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Cell Relay Retreat>List Archive>month:1995-Apr> msg00345



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Re: TCP window size? Cell-level pacing?

  • From: raj@cup.hp.com (Rick Jones)
  • Date: Sat, 22 Apr 1995 04:21:09 -0500, 22 Apr 1995 02:08:31 GMT

Bill Halverson (wjhalv1@pacbell.com) wrote:
: "Scott D. Weberg" <sweberg@wes.army.mil> wrote: 
: >But I still don't know what the "TCP window size" is - and how it is 
: >set.  There seems to be no socket routines that allow you to set 
: >the TCP window size.  Can someone tell me how you set it?  Is it 
: >something the sys admin has to do? 
: I think the buffer size is equivalent to the TCP window size.  Can you   
: set a different value for each socket, if you chose to? 

In a BSDish system and probably others, the TCP window size will be
the size of the receive socket buffer - ie setsockopt(SO_RCVBUF). Each
side can be advertising a different window size.

It is generally best to make your setsockopt(SO_*BUF) calls _before_
your calls to either connect() or listen(). If the system is
configured to have a larger default that you will be setting, your
setsockopt call may fail if called after those system calls -
"shrinking" the TCP window on an existing connection is considered a
bad thing.

Some examples can be found in the netperf benchmark source -
http://www.cup.hp.com/netperf/NetperfPage.html.

rick jones