CableLabs Next-Gen Broadband Project Envisions Multigigabit Speeds
Data-Over-Coax Technology Would Eliminate 6-MHz Channel Divisions
By Todd Spangler -- Multichannel News, 4/25/2010 8:28:16 AM
Cable's next major broadband technology platform may throw DOCSIS out the window -- but it is envisioned to let operators economically deliver gobs of bandwidth over existing coaxial cable.
CableLabs, the industry's research and development consortium, is in the earliest stages of investigating a new platform for data-over-coax transmission reconceived from the ground up, according to people familiar with the project.
The concept, if it comes to fruition, could let cable operators deliver extremely high speeds downstream, of up to 5 Gigabits per second -- or even more.
The new platform potentially represents a major architectural change for existing cable systems. "It's almost a complete relook at how you do data over coax," said a cable-technology executive briefed on the CableLabs project. "If you were to convert all the spectrum in a typical cable system to data you could easily get 5 Gigabits per second."
But there are a number of caveats.
CableLabs currently is only investigating the approach, and the work might not ever result in a technical specification. Also, this new data-oriented technology likely would not be compatible with current DOCSIS cable modem equipment.
Asked to comment on the project, CableLabs spokesman Mike Schwartz said, "CableLabs is in business to explore many different technologies on behalf of its members." He declined to comment further.
The initiative underscores the cable industry's position that the hybrid fiber coax (HFC) network architecture will be sustainable for many years -- if not decades -- without requiring a complete fiber-to-the-home buildout.
Executives familiar with the project said CableLabs is exploring new advanced media access control (MAC) and physical-layer (PHY) components for cable broadband equipment that would do away with the traditional 6-MHz channel divisions used in cable systems today.
Theoretically, CableLabs' current DOCSIS 3.0 spec can deliver multiple gigabits-per-second speeds. The specification "bonds" multiple 6-MHz channels together to aggregate the bandwidth provided by each one (typically about 38 Mbps downstream).
The post-DOCSIS approach, by eliminating the 6-MHz divisions, potentially would be far more efficient.
Even if the new data-over-coax platform never sees the light of day, DOCSIS 3.0 should provide cable operators ample bandwidth delivery for the next several years. The specification requires support for a minimum of four downstream channels (for a total of 160 Mbps) but chip suppliers have already delivered eight-channel products that deliver more than 300 Mbps down.
Cisco Systems, for one, has developed a DOCSIS 3.0 cable modem with Broadcom's silicon to bond together eight downstream channels, capable of delivering more than 300 Mbps.
And, in 2008, Cisco demonstrated a prototype of a system emulating a DOCSIS 3.0 cable modem operating at 1 Gbps by delivering the data over an optical network. That setup, however, would require an all-fiber network.
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This isn't news... the nice people at the OECD wrote this ages ago already. Including the explanation why this is theory and not practice www.oecd.org/dataoecd/49/8/40390735.pdf (page 18 ) With current technology it might
be possible to send up to 5 Gigabit/s (upstream and downstream combined) over an HFC network if no
analogue or digital TV-channels were broadcast and all bandwidth was used for data networks.
Rudolf - 4/26/2010 5:53:20 PM EDT -
re: the upstream - Since this project encompasses new MAC and PHY layers, you're talking about new CPE and headend equipment anyway. So throwing more spectrum at the upstream shouldn't be as difficult.
Todd Spangler - 4/26/2010 10:36:44 AM EDT -
It is true that the big problem with the HFC architecture is asymmetry. The meager 37MHz of dirty bandwidth in the upstream compares poorly with the >900MHz of clean downstream spectrum. Data services from cable usually have an asymmetry of 10:1 or more as a result. No amount of modulation improvements (such as wideband OFDM) will fix this. However if the cable industry decides to move the diplex filter splitting higher than 42MHz, this can be solved. At a cost of course.
Hal Roberts - 4/26/2010 9:50:49 AM EDT -
The problem with DOCSIS isn't the downstream, it's the asymmetrical upstream. While the downstream bandwidth will be adequate for the near term, the upstream will not be.
Increasingly, services are moving to the cloud. In order to be responsive and effective, symmetrical bandwidth is required. Even today, multi-gigabyte uploads are common (Google Docs, Dropbox, etc.). In a few years that will be trivially small.
Telecoms (e.g. FIOS) are already offering symmetrical residential service. Google is trialling Gig-E. Cable needs to get past its historical "TV" architecture to compete effectively.
Mace Moneta - 4/25/2010 2:53:43 PM EDT
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