Curtis,
I agree with you. I'd also like to add some thoughts.
Although there seems to be a lot of traffic on this list regarding TCP
performance over satellite, it seems that we're trying to solve a problem
that's already been solved. Adjusting the window size to compensate for
the BANDWIDTH*DELAY PRODUCT the ultimate solution. The problem seems to be
how to get it done on any particular platform. Your comment about the
"setsockopt" is the key.
The reference in another message today about a patch (SUN's CONSULT-TCPLFN)
for Solaris 2.5.1 and below, adds support for Long Fat Networks
(RFC1323-TCP Extensions for High Performance). It is included in 2.6 (so
I've been told).
Finally, there is one other nit that might present an obstacle to high
performance. If the default values for Solaris' retransmit timers
(tcp_rexmit_interval_initial, tcp_rexmit_interval_min,
tcp_rexmit_interval_max) are set below the RTT, then Solaris will
retransmit unacknowledged packets in spite of the fact that the RTT has not
yet expired. For example, it the RTT is 750 ms, make sure that the
retransmit timers are set to 1000 ms or more to preclude unnecessary
retransmissions.
Selective acknowledgements would be helpful, but I agree not essential.
Regards,
Chuck
At 11:56 AM 11/10/97 -0500, Curtis Villamizar wrote:
>
>In message <[email protected]>, matthew halsey
writes:
>> Aaron, Mark et al
>>
>> In addition, if it is not there already, we could add a graph/table
showing
>> max possible throughput for a variety of window sizes with some markers of
>> where typical TCP stacks place their windows.
>> E.g. I think Microsoft adopts 8kByte window => max thruput = 8192 x 8 /
0.6s
>> = 109 kbps.
>> Sun = ?
>> FTP = ?
>>
>> What do you think?
>>
>> Matt
>
>
>To provide decent service over satellite both ends need to have a
>large buffer configured. BSD defaults to 16KB but it is typically
>settable to 256KB without changing a constant in the kernel. Then it
>can be set to up to 2GB.
>
>To what extent is sending a single TCP flow at high speed an issue in
>non-military applications? Keeping a remote web cache synched, bulk
>smtp relay transfer, and bulk nntp transfer can all be configured to
>use large windows if the pair is known to have a sat link between.
>
>The applications that do need high speed single flows just have to
>increase window size in the application using setsockopt. A host that
>is dangling off a seatellite link can also change the default window
>size in the kernel to something more appropriate.
>
>I suppose Windoze and NT users are out of luck.
>
>Curtis
>
>
Staff Systems Engineer (610) 531-3771
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King Of Prussia, PA [email protected] 1
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