Frame relay is a telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service provider figures out the route each frame travels to its destination and can charge based on usage.
Frame relay is based on the older X.25 packet-switching technology which was designed for transmitting analog data such as voice conversations, frame relay is a fast packet technology, which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply “dropped.” (Thrown away). The end points are responsible for detecting and retransmitting dropped frames.
Network diagram of Frame relay:
Some are the Keywords use in Frame relay:
Access line—A communications line (for example, a circuit) interconnecting a Frame-Relay-compatible device (DTE) to a Frame Relay switch (DCE)
- Backward explicit congestion notification (BECN)—A bit sent in reverse direction to the data flow. It is set by a Frame Relay network to notify an interface device (DTE) that congestion avoidance procedures should be initiated by the sending device.
- Committed information rate (CIR)—The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over time interval Tc. CIR, measured in bits per second (bps), is one of the key negotiated tariff metrics.
- Data-link connection identifier (DLCI)—A unique number assigned to a permanent virtual circuit (PVC) end point in a Frame Relay network. Identifies a particular PVC endpoint within a user’s access channel in a Frame Relay network and has local significance only to that channel.
- 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. The network side can also set the DE bit and, on congestion, will first drop frames that have this DE bit set. Frames with the DE bit set are considered “Be-excess” data. See also “excess burst size (Be)” below.
- Forward explicit congestion notification (FECN)—A bit sent in the same direction as the data flow. It is 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 “backward explicit congestion notification (BECN)” above.
- Local Management Interface (LMI)—A set of enhancements to the basic Frame Relay specification. LMI includes support for a keep alive mechanism, which verifies that data is flowing, and for a status mechanism, which provides an on-going status report on the DLCIs known to the switch