Typical architecture

IP-telephony network (as recommended by ITU-T H.323) is a collection of the following devices connected to IP-based networks:

• gateway;
• gatekeeper;
• monitor.

Architecture of IP-telephony network consists of gateways connected by IP-network in the telephone network , providing a direct connection to a subscriber and perform encryption, compression and packing of voice/data and their recovery. All mechanism of interaction gateways controlled by administrator. For the convenience of remote configuration and network administration can be used monitor. These three components from different manufacturers may have different names, but they all perform the functions summarized higher. In addition to the higher requirements, equipment for IP-telephony should support several possibilities.

Functions:

• answer to the call of the caller PBX / PSTN;
• a connection to a remote gateway;
• a connection to the called party PBX / PSTN;
• compression, packing and restoring voice / data.

Thus, a gateway - a basic and integral part of the architecture of IP-telephony, the telephone network directly connecting to the network IP. Gateways from different manufacturers differ in how they connect to the telephone network, capacity, hardware platform, implemented codecs, interfaces and other features. But they all perform the above functions, which are the basic technologies for IP-telephony.

Gatekeeper - is an additional device connected only to IP-network, and carries in itself all logic of the IP-telephony network.

Functions:

• authentication and authorization of caller;
• distribution of calls between gateways;
• billing.

Monitor - an optional add-on IP-telephony network, connected only to IP-based network used for remote configuration and support for other network devices - gateways and gatekeepers. Features: interface for remote configuration of parameters of gateways and controllers through the IP-network. Monitor is a handy tool for configuration and network administration. In the first gateways for this used standard network applications. Later, in order to optimize the manufacturers of IP-telephony began to produce their own applications for these purposes. Besides described above requirements, the equipment for IP-telephony should keep a few possibilities:

• The transfer of control information. Tones are not distributed freely over the Internet. Coding and a breaking of IP-packets distort beyond recognition at the other end of communication. Thus, the telephone server should determine the tones locally, suppress their transmission, and then generate on the other end. While there is no standard for the transmission of DTMF via the Internet, but now different groups are developing on this issue, which gives hope for appearance of this standard in the near future.
• The interface with the telephone lines. In connection with the server's phone line telephone imposed two conditions. Communication must meet the standard, adopted in all major countries, as the largest economy, brought by IP-telephony, - on international calls. The solution must be scalable. Depending on the task before the system integrator, the system can vary from two lines for a small company to a few thousand lines for a major service provider (operator).
• Supports full-duplex. Telephone connection is full duplex, that is, both of you can talk simultaneously. A good solutions for IP-telephony is also full duplex.