Chapter 17. VoIP

Table of Contents

17.1. What is VoIP?
17.2. Registration and Proxies
17.2.1. Registrar
17.2.2. Proxy
17.3. Home/office phone system
17.4. Network Address Translation
17.5. Number plan
17.6. Telephone handsets
17.7. VoIP call carriers
17.8. Hunt groups
17.8.1. Ring Type
17.8.2. Ring order
17.8.3. Overflow
17.8.4. Out of hours
17.9. Directory
17.10. Call pickup/steal
17.11. Busy lamp field
17.12. Using RADIUS
17.12.1. RADIUS accounting
17.12.2. RADIUS authentication
17.12.2.1. Call routing by RADIUS
17.13. Call recording
17.14. Voicemail and IVR services
17.15. Call Data Records
17.16. Technical details
17.17. Custom tones

17.1. What is VoIP?

Voice over IP (VoIP) is simply a means of carrying voice (telephone calls) over Internet Protocol (the Internet). Instead of using pairs of wires to carry the signal electrically, the sound is sampled and converted to a sequence of bytes. This is normally what is done in the telephone exchange before the data is sent over the telephone network. The key difference with VoIP is that the bytes are placed in packets, typically 20ms long, and these are sent via Internet Protocol. Unlike the telephone network, IP can cause packets to be delayed, lost or even copied. It is the job of the receiving end to cope with this and produce the audio again for the recipient to hear.

The end result is that telephone calls can be made over the Internet. This can cause confusion as this is often seen simply as free calls. Apart from costs for Internet traffic, this is indeed true where calls do not involve the traditional telephone network and you control both ends, but typically you will need to subscribe to a carrier who can route calls to and from the traditional telephone network.

The FB2900's role in this it to handle the IP packets used for VoIP. It does not get involved in converting sound to, or from, packets of data, but in passing those packets of data between VoIP devices and carriers. The protocol involves complex sequences of messages for control and authentication which the FB2900 handles.