> 2) is there a method to get the actual WINSZ of TCP sender from the
> TCP implementation (I know it is not in the packets itself)
Some systems have a "netstat" command that will report not only the
endpoint address/port pairs, and the state, of TCP connections, but will
also report the send window (as reported by the peer, presumably) and
receive window (as advertised by the machine on which "netstat" is being
run).
The SunOS 5.x "netstat" does this, as does the "netstat" in all current
releases of software from Network Appliance (I think I put that in when
I was adding NFS-over-TCP support, so it's been there for a while - I
picked up the idea from SunOS 5.x).
I don't know what other OSes have a "netstat" command that does that.
Unfortunately, neither the "netstat" on a Red Hat 6.x machine here nor
the "netstat" on my desktop W2K machine at work do; perhaps there are
other versions of "netstat" for Linux that do. The NetApp one is based
on the BSD one, so the fact that I had to add it suggests that BSD ones
may not do so, either.
There are probably, on some implementations, implementation-dependent
ways of getting it from the implementation, but I don't know what they
are.