2. Conclusion

The second part of this dossier describes the protocols implemented in networks to offer IP telephony and Internet telephony services. The associated standards originate both from "classic" telecoms bodies such as the International Telecommunications Union and 3GPP, and from organizations such as the Internet Engineering Task Force (IETF). These two schools of thought have given rise to a number of protocols that have coexisted and fed off each other for the sake of improvement. This is particularly true of the SIP protocol proposed by the IETF and enhanced by 3GPP for the IMS domain of UMTS, and the Megaco protocol proposed by the IETF and adopted by ITU through the H.248 specification. The protocols follow one another, and here are a few trends.

• Transmission protocols

  The transmission of user data, i.e. the voice...