Question

1. Suppose N packets arrive simultaneously to a link at which no packets are currently being transmitted or queued. Each packet is of length L and the link has transmission rate R (need proof).

1) What is the transmission time for the 10^thpacket?

2) What is the average queue delay for the last three packets?

3) What is the average transmission delay for the last three packets?

4) What is the delay for the 21^stpacket including queue delay and transmission delay?

Answer 1

1) Transmission Time : L / R

  

2) Average Queue Delay :

   note : Assuming Arrival rate = 1

L = Length of Packet , R = Transmission Rate

   Average Queuing Delay for last third packet = (N-3)*L / R

   Average Queuing Delay for last second packet =(N-2)*L / R

   Average Queuing Delay for last packet = (N-1)*L / R

So finally Average Queuing Delay for the last three packet = ( ((N-3)*L / R) +( (N-2)*L / R ) + ( (N-1)*L / R ) ) / 3

= ( (N-3)*L + (N-2)*L + (N-1)*L ) / 3R

3 ) Average Transmission Delay for last 3 packets :

Note : Lets have Bandwidth = B

Average Transmission Delay = L / R + L / R + L / R

   = 3L / R

4 ) Delay for 21st packet :

Queue Delay : ( 20 L ) / R

   Transmission Delay : L / R

   Total Delay = Queue Delay + Transmission Delay

= ( 21 L ) / R