GigE is laying a fast track to become
cable’s transport of choice for video-on-demand
It's not exactly like the leap from a coal-fed choo-choo to an ultra-sleek bullet train, but Gigabit Ethernet appears to be well on its way to becoming a viable transport alternative for cable operators who are plotting their video-on-demand network designs, build-out plans and content slates.
A shift to Gigabit Ethernet, which supports data transfer rates of 1,000 megabits per second, could eventually supplant several traditional and legacy transport mechanisms, including direct QAM (quadrature amplitude modulation) in Motorola-based cable systems, ASI (Asynchronous Serial Interface) in Scientific-Atlanta-based grids, as well as ATM (Asynchronous Transfer Mode) in many DSL environments.
In the case of GigE, the advantages appear to touch both sides of the technical/operational equation, allowing cable operators to leverage a VOD transport platform comprised of commodity parts, a more centralized server infrastructure, a deeper capacity well, and, perhaps most importantly, a lower cost proposition.
For example, if an operator builds out a GigE network for 10 percent contention, it would only have to match the server support at six percent. ASI, in contrast, leverages point-to-point connections, meaning the network and the servers would have to be built out to handle exactly the same usage.
GigE, from a server standpoint, is also designed to be more efficient than ASI, transferring data at theoretical levels approaching 900 Mbps. In comparison, a single ASI can put forth roughly 213 Mbps.
Although current outputs are a moving target, SeaChange International Inc., for example, intends for its GigE-capable servers to pump out between 900 Mbps and 930 Mbps by the end of this year, says company Vice President of Strategic Planning Yvette Gordon-Kanouff.
Those additional titles can turn into additional revenue. Southwell estimates that just one additional VOD movie buy per month per customer can trim an operator's break-even point on the infrastructure from three years to just over one year.
GigE also lends itself to a more centralized VOD architecture, which can provide cost savings to cable operators. For example, in early VOD implementations, operators tended to install servers at the hub site in a more distributed fashion, because the cost of transport was quite high.
If the content housed there is highly used, that's not such a bad thing. However, if that content is accessed infrequently, then an operator is repeating that storage against the cost of the servers.
Instead, less frequently accessed content could be stored in a more centralized and more server-efficient array–another area where GigE can lend a helping hand.
Still, the term "centralized" is a bit of a misnomer when it comes to VOD, says nCUBE Senior Vice President, Broadband Strategy and Product Management Jay Schiller. Instead of representing a monolithic server site, a centralized server architecture is really a hybrid system that provides a greater "centralized effect," allowing for fewer server sites.
Another feather in GigE's cap is its ability to use a switched architecture, allowing an operator to "switch" connectivity to any set-top box in the network, as opposed to an architecture where the server itself owns the bandwidth of a specific area and a specific set-top box.
Some of those costs are saved thanks to the high commoditization of GigE components. "ASI is a standard, but I can count on one hand the number of vendors that are manufacturing network cards for ASI, as opposed to GigE, which I really cannot count," notes Ben-Natan. "In terms of dollars per stream," he adds, "you're really talking very low figures, even below $20 per stream just for the transport, which used to be on the order of $200 when people did it with analog DWDM."
Harmonic, as one example, sells systems for between $25 and $30 per stream. "Down the road, it will go to $20 and $10; no doubt about it," Ben-Natan says.
Southwell notes that he expects ASI vendors to lower their prices to compete with GigE. Still, "it's one thing to give it away; it's another to offer it at a price where you can actually sustain the business," he adds.GIGE GAINS MSO SUPPORT
Because of these collective benefits, cable operators are starting to leverage GigE in many of their new video-on-demand deployments.
Charter Communications, already in the throes of a big transition following Diva Systems' bankruptcy, is installing both ASI and Gigabit Ethernet transport systems in its VOD markets. Charter is tapping GigE in markets where it's using the nCUBE platform/Scientific-Atlanta network combo, and leveraging ASI and Concurrent servers in Motorola-based networks.
Charter eventually plans to migrate all of its VOD markets to GigE, as well, once Concurrent's cable-based GigE products are ready to roll, says Don Loheide, the MSO's vice president of engineering and technology.
Concurrent’s GigE server implementation for cable
operators should be ready
to roll in a matter of months.
Comcast Cable's first flirtation with GigE is taking place in its home base of Philadelphia, where the MSO is undertaking one of the most advanced cable VOD installations to date. In addition to offering on-demand access to a slate of top-tier movies, Comcast plans this fall to offer roughly 1,500 hours of VOD content.
"We can support more streams with [GigE], which helps us in a lot of areas," says Comcast Vice President of Digital Television Mark Hess. That will come in handy as Comcast prepares to handle contention rates in the range of 10 to 15 percent. "We're telling [the field] as they put their architectures together to consider GigE as the main way to go," Hess notes.
Time Warner Cable also is giving GigE some attention, most recently for its VOD rollout in Green Bay, Wis. "GigE is evolving and will be a [strong] transport medium as we grow streams out of the headend," says Reggie Workman, the MSO's vice president of engineering.
He adds that the MSO's decision to go with GigE will largely depend on the number of streams required by the system. However, Time Warner, even in Green Bay, has not reached a streaming density level that would actually require the operator to use GigE, he notes.
While Time Warner Cable is in the budding stages of GigE deployment, expect the MSO's parent company, AOL Time Warner, to take a hard look at GigE for its budding everything-on-demand initiative known as MystroTV. That project, headed by AOL Time Warner's Personal Interactive Video Group President Jim Chiddix, is expected to harness a massive number of streams.
Cablevision Systems Corp., meanwhile, is using Harmonic's gear in the NYC area, where the MSO offers an ambitious slate of VOD programming that ranges from first-run movies and subscription VOD content, to "free-on-demand" titles from services like MagRack.
Despite GigE's inherent advantages, don't expect operators to execute a wholesale switch-out to GigE anytime soon, leaving their ASI investments to lay fallow. "But we might do a hybrid and we might upgrade some [networks], depending on what we're doing in the marketplace," says Hess.
Schiller notes that most MSOs are asking nCUBE to help them plan where it makes the most sense to install a GigE operation, but adds "there's not a mad rush" from operators to execute an ASI-to-GigE migration.
Gordon-Kanouff agrees that migrating a legacy ASI system to GigE doesn't make much sense for now, as an operator would have already paid for the VOD network infrastructure, including receivers, transmitters and the video servers. "I think you'll see ASI servers stick around for some time, because they're running and they're working...and touching them adds cost," Connolly adds.VENDORS GET GIGE WITH IT
Transport equipment providers and server vendors alike are already offering GigE capabilities today, or plan to by the time MSOs deploy the technology en masse.
On the transport side of the equation, Marlborough, Mass.-based Artel Video Systems has its sights set on GigE following initial forays involving ASI transport technology, including support for Time Warner Cable's subscription-VOD offering in Cincinnati.
Director of Product Marketing Dave Pecorella says Artel plans to have a multiple-channel GigE transport prototype ready for trials later this year, and then roll out those products commercially sometime in 2003.
Scientific-Atlanta has introduced a GigE transport system called the Prisma GbE for S-A systems that embed the conditional access with the QAM. The company targets non S-A systems via its Continuum GbE product line.
Internet Photonics also markets a GigE transport system for cable-based video-on-demand through products such as the Lightstack MX.
On the server front, nCUBE Corp., thanks in part to its experience with telcos, has supported GigE for years. "As GigE has come into the fold on cable, we've been able to leverage that into the cable market," Schiller says.
Concurrent Computer Corp. shipped its first GigE implementation about 18 months ago to support a DSL-based VOD deployment in China with Shanghai Telecom. Closer to home, Concurrent's cable GigE product is in the laboratory phase, and should be ready for prime time "in a matter of months," Chism says.
MidStream’s IP2160 server sports dual
native GigE connectors.
Longer-term, vendors and some cable operators are also mulling how 10Gigabit Ethernet technology and Resilient Packet Ring (RPR) might fit into their VOD transport plans.
Scientific-Atlanta’s Prisma GbE
"It's still cheaper to do a couple of wavelengths of GigE," Charter's Loheide agrees.
When exactly 10GigE will become affordable enough for cable operators to use in their VOD deployments is still anybody's guess, but if recent history is any indication, 10GigE component costs could come down faster than some initially might expect. "I would've said GigE was too expensive a few years ago," Gordon-Kanouff says.
Scientific-Atlanta, meanwhile, offers Prisma IP, a Resilient Packet Ring-based optical transport platform that S-A repackages and sells through its partnership with Luminous Networks. RPR, because it's a layer 2 technology, can co-exist with ASI and GigE implementations.
"We're very bullish on RPR-based networks, and one of the applications that we'll carry on these networks is VOD," Connolly says.