[asterisk-users] Is Asterix right tool for me?

[Dave Platt]

> Hi ,
> I am a newbie with Asterix and not sure if Asterix is a right tool for my needs.
> 
> Let's suppose this scenario :
> I have a telephone line in one office( all calls are paid to telephone operator).
> In other offices I have only internet connections.
> Is it possible to use Asterix so that I can make telephone calls from ALL offices( without 
> direct telecom connection) ? if so, what telephone equipment would they have to use (VoIP 
> telephones?)

Yes, indeed, Asterisk can give you this capability.  There are several
different approaches which can be used - which one you choose will
depend on your needs.

You'll need to equip your office users with VoIP telephones.  These can be
either dedicated IP-capable phones (usually running the "SIP" voice
protocols), or "softphone" software packages running on their PCs
(again, implementing SIP).  Dedicated "hard" IP phones can be had for
anywhere from $50 on up.

Softphone programs range from completely free to significant amount
of money, depending on what capabilities you want.  Simple ones
will emulate a one-line phone (often with a built-in contact list
and autodialer) while more complex ones can emulate a multi-line
business phone.  You would probably want to equip each PC with a
handset or headset of some sort rather than depending on the built-
in microphone and speaker.  USB-connected handsets are widely
available;  they're usually marketed as being for Skype, but most
of them simply register as USB audio devices and will thus work
with almost any soft-phone.

You'll want at least one system running Asterisk, to act as the
"hub" for your offices.  If you have a large number of users in
a particular office, and if they will wish to phone one another
within the office or working region, it may make sense to place
an Asterisk server in that office so that phone-to-phone traffic
stays within the office and doesn't have to travel over the public
Internet... this will reduce voice latency (delay) and perhaps
reduce your Internet bandwidth costs.

Each "hard" or "soft" IP phone will register with one of the
Asterisk servers, so that it can receive calls through that
server.  Urgent advice:  assign each such phone a unique,
difficult-to-guess username (*not* just the extension number you
are planning to assign to it) and assign it a *very* difficult-
to-guess "secret" (password).  Long, randomly-generated strings of
letters, digits, and symbols make the best secrets.  You *really*
do not want somebody from outside your system to be able to guess
a phone's username and password, or they'll be able to make calls
overseas for which *you* will be financially responsible (this can
be a *very* expensive problem if you don't take care!)

As to getting back onto the PSTN (public switched telephone network),
there are several different approaches you can take.

As others have suggested, the best is probably to purchase a SIP
account from one of the many different VoIP providers available.
Prices, services, and quality vary.  You'll probably be best off
picking one which is known to provide good service in your area,
and has an Internet-to-PSTN interchange switch close to you
(network-wise).

This SIP provider can do two things for you:

-  They can accept outbound SIP calls from your Asterisk server
   (and/or directly from your IP phones) and route these calls
   onto the PSTN.  This is what you'll want to do, in order to
   allow your offices that have only Internet connections to make
   phone calls.

-  They can provide you with any number of PSTN phone numbers,
   (in your own country or elsewhere) and route calls to these
   numbers to your Asterisk server.

Phones in your Internet-connected offices could make calls out
to the PSTN via any of several methods:

-  They could place calls directly to the SIP provider's servers.
   This would have the least latency and overhead, but the worst
   security problems (every phone would have to have an authorized
   account with the provider, or share a single outbound account
   and secret... not a good idea).

-  They could register with, and then place calls through your
   organization's main (or only) Asterisk server.  The server
   can restrict call destinations on a per-phone basis if
   necessary, provide centralized logging, etc.

-  Offices which have their own Asterisk server, could place
   calls through that server and out to the SIP provider,
   rather than going through the main company server.  This would
   provide somewhat better delay and call quality in many cases,
   and still give you a limited number of somewhat-centralized
   servers which would manage call security and authorization.