Two DTEs are communicating via modems and RS 232D interfaces over a half-duplex

Question

Two DTEs are communicating via modems and RS 232D interfaces over a half-duplex link. Data transmission is one directional with each message of length M. After a message is transmitted, the sender waits for an acknowledgement message of length na before sending another message. Determine the maximum effective data rate in bps and link utilization assuming error-free operation and the following parameter values: R (line bit rate) = 9600 bps; M (message length) = 1000 bits (all data bits); nh (overhead in each message packet) = 24 bits; na (acknowledgement length) = 24 bits; tp (propagation time in one direction) = 1 msec; and RTS-CTS delay (minimum transition time) 10 msec at message transmitting end and 20 msec at message receiving end (acknowledgement transmitting end). All other delays during message transmission and reception are negligible.

Explanation / Answer

M (message length) = 1000 bits

nh (overhead in each message packet) = 24 bits

total = 1000 + 24 = 1024 bits

R (line bit rate) = 9600 bps

so time taken to transmit total message = 1024/9600 = 106.67 msec

na (acknowledgement length) = 24 bits

time taken to send ack = 24/9600 = 2.5 msec

tp (propagation time in one direction) = 1 msec

so both side = 2 msec

RTS-CTS delay (minimum transition time) at message transmitting end = 10 msec

RTS-CTS delay (minimum transition time) at message receiving end (acknowledgement transmitting end) = 20 msec

total time to send data = 106.67 + 2.5 + 2 + 10 + 20 = 141.17 msec

maximum effective data rate = bits/sec = 1048/141.17 = 7423.67 bps

link utilization = 7423.67/9600*100 = 77.33%

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