Don't be left behind as Voice overIPcomes into full flower.
—Jeff Aldridge
This chapter discusses basic VoIP terminology and concepts. Even the acronym VoIP is an example of the rampant jargon you have to master to understand and deploy VoIP. There is lots of terminology to cover, from both the telephony and data-networking communities. The proper terminology is used throughout this book, but terms are introduced and explained in plain English.
IPtelephony is a phrase that is often used synonymously with VoIP. Both IP telephony and VoIP refer to the components and technology needed to place telephone calls over an IP-based network. This book uses VoIP as an umbrella term to cover all aspects of IP telephony.
This chapter starts with some call fundamentals. A telephone call occurs in two stages:
Setting up the telephone connection between the person making the call (the caller) and the person receiving the call (the callee)
- Getting from one telephone to the other, through everything that is in the middle.
- Committing the resources to that call, so that once the callee gets it, the callee gets to keep it, and the call is not unexpectedly terminated right in the middle.
- Ending the call when it is complete.
- Billing someone for the call.
The call itself
- People or computers speak to one another for some amount of time
- Voice (audio) is translated into a format that is sent over a network
- The digitized audio information is transformed back into sound
Both stages involve specialized equipment and a set of rules that guides the operation of that equipment. This chapter first looks at how telephone calls work in the telephony community and then looks at how telephone calls work in the data-networking community.
