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Exchange technology

Development History

The rapid development of network technology, Ethernet occupies a dominant position. In order to adapt to the challenges brought about by the deepening of network applications, the scale and speed of the network are developing rapidly. The speed of the local area network has been increased from the initial 10Mbit/s to 100Mbit/s, and the Gigabit Ethernet technology has also been widely used.

For users, under the premise of reducing costs, ensuring high reliability, high performance, easy maintenance, and easy expansion of the network is closely related to which networking technology is adopted; for equipment manufacturers , On the basis of ensuring the realization of user network functions, how to obtain more considerable profits, using the advantages and disadvantages of networking technology, has become a means to increase profits.

In the specific networking process, whether to use the mature traditional layer 2 switching technology, or use the routing function of the layer 3 switching technology, or use the high network service level Layer 7 switching technology.

In the trade-off of these technology choices, the three technologies of layer 2 switching, layer 3 switching and layer 7 switching are better and worse, and what kind of environment are they suitable for?


Traditional layer 2 switching technology

When it comes to switching, in a broad sense, any data forwarding is It can be called an exchange. However, the traditional, narrowly defined Layer 2 switching technology only includes the forwarding of the data link layer.

Layer 2 switches are mainly used in small LANs, and the number of machines is less than 20 or 30. In such a network environment, broadcast packets have little effect. The fast switching function and multiple connections of the layer 2 switches Incoming ports and low prices provide a perfect solution for small network users.

In short, switched LAN technology makes dedicated bandwidth for users to enjoy, which greatly improves the efficiency of LAN transmission. It can be said that among the technologies of network system integration, the layer 2 switching technology directly facing users has already got a satisfactory answer.

Layer 3 switching technology with routing function

Layer 3 switching technology is a switching technology that only appeared around 1997. It was originally In order to solve the problem of the broadcast domain. After years of development, layer 3 switching technology has become the main force in building a multi-service converged network.

In a large-scale local area network, in order to reduce the harm of broadcast storms, the large-scale local area network must be divided into multiple small local area networks according to factors such as function or geographical area. This will inevitably lead to a large number of mutual visits between different subnets. However, the use of layer 2 switching technology alone cannot achieve mutual access between subnets.

In order to solve this problem technically, network manufacturers use layer 3 switching technology to develop layer 3 switches, also called routing switches, which are an intelligent combination of traditional switches and routers.

To put it simply, the switching technology that can handle network layer 3 data forwarding is the layer 3 switching technology.

From the hardware point of view, in the layer 3 switch, the layer 3 routing hardware module related to the router is also plugged into the high-speed backplane/bus. This method allows the routing module to exchange data with other modules that need routing at high speed, thus breaking through the traditional external router interface rate limitation.

Layer 3 switches are designed for IP, with simple interface types, strong layer 3 packet processing capabilities, and a much lower price than routers with the same speed, making them very suitable for large-scale local area networks.

Layer 3 switching technology is quite mature today, and at the same time, the development of layer 3 switches has never stopped. The development of layer 3 switching technology and layer 3 switching equipment will surely promote the informatization reform of the entire society on a deeper level and gain an increasingly important position in the entire network.

Layer 7 switching technology with network service functions

Layer 7 switching technology unlocks each layer of encapsulation of each data packet layer by layer, And identify the information of the application layer to realize the identification of the content.

Make full use of bandwidth resources to manage applications and content on the Internet, which has increasingly become the focus of service providers' attention. How to solve the problem from the transport layer to the application layer, the network technology that specifically manages the transport layer to the application layer has become very important. This is the most fundamental reason for the development of layer 7 switching technology.

To put it simply, the switching technology that can handle data forwarding at the network application layer is the 7th layer switching technology. Its main purpose is that in the case of bandwidth applications, below the network layer is no longer the key to the problem. Instead, it is to improve the level of network service and complete the transformation of the Internet to intelligence.

Layer 7 switching technology realizes all high-level network functions through application layer switches, enabling network managers to better allocate network resources at a lower cost.

From the hardware point of view, the 7-layer switch concentrates all functions on a dedicated special application integrated circuit or ASIC. ASICs are cheaper than traditional router CPUs and are usually distributed on network ports. A single device includes 50 ASICs, which can support hundreds of interfaces. The new ASIC allows smart switches/routers to forward data at extremely fast speeds on all ports. Layer 7 switching technology can effectively achieve data flow optimization and intelligent load balancing.

In the Internet, Intranet, and Extranet networks, Layer 7 switches are very useful for ambitions. For example, business-to-consumer e-commerce, online customer support, personnel planning and construction, marketing automation, customer service, firewall load balancing, content filtering and bandwidth management.


Switching technology is evolving in the direction of intelligence, from the initial layer 2 switching to the layer 3 switching, it has evolved to Exchange of the 7th application layer of the network. Its fundamental purpose is to ensure high reliability, high performance, easy maintenance, and easy expansion of the network under the premise of reducing costs, and ultimately achieve intelligent network management.

Related information

Communication network system

Communication network is mainly composed of three kinds of equipment: ①User equipment, such as telephone; ②Transmission equipment, such as cables, multiplexing devices, optical fibers, antennas, etc.; ③Switching equipment, such as telephone exchanges. The communication network system is to study how to form the most economical and effective communication network of switching equipment, transmission equipment and user equipment. This involves the optimization of switching office site selection and capacity, attenuation allocation, call loss allocation, routing planning, numbering system, signaling (also known as signal) mode, short-term and long-term business forecasts and corresponding development plans. And how to transition from analog network to digital network, etc.

Traffic issues

Study the relationship between the three parameters of the switch. The three parameters are: ①the number of switching equipment configuration; ②service level; ③the number of outgoing or incoming calls and the length of the talk time for each user equipment during the busiest period of time. Due to the different types of switching equipment, there are two ways to measure the service level. One is to treat the call as a loss immediately when the public equipment of the switch is busy. At this time, the user can generally hear the busy tone, that is, the obvious loss. The other is the connection delay, waiting for the public equipment to be idle before being connected. The waiting time is an indicator of the service level.

Technical performance and indicators

Due to the different types of switches and the scope of use, users have different requirements for their technical performance and indicators. Must first be determined during development. For example, for long-distance switches, it is necessary to determine the requirements for routing performance, the coordination requirements between long-distance and the city, the requirements for automatic or semi-automatic connection, the billing requirements, and the performance of maintenance and testing. To determine the adaptable communication network, the coordination with other standards, the long-distance coordination, the performance of special services and special services, the recovery control method and the maintenance test, etc., it is also necessary to clarify the transmission index, intra-office loop index and subscriber line index. Etc. These indicators are directly related to the service capability and quality of the switch.

Signaling method

Mainly refers to the way of transmitting signaling (signal) between exchanges. Taking telephone communication as an example, signaling can be divided into register signaling and line signaling according to content. ① Register signaling: signaling that transmits the number, category, and user status of the calling and called users. ②Line signaling: monitoring the signaling of off-hook and on-hook of the calling and called users. According to the relationship between its transmission route and call route, signaling can be divided into channel associated signaling and common channel signaling. The channel associated signaling is combined with the voice channel and transmitted on the same voice channel; the common channel signaling is the signaling of many voice channels is combined and transmitted on a dedicated public signaling channel, such as the International Telegraph and Telephone Consultative Committee (CCITT). ) Suggested No.6 and No.7 signaling, the former is suitable for analog networks, and the latter is suitable for digital networks.

In the 32-channel A-law pulse code modulation transmission of channel-associated signaling, the 16th time slot has a 4-bit code to transmit signaling, and its signaling arrangement is called DR2 internationally. If it is transmitted in analog mode, it is generally divided into the electrical characteristics of the transmission signaling, and it can also be divided into DC signaling (or DC flag) and audio signaling. DC signaling is mainly used for line signaling of local telephone space division switches; audio signaling is mainly used for register signaling. When the carrier is used for long-distance transmission, line signaling is also audio signaling.

China's audio register signaling uses multi-frequency mutual control. Signaling is divided into forward and backward. Forward signaling is user number and service category signaling, using 2 of 6 to form 15 digital signaling; backward signaling is control confirmation and called user status signaling, using 2 of 4 to form 6 A digital signaling. China's multi-frequency signaling is consistent with the international R2 signaling in terms of frequency and electrical characteristics, but there are differences in sending procedures and meanings. Since the signaling method involves the mutual cooperation between exchanges and the inter-office signaling coordination of international communications, strict uniformity is required.

Logic circuit, pulse digital technology and computer technology

The telephone exchange is a complex and huge logic circuit. In the mid-1960s, electronic exchange began to use computer technology to form program-controlled exchanges, and the control method was qualitatively improved. The main feature of program-controlled switching is to replace traditional wiring logic control with stored program control, and most of the logic circuit functions composed of hardware are completed by software. With the increasing requirements of new business functions and maintenance and management, the software of program-controlled exchange is becoming larger and larger, and software failures increase. In order to solve this problem, high-level language programming has been adopted internationally, and the International Telegraph and Telephone Consultative Committee recommends CHILL language as the high-level language of the exchange. The application of pulse digital technology in the exchange is to form a logic circuit, which uses pulse timing to complete the logic control; the other is to use the principle of pulse coding technology to form a speech circuit and exchange various information.

Although the local telephone exchange switches have different standards, they all have the following basic functions: ①identify the call source, that is, identify the number and category of the call source; ②receive the called user’s number dialed by the calling user, among which Including the numbers of the calling and called users and other necessary information transmitted between exchanges; ③Decoding, that is, decoding the called office direction, in order to find routing and determine the way of transmitting signaling, and also to the called Decode the user’s category; ④Select the path, including the selection of idle trunks and idle links, which can be space-divided or time-division; ⑤Communicate between the user equipment of the office, between the trunk, and between the user equipment and the trunk They can also be space-division or time-division; ⑥ ring the user equipment, feed the call power, monitor the answer and release; ⑦ billing, China adopts the billing method from the call between the two parties, the billing method is divided into single There are two kinds of billing and double billing (taking into account the two factors of time and distance); ⑧There are many methods for maintenance testing and management, such as routine testing of various equipment, fault alarm, display, recording, analysis and diagnosis, and Fault location judgment, traffic statistics and service quality observation.

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