May 30, 2017
The first Full Duplex (FDX) DOCSIS deployments are still years away, but Cisco is providing one of the first* proof-of-concept demos this week at the ANGACOM show in Cologne, Germany.
What's more, Cisco Systems Inc. (Nasdaq: CSCO) Fellow and CTO of Cable Access John Chapman is going on the record to say the technology will provide "fiber-equivalent speeds" and will be "probably the most revolutionary thing to ever happen in our environment in cable."
The promise of FDX is that it will allow downstream and upstream traffic to occupy the same spectrum in the last mile of coaxial plant leading to subscriber homes. If it can deliver as promised, that will mean that cable operators can offer symmetrical 10-gigabit speeds without the expensive and time-consuming effort of replacing every bit of coaxial network with fiber.
The demo at ANGACOM doesn't show true FDX performance because today's cable modems can't support it. However, the demo does show a critical enabling component for Full Duplex DOCSIS, the FDX echo canceler. (See also Full Duplex Is a Go; Cable Aims for 10 Gig.)
An echo canceler allows a node to send and receive traffic at the same time by filtering out transmission noise so the device can simultaneously "hear" incoming signals while sending out its own messages. At ANGACOM, Cisco is demonstrating that capability by using a chunk of spectrum in the frequency band between 108 and 204 MHz. The echo canceling takes place between Cisco's Remote PHY device (RPD) with FDX technology sitting in the optical node and cable modem silicon provided by Intel Corp. (Nasdaq: INTC). (See also The Cable DAA Vendor Race Begins and Cisco Debuts Remote PHY Solution.)
Cisco's Chapman says the company has also open sourced its echo canceling solution as part of the OpenRPD software project with CableLabs. (See Cisco Open Sources Remote PHY Device.)
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Full Duplex DOCSIS may be a critical development for extending the life of hybrid fiber-coaxial networks, but it won't solve that problem on its own. Enabling higher broadband speeds first requires an upgrade to DOCSIS 3.1, and then a fiber deep deployment that pushes fiber all the way to the last active electronic device in a network. Comcast has been aggressive in pursuing this Node-plus-0 (N+0) architecture, but much of the cable infrastructure in the US still uses multiple amplifiers beyond the optical node to transmit signals over longer lengths of coaxial cable. Operators will have to commit to driving fiber deeper into their networks if they want to take advantage of FDX DOCSIS.
Chapman also predicts that FDX technology won't be commercially available until at least 2019. Between now and then, cable companies will have to decide if they want to invest in the other network upgrades necessary to prolong the lifespan of their HFC infrastructure, and/or if there are situations where it makes sense to forego the complexity and instead spend the money to take fiber all the way to the home.
*Editor's Note: This story has been updated. An earlier version said that Cisco was first to demonstrate Full Duplex DOCSIS, but Nokia held its own FDX demo last year. See Nokia Demos 10-Gig Over HFC.
— Mari Silbey, Senior Editor, Cable/Video, Light Reading
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