Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!munnari!otc!uqcspe!miw From: miw@uqcspe.OZ (Mark Williams) Newsgroups: comp.dcom.modems Subject: Re: What is Max speed possible on phone lines? Message-ID: <1641@uqcspe.OZ> Date: Fri, 30-Oct-87 01:07:20 EST Article-I.D.: uqcspe.1641 Posted: Fri Oct 30 01:07:20 1987 Date-Received: Thu, 5-Nov-87 05:58:16 EST References: Reply-To: miw@uqcspe.oz (Mark Williams) Organization: Prentice Computer Centre, University of Queensland Lines: 31 In article WANCHO@SIMTEL20.ARPA ("Frank J. Wancho") writes: >The highest "speed" possible on conventional dialup lines is 1200 >baud. ... > However, the highest bit >rate possible is a function of the bit-encoding technique used to >squeeze more bits per baud using analog technology. Almost, but not quite. The V.32 standard for 9600 bps modems actually specifies 2400 baud. The highest bit rate possible is purely a function of bandwidth and signal to noise ratio. The bandwidth of a normal voice circuit is 3 khz. This is ensured by anti-aliasing filters on the local loop. These are needed to allow the analog signal on your local loop to be converted to a 64kbps digital stream. Now to work out the best possible signal/noise ratio. In practice, you just take this from the guaranteed figure as given by your friendly telco. For example, if your S/N is 40 dB, the maximum possible bit rate is given by: Bandwidth*(Log base 2(1+S/N)) = 3000* (Log base 2(1+100)) (S/N in power ratio, not dB) = 19931 bps You will, of course, never achieve this, since it assumes that the S/N is constant and that you use the full dynamic range, and that you use the best possible modulation technique. Mark Williams -- The views expressed above are not necessarily those of my employer. In a couple of hours they may not even be my own. Small boys throw stones in fun, but the frogs die in ernest. -- Mark Twain.