Packet selection technique for clock recovery over packet networks

Abstract

The primary challenge in the design of a clock recovery system for packet networks is to deal with Packet Delay Variations (PDVs) - that is, the variation of the packet transit delays introduced by queuing process in Network Elements (NEs) such as switches and routers. In order to obtain clean signal from recovered clock various techniques are employed to mitigate the effect of the PDVs. One of such mechanisms, referred to as Packet Selection Algorithm (PSA), reduces recovered clock noise variance by filtering incoming timing packets in such a way that only packets complying with predefined selection criteria are passed to the clock recovery algorithm. Since it is a non-trivial task to find optimal PSA criteria analytically using output variance minimization, this paper introduces a probabilistic approach for the PSA optimality analysis. Based on this probabilistic analysis a new packet selection technique is proposed, which outperforms prior art when compared in simulation by means of Time Deviation (TDEV) standardized metric.