Impact of CCAP to CM Distance in a Remote PHY Architecture (2015)

By John T. Chapman, Gerry White, and Hang Jin, Cisco

The Remote PHY architecture currently being specified by CableLabs and developed by multiple vendors has the potential to change the DOCSIS access network significantly.

The basis of the architecture is to move the PHY and the digital to analog conversion from the CCAP device in the hub to the optical node and replace the analog optical link between CCAP and the node with a digital link such as 10G Ethernet.

This removes the distance limitations imposed by the analog link and could in theory enable the CCAP core to be located in a remote data center thousands of kilometers from the CM. The DOCSIS protocol must continue to operate between CM and CCAP both within the normal 100 mile (160 km) DOCSIS range and over this new extended distance.

This paper looks at how this type of system could be deployed and the impacts of increasing the distance between the CM and the DOCSIS cores on throughput and latency seen by the end user. The paper is in three parts: theory, simulation and test.

Part One explains the R-PHY approach and discusses some potential deployment scenarios. It looks at the impact on the DOCSIS protocol of moving the CCAP core to a remote data center and using an IP network to connect the core to the R-PHY node.

Part Two describes a simulation model developed to investigate the relationship between CM to CCAP distance and DOCSIS performance. The model has been used to investigate the impact of both latency and jitter in the network connecting the CCAP core to the Remote PHY and the paper will present these results

Part Three describes a series of experiments performed to validate the model and confirm the impact of extended distances in a real world deployment. The paper presents these results and compares them with the theoretical analysis and the simulated data.

This paper also discusses on how a Remote PHY based CMTS can operate at distances much further than an I-CMTS.

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