[8719] in Commercialization & Privatization of the Internet
Re: A New Access Paradigm?
daemon@ATHENA.MIT.EDU (Stephen Williams)
Wed Dec 1 14:34:58 1993
From: sdw@meaddata.com (Stephen Williams)
To: welch@oar.net
Date: Wed, 1 Dec 1993 14:34:23 -0500 (EST)
Cc: bbx!kitsune!cheeks@cs.unm.edu, amr@cnri.reston.va.us, com-priv@psi.com
In-Reply-To: <199312011831.NAA03538@valhalla.oar.net> from "welch@oar.net" at Dec 1, 93 01:31:23 pm
The Microcom V.Fast modem that was the first announced was about $500 and
was capable of using the parallel port for io. A bidirectional
parallel port is about $40 and can do 200k-800k/sec.
Of course, it shouldn't really be that tough to integrate a $50 NE2000
ethernet board into a modem to make a combo terminal server.
A buffered serial port can do 115kbps with very little problem in a
modern machine with reasonable software. Laplink is a prime example:
it can do 115k on most machines with normal serial ports. Of course
it's dedicated and probably doesn't use interrupts, but with a 16 byte
fifo, most machines can handle the io with interrupts. Technically,
you only need ~7200 interrupts per second to handle 115k on a 16550
fifo, although it is generally higher since you set the threshold
somewhere in the middle.
This is all on a standard PC. Suns have terrible serial ports and can
barely handle 19200.
> My understanding is that V.fast means 28.8 kbps bit rate. To
> get 230.4 kbps you would need an 8x compression ratio! Unless your
> net traffic consists of only 'R' characters or something,
>
> Not to mention the fact that your serial interface is going to have to
> be able to pump those 'R's to the modem at 230.4 kbps. Lots of current
> machines have trouble with 56 kb, let alone 115.
>
> ..arun
>
> ----------------------------------------------------------------------
> Arun Welch 1224 Kinnear Rd
> Network Engineer Columbus, OH 43212
> OARnet welch@oar.net
sdw
--
Stephen D. Williams Local Internet Gateway Co.; SDW Systems 513 496-5223APager
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