What is a telephone network

The telephone network is the communication network that open the telephone energy for the general User Service. The earliest form of telephone communication is only two telephones, which are connected by wires, however, when the number of telephone users in a region to increase the number of users can 22 call each other, you need to set up a telephone exchange, by the switch to complete the connection of any two users, then formed a switch as the center of a single bureau system telephone network. In a particular area (or city) as the number of users continues to increase, a number of telephone offices will be established, and then the bureaux can be connected by relay lines to form a multiple-station telephone network.

The telephone network is composed of three branches of the switch, the transmission Circuit (subscriber line and the relay circuit) and the user terminal equipment (i.e. telephones).

According to the use of telephone range classification, telephone network can be divided into local telephone network, domestic long-distance telephone network and international long-distance telephone network. A local telephone network is a telephone network consisting of an end board, an Exchange bureau, a trunk line, a long city trunk, and a subscriber and a telephone, in a numbered area of a uniform number length. For example, the services of the Beijing local telephone network include the urban part, the suburban part and the 10 counties and their rural parts. So Beijing local telephone network is a large local telephone network. The domestic long-distance telephone network refers to the nationwide long-distance call telephone network between the cities, each city has one or several long-distance telephone station, each long-distance bureau is connected by all levels long-distance circuit. International long-distance telephone network is refers to the world's telephone network to connect each other for international call network. For some, each country needs to have one or several international telephone offices for international and spoken connections. An international long-distance call is actually made up of the domestic network of the Speaker state, the International Bureau of the State, the International Bureau of the International Circuit and the recipient state, and the domestic network of the recipient State.

It should be noted that the addition of a small number of equipment in the telephone network can also transmit faxes, medium-speed data and other business.

The network structure of telephone network is basically divided into two forms: mesh network and graded sinks network. Mesh network for each end of the connection, applicable to the large number of traffic between the Bureau, the hierarchical Network for the tree-like net, the volume of traffic transfer, applicable to the small amount of traffic between the Bureau.

The network structure of China's long-distance telephone network is graded sinks network, the grade of long-distance telephone network is divided into five levels, C1 is a large area Exchange center, C2 for the Provincial Exchange Center, C3 for the Regional Exchange Center, C4 for the County Exchange Center. By the end of 1992 there were 8 C1 (Beijing, Shenyang, Shanghai, Nanjing, Guangzhou, Xi ' An, Chengdu), and 3 international bureaus (Beijing, Shanghai and Guangzhou). The network structure of the local telephone network generally sets up the two levels of the remit Board (TM) and the End Bureau (C5). TM Bureau can be divided into local calls to the Board, the effect of the Exchange Bureau, Nonghua and so on, C5 called the five-level switching center, that is, the local telephone network end bureau.

The current development direction of the telephone network for the program-controlled digital network, that is, all levels of the switching center of the programmable digital switch, transmission circuits are digital circuits. SPC Digital Network communication quality, high degree of automation, so rapid development. At present, the degree of programmable digitalization in China has reached more than 85%. The next development direction of the telephone network is the implementation of the Narrowband Integrated Services Digital Network (N-ISDN) and the Broadband Integrated Services Digital Network (B-ISDN).