Question

Consider a sender that uses the Selective Repeat Protocol and is connected to a receiver via a channel that does not reorder messages. Assume that the sender has a window size of k=6, and a sequence number range of 256. Answer the following questions (with justification) assuming that at time t the next in-order packet the receiver is expecting has sequence number m (where m is somewhere well within the range and the sequence number space does not wrap around).

Enumerate all possible ranges of sequence numbers corresponding to the sender’s window at time t in terms of k.

Answer 1

The sender's window in the Selective Repeat Protocol with a window size of 6 and a next expected sequence number m will include sequence numbers from m to m+5.

Step-by-step explanation:

The question pertains to the Selective Repeat Protocol, which is a method of error control in data communications where the sender can send multiple frames before needing an acknowledgment for the first frame, but is constrained to a limited number of frames (the window size).

With a window size (k) of 6, and assuming that the sequence numbers are well within range and do not wrap around, the ranges of sequence numbers of the sender’s window at time t, when the next expected packet by the receiver has a sequence number m, would be from m to m+5.

This is because the sender can send up to k frames starting from the expected frame, hence the last frame in the window would have the sequence number m+5. It is important that the sequence numbers do not exceed the range of 256 to avoid overlap or confusion in identifying frames.