR traffic, it specifies the acceptable tolerance of the CDV (jitter).

Cell - The 53-byte basic information unit within an ATM network. The user traffic is segmented into cells at the source and reassembled at the destination. An ATM cell consists of a 5-byte ATM header and a 48-byte ATM payload, which contains the user data.

Central Office (CO) - Telephone company switching office. This is where you would find the local telco switch that connects to your telephone.

Central Office Line - The link connecting a station to a central office.

Central Office Trunk - The link connecting a central office to a PBX or another switch.

CER (Cell Error Rate) - A QoS parameter that measures the number of transmitted cells that are erroneous over a specific period of time (i.e., those that contain errors when they arrive at the destination).

Channel - A path for electrical transmission between two or more points. Also called a link, line, circuit or facility.

Channel Bank - Equipment that connects multiple voice channels to high speed links by performing voice digitization and Time Division Multiplexing. Voice is converted to a 64 kbps signal (24 channels into 1.544 Mbps in countries offering T1 services, such as the U.S.A.; 30 channels into 2.048 Mbps in countries offering E1 services, such as in Europe).

Channelized ATM STM-1 - An STM-1 ATM circuit, which can handle VC-12 traffic individually or in bundles via the SDH network

Channelized T1/E1 - T1 or E1 service that is divided into individual 64 kbps channels (or channels that are multiples of 64 kbps such as a 256 kbps channel made from four 64 kbps channels), as opposed to unchannelized service, which uses the entire bandwidth of the T1 (1.544 Mbps) or E1 (2.048 Mbps). Channelized T1 or E1 lines can consist of switched lines with in-band signaling or leased lines.

Characteristic Impedance - The termination impedance of an electrically uniform transmission line.

CI (Congestion Indicator) - A field in the RM-cell that indicates congestion in the network which can ultimately lead to the source reducing its allow cell rate (ACR).

CIF (Cell Information Field) - The payload (48 bytes) of the ATM cell.

CIR (Committed Information Rate) - A term used in Frame Relay, which defines the information rate that the network is committed to provide to the user, under any network conditions.

Circuit Emulation - A connection over a virtual circuit-based network providing service to the end users that is indistinguishable from a real point-to point, fixed-bandwidth circuit. Services based on circuit emulation (Circuit Emulation Services or CES) offer traditional TDM trunking (at n x 64 kbps, fractional T1/E1, T1/E1 or T3/E3) over a range of transport protocols, including ATM, Internet Protocol (IP), MPLS and Ethernet.

Circuit Emulation Service - New technology for offering circuit emulation services over packet-switched networks. The service offers traditional TDM trunking (at n x 64 kbps, fractional E1/T1, E1/T1 or E3/T3) over a range of transport protocols, including Internet Protocol (IP), MPLS and Ethernet.

Clock - A term for the source(s) of timing signals used in synchronous transmission.

CO (Central Office) - Telephone company switching office. This is where you would find the local telco switch that connects to your telephone.

CODEC (Coder/Decoder) - An audio codec converts analog audio signals to digital signals for transmission over digital circuits, and then converts the digital signals back to analog signals for reproduction.

Composite Link - The line or circuit carrying multiplexed data which connects a pair of multiplexers or concentrators. Also called aggregate or main link.

Compression - Any of several techniques that reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.

Concentrator - Device that serves as a wiring hub in star-topology network. Sometimes refers to a device containing multiple modules of network equipment.

Configuration Planner - RADview configuration planner makes it possible to configure products in advance, without having to connect to a physical product.

Congestion - A state in which the network is overloaded and starts to discard user data (frames, cells or packets).

Congestion control - A resource and traffic management mechanism to avoid and/or prevent excessive situations (buffer overflow, insufficient bandwidth) that can cause the network to collapse. In ATM networks, congestion control schemes may be based on fields within the ATM cell header (CLP, EFCI within the PTI) or may be based on a more sophisticated mechanism between the ATM end-system and ATM switches. The ATM Forum has developed a mechanism based on rate control for ABR-type traffic. In Frame Relay networks, congestion is handled by the FECN, BECN and DE bits.

Constant Bit Rate - See CBR.

Contention - A condition arising when two or more data stations attempt to transmit at the same time using the same link or channel.

Control Characters - In communications, any extra transmitted characters used to control or facilitate data transmission (for example, characters associated with polling, framing, synchronization, error checking, or message delimiting).

Control Signals - Signals passing between one part of a communications system and another (such as RTS, DTR, or DCD), as part of a mechanism for controlling the system.

CORBA - The acronym for Common Object Request Broker Architecture, OMG's open, vendor-independent architecture and infrastructure that computer applications use to work together over networks. One of its most important uses is in servers that must handle large number of clients, at high hit rates, with high reliability, such as network management systems.

CPE (Customer Premises Equipment) - Generally refers to communications equipment located at the customers' premises for use with communication service providers' services. In some cases, these are customer-owned or leased; in other cases, these are the property of the service provider.

CRC (Cyclic Redundancy Check) - A data transmission error-detection scheme. A polynomial algorithm is performed on the data, and the resultant checksum is appended at the end of the frame. The receiving equipment performs a similar algorithm.

Cross Connect

A network device used by telecom carriers and large enterprises to switch and multiplex low-speed voice and data signals onto high-speed lines and vice versa. It is typically used to aggregate several E1/T1 lines into a higher-speed electrical or optical line as well as to distribute signals to various destinations.

Crosstalk - An undesirable condition that happens when a communication from one line can be heard on another independent line. This is usually caused by inductive or capacitive coupling, or by an electrical short circuit between adjacent lines.

CSMA/CD (Carrier Sense Multiple Access/Collision Detection) - In this protocol, stations listen to the bus and only transmit when the bus is free. If a collision occurs, the packet is retransmitted after a random timeout. CSMA/CD is used in Ethernet.

CSU (Channel Service Unit) - Equipment installed on customer premises at the interface to phone company lines to terminate a DDS or T1 circuit. CSUs provide network protection and diagnostic capabilities.

CSU/DSU (Channel Service Units/Data Service Units) - CSUs and DSUs are usually grouped together. They convert carrier line signals to digital signals.

CTS (Clear To Send) - A modem interface control signal from the data communications equipment (DCE) indicating to the data terminal equipment (DTE) that it may begin data transmission.

Current Loop - Method of data transmission. A mark (binary “1”) is represented by current on the line, and a space (binary “0”) is represented by the absence of current.

 Glossary

A - C

D - F

G - K

L - O

P - S