help wrt UUCP between 3B1 OBM and TB

Greg Andrews gandrews at netcom.COM
Mon May 6 11:40:31 AEST 1991

In article <98083 at becker.UUCP> bdb at becker.UUCP (Bruce D. Becker) writes:
>In article <1991May4.210605.28387 at sceard.Sceard.COM> mrm at Sceard.COM (M.R.Murphy) writes:
>|I've a friend with a 3B1 using OBM to attempt UUCP connection
>|to two systems, each with a TB (one TB+, one 2500). 

  [parts of description deleted]

>|The 3B1 will not successfully complete a UUCP session with either TB
>|system. A representative log entry from one of the TB sites is:
>	The Telebit does something different when
>	running with interface speed locked, such
>	that connections to 3B1 OBM's won't work.
>	Apparently connection is possible when it
>	runs with unlocked interface, and without
>	flow control.

The most common problem is that the OBM barfs big-time on the Telebit PEP
answer tones.  The normal way to handle this is to set the Telebit modems 
to issue the PEP answer tones last (S92=1).  The OBM sees just the usual 
2400/1200 answer tones and is happy ever after.

The thing that Telebit modems do differently with a locked interface speed
is perform "stop bit deletion".  This is a condition where the transmitting
modem leaves off a character's stop bit once in a while, and the receiving
modem puts the stop bit back on the character before passing it on to the
computer.  This is done every 8th character by Telebit modems.

However:  Stop bit deletion is allowed in the 'specification' (actually
the correct term is recommendation) for V.22bis, and that's the only type
of connection where Telebit modems delete stop bits.  V.22bis is the 2400 
bps modulation.  A modem that can't handle missing stop bits would seem to 
be not fully compliant with V.22bis.

As far as I know, the OBM is a *1200* bps modem, using the Bell 212 or maybe
the V.22 modulation.  I'm not aware of any 2400 bps OBMs.  Telebit modems
don't do stop deletion for Bell 212 connections, so I can't see where that
would affect an OBM.  I think M.R.'s problem is more likely due to the OBM
having trouble with the PEP answer tones rather than stop bit deletion.

 |  Greg Andrews   |       UUCP: {apple,amdahl,claris}!netcom!gandrews    |
 |                 |   Internet: gandrews at netcom.COM                      |

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