| CA | Cell Arrival |
| CAC | Connection Admission Control. An ATM function which determines whether a virtual circuit ( VC) connection request should be accepted or rejected. |
| CBDS | Connectionless Broadband Data Service |
| CBR | Constant (or Continuous) Bit Rate. One of the five ATM classes of service, which supports the transmission of a continuous bit-stream of information where traffic, such as voice and video, needs to meet certain QoS requirements (see also QoS Classes). |
| CBR interactive | Constant Bit Rate interactive |
| CBR non-interactive | Constant Bit Rate non interactive |
| CC | Continuity Cell. A cell used periodically to check whether a connection is idle or has failed (i.e. at the cross-connect nodes), in order to guarantee a continuation in the flow of the information cells. Continuity checking is one of the OAM function types for fault management (see also AIS, RDI). |
| CCITT | Consultative Committee on International Telegraphy and Telephony. A standards and specifications body whose published recommendations cover a wide spectrum of areas which include definition of terms, basic principles and characteristics, protocol design, description of models and other specifications. Currently known as ITU-T. |
| CCR | Current Cell Rate. A field in the RM cell header that indicates the current complying cell rate a user can transmit over a virtual connection ( VC). |
| CCS | Common Channel Signaling |
| CCSS7 | Common Channel Signaling System 7 |
| CDT | Cell Delay Tolerance |
| CDV | Cell Delay Variation. A QoS parameter that measures the difference between a single cell's transfer delay (CTD) and the expected transfer delay. It gives a measure of how closely cells are spaced in a Virtual Circuit ( VC). CDV can be introduced by ATM multiplexers ( MUXs) or switches. |
| CDVT | Cell Delay Variation Tolerance. Used in CBR traffic it specifies the acceptable tolerance of the CDV (jitter). |
| CEI | Connection Endpoint Identifier |
| CER | Cell Error Rate. A QoS parameter that measures the fraction of transmitted cells that are erroneous (they have errors when they arrive at the destination). |
| CES | Circuit Emulation Service. An ATM provided class of service, where TDM-type, constant-bit-rate (CBR) circuits are emulated by the AAL1. |
| CI | Congestion Indication. A bit in the RM cell to indicate congestion (it is set by the destination if the last cell received was marked). |
| CIF | Cell Information Field. The payload (48 bytes) of an ATM cell. |
| CIP | Carrier Identification Parameter |
| CIR | Committed Information Rate. A term used in Frame Relay, which defines the information rate the network is committed to provide the user with, under any network conditions. |
| CL | Connectionless |
| CLNAP | Connectionless Network Access Protocol |
| CLNP | Connectionless Network Protocol |
| CLNS | Connectionless Network Service |
| CLP | Cell Loss Priority. A 1-bit field in the ATM cell header that corresponds to the loss priority of a cell. Lower priority (CLP = 1) cells can be discarded under congestion situations. |
| CLR | Cell Loss Ratio. A QoS parameter that gives the ratio of the lost cells to the total number of transmitted cells. |
| CLS | Connectionless Server |
| CLSF | Connectionless Service Function |
| CME | Component Management Entity |
| CMI | Coded Mark Inversion |
| CMIP | Common Management Information Protocol. An ITU-T-defined management interface standard that can support administration, maintenance and operation information functions (see also OAM&P). |
| CMR | Cell Misinsertion Rate. A performance measure that is defined as the number of misinserted cells (those that arrive from the wrong source) per (virtual) connection second. |
| CN | Copy Network |
| CNM | Customer Network Management |
| CO | Connection Oriented |
| COD | Connection Oriented Data |
| COM | Continuation of Message. A PDU that is part of a message. |
| COS | Class of Service. See QoS Classes. |
| CP | Connection Processor |
| CPCS | Common Part Convergence Sublayer. Part of the AAL convergence sublayer (CS). It has always to be present in the AAL implementation. Its task is to pass primitives to the other AAL sublayers ( SAR, SSCS). It supports the functions of the standardized Common Part AALs: AAL1, AAL3/4 and AAL5. |
| CPE | Customer Premises Equipment. Computer and communications equipment (hardware and software) used by a carrier's customer and located at the customer's site (see also DTE). |
| CPG | Call Progress Message |
| CPI | Common Part Indicator. A one-byte field in the header of the CPCS-PDU in AAL3/4 that indicates the number of bits the BASize field consists of. |
| CPN | Customer Premises Network |
| CPN | Calling Party Number |
| Crankback IE | Crankback - Information Element |
| CRC | Cyclic Redundancy Check. A bit-errors detection technique that employs a mathematical algorithm, where, based on the transmitted bits, it calculates a value attached to the information bits in the same packet. The receiver using the same algorithm recalculates that value and compares it to the one received. If the two values do not agree the transmitted packet is then considered to be in error. |
| CRCG | Common Routing Connection Group |
| CRF(VC) | Virtual Channel Connection Related Function |
| CRF(VP) | Virtual Path Connection Related Function |
| CRM | Cell Rate Margin. A measure of the residual useful bandwidth for a given QoS class, after taking into account the SCR. |
| CS | Convergence Sublayer. The upper half of the AAL. It is divided into two sublayers, the Common Part (CPCS) and the Service Specific ( SSCS). It is service dependent and its functions include manipulation of cell delay variation (CDV), source clock frequency recovery, forward error correction ( FEC). Though each AAL has its own functions, in general the CS describes the services and functions needed for conversion between ATM and non-ATM protocols (see also SAR). |
| CS1 | Capability Set One |
| CS2 | Capability Set Two |
| CSI | Convergence Sublayer Indication |
| CSPDN | Circuit Switched Public Data Network |
| CSR | Cell Missequenced Ratio. A performance measure that is defined as the number of missequenced cells (those that arrive in the wrong order) per (virtual) connection second. |
| CSU | Channel Service Unit |
| CTD | Cell Transfer Delay. A QoS parameter that measures the average time for a cell to be transferred from its source to its destination over a virtual connection (VC). It is the sum of any coding, decoding, segmentation, reassembly, processing and queueing delays |
| CTV | Cell Tolerance Variation |
| DA | Destination MAC address |
| DA | Destination Address |
| DCC | Data Country Code |
| DCE | Data Communication Equipment |
| DD | Depacketization Delay |
| DLC | Data Link Control |
| DES | Destination End System |
| DLCI | Data Link Connection Identifier |
| DMDD | Distributed Multiplexing Distributed Demultiplexing |
| DN | Distribution Network |
| DQDB | Distributed Queue Dual Bus. The IEEE 802.6 standard is a MAN, protocol based on 53-byte packets that can support connectionless and connection-oriented, isochronous integrated services. It is implemented as two unidirectional buses configured in a physical ring topology. |
| DS | Distributed Single Layer Test Method |
| DS-0 | Digital Signal 0. Physical interface for digital transmission at the rate of 64 Kbps. |
| DS-1 | Digital Signal 1. Physical interface for digital transmission at the rate of 1.544 Mbps. Also, known as a T-1 standard, it can simultaneously support 24 DS-0 circuits. |
| DS-2 | Digital Signal 2. Physical interface for digital transmission at the rate of 6.312 Mbps. |
| DS-3 | Digital Signal 3. Physical interface for digital transmission at the rate of 44.736 Mbps. |
| DS3 PLCP | Physical Layer Convergence Protocol |
| DSE | Distributed Single Layer Embedded Test Method |
| DSID | Destination Signaling Identifier |
| DSS2 | Setup Digital Subscriber Signaling #2 |
| DSU | Data Service Unit. Equipment at the user end that acts as a telephony-based interface between low-rate (i.e. 56 kbps) services and higher rate circuits. |
| DTE | Data Terminal Equipment |
| DTL IE | DTL - Information Element |
| DXI | Data Exchange Interface. A frame-based ATM interface between a DTE (such as a router or a local switch) and a DCE. DXI interfaces to the ATM UNI and has been chosen by the ATM Forum as an affordable solution for providing ATM capabilities over WAN. |