August 22, 2008

Bandwidth Model Finds Good Fit

Bandwidth—understood as spectrum on a cable plant—has been the topic of the past year, or two or more.

How much is enough and what is the best way to get it? High-stakes questions, but it takes a mind-numbing variety of if-then scenarios to determine the most cost-effective bandwidth optimization answers.

Enter a model that Cisco was talking about at Cable-Tec Expo, and that Cisco Fellow and Chief Architect (and sometimes contributor John Chapman reportedly discussed at Light Reading’s video strategy event this summer.

What it does is crunch data to recommend a combination of solutions, including analog reclamation, switched digital video (SDV), and 1 GHz upgrades.

"It is very flexible and easy for each individual user to plug in the specifics of a hub or portion of the network...and get an instant readout," Marty Mattingly, Cisco consulting systems engineer, said.

"We are not advocating one (bandwidth optimization) approach over another. We are classify(ing) with what type of plant it is more attractive to use (which) capacity options," Mattingly said.

Example Favors 1 GHz

For illustrative purposes, Cisco used a mock network incorporating the same set of variables for each optimization alternative. The example uses a 35,000 home hub segmented into 500 home nodes, and forecasts what will happen over five years.

In this scenario, a network upgraded to 1 GHz had almost 30 channels left at the end of the modeling period. There were "substantially" less for 750 MHz networks, which used analog reclamation, SDV or both to gain bandwidth.

"There certainly is a onetime capital expenditure in year one of (the 1 GHz) model to upgrade the physical capacity of the network, but there are a variety of reasons to choose this approach," Mattingly said, listing the expectation of having to upgrade eventually and rising cost of labor.

It’s an approach, at any rate, which Cox Communications advocated early. In this article on Cox’s Orange County/Palos Verdes system, “1 GHz upgrade” was a definite part of the team’s mission.

According to Cisco’s analysis, analog reclamation and SDV may have a quicker turnaround in some instances, but they require "constantly" migrating bandwidth or the manipulation of the network to maintain capacity. In addition, with the former, some subscribers will remain analog only. Operators will need to purchase digital terminal adapters, which are estimated to cost $40 per device.

"When we drove the model, 25 percent of total capex required to maintain the network was used to purchase DTAs for the subscriber base," Mattingly said.

Cisco already has conducted modeling sessions for five of the top MSOs. A sit-down with Cisco currently is the only way to access the model, but the company is developing a web version.

- Monta Hernon