Bettina,
the best would be to have a trace (of about 1 minute) of a starting TCP session available using tcpdump or equivalent tool, in order to check a number of things, a.o.
- advertised windows when you see the session is at maximum throughput ?
- number of tcp retransmits ?
- socket SEND and RECV sizes of both sink and source sockets ?
Could you provide such a trace that is taken from the ethernet on the sending AND connecting side ?
Do you have tools to see buffers in the routers or packet drops ?
Can you say someting on the satellite link performance ?
Are PPP checksums errors increasing on the 3COMs ?
If you do the test with ttcp and use UDP (option -u) instead of TCP, are lots of packets dropped somewhere because of these PPP CRCs ?
Can you put one interface in loopback and see at least that all the packets that exit one serial interface come back ?
In the first place I would get rid of all bridging/compression etc in order to scale down the problem.
Regards,
Frank
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