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receive window and length

asked 2019-07-26 22:11:23 +0000

dometh gravatar image

updated 2019-07-27 21:50:07 +0000

Jim Aragon gravatar image

hello: My receive window on receiver (calculated window size) is 262656. my sender is only sending 60 bytes of data but then receiver says its window is full. how is that possible? thanks

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answered 2019-07-27 16:10:40 +0000

Hi,

It would be nice to have actual trace file to explain it to you better.

There are several things to consider.

1) Do you mean [Window Full] warning? If yes - this is not receiver's message, but comes from Wireshark itself. All receiver can do to stop transmitting is advertising Zero Window.

2) Capture point is very important to keep in mind. I suspect this capture was done on sender side.

So, here you have to remember that some amount of sent data is still on the wire "flying" to receiver. The sender calculates this value (Bytes_Sent minus Bytes_ACKed). You can find amount on data in flight by plotting "Bytes in flight" Wireshark field.

I assume including these last 60 Bytes there are exactly 256256 Bytes in Flight.

So, Wireshark sees: when all the data already been sent (but not yet ACKed) will come to receiver, it will occupy all RWIN. So, Wireshark issues "Window Full" warning.

It does not mean RWIN is gonna be fully occupied (ZeroWindow condition), but it DOES mean the sender can't send anymore until it gets the next ACK.

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that make sense, is there anyway to count cumulative bytes in flight which are not being ack. i can see bytes in flight but is that a total? if that is the case i dont see that many bytes in flight which would add up to explain zero window situation. and yes capture was done at sender side. also i dont see memory or cpu being saturated so . i am thinking to upgrade tcp/ip stack. any suggestion.

dometh gravatar imagedometh ( 2019-07-28 00:27:03 +0000 )edit

This is perfect time to see the capture or at least a screenshot.

Total Bytes in flight = bytes sent (SEQ + last TCP.len) - bytes ACKed, this is what Wireshark Bytes in flight field shows.

But don't forget that Wireshark's perspective could be different from sender's perspective as Wireshark calculates all values looking at the incoming packet stream which depends on capture point placement and other factors.

Packet_vlad gravatar imagePacket_vlad ( 2019-07-29 09:03:39 +0000 )edit

where can i upload the trace or screenshot? i dont see that option on this forum

dometh gravatar imagedometh ( 2019-07-29 13:08:45 +0000 )edit

You can use any file sharing service (Google Drive, Dropbox etc) and post a link here. Trace file is preferable.

Packet_vlad gravatar imagePacket_vlad ( 2019-07-29 13:31:08 +0000 )edit

here is the link to capture.slow printing.. main issue was on sender side (application was not sending enough data), which we resolved but at that time also saw zero window issue on receive side. 192.168.0.1 is the printer which is getting data from sap to print

https://drive.google.com/file/d/1r73h...

dometh gravatar imagedometh ( 2019-07-30 21:43:51 +0000 )edit

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Asked: 2019-07-26 22:11:23 +0000

Seen: 60 times

Last updated: Jul 27