S-x86; You too can make your internal modem run PPP with asppp !!!

PPP-ers,

    After much trial and error, I finally figured how to get internal
modems to work under Solaris.  It turns out that if you follow the
instructions (answerbook and FAQ's), ppp will work fine for an external
modem, but internal modems (at least 2 that I have tried so far) will fail.
I have only tried 56K modems (Best Data and Diamond), and don't know if
this is also a problem with slower modems or other modem vendors, although
I suspect it is since I see references to the symptoms long before 56K
modems existed.

    The symptom is that tip and cu appear to work fine, but ppp connects
and logs in and subsequently fails miserably.  The asppp.log file (with
debug enabled) reports numerous BAD FCS errors in the input stream.  I saw
this symptom mentioned in many places in the digests, but never came across
an asppp based solution.  The only solutions seemed to involve external
modems or pppd.  Since I am running Solaris 2.6, and pppd is reported not
to work yet for 2.6, and the only external modems I have are 28K, I was
forced to find a solution.

    The solution is that the P_ZERO and/or STTY pseudo expect/send pairs
must be the first thing in the Dialers script.  They must appear before the
first AT command is sent to the modem.  All of the documentation I have
seen says to put the P_ZERO in the beginning of the Systems file entry and
put the STTY at the end of the Dialers entry.  In both cases, these are
executed, after the modem has autosensed the input characteristics of the
serial port.  Apparently, if these are changed after the autosense, the
UART on the modem card gets into some funny state.  It appears to be some
kind of parity problem or other problem with the most significant bit,
since the cause of all of the BAD FCS errors is always an upper bit being
set when it shouldn't be.  This doesn't appear to be a problem with
external modems where the UART is a physically independent device.

    Here are what the Systems and Dialers entries should look like for a
SUPRA 56K modem (you should be able to figure out the Devices entry).  Note
that your chat scripts might be different (i.e. --gin: instead of --name:).

Systems entry:

ppphost Any ACU 115200 5551212 "" \n name:--name: pppuser word: PpPpAsSwD

Dialers Entry:

supra  =,-, ""     P_ZERO "" STTY=crtscts,crtsxoff ""
\dA\pTZ&F0&D0E1V1W1Q0L0S2=255S10=254S9=12S41=131S42=131S109=62T\r\c OK\r
\EATDT\T\r\c CONNECT

    Some of the S register settings are undocumented in the SUPRA 56K
manual and probably are not that important, although it does seem to work.
These were actually taken from the setup for an older, 28K SUPRA FAX modem.

    Someone should probably integrate this info with the appropriate FAQ's.

George White
george@palisad.com
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