Path: utzoo!utgpu!water!watmath!softart!ashok
From: ashok@softart.UUCP (Ashok C. Patel)
Newsgroups: comp.dcom.modems
Subject: Re: hayes 9600 vs. trailblazer
Message-ID: <38@softart.UUCP>
Date: 15 Apr 88 20:04:27 GMT
References: <8804110136.AA16978@ucbvax.Berkeley.EDU> <15612@onfcanim.UUCP> <494@edsews.EDS.COM> <280@telebit.UUCP>
Organization: Softart Microsystems Inc., Waterloo Ont. Canada
Lines: 39

> 3.  With regard to compressing data in the modem versus in the computer, let's
>     think about a hypothetical example. Suppose you have a modem link that 
>     runs at 19.2K (perhaps using a Telebit TrailBlazer). So the maximum speed
>     that the link could run would be limited by the RS-232 connection between
>     the modems and the computers. OK? 
> 
>     Now, if we compress in the computer, we can send the COMPRESSED output out
>     at 19.2K. This means the ACTUAL THROUGHPUT would be the 19.2K link speed
>     times the compression ratio. If we use a compression ratio of 1.5:1, then
>     the actual throughput would be 28.6K. But if we did compression in the
>     modem, we'd always be limited by the link speed to 19.2K. OK?
> 
>     You can achieve throughput rates above the link speed by pre-compressing
>     the data in the computer. You are limited by link speeds if you compress
>     in the modem.
> 

This is only true if your DTE (computer) and DCE (telephone line) data rates
are equal.  That is, the DTE is running at 19.2K and the DCE is running
at 19.2K.  But if you could break the DTE data rate free from the DCE data rate
(say 38.4K) then you would get the 28.6K throughput by doing compression
in the modem.  But then, you will have to worry about flow control between
the modem and the computer.  Sometimes a nasty thing to fret over...

> Regards,
> 
>===============================================================================
>Richard Siegel                          Phone:                   (415) 969-3800
>Senior Systems Engineer                 UUCP:  {uunet,ames,hoptoad}!telebit!rls
>Telebit Corporation                      ARPA:  telebit!rls@ames.ARPA
>                                 
>            "When the going gets tough, the weird turn pro"...HST
>===============================================================================

likewise,

-------------------------
Ashok C. Patel
Softart Microsystems Inc.