Newsgroups: comp.dcom.modems
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Hayes 9600 sysop offer - a sour deal.
Message-ID: <1988Oct13.170919.10521@utzoo.uucp>
Organization: U of Toronto Zoology
References: <8810081712.AA14615@ucbvax.Berkeley.EDU> <1394@percival.UUCP> <16738@shemp.CS.UCLA.EDU>
Date: Thu, 13 Oct 88 17:09:19 GMT

In article <16738@shemp.CS.UCLA.EDU> casey@cs.ucla.edu (Casey Leedom) writes:
>  There are a *LOT* of applications that need as much bandwidth as you
>can muster in *BOTH* directions.  The Austrailian equivalent to UUCP for
>one (ACS?) which transfers in both directions simultaneously...

However, you can turn this argument around:  the Australian networking stuff
exploits both directions on the theory that both are usually there.  That
arguably was an artifact of the modem technology of the time.  The biggest
(in terms of volume) application for uucp et al is news transfer, which is
usually *highly* asymmetrical and cannot fully use a symmetrical path.  For
that application, it is not merely okay but *better* to have a half-duplex
channel running twice as fast.

> running a
>multiplexed communication channel across a dial up link...

This again depends on how that channel is being *used*.  The one significant
win of a full-duplex path is in applications that care about response time
rather than throughput.  The obvious case is humans typing.  A less obvious
case is a lot of network protocols.  But if what you're doing is bulk file
transfer and your protocol is prepared to cope with long ack delays, there
really is no advantage to full-duplex communication if it means that you
take a factor-of-2 speed hit.

>...  Until new modems came along that mirrored UUCP's half duplex
>nature, it was pathetic...

I have news for you:  fast half-duplex modems considerably pre-dated fast
full-duplex modems, for quite fundamental reasons.  They've only recently
gotten popular in the uucp world, but occasional groups have (I'm told)
been using them for uucp for a long time.
-- 
The meek can have the Earth;    |    Henry Spencer at U of Toronto Zoology
the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu