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@ Cable-Tec Expo: Planning for capacity constraints

Wed, 10/17/2012 - 4:01pm
Brian Santo

The “Bandwidth Hunger Games” session was down to three last contestants: Cisco’s Ron Hranac, Motorola’s John Ulm and InnoTrans’ Mani Ramachandran, who covertly stalked each other, each waiting for the others to make the fatal mistakes that would leave a single survivor to emerge alive from the conference room, dirty, exhausted, and perhaps damaged, but ultimately triumphant.

So … not really. The three were on hand to discuss different strategies for coping with bandwidth constraints as cable technology and cable networks keep evolving.

Ulm, fellow of the technical staff at Motorola Mobility, spoke of some of the options MSOs have for addressing bandwidth constraints in the immediate future. MSOs serve themselves best, Ulm argued, not by addressing each bandwidth crunch with a tactical response, but by developing a long-term plan for service migration that includes planning for stepped up capacity expansion.

Node splits remain a key option, though it is commonly held that each successive round of splits gets more expensive and provides less return. Analog reclamation is also an option for the many companies that have yet to go all-digital.

Looking forward, cable operators could distribute hybrid gateways that would distribute both MPEG and IP video, and when necessary, convert, or transcode, video in one format into the other. Another alternative would be switched digital video (SDV).

Motorola conducted several case studies and concluded that those two elements are two of the most valuable options. Every MSO is coming from a different place and will have different paths and priorities. You have to look at your own services and how fast they're ramping up, Ulm said. But given the case studies, SDV is critical to gain back bandwidth, he explained, and gateways are important to help minimize the impact of IP video growth.

Hranac was on hand to give a paper (written by his Cisco colleague John Chapman) that jumped ahead in time a bit, and he commented on some of the longer-term solutions – and some of the problems that might ensue from those solutions.

Cable operators are going to need to allocate more upstream bandwidth, carving it out of current downstream spectrum. Going from 5 MHz to 42 MHz and going up to 85 MHz is possible with the version of DOCSIS we have today, Hranac noted. But MSOs are going to need to eventually allocate several hundred MHz of spectrum to the downstream.

There are perils to that, however. Things like MoCA, and even GPS, could be impacted.

“GPS is a biggie,” Hranac said, pointing to how LightSquared had its business plan undercut because of potential interference with military GPS signals.

If cable were to expand its downstream spectrum, there’s the potential for signal leakage in the L3 Band the U.S. government uses for nuclear detonation detection.

“We really don't want signal leakage there,” Hranac observed. One solution might be to simply not use that band at all – “notch that out,” he said.

There might also be what Chapman has tagged as ADI – adjacent device interference. If a split is created, could that create debilitating interference with legacy devices? Some CPE, like gateways, might end up getting blasted. If you can upgrade, fine, but if not, you may have to install filters on some legacy systems, he explained.

Out-of-band (OOB) is another biggie, Hranac said. There will be interference here, he stated, but there will be multiple countermeasures, including leveraging the fact that many legacy set-tops have tuners in the OOB circuit that could be reset with firmware.

There is no getting around an increasing reliance on and expansion of fiber networking, and effective fiber networks will require increasingly agile transmitters. Ramachandran covered chirp-free transmitters. Some new versions, he said, provide superior performance at lower prices than before.

Chirp-frees can do 16 wavelengths up, 16 down, with a range of up to 80 km. The devices are appropriate in a range of network configurations, including node splitting, Fiber Deep and centralized RFoG designs.

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