Re: Question about the -s Parameter

Rick Jones (
Thu, 15 Jul 1999 10:33:34 -0700

[asking for return receipt when sending to a mailing list seems triffle
strange... :) ]

Heico Salfeld wrote:
> Hi there!
> I have a question about the -s option. In the manual of revision 2.1 it
> says that this will set the local send and receive buffer sizes to the
> value specified. The -S option will do the same for the remote system.
> What kind of buffer is actually meant...:
> 1) Is this just a buffer of the system's input and output functions?
> 2) Or does this parameter set the maximum window size of TCP, and can
> reach up to the max. CWND of 64 kBytes which is defined in the OS?

I guess it depends on the transport implementation. The -S and -s
options specify the values passed in setsockopt(SO_SNDBUF|SO_RCVBUF)
calls. On BSDish stacks, the SO_RCVBUF setting, controls the TCP window.

SO_SNDBUF tends to control how much the sender can have outstanding at
one time.

CWND can be more than 64KB if the window is more - though there are some
stacks which place a configurable limit on cwnd.

The maximum data outstanding at any one time on a TCP connection will
(more or less) be the minimum of the sender's SO_SNDBUF, the receiver's
window/SORCVBUF and the senders cwnd.

> In both cases: is it correct that it is counted in bytes?


> BTW: I am sending TCP over a satellite link with a RTT of 560 msec. Any
> suggestions with which params it's mostly worth to play around?

The -s and -S are good ones.

rick jones

these opinions are mine, all mine; HP might not want them anyway... :)
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