Question

The source host a is going to send 10kb (10240byte) of data to the destination host b over an established tcp connection, which has a window size (rwnd) of 5kb (5120byte) and a maximum segment size (mss) of 1kb (1024byte). assuming go-back-n is used in tcp. suppose there are errors in the transmissions. for each of the following independent transmission error cases, please calculate the total number of segments sent out from the source (including retransmissions) in order to complete the transmissions of the 10kb data to the destination.

case a. the 3rd segment is corrupted. other transmissions are fine. what is the total number of segments sent out from the source (including retransmissions)? answer: 10 .
case b. the 3rd segment is correctly received, but the ack to the 3rd segment is lost. other transmissions are fine. what is the total number of segments sent out from the source (including retransmissions)? answer: 10 .
case c. the 8th segment is lost. all other transmissions are fine. what is the total number of segments sent out from the source (including retransmissions)? answer: 11 .
case d. the 10th segment is lost. all other transmissions are fine. what is the total number of segments sent out from the source (including retransmissions)? answer: 11 .
case e. the 10th segment is correctly received, but the ack to the 10th segment is lost. other transmissions are fine. what is the total number of segments sent out from the source (including retransmissions): answer: 11 . note: please fill in integer numbers only in the blanks

Answer 1

The calculations of the number of segments sent including retransmissions for each error case show that for a single segment error, the retransmission starts from that segment up to the current window size, resulting in totals of 10 for Case A and B, and 11 for Cases C, D, and E.

Step-by-step explanation:

The question revolves around the concept of TCP (Transmission Control Protocol) transmissions and how retransmissions are handled in the presence of errors using Go-Back-N ARQ (Automatic Repeat reQuest). The source host needs to send 10 KB of data to the destination host while adhering to given window size and segment size constraints.

Case A: If the 3rd segment is corrupted, TCP performs retransmission starting from the 3rd segment. Since the window size is 5 KB, segments 3 to 7 would be retransmitted. With successful transmission of the remaining segments, the total count will be 10 segments.

Case B: In case the ACK for the 3rd segment is lost, the source host assumes a timeout and retransmits from segment 3 to 7. Hence, the total is still 10 segments sent.

Case C: If the 8th segment is lost, segments 8 to 10 would have to be retransmitted, totalling 11 segments sent.

Case D: The loss of the 10th segment requires a retransmission of just that segment, resulting in a total of 11 segments sent.

Case E: When the ACK of the 10th segment is lost, the source host will retransmit from the 10th segment, resulting in 11 segments sent.

The Go-Back-N protocol dictates retransmission of all segments from the point of failure up to the current window size. With the given constraints, the precise number of segments to be sent, including the retransmissions, are calculated for each case by considering consecutive blanks in the segment sequence caused by errors.