Research On Clock Recovery Mechanism About TDM Services Based On PBT Networks

Ethernet technology, due to simplicity, efficiency, low cost and other characteristics, has been rapidly developed and now more than 95% of the data services is beginning and ending on the Ethernet. The metropolitan network which is between the core network and user network has become a bottleneck in the development of the whole network capacity. In order to meet the user's multi-service needs, the costs push the carrier Ethernet technology into the main location of metropolitan area network. For a long time, the reliability of the traditional Ethernet is principal cause which is restricting the use of Ethernet in the telecommunications network. On the purpose of applying Ethernet into telecommunications networks, we combine the traditional Ethernet of the simplicity, efficiency, low cost and next generation SDH network performance, reliability and carrier-class network management and other features, thus the conception of carrier-class Ethernet is also emerge. PBT inherits the forwarding strategies and modify the frame structure by redefining the standard frame header field after the way of tricks of Ethernet. It has become one of the promising carrier-grade Ethernet, as meeting the requirements of next-generation metropolitan area network.With the surge of global telecommunications data services and the rapid development of IP services, the operator's income also mainly comes from the traditional TDM service. How to make PBT networks carrying TDM services and giving consideration both existing business and future network development have become the focus of operators. In this paper, TDM services will seamlessly be transplanted to packet networks by circuit simulation technology. This will not only protect existing invested equipment but also can reduce the transmission costs of traditional TDM services and it is a good transition program from the circuit networks to packet networks.The main contents in the dissertation are that TDM clock recovery mode of adapting to PBT Packet Networks is presented. In the chapter 1 the status of the development of PBT network and circuit simulation at home and abroad and the characteristic of traditional TDM networks and packet networks are introduced and the importance and significance of clock recovery is showed in the circuit simulation. In the chapter 2 the basic principles of PBT network which carries TDM services by basing on circuit simulation mechanism of Ethernet is introduced. In the chapter 3 the critical technology of transport TDM service and kinds of common clock recovery methods are studied, then the key question is clock recovery when carried the TDM service is elaborated. In the chapter 4 the clock recovery algorithm is researched, and an improved fast-adaptive clock recovery method through comparing with the shortcomings of traditional adaptive clock recovery method is proposed. In the chapter 5 the FPGA implementation of fast-adaptive phase-locked loop is introduced and the superiority of the adaptive method through simulation is showed. Chapter VI sums up this article and the suggestion for future research is issued.