Question

We have noted that there can be no input queuing if the switching fabric is n times faster than the input line rates, assuming n input lines all have the same rate. Explain why this is the case.

Answer 1

Consider the given data:

Assume packet length=n

Maximum queuing delay= (n–1)D

All packets are of the same length, n packets arrive at the same time to the n input ports, and all n packets want to be forwarded to different output ports.

a)  The maximum delay for a packet for the memory = (n-1)D

b)  The maximum delay for a packet for the bus = (n-1)D

c)  The maximum delay for a packet for the crossbar switching fabrics=  0