Path: utzoo!attcan!uunet!elroy.jpl.nasa.gov!usc!apple!netcom!gandrews
From: gandrews@netcom.COM (Greg Andrews)
Newsgroups: comp.dcom.modems
Subject: Re: PEP vs. v.32
Summary: Half duplex V.32 = 19200 bps?  I doubt it.
Message-ID: <26254@netcom.COM>
Date: 1 Mar 91 02:00:03 GMT
References: <1991Feb27.185340.3897@shaman.com>
Followup-To: comp.dcom.modems
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 33

In article <1991Feb27.185340.3897@shaman.com> jiro@shaman.com (Jiro Nakamura) writes:
>
>  I have a question for the peanut gallery. I know that PEP uses a number
>of different frequencies for DAMQAM, achieving an average throughput of
>10,000 to 18,000 bps in one direction, with a smaller opposite channel
>in the opposite direction (I think it was about 30bps?)
>

You're confusing PEP with HST.  HST has the low speed back channel
while PEP is completely half-duplex (data flows in only one direction 
at a time).  I believe the HST 14400 modulation uses a 450 bps back
channel.

>  Now, this is great raw throughput. But a v.32 achieves 9600 bps in
>each direction, so theoretically it *could* do 19200 in one direction.
>No? If v.32 was set up as a half-duplex system with all of its resources
>going one way, it could do 19200 easily. 

I can't speak directly to that (perhaps Toby can help us with the
details), but I'm fairly certain that V.32 can't increase the bit
rate.  At least not V.32 *as such*.  

>  I would think PEP, using more of the available frequency bandwidth
>should be able to get consistently 18,000 bps or higher. Why not? 

Error correction.  PEP does consistently get 16,000-18,000 bps over
phone lines in the US.  The overhead of the error correction protocol
is what gives you throughput of just 12,000-14,000 bps.

-- 
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| Greg Andrews      |   gandrews@netcom.COM |
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