Path: utzoo!news-server.csri.toronto.edu!rutgers!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!samsung!olivea!oliveb!amdahl!netcom!gandrews
From: gandrews@netcom.COM (Greg Andrews)
Newsgroups: comp.dcom.modems
Subject: Re: Slow T2500 transfer with long distance calls
Summary: Modems are probably retraining
Keywords: Trailblazer, T2500, PEP
Message-ID: <27963@netcom.COM>
Date: 12 Mar 91 19:33:59 GMT
References: <356@alderan.uucp>
Followup-To: comp.dcom.modems
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 43

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 delays during login deleted]
>
>To me, it looks like that the modem(s) are buffering data, and don't 
>transmit or retransmit the data as long their buffer is not full or some 
>long timeout value (+30 sec.). I know that this sounds stupid, but that's 
>the way it looks like.
>
>Like I said, this only happens when I call a host in the USA. All my
>PEP connections here in Germany run just fine.
>

You're probably seeing the modems retraining.  A PEP retrain takes 10
or 15 seconds, and the modems can often achieve a long distance link
only to retrain very soon afterward.  Sometimes the modems will need
to retrain three or four times before they are able to overcome problems
in the phone line.  Very long distance calls and/or satellite links like
calls from Europe to the USA can have this trouble.  You can check if
this is really happening by turning your speaker on all the time and
listening to the sounds the modems make.  Set M2 and adjust S61 to a
comfortable speaker volume and listen to the connection.  A retrain
sounds just like the PEP answer tones, so it's easy to tell when the
modems are retraining.

After a few retrains the modems have tuned the PEP characteristics to
make the connection stable, and the communications continue without
interruptions.  You can adjust a couple of registers in the modem to
put PEP into the same state without needing to perform retrains.  Telebit
tech support can advise you of which registers and what values to use.
You can send e-mail to modems@telebit.com or uunet!telebit!modems if
a phone call would cost too much from Germany.


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