The Research On Telecom Network's Clock Synchronization Based On Standard IEEE 1588

All-IP is the most significant character for the next generation telecom network. However, comparing to Wireless Access Network and Core Network, Transmission Network is hard for evolution. The core problem is that how to use Packet Switch Network to carry traditional TDM services in SDH network. Traditional TDM services include voice services and clock synchronization services. For voice services, we can use VoIP and Circuit Emulation Service. These technologies are mature and vast applied. However, for clock synchronization services, the solutions and technologies are still studied.Clock synchronization includes frequence synchronization and time synchronization. Telecom network has rigorous requirements for both fequence synchronization and time synchronization. As a mature network time synchronization standard, Standard IEEE 1588 has the best performance to rise equipment's synchronization precision. Meanwhile, for telecom network evolution from Circuit Switch to Packet Switch, Standard IEEE 1588 is the most efficient long-term solution.Standard IEEE 1588 explains how to use timing messages to calculate the offset between master clock and slave clock. However, the standard does not illuminate th way that when offset is calculated, salve clock adjust its local time. This paper suggests Graduat Adjustment Algorithm which can appearently avoid time hopping.The synchronization algorithm of Standard IEEE 1588 depends on a hypothesis: the down link and up link between two communication ends are symmetric. However, this hypothesis largely limits the standard's applications. This paper first does quantitative analysis on error due to link's asymmetry. Secondly, factors which lead to link asymmetry are studied here. This paper points out that protocol stack delay and network delay lead to significant randon variation, therefore should be eliminated when IEEE 1588 is applied. Third, this paper studies synchronization algorithm for PTP supported asymmetric links, and offers two solutions. Finally, this paper lays emphasis on synchronization algorithm for non-PTP supported asymmetric links, and points out that Non-slide Window Average Filter technology can significantly approve synchnization performance. Besides, when width of the window is larging, the precision is higer. Through average filter, the propagation delay's Gaussian noise due to non-PTP devices can be eliminated.