Comcast Corp. (Nasdaq: CMCSA, CMCSK) is using the fiber-to-the-home (FTTH) capabilities of its Metro Ethernet platform to power a new residential broadband service with a maximum downstream speed of 305 Mbit/s and a potential 65 Mbit/s upstream.

The cable operator is using Docsis 3.0 technology for its widely deployed 105Mbit/s (downstream) high-speed Internet residential service, and has even demonstrated how that service could ultimately achieve speeds of more than 1 Gbit/s on live cable plant. (See Comcast Plugs In Cisco for 1-Gig Docsis Demo .)

Despite that potential, Comcast is keeping Docsis 3.0 on the sidelines for its newest, fastest residential broadband tier, called Extreme 305, which is being offered in several major markets in the Northeastern U.S., including Boston, Philadelphia, Baltimore and Washington, D.C.

In terms of speeds, it matches Quantum FiOS, a new GPON service from Verizon Communications Inc. (NYSE: VZ) that offers 300 Mbit/s downstream and 65 Mbit/s up. (See FiOS Speeds & Prices Take a Quantum Leap .)

Comcast didn't provide much technical detail about the systems that will enable Extreme 305 when it announced the new service in July, and didn't add much detail last week when the service was launched, causing some observers to falsely assume it was a Docsis 3.0 offering. But the company has confirmed that Extreme 305, at least initially, is fiber-based. (See Comcast Revs Up Pricey 305-Meg Tier, Comcast's Fastest Broadband Starts Cap-Free and Comcast's Technicolor Dream Gateway.)

This post at Broadband Reports outlines some of the service's technical criteria, noting that eligible customers must be within reach of Comcast's Metro Ethernet platform, which the MSO is already using to go up-market to serve mid-sized business customers. Extreme 305 also appears to be limited to single-dwelling units that are located less than one-third of a mile from a fiber access node. In the home, the service relies on the Netgear Inc. (Nasdaq: NTGR) R6300, an 802.11ac Wi-Fi router. (See Ciena, Cisco & Juniper Get Piece of Comcast's MetroE.)

Essentially, Comcast is fighting fiber with fiber. It's utilizing a business-class platform to deliver a high-end residential service as it tries to discover what sort of demand there is for an uncapped 300Mbit/s product that currently sells for US$300 per month. And, according to this statement from Comcast spokesman Charlie Douglas, it appears that Comcast will use the fiber-based approach as a placeholder for very high-capacity residential broadband services until it makes business sense for the MSO to make significant changes to its Docsis platform:

The status of Docsis 3.0
The latest generation of high-volume Docsis 3.0 modems and gateways can bond eight downstream channels, enough for bursts in the area of 300 Mbit/s, though sustained speeds would be much lower than that. Hitron Technologies Inc. , Arris Group Inc. (Nasdaq: ARRS) and other Docsis 3.0 CPE vendors are also developing models based on new silicon from Intel Corp. (Nasdaq: INTC) that can bond 16 or 24 downstream channels and up to eight upstream channels. The 24-channel version can achieve downstream rates near 1 Gbit/s when fully loaded. (See Intel's New Docsis 3.0 Chip Guns for 1-Gig .)

But those products are still in their infancy. Hitron, for example, plans to submit a wireless gateway based on the 24-channel configuration to CableLabs for certification testing this November. Results from that test wave aren't expected until late February 2013. Some of the major cable modem termination system (CMTS) vendors, meanwhile, are working on new software that can accommodate these beefier channel-bonding capabilities. Depending on the vendor, that software may not be ready until mid-2013. (See 1-Gig Cable Gateway Gets Ready for Its Close-Up .)

— Jeff Baumgartner, Site Editor, Light Reading Cable