Development and trend of telecom network Exchange technology

First, the Network Exchange technology development process

1. Circuit Switching Technology

Network switching technology has undergone four stages of development, such as circuit switching, packet switching, packet switching and ATM technology. Public telephone Network (PSTN) and mobile networks (including GSM network and CDMA network) are all circuit switching technology, its basic feature is the use of connection-oriented approach, before the two sides to communicate, the need for both sides to allocate a fixed bandwidth communication circuit, Communication between the two parties in the communication process will always occupy the allocated resources, until the end of communication, and in the process of building and releasing the circuit need to use the relevant signaling protocol. The advantage of this approach is that in the communication process can be guaranteed to provide users with sufficient bandwidth, and real-time, the delay is small, the cost of switching equipment is low, but at the same time the disadvantage is that the network bandwidth utilization is not high, once the circuit is established regardless of whether the communication between the two sides is in the state, the distribution of the circuit has been occupied.

2. Packet switching technology

Circuit switching technology is mainly used for transmission and voice-related business, this network Exchange method for data services, has great limitations. First, the data communication has a strong burst, peak bit rate and average bit rate difference, if the use of circuit switching technology, if the peak bit rate allocation circuit bandwidth will cause a great waste of resources, if the average bit rate allocation of bandwidth, it will result in a large number of loss. Secondly, compared with the voice service, the data service has no strict requirements for the delay, but it needs to carry out error-free transmission, while the speech signal can have a certain degree of distortion but the real time must be high. Packet switching technology is a kind of exchange method, which is based on the characteristics of data Communication service. Its basic characteristic is to use the method of storing and forwarding without connection, dividing the data needing to be transmitted according to a certain length into many small pieces of data, and adding the corresponding header field before the data, which is used to select the data and verify the function. Grouped as the basic unit of data transfer. Using packet switching technology, you do not need to establish a connection before you communicate, each node will first receive the packet from the previous node and save it in a buffer, and then select the appropriate link to send it to the next node according to the address information in the packet header. In this way, the bandwidth can be allocated dynamically according to the requirements of the user and the ability of the network in the communication process. Packet switching is more efficient than circuit-switched circuit, but has a large delay.

3. Message exchange Technology

Packet switching technology and packet switching technology are similar, also uses the storage and forwarding mechanism, but the message exchange is the message as the transmission unit, because the message length difference is very big, the long message may cause the very big time delay, and to each node the buffer allocation is also more difficult, in order to satisfy each kind of length message needs and achieves the high efficiency goal , nodes need to allocate buffers of different sizes, or they can cause data transfer failures. In practical application, message exchange is mainly used for communication service with short transmission message and low real-time requirement, such as public Telegraph network. Packet Exchange is a bit earlier than packet switching, and packet switching is based on packet switching, which divides packets into packets for transmission, and balances transmission delay and transmission efficiency, which is widely used.

4. ATM Technology

The wide application and development of packet switching technology, with the coexistence of two networks, the circuit-switched network and the packet-switched network transmitting the data service, the communication between voice service and data service has prompted people to think of a new technology to provide the advantages of circuit switching and packet switching. And at the same time to provide users with a unified service, including voice services, data Services and image information, from the original CCITT in the late 1980s proposed a broadband integrated Services digital network concept, and proposed a new technology-asynchronous Transfer Mode (ATM). ATM technology combines the connection-oriented mechanism with the grouping mechanism, which needs to establish a certain bandwidth connection before the communication begins, but the connection does not monopolize a physical channel, but rather a physical channel with other connection statistics, while all media information, including voice, Both data and image information are segmented and encapsulated into fixed-length groupings for transmission and exchange in the network. Another prominent feature of ATM is that it puts forward a complete mechanism to guarantee QoS, at the same time, because the optical fiber communication provides a low bit error rate transmission channel, the flow control and error control can be moved to the user terminal, the network is only responsible for the exchange and transmission of information, so as to reduce transmission delay, ATM is very suitable for high-speed data delivery services. Technically, ATM is almost unassailable, but the complexity of ATM technology has led to expensive ATM switches, and the ATM technology has not introduced new business to drive the ATM market, thereby restricting the development of ATM technology. At present, ATM switches are mainly used in backbone networks, which mainly utilize the high-speed and QoS guarantee mechanism of ATM exchange, and mainly provide semi permanent connection.

Integration of circuit switching technology and packet switching technology

1. Integrated Switch Technology

Although ATM technology does not allow people to achieve the "integrated business" dream, but people have been looking for a way to achieve in a network to provide a variety of business, telecom operators also want to make full use of current network resources, as far as possible to provide users with rich business. The first proposed technology is integrated switch technology, mainly through the transformation of the existing circuit switching network to support both circuit switching and broadband switching (including ATM Exchange and IP Exchange) purposes. Many manufacturers have also developed a comprehensive switch, and the relevant industry standards "integrated switch technical Specifications" has also been enacted and promulgated. The integrated switch has the function of narrowband switch, and also has the function of the broadband switch. At present, there are two main ways to realize the integrated switch: one is to adopt a hybrid switching node, in which there are multiple independent exchange matrices, namely circuit exchange matrix, ATM and IP packet switching module, and the traditional PSTN call is mainly handled by the circuit switching module. The broadband-related business is processed by the Broadband packet processing module, and the protocol conversion is required when two modules need to interact. The other is the integration of switching nodes, the integrated switch basically only a single ATM or IP Exchange matrix, such as the Shanghai Bell's broadband switch S12 p3s is directly using ATM technology as the core Exchange technology, all the media information is converted into ATM in the switch internal processing, At the same time, the external support circuit switching network, ATM network and IP network. Integrated switches with converged mode have great advantages in flexible and fast business deployment because they have been changed into unified Exchange platform. Integrated switches because of a variety of functions, so the cost is also relatively high, mainly used in the larger volume of the Gateway Bureau and End Bureau, not suitable for the whole network implementation.