I have got the following question from a course:

"Assume a TCP connection over the internet with a useable bandwith of 300Mbps. Assume that some packets are transported with a very high delay. At which delay time serious problems may occure? Is this a realistic problem?"

I calculated that at a delay time of ~2 minutes, there will be an overflow within the sequence counter (if you assumed that it started with 0). According to RFC the sequence counter will overflow to zero. I found no "what to to if this happens" within the RFC, but maybe i overlooked it.

My question is: What will happen? Is this simply a limitation of TCP? Are there workarounds (except of using a larger sequence counter)?

migrated from stackoverflow.com Jan 20 '10 at 20:05

This question came from our site for professional and enthusiast programmers.


Well, the relevant RFC tells you how to do this right (and actually solves the problem). See http://www.apps.ietf.org/rfc/rfc1323.html section 4.


I don't think the overflowing in itself is a problem, you'll only get a problem when you receive a packet with a sequence number that is inside the current receive window but is actually from (a multiple of) 4 GiB ago in the data stream. For this to happen, the packet would have to be delayed for two minutes according to your calculation (sounds plausible). In practice I don't think this would happen too often as there usually isn't that much buffer space in all intermediate systems (it would also need to be in the order of 4 GiB).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.