# hw3 - that at time t , the next in-order packet that the...

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CS 118 Spring 2008 : Homework 3 Problem 1 Problem 1 In the rdt3.0 protocol, the ACK packets that ﬂow from the receiver back to the sender don’t have sequence numbers, even though they do have the ACK ﬁeld that contains the sequence number of the packet that they are acknowledging. Why don’t these ACK packets need sequence numbers? Problem 2 True or false (give justiﬁcations for your answers): a In the SR protocol, it is possible for the sender to receive an ACK for a packet that falls outside of its current window. b In the GBN protocol, it is possible for the sender to receive an ACK for a packet that falls outside of its current window. c The alternating-bit protocol is the same as the SR protocol with a sender and receiver window size of 1. d The alternating bit protocol is the same as the GBN protocol with a sender and receiver window size of 1. Problem 3 Consider the GBN protocol with a sender window size of 3 and a sequence number range of 1,024. Suppose
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Unformatted text preview: that at time t , the next in-order packet that the receiver is expecting has a sequence number of k . Assume that the medium does not reorder messages. a What are the possible sets of sequence numbers inside the sender’s window at time t ? Justify your answer. b What are all possible values of the ACK ﬁeld in all possible messages currently propagating back to the sender at time t ? Justify your answer. Problem 4 Consider a reliable data transfer protocol that uses only negative acknowledgments. Suppose the sender sends data only infrequently. Would a NAK-only protocol be preferable to a protocol that uses ACKs? Why? Now suppose the sender has a lot of data to send and the end-to-end connection experiences few losses. In this second case, would a NAK-only protocol be preferable to a protocol that uses ACKs? Why? Page 1 of 1...
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## This note was uploaded on 04/28/2010 for the course CS 118 taught by Professor Chu during the Spring '08 term at UCLA.

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