Two hosts are connected via a packet switch with 10^7 bits per second links.…
2015
Two hosts are connected via a packet switch with 10^7 bits per second links. Each link has a propagation delay of 20 microseconds. The switch begins forwarding a packet 35 microseconds after it receives the same. If 10000 bits of data are to be transmitted between the two hosts using a packet size of 5000 bits, the time elapsed between the transmission of the first bit of data and the reception of the last bit of the data in microseconds is____________.
Answer: 1575 — Key values: link rate R = 10^7 bits/s, packet size = 5000 bits, propagation delay per link = 20 µs, switch forwarding delay after full reception = 35 µs.…
Attempted by 88 students.
Show answer & explanation
Correct answer: 1575
Key values: link rate R = 10^7 bits/s, packet size = 5000 bits, propagation delay per link = 20 µs, switch forwarding delay after full reception = 35 µs.
Transmission time for one packet = 5000 / 10^7 = 0.0005 s = 500 µs.
Timeline for the first packet:
Host finishes sending packet 1 at 500 µs; last bit reaches the switch at 500 + 20 = 520 µs. The switch waits 35 µs and starts forwarding at 520 + 35 = 555 µs. It finishes transmitting packet 1 at 555 + 500 = 1055 µs, and the last bit arrives at the destination at 1055 + 20 = 1075 µs.
Timeline for the second packet (sent immediately after the first):
Host finishes sending packet 2 at 1000 µs; last bit reaches the switch at 1000 + 20 = 1020 µs. The switch waits 35 µs and starts forwarding at 1020 + 35 = 1055 µs. It finishes transmitting packet 2 at 1055 + 500 = 1555 µs, and the last bit arrives at the destination at 1555 + 20 = 1575 µs.
Therefore, the time from the first transmitted bit (t = 0) to the last received bit is 1575 µs.