Imagine a TCP session over wireless where the congestion window is fixed at 5 segments (congestion control is turned off and no fast retransmits). Segments may get lost but are not reordered. Assume the sender has a long file (hence continuous byte stream) to send. The receiver has a close-to-infinite buffer and it sends an acknowledgment as soon as it receives a segment, i.e., acknowledgments are not deferred. Similarly, the sender transmits a segment as soon as it can. Each segment carries 1000 bytes and the time to transmit a segment is 2 ms. Assume that transmission of ACK takes negligible time. Note that the retransmission timer for a segment is started after the last bit of the segment is sent. Assume Go-Back-5, and accumulative ACK are used.

For each question, provide the answer(s) and a brief explanation.

1. Suppose two data segments with byte sequence numbers 3000 and 15000 are lost once during the transmission. How many segments get retransmitted under each of the following conditions?

a Round trip time = 100 ms, Timeout = 102 ms

b Round trip time = 100 ms, Timeout = 152 ms 

 

2. Suppose acknowledgments corresponding to the above data segments are lost instead of the data segments. How many segments get retransmitted under the above conditions?

a Round trip time = 100 ms, Timeout = 102 ms 

b Round trip time = 100 ms, Timeout = 152 ms