Question
Consider sending a large file from a host to another over a TCP connection that has no loss.
a. Suppose TCP uses AIMD for its congestion control without slow start. Assuming cwnd increases by 1 MSS every time a batch of ACKs is received and assuming approximately constant round-trip times, how long does it take for cwnd increase from 6 MSS to 12 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
a)
Given data:
Assuming cwnd increases by 1 MSS every time a batch of ACKs is received and assuming approximately constant round-trip times.
Then transmission rate of TCP is 
=w bytes/RTT
cwnd increases by 1 MSS if every batch of ACKs received.
The below steps are take for cwnd to increase from 6 MSS to 12 MSS:
- 1 RTTs to to 7 MSS.
- 2 RTTs to 8 MSS.
- 3 RTTs to 9 MSS.
- 4 RTTs to 10 MSS.
- 5 RTTs to 11MSS.
- 6 RTTs to 12 MSS.
b)
Given data:
Connection up through time = 6 RTT
Average throughout (in terms of MSS and RTT) =(6+7+8+9+10+11)/6
=8.5 MSS/RTT