What are the widely used switching technologies in computer networks?

I. Network switching technology development history 1. Circuit switching technology network switching technology **** experienced four stages of development, circuit switching technology, message switching technology, packet switching technology and ATM technology. The public telephone network (PSTN network) and mobile network (including GSM network and CDMA network) use circuit-switching technology, which is basically characterized by the connection-oriented way, before the two sides communicate, it is necessary to allocate a communication circuit with fixed bandwidth for both sides of the communication, and both sides of the communication process will occupy the allocated resources until the end of the communication and the establishment and release of the circuit are required to utilize the relevant resources in the process. In the process of establishing and releasing the circuit, it is necessary to utilize the relevant signaling protocols. The advantage of this method is that it can guarantee enough bandwidth for users in the communication process, and it has strong real-time, small delay and low cost of switching equipments, but the disadvantage is that the bandwidth utilization of the network is not high, and the allocated circuits are occupied once the circuits are established regardless of whether the two sides of the communication are in the talking state or not. 2. Packet switching technology Circuit switching technology is mainly suitable for transmitting voice-related services, this kind of network switching method is not suitable for the data communication, but for the data communication. This network switching method has great limitations for data services. First of all, data communication has strong suddenness, and the difference between peak bit rate and average bit rate is large. If circuit switching technology is used, if the circuit bandwidth is allocated according to the peak bit rate, it will cause a great waste of resources, and if the bandwidth is allocated according to the average bit rate, it will cause a large amount of data loss. Secondly, comparing with voice service, data service does not have strict requirements on delay, but needs to be transmitted without error, while voice signal can have a certain degree of distortion but real-time must be high. Packet switching technology is a kind of switching method proposed for the characteristics of data communication service, and its basic characteristic is that it is oriented to no connection and adopts the store-and-forward method, which divides the data to be transmitted into many small segments of data according to a certain length, and increases the corresponding header fields used for routing and checking of data before the data as the basic unit of data transmission, i.e., packet. With packet switching technology, there is no need to establish a connection before communication, each node first receives the packet sent by the previous node and saves it in the buffer, and then selects the appropriate link to send it to the next node according to the address information in the header of the packet, so that the bandwidth can be dynamically allocated according to the user's requirements and the network's capacity in the communication process. Packet switching has a higher circuit utilization rate than circuit switching, but the delay is larger.3. Message switching technologyMessage switching technology is similar to packet switching technology and also adopts the store-and-forward mechanism, but message switching takes the message as the transmission unit, and due to the great difference in the length of the message, the long message may lead to a large delay, and the allocation of the buffer zone is also more difficult for each node, so in order to meet the needs and achieve the high efficiency of various lengths of messages, the node can use the buffer zone as the transmission unit. In order to meet the needs of various message lengths and achieve high efficiency, the nodes need to allocate buffers of different sizes, otherwise it may cause the failure of data transmission. In practice, message switching is mainly used for communication services with shorter messages and lower real-time requirements, such as public telegraph networks. Message switching appears earlier than packet switching. Packet switching is based on message switching and divides messages into groups for transmission, which balances transmission delay and transmission efficiency, and thus has been widely used.4. ATM TechnologyThe wide application and development of packet switching technology has led to the emergence of two major networks, namely, the circuit-switched network for transmitting voice services and the packet-switched network for transmitting data services***. *The situation that voice service and data service are transmitted in separate networks prompts people to think about a new technology to provide the advantages of circuit switching and packet switching at the same time, and provide users with unified services, including voice service, data service and image information, which led to the concept of broadband integrated service digital network put forward by the former CCITT in the late 1980's, and proposed a brand new technology --- Asynchronous Transmission Mode (ATM). --Asynchronous Transfer Mode (ATM) combines connection-oriented and packetized mechanisms, whereby a connection with a certain bandwidth is established according to the user's requirements before the communication starts, but the connection does not exclusively occupy a certain physical channel but statistically multiplexes a certain physical channel with other connections, and at the same time, all media information, including voice, data, and image information, is transmitted to and from the network. All media information, including voice, data, and image information, is segmented and encapsulated into fixed-length packets to be transmitted and exchanged in the network.Another outstanding feature of ATM is that it proposes a complete mechanism to guarantee QoS, and because fiber-optic communication provides a low-bit-error-rate transmission channel, it is possible to move the flow control and error control to the user's terminal, and the network is responsible for only the exchange and transmission of information, which leads to a reduction in the transmission delay, and ATM is very suitable for transmitting high-speed data. ATM is very suitable for transmitting high-speed data services. From the technical point of view, ATM is almost flawless, but the complexity of ATM technology has led to extremely expensive ATM switches, and no new services have been introduced in ATM technology to drive the ATM market, thus restricting the development of ATM technology. At present, ATM switches are mainly used in backbone networks, mainly utilizing the high speed of ATM switching and the guarantee mechanism of QoS, and mainly providing semi-permanent connections. The integration of circuit switching technology and packet switching technology 1. Comprehensive switching technology Although ATM technology does not let people realize the dream of "comprehensive services", people have been looking for a way to try to realize the provision of a variety of services on a network, and telecommunication carriers also hope to make full use of the resources of the existing network and try to provide rich services for users. Telecom operators also want to fully utilize the existing network resources and provide as many services as possible to their subscribers. The first technology proposed is the integrated switch technology, which is mainly used to support circuit switching and broadband switching (including ATM switching and IP switching) at the same time by modifying the existing circuit switching network. Many manufacturers have successively developed integrated switches, and the relevant industry standard "Technical Specification for Integrated Switch" has also been formulated and promulgated. Comprehensive switch has the function of narrow-band switch, and at the same time, it also has the function of broad-band switch. There are two main ways to realize the current integrated switch: one is to adopt the way of hybrid switching node, and there are several independent switching matrices configured inside the switch, i.e., circuit switching matrix, ATM and IP packet switching module, and the traditional PSTN call is also mainly handled by the circuit switching module, while the service related to the broadband is handed over to the broadband packet processing module for processing, and protocol conversion is required for the interaction between the two modules. When the two modules need to interact with each other, protocol conversion is required. The other is the way of converged switching node, basically there is only a single ATM or IP switching matrix inside the integrated switch, for example, S12 P3S of Shanghai Bell's broadband switch directly adopts ATM technology as the core switching technology, and all media information is converted into ATM signals to be processed inside the switch, while externally, it supports circuit-switched network, ATM network and IP network at the same time. The integrated switch adopting the convergence method has a great advantage in flexible and rapid service deployment because it has been changed to a unified switching platform internally. Because of the integrated multiple functions, the cost of integrated switch is relatively high, mainly used in the gateway bureau and end bureau with large service volume, not suitable for the implementation of the whole network. 2. IP telephony technology integrated switch mainly adopts the modification of circuit switch to support packet switching, in the process of exploring the convergence of circuit switching and packet switching technology, people also hope to utilize packet network to transmit voice service, at this time, based on Web, the integrated switch also supports circuit switching network, ATM network and IP network. In the process of exploring the integration of circuit-switching and packet-switching technologies, people also want to use packet networks to transmit voice services, and at this time, based on the emergence of Web applications, the Internet network has developed at an astonishing speed, and eventually developed into a global network, and people use the Internet network to get various services. Internet network is mainly used for transmitting data service, along with the great success of Internet, it has made IP technology become the pillar technology of future information network, TCP/IP based network technology not only becomes the dominant technology for transmitting data service, but also traditional telecommunication carriers start to try to use IP technology to transmit voice service. Nowadays, traditional telecommunication carriers have generally set up their own IP networks. In addition to providing relatively low-profit data services on IP networks, the carriers hope to fully utilize the existing resources to provide users with a wealth of services, most notably voice services, which still belong to the most important source of income for the operation, and the earliest application of transmitting voice services on packet networks is IP telephony. IP telephony has now become a familiar service, and it mainly adopts the H.323 series protocols, including H.225 signaling protocol for call establishment and H.245 protocol for media channel establishment, and the voice service is transmitted in the IP network by means of RTP packet. Although the voice quality of IP telephony is not as high as that provided to users by traditional circuit-switched networks, the H.323 protocol is generally recognized as the most mature protocol currently supporting voice, image and data services over packet networks, and is now widely used in the field of IP telephony. There are many VoIP networks formed using the H.323 protocol in operation around the world. However, some disadvantages of H.323 are also obvious. First, the call control signaling in H.323 is based on Q.931, a protocol based on the UNI interface, which is relatively simple and has no definition of the NNI interface. This is fine for computer-to-computer calls within a private network, but to provide nationwide services and PSTN-toPSTN connectivity you must rely on the NNI interface. Second, H.323 networks use centralized gateways, which have to handle both media streams and signaling streams, which also limits the development of H.323 networks in terms of processing power. Currently, ITU-T is further expanding and revising the H.323 series of protocols based on the experience of IETF related specifications. In addition, compared with SIP, the scalability of H.323 protocol is poor, and in order to provide similar services to users on circuit-switched networks in the H.323 network, many manufacturers have extended the H.323 protocol, so the interconnection between H.323 devices of different manufacturers is also an important issue facing the development of an H.323 network. However, the successful application of IP telephony and a considerable degree of market share let people see the dawn of business convergence, people gradually recognize that in the packet network can be transmitted voice services, and can achieve a more ideal communication effect. And packet switching has a number of potential performance advantages, one of which is the efficient utilization of the transmission channel's communication capacity, especially for bursty transmissions. Although voice does not exhibit as much burstiness as interactive data, it still exhibits a certain amount of burstiness in the form of bursts/silence periods. The average length of the burst period depends on the silence detector used, and in a typical telephone conversation, a single voice source is active only about 35-45% of the time. Another advantage is statistical multiplexing, so that call blocking is a function of the average bandwidth required, rather than the peak bandwidth. This allows for more flexibility in transmission control, billing, etc. Because of these advantages, voice over Internet applications, especially IP telephony, has become one of the most compelling applications in the "triple play" wave. Third, softswitch technology with the development of IP telephony technology, the communications industry has basically reached the core of the future telecommunications network will use packet switching technology *** knowledge, and in this *** knowledge, for the shortcomings of the current IP telephony technology from a technical point of view to improve, first of all, the gateway to call control and media switching functions are separated, and ultimately put forward the concept of softswitch. Although softswitch technology still adopts packet network as the bearer network, from the technical point of view, softswitch technology can still be regarded as another milestone in the development of switching technology. The traditional circuit-switched and packet-switched networks concentrate too much intelligence in each network node. In circuit-switched networks, the network nodes are not only responsible for call control and handling all the information related to the call, but also responsible for the establishment of voice paths, and at the same time, in circuit-switched networks, many services need to configure the relevant business logic in the network nodes, and at present, many services need to make data in the end office to make data, which also restricts the timely provisioning of services. In the packet-switched network represented by H.323 network, as mentioned above, the gateway equipment also needs to simultaneously perform call control and media stream establishment, and the packet processing delay is long and the requirements for the network nodes are relatively high. A new concept proposed by softswitch technology is to separate call control, bearer establishment, and business logic, and connect and communicate between entities through standard protocols, so that services can be provided more flexibly on the network. The softswitch equipment is actually a software-based distributed switching/control platform, which is an entity that realizes the "call control" function of traditional program-controlled switches. It separates the call control function from the traditional gateway and exposes the protocols between service, control, access and switching, thus truly realizing a multi-vendor network operating environment and allowing for the easy introduction of multiple services. The adoption of softswitch technology to build telecom networks is moving from the experimental stage to the commercial stage, and carriers at home and abroad have devoted great enthusiasm to softswitch technology, hoping to utilize it to achieve the purpose of expanding service types and increasing market share. From the perspective of standards, domestic and foreign standard organizations are stepping up the development of a series of technical specifications related to softswitch technology, which is not only regarded as the core technology for the development of fixed networks, but also regarded as the core technology for the future network of mobile networks. Softswitch technology from the proposed, development to perfection and maturity, but also need to experience the test of technology and market test. Hope to adopt