Switching to VoIP

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Chapter 12: PSTN Trunks

Using some Asterisk dial-plan wizardry, you can preserve the original caller’s caller

ID information throughout the interswitch calling process:

# West office extensions.conf

...

[default]

exten => _30XX,1,SetCIDNum(${EXTEN})

exten => _30XX,2,Dial(Zap/1/5551300,35,mD(${EXTEN}))

In this case, Asterisk will supply the originating extension number as the caller ID

number.

SetCIDNum establishes the caller ID number for outgoing channels on the

current extension. This config would, of course, have to be mirrored for the East

office:

# East office extensions.conf

...

[default]

exten => _34XX,1,SetCIDNum(${EXTEN})

exten => _34XX,2,Dial(Zap/1/5551340,35,mD(${EXTEN}))

Asterisk’s built-in variables, like EXTEN, are case-sensitive! ${EXTEN}

works fine but ${exten} does not. User-defined variables, on the other

hand, are case-insensitive.

Routing PSTN Calls at Connect Points

In the previous section, we covered using PSTN trunks to facilitate users in the same

organization calling each other. The following projects describe ways of using PSTN

connect points for elegantly interfacing your PBX to the PSTN. This includes setting

up outbound rollover groups, using automatic call distribution (ACD) to intelli-

gently handle incoming calls, and leveraging common PSTN trunk features