[I've trimmed the follow-up to just c.s.h.hpux...]
 
[log in to unmask] wrote:
: I am bridging FDDI over ATM (sonet oc3 net) and need to increase
: window size in IP.  Traces show window size at 8136 and frames are
: about 4k so I can only send one frame without a definite responce
: being returned.  This causes low FDDI utilization and poor
: performance as propagation delay over WAN cannot be avoided.
 
The default TCP window size (IP has no concept of a window...) in
HP-UX 9.X is 8192 bytes. I'm a bit surprised that it would show 8136.
For 9.X the only way to change the system default is to use adb to
poke the tcp_sendspace and tcp_recvspace variables.  The better thing
to do is to modify the application to use setsockopt on *both*
SO_SNDBUF and SO_RCVBUF (even on the sender).
 
On HP-UX 10.X the default is increased to 32768 bytes. There is a tool
in 10.X called nettune which can be used to alter the default TCP
window size. Of course, setsockopt still works - and may be preferred
since the administrator could decide to shrink the default on you at a
later time.
 
10.X also provides support for RFC 1323 - the TCP "large windows" RFC.
However, it is not enabled by default - and for some inexplicable
reason only adb, not nettune can be used to enable it. There are *two*
variables that *must* be poked - tcp_dont_tsecho and tcp_dont_winscale
must both be set to zero. When this is done you can get a window size
of just shy of 256KB.
 
rick jones