Homework: 22C:178 & 055:134

Computer Communications Fall 1998

Assignment 7

[no due date]

Nothing to turn in for this assignment! This homework just provides additional problems to consider in preparation for the second examination.

(This is question 11 from the textbook.) Consider an ARQ protocol that uses only negative acknowledgements (NAKs), but no positive acknowledgements (ACKs). Describe what timeouts would need to be scheduled. Explain why an ACK-based protocol is usually preferred to a NAK-based protocol.

Suppose a 500MB file is to be copied from host A to host B over a five hop, store-and-forward path of nodes and links. Each node uses the stop and wait protocol to send packets on its links, with a packet size of 8KB, 24 bytes of which are reserved for the header. ACKs are 24 bytes long. Each link has 100Mbps bandwidth, and the propagation delay on each link is 500 microseconds. What is the total time needed to copy the file?

(This is question 24 from the textbook.) For a 100-Mbps token ring network that uses delayed release (RAR), has a token rotation time of 200 microseconds, and allows each station to transmit one 1-KB packet each time it possesses the token, determine the network's maximum effective throughput rate (maximum effective bandwidth).

Repeat the previous question, but calcuate the maximum effective bandwidth if there is only one station that is the sender (all but one station do not send any packet).

What about if the immediate release strategy (RAT) is used for the previous two questions? What difference will that make in the answers?