Principles and structures of IP phones in IP routing technology

The IP routing technology has been widely used in various fields and is gradually being upgraded. Here we mainly analyze the principle structure and key technologies of the IP routing technology. With the rapid development of optical networks and the application of digital transmission technology, problems such as bandwidth and service quality, which were regarded as bottlenecks in data communication networks, have been solved one by one, it promotes the rapid development of IP routing technology and brings various applications closer to IP addresses. IP phones, also known as IPPHONE or VoIP, are a typical application.

I. Concept of IP Phone

An IP phone is a new service that uses Internet technology or network for voice communication. From the perspective of network organization, there are two popular methods: one is voice communication over the Internet, which is called network telephone; the other is using IP routing technology, voice communication between telecom operators through a point-to-point connection over a leased line is called an economic phone or a cheap phone. Compared with the two, the former has the advantages of low investment and low price, but has important defects such as no service level and full-process call quality cannot be guaranteed. This method is mostly adopted by computer companies and data network service companies. Compared with the former, the latter has a large investment and a high price. However, because it is specially used for telephone communication, it has a certain level of service and the quality of Full-process calls is guaranteed. This method is mostly adopted by telecom operators.

There is a significant difference between an IP phone and a traditional phone. First, traditional telephones use public telephone networks as the media for voice transmission, while IP Phones convert voice signals between public telephone networks and the Internet to compress and encapsulate voice signals, the IP address routing technology allows multiple users to share the same bandwidth resources, which changes the way that a traditional phone is monopolized by a single user and saves the cost of using a separate channel. Secondly, thanks to technologies and market promotion, the technology for converting voice into IP packets has become more practical and inexpensive. At the same time, the price of digital signal processors, one of the core components of IP phones, is declining, as a result, the telephone cost is greatly reduced, which is particularly evident in the use of international telephone and communication fees, which is also an important reason for the rapid development of IP phones.

Ii. Basic principles of IP Phones

IP phones, also known as IPPHONE or VoIP, are segmented and digitalized transmission technologies based on IP routing technology. The basic principle is to compress and encode voice data using a speech compression algorithm, then, package the voice data by IP address and other related protocols, transmit the data packets to the receiving location through the IP network, and then concatenate the voice data packets. After decoding and decompression, the original voice signal is restored to achieve the purpose of transmitting voice over an IP network. The IP telephone system converts analog signals of ordinary phones into IP data packets sent by computers over the Internet, and also converts received IP data packets into analog electrical signals of sound. After the conversion and compression of the IP Phone System, the transmission rate of each common phone is approximately 8 ~ 11 kbit/s bandwidth. Therefore, when using a bandwidth with a transmission rate of 64 kbit/s, the number of IP phones is 5 ~ 8 times.

IP Phone gateway is the core and key device of an IP Phone. The IP Telephone Gateway has the routing management function, which maps the telephone area numbers of various regions to the IP addresses of the corresponding regional gateways. The information is stored in a database and related processing software provides call processing, digital voice packaging, route management, and other functions. When a user calls an IP address, the IP address Telephone Gateway determines the IP address of the corresponding Gateway Based on the telephone area code database, adds the IP address to the IP address data packet, and selects the best route, to reduce transmission latency, IP data packets are sent over the Internet to the destination IP Phone gateway. For areas where the Internet does not extend to or where no gateway is yet set up, you can set a route. The nearest gateway transfers the route through the long-distance telephone network to implement communication services.

III. Basic Structure of IP Phones

The basic structure of the IP Phone is composed of the gateway GW) and the gatekeeper GK. The main functions of the gateway are signaling processing, H.323 protocol processing, voice codec, and routing protocol processing. The Gateway provides the relay interfaces connected to the PSTN network and the interfaces connected to the IP network respectively. The main functions of the network guard are user authentication, address resolution, bandwidth management, route management, security management, and regional management. A typical Call process is that a call is initiated by a PSTN voice switch and connected to the gateway through a relay interface. After the gateway obtains the called number that the user wants to call, it sends a query message to the network guard, the Network Guard searches for the IP address of the called network guard and determines whether to establish a connection based on network resources. If a connection can be established, the IP address of the called Gateway is notified to the Gateway. After obtaining the IP address of the called gateway, the gateway establishes a call connection with the other gateway through the IP address, the called-side gateway initiates a call to the PSTN network and the switch calls the called user. After the called-side gateway is detached, the voice channel between the called-side gateway and the switch is connected, gateways use the H.245 protocol for capability exchange to determine the codec used for the call. After the capability exchange is completed, the caller can start the call.