Store-and-forward & queuing delay
q distance = d meters; speed of propagation = s m/sec q transmission rate of link = R1 and R2 bits/s
q Consider sending two packets A and B back to back
q Case 2: Assume R1 > R2 Q: is there a queuing delay? how much is this delay?
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Answer (queue is empty initially):
Time for last bit of 2nd pkt to arrive at router: d1= L/R1 + L/R1 + d/(2s) Time for last bit of 1st pkt to leave router: d2= L/R1 + d/(2s) + L/R2 Queueing delay = d2 – d1 = L/R2 – L/R1 if positive, otherwise 0. Hence: when R1 < R2, queueing delay = d2 – d1 = 0
q Case 1: Assume R1 < R2
when R1 > R2, queueing delay = d2 – d1 = L/R2 – L/R1
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