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

[Aaron Leonard]

>>>  - 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).
>
>   

Your memory is probably correct.  DSP resources are, or can be, used for the following "ISDNish" protocols:

    * V.110 (inbound and outbound)
    * V.120 (DSPs necessary for outbound, optional for inbound)
    * 64/56k sync framed PPP/HDLC calls (inbound and outbound) (DSPs
      only needed if the trunk card doesn't have enough onboard HDLC
      framer resources - this only applies to CT3 cards, not to CT1/CE1).

LAPB-TA never uses DSP resources.

Obtw - we do not support outbound LAPB-TA, only inbound.  So if you need
to do callback (which some of you European fellows seem to favor for
some reason) ... the 5350 wouldn't be suitable.

>>>  - 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?
>   

Ah ... by the magical "transport input lapb" command which I somehow
managed to omit from my previously posted sample config.  Let me try it
again, with the missing command in place:

ip telnet quiet
aaa authentication login DIALIN none
aaa authorization exec DIALIN none
no banner incoming
!
interface serial BLAH:15
  isdn incoming-voice modem
  autodetect encapsulation lapb-ta
!
line vty 0 4
  location first 5 VTYs are used for administrative telnet/ssh
  transport input ssh telnet
line vty 5 34
  location VTYs for LAPB-TA (X.75) callers
  transport input lapb
  login authentication DIALIN
  authorization exec DIALIN
  autocommand telnet 1.2.3.4
  no exec-banner
  escape-character NONE
  special-character-bits 8
line 1/0 1/59
  location TTY lines for modem callers
  login authentication DIALIN
  authorization exec DIALIN
  autocommand telnet 1.2.3.4
  no exec-banner
  escape-character NONE
  special-character-bits 8

So the LAPB-TA calls will go to VTYs 5 thru 34, while the administrative telnet/ssh connections will go to VTYs 0 thru 4.

Cheers,

Aaron