Telephony on IP

Since the invention of the first telephone by Alexander Graham Bell in 1869, telephony systems have evolved considerably: from circuit switching to packet switching, then to voice-over-IP, GSM and voice-over-IP over mobile networks. Today, telephony is experiencing one of the most critical periods in its technological evolution.

In recent years, there has been growing interest in the convergence of traditional telephony systems with computer networks. The integration of telephony flows, including signaling and communications, is now widespread in computer networks. A single network is used to carry voice and data in a system known as "Voice over IP" (VoIP) [16] .

Numerous advantages, including simplicity of administration and lower deployment costs, justify software publishers' interest in this technology. Since the early 80s, they have been seeking to use the computer network to carry voice. The emergence of the H.323 and SIP protocols gradually led telecom manufacturers to integrate this IP dimension into their solutions, with a view to voice-data convergence. Initially, this convergence took the form of optional cards to be integrated into existing PABXs (Private Automatic Branch eXchange), but today it is offered natively. Beyond the establishment of voice calls, the aim is to substitute the IP network for the telephone infrastructure, including fax and modem equipment, SMS/MMS services, videophony, and so on. This is a broader concept, combining several techniques in a single Telephony over IP (ToIP) architecture. ToIP is, in fact, the first real alternative to traditional telephony networks based on circuit-switching technology that is over 100 years old.

ToIP is not Internet telephony, despite the confusion often perpetuated in the media. The term "Internet telephony" is specifically used when the public Internet network is used to establish telephone communications. The Internet we use every day is a network of networks that no single organization controls or manages as a whole, and which does not guarantee quality of service. In contrast, telephony over IP is entrusted to a network managed by a single entity, either a company for its internal needs, or a telecommunications operator.

The following chapter introduces the general concepts of network architectures required to implement a ToIP system. The protocols that can be used to transport multimedia and data streams will then be detailed. Once these common elements have been defined, the following chapters will present the major solutions available on the market: H.323 [26] , SIP [9]...