This is a question from an old exam that ive been trying to work out:

The 40000 bit file is split into 10 packets with a 400 bit header added to each packet The link from A to R is 500 km long and from R to B is 250 km long with a capacity of 2 Mbps for both links. The propagation speed is 250 000 km/s for both links. The router uses store and forward, do not account for checksum verification and delay from moving the packets to the correct outbound socket. A does not wait for ACK flags before sending the next packet.

My attempt:

40000/10 + 400=4400 bits per packet

Transmission delay(dtrans): 4400/2*10^6=0.0022 seconds (packet length/link capacity)

propagation delay between A and R(dpropAR): 500/250000=0,002 seconds

propagation delay between R and B (dpropAB): 250/250000=0,001 seconds

(link-length/propagation speed)

I'm having trouble putting the delays together. I believe it to be 10*(2*dtrans+dpropAR+dpropAB) but im getting the wrong answer.

My thinking: one transmission delay for A and one for B, thats 2*transdelay and one dpropAR and one dpropAB for each time the packet is sent to a node. All of that repeated 10 times over.

Is my approach somewhat accurate or am i going about this the wrong way?

Thank you.


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