Path: utzoo!dciem!nrcaer!scs!spl1!laidbak!att!osu-cis!tut.cis.ohio-state.edu!ukma!david From: david@ms.uky.edu (David Herron -- One of the vertebrae) Newsgroups: comp.dcom.modems Subject: Re: BYTE high speed modem article and the Telcor Accelerator 2496MA Message-ID: <9574@e.ms.uky.edu> Date: 7 Jun 88 01:14:15 GMT Article-I.D.: e.9574 References: <12997@shemp.CS.UCLA.EDU> <1711@looking.UUCP> <431@dmk3b1.UUCP> <989@datapg.DataPg.MN.ORG> Reply-To: david@ms.uky.edu (David Herron -- One of the vertebrae) Organization: U of Kentucky, Mathematical Sciences Lines: 35 In article <989@datapg.DataPg.MN.ORG> sewilco@datapg.DataPg.MN.ORG (Scot E. Wilcoxon) writes: >In article <431@dmk3b1.UUCP> dmk@dmk3b1.UUCP (David Keaton) writes: >>One thing that caught my eye in the Byte article was the pair of graphs >>where one modem fell off a cliff when the signal to noise ratio got bad, >>and a PEP modem took a wild path down to zero throughput. Their >The BYTE article did not mention the elapsed time of the test. The >graph seems to have throughput peaks which are too jagged to have >had a long period of time between modem frequency adjustments. Anyone >have figures on how often a PEP modem hits a line change which requires >frequency adjustment? Read the similar article in Data Communications -- it has a better explanation of the test procedure. The thumbnail sketch of the test procedure: They simulate a phone company. That is, there's a local loop, a box converting to a 4-wire circuit, a noise inserter, another box converting back to a 2-wire circuit, and another local loop. The noise inserter is programmable to insert any desired signal-noise ratio into the system -- sorry I don't remember details about the type of noise. At each noise setting they transmit at least 80K of data using their protocol and measure how long it takes to transmit the data. Then they bump the noise by one notch (1 db?) and do it again. They keep this up until the modem fails or something like that. The 80K of data would take 80 to 100 seconds to transmit through these modems, which would be far and away enough time for the trailblazers to handle re-training and the like... -- <---- David Herron -- The E-Mail guy <---- s.k.a.: David le casse\*' {rutgers,uunet}!ukma!david, david@UKMA.BITNET <---- <---- Goodbye RAH.