Improving Upstream Efficiency (2021)

By Karthik Sundaresan, Tom Williams, Sheldon Webster, Alberto Campos & Doug Jones, CableLabs

Cable operators are facing an unprecedented increase in upstream traffic usage because of the shift to working/schooling from home, and the reliability, capacity, and efficiency of the upstream is top of mind for all operators. This paper is focused on improving the efficiency of the DOCSIS upstream (DOCSIS3.0 SC-QAM and DOCSIS 3.1 OFDMA) channels. The paper will document some of the upstream engineering problems seen by operators and make robust recommendations on how improve those situations. There are thousands of upstream parameter settings and control knobs available to an operator and much of the time operators leave those settings at their default values. This paper will investigate areas (for SC-QAM & OFDMA) such as mini slot size, FEC, Cyclic Prefix, FFT size, frame size, pilot patterns, channel size, guard bands, profile definition, CMTS settings for changing IUCs, etc., and make recommendations on each of those parameters and settings. This paper will also explore configuration file service parameters for a cable modem (CM) and make recommendations for better performance on the upstream. Ultimately, this paper will help operators understand optimized upstream configurations and settings for production deployments.

This paper assumes some background understanding of both DOCSIS 3.0 and DOCSIS 3.1 upstream technologies. Here we try to provide an understanding of different upstream channel parameters (which an operator can tweak) and then the pros and cons of choosing different values for that parameter. Based on these tradeoffs we make recommendations on optimal values for each of these channel parameters or network configurations.

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