AW: OS/2 2.11: TCP/IP over 384 kb/s satellite link

From: MICHAEL.DZIK@LHSYSTEMS.COM
Date: Fri Jan 09 1998 - 01:11:04 EST


Dear Bettina,

OS/2 usually offers a window size of 28 kbyte. This is enough to load
your 384 kbps satellite channel.

Nevertheless your stack OS/2 stack seems to be rather old. I did some
testing with OS/2 Warp 3.1 recently over a satellite channel with 512
kbps. My TCP/IP stack was TCP/IP v3.0 for OS/2 CSD. That one is still
buggy. Its behaviour is quite interesting (I monitored all tests with a
protocol analyzer (sniffer)):

 At the beginning of a TCP session the full bandwidth capacity was used
very quickly according to slow start. Although the TCP window was only
28 kbyte the stack tried to achieve more and put additional load on the
line. (From my point of view), my routers (Bay ASN 32 Mbyte) quickly
became overloaded. Timeouts came, one after 3 and one after 5 seconds.
After that there was a complete breakdown of throughput. Still the
TCP/IP stack did not lose its session - instead it started to transfer
data using "stop-and-go", which is certainly not an optimal way of
transfering data over a Geo.

Could you check if your stack behaves similary? If yes you can only
achieve better throughput by increasing your MTU or updating your OS/2
system with the NEWEST TCP-stack release of OS/2. As far as I know my
bug was fixed recently - but I haven't tested it yet - our systems were
switched to MS Windows NT anyway.

Regards,

Michael Dzik

        Please help, if you have any idea:
        We have a direct satellite link between Russia and Germany. One
PC and
        one Router on both sides and in between the satellite. Our link
should
        provide a transparent TCP/IP connection with 384 kb/s. We are
using
        OS2/2.11 and IBM TCP/IP version 2.0 for data transfer. The
effective
        data rate is much too low to be used for any data transfer.

        Problem: How could we get access to the TCP/IP parameters that
should be
        changed? Tcpipcfg does not offer enough parameters to change.

        Thank you in advance for your help,

        Bettina Pieper



This archive was generated by hypermail 2b29 : Mon Feb 14 2000 - 16:14:34 EST