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