Comparing the quality of standard telephony over public networks with the first generation of VoIP devices is not in favor of the latter, primarily because of low reliability and poor quality of service. However, the emergence of sophisticated modern applications and devices – high-performance switches and routers that use advanced quality of service (QoS) mechanisms for digital signal processors (DSPs) – eliminates many problems of second-generation VoIP systems.
IP-telephony refers to the technology of using an IP network (The Internet or any other) as a means of organizing and conducting telephone conversations and faxing in real time. IP-telephony is one of the most complex applications of computer telephony.
In general, voice transmission in an IP network in processed in the following way. The incoming call and the signaling information from the telephone network are transmitted to the edge network device, called the telephone gateway, and processed by a special card of the voice service device. The gateway, using the control protocol of the H.323 type, redirects the signaling information to another gateway located on the receiving side of the IP network. The receiving gateway provides transmission of signaling information to the receiving telephone equipment according to the plan of numbers, ensuring end-to-end connection. Once the connection is established, the voice on the input network device is digitized (if it was not digital), encoded in accordance with standard ITU algorithms, such as G.711 or G.729, compressed, encapsulated in packets, and sent to the remote device using a stack TCP / IP protocols.
Thus, using an IP network, you can exchange digital information to send voice or fax messages between two computers in real time. The use of the Internet will make it possible to implement this service on a global scale.
The main problems in building an IP network for the transmission of telephone traffic are the mechanisms for managing delays and maintaining sufficient bandwidth. In addition, methods of setting tariffs for services and billing for their use are important, as well as options for payment of additional services in the IP network, such as call forwarding, subscriber number determination, routing depending on the time of day.
An important issue is the evaluation of the profitability of the new technology. Is the combination of communications tools on the basis of IP is a significant saving? The answer to this question can be obtained only with a comprehensive examination of the problem. Perhaps this is the case. If the cost of information transfer over the network is only 15-20% of the total cost of supporting the network infrastructure, then 70% savings in network costs may not seem so attractive compared to the amount of work that will need to be done to transfer all functions on a universal basis. Besides, if comparing with a number of resources spent on the creation of a universal infrastructure and the possibility of using existing equipment.
This is only a small part of all the problems associated with the introduction of universal lines of communication. Therefore, as a rule, the offer for the integrated network service providers starts with the creation of small specialized networks, where the integration technologies and combining various types of communication tools are tested. However, even now we can talk about the reality of building an integrated infrastructure.