Brief Introduction to the classification and development of network exchange technology

1. Circuit Switching Technology

The network switching technology has gone through four stages: Circuit Switching Technology, packet switching technology, group switching technology and ATM technology. Both the Public Telephone Network (PSTN) and the mobile network (including the GSM network and CDMA network) Adopt circuit switching technology. The basic feature of this technology is to adopt connection-oriented methods before both parties can communicate with each other, A communication circuit with fixed bandwidth needs to be allocated to both parties, and the communication parties will occupy the allocated resources until the communication ends, related Signaling Protocols must be used during circuit establishment and release. The advantage of this method is that in the communication process, the user can be guaranteed to provide sufficient bandwidth, and the real-time performance is strong, the latency is small, and the switching device costs are low, however, the disadvantage is that the bandwidth utilization of the network is not high. Once the circuit is established, the allocated circuit is always occupied no matter whether the communication parties are in the call status.

2. Group Exchange Technology

Circuit Switching technology is mainly applicable to voice-related transmission services. This network switching method has great limitations for data services. First, data communication is very abrupt. The peak bit rate and the average bit rate differ greatly. If circuit switching technology is used, allocating circuit bandwidth at the peak bit rate will cause a great waste of resources, if the bandwidth is allocated at the average bit rate, a large amount of data will be lost. Second, compared with the voice service, the data service has no strict requirements on latency, but requires error-free transmission. However, the voice signal may be distorted to a certain extent, but must be highly real-time. The group exchange technology is a kind of exchange method based on the characteristics of data communication services. Its basic feature is to adopt the storage forwarding Method for connectionless data communication, divide the data to be transmitted into many small pieces of data according to a certain length, and add the corresponding header fields used for data selection and verification before the data, as the basic unit of data transmission, it is grouping. Using the group exchange technology, you do not need to establish a connection before communication. Each node first accepts the Group sent by the previous node and stores it in the buffer zone, then, select an appropriate link based on the address information in the group header and send it to the next node. In this way, you can dynamically allocate bandwidth based on your requirements and network capabilities during the communication process. Group switching is more efficient than circuit switching, but has a high latency.

3. Packet Exchange Technology

The packet exchange technology is similar to the group exchange technology. It also uses the storage and forwarding mechanism, but the Packet Exchange is based on the packet as the transmission unit. Due to the large difference in the message length, long packets may cause great latency, in addition, it is difficult to allocate a buffer for each node. To meet the needs of various length packets and achieve efficient performance, the node needs to allocate a buffer of different sizes, otherwise, data transmission may fail. In practical applications, Packet Exchange is mainly used for communication services with short message transmission and low real-time requirements, such as public telegraph networks. Packet Exchange compared to group exchange occurs earlier. group exchange divides messages into groups for Transmission Based on Packet Exchange, balancing transmission latency and transmission efficiency, thus it is widely used.

4. ATM Technology

The extensive application and development of group switching technology have led to the coexistence of the Circuit Switching Network for voice transmission and the group switching network for data transmission, the network-based transmission of voice and data services has prompted people to think about a new technology that provides both the advantages of circuit switching and group switching, and provides unified services to users, including voice services, data services, and image information, the original CCITT proposed the concept of Broadband Integrated Business digital network at the end of 1980s, and proposes a new technology-asynchronous transmission mode ATM ). The ATM technology combines the connection-oriented mechanism with the grouping mechanism. Before the communication starts, you need to establish a certain bandwidth connection according to the user's requirements. However, the connection does not exclusively occupy a physical channel, it is used to repeat a physical channel with other connection statistics, and all media information, including voice, data, and image information, is divided and encapsulated into fixed-length groups for transmission and exchange in the network. Another outstanding feature of ATM is to propose a complete mechanism to ensure QoS. At the same time, because Optical Fiber Communication provides a transmission channel with low error rate, traffic control and error control can be moved to the user terminal, the network is only responsible for information exchange and transmission, thus reducing transmission latency. ATM is very suitable for high-speed data transmission. From a technical point of view, the ATM is almost impeccable, but the complexity of the ATM technology leads to the extremely high cost of the ATM switch, and there is no new service to drive the ATM market in the ATM technology, this restricts the development of ATM technology. At present, ATM switches are mainly used in backbone networks. They mainly use the high-speed and QoS Assurance mechanisms of ATM switching and provide semi-permanent connections.

1. Development of Network Exchange Technology