Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!hayes!tnixon
From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: Clarification on MNP4 and Everex 24+
Message-ID: <3776.27b7ea0d@hayes.uucp>
Date: 12 Feb 91 13:13:49 GMT
References: <6779.27B72B77@zswamp.fidonet.org>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 51

In article <6779.27B72B77@zswamp.fidonet.org>,
root@zswamp.fidonet.org (Geoffrey Welsh) writes: 

> In a letter to All, Larry Snyder (larry@nstar.rn.com ) wrote:
> 
>  >the buffers are great for file transfers - but for 
>  >interactive use
>  >with on-line hot keys - they can create problems.   I wish 
>  >there was
>  >a way on the fly to enable and disable the buffers from 
>  >within the BBS
>  >hostware - without leaving the system open for users to play 
>  >with the modem configurations (maybe there is such a way?)
> 
>    Not that I know of.  Certainly it helps to be able to cut the HST's buffers 
> back to 128 bytes when not in MNP mode, as that cuts the hotkey response delay 
> for 2400 and 1200 baud callers to less than a second; hopefully the data will 
> move quickly enough at 9600 that the dumping of the buffer won't take long.

I'm confused as to what the issue is here.  The size of a modem's 
TRANSMIT buffer has NOTHING to do with propagation of function key 
transmissions, etc., any more than it has to do with forwarding of 
single keystrokes in echoplex environments.  All modem manufacturers 
optimize their implementations to handle interactive traffic as 
expeditiously as possible, since the typical user's tolerance for 
echo delay is very low (around 100 msec).  

All modems I'm aware of DO NOT use a "timeout" or wait for some 
minimum number of characters to be available, but use what is
called "stream-mode packet forwarding".  As soon as even ONE
character is available for transmission, the modem begins
transmitting a frame to contain that character; since the header is
at least four octets long, it is possible that additional characters
come from the DTE during this process.  If so, these are added to
the same frame.  So long as additional characters come from the DTE,
they will continue to be added to the same frame, until the maximum
frame size is reached or the modem runs out of data and must close
the frame.  

So, as I said, I don't understand the concern about buffer size.  
Large buffers do NOT increase propagation delay of small bursts of 
data.  Their primary negative impact is when you attempt to _cancel_ 
a _long_ transmission.

	-- Toby

-- 
Toby Nixon, Principal Engineer    | Voice   +1-404-449-8791  Telex 151243420
Hayes Microcomputer Products Inc. | Fax     +1-404-447-0178  CIS   70271,404
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