By Karthik Sundaresan, Cable Television Laboratories Inc.; Doug Jones, Cable Television Laboratories Inc.
Every generation of DOCSIS® technology includes requirements for backward compatibility with the previous generation to enable seamless transitions. With a DOCSIS 4.0 cable modems (CM), there is opportunity to further exploit the capabilities of a currently deployed DOCSIS 3.1 cable modem termination system (CMTS). Specification work was completed clarifying the behavior of DOCSIS 4.0 CMs with DOCSIS 3.1 CMTSs. This paper examines these possibilities, it discusses how a DOCSIS 3.1 CMTS negotiates capabilities with a DOCSIS 4.0 CM, how a DOCSIS 4.0 CM, either FDD (frequency division duplex, (also known colloquially as Extended Spectrum DOCSIS), and FDX (full duplex) will operate with various diplex filters on the DOCSIS 3.1 network, and how a DOCSIS 4.0 CM can be used to increase capacity on an existing HFC network. With recent product upgrades, a DOCSIS 3.1 CMTS can now support up to five (or more) OFDM channels; however, currently available DOCSIS 3.1 CMs only support two OFDM channels that have a peak downstream rate of about 5 Gbps. Operating a DOCSIS 4.0 CM on a DOCSIS 3.1 CMTS (with additional OFDM channels), can support a downstream peak capacity of up to 8.8 Gbps—a 75% increase relative to currently deployed DOCSIS 3.1 CMs. With higher capacities, operators can provide enhanced services and faster downstream speed tiers even before implementing DOCSIS 4.0 network topology changes and installing DOCSIS 4.0 CMTSs. For DOCSIS 4.0 CMs to become operational, a DOCSIS 3.1 CMTS may need a software update. This update enables a DOCSIS 3.1 CMTS to gracefully interpret and negotiate DOCSIS 4.0 modem capabilities, thereby enabling DOCSIS 4.0 CMs to be operated on a DOCSIS 3.1 CMTS. This paper touches on other dependencies such as support by the CMTS for bigger certificate sizes, and bonding on more than two OFDM channels, support for OUDP testing and overlapping channels. We will also report on lab testing results that we plan to conduct.