[Asterisk-Users] ISDN phones & Asterisk, ASDI and then some

[Iain Stevenson]

Patrick,

--On Tuesday, April 22, 2003 12:58 am +0200 Patrick 
<idefix at puzzled.xs4all.nl> wrote:

> I hopefully correctly understand
> that I can use a plain cheap isdn4linux supported ISDN (passive) TA to
> hook up the PC to the ISDN line from the telco (FXO card?).

Yes you can.  I have had asterisk running with an Elsa card I picked up for 
£5.  However, most cheap cards are "passive" (ie they don't have much 
processing on board) and rely on the isdn4linux software.  Isdn4linux 
presents a modem like interface to asterisk.  The limitations I have found 
(in the UK) are principally with echo on the local side although some delay 
is also introduced (not serious).

In contrast, active cards (eg some of those from AVM) have on-board 
processing and support the CAPI interface.  Some also support echo 
cancellation.  You operate these cards with the asterisk chan_capi driver. 
People seem generally to be happy with that although I have no experience 
with it.

> Next in the
> PC I also need a FXS card like a Digium TDM10B or PhoneJack so I can
> hook up an analog phone to it.
>
> In sort of graphics:
>
> analog phone === FXS card - PC - FXO card === Telco/PSTN
>                  PhoneJack       ISDN TA      ISDN
>                  Digium TDM10B
>
> Questions:
> 1) Is my description above right?
>

Not exactly.  You could connect a phone to the PC through an USB adapter, 
which would go:

  analogue phone === USB interface (S100U) - PC - ISDN card === Telco/PSTN
                                                                ISDN

If you have an ordinary analogue PSTN line, buying the Digium Devkit Lite 
would be a good starting point.  You could use an FXS card for a local 
analogue phone as you suggest but there would be no need for an FXO card if 
you have an ISDN card in the PC.

If you have an ISDN TA then you could install an X100P in the PC and 
connect it to the TA (I have done this).  However, be warned that the 
Digium hardware assumes US signalling voltage patterns on the line.  These 
may not be provided by your TA (I had to modify the driver code to get the 
X100P to work with my ISDN TA - it now works fine).

> 3) is it possible that an existing pbx infrastructure is upgraded to an
>    * solution where the existing phones can talk to * just fine?
>    In other words: is there a general compatibility between phones from
>    various brands and PBX's from other brands? It would financially be
>    less attractive if a customer would have to buy a whole new set of
>    phones...

Probably not - commercial IP PBX vendors have a problem with this in the 
market.  Commercial products such as 3Com's NBX can be equipped with 
adapters (from Citel) so that they work with Nortel digital PBX phones. 
There are other options but in general PBX vendors like people to keep 
their phones and PBX ;-)

  Iain