On Sat, 19 Jan 2002, Ken Caldwell wrote: > <quote who="Howard Lowndes"> > > > > > I've been doing some quantified analysis of the performance of a few PSTN > > modems, mainly because I have one that I think is doing something odd. > > > > The modems in question are: > > A Global Express connected to a P120/64Mb > > B Swann Smart connected to a P120/64Mb > > C D-Link connected to a P120/64Mb > > D Dynalink (I think) connected to a Celeron 733/128Mb > > Were the tests all carried out over the same 'phone line or four > different lines?
A, B & C were on one phone line with D on a different line. > I may be way of track here, but I imagine the ping time is the time it > takes to receive a correct response to the transmitted ping. When the > link is first set up the modems negotiate the fastest satisfactory speed > for that particular connection. The algorithm used is sometimes unduly > optimistic leading to bit errors. The modem then asks for that byte to > be repeated and does not emit the data to the computer until it has > received it correctly. > > If the problem is of this nature it can sometimes be alleviated by > explicitly instructing the modem not to attempt connecting above a > certain speed (say 22kbps). (There is an AT command for this with some > modems) > > Bit errors are not just caused by noisy lines or excessive attenuation > but can be caused by strange frequency and phase response. Yes, I agree that, but it still doesn't explain the wide difference (220msec -v- 450mssec) between type 17 -v- type 50 pings in the case of modem D. -- Howard. LANNet Computing Associates - Your Linux people Contact detail at http://www.lannetlinux.com "We are either doing something, or we are not. 'Talking about' is a subset of 'not'." -- SLUG - Sydney Linux User Group Mailing List - http://slug.org.au/ More Info: http://lists.slug.org.au/listinfo/slug
