Question

Suppose there are 4 routers in sequence between Host A and Host B, all of which use store-and-forward routing. What is the total end-to-end delay for a packet originating from Host A with destination Host B, under the following conditions.

◘ Each of the link transmission rates are 9.4 Mbps
◘ The total distance from Host A to Host B along its path of transmission is123.4 km
◘ The speed of propagation through the transmission medium is is 2.5 x 10 m/s
◘ The packet size is 2 KiB

Remember that you must also uplink from Host A to the first router. Give answer in milliseconds, rounded to 1 decimal place, without units (e.g. for 0.12345 seconds you would enter "123.5" without the quotes).

The answer is 9.2

Why is this the correct answer?

Answer 1

Please note: The speed of propagation you have mentioned in your question is 2.5x10 which is not possible. It must be a typo. I am assuming it to be 2.5x10^8 m/s, if its wrong correct me in comment section.

ANSWER -

Given that there are 4 routers, so there occurs multiple transmission delay because whenever a router receives a packet there occurs a delay.

So, to calculate transmission delay from one router to another we use L/R formula. We know that packet size is 2 KiB and transmission rate is 9.4 Mbps.

Transmission delay of one router = (L/R) = (2 KiB x 8192) / (9.4 Mbps x 10^6) =1.74297x10^(-3) secs

Convert into milliseconds, 1.74297x10^(-3) x 10^3 = 1.74297 ms

1.74297 ms is the transmission delay of one router. There are total 4 routers, so to calculate the total transmission delay of all the 4 we multiply the transmission delay of one router with the total number of routers plus one which is 4+1 = 5 here.

Total transmission delay of 4 router = (R+1) x 1.74297 ms = 5 x 1.74297 ms = 8.7145 ms

Next we have to calculate the propagation delay. Given that path of transmission from Host A to B is 123.4 km and speed of propagation is 2.5x10^8, we can get

Propagation delay = (D/S) = ( (123.4x1000 m) / (2.5x10^8 ms) ) = 4.936x10^(-4) secs

Convert into milliseconds, 4.936x10^(-4) x 1000 = 0.4936 ms

So, the total end-to-end delay for a packet originating from Host A with destination Host B is,

Total transmission delay of 4 router + Propagation delay = 8.7145 ms + 0.4936 ms = 9.2081 ms.

Total delay will be 9.2 ms from Host A to Host B.

Please comment if u need any more info. Please do leave a like, it would mean a lot. Thanks :)