Page 351 - Asterisk™: The Future of Telephony

Inbound call to DID
Passed to PBX
PSTN PRI/BRI/Analog
PRI/BRI/Analog
Relayed out to Legacy PBX
SIP/IAX/H323
Cell phone cell phone VoIP call
Delivered to PBX telephone
home office
Database/Web/
VoIP Application server
IP telephone
PRI/BRI/Analog
Remote Asterisk Delivered to
remote PBX Remote PBX
Figure 15-1. Asterisk as a PBX gateway
Some Things That Are Now Possible

So what sorts of things can be built using Asterisk? Let’s look at some of the things
we’ve come up with.

Legacy PBX migration gateway
Asterisk can be used as a fantastic bridge between an old PBX and the future. You can
place it in front of the PBX as a gateway (and migrate users off the PBX as needs dictate),
or you can put it behind the PBX as a peripheral application server. You can even do
both at the same time, as shown in Figure 15-1.

Here are some of the options you can implement:
Keep your old PBX, but evolve to IP
Companies that have spent vast sums of money in the past few years buying pro-
prietary PBX equipment want a way out of proprietary jail, but they can’t stomach
the thought of throwing away all of their otherwise functioning equipment. No
problem—Asterisk can solve all kinds of dilemmas, from replacing a voicemail
system to providing a way to add IP-based users beyond the nominal capacity of
the system.
Find-me-follow-me
Provide the PBX a list of numbers where you can be reached, and it will ring them
all whenever a call to your DID (Direct Inward Dialing, a.k.a. phone number)
arrives. Figure 15-2 illustrates this technology.

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