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From: root@minixug.mugnet.org (MINIXUG-ONLINE System Manager)
Newsgroups: comp.dcom.modems
Subject: Re: What all does S120=16 do?
Message-ID: <910322577@minixug.mugnet.org>
Date: 22 Mar 91 22:34:22 GMT
References: <28581@netcom.COM>
Organization: MINIX User Group Holland (NLMUG)   -  MUGNET  -
Lines: 51

gandrews@netcom.COM (Greg Andrews) wrote:
> In article <1991Mar16.160708.152892@ramona.Cary.NC.US> andrew@ramona.Cary.NC.US (Andrew Ernest) writes:
>>In article <9908@discus.technion.ac.il> devil@techunix.BITNET (Gil Tene) writes:
>>>To detail : S120=12 means no use only LONG packets, no micro
>>
>>What are the side-effects of S120=16?  This is the value Telebit
>>says turns off the short burst of V.25 tone at the beginning of
>>each PEP answer tone.  This tone, which appeared in the BC5.10A
>>firmware upgrade for my TB+, caused my neighbors with older firmware
>>to no longer be able to connect to my modem.  S120=16 solved the
>>problem but I am now curious if that register value (16) has any other
>>effect I should know about (like packet size, etc).

S120=16 causes the firmware to ONLY send "long" packets, like in file
transfer ("spoofed") mode.  This is nice for links that have clicks in
them (like my link from The Netherlands to Japan), since the firmware
spends less time re-synching.

With micro-packets and short-packets (interactive resp. normal operation),
the firmware sometimes gets completely out sync, after which it has to
do a resynch ("retrain")..  this is annoying, and sometimes this can be
prevented by just simply increasing S120 to 12 (only short + long pkts)
or even 16 (only long pkts).

The disadvantage of 12 and 16 is, of course, that interactive operation
(login and such) gets really bad, since for each _character_ typed in,
the TB sends a _long_ packet, instead of a micropacket.  This, of course,
results in very long delay times.

So, on my link to Japan, login is very inefficient, as is file switching
during transfers.  So: we only send _ONE_ large (4-10Mbyte) file per
session, which makes up for login time loss...

> It turns off all of the mods put into the PEP modulation to combat trouble
> with echo cancellation devices on fiberoptic long distance carriers.
> One of the changes was a 3 second V.25 answer tone when the modem first
> answers the phone, even if PEP tones are first.  Previous versions of
> firmware didn't put out the V.25 answer tone before the PEP tones.
No, that is S121=1 .
S120 is for setting the low-level packet protocol specs (detail: packet
sizes).  With J6 (enter maintenance mode) you can also issue several
other register commands to further optimize the PEP protocol for a given
link situation...

All this "low level PEP optimization settings" stuff is documented in a
text file available from Telebit Corporation...

I could post it here, but I am sure that is not what people want...

Fred van Kempen
waltje@uwalt.nl.mugnet.org