Re: 4.2/4.3 TCP and long RTTs
8 Dec 1986 10:14-EST

        I would suggest that you try limiting unacknowledged data on the TCP
connection to an amount which will not cause fragmentation over the paths
that you are using. I suspect that the problem you are seeing is that
packets are being generated which require fragmentation. The usual
fragmentation algorithm dumps n consecutive packets into the net; if
any of the n get lost, reassembly cannot occur and retransmission is
required. It was formerly the case that some interfaces could not receive
back to back packets from the net; it may still be; if so, a fragmented
packet will "never" get through. Also, I suspect that the IP sequence
number in retransmitted TCP packets is different from the original;
consequently, fragments from different retransmissions cannot be recombined.
Does your RDP implementation specify the IP sequence number? Can you tell
if your host is receiving fragments and having to discard them? Do you
get any ICMP fragment reassembly time exceeded messages? Can you find out
what the initial time-to-live value is for the TCP connection and the RDP?
Let us know what you find.


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