Fixed Assignment: Performance
Fixed assignment protocols ideal for continuous streams, but bad for data because it exploits only spatial multiplexing.
With ideal statistical multiplexing (“using channel when packets are waiting”), M/M/1 queueing analysis says that the mean delay:
- E(T) = 1/(?-?), where ? is the mean arrival rate and ? is the mean service rate
With fixed assignment, each channel has service rate ?/N and assuming arrival rates of ?/N, and separate M/M/1 queues, we find:
- E(T) = 1/(?/N - ?/N) = N/(?-?)
- So, use of fixed assignment protocols for packet switched data implies an increase in mean delay by a factor of N !!