Queuing Delay
Consider the queuing delay in a router buffer, where the packet experiences a delay as it waits to be transmitted onto the link. The length of the queuing delay of a specific packet will depend on the number of earlier-arriving packets that are queued and waiting for transmission onto the link. If the queue is empty and no other packet is currently being transmitted, then our packet’s queuing delay will be zero. On the other hand, if the traffic is heavy and many other packets are also waiting to be transmitted, the queuing delay will be long.
Assume a constant transmission rate of R = 400000 bps, a constant packet-length L = 3300 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1.
Question List
1. In practice, does the queuing delay tend to vary a lot? Answer with Yes or No
2. Assuming that a = 30, what is the queuing delay? Give your answer in milliseconds (ms)
3. Assuming that a = 83, what is the queuing delay? Give your answer in milliseconds (ms)
4. Assuming the router's buffer is infinite, the queuing delay is 1.7808 ms, and 950 packets arrive. How many packets will be in the buffer 1 second later?
5. If the buffer has a maximum size of 610 packets, how many of the 950 packets would be dropped upon arrival from the previous question?
Solution
1. Yes, in practice, queuing delay can vary significantly. We use the above formulas
as a way to give a rough estimate, but in a real-life scenario it is much more complicated.
2. Queuing Delay = I(L/R)(1 - I) * 1000 = 0.2475*(3300/400000)*(1-0.2475) * 1000 = 1.5365 ms.
3. Queuing Delay = I(L/R)(1 - I) * 1000 = 0.6848*(3300/400000)*(1-0.6848) * 1000 = 1.7808 ms.
4. Packets left in buffer = a - floor(1000/delay) = 950 - floor(1000/1.7808) = 389 packets.
5. Packets dropped = packets - buffer size = 950 - 610 = 340 dropped packets.
That's incorrect
That's correct
The answer was: Yes
The answer was: 1.5365
The answer was: 1.7808
The answer was: 389
The answer was: 340