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General Terms

VoIP protocols

There are many protocols involved in the various functions of VoIP services. However, the two most popular protocols used for the signaling of calls are H.323 and SIP. Interoperability of clients to services relies primarily on signaling and secondarily on the exchange of media. For a general discussion of VoIP, check Wikipedia

VoIP codecs

The term codec refers to the method of coding/decoding of the media data (voice and video) to meet bandwidth requirements of the available network channel. A caller device has to support the same codecs as those available on the other side, i.e. the called device or server. Otherwise the exchange of media may not take place, even though call signaling negotiation has been successful. There are many codecs available for voice, the most popular of which are the G.xxx series as standardized by the ITU. The most commonly available codecs are: G.711 - Pulse code modulation (PCM) demanding a 64 kbps channel and  G.729 - Conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP) demading a 8 kbit/s channel. For a general discussion of Voice Codecs, see Wikipedia

VoIP services

Attempting a simple classification of VoIP services

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, for the purposes of this cookbook, we see:

•  basic services: registration of endpoint on servers, call routing, location and call translation

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• value-added: voice-mail, missed call notification
• enhanced communication services: interoperability of voice calls with other media, like video, instant messaging, as well as trusted domain infrastructure to support level of trust indication to the end user

SIP Proxy server

H.323 Gatekeeper

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