Section 6.1. The

6.1. The "Dumb" Transport

In a VoIP network, each loop, or pathway, from caller to receiver is virtualized and controlled using software. So, during times of silence, for instance, the call's pathway doesn't need to utilize a full amount of bandwidth, and the shared resources of the network may be better utilized by another callor perhaps by another application altogether.

LAN and WAN data links, each capable of carrying TCP/IP, are just systems for moving bits, and the low layers don't distinguish between voice and data traffic, because it's all just TCP/IP packets. This dumb-transport notion allows for changes to VoIP's internal workings for voice digitization and calling features, just as it allows database application developers, for example, to add new functions to their systems. Future changes to the voice network, especially those that increase bandwidth economy, are simplified because the data link and the voice carrier aren't codependent.

Compare that to the trusty old voice T1, which is a rigidly defined data link designed with DS0 voice channels in mind: each channel is fixed at 64 kbps, and there can be 24 simultaneous phone calls per T1.

T1s are prevalent mainly in North America. In many other parts of the world, high-density digital voice links are called E1 and allow 31 simultaneous phone calls.

Of course, all of VoIP's economy and flexibility come at a price: sophistication of infrastructure. Many traditional telephone technicians aren't hip to what TCP/IP brings to the table: disaster survivability , a uniform addressing scheme, data link independence, and better integration with directory services. So, a lot of so-called "phone guys" bash IP telephony, dismiss it as a fad, or even claim that it doesn't work. If you've done the first several projects in this book, then you know how incorrect those claims arebecause you've already used a simple VoIP network successfully.