Telecommunications problem involving point to point communication: a.) What is t

Question

Telecommunications problem involving point to point communication:

a.) What is the effect on line utilization of increasing message size so fewer messages are required, and are other factors unchanged?

b.) What is the effect on line utilization of increasing the number of frames for a constant message size?

c.) What is the effect on line utilization of increasing the frame size?

d.) Why is it not necessary to define a REJ0 and REJ1 (reject frames) for the stop and wait ARQ?

Consider a full duplex point to point communication link is using the stop and wait flow control scheme. A series of messages is to be sent where each message is broken up into a series of frames. Also assume there are no errors present is broken up into a series of framesAlso assume there are no errors present.

Explanation / Answer

.
a. Because only one frame can be sent at a time, and transmission must stop until an
acknowledgment is received, there is little effect in increasing the size of the message
if the frame size remains the same. All that this would affect is connect and
disconnect time.
b. Increasing the number of frames would decrease frame size (number of bits/frame).
This would lower line efficiency, because the propagation time is unchanged but
more acknowledgments would be needed.
c. For a given message size, increasing the frame size decreases the number of frames.
This is the reverse of (b)

d.In fact, a REJ is not needed at all, since the sender will time out if it fails to receive an
ACK. The REJ improves efficiency by informing the sender of a bad frame as early as
possible.

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