DOCIS heads north
Canada's Cogeco Cable has gone where no MSO has gone before: it has commercially deployed DOCSIS (Data-Over-Cable Service Interface Specification) cable modems to all but one of its systems in Ontario, Canada. The only exception is Kingston, where Cogeco Cable has clustered its older LANCity modems to use up their effective lifespans. All told, "We currently have 16,000 Internet customers in Ontario, and probably 12,000 of them are DOCSIS (modem users)," says Denis Belanger, Cogeco Cable's vice president of engineering and development. "We're not in a trial with these modems anymore. All 12,000 of our customers use (them)."
"They're good," he adds. "We would stopped deploying them if they were no good. The deployment began in August 1998, and the only new modems we are ordering for our Ontario Division are DOCSIS."Modem standards
The DOCSIS roll out is the fruit of Cogeco Cable's long-standing commitment to open cable modem standards. It came about through the joint efforts of Cogeco Cable, Cisco Systems, Samsung Corp. and CableLabs. Samsung supplied the modems, namely the "InfoRanger." In keeping with DOCSIS 1.0 specifications, the InfoRanger offers a downstream data rate of 40 Mbps, and an upstream variable rate ranging from 128 kbps to 10 Mbps. The limiting factors are the Internet and the PC's capabilities.
Ironically, although the Samsung InfoRanger is a DOCSIS modem, it has yet to be certified as such. In fact, it's still being checked for compliance by CableLabs.
Despite this, Cogeco Cable decided to deploy the InfoRanger last year. That's because the company has tested this modem carefully, and decided that any further changes to it would only be software-based. Making these changes would be easy, says Belanger. New programming would be sent downstream to the units, right within subscribers' homes.
"When we got to the point (where) we were absolutely sure that there were no hardware issues anymore, we decided to move forward," he recalls. "We're normally pretty aggressive in deploying technologies.Once we've decided to move forward, we move." Since then, nothing has happened to shake Cogeco Cable's faith in the InfoRanger. There have been a lot of software upgrades, to be sure, but software has been the only problem.System configuration
Meanwhile, Cisco developed the headend interfaces for the modems, which are known as uBR7246 DOCSIS cable modem termination systems, or CMTS, for short. As configured by Cogeco Cable, each CMTS is handling anywhere from 500 to 1,300 DOCSIS modems apiece. Here's how they fit together. At the subscriber end, the incoming coax cable is split between the user's TV and their cable modem. Ideally, up to four TVs/modems can be handled by a single line. More can be added, says Belanger, but only if some kind of amplification is installed.
From the house, the coax travels back to a 2,000-household fiber optic node, or "pocket." It connects to the CMTS at the headend. In turn, the CMTS connects to Cogeco Cable's fiber optic backbone, and ultimately, to the Internet itself. The CMTS is responsible for managing the specific system's Internet service. It queues incoming signals from each modem, dealing with them on a "first-come, first-served" basis. It also interfaces with the Web itself, shifting information to and from subscribers.
So how is Cogeco Cable's DOCSIS-based Internet service working? Just great, says Belanger. DOCSIS' first big plus is its capacity. Explains Belanger, "Recent studies show that you can get as many as 600 simultaneous users on a DOCSIS channel." This is possible because "the protocol is very efficient, the system is very robust, and the collisions are managed in a very efficient way." His conclusion? "You can achieve very high penetration with DOCSIS, and still let the user have a very high-speed experience." Of course, node size matters. To keep the CMTS and DOCSIS channel from being swamped, "We try to stick to 2,000-household nodes," Belanger says. Still, "You can have 5,000-household or bigger DOCSIS nodes, and make it work properly as well."
DOCSIS' second big advantage is its robustness in dealing with ingress noise. "That's one of its benefits over the previous proprietary technologies we were using," says Belanger. "We even combined six pockets together, and the system was still working."
And of course, the third big benefit of using DOCSIS is the fact that it is "open standard." Being such, cable companies can buy DOCSIS modems from a wide range of equipment suppliers. This reduces their cost by introducing competition into the market. It also future-proofs them to some extent, because they're not reliant on a single proprietary technology. In other words, if a single DOCSIS manufacturer goes under, companies like Cogeco Cable can always buy new DOCSIS modems elsewhere.Proven technology
For Cogeco Cable, the DOCSIS modem deployment has been a very good experience. The equipment is reliable, robust and it works. That's why the company is starting to roll out DOCSIS technology to its Quebec territories as well. One thing is clear: DOCSIS is no longer an experimental modem technology. It works. Cogeco Cable has proved it.