[Asterisk-Users] isdn, modem, etc.

[Anthony Wood]

On Tue, Nov 04, 2003 at 02:43:36AM +0300, Shoval Tomer wrote:
> I see many posts about using ISDN cards and modem cards.

In my list lurking, I have gathered:

ISDN comes in two flavours, Euro and US, and two sizes BRI(2
lines)/PRI (24-30 lines) hardware generally only supports one size and
flavour.

ISDN has many advantages because the signalling (e.g. The person you
are ringing picked up, hung up, callerID etc.) is digital already and
is well defined.  If you are using analogue lines all this info is
learned through what seem to me to be hacks.

for more than 10-14 lines it is recommended to go with ISDN PRI (this
is probably called T1 or E1 in your country)

for 1 or 2 lines use a digium X100P per line, but there are some
issues with UK CallerID, Asterisk not hanging up, and hardware not
approved in certain countries


for in between you can use ISDN BRI - either an ISDN4linux supported device (e.g. NetJet) or a CAPI supported device (e.g. AVM Fritz!Card PCI)
I only hear good things about the CAPI devices and drivers (chan_capi).
The NetJets give echo to your internal phone users using chan_modem_i4l, but sound ok to those on the outside.

> Does this mean I can use a regular modem (that supports voice) as an FXS, or
> FXO ?

No.  Most modems only support half-duplex voice over serial, and the linux stuff only supports half-duplex voice AFAIK.
Maybe you can hack something together, I haven't heard of anyone using it in any environment yet.
 
> If so, can you provide an example.

there are drivers for chan_modem_aopen and chan_modem_bestdata, but I don't know if they work or not.

> It might be the easiest way to test Asterisk's collaboration with the PSTN (or
> analog phones) and provide proof of concept to non-believers.

No, this is not the easiest way.  I think the easiest way is to order a Dev Kit from digium, or
if you have an ISDN BRI line handy, an AVM Fritz!Card Dev Kit from junghanns.net (the chan_capi developer)
together with a TDM20P. (2 FXS).

If you are keen and have more time than money, many people would like you to program your own channel (a combination
of chan_local and chan_modem which uses a modem and a soundcard to do FXO full duplex.

FXS requires something to generate the ring voltage (~75 Volts), which modems don't have.

cheers,
Woody