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@ The Cable Show: Comcast gets to 1 Gbps on its Chicago network

Fri, 06/17/2011 - 8:25am
Brian Santo

Comcast demonstrated data download speeds in excess of 1 Gbps at the Cable Show, in a demonstration run over its existing network in Chicago.

The company offered few technical details beyond the fact that it bonded 32 DOCSIS channels to achieve that level of throughput, and that the signals ran through 11 miles of HFC plant. Cisco confirmed that Comcast was using two of its 16DSx4 U.S. prototype modems to receive the 32 DOCSIS downstream channels for the demo.

During the demo, CEO Brian Roberts downloaded the entire fifth season of the NBC half-hour sitcom "30 Rock" in just more than a minute and a half.

Arris meanwhile demonstrated transmission speeds that exceeded the Comcast demo's by a factor of four. Arris may have got less press for its achievement by virtue of the fact that the demo stopped at a Fiber Node. It probably doesn't help Arris that they don't have a spokesman heading toward Steve Jobs territory in terms of star power.

Arris ganged four of its new 32 Downstream Cable Access Modules (32D CAMs) to aggregate 128 DOCSIS downstream channels into the Fiber Node to sustain downstream transmission of about 4.5 Gbps.

Arris also showed a proof-of-concept of a 5-200 MHz high-split DOCSIS upstream system with 575 Mbps of DOCSIS upstream bandwidth being transmitted over 24 DOCSIS Upstream channels out of a single Fiber Node, using a single Arris 24U CAM.

Earlier this year, Cisco achieved downstream rates of 1.6 Gbps on the downstream and 300 Mbps on the upstream. The demo bonded 48 downstream channels using 256 QAM and 12 upstream channels using 64-QAM in the upstream.

In a blog yesterday reminding people of that demo, John Chapman, CTO of Cisco's Cable Access Business Unit, said "clearly, there's a lot more breathing room for wideband IP services.

"The math goes like this: 134 digital, 6 MHz channels downstream, modulated with 256 QAM, yields a total potential throughput of over 5 Gigabits per second of capacity," he wrote.

For more years than anyone wants to remember, the cable industry has been very patiently explaining to people who have been wowed by fiber to the home (FTTH) installations that yes, HFC networks can be modified to compete for years and years to come with all-fiber networks.

And as cable has been reiterating for years, channel bonding is only one of several techniques to buy more bandwidth. Execs from Comcast, Motorola and Arris discussed several of them, including the potential of splitting nodes, at a Cable Show session earlier in the week called HFC-ing the light.

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