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# Computer Networking : A Top-down Approach

Authors:
James F. Kurose, Keith W. Ross
Exercise:
Problems
Chapter:
Transport Layer
Edition:
6
ISBN:
9780132856201
Question:
44
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### 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?

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

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