By John T. Chapman, Rakesh Chopra, Laurent Montini, CIsco

DOCSIS and the HFC plant present many challenges why it is difficult to propagate network timing information from the headend, through a DOCSIS network and into a CPE device with any degree of accuracy. These challenges include: • HFC plant asymmetry, • DOCSIS asymmetry due to the upstream scheduler variability, • unknown asymmetrical plant delay between CMTS and CM, • unknown delay of CMTS and CM PHYs, • uncalibrated ranging. This paper proposes a solution called DOCSIS Timing Protocol (DTP) and discusses how DTP can address these challenges in a DOCSIS system and what specification and product changes are needed to the DOCSIS CM, CMTS, and DTI Server. The resulting design can support the generation of precision timing protocols such as NTP, PTPv2 (IEEE Std1588-2008) and Synchronous Ethernet that can serve new and evolving CPE devices with traceable time and frequency synchronization requirements.

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