#Constant tcp retransmission wireshark full#
#Constant tcp retransmission wireshark free#

It's missing 'c' because it expects a continuous increase of numbers and 3 is missing. Now, suppose the friend gets ('b', 2), but then ('d', 4). The numbers are used in case the packets/messages arrive out of order. Imagine you want to send the letters of the alphabet to a friend over the Internet. The most likely candidate will be the router where the path. So, what are the things that need to investigated further?Ī) The bulk packet loss, always after a large burst of 100 KB, points to a device in the path that only has a 100 KB buffer space.

#Constant tcp retransmission wireshark free#

At this point, in-flight data is zero and the sender is now free to begin the whole pattern all over again.

#Constant tcp retransmission wireshark full#

It looks like the sender eventually waits for every sixth round trip so that it can send a full 6-packet application 'block' (there's a Push flag at the end of these 6-packet bursts).ħ) Eventually, the original large gap has been completely filled-in and we see the Ack line jump all the way up as the original two large bursts and all the smaller 'new' bursts are fully acknowledged.

The dark blue circle is around the initial two large bursts, the red circle is around all the single packet retransmissions and the light blue circle is around all the small bursts of new packets. Also, after several RTTs (perhaps as the sending congestion window is opened), the sender begins to send small bursts of new data so that the in-flight value of 250 KB is maintained.Ħ) On the second chart below, we've zoomed-out to encompass a full pattern and the start of the next one. Following the horizontal 'Ack line' on the chart we see the single retransmitted packet and the step up of the Ack line.Ĥ) One RTT after that, there's another single packet retransmission.ĥ) The large initial gap in the received data is then filled in at the rate of just one packet per RTT.

The large number of original lost packets trigger many Dup-ACKs and in response, the sender retransmits a single packet to begin to fill the gap.

The sender manages to maintain close to this 'in flight' value throughout the whole period.ģ) One RTT later, the sender receives ACKs for the 100 KB that wasn't lost and manages to transmit a further 100 KB without any errors. In the first TCP-Trace chart below, we see the 100 KB successful burst, the yellow area with no packets, a few subsequent packets that made it through, then one RTT later the second 100 KB burst.Ģ) The server's receive window is close to 1 MB, but the sender appears to use its own RWIN of 261,288 bytes as its own transmit 'limit'. Here are my key observations (with some supporting TCP Trace charts below):ġ) The client sends a large burst of 250 KB, but large portions are lost after the first 100 KB. I'll define the large burst of packets as the start of the pattern. A particular pattern is repeated again and again - at roughly 7 second intervals - with about 500,000 KB transferred per interval. There's a very consistent regularity to the way the packets flow from the client to the server.