Different types of IP telephony

Today IP Telephony is a very powerful and economical communication options.

IP telephony is the integration and convergence of voice and data networks, services, and applications. Internet telephony uses the Internet to send audio, video and data between two or more users in the real time.

Internet Engineering Task Force (IETF) defines the IP telephony is the exchange of information primarily in the form of speech that utilizes a mechanism known as Internet Protocol.

ITU-T Study-Group 2 (SG2) issued the following explanations of the term IP telephony: "IP is an abbreviation for Internet Protocol. It is a communications protocol developed to support a packet-switched network.

The main motivation of development of IP Telephony is the cost saving & integrating new services. Internet telephony integrates a variety of services

Vocaltec introduced the first Internet telephony software product in early 1995, running a multimedia PC, the Vocaltec Internet Phone. In 1996, Vocaltec announced it was working with an Intel Company (Dialogic Corporation, an Intel acquisition made in 1999) to produce the first IP telephony gateway. The technology has improved to that point where conversations are easily possible. Gateways are the key to bringing IP telephony into the mainstream. By bridging the traditional circuit-switched telephony world with the Internet. Internet telephony technology has caught the world's attention.

Different types of IP telephony:

There are four types IP telephony according to terminal equipment and types of network.

2.1: PC-to-PC:

The calling and called parties both have computers that enable them to connect to the Internet, usually via the network of an Internet service provider (ISP). The two correspondents are able to establish voice communication. Both users have to be connected to the Internet at that time and use IP telephony software. In this the caller must know the IP address of the called party.

2.2. Phone-to-phone over IP:

The calling and called parties are both subscribers to the public telephony network (fixed or mobile) and use their telephone set for voice communication in the normal way.

There are two methods for communicating by means of two ordinary telephone sets via an IP or Internet network.

Use of gateways:

One or more telecommunication players have established gateways that enable the transmission of voice over an IP network in a way that is transparent to telephone users. It works in “managed IP network” i.e. a network, which has been dimensioned in such a way as to enable voice to be carried with an acceptable quality of service.

Use of adapter boxes:

A number of companies market boxes, which resemble modems and are installed between the user's telephone set and his connection to the PSTN.

The calling party initiates his call in the same way as in a conventional telecommunication network. The first phase of the call is set-up on that network, however, immediately after this the boxes exchange the information required for the second phase. Data they have exchanged and the pre-established parameters, establish a connection between each of the two correspondents and their respective ISP. Once the call has been established, the boxes locally convert the voice signals into IP packets to be transported over the Internet

2.3. PC-to-Phone:

When the computerized user wishes to call a correspondent on the latter's telephone set, he must begin by connecting to the Internet in the traditional manner via the network of his ISP. Once connected, he uses the services of an Internet telephony service provider (ITSP) operating a gateway, which ensures access to the point that, is closest to the telephone exchange of the called subscriber. It is this gateway that will handle the calling party's call and all of the signaling relating to the telephone call at the called party end.

2.4. Phone-to-PC:

The calling party is the telephony user and the called party is the PC user.