This is a static archive of our old Q&A Site. Please post any new questions and answers at ask.wireshark.org.

TCP problem

![alt text][1]

This one capture at site B. I try to understand this. After [SYN], the server at site A just keep pushing the data to server at site B, but I did not see any [ACK] back at site B. I only see the Window size 92 but with unknown scaling. They communicate over satellite link. Any body can point out what going on? Is it due to the nature of Satellite link ?

tcp

asked 13 Jun '12, 16:38

pixaround
1●1●1●1
accept rate: 0%

Did you see any packets at all going from B to A? Such as the SYN-ACK at the start of the TCP connection? Is it possible that your capture interface is just not capturing packets originating at B?

The main difference about a Satellite link is that because of its long latency the TCP window will need to be negotiated to a much higher value than needed on a shorter link carrying the same number of bits per second.

(18 Jun '12, 16:21) inetdog

One Answer:

satellite links exist in different types. Two (among others) are:

Two-way satellite communication (up-/download via satellite)
One-way receive, with terrestrial transmit (download via satellite, upload via Modem, ISDN, GPRS, 3G etc.)

The third packet from the bottom ACKs the receipt of some bytes. If you don't see that data in Wireshark (your screenshot indicates that), there are two possible reasons:

There is something wrong with your wireshark setup (hard to tell without further information)
OR, you see only one half of the communication, as the other half takes a different "route" (Modem, ISDN, 3G) that Wireshark is unable to see.

Based on the information you provided, I assume the later.

Regards
Kurt

answered 18 Jun '12, 16:58

Kurt Knochner ♦
24.8k●10●39●237
accept rate: 15%

edited 18 Jun '12, 17:36