• AAL (ATM Adaptation Layer):

    AAL is the rules for breaking up a higher level protocol data unit (PDU) into ATM cells for transmission on the network, and for reassembling the PDU at the other.

  • ABR (Available Bit Rate):

    An ATM service class where the network makes a "best effort" to meet the application's bandwidth requirements. It differs from UBR in that it uses a feedback mechanism whereby the network informs a source of an acceptable transmission rate. If the source complies, the network guarantees a low CLR.

  • ACR (Allowed Cell Rate):

    The rate at which an end system is permitted to send, determined by the rate contained within the ABR RM cells.

  • AFI (Authority and Format Identifier):

    The AFI field identifies the type of address used in the DSP

  • AHFG (ATM Host Functional Group):

    ATM-connected host within MPOA.

  • ANSI (American National Standards Institute):

    A US standards organization. ANSI may submit proposals to the ITU.

  • ARP (Address Resolution Protocol):

    Internet protocol used to map an IP address to a MAC address. It allows host computers and routers to determine the data link layer addresses through the ARP Request and ARP Response process.

  • ATM (Asynchronous Transfer Mode):

    A switching and multiplexing technology based on the segmentation of voice, video, and data traffic into equal length cells which are then interleaved over a physical connection in a time-asynchronous manner. This contrasts with TDM where different traffic sources are assigned fixed timeslots.

  • ATM address:

    An end system identifier based either on the ISDN-format E.164 address for public ATM networks or on an NSAP-format address for private ATM.

  • ATM ARP:

    The address resolution mechanism between an ATM end system and an RFC 1577 (Laubach, 1993) ATM address resolution server. The ATM ARP is used to resolve IP network layer addresses to ATM addresses. ATM ARP servers will evolve to NHRP servers.

  • ATM DSU (Data Service Unit):

    A unit external to an ATM end system used to convert between the HDLC-based ATM DXI and the ATM UNI by segmenting data frames into ATM cells.

  • ATM Forum:

    A multivendor organization with the task of adapting international standards into implementation agreements, or developing standards where none exist. The organization consists of equipment vendors, service providers, research organizations, and end users.

  • ATM layer:

    The layer between the AAL and the physical layer containing ATM cells. This is where switching of ATM cells is accomplished

  • ATM switch:

    Intermediate system optimized to switch ATM cells. Divided into four classes: workgroup, campus/enterprise, central office access, and central office. The latter three classes are usually equipped with multiservice interfaces, such as circuit emulation, frame forwarding, and sometimes video.

  • B-ICI (Broadband Inter-Carrier Interface):

    The ATM trunking interface between two service providers.

  • B-ISDN:

    Broadband ISDN. A high-speed network providing voice, data, and video services which evolved from ISDN. ATM was chosen by the ITU-T as the technology to deliver B-ISDN.

  • B-ISUP (Broadband ISDN User's Part):

    A SS7 protocol which defines the signaling messages to control connections and services. It is used to establish, maintain and release broadband switched network connections accross an SS7/ATM network.

  • BT (Burst Tolerance):

    The number of cells which an ATM source may send back-to-back. When discussing CAC, this is the depth of the second leaky bucket.

  • BUS:

    (Broadcast and Unknown Server). A component within LANE which receives and then retransmits all broadcast, multicast, and unknown traffic over the ELAN.

  • CAC (Connection Admission Control):

    Actions taken by the ATM network to accept or reject a connection request based on its QoS requirements, and then to route this connection across the network.

  • CBR (Constant Bit Rate):

    An ATM service class providing for the support of constant bit streams such as those generated by PABXs. The CBR class specifies a PCR, CDV, and CLR, thus guaranteeing bandwidth and QoS.

  • CCITT (Comite Consultatif International Telegraphique et Telephonique):

    Consultative Committee on International Telegraphy and Telephony.

  • CCR (Current Cell Rate):

    The currently acceptable transmission rate for an end system as defined by RM cells within ABR.

  • CCS (Common Channel Signaling);

    Voice signaling based on use of a separate signaling channel, used by ISDN PABXs.

  • CDV (Cell Delay Variation):

    A QoS parameter specifying the variance in delay between ATM cells. The maximum acceptable CDV is referred to as the Cell Delay Variation Tolerance, or CDVT.

  • Cell:

    The 53-byte basic information unit within an ATM network. An ATM cell consists of a 5-byte ATM header containing address information and a 48-byte ATM payload which contains the user data.

  • CER (Cell Error Ratio):

    Ratio of errored cells to total cells across a VCC or VPC.

  • CES (Circuit Emulation Service):

    ATM Forum service supporting VCCs which emulate a CBR dedicated circuit.

  • CI (Congestion Indicator):

    Field within RM cell set by destinations to 1 informing the source to decrease its ACR.

  • Classical IP and ARP over ATM:

    A standardized model where ATM acts as a high-quality link layer transport for higher-layer protocols. The Classical model is defined in RFCs 1577 (Laubach, 1993) and 1483 (Heinanen, 1993), and was the first deployed ATM architecture.

  • CLP (Cell Loss Priority):

    A one-bit field in the ATM cell header specifying whether or not the cell is more (CLP=1) or less (CLP=0) likely to be discarded by an ATM network experiencing congestion.

  • CLR (Cell Loss Ratio):

    Ratio of lost cells to total cells transmitted across a VCC or VPC.

  • Congestion control:

    A method by which congestion across the ATM network is reduced. Congestion control schemes may be based on fields within the ATM cell header (CLP, EFCI within the PTI) or may be based on more sophisticated mechanisms between ATM end systems and ATM switches. The ATM Forum has developed a mechanism based on rate control for ABTJ-type traffic.

  • Connectionless service:

    A service where no end-to-end connection is established. Instead, all data is sent over a VC to a connectionless server, which then establishes a connection to the destination. Switched Multimegabit Data Service (SMDS) and Connectionless Broadband Data Service (CBDS) over AAL3/4 are two examples of this service.

  • Connection-oriented services:

    An end-to-end connection is signalled and established prior to data transmission. Classical IP over ATM using AAL5 is an example of a connection-oriented service.

  • CPCS (Common Part Convergence Sublayer):

    A sublayer within the ATM AAL providing for packet framing and error detection. Used by all services which use the specific AAL.

  • CPE (Customer Premise Equipment):

    A term for the networking equipment located at the customer's site.

  • CRC (Cyclic Redundancy Check):

    A checksum appended to CS-PDUs to ensure that the upper-layer data has not been corrupted.

  • CRS (Cell Relay Service):

    Most basic of ATM services supporting the exchange of cells between ATM-connected end systems.

  • CS (Convergence Sublayer):

    The sublayer of the ATM AAL where traffic is adapted based on its type before undergoing segmentation into cells (SAK process). The CS includes the CPCS and the SSCS.

  • CS-PDU (Convergence Sublayer Protocol Data Unit):

    The information frame generated by the CS before undergoing SAR.

  • CS-PDU (Convergence Sublayer Protocol Data Unit):

    The information frame generated by the CS before undergoing SAR.

  • CTD (Cell Transfer Delay):

    Average transit delay of cells across a VCC or VPC.

  • CUG (Closed User Group):

    Secure grouping of users within a community of interest. May be at Layer 2 (ATM, Frame Relay) or Layer 3 (Tag, Access Lists).

  • DS-0 (Digital Signal Level 0):

    64 Kbps level of North American Digital Hierarchy.

  • DS-1 (Digital Signal Level 1):

    1.544 Mbps level of North American Digital Hierarchy, supporting 24 DS-0 signals. Sometimes called Tl.

  • DS-3 (Digital Signal Level 3):

    44.736 Mbps level of North American Digital Hierarchy, supporting 28 DS-1 signals. Sometimes called T3.

  • DSS2 (Digital Subscriber Signaling System #2):

    B-ISDN UNI signaling.

  • DTE (Data Terminal Equipment):

    Equipment at the customer end of a circuit. The network end is sometimes called the DCE.

  • DTL (Designated Transit List):

    PNNI-generated list of ATM switches to be transited across an ATM network.

  • DXI (Data Exchange Interface):

    An HDLC-based ATM interface defined between a packet-based ATM end system and an external ATM DSU supporting the ATM UNI.

  • El (European Signal Level 1):

    2.048 Mbps transport rate within the European PDH hierarchy, supporting 32 x 64 Kbps channels.

  • E-2 (European Signal Level 2):

    8.192 Mpbs transport rate within the European PDH hierarchy, supporting 4 E-l signals. E-2 is not widely deployed.

  • E-3 (European Signal Level 3):

    34.368 Mbps transport rate within the European PDH hierarchy, supporting 16 E-l or 4 E-2 signals. At high data rates, E-4 at 140 Mbps is also defined.

  • EFCI (Explicit Forward Congestion Indication):

    Bit in PTI field of the ATM cell header which may be set by a switch under times of congestion. The EFCI is one form of ABR service.

  • ELAN (Emulated LAN):

    The ATM segment of a Virtual LAN (VLAN) based on the ATM Forum LANE standard. A VLAN consists of an ELAN segment along with traditional (sometimes called 'legacy7) LAN segments.

  • ER (Explicit Rate Mode):

    One form of feedback under ABR service which defines the rate at which the end system may transmit. A switch supporting this mode will indicate this rate in either forward or backward Resource Management cells.

  • ETSI (European Telecommunications Standards Institute):

    Develops standards for use by service providers within Europe.

  • GCAC (Generic Connection Admission Control):

    A form of CAC used by PNNI when routing a connection request.

  • GFC (Generic Flow Control):

    A four-bit field within the ATM cell header which may be used to identify whether or not an ATM system implements congestion control. At present, the GFC field is unused.

  • header:

    The first five bytes of an ATM cell containing a VC identifier consisting of a VPI and a VCI, along with fields for HEC, CLP, GFC, CRC, and PTI.

  • HEC (Header Error Control):

    A one-byte field within the ATM cell header providing for error detection. If an error is detected, the cell will be discarded before undergoing re-

  • ICR (Initial Cell Rate):

    The rate at which an ABR end system will begin transmitting before receiving the ER via RM cells.

  • IDI (Initial Domain Identifier):

    The initial domain identifier (IDI) field identifies which domain the DSP part belongs to.

  • IDP (Initial Domain Part):

    Initial domain part. The IDP part of an NSAP identifies which national or international group has defined the NSAP format for a given NSAP. It is partitioned into two parts, the authority format identifier (AFI) and the initial domain identifier (IDI). IDP spaces are managed by organizations such as AFNOR, ANSI and NIST.

  • IEEE (Institute of Electrical and Electronics Engineers):

    The Institute of Electrical and Electronics Engineers is a professional organization whose activities include the development of communications and network standards.

  • ILMI (Integrated Local Management Interface):

    The Integrated Local Management Interface provides a mechanism by which ATM-attached devices, such as hosts, routers, and ATM switches are able to transfer management information. It is based on SNMP (Simple Network Management Protocol).

  • I-PNNI (Integrated Private Network-Network Interface):

    Use of PNNI for both ATM and Layer 3 routing.

  • ISDN (Integrated Services Digital Network):

    International digital network supporting voice, video, and data over multiples of 64 Kbps circuits.

  • ITU (International Telecommunications Union):

    International standards body including all PTTs under UN treaty. The group responsible for communications standards is the ITU Telecommunications Standards Sector (TSS), formerly the CCITT.

  • LANE (LAN Emulation or LAN Emulation Service):

    An ATM Forum standard providing for the support of native LAN protocols across an ATM network by emulating the MAC protocol. LANE defines a single Virtual LAN (VLAAO consisting of traditional LAN segments and an Emulated LAN (ELAN) segment across the ATM network. Routers will connect multiple VLANs. LANE provides for ATM-attached systems acting as LECs communicating with an LECS, LES, and BUS across an ELAN.

  • LEC (LAN Emulation Client):

    The LANE process residing in LAN switches, routers, PCs, and workstations attached to the LAN Emulation Service. This provides VLAN functionality to non-ATM-aware end systems residing on traditional LAN segments connected to LAN switches and routers.

  • LECS (LAN Emulation Configuration Server):

    A component within LANE providing basic configuration information for a LEC that wishes to participate in LANE, allowing network administrators to control which LECs may join which VLANs. The most basic information returned to the LEC is the location of the LES.

  • LES (LAN Emulation Server):

    A server function within LANE providing for LEC registration, MAC to ATM address resolution, and security management of a VLAN.

  • LNNI (LAN Emulation Network-to-Network Interface):

    The interface between two or more servers within LANEv2.

  • MBS (Maximum Burst Size):

    The number of cells at the peak cell rate which may traverse an ATM VC.

  • MCR (Minimum Cell Rate):

    The minimum transmission rate which the network guarantees to an ABB. end system. This equates to a field in the RM cell below which the ER may not be set.

  • MCTD (Mean Cell Transfer Delay):

    The average delay for ATM cells across an ATM connection.

  • MPC (MPOA Client):

    Edge device (LAN switch, router, or host) within MPOA network.

  • MPLS (Multi-Protocol Label Switching):

    Method of integrating IP and ATM more closely through label swapping. Operates 'connectionless' rather than signaling end-to-end connections.

  • MPOA (Multiprotocol over ATM):

    Standard which defines how routers, LAN switches, and hosts running multiple Layer 3 protocols may optimize forwarding paths and multicasting across ATM while taking advantage of ATM QoS capabilities.

  • MPS (MPOA Server):

    Controlling entity within an MPOA domain; handles routing, registration, and address resolution.

  • NIC (ATM Network Interface Card):

    Network Interface Card is a term used to describe a peripheral circuit board or card installed in a computer that facilitates connection to a LAN. NICs may implement networking technology such as ATM, Ethernet, or token ring. NICs connect to some shared medium, such as an Ethernet cable, or they may connect to a switch.

  • N-ISDN (Narrowband Integrated Services Digital Network):

    Predecessor to the B-ISDN, N-ISDN encompasses the original standards for the ISDN.

  • NHRP (Next Hop Resolution Protocol):

    A protocol optimizing routing across NBMA networks, allowing end systems to open VCs across LIS boundaries.

  • NLPID (Network Level Protocol ID):

    The NLPID field designates what encapsulation or what protocol follows.

  • NNI (Network-Node Interface or Network-to-Network Interface):

    The NNI is better characterized as a switch-to-switch interface. The ATMF has defined a Private-NNI (P-NNI) to connect switches within a single management domain. The B-ICI may also be considered as a class of the NNI, though between service providers.

  • OSI reference model:

    A seven-layer reference model for internetworking. Each layer interacts only with the layers directly below and above it; layers interact virtually between end systems which are connected by intermediate systems. The layers are physical, data link, network, transport, session, presentation, and application.

  • Payload:

    The 48-byte segment of the ATM cell containing user data. Any adaptation of user data via the AAL will take place within the payload.

  • PBX (Private Branch Exchange):

    A CPE telephone exchange which may be connected to the traditional N-ISDN network or to an ATM CES.

  • PCR (Peak Cell Rate):

    The maximum cell transmission rate within a VC.

  • PDH (Plesiochronous Transmission Hierarchy):

    A public transmission hierarchy based on a non-synchronous alignment of octets at different levels of multiplexing. PDH is only bit-synchronous. PDH networks are in the process of being replaced with SDH networks. Examples of PDH transmission rates include El and E3.

  • PDU (Protocol Data Unit):

    The basic unit of information at a layer of the networking stack which is exchanged with a peer entity which contains control information and user data.

  • PHY (Physical Layer):

    The layer of the protocol stack where the ATM layer is encapsulated for transmission over a given physical medium. The physical layer consists of a medium-independent sublayer providing convergence and a medium-dependent sublayer tied to a given physical medium type and rate.

  • PNNI (Private Network-Network Interface):

    The interswitch interface within a private ATM domain. The PNNI trunking protocol providing for hierarchical ATM-layer routing and QoS support.

  • PTI (Payload Type Identifier):

    A three-bit field within the ATM cell header indicating the AAL used, whether congestion has been experienced (EFCD, and whether or not the cell contains OAM information. When an AAL5 frame passes through SAR, the PTI within the last cell identifies the end of this AAL5 frame.

  • PVC (Permanent Virtual Circuit):

    A preconfigured logical connection between two ATM systems. This contrasts with SVCs.

  • Quality of Service (QoS):

    The requirements of an ATM VC in terms of bandwidth, cell loss, delay, and jitter.

  • RFC 1483 (Multiprotocol Encapsulation over ATM Adaptation Layer 5):

    Specifies the encapsulation of multiprotocol data for transmission over an ATM network. RFC 1483 makes use of AAL5 in the support of PVCs and SVCs. The two methods defined in this RFC are VC muxing (each protocol uses its own VC) and LLC/SNAP encapsulation (different protocols are identified by a different LLC/SNAP header and are sent over the same VC).

  • RFC 1577 (Classical IP and ARP over ATM):

    Specifies an architecture for the support of IP over ATM, also defining an ATM ARP server. RFC 1577 relies on RFCs 1483, 1626, and 1755.

  • RFC 1626 (IP MTU over ATM AAL5):

    Defines a 9180-octet Maximum Transmission Unit (MTU) over ATM.

  • RFC 1755 (ATM Signaling Support for IP over ATM):

    Specifies the method of signaling SVCs within the Classical model.

  • RM (Resource Management Cell):

    Special ATM cell used to regulate traffic flow within the ABR service.

  • Router:

    An intermediate system within an internetwork capable of generating Layer 3 (network layer) forwarding information by running a routing protocol (IS-IS, OSPF, E-IGRP, and so on) and then forwarding data packets based on this information.

  • Routing:

    Layer 3 (network layer) forwarding of datagrams based on a calculated routing table.

  • SAR (Segmentation and Reassembly Sublayer):

    The sublayer where PDUs are segmented and rebuilt into/from ATM cells.

  • SAR-PDU (Segmentation and Reassembly Protocol Data Unit):

    Information which has been segmented by the SAR sublayer.

  • (Sustainable Cell Rate):

    The maximum burst rate which a VC may maintain.

  • SDH (Synchronous Digital Hierarchy):

    A transmission hierarchy based on a synchronous alignment of bits at different levels of multiplexing. Though originally deployed in public networks as a replacement for the older PDH, SDH is now deployed within local ATM networks. An example of an SDH transmission rate is STM-1.

  • Signaling:

    The procedure used to establish a connection over the ATM network. Signaling within ATM is based on Q.2931; this has been adapted by the ATM Forum as UNI 3.1./4.0. Some signaling- implementations are also based on UNI 3.0 derived from an earlier ITU draft.

  • SNMP (Simple Object Access Protocol):

    SNMP is an IETF protocol used for network management. Even though SNMP is one of the TCP/IP protocols, it is not restricted to use in TCP/IP networks. The success of SNMP is mostly due to its simplicity and lightweight features. The managed objects supported by a given device are encoded in its MIB or schema description. SNMP entities include managers and agents (both proxy and non-proxy), and a simple messaging protocol is used between these entities. Operations from the manager side include set (modify) and get (retrieve), and agents can respond these with reference to a security framework. Agents can also issue notifications or traps to manager in order to indicate important events.

  • SONET (Synchronous Optical Network):

    The North American variant of the SDH. An example of a SONET transmission rate is STSSc.

  • SSCS (Service-Specific Convergence Sublayer):

    A sublayer within the AAL relating to the type of data traffic. The resulting PDU will be service (for example, SMDS or Frame Relay) dependent.

  • STM (Synchronous Transfer Mode):

    A transmission technology whereby different data streams always receive the same bandwidth when combined over a single physical connection. STM is Time Division Multiplexing (TDM).

  • SVC (Switched Virtual Circuit):

    A logical ATM connection established via signaling. End systems transmit their UNI 3.1, or 4.0 signaling request via the Q.2931 signaling protocol.

  • Switched LAN:

    Replacement of a shared hub by LAN switches where each user or segment is provided with the full LAN bandwidth. Requires no end system changes.

  • Tag Switching:

    Label swapping technique originally proposed by Cisco Systems; evolving into MPLS.

  • TC (Transmission Convergence Sublayer):

    A sublayer within the physical layer where cells are prepared for transmission by the PMD sublayer.

  • TDM (Time Division Multiplexing/Multiplexer):

    Method of combining multiple lower-speed signals into a higher rate by placing each channel within a known timeslot. TDMs form the core of many enterprise internetworks, and are being replaced by ATM.

  • Traffic shaping:

    Control by an end system of originating traffic parameters such as average bandwidth, peak bandwidth, burst, and CLP in order to meet the traffic contract.

  • UBR (Unspecified Bit Rate):

    Service type where user requests a PCR but has no guarantees as to throughput, latency, or CLR. UBR is 'best effort' service. A form of UBR where we specify a MCR is known as UBR+ (not to be confused with UBR + TPD/EPD).

  • UNI (User-Network Interface):

    The interface between an ATM switch and an ATM-capable end system. Requirements for the UNI are defined by the ATM Forum in a series of standards, the most recent being UNI 4.0.

  • UPC (Usage Parameter Control):

    Actions taken by an ATM network to monitor and control traffic. This protects the network and its service guarantees from sources which unintentionally or intentionally violate their traffic contract.

  • UTOPIA (Universal Test and Operation Physical Interface for ATM):

    A physical layer interface between ATM devices.

  • VBR (Variable Bit Rate):

    Traffic containing bursts but centered around an average bandwidth. VBR, divided into real-time (rt-VBR) and non-real-time (nrt-VBR) traffic requires the same service guarantees (that is, delay, cell loss, and timing) which are provided by CBR.

  • VC (Virtual Channel or Virtual Connection):

    A connection between two ATM systems. When used for data, a single VC may support one or many network layer protocols. Multiple Virtual Channels share a Virtual Path, and may be concatenated into a VCC.

  • VCC (Virtual Circuit Connection):

    An end-to-end connection consisting of a concatenation of two or more Virtual Channels between two endpoints. VCCs may be bundled into a VPC.

  • VCI (Virtual Channel Identifier):

    Used to identify each VC across the UNI or NNI. The VCI is a 16-bit field within the ATM cell header.

  • VLAN (Virtual LAN):

    A network architecture which allows geographically distributed users to communicate as if they were on a single physical LAN by sharing a single broadcast and multicast domain. ATM Forum LAN Emulation supports VLANs.

  • VP (Virtual Path):

    A grouping of virtual channels (VCs), important between ATM switches to facilitate management. Multiple VPs form end-to-end VPCs.

  • VPC (Virtual Path Connection):

    An end-to-end connection consisting of two or more Virtual Path links (VPs).

  • VPI (Virtual Path Identifier):

    Used to identify each VP across the UNI or NNI. The VPI is an 8-bit field at the UNI; 12 bits at the NNI (no GFC).

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