What IP telephony architecture
is all about. The hard facts on softswitches.

Isn't it frustrating when everyone tells you that you should be running IP telephony because of the potential reduction in TCO, the great ROI, the productivity enhancements and how convergence is the way of the future, yet nobody actually tells you how it works? How exactly are you supposed to connect IPT into your existing phone system?

What are all these media servers and gateways and what's so special about an IP phone? Here we'll take a quick look at the basics of IPT operation. Traditional PBX vs. IPT architectures First off, think of an IPT setup as a sort of exploded PBX. We're talking here about a pure IP setup, not a hybrid where IP functionality is ported onto an existing PBX, as that keeps more of the traditional architecture. With a PBX, you have call processing, voice switching, line cards to connect to handsets and trunks to the outside world.

IPT is much the same but does it in different boxes rather than (typically) one large set of co-located racks. The call processing - ie who wants to talk to whom - is done by what's commonly called a softswitch, IP PBX or media server. The latter name gives it away. Typically, it is a server, running a cut-down or hardened version of the OS, be it Linux or Windows, with call handling software. Instead of the multiprocessor PBX, you have multiple softswitches, both for resilience and to allow scalability - to a large extent, these can be managed as one entity as far as configuration goes.

The voice switching, instead of being done on the backplane of the PBX, is done over your LAN. Once the softswitch tells a handset the IP address that relates to the phone number it's trying to contact, it can bow out, leaving IP to do its thing and let the two endpoints communicate directly. This is why softswitches are so much smaller, both in terms of processing power and physically, than a TDM-based PBX. more>>>