Abstract: With the vigorous development of mobile Internet, IMS, LTE and other services, a large number of video and data IP services continue to emerge, making SDH / MSTP-based metro transport networks facing huge challenges. High-capacity, high-efficiency, low-cost operation requirements and comprehensive bearer requirements for high-quality services such as mobile backhaul and large customer dedicated lines have forced the metropolitan transport network to realize the transition from the traditional circuit-switched transport network to the new generation of packetized bearer networks. Comprehensive evolution.
PTN application status and background
Since 2007, China Mobile has organized more than ten rounds of 100,000 tests on PTN equipment with full packet switching core, including large-scale testing of centralized procurement, multi-vendor interoperability, and new functions. For the deployment of PTN in all cities across the country, the deployment volume has reached 400,000 terminals. PTN has been widely used in China Mobile's existing network.
The unified bearer of GSM / TD-SCDMA / LET is an inevitable trend in the development of mobile transmission networks. In the GSM era, the base station uses the TDM E1 interface, and the BSC uses the E1 or STM-1 interface. In the early stage of the TD-SCDMA era, the base station chose the IMA E1 interface, and the RNC is based on the channelized STM-1 interface, which evolved into the FE / GE interface type Mainly; in the LTE era, eNodeB base stations mainly use GE interfaces, and S-GW uses 10GE interfaces. At the same time, with the continuous emergence of new bearer applications such as small base station construction and large customer dedicated lines, the metropolitan area network has begun to gradually carry E1 / STM-1 (2M / 155M rate) TDM services to gradually carry FE / GE / 10GE Ethernet services are mainly transformed, and various interfaces will coexist for a long period of time. As a bearer device, PTN provides diverse access capabilities, higher port rates and greater port capacity for mobile transport networks.
Currently, PTN has been applied in more than 80 operators and 65 countries around the world including China Mobile, Vodafone in Europe, FT / Orange, T-Mobile, KDDI in Japan, eAccess, and Singapore Telecom.
New application requirements for mobile bearer networks
The passenger line dedicated bearer, TD-LTE backhaul bearer, and network reliability are the most important new application requirements for the current mobile bearer network. At the same time, they also pose new challenges to PTN, which is the main application technology of the mobile bearer network:
1) Study a new networking structure to improve interconnection and interoperability; how to solve the cross-city, cross-province passenger line carrying, what type of equipment and interface mode of the provincial and inter-provincial trunks to carry the private line business, between different manufacturers How to implement PTN interoperability and other issues force operators to develop a new networking structure and maximize the interoperability of PTN equipment from different manufacturers;
2) Support flexible service attribution, maximize statistical multiplexing under heavy traffic pressure to meet TD-LTE bearer needs; TD-LTE bearer, wireless architecture evolves from point to point to multipoint to multipoint, how does the bearer network meet horizontal X2 service, flexible attribution S1-Flex service, LTE base station average 150M peak 450M large bandwidth access, aggregation and core layer traffic pressure, how to end-to-end statistical multiplexing, and how to inter-manufacturer static Layer 3 function interoperability issues ;
3) Multi-point failure effective protection, improve the overall reliability of the network. Under the current network structure, how to ensure network security with minimum resource consumption and effectively solve the problem of multi-point failure.
PTN technology evolution
In order to meet new challenges, PTN needs to make corresponding technological evolution:
1) Evolution of the networking structure: Double access to the aggregation layer at the access layer can solve the problem of single-point failure at the access aggregation crosspoint. The aggregation core layer PTN provides 40GE links to form a large-capacity scheduling channel to achieve efficient transmission of IP-based broadband services ; The access layer provides 10GE to meet the needs of high-traffic access, and miniaturized low-cost equipment to meet the diverse personalized access needs of group customers;
2) The introduction of the static three-layer function at the core layer: Solve the multi-point to multi-point service bearing needs of the X2 service and S1-Flex service; deploy three-layer VPN FRR and VRRP to achieve node failure protection; The route automatic calculation and deployment function simplifies the route configuration;
3) Promote the maturity of ring network protection technology: solve the problem that linear protection has fault points and escape paths in both the working and protection paths, but the business cannot escape, realize that the business and the ring exist independently, and can be forwarded and switched based on the ring channel;
4) Cross-vendor interoperability technology: At the present stage, when the first and second trunks are connected by different manufacturers, the UNI mode is used for interworking; actively promote the inter-manufacturer NNI interoperability. When the NNI interoperability matures, when the trunk inter-manufacturer interoperability, the NNI mode is preferred.
Standardization issues and advancement
With the strong support of the Chinese government, China Mobile, Huawei and other companies jointly promoted ITU-T SG15 to formally adopt and implement the development of two MPLS-TP OAM standards. At the December 2011 plenary meeting, ITU-T approved G.8110.1 Multi-protocol label switching (MPLS-TP) network architecture "standard, determined to pass G.8113.1" MPLS-TP operation management and maintenance applied to the transmission network environment "standard and submitted to WTSA-12 for approval.
China Mobile is the first company in the world to complete the establishment of enterprise standards for PTN equipment. Foreign operators have widely cited China Mobile enterprise standards as their own technical specifications. According to the CCSA industry standard "PTN General Technical Requirements" completed by China Mobile Enterprise Standards and the "PTN Equipment Technical Requirements" led by China Mobile, it is clearly stated that ITU-T G.8113.1 (that is, G-Ach + Y.1731 program) is PTN The only standard of the OAM mechanism in the network, the line standard also specifies the standard requirements for ring network protection. In 2011, China Mobile and the Telecommunication Research Institute of the Ministry of Industry and Information Technology jointly organized the multi-vendor MPLS-TP OAM interoperability test on G-ACh + Y.1731 OAM three times, which fully verified the PTN OAM solution in technical solutions and products. Feasibility and maturity in development and network applications.
to sum up
PTN is a new-generation transport network technology based on an all-IP packet core. It inherits the transport characteristics of SDH end-to-end connectivity, high performance, high reliability, easy deployment, and good maintenance. It has good network management capabilities; multi-service bearing platform and Powerful QoS management mechanism provides efficient and reliable guarantee for the development of all services; high-precision time synchronization technology provides terrestrial transmission capabilities, get rid of the dependence on GPS, improve network security; PTN layered network architecture can be very good Meet the needs of China Mobile's network and business development. In recent years, almost all mainstream equipment manufacturers in the world have invested in the research and development and commercialization of PTN. The continuous growth of the PTN industry chain has promoted the maturity of PTN technology, standards and applications, laying a solid foundation for PTN large-scale commercial use.
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