On Sun, May 13, 2007 at 11:05:29PM -0700, Eugene Stemple wrote:
> I am seeing an abnormal delay in packets passed over a PPP link
> (a null modem cable between two Linux systems) and would post a
> formal bug report if I were more confident which package maintainer
> to report to.
> It might be in the pppd process or it might be in the compiled
> kernel ppp support code. I can do the "reportbug" program to get
> this properly entered in the bug tracking system so just tell me
> which seems to be the appropriate package.
>
> Here is a brief description:
> ---
> When a single packet is received from the serial port there is
> approx. a 60% probability that it will NOT be passed thru to the
> application for approx. 3.75 SECONDS. Or, until another packet
> arrives and (apparently) "pushes" it throught the pipe.
> This effect is seen in ping tests, in ftp transactions, and in
> tcp (html) sessions passing over this PPP path. I've used tcpdump
> to capture time information simultaneously at both ends of the PPP
> path to verify that the delayed packet was, in fact, sent from one
> end but not released by the ppp process at the other end.
> --------------------------------------------------------------
[snip 'more details' as they endorse the description]
Well, it looks like a PPP link-level problem...
Questions:
- I presume both peers are the same kernel/ppp version?
- What sort of cable are you using ? RS232 is not really *one*
standard, but many. Most importantly: is it a 3-wire or 7-wire (iirc
"7" but not quite sure about the exact number).
- What are you ppp options (on both sides, obviously excluding any
password stuff) ? I'd expect to see the ppp options matching the
cable type. Flow control and compression is especially interesting
here. Also, if chap-interval/eap-interval is set, this will
obviously cause a serial-link-"lump" every N seconds...
- Anything suspicious in the kernel logs about the serial ports?
(either side?)
- Any interesting system log entries from ppp?
If none of the above bears fruit, you may get some results from running
ppp manually with debug switched on ("pppd $usual_options debug
nodetach")...
Hope this helps
--
Karl E. Jorgensen
karl@jorgensen.org.uk http://www.jorgensen.org.uk/
karl@jorgensen.com http://karl.jorgensen.com
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