Page 169 - Asterisk™: The Future of Telephony

${EXTEN:1} would give us everything after the first digit, 4169671111 (if the number of
digits to return is left blank, it will return the entire remaining string).
This is a very powerful construct, but most of these variations are not very common in
normal use. For the most part, you will be using ${EXTEN:1} to strip off your external
access code.

Enabling Outbound Dialing
Now that we’ve introduced pattern matching, we can go about the process of allowing
users to make outbound calls. The first thing we’ll do is add a variable to the
[globals] context to define which channel will be used for outbound calls:
[globals]
JOHN=Zap/1
JANE=SIP/Jane
OUTBOUNDTRUNK=Zap/4
Next, we will add contexts to our dialplan for outbound dialing.
You may be asking yourself at this point, “Why do we need separate contexts for out-
bound calls?” This is so that we can regulate and control which callers have permission
to make outbound calls, and which types of outbound calls they are allowed to make.

To begin, let’s create a context for local calls. To be consistent with most traditional
phone switches, we’ll put a 9 on the front of our patterns, so that users have to dial 9
before calling an outside number:
[outbound-local]
exten => _9NXXXXXX,1,Dial(${OUTBOUNDTRUNK}/${EXTEN:1})
exten => _9NXXXXXX,n,Congestion()
exten => _9NXXXXXX,n,Hangup()

Note that dialing 9 doesn’t actually give you an outside line, unlike with
many traditional PBX systems. Once you dial 9 on an analog line, the
dial tone will stop. If you’d like the dial tone to continue even after
dialing 9, add the following line (right after your context definition):
ignorepat => 9
This directive tells Asterisk to continue to provide a dial tone on an
analog line, even after the caller has dialed the indicated pattern. This
will not work with VoIP telephones, as they usually don’t send digits to
the system as they are input; they are sent to Asterisk all at once. Luckily,
most of the popular VoIP telephones can be configured to emulate the
same functionality.

Let’s review what we’ve just done. We’ve added a global variable called OUTBOUND
§
TRUNK, which simply defines the channel we are using for outbound calls. We’ve also
added a context for local outbound calls. In priority 1, we take the dialed extension,

Building an Interactive Dialplan | 141