Just for laughs, the next time you see this degradation,
try changing the dsu mode to something different than what
it is, on both ends.
I have recently seen this same behaviour, on a very lightly
loaded ds3, and (for various reasons I won't go into) changing
the dsu mode from 0 to 1, or 1 or 2, etc. "fixed" this problem.
I am currently talking with cisco as to why this may have
happened.
On Tue, Feb 15, 2000 at 11:56:38AM -0500, Oded Comay wrote:
> Allow me to fill in (see below).
>
> On Tue, 15 Feb 2000, Ron Buchalski wrote:
>
> >>From: Hank Nussbacher <hank@att.net.il>
> >>To: cisco-nsp@puck.nether.net
> >>Subject: PA-T3 question
> >>Date: Tue, 15 Feb 2000 07:10:49 +0200
> >>MIME-Version: 1.0
> >>
> >>Running 12.0(5)S on a pair of 7505 routers with a PA-T3 in each.The PA-T3
> >>card is:
> >>
> >>TAU-gp2#sho contr serial
> >>Serial0/0/0 -
> >> Mx T3(1) HW Revision 0x3, FW Revision 2.56
> >>
> >>The physical line is a satellite T3 line.Occassionally, the RTT starts to
> >>jump from the normal 560ms and reaches 1400ms.It starts its climb over a
> >>period of times and can may take a few hours of slow climbing till it
> >>reaches unbearable levels and someone notices it and does a reset.Only a
> >>'clear interface' will make the line act normal again.
> >>
> >>The physical line and modems have all been checked and the suspicion now
> >>lies on IOS or the PA-T3 cards.
> >
> >Are you plugging directly into a satellite modem, or are you using a
> >terrestrial (telco) circuit to get to the satellite earth station?It
> >almost sounds like you have a clocking problem on the satellite link.
>
> There are local loops at both sides.
>
> >Even though the satellite is geosynchronous (fixed position), it's actual
> >distance to the earth varies throughout the day.Because of doppler
> >effects, the data rate changes as well.Normally a point-to-point satellite
> >link will be set up with one end clocking the circuit as the master, and the
> >other end set to loop the receive clock (slave) and use it to transmit back
> >to the master site.On the receive side at the master site should be a
> >receive buffer that will absorb the rate variations throughout the day.
> >
> >If the buffering is missing, or screwed up, it may manifest itself in what
> >you're seeing.The PA-T3 does not have adequate (physical layer) buffering
> >to handle a satellite link.This should be handled by the satellite service
> >provider.
>
> The modems do have anti-Doppler-effect buffers. In fact, the link wouldn't
> work without them for more than a few minutes. Also, the magnitude of the
> RTT deviation (a second, and sometimes even more) is much too large with
> respect to Doppler effect in this environment (buffers of several mili-secs
> worth of traffic are enough).
>
> So the question remains: where do the packets spend this extra second? Note
> that if packets are not lost (I suspect at least some do) than at T3 rates
> a second is quite a bit of buffer space.
>
> If you know of a site with a similar configuration, please let us know, and
> we'll check with them to see what they experience.
>
> Thanks,
> Oded.
>
> >
> >-rb
> >
> >______________________________________________________
> >Get Your Private, Free Email at http://www.hotmail.com
> >
>
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:10 EDT