Glossary 

A	Access Line
	A communications line (like a circuit) interconnecting a frame-relay-compatible device (DTE) to a frame-relay switch (DCE).
	Access Rate (AR)
	The data rate of the user access channel. The speed of the access channel determines how rapidly (maximum rate) the end user can inject data into a frame relay network.
	American National Standards Institute (ANSI)
	Devises and proposes recommendations for international communications standards. See also CCITT.
B	Backward Explicit Congestion Notification (BECN)
	A bit set by a frame relay network to notify an interface device (DTE) that congestion avoidance procedures should be initiated by the sending device.  See also FECN.
	Bandwidth
	The range of frequencies in which data can pass over a given transmission channel within a frame relay network, expressed in Kilobits per second. The bandwidth determines the rate at which information can be sent through a channel. The greater the bandwidth is, the more information can be sent in a given amount of time.
	Bridge
	A device that supports LAN-to-LAN communications. Bridges may be equipped to provide frame relay support to the LAN devices they serve. A frame-relay-capable bridge encapsulates LAN frames in frame relay frames and feeds those frame relay frames to a frame relay switch for transmission across the network. A frame-relay-capable bridge also receives frame relay frames from the network, strips the frame relay frame off each LAN frame, and passes the LAN frame on to the end device. Bridges are generally used to connect LAN segments to other LAN segments or to a WAN (wide area network). They route traffic on the Level 2 LAN protocol, which occupies the lower sub layer of the LAN OSI data link layer. See also Router.
	Burstiness
	In the context of a frame relay network, information that does not use the total bandwidth of a circuit 100 percent of the time. Hence, data only uses the bandwidth sporadically. During pauses, channels are idle and no traffic flows across them in either direction. When data is sent intermittently, and in between data transmissions the channel experiences idle time (waiting for DTE to respond for the sent data) – this data is considered to have bursty nature. Such is Interactive data connecting LAN-to-LAN.
C	Channel
	Generically refers to the user access channel across which frame relay data travels.  A given T1 or E1 physical line, may be configured to be one of the following: Unchannelized  The entire T1/E1 line is considered a channel, where:  · The T1 line operates at speeds of 1.536 Mbps and is a single channel consisting of 24 T1 time slots.  · The E1 line operates at speeds of 1.984 Mbps and is a single channel consisting of 20 E1 time slots.  Channelized  The channel is any one of N time slots within a given line, where:  · The T1 has 24 time slots, which each may be considered a channel operating at speeds in multiples of 56/64 Kbps to 1.536 Mbps. · The E1 has 31 time slots, which each may be considered a channel operating at speeds in multiples of 64 Kbps to 1.984 Mbps. Fractional  The T1/E1 channel is one of the following groupings of consecutively or non-consecutively assigned time slots:  · N T1 time slots (NX56/64Kbps where N = 1 to 23 T1 time slots per T1 channel).  · N E1 time slots (NX64Kbps, where N = 1 to 30 time slots per E1 channel).
	Committed Burst Size (BC)
	The maximum amount of data (in bits) that the network agrees to transfer, under normal conditions, during a time interval TC. See also BE.
	Comite Consultatif International Telegraphique et Telephonique (CCITT)
	International Consultative Committee for Telegraphy and Telephony. A standards organization that devises and proposes recommendations for international communications. See also ANSI.
	Committed Information Rate (CIR)
	The committed rate (in bits per second) at which the ingress access interface trunk interfaces, and egress access interface of a frame relay network transfer information to the destination frame relay end system under normal conditions. The rate is averaged over a minimum time interval TC.
	Committed Rate Measurement Interval (TC)
	The time interval during which the user can send only BC and BE. In general, the duration of TC is proportional to the "burstiness" of the traffic and is computed as TC = BC/CIR. TC is not a periodic time interval. Incoming data triggers the TC interval, which continues until it completes its commuted duration, and so TC is used for measureing incoming data. See also CIR.
	Cyclic Redundancy Check (CRC)
	A computational means to ensure the accuracy of frames transmitted between devices in a frame relay network. The mathematical function is computed, based on the content of the frame, before the frame is transmitted at the originating device. This value is compared with a recomputed value of the function at the destination device. See also FCS.
D	Data Communications Equipment (DCE)
	Term defined by both frame relay and X.25 committees, that applies to switching equipment and is distinguished from the devices that attach to the network (DTE).
	Discard Eligibility (DE)
	A user-set bit indicating that a frame may be discarded in preference to other frames if congestion occurs, to maintain the committed quality of service within the network. Frames with the DE bit set are considered be excess data. See also BE.
	Data Link Connection Identifier (DLCI)
	A unique number assigned to a PVC end point in a frame relay network. This number has local significance only to a segment of a virtual circuit between a particular PVC endpoint and a end user's device (channel), which it represents. DLCI are configured on a frame relay interface.
E	Excess Burst Size (BE)
	The maximum amount of uncommitted data (in bits) in excess of BC that a frame relay network can attempt to deliver during a time interval TC. This data is generally delivered with a lower probability than BC. The network treats BE data as discard eligible. See also BC.
F	Forward Explicit Congestion Notification (FECN)
	A bit set by a frame relay network to notify an interface device (DTE) that congestion avoidance procedures should be initiated by the receiving device. See also BECN.
	Frame Check Sequence (FCS)
	The standard 16-bit cyclic redundancy check (CRC) used for HDLC and frame relay frames. The FCS detects bit errors occurring in the bits of the frame between the opening flag and the FCS. It is only effective in frames no larger than 4096 octets. See also CRC.
	Frame Relay Frame
	A variable-length unit of data, in frame-relay format that is transmitted through a frame relay network as pure data. Contrast with Packet. See also Q.931.
	Frame Relay Network
	A telecommunications network based on frame relay technology. Data is multiplexed. Contrast with Packet-Switching Network.
	Frame Relay Interface
	A physical interface that is configured to carry frame relay traffic.
H	High Level Data Link control (HDLC)
	A generic link-level communications protocol developed by the International Organization for Standardization (ISO). HDLC protocol manages synchronous, code-transparent, serial information transfer over a link connection. See also SDLC.
	Hop
	A single trunk line between two switches in a frame relay network. An established PVC consists of a certain number of hops, spanning the distance from the ingress access interface to the egress access interface within the network.
I	ISDN - Integrated Service Digital Networks
	An early, CCITT-adopted protocol  reference model intended for providing a ubiquitous, end-to-end, interactive,  digital service for data, audio and video. ISDN is available as BRI, PRI and B-ISDN.
L	LAN Segment
	In the context of a frame relay network supporting LAN-to-LAN communications, LAN segment is a LAN linked to another LAN by a bridge.  Bridges enable two LANs to function like a single, large LAN by passing data from one LAN segment to another. For communication with each other, the bridged LAN segments must use the same native protocol.  See also Bridge.
	Link Access Procedure on the D-channel (LAPD)
	A protocol that operates at the data link layer (layer 2) of the OSI architecture. LAPD is used to convey information between layer 3 entities across the frame relay network. The D-channel carries signaling information for circuit switching. Contrast with LAPB.
P	Packet
	A group of fixed-length binary digits including the data and call control signals. The data, call control signals, and possible error control information are arranged in a predetermined format to be transmitted via PSN. Packets do not always travel the same pathway but are arranged in proper sequence at the destination side before forwarding the complete message to an addressee.
	Packet-Switching Network
	A telecommunications network based on packet-switching technology, wherein a transmission channel is occupied only for the duration of the transmission of the packet.
	Permanent Virtual Circuit (PVC)
	A frame relay logical link, whose endpoints and class of service are defined by network management. This is defined between two end points of a circuit. The PVC is identified by the DLCI's configured across the network. When there is data to be sent, the DTE searches for a path through the network which is identified by the DLCI.
Q	Q.931
	Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the  circuit-oriented nature of ISDN allocates bandwidth in fixed increments of 64 kbps. Q.931 does manage connection setup and breakdown. Like TCP, Q.931 documents both the protocol itself and a protocol state machine.
R	Remote bridge group
	Remote Bridges are statically configured as members of a remote bridge group by management. All members of a remote bridge group are connected by one or more virtual ports. In a Frame Relay network there must be a full mesh of Frame Relay VCs between bridges of a remote bridge group.  Otherwise, the bridge network must be divided into multiple remote bridge groups.
	Router
	A device that supports LAN-to-LAN communications. Routers may be equipped to provide frame relay support to the LAN devices they serve. A frame-relay-capable router encapsulates LAN frames in frame relay frames and feeds those frame relay frames to a frame relay switch for transmission across the network. A frame-relay-capable router also receives frame relay frames from the network, strips the frame relay frame off each frame to product the original LAN frame, and passes the LAN frame on to the end device. Routers connect multiple LAN segments to each other or to a WAN. Routers route traffic on the Level 3 LAN protocol (e.g., the Internet Protocol address).  See also Bridge.
S	Statistical Multiplexing
	Interleaving the data input of two or more devices on a single channel or access line for transmission through a frame relay network. Interleaving of data is accomplished using the DLCI.
	Synchronous Data Link Control (SDLC)
	A link-level communications protocol used in an International Business Machines (IBM) systems. SDLC protocol manages synchronous, code-transparent, serial information transfer over a link connection and is a subset of the more generic High-Level Data Link Control (HDLC) protocol.