Muxing: Arbitration
Fixed TDM
- Arbitration is necessary when a sub-channel is assigned to an input channel (even where the wide main channel has enough bandwidth)
- This operation is usually called 'circuit setup'
- Centralized reservation scheme at headend: allocation of individual or periodic frames
Variable TDM
- Collision (parallel to backoff): an input channel simply sends its traffic, but has some way to tell whether the traffic was accepted
- Scheduling (parallel to backpressure): input channel makes a request for service and the multiplexer eventually grants it
- centralized, as in many I/O busses, or
- distributed, as in a daisy-chained bus or a token ring like FDDI.