Basic knowledge of group exchange network

We all know that, according to the status of the group exchange network in the network, there are two types of switch and local switch, which play an important role. The Group switching network is a new type of switching network after the Circuit Switching Network and the packet switching network. It is mainly used for data communication. Group exchange is a storage-based forwarding method. It divides user messages into groups with a certain length and forwards packets by group.

Therefore, it is more efficient than circuit switching, and has lower latency than packet switching, and has the capability of real-time communication. Based on the statistical time-division multiplexing principle, the group exchange combines a data link into multiple logical channels to form an information transmission path between the caller and the called user, which is called a virtual circuit (V.C) implement grouped transmission of data. The group exchange network has the following features:

(1) group switching has the capability of multiple logical channels, so the circuit utilization rate of the trunk line is high;

(2) terminals of different code types, rates, and procedures on the group exchange network can be interconnected;

(3) The Packet Exchange Network has the ability to detect and correct errors, so the error rate transmitted by the circuit is extremely small;

(4) the network management function of the group exchange network is strong.

The basic services of the group switching network are two types: switched virtual circuit (SVC) and permanent virtual circuit (PVC. The switching virtual circuit is like a telephone circuit, that is, when two data terminals need to communicate, call the program to establish a circuit (that is, virtual circuit), and then send data. After the communication ends, use the disconnection program to remove the virtual circuit. Like a leased line, a permanent virtual circuit provides a permanent logical connection between two terminals in the group network during the contract application period. No call setup or disconnection procedure is required. In the data transmission phase, the permanent virtual circuit is the same as the switched virtual circuit. The group switch data network is composed of a group switch, a network management center, a remote concentrator, a group assembly and removal device, and a transmission device.

(1) The group switch implements the interface protocol (X25) between the data terminal and the switch, and the signaling protocol (such as X75 or internal protocol) between the switch ), it also provides storage and forwarding in A group manner, supports the sub-networking service, and completes routing selection, monitoring, billing, and control in collaboration with the Network Management Center. Based on the status of the group exchange network in the network, there are two types of switch and local switch;

(2) The Network Management Center (NMC) works with the group exchange network to ensure the normal operation of the network. Its main functions include network management, user management, measurement management, billing management, operation and maintenance management, route management, network statistics collection, and necessary control functions, is the core of network-wide management;

(3) The main function of the grouping and disassembling device (PAD) is to convert the non-grouping format of the ordinary character terminal into the grouping format and group the data streams of each terminal, group-based multiplexing is performed on a collection channel, and the recipient converts the received group format in the opposite direction.

(4) The function of the remote concentrator is similar to that of a group switch. Generally, it contains the PAD function. It is only connected to a group switch and has no routing function. It is used in areas where users are concentrated, it is generally installed in the telecommunications department.