At 10:44 AM 7/9/98 +0700, Tony S. Hariman wrote:
Does anybody have experience having a T1 circuit with PPP encapsulation getting only 1290 Kbps maximum throughput looking at "sh int" result from cisco router or MRTG ?
This is the explanation our upstream provider gave us:
You have a 1.536Mbps port. However, there is the overhead from PPP and the translation overhead which takes place in all circuits. Judging by your settings that limit ends up somewhere between 1.3 and 1.4. This overhead would be the non-data portion of cells or frames for example. For example, you might have 1.3 Mbps of data which gets framing or cell information appended onto it before sending taking up additional bandwidth. It is to be expected in all circuits.
That is.... well, not correct. (Please insert favorite euphemism for "not very smart" in regards to this upstream.) First of all, PPP overhead is not even close to 200 Kbps on a T1. Second of all, I believe MRTG includes the overhead in it's graphs. Could someone please correct me on that if I'm wrong? And lastly, there are no "cells" in PPP. If you are doing ATM over that T1, you would have cells. But you say you are doing PPP, not ATM. Besides, I think you'd get less than 1.3 Mbps - probably more like 1.1 or 1.0. According to my MRTG graphs, the most I've ever gotten on a PPP encapsulated link is 1521.4 kb/s. I think that's a bit higher than your upstream told you is possible. :) This is a Cisco talking to a Bay router (hence the PPP encap as opposed to HDLC). So tell your upstream he's full of it.
Tony S. Hariman
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