The Big Picture

VoIP devices, protocols, and codecs combine their roles to form the complete service you experience whenever you make an Internet phone call (Figure 1.8).

Figure 1.8. A typical Internet phone scenario

As you can see, you do not actually connect your phone to any telephone company's system. There is no requirement for you to remain in one place; in fact, you can be literally anyplace on Earth that has Internet connectivity and make a call as though you were right in your armchair at home. The called party will hear no difference (Internet connection quality being the same), and you will continue to receive calls on your home number even while you're on vacation in Paris!

Imagine traveling with your local phone and being able to check in with friends and neighbors without the high-priced hotel phones or calling cards you typically use on a trip.

Follow an Internet phone call step by step as it is initiated by a VoIP caller (Figure 1.9):

Figure 1.9. A VoIP call step by step

1.	When a VoIP caller picks up a phone or initiates a call using a softphone, the VoIP session protocol signals the VoIP provider. The caller's TA (telephone adapter) generates a familiar dial tone. Then the caller begins to dial the number.
2.	The tones of the phone handset are converted by the TA or the softphone software to a destination telephone number. The session protocol transmits this number to the VoIP provider.
3.	The VoIP provider uses standard telephone signaling to access the correct line at the phone company.
4.	The destination telephone begins to ring as the phone company transmits a ring-back signal to the VoIP provider.
5.	The VoIP provider passes the ring-back tone to the caller via the VoIP session protocol.
6.	When the called party picks up, the call is connected, and voice codec data begins to flow back and forth between the caller and the VoIP provider.
7.	The VoIP provider translates this data to analog voice signals, which the phone company passes to the called party.

Internet telephony resources

Are you the type of person who needs to know more about your phone than just how to hook it up? Do you lose sleep wondering what makes it work or whether your conversations are truly confidential?

This section explores some VoIP resources you can use to learn more about VoIP technology, codecs, protocols, and standards. I'll list a few Web sites (mine included) where you can learn more.

If you could care less? Well, I'll see you in Chapter 2 in just a minute.

More about VoIP standards

VoIP standards are ratified by the International Telecommunication Union (ITU-T) and the Internet Engineering Task Force (IETF). Indeed, most of the codecs used in VoIP were created for use in traditional telephone systems. The SIP session protocol was ratified by the IETF and has been integrated with the ITU-T standards to allow interoperability. You can learn more about the standards behind VoIP at my Web site (www.firethephoneco.com), the Web site of the ITU-T (www.itu.int/itu-t), or that of the IETF (www.ietf.org). Especially interesting for those who need good bedtime reading is the IETF's SIP Request for Comments document, RFC 3261 (www.ietf.org/rfc/rfc3261.txt).

You can find a good discussion of VoIP codecs at the VoIP Wiki:

www.voip-info.org/wiki-Codecs

Keep on reading

Chances are that if your question hasn't been answered yet, it will be in the next several chapters, which discuss the evaluation, installation, and optimization of your Internet phone service. You'll use everything discussed in this chapter and more as you go through this process.

Let's rejoin the group now, shall we?

What's a Wiki?

Wiki is short for wiki wiki, which means quick in Hawaiian. A wiki is a user-managed online information forum. Users can register to contribute to articles, refining the content and meaning of items that they specialize in. In addition to the VoIP Wiki, other popular wikis are

• Wikipedia (www.wikipedia.org). One of the largest wikis in existence. With more than 500,000 articles in more than 20 languages, Wikipedia is one of the most complete online encyclopedias.

• Portland Pattern Repository Wiki (http://c2.com/cgi/wiki) The first wiki. This site is still the best source for wiki information and history. Many folks learn to wiki here.