Jun 13, 2015 · If like the graph in "Computer Networking: A Top Down Approach" book, just use a straight line in T16 to represent the Fast Recovery process, then the cwnd in T17 should be 21 MSS instead of (21+3) MSS, because when it transitions from Fast Recovery to Congestion Avoidance, the cwnd will down to the value of ssthresh. So the graph in book is wrong.

Jun 13, 2020 · So, when you receive 3 duplicate ACKs in a row you cut cwnd to half and perform a fast retransmit, from now on you're trying to not just idle while waiting for the next new ACK (1 RTT at best). Once you enter fast recovery, you send new data with. cwnd= original cwnd + # of duplicate ACKs received

Nov 26, 2018 · (a) If TCP sends 4KB segments, how many RTTs does it take to send the file, assuming that there are no segment losses? (b) Describe what happens if the first segment sent after the send window reaches 1MB is lost. Assume that the version of TCP you are using does not implement fast retransmit and fast recovery.

Jan 8, 2018 · DupACKs are part of a failure recovery mechanism called: TCP Fast retransmit, ensuring the reliability of TCP protocol. A duplicate acknowledgment is sent when a receiver receives out-of-order packets (let say sequence 2-4-3). Upon receiving packet #4 the receiver starts sending duplicate acks so the sender would start the fast-retransmit process.

TCP then performs a retransmission of what appears to be the missing segment, without waiting for a retransmission timer to expire. The reasoning for not doing the retransmit until the third duplicate seems to be that until that point it's more likely to just be out-of-order delivery and the retransmit isn't really needed.

Jun 10, 2016 · Reno: The successor to Tahoe, goes into fast recovery mode upon receiving three duplicate acks thereby halving the ssthresh value. For each successive duplicate acks (fourth, fifth, sixth), cwind increases by 1. Once the receiver finally receives the missing packet, TCP will move to congestion avoidance or slowstate upon a timeout.

From my understanding, TCP Reno basically works as follows (RFC 5681, 3.1, 3.2). Upon receiving three duplicate acknowledgements, it sets ssthresh = cwnd/2 and then cwnd = ssthresh. In case of a timeout, ssthresh = cwnd/2, cwnd = 1 is set and slow start initiated. It appears to me that the ssthresh value set during fast recovery is never used.

Apr 26, 2014 · Based on the paper and Wikipedia's description of slow start, it wants TCP to start with a congestion window of size 1 after a loss event occurs. Based on congestion avoidance's AIMD algorithm, the congestion window should be halved after a packet loss. Which algorithm will take precedence when a packet loss occurs?

In some applications TCP is faster (better throughput) than UDP. This is the case when doing lots of small writes relative to the MTU size. For example, I read an experiment in which a stream of 300 byte packets was being sent over Ethernet (1500 …

Dec 26, 2018 · Each retransmission of ACK 100 will include a TCP SACK option indicating the aggregate of bytes that have been received after the missing segment that are pending if the gap is filled; Given what you show you should see SACK indicating that offsets 120-135, then 120-141, then 120-157. When the missing 20 bytes are transmitted, you will see ACK 157