Frame Relay PCI
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Frame Relay is a successor of X.25, but it doesn't use the OSI layer 3 (network) as X.25 does. Frame Relay allows higher data rates and relies on WAN links with very low bit error rates (BER).
The Frame Relay header may consist of 2, 3, or 4 bytes depending on the address length.
Frame Relay performs connection-oriented point-to-point data exchange.
Frame Relay is capable of dynamic bandwidth allocation (bandwidth on demand): bandwidth not being used by a current connection can be used by any other connection (that may exceed its committed information rate by this).
The Frame Relay access nodes will mark frames that exceed the CIR by setting the DE bit to one (DE=1). If network congestion occur, frames with DE=1 will be discarded first by the frame handlers (i.e. Frame Relay routers).
Frame Relay supports congestion control, but it does not have congestion avoidence capabilities.
Frame Relay supports SVCs and PVCs, but it is mostly used on PVC links.
LMI - Local Management Interface
Link setup and connection release are done by the LMI protocol. LMI is conveyed in Frame Relay's data field.
DATA (1-4500 bytes) (Frame Relay)