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RE: Cisco PPP DS-3 limitations - 42.9Mbpbs?

  • From: Daniel Golding
  • Date: Wed Feb 20 11:34:08 2002



If you are just doing testing, then sending a stream of UDP echos across,
using something like a Digital Lightwave is the easiest way of testing,
provided your target system will take the traffic (this is a good way to
crash most windows boxes, for example). PPP and HDLC both have very little
in the way of overhead. The same can be said for c-bit framing. You should
be getting something like 96% efficiency, which gets you to the 42.9mb/sec
number. PPP has something like 7 bytes of overhead per frame. Various forms
of DS3 framing are discussed here:
http://www.dl.com/ResearchCenter/Training/t3/t3fund.pdf.

ATM, for comparison, will usually max at around 36mb/sec for a DS3. YMMV of
course, and in actual operation, due to peaks and 5 minute sampling, you
will see lower bit rates.

- Daniel Golding

> -----Original Message-----
> From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of
> Stephen J. Wilcox
> Sent: Wednesday, February 20, 2002 11:09 AM
> To: Randy Bush
> Cc: nanog@merit.edu
> Subject: Re: Cisco PPP DS-3 limitations - 42.9Mbpbs?
>
>
>
> Hmm, reasonable explanation..
>
> presumably this can be improved (a little) with increased interface
> buffers.. ? and possibly non fifo queuing eg custom queuing in favour of
> TCP rathen than UDP/ICMP etc which wont have the backoffs
>
> Cheers
>
> Steve
>
> On Wed, 20 Feb 2002, Randy Bush wrote:
>
> > > we run HDLC on DS3 and we max at about 40.something too
> >
> > if you're using five min (or three min) samples, and you're seeing 70%,
> > peaks are likely much higher and some users' packets are being dropped.
> > by 80%, enough packets are being dropped that users are likely to see
> > the effects of exponential backoff.  things do not improve above 80%.
> >
> > randy
> >
>
> --
> Stephen J. Wilcox
> IP Services Manager, Opal Telecom
> http://www.opaltelecom.co.uk/
> Tel: 0161 222 2000
> Fax: 0161 222 2008
>





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