With the rapid development of modern communication switching technology, this paper mainly introduces and explains various switching technologies commonly used in the current network and the key technical principles used in data communication. Circuit switching technology in telephone communication: telecommunication network signaling system; Packet switching technology and frame relay technology used in data communication; ATM technology in broadband switching: layer 2 switching, IP switching and MPLS technology used in computer networks; Optical switching technology and the latest soft switch and NGN technology.

Keywords: optical switching technology; Dynamic broadband; time division switching

With the continuous development of communication technology and computer technology, people have higher and higher requirements for network services. These network services need corresponding transmission switching technology, so circuit switching technology can not meet the requirements of various new services. Based on this situation, various switching technologies have emerged to meet different business needs. Among all kinds of switching technologies, optical switching technology is a prominent new switching technology. This paper discusses the technical characteristics and application of optical switching from three aspects: classification, technical characteristics and optical switching mode.

Optical switching technology is the core technology of all-optical communication network and plays an important role in modern communication technology. With the continuous development of modern science and technology, we need to build a high-quality broadband communication network in the communication network, and achieving a highly transparent and active all-optical communication network is our highest construction goal.

First, the classification of optical switching

We call the switching mode that the input end of optical signal can be directly switched to the output end without the conversion of optical/electrical converter as optical switching. According to the wavelength and the number of groups, it can be divided into optical path optical switching and packet optical switching.

1. optical path optical switching

Optical path optical switching is essentially a way of optical path switching. Based on the functions of optical add-drop multiplexer (OADM) and 0Ptical Cross Connect (OXC), the wavelength routing mode is flexible. The transmission link is established through bidirectional signaling of the control plane, and the corresponding wavelength signals are distributed after the transmission channel is established.

In DWDM network, it is realized in the form of wavelength exchange. In each link of adjacent nodes, one switched optical channel corresponds to one wavelength. Its advantages are high speed, high data transmission efficiency and high transparency, which is very suitable for the establishment and use of SDH networks. The processing granularity of OCS network resources is divided by wavelength. If the number of wavelengths is limited, some of them must be converted into optical/electrical/optical wavelengths to avoid data congestion. In the ordinary processing mode, dynamic allocation is adopted, which has obvious shortcomings and takes a long time to establish a response. The multi-protocol wavelength switching technology formed by the combination of OCS and multi-protocol label switching can realize the function of intelligent dynamic wavelength link routing and protection. Let's talk about the disadvantages of this exchange method, which is essentially circuit exchange. The inherent disadvantage of circuit switching is that in the data transmission link, all nodes must maintain channel resources, and this situation must be maintained until the end of transmission, when the channel can be dismantled. The problem is that even if the channel resources are not occupied, other data cannot use the channel at this time. Such low usage efficiency will greatly reduce the channel utilization and the corresponding broadband utilization.

2. Packet optical switching

Packet optical switching is based on time division multiplexing, and the switching function is realized by the principle of time slot switching. Time division multiplexing: Time is divided into frames, and each frame is divided into n time slots, which are allocated to n signals, and then these n signals are multiplexed onto one optical fiber. At the receiving end, the original signal of each channel is recovered by the demultiplexer. Time slot interchange: the signal interchange of each time slot in a time division multiplexed frame. Firstly, that multiplex signal passes through a tap, and at the same time, the signal of each time slot is transmit on each outlet of the tap in turn; Then these signals pass through different optical delay devices to get different delay times; Finally, these signals are recombined with a multiplexer.

The structure of OPS core node includes multiplexer/demultiplexer, input and output interfaces, internal buffer and controller. The function of the input interface is: (1) the input data signal forms a perfect quality signal; (2) detecting signal drift and jitter; (3) Arrange appropriate payloads at the beginning and end of each packet; (4) aligning data packet capture synchronization and switching time slots; (5) sending the letterhead to the controller; (6) The external transmission wavelength is converted into an internal switch. The output interface must complete the following functions: the output signal formation overcomes the crosstalk and damage caused by the switch board and restores the signal quality; For the payload of information, the internal wavelength is converted to the external wavelength as needed; Because the distance between the switch boards of the signal is different and the insertion loss is different, the signal power is different and a balanced output power is needed.

Second, the characteristics of optical switching technology

With the development of communication network to all-optical platform, the functions of network optimization, routing, protection and self-healing are becoming more and more important in the field of optical communication. Optical switching technology can ensure the reliability of the network and provide a flexible signal routing platform. Using wavelength converter, burst packets can be sent at a wavelength different from the specified output line when contention occurs. This solution is the best in contention packet delay, and it is suitable for circuit-switched and optical packet/burst-switched networks, but it requires fast adjustable converters. The recent research results show that wavelength switching is one of the most potential options in packet-switched optical networks, which can effectively reduce the packet loss rate of optical packets/bursts, especially in multi-wavelength DWDM systems, so the fast tunable wavelength converter is the focus of current research.

Third, the way and application of optical switching

There are three ways to divide and multiplex optical signals: space division, time division and wavelength division. Accordingly, there are three kinds of optical switching: space division, time division and wavelength division. Complete the exchange of space channel, time channel and wavelength division channel respectively. The characteristics of these three conversion methods and their implementation schemes are different. If two or more optical signals are exchanged at the same time, it is called composite optical switching.

1. air separator

The basic principle of space division switching is the array switch of optical switching elements, which is properly controlled. In essence, it is a process completed in the spatial domain of optical signal exchange. The path can be formed between the input and output optical fibers in any way. The switching elements of air separation switches can generally be divided into mechanical, photoelectric conversion, composite waveguide and total reflection laser diode gate switches. The length of parallel waveguides and the phase difference between the two waveguides are variable, so it is necessary to choose appropriate parameters, and the beams on the waveguides are completely staggered. If a certain voltage is applied to the electrode, the refractive index and phase difference can be changed.

2. Time-sharing switch

Time Division Multiplexing (TDM) is a common multiplexing method in communication networks. Optical time division multiplexing (OTDM) is similar to electrical time division multiplexing, which divides a multiplexed channel into several time slots, each baseband data optical pulse stream occupies one time slot, and N baseband channels are multiplexed into high-speed optical data stream signals for transmission.

To complete time-sharing switching, there must be a time-slot switching to realize the time-slot switching and time-slot output function of the input signal. Time division multiplexed signals must be written into the memory in turn, and then read out in turn to complete time slot switching. Based on the working principle of optical fiber delay line in time-sharing switch, the first time-division multiplexed optical signal passes through optical splitter, so that each exit has only a certain time slot optical signal at the same time; Then let these signals pass through different optical retarders to get different delay times; Finally, it is suggested that these signals be multiplexed by an optical synthesizer to complete a time-division switch.

3. Wavesplitter

Generally speaking, in an optical multiplexing system, both the source end and the destination end can use the same wavelength to transmit signals. If the same wavelength is not used in multiplexing, it will inevitably lead to more and more complexity for each terminal. The wavelength switch needed for wavelength separation and exchange is to divide the space of optical sub-channels by demultiplexer, and perform wavelength exchange (w/c) on each wavelength channel, which is multiplexed after exchange and output through optical fiber. The future optical switching technology will certainly promote the great development of communication networks, and the era of large capacity and high speed will surely come. It is believed that in the near future, China's optical switching network technology will become an effective driving force for the great development of communication technology, and communication technology will enter a stage of high efficiency and high quality development.

Four. Concluding remarks

To sum up, optical switching is mainly divided into two types: optical path optical switching and packet optical switching. Strengthening the application of optical switching technology in communication data transmission is helpful to improve the speed of data transmission and ensure the quality. Therefore, it is necessary to pay more attention to the application of optical switching technology in communication network, and constantly study the application of spatial optical switch and time optical switch in communication transmission.