Suppose a TCP connection has reached a steady state, in which the sending rate e

Question

Suppose a TCP connection has reached a steady state, in which the sending rate exhibits a periodic behavior with each period consisting of two phase:

1. Slow start to reach a threshold

2. Addictively increase until congestion occurs. Assume the TCP segment size is M bytes, and the round trip time is 1 second. Let the duration of first and second phase be T1 and T2 seconds, respectively.

Find:

1. The sending rates at the end of phases 1 and 2, respectively,

2. The average sending rate of the TCP connection,

3. The packet loss probability (hint: there is one packet loss for each period)

Explanation / Answer

Sending rate is the rate at which the data is delivered successfully to other end which is also known as throughput.

So,

throughput or sending rate = maximum segment size / round trip time

Consider the following notations:

STT - saw tooth time in seconds.

RTT - roundtrip time

MTU - maximum transfer unit

MSS - maximum segment size

PLR - packet loss rate.

  
Given theSTT,
window size is w*MSS and given RTT,
TCP's transsmission rate is = (w*MSS)/RTT
During the congestion avoidance phase, TCP probes for additional bandwidth by increasing w by one each RTT until loss occurs which is denoted by W the value of w at which loss occurs.
Assuming that the RTT and W are approximately constant over the duration of the connection, the TCP transmission rate ranges from (W*MSS)/(2RTT) to (W*MSS)/RTT.

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