Big Upstream Upgrades

Business Services Drive Need to Boost DOCSIS Uploads

By Todd Spangler -- Multichannel News, 6/21/2010 12:01:00 AM

Delivering screaming fast 100-Megabit-per-second downloads may be the relatively easy part.

For cable’s DOCSIS 3.0 deployments, reaching comparable upload speeds is another story. It will take some heavy lifting to boost upstream capacity, which historically has been confined to the noisy 5-to-42-Megahertz slice of radio-frequency spectrum.

“The upstream is the Achilles’ heel for cable operators,” said Brian O’Neill, senior marketing manager for Motorola’s Access Networks Solutions business unit.

And as the industry increasingly aims DOCSIS high-speed-data services at small and midsize business customers, MSOs will be under even more competitive pressure to increase upstream bandwidth. Many businesses rely on big upstream pipes to transmit large files and video, and they’re accustomed to symmetrical- bandwidth offerings such as telco T-1 connections.

Moreover, “it’s not just best-effort, as with residential,” noted John Dahlquist, vice president of marketing for Aurora Networks.

There’s no one-size-fits-all answer to maximizing cable’s upstream path. But regardless of the approach, “you’re going to have spend money to get there,” said John Chapman, Cisco Systems fellow and chief architect for its access and transport technology group.

The good news: DOCSIS can provide up to 1 Gigabit per second upstream potentially for as little as 10% of the cost of a fiber to- the-premises buildout, according to Chapman’s analysis.

Perhaps the most straightforward technique is to perform node splits, by allocating the 5- 42 MHz spectrum — capable of delivering around 100 Mbps of usable bandwidth with DOCSIS 3.0 channel-bonding — across a smaller number homes (for example, reducing a service group from 500 homes to 100 homes).

Other approaches are more complicated. Allocating 5-200 MHz for upstream data can provide close to 1 Gbps throughput without deeper fiber deployment, but that would require eliminating several dozen analog channels. In Chapman’s “top split” scenario, upstream channels could be placed above 1 Gigahertz — but that would necessitate more expensive plant upgrades.

“The answer [for expanding upstream DOCSIS capacity] will be different potentially for business versus residential,” Chapman said. “It depends on whether you have to support existing customers on a segment.”

Motorola, for its part, believes operators still have the opportunity to boost the upstream by taking full advantage of DOCSIS 2.0 features.

“The dirty little secret is that less than 50% of the upstream channels are using 2.0,” O’Neill said. “There’s this whole latent potential that just needs to be tapped.”