Path: utzoo!utgpu!watserv1!watmath!att!linac!uwm.edu!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ira.uka.de!fauern!faui43.informatik.uni-erlangen.de!eckert
From: eckert@immd4.informatik.uni-erlangen.de (Toerless Eckert)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Ether-X25-Ether, strange(?) delays
Message-ID: <1991Jun10.165045.21732@informatik.uni-erlangen.de>
Date: 10 Jun 91 16:50:45 GMT
References: <bof.676539524@vieta.math.uni-sb.de>
Organization: CSD., University of Erlangen, Germany
Lines: 50

From article <bof.676539524@vieta.math.uni-sb.de>, by bof@vieta.math.uni-sb.de (Patrick Schaaf):
[...]
> The Questions:
> 
>   - Is it possible for Sun's TCP implementation to explode retransmission
>     timeouts to minutes' frequency?

From my experience: yes, though other TCP (notably 4.2bsd) are even worse
and have the problem of coming to a full stop completely.

>   - Is it possible to make TCP work better (smoother) in such an extreme
>     environment, and if, how (explanations based on the 4.3BSD code would
>     be best).

I've never tried to fiddle around in the kernel for this purpose.
My simple solution was alway to use X28/X29 instead of telnet for those
slow X.25 based connections (for ftp it really doesn't matter how fast
it is).

>   - Is there a possibility to monitor the RTT estimates on the distant
>     Sun? I would be very interested to study the delays.

Use 'ping -s'

>   - Did I forget to ask something relevant?

If the PC is DOS based, the TCP/IP may not really be 4.3 derived and may
have problems with reassembling fragmented IP frames. This leads
to the effect that TCP connections hang absolutely even though more
IP traffic over the same SVC is still floating.

Don't use x25manager, use x25mgr which comes with SunNet X.25 7.0.
Try to fiddle with the MTU on both the cisco and the sun side, use
the same value on both ends. (RFC877 specifies 576 as a minimum, but
for faster interactive performance you may prefer 128).

Use the maximum available X.25 packet size for the link.
Use window size 7 if negotiatable.

Best question: ask for a faster link. The sun can handle up to 64kbps if
it's a sun4 (over the cpu ports).
(This is not the general purpose answer for overloaded or misworking
circuits, but for 9600 IP/X.25 links it is).

Hope that helps a little
---

             Toerless.Eckert@informatik.uni-erlangen.de
    /C=de/A=dbp/P=uni-erlangen/OU=informatik/S=Eckert/G=Toerless
             bandwidth - the final frontier.