Frame relay is a WAN service that is designed to connect two points that require only intermittent communications. - It was first designed for transport across ISDN (Integrated Services Digital Network) infrastructure.
Each frame relay PDU (protocol data unit) has a field: - Flag Field - high level data link synchronization
- Address Field - Occupy either octet 2 to 3, 2 to 4, or 2 to 5
- Information Field - maximum number of data bytes that a host can pack into a frame
- Frame Check Sequence Field - implement error detection to avoid wasting bandwidth due to the transmission of erred frames
Congestion Control - Admission Control - principal mechanism used in frame relay to ensure the guarantee of resource requirement once accepted
- Committed Information Rate (CIR) - average rate (in bit/s) at which the network guarantees to transfer information units over a measurement interval T. This T interval is defined as: T = Bc/CIR
- Committed Burst Size (BC) - maximum number of information units transmittable during the interval T
- Excess Burst Size (BE) - maximum number of uncommitted information units (in bits) that the network will attempt to carry during the interval
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