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From: devil@techunix.BITNET (Gil Tene)
Newsgroups: comp.dcom.modems
Subject: Re: Slow T2500 transfer with long distance calls
Keywords: Trailblazer, T2500, PEP
Message-ID: <9908@discus.technion.ac.il>
Date: 15 Mar 91 13:06:03 GMT
References: <356@alderan.uucp>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: Technion, Israel Inst. of Technology
Lines: 57

In article <356@alderan.uucp> chris@alderan.uucp (Christoph Splittgerber) writes
:
>
>However, when I do very long distance links (e.g. to the USA) in PEP
>modus, my Trailblazer does behave very strange. I understand that I
>should not expect 1400 char/sec but just imagine this:
>
> ( description of long (~30 sec.) delays and slow throughput.)
>

I have a setup that works pretty well for overseas calls. It uses
two undocumented T2500 registers : S120 and J6 S36.

I suggest that you keep your speaker on for the duration of
the call using ATM2. It is a good idea to listen to the modem
and try to notice what is happening (I think I should be able
to whistle PEP by now :-)). What you have described above are
obviously PEP retrains, which are as close to loosing a connection
as you can get. A retrain on long distance lines typically takes
about 15 sec.

What works well for me is : AT S120=12 J6 S36=2 S121=1

To detail : S120=12 means no use only LONG packets, no micro
            or medium sized packets. This cuts down heavily
            on retrains. It makes interactive links much worse
            but does'nt really hurt throughput.

            J6 S36=2 sets the beep length of a beep sent
            ahead of a packet. This deals with a problem
            caused by compansion: where the beggining of
            a packets gets chopped off because of a
            period of silence just before it. Unfortunatly
            this register is not negotiable, which means that
            only the packets going OUT from you modem
            get saved by this feature.

            S121 is documented, it takes care of echos on long
            distance lines.

You shouldn't expect miracles. I get about 300-500 bps FROM UUNET,
and about 500-700 TO UUNET (that J6 s36 makes the difference).
I think this could be better, but I wouldn't expect anything
more than 800bps for that distance.

BTW, does anyone know if J6 S36 is negotiable in the V7.0 PROMs ?
I really wish it was...

HtH,

-- Gil.

--
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-- Gil Tene                     "Some days it just doesn't pay    --
-- devil@techunix.technion.ac.il  to go to sleep in the morning." --
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