[cisco-nas] X.75 and modem dial-in, autocommand to TCP

[Gert Doering]

Hi,

On Wed, Mar 11, 2009 at 12:10:56PM -0700, Aaron Leonard wrote:
> >  - as far as I understand AS5xxx boxes, this should be doable with
> >    an AS5350 or the like
> 
> Yes.

Cool :-)

> >  - what do I need to terminate X.75 calls?  Do I need modem DSPs, or 
> >    will the X.75 be handled by the "digital side"?
> 
> The framing for incoming "X.75" calls (which we call "LAPB-TA") are
> handled by the onboard framers in the T1/E1/T3 trunk card plus IOS
> software, so no DSPs are used for this application.

Even better.  (I seem to remember that there was "something ISDNish"
that needed DSP resources, but maybe I mixed up things).

> >  - I assume that X.75 calls will end up on a "line async ...", 
> actually on a vty line

How do you know/control which vty is being used?

> > so I can
> >    put an "autocommand" there, to immediately connect from the router
> >    to the host at CONNECT time (*no* prompting or any sort of messages
> >    from the router is permitted).
> 
> Yep.

Cool.  I need to test that :-)

[..]
> ip telnet quiet

Ah.  Magic!

> line vty 5 34
[..]
>   escape-character NONE
>   special-character-bits 8

More magic :-)

> >  - is there Cisco gear that can handle X.75 on BRI lines (so we could
> >    develop and test this on an ISDN S0 port, without disconnecting the 
> >    whole PABX)?
> >   
> 
> Actually, you could configure your 5350 to do TDM switching for all
> calls other than those to a special test number.  

Interesting approach, but I *think* I'll get something-with-a-PRI first,
avoid more complications.  The customer is a bit nervous about this whole
dial-in thing anyway... so they can test this for a few weeks, without
endangering their existing stuff at all.

[..]
> But ... yes, any ISR (1800/2800/3800) that supports data BRI calls,
> should also support LAPB-TA.  You will need an image that supports this
> (check Feature Navigator http://www.cisco.com/go/fn - "ISDN LAPB-TA").

FN claims that this is available on 3640 in 12.0T/12.1 and up.  In all
available IOS features, that is, "IP only" or better.

Which is cool, because we have a heap of 3640+NM-8Bs lying around 
(formerly being used to terminate ISDN leased lines) that I can use 
for testing.

> >  - some of the clients have 'issues' with X75 window and block sizes - can
> >    this be tuned on the Cisco side, as in "we need to have the X75 block
> >    size set to 4096 byte on reception, 8192 on transmission"?
> 
> Ooh, not aware of any way to do that.  (Nor have I ever heard of anyone
> *need* to.)

There are "known issues" with some sort of windows ISDN card dialling into
some other sort of ISDN modems (Blatzheim) which just doesn't work 
properly for bulk transfers over X.75 (i.e.: zmodem) unless a window size
mismatch is fixed.

I don't know exactly yet what the mismatch *is*, and why it is causing 
issues...

In any case - thank you very much, this is very cool! :-))

gert

-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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