asterisk users - Dec 2004 - Linking asterisk to an existing small office PBX

Hi All

I've done some reading on the wiki and read some of the mailing list 
archives, but can't see anything on this. I guess this means I'm either 
searching on the wrong thing, or have totally the wrong idea... Can anyone 
suggest if the following is possible?


Currently, our office has a 24 analogue extension PBX, and 2 ISDN lines
providing it with external connectivity. We have several analogue
extensions spare, but no capacity to add fancier connectors to link to an
asterisk system (as most of the PBX linking guides detail). All our phones
are bog standard analogue ones.

We'd like to use an asterisk system to allow some calls to be routed out 
via a VoIP gateway. We'd also like to allow some inbound SIP calls to be 
handed to the PBX.


I was considering building an asterisk system, and adding a few FXS cards
to it. I'd plug these into the spare analogue extensions on the PBX (is it
FXS, and not FXO I'd need when connecting to a PBX?) If people wanted to
make a call using a VoIP gateway, they'd dial one of the asterisk
extensions. They would then be connected to the asterisk box by the PBX,
and could dial the real number they wanted. Finally, asterisk would
connect them to an external SIP gateway, which would do something useful
with the call.

Additionally, I'd like people working from home to be able to connect via 
SIP to the asterisk box, and then have their calls routed to the PBX down 
an analogue line.


Is this possible, and is it even a desirable setup?

Thanks
Nick

> I've done some reading on the wiki and read some of the mailing list 
> archives, but can't see anything on this. I guess this means I'm
either
> searching on the wrong thing, or have totally the wrong idea... Can anyone 
> suggest if the following is possible?
> 
> Currently, our office has a 24 analogue extension PBX, and 2 ISDN lines
> providing it with external connectivity. We have several analogue
> extensions spare, but no capacity to add fancier connectors to link to an
> asterisk system (as most of the PBX linking guides detail). All our phones
> are bog standard analogue ones.
> 
> We'd like to use an asterisk system to allow some calls to be routed
out
> via a VoIP gateway. We'd also like to allow some inbound SIP calls to
be
> handed to the PBX.
> 
> I was considering building an asterisk system, and adding a few FXS cards
> to it. I'd plug these into the spare analogue extensions on the PBX (is
it
> FXS, and not FXO I'd need when connecting to a PBX?) If people wanted
to
> make a call using a VoIP gateway, they'd dial one of the asterisk
> extensions. They would then be connected to the asterisk box by the PBX,
> and could dial the real number they wanted. Finally, asterisk would
> connect them to an external SIP gateway, which would do something useful
> with the call.
> 
> Additionally, I'd like people working from home to be able to connect
via
> SIP to the asterisk box, and then have their calls routed to the PBX down 
> an analogue line.
> 
> Is this possible, and is it even a desirable setup?
Yes, all of that is possible with lots of folks already doing it.

The extension appearances on your existing pbx are "fxs", therefore
the
mating interface on asterisk has to be an "fxo". The digium TDM04B is
one example of a 4-port pci card supporting 4 fxo interfaces.

If each of those four fxo interfaces were connected to unused extensions
from your old pbx, incoming voip calls (via the Internet) can be routed
to any of those four fxo ports. Likewise, an existing pbx user could
dial "8" as an example, and be sent to asterisk via those same four
ports.
You would need to be able to set up the dialplan in both the old pbx
and asterisk to handle the exact dialed digits the way that you want.

It is highly unlikely the old pbx can be made to forward callerid
numbers to asterisk, etc.

As time and budget permit, you could migrate to using SIP phones on the
asterisk side as well, displacing the old pbx analog phones.

On Tue, 7 Dec 2004, Nick Burch wrote:
> Currently, our office has a 24 analogue extension PBX, and 2 ISDN lines
> providing it with external connectivity. We have several analogue
> extensions spare, but no capacity to add fancier connectors to link to an
> asterisk system (as most of the PBX linking guides detail). All our phones
> are bog standard analogue ones.
> 
> We'd like to use an asterisk system to allow some calls to be routed
out
> via a VoIP gateway. We'd also like to allow some inbound SIP calls to
be
> handed to the PBX.
You could put Asterisk between the old pbx and the incoming isdn lines. A 
four port isdn card would be used in the Asterisk box. This way all 
functions should be available to both the old pbx and the new Asterisk 
box.

Peter

On December 7, 2004 07:51 am, Nick Burch wrote:
> Currently, our office has a 24 analogue extension PBX, and 2 ISDN lines
> providing it with external connectivity. We have several analogue
> extensions spare, but no capacity to add fancier connectors to link to an
> asterisk system (as most of the PBX linking guides detail). All our phones
> are bog standard analogue ones.
Ok so you have two ISDN PRI or two ISDN BRI?  (i.e. how many simultaneous 
calls can you make or take to the phone network?)

And you're saying you have 24 regular old phones -- the kind you can plug in
to a regular phone jack and use normally.  There are no soft buttons or fancy 
displays or anything?
> We'd like to use an asterisk system to allow some calls to be routed
out
> via a VoIP gateway. We'd also like to allow some inbound SIP calls to
be
> handed to the PBX.
No problem.  Although I would not use FXS cards -- with 24 phones that is ripe 
for a channel bank, and since they're FXS and not FXS pretty much any
channel
bank you can find will work just fine; I recommend the Adit600 personally but 
they are pricier than the older Access Bank I and II (I handles 1 T1, II 
handles 2) -- ABI/IIs can handle FXS lines without any issues whatsoever.  
They don't work worth a shit for FXO ports though, since they don't have
functioning far-end disconnect supervision (i.e. they can't tell when the 
other side has hung up).

So a T100P and an ABI will handle all your existing phones without any worry 
whatsoever.  Price: US$500 for the T100P and ~US$250 or so for an ABI off of 
ebay.

Any old Asterisk box will handle SIP phones, so as long as you have an 
ethernet card it'll work.

Depending on what you have for incoming lines (see my question above) you'd 
either use a T100P (total 3, may as well get a TE405P) or a single Sangoma 
A102u (2 T1s in 1 PCI card), or some kind of ISDN BRI card -- I am *not* 
familliar with the ISDN BRI stuff, so I'll defer that to someone else.

Depending on what your existing KSU or PBX is doing you can get rid of the 
thing altogether and let Asterisk do all your phone stuff, or try and 
integrate the two.  I have successfully integrated * with Norstar MICS (PRI 
and POTS) and am currently working on an NEC system whose model name escapes 
me at the moment.  The only reason I'm integrating them instead of replacing
them is that the people I'm doing this for are quite fond of their digital 
phones.  :-)

-A.

Hi!
> On December 7, 2004 07:51 am, Nick Burch wrote:
> > Currently, our office has a 24 analogue extension PBX, and 2 ISDN
lines
> > providing it with external connectivity. We have several analogue
> > extensions spare, but no capacity to add fancier connectors to link to
an
> > asterisk system (as most of the PBX linking guides detail). All our
phones
> > are bog standard analogue ones.
> 
> Ok so you have two ISDN PRI or two ISDN BRI?  (i.e. how many
> simultaneous calls can you make or take to the phone network?) 
With 24 analog extensions 2 PRI seems rather unlikely... :-) So let's 
assume 2xBRI = max. 4 simulatenous calls.
> > We'd like to use an asterisk system to allow some calls to be
routed out
> > via a VoIP gateway. We'd also like to allow some inbound SIP calls
to be
> > handed to the PBX.
> 
> Depending on what you have for incoming lines (see my question above)
> you'd either use a T100P (total 3, may as well get a TE405P) or a
> single Sangoma A102u (2 T1s in 1 PCI card), or some kind of ISDN BRI
> card -- I am *not* familliar with the ISDN BRI stuff, so I'll defer
> that to someone else. 
As Peter S. pointed out I think he really wants to go for a Quad-BRI card 
that allows for NT mode, and thus put Asterisk between the old PBX and 
the telco. Using analog ports on the PBX is clearly not a solution to be 
favoured.

Cheers, Philipp