Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 13: Network Infrastructure for VoIP

But redundancy costs money. It may be tough to justify a completely redundant net-

work and even tougher to manage one so that, when failures occur, it behaves as

originally envisioned. Moore’s Law infers that whatever capacity you make avail-

able, your application will become dependent upon it and grow to exhaust it—even

if it’s placed there for backup reasons to begin with. So, even if you have double the

capacity needed for every link—in the name of redundancy—you may still find your-

self in a state of panic when that capacity is merely reduced.

PSTN trunk failures

Some types of network links are easier to make redundant than others. IP links can

be automatically failed over using dynamic routing at the network layer, but voice

T1s and phone lines aren’t so simple. A PRI, for example, may go down—and when

it does, all of its DID numbers and inward signaling configuration will become

unavailable to the PBX. Even if a second PRI exists that the PBX can use for out-

bound calls, some emergency switch at the telephone company will have to occur in

order to reroute inbound calls to the second circuit.

The same is true of POTS and Centrex lines. If you have 10 POTS lines in a hunt

group and the line with the published number (the lead line) ...