Path: utzoo!attcan!uunet!husc6!bloom-beacon!oberon!orion.cf.uci.edu!paris.ics.uci.edu!venera.isi.edu!aero!elroy!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.dcom.modems
Subject: Re: Trailblazer detailed info wanted
Summary: 1803.1 bytes per second
Keywords: telebit modem specs, async start/stop bit overhead
Message-ID: <8698@cit-vax.Caltech.Edu>
Date: 25 Nov 88 08:41:30 GMT
References: <1615@sater.cs.vu.nl> <303@telebit.UUCP>
Organization: California Institute of Technology
Lines: 20

In article <303@telebit.UUCP>, rls@telebit.UUCP (Richard Siegel) writes:
>				   This 18031 bps is then reduced by
> about 20% to allow for the CRC overhead, to about 14400 bps of data
> throughput.

Isn't this 20% due to start/stop bits, not the CRC?  A 16-bit CRC is
tiny compared to a PEP packet.

>	   In "file transfer mode" the modem uses 136 msec packets
> (that transfer at 7.35 baud) that contain 256 bytes of data.

That multiplies out to 1881.6 bytes per second.  It sounds like a
PEP packet header of 10 or 11 bytes is deducted from that 256 bytes
per packet, to arrive at 1803.1 bytes per second.  I assume this is
what "18031 bps" really means.

A 14400 bps synchronous modem has the same data throughput (1800
bytes per second) because it doesn't need start/stop bits.

Don Speck   mangler@csvax.caltech.edu	{amdahl,ames!elroy}!cit-vax!speck