Voice transfer on channels the Internet.

A few years ago there was a new type of service in the Internet - a voice communication (IP-phone, Vocaltec). Today there are 30 million subscribers who are regularly using IP-phone and its analogs, it is expected to 200 million until the end of the current decade, transmission quality gradually approaches the level of digital telephony.

Among users there are those for whom it is only a possibility of communication, as for radio fans; but more and more people use IP-phone for business contacts or even as object of business

There are two shrinking algorithms of sound information used for ip-telephone negotiations: GSM (global system for mobile communications, ftp.cs.tu-berlin.de/pub/local/kbs/tubmik/gsm) which provides compression ratio 5, and an algorithm of DSP group (true speech) with compression ratio of data 18 (works with frequencies of 7.7 kbps). Adding of hardware of compression of information allows to reduce a necessary band till 6.72 the Kbps. Loss of 2-5% of packets remains unnoticed, 20% leaves talk clear. In table 2.4.3.1 dependence of a necessary band of the telecommunication channel on the frequency of time gating of a sound signal which defines quality of reproduction is provided.

Table 2.4.3.1.

In case of implementation of an IP telephony it is desirable that network infrastructure provided:

Delay period in one side less than 100 ms.

Probability of loss of a packet less than 5%.

The equipment shall conform to requirements of H.323v2, and safety mechanisms - to the H.235 standard.

Existence of function of the gatekeeper in the router/gateway (locks installation of new telephone connections in the absence of necessary resources)

One of possible implementations of the IP telephony is shown in fig. 2.4.3.1. (MVD Multiflex Voice/WAN the module which is switched on in the router, for example, of Cisco-3662).

Fig. 2.4.3.1. Example of implementation системв IP telephony

 

In a figure the MVW module (Multiflex Voice/WAN) included in the router, for example, of CISCO-3662 serves for communication with a generally available telephone network. If the network of an azmeshchen in Rio de Janeiro, and Moscow, then any client of the lower network is able to talk to the client in Rio of an esplatno with clients of telephone networks about local rates. In the left part of a figure telephone sets which are connected directly to a segment of a local area network are shown. Such instruments already went on sale.

Communication can be carried out as with a traditional old analog telephone network, and with ISDN. Telephone sets can be connected directly to the router interface, to the network workstation or to the special LAN adapter.