Cable Leaders Unveil Plans for New DOCSIS 3.1 Broadband Spec
ORLANDO -- Seeking to maintain cable’s competitive edge in selling broadband service and forestall the need to lay fiber all the way from headends to the home, industry technologists started drafting a new technical standard designed to enable the ISPs to provide downstream and upstream speeds greater than 1 Gbps. In a special session at the Society of Cable Telecommunications Engineers conference, engineers from CableLabs, SCTE, Comcast, Time Warner Cable and Cox Communications spelled out their plans to create and deploy the proposed DOCSIS 3.1 specification over the next two years. While the plans have been a somewhat open secret in the industry for months, the session marked their first public airing and discussion. Also Thursday, the cable industry for the first time acknowledged publicly the coming 3.1 spec form CableLabs (CD Oct 19 p15) , via a release from SCTE (http://xrl.us/bnu3nn).
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The engineers confirmed that the envisioned DOCSIS 3.1 platform will be able to support data speeds of at least 10 Gbps downstream and 1 Gbps upstream, far more than the current DOCSIS 3.0 standard. In recent months, cable equipment manufacturers have openly mused about having the new standard support downstream data speeds as high as 10 Gbps and upstream speeds as much as 2 Gbps. Cablevision and Comcast are among those relying on DOCSIS 3.0 to offer broadband services that approach or top 100 Mbps in the downstream but offer much less capacity in the upstream. Deployments by AT&T and Verizon can have even faster speeds, those telcos have said.
To reach cable’s new capacity targets, technologists said they aim to boost the industry’s spectral efficiency by at least 25 percent. In the boldest move, they are urging the industry to switch from its existing 6 MHz- and 8 MHz-wide channel spacing to smaller orthogonal frequency divisional multiplexing (OFDM) subcarriers over time. The North American DOCSIS platform uses 6 MHz-wide channels that each pump out about 40 Mbps. With DOCSIS 3.1, the industry hopes to squeeze out more bits per hertz by chopping 200 MHz-wide blocks into thousands of smaller, 20KHz-to-50KHz-wide subcarriers.
Engineers said cable operators could use those 200 MHz-wide blocks, far bigger spectrum blocks than they now create by bonding 6 MHz channels under DOCSIS 3.0, to produce data paths as large as 1 GB. They said cable operators could then bond the 200 MHz-wide channels together to create multi-gigabit capacities. That would let operators match fiber-to-the-premises speeds without having to extend their own fiber networks all the way to subscribers’ homes. “We could bond a lot of carriers now,” said Jeff Finkelstein, Cox senior director-network architecture. “But just because we could doesn’t mean we should."
Plans call for teaming up OFDM with low density parity-check (LDPC), a system that consumes less bandwidth than the industry’s current approach. Matt Schmitt, CableLabs director-DOCSIS specifications, said LDPC’s adoption will let cable operators pump out more bits per hertz by using higher orders of QAM modulation, including 1024 QAM and 4096 QAM, in both the downstream and the upstream paths. Cable providers typically now use 256 QAM in the downstream. While it would take 780 MHz of spectrum to get 5 Gbps using DOCSIS 3.0, Schmitt noted it should take 500 MHz with 3.1.
The cable technologists believe the switch to OFDM will open up the cable market for more chipset and equipment vendors and help cut costs as broadband usage rates continue to climb. The DOCSIS 3.0 silicon market is now dominated by two chip suppliers: Broadcom and Intel. A third, STMicroelectronics, recently entered the market. Getting costs down “is a key part of DOCSIS 3.1,” said Cox Chief Technology Officer Kevin Hart on another panel. Cable technologists hope to reduce the amount of time it takes to create new broadband specs and then turn them into actual products. After starting work in earnest about two months ago, CableLabs officials expect to finish the core DOCSIS 3.1 specifications next year and anticipate seeing initial products from equipment vendors as soon as 2014, Schmitt said. Until now, the average DOCSIS spec has taken three to four years from start to finish. Cable engineers said they expect the first new cable modems to be 3.1/3.0 hybrids that can bond at least 24 downstream channels and eight upstream channels, which will be the minimum channel-bonding requirement for the proposed 3.1 standard. They said 3.1 will be backwards compatible with DOCSIS 3.0 and 2.0 (CD Oct 17 p8).
The first DOCSIS 3.1 products likely to emerge will be consumer premises equipment, such as cable modems, predicted Jorge Salinger, Comcast access architecture vice president. This would enable vendors to seed the market with 3.1 devices before the networks are upgraded, paving the way for the migration to the new standard while avoiding any potential “brake points,” he said. Salinger said he expects the DOCSIS 3.1 downstream path to be ready before its upstream counterpart. He said Comcast is considering a new spectrum reclamation phase, which would set aside space for 3.1 that could also ease the company’s transition to Internet Protocol video.