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.
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.
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).
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.
AWG - The American Wire Gauge System, which specifies wire width.
B
Backhaul - Transporting traffic between distributed sites (typically access points) and more centralized points of presence. See Cellular Backhaul.
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.
Best effort - A QoS class in which no specific traffic parameters and no absolute guarantee are provided. Best effort includes UBR and ABR.
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.
Bridge - A device 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.
C
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.
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.
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.
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.
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.
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.
Glossary
