Why does the maximum packet lifetime have to be large enough to ensure that not only the packet but also its acknowledgements have disappeared?

Consider the GBN protocol with a sender window size of 4 and a sequence number range of 1,024. Suppose 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. Answer the following questions: a. What are the possible sets of sequence numbers inside the sender's window at time !? 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? Justify your answer.

For each of following ICMP messages, list their possible senders (routers, non-destination hosts, and destination hosts). a) Type: destination unreachable,Code: 2/3 – protocol/port is unreachable b) Type: source quench,Code: 0 c) Type: time exceeded,Code: 1 (note when the final destination does not receive all of the fragments in a settime, it discards the received fragments and sends a time-exceeded message (code 1) tothe original source) d) Type: Redirection,Code: 1 – redirect to a host-specific route

Take into account that the sender is aware of, and prepared for, a continuous roundtrip delay. Given that packet loss is possible with Protocol Rdt 3.0, is a timer still necessary? Explain.