The fixed telephone network has played a huge and irreplaceable role in the process of promoting social development, bringing great convenience to people's communication. However, just as fixed-line telephones replaced letters and telegraphs at that time, various emerging communication methods began to be gradually accepted by people. Under the new situation, fixed-line operators operating PSTN are facing increasingly severe challenges. First, the vigorous development of the Internet has subverted the traditional telecommunications business model. The Internet-based voice value-added services are developing rapidly. PSTN voice services are increasingly diverted by other communication methods such as VoIP and instant messaging, especially traditional long-distance calls. The business is most affected by IP phones. Second, with the popularization of monthly subscriptions and one-way charges for mobile voice services, the replacement of fixed networks by mobile networks is becoming more and more serious, resulting in the continuous decline in the number of fixed network users and fixed voice services, and pure voice services are far from satisfactory The needs of users, diversified, personalized and interactive integration services are the general trend. Third, from the perspective of the fixed telephone network itself, the TDM network is facing many problems, including: with the decline in business volume, the utilization rate of equipment is reduced; there are many equipment models, long network access time, aging, and a high failure rate; There is a lack of spare parts, there are hidden safety risks, and the support of manufacturers is weakened. The profit space for fixed voice services is getting smaller and smaller. Operators' efforts can only delay the decline in fixed-line revenue, but cannot fundamentally change this trend. There is an urgent need to find new ways of sustainable development-through a series of Operational implementation of network transformation and updating methods to optimize the fixed voice network economically and reasonably, improve market responsiveness, meet the diversified business needs of current users, and achieve energy conservation and emission reduction. 2 Optimization of fixed voice network Studying the optimization of fixed voice networks requires comprehensive consideration of the following factors to formulate a general idea of ​​network optimization. a) Network evolution trend. It conforms to the trend of network broadband evolution and enhances the network's business opening capabilities. b) Network architecture design. Gradually realize the end-to-end flat network structure and reduce the transfer of existing long-distance traffic. c) Energy saving and emission reduction. Promote the end-bureau as the unit, withdraw the entire scale of equipment from the network to achieve better energy-saving and emission-reduction effects. d) Light advances and retreats from copper. Promote the large-scale withdrawal from the distribution cable on the user side to the backbone cable between the offices. e) Resource utilization. To further improve the efficiency of the PSTN end office resource use in the network. The optimization of the fixed voice network is mainly aimed at the TDM network, especially the TDM end office. Combining with the existing problems, there are two main types of optimization methods for the TDM end office: one is the non-IP transformation, which mainly includes the withdrawal of the board and the reduction of capacity. Head-to-head, etc .; the other category is IP transformation, including AG packaging, new AG, and FTTx transformation. 2.1 Non-IP transformation and optimization methods This type of transformation is only the adjustment and optimization of the existing network TDM. The transformed end office equipment is still a TDM end office and does not support IP interfaces. 2.1.1 Volume reduction This method is mainly aimed at the end office with a low installation rate, removing idle user boards and relay boards to reduce the capacity of the equipment on the network, so as to achieve the purpose of reducing floor space and power consumption. The main measures are: priority to reduce the load in the order of the whole rack and the whole frame; for large-scale switching equipment, the port is adjusted "last to the front"; for the whole rack and the whole frame such as Bell and Nortel, it is difficult to reduce the load Switching equipment is carried out by reducing the user interface board; try to free up the entire module, the entire frame, and the entire rack, especially the rack near the end. When using this method, there are several situations that need attention. a) For the plates with long service life, if the old ones are used, there is the possibility of increasing maintenance costs and reducing the stability and safety of the system. b) If the port density of some old boards is too low, it will cause waste if the slots are also occupied. c) The slot of the frame of some equipment is full. If you want to use the old original card, you need to add a frame, and you need to invest another. 2.1.2 Withdrawal This method is mainly to transform the end office into a modular office of the same model and download it to other end offices; the equipment cable and the outgoing copper cable maintain the status quo, no line cutover is required, only data adjustment is performed, and the mother The head of the bureau was turned off and the service was cancelled. When using this method, there are several situations that need attention. a) Need to merge with the same model, otherwise it is not compatible. b) It is required that the transformed end office user board equipment and lines are of good quality. c) Small-capacity combination, otherwise it exceeds the processing range of the control module. d) S1240 needs to add a new cabinet, and the cutover is complicated, so it is not recommended. 2.2 Optimization method of IP transformation This method includes the transformation of existing TDM equipment, the addition of AG encapsulation methods for IP upstream ports, and the replacement of TDM with new equipment that supports IP ports such as AG and PON. 2.2.1 AG encapsulates this method Add a new VoIP main control board or main control frame to replace the narrowband main control module of the original switching equipment, and connect the modified end office to the soft switch or IMS. The equipment cable and the outgoing copper cable maintain the status quo. Adjust the data, and power off the system rack and the common board after the cutover transformation is completed. When using this method, there are several situations that need attention. a) The user board equipment and line quality are required to be good. b) After the transformation, it can still only provide voice services. c) The cost is relatively high, 40 ~ 86 yuan / line. d) The area of ​​less than 500 gates is not applicable. At the same time, it needs to expand the softswitch or implement IMS access. 2.2.2 New AG mode This method is mainly used in areas where voice demand is the main factor. New AGs can choose to replace existing TDM equipment in the core computer room or the computer room close to the user side. Among them, close to the user-side computer room is conducive to the optical cable entry and exit of the backbone cable. 2.2.3 FTTx method The FTTx transformation method mainly combines broadband upgrade and speed-up and the optical copper entry and exit project. The original users are accessed by moving down the access equipment, and the new equipment is upstream connected to the softswitch or IMS system. FTTx includes FTTB / C and FTTH. a) The FTTB / C method retains the cable from the junction box to the user terminal, and the degree of optical entry and exit is relatively high, and the user can retain the original terminal, so the user can hardly feel the impact before and after the cutover. b) The FTTH mode has the highest degree of optical access and copper retreat. The user can keep the original narrowband voice terminal or use a broadband voice terminal. 2.3 Optimization summary of fixed voice network From the point of view of economic benefits, except for the withdrawal of the board and volume reduction and the merger of the heads, the investment recovery period of other transformation methods is more than 10 years. Among them, due to the greater operability of the board reduction and capacity reduction, under the circumstances of limited funds, operators are more suitable to adopt the optimization method of board reduction and capacity reduction to reduce equipment energy consumption and increase the network installation rate; At this time, considering the evolution of future technologies and the cooperation with the optical system, the FTTx transformation method can be adopted more. For FTTx transformation, it is recommended that the TDM end office with the following conditions be given priority to implement transformation. a) Equipment with high failure rate, insufficient technical support, and potential safety hazards. b) Equipment with severe copper aging and poor line quality in the coverage area. c) Equipment with a service life of more than 15 years on the network. d) Equipment with relatively high energy consumption for equipment operation. e) Equipment with a low proportion of equipment capacity and quantity. f) Equipment with a large floor area in the machine room. g) Equipment with low installed rate. 3 Next evolution of fixed voice networks 3.1 Evolution direction of fixed voice network The needs of users determine the future development direction of fixed voice networks. Whether the telecommunications network or the Internet is used for carrying services is still controversial. On the whole, the driving force for the future evolution of fixed voice networks mainly comes from the following two aspects. a) Business provision. Telecommunications services mainly include basic and supplementary services, intelligent services and multimedia services. Among them, the first two types of services are mainly provided by telecommunications networks, while multimedia services, IMS and the Internet can be provided. The types of services and service experience provided by the Internet are better than IMS. The so-called "cloud management end" concept to a certain extent reflects another direction of future telecommunications services, but it is still in the conceptual stage, and it is a disruptive change to the existing telecommunications operators' network, business and operation management. Cut into the telecommunications business from the Internet. It is difficult to form an industrial scale in a short time. b) Evolution of equipment and network architecture. With the continuous development of communication technology, from traditional TDM to soft switching, it gradually develops to IMS. From the perspective of standardization, protocol type, service type, access, terminal, energy consumption, and interface openness, IMS is The technical standards that can be seen are the most mature, have the best industry support, and have been commercialized. The equipment and architecture of fixed and mobile networks are all evolving to IMS. In general, from the perspective of the two driving forces of the current fixed network evolution, IMS is a relatively clear direction of evolution. 3.2 Business and implementation under IMS 3.2.1 Business overview under IMS The services in IMS are mainly divided into three categories: basic and supplementary services, traditional smart services and IMS new services. a) Supplementary services mainly include calling number identification display / restriction / overrun, call forwarding / waiting / holding, three-way calling, outgoing call restriction, do not disturb service, abbreviated dialing, hotline service, alarm clock, blocking service, fax service, etc. b) Traditional smart services mainly include VPN, prepaid, One Number, mobile phone H code translation, Yueling and card services. This type of business includes both national and local deployments. c) New IMS services, including multimedia telephony, color ring back tone, color image, conference, instant messaging, unified centrex, click-to-dial, converged one number, converged video (IPTV), IP call center (IPCC), interactive voice and video response system (IVDR) etc. Among the above services, the first and second categories belong to the services already provided by the existing network, and the third category are the special services provided in the IMS environment. 3.2.2 Business realization under IMS Under the IMS architecture, all services can be implemented by setting the corresponding AS. However, for the inheritance of traditional intelligent services, considering the consistency of services and the difficulty of network cutover, the following three methods are generally adopted. Method 1: The voice path detours back to the existing gateway to trigger intelligent services. Calls in the IMS domain are routed to the fixed network gateway through the MGCF, and intelligent services are triggered to the existing intelligent network SCP through the gateway. This method has low technical difficulty, and service triggering and service control are implemented using the existing gateway and SCP respectively, but IM-MGW to the gateway needs to occupy a large voice port. Method two: through IMS-SSF. This method simplifies the business process of IMS users. IM-SSF is responsible for completing the conversion of INAP / CAP / SIP protocol to IMS SIP protocol and completing service triggering, while service control is still completed by SCP. In this way, there is no need to divert the communication path to the gateway, so there is no need to occupy additional port resources from the IM-MGW to the gateway, but it is necessary to complete the connection test between IM-SSF and the provincial or even local SCP, which is slightly more technically difficult. Method 3: Create a new AS platform to replace the existing SCP equipment. Service triggering and service control in this way are implemented in the IMS, and there is no roundabout, but traditional smart services in the province are deployed in accordance with the province or even locally, and their business logic is different. Therefore, the new AS completely inherits the existing 3.3 Evolution strategy of fixed voice network 3.3.1 Overall steps of fixed voice network evolution In view of the current coexistence of fixed voice network TDM and softswitch, the evolution of fixed voice network can follow the following steps. The first step is to change the PSTN network to an opportunity to deploy an IMS network on a large scale, control the expansion of fixed network softswitches, and form a TDM + softswitch + IMS network architecture. The second step: TDM users have basically completed the migration to IMS, forming a network architecture of IMS + softswitch and realizing flat network. The third step: After the fixed network softswitch equipment is upgraded, it will access the IMS network as a whole, and IMS becomes the only core control network of the fixed network. 3.3.2 TDM equipment evolution strategy After the introduction of IMS, the evolution of existing network TDM equipment to IMS has the following two modes. a) After AG encapsulation, access to the IMS core network. b) Through the transformation of FTTx, all the TDM equipment will be withdrawn from the network. The FTTx transformation method has no additional requirements for existing TDM switches, while the AG encapsulation method requires equipment manufacturers to provide specific encapsulation solutions. At present, among mainstream manufacturers, Nokia Siemens Networks, Bell and ZTE have all provided mature AG packaging solutions. 3.3.3 Softswitch equipment evolution strategy 3.3.3.1 Softswitch end office evolution strategy Currently, there are two ways for soft switch end office evolution to IMS. a) AGCF + H.248 AG mode. Transform the softswitch SS to AGCF, or build a new AGCF, and the AG will remain unchanged. b) SIP AG method. The interface protocol of Softswitch AG is upgraded from H.248 to SIP, and Softswitch SS is no longer used. From the perspectives of standardization, commercial maturity, business capabilities, and difficulty of transformation, the current AGCF + H.248 AG method has certain advantages. Currently, the domestically deployed IMS commercial networks mainly use this method. 3.3.3.2 Evolution strategy of the softswitch gateway The softswitch gateway SS is transformed into MGCF, and TG evolves into IM-MGW, which is used for voice communication between IMS and other networks of China Unicom. 3.3.3.3 Evolution strategy of SDC SDC is mainly used when the fixed network is intelligent, and is used to centrally store the user's business attribute data. It is very similar to the HSS function in IMS. Therefore, SDC also has the possibility of evolution to HSS. However, the user data structure, authentication method, interface protocol, etc. of the SDC device are different from HSS, and the available resources in the software are limited; most manufacturers' HSS are developed based on new hardware platforms such as ATCA. The models are old and have limited processing power, and subsequent support and maintenance are also difficult. Therefore, the significance of upgrading SDC hardware to HSS is not significant. Therefore, when evolving to IMS, SDC adopts the following strategies. a) In the coexistence phase of IMS and fixed-line softswitch, SDC only serves fixed-line softswitch. b) When the fixed network softswitch needs to evolve to AGCF, the data in the SDC migrates to the HSS, and the SDC gradually withdraws from the network. 4 Conclusion After clarifying the next development direction of IMS as a fixed voice network, the optimization work of the fixed voice network can be summarized as achieving network slimming through measures such as backboard reduction and volume reduction, and gradual evolution towards the goal by replacing TDM with IMS. As a new technology, IMS introduces many aspects of network construction and maintenance such as business, network, support, transmission and supporting. Therefore, the preparation of operators in the early stage of IMS construction is very important, and during the construction of IMS, it needs Handle the network division and interconnection between softswitch and IMS to ensure the stable and healthy development of fixed voice network. Surface Treatment DC Power Supply Electrolysis Dc Power Supply,Charging Dc Power Supply,Motor Test Dc Power Supply,Experiment Dc Power Supply Yangzhou IdealTek Electronics Co., Ltd. , https://www.idealtekpower.com