Question

Consider sending a large file from a host to another over a TCP connection that has no loss. Suppose TCP uses AIMD for its congestion control without slow start. The initial MSS=4 and cwnd increases by 1 MSS every time a batch of ACKs is received. Assume approximately constant round-trip times. a. how long does it take for cwnd increase from 5 MSS to 9 MSS (assuming no loss events)? b. What is the average throughout (in terms of MSS and RTT) for this connection up through time =6 RTT?

Answer 1

Answer : Given data

* Suppose TCP uses AIMD for its congestion control without slow start.

* The initial MSS=4 and cwnd increases by 1 MSS every time a batch of ACKs is received.

=>TCP uses AIMD for congestion control without slow start.

=>Initial window size = 4 MSS

=>Congestion window(cwnd) increases by 1 MSS every RTT.

(a)

=>cwnd increases from 5 MSS to 9 MSS

Explanation:

=>cwnd window will increase by 1 MSS every RTT

5 MSS | 6 MSS | 7 MSS | 8 MSS | 9 MSS

=>As we can see we are required 4 RTT to reach 9 MSS from 5 MSS cwnd size hence time required = 4 RTT

(b)

=>Time = 6 RTT

Explanation:

=>cwnd window will increase by 1 MSS every RTT

=>Initial window size = 4 MSS

4 MSS | 5 MSS | 6 MSS | 7 MSS | 8 MSS | 9 MSS | 10 MSS

=>We can see after 6 RTT congestion window(cwnd) = 10 MSS

Calculating average throughput:

=>Average throughput = window size/time

=>Average throughput = 10 MSS/6 RTT

=>Average throughput = 5 MSS/3 RTT

___________THE END____________