TORONTO – With the advantage of hindsight, Cogeco Cable and vendor Arris Group shared some lessons from their DOCSIS 3.0 implementations with attendees during a session Wednesday at the SCTE Canadian Summit.
According to Steven Krapp, Arris’ director of product management, some of those key considerations are related to spectrum, output power, noise funnelling and combining loss.
Krapp’s first recommendation is that organizations use downstream channel bonding – available as 4-channel bonding today, but 8-, 16- and 24-channel bonding capabilities are on the product horizon, he said.
One advantage to DOCSIS 3.0 channel bonding is that dynamic load balancing can be used as a more effective method of augmenting capacity in the system than traditional node splitting, he explained.
In terms of spectrum considerations, organizations must identify where they’re going to place the multiple channels for DOCSIS 3.0, Krapp continued. While DOCSIS itself has no restrictions on where these channels can be placed, network components such as cable modems, cable modem termination systems (CMTSs) and QAM devices do have spectrum restrictions.
“I’d say 90-plus percent of all deployments are using contiguous spectrum for their channels because it’s easier for them to manage that than to have to worry about the different abilities of the different loads, and the different CMTSs and different edge QAMs,” Krapp said. “So the rule of thumb is contiguous spectrum is best, but keeping the spread of DOCSIS 3.0 channels under 80MHz to avoid any issues is what I’d suggest.”
Output power is a topic that has become controversial, Krapp continued.
“If you talk to most cable operators, their idea is the higher (the output power) the better – give them as much power as you can”, he said. “As a vendor of edge QAM equipment, we’d love to do that, but again there are constraints to be able to meet noise and power constraints that are specified by CableLabs and DOCSIS and that are imposed on us.”
The DOCSIS 3.0 Radio Frequency Interface specification dictates that output power be decreased as the number of DOCSIS 3.0 channels increases, resulting in lower output power than was allowed in the past.
“What this means for operators is they need to make sure the combining loss between their CMTS equipment and their lasers is not such that there’s too much loss for these levels ,” said Krapp.
If operators decide to combine multiple upstream service groups into a larger service group, they need to keep in mind that they’re not only combining signals, they’re combining noise as well.
“So you need to measure noise before and after combining, and make sure you have the SNR (signal-to-noise ratio) that you need for the channel signalling that you desired before,” Krapp added.
To help alleviate some of the noise funnelling issues, Arris recommends using frequency stacking.
“This is where a single RF port receives multiple upstreams from the same service group,” Krapp explained.
He also said that frequency stacking results in less combining loss, so therefore cable modems don’t have to transmit at as high a level. Furthermore, frequency stacking actually helps to increase the receive power at the CMTS.
In a highly technical presentation, Cogeco Cable engineers provided a checklist of items that organizations should consider as they prepare to implement DOCSIS 3.0. These considerations included spectrum availability and frequency migration for downstream channels, IP scopes requirements for bonded channel overlay for multiple nodes, CMTS software testing, modular CMTS (M-CMTS) infrastructure deployment, and capacity planning.
It may seem an obvious point, but DOCSIS 3.0 implementers must ensure that every component in their network is able to support the higher DOCSIS 3.0 throughput, said Kira Gurovskaya, manager of IP network access in the engineering group at Cogeco Cable.
“Basically, every component in the traffic pass should be able to support DOCSIS 3.0 speeds. Otherwise, your customer might not be able to get the advertised speed,” she said.
As part of its DOCSIS 3.0 migration planning, Cogeco developed a special high-speed network certification procedure to make sure that it did not have any bottlenecks in the network, Gurovskaya shared.
In addition, customer premises equipment also needs to support the higher speeds of DOCSIS 3.0, she continued. CPE equipment includes modems, routers, network interface cards and the customer’s computer operating system.
