Switching to VoIP

This is the Title of the Book, eMatter Edition

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

Distributed Versus Mainframe

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The core is kind of like the 10-lane interstate highway: a lot of people drive on it, but

nobody’s driveway is an entrance ramp to it. So, while billions of hosts may send and

receive data that crosses the Internet core (backbone), almost none of those hosts are

directly connected to the core.

Instead, IP network endpoints connect to disparate network links that share high-

capacity aggregate connections to the core. These links are collectively known as the

edge. The edge is like the surface streets that surround the 10-lane interstate high-

way. Most traffic that ends up on the big highway originates from the surface streets.

A key difference between distributed and mainframe computing follows this anal-

ogy: in a mainframe environment, such as the PSTN, all the endpoints have a direct

connection to a core—the central office switch. Likewise, in a PBX system, all the

endpoints have a direct connection to a core—the PBX switch. So, all the driveways

in a mainframe town are actually entrance ramps right onto the big highway.

VoIP facilitates the build-out of the networking smarts that normally exist at the tra-

ditional PSTN core, so that application functionality gets closer and closer to the

edge of the network. This is similar to the way distributed ...