Cable modem speeds are about to zoom a whole lot higher. Thanks to the magic of channel bonding, DOCSIS 3.0 modems will soon be able to reach 300+Mbps—though cable users won't see Internet speeds in that range anytime soon.

DOCSIS is the cable modem spec that defines IP transfer across a cable company's hybrid fiber coax (HFC) system. Unlike earlier DOCSIS implementations, version 3.0 of the spec introduced channel bonding, a technology that can use parallel 6Mhz cable channels to transmit data. With each channel capable of around 40Mbps, DOCSIS 3.0's baseline requirement that four channels be bonded meant that the cable industry had a technology that could compete with fiber by offering 160Mbps of bandwidth. (Comcast, one of the most aggressive of the cable operators, has already rolled out 50Mbps speed tiers.)

But four channels is merely a minimum. Last year, Texas Instruments announced that its Puma5 DOCSIS 3.0 equipment would support the bonding of eight channels, and Broadcom announced the same thing at this year's CES.

Eight channels offers 320Mbps of downstream bandwidth (these two systems feature only four bonded upstream channels, so they aren't designed for symmetrical connections), and cable operators must be pleased to see that their IP delivery solution has the headroom to compete with FiOS. CableLabs, the industry's research consortium, believes that the system can scale to "potentially gigabits per second."

Now, only days after the Broadcom announcement, Cisco has revealed its plan to develop a new DOCSIS 3.0 modem based on the Broadcom silicon. According to Multichannel News, the device will be submitted for CableLabs certification this spring, with widespread deployment scheduled for 2010.

Not that home users will see 320Mbps downloads any time soon; the new silicon is more about offering future room to grow than it is about immediate speed bumps. Cable operators aren't yet taking advantage of even existing DOCSIS 3.0 capability in full, but a 320Mbps ceiling certainly gives operators like Comcast the ability to match Verizon's speed increases at its discretion as the two companies play hare to AT&T's U-Verse tortoise.