The industry is “looking at what people are calling advanced MAC and PHY [for media access control and physical layer], which is about how they could take Ethernet to the home,” says John Dahlquist, vice president of marketing at Aurora Networks. “Whenever you go through the standardization process it takes a long time, so we’re actually looking at doing something in parallel but trying to stay up with CableLabs as fast as we can.”
Any such discussions underway at CableLabs remain under wraps. Spokesman Mike Schwartz would only say, “It’s not for public consumption at this point.”
As reported last year (March, p. 18), the case for exploiting commodity-priced GigE technology to deliver IP services has gained traction with the cable industry’s embrace of IP as the future conduit for subscription TV services. But it remains to be seen how readily operators will jump to a whole new architecture, given the ongoing focus on migration to IP via the bonded-channel DOCSIS 3.0 platform.
“In the long run it’s easy to speculate things will get faster and simpler, but the details are far from clear,” says Jim Chiddix, former Time Warner Cable CTO and a strategist who sits on the boards of several industry entities, including Virgin Media in the U.K. and U.S.-based technology supplier ARRIS. “There’s no reason the cable plant can’t support gigabit Ethernet when operators decide the time is right for the market. But there’s complexity and investment involved in delivering it, and the question is what’s going to pay for that next step.”
But there’s no denying the appeal of the “dumb-pipe” approach. “DOCSIS was designed to address issues in a totally different network environment where you had to make things conform to performance requirements with relatively low capacity and long reach,” Dahlquist notes.
“There were a lot of issues pertaining to avoiding delays on the roundtrip from the headend to cable modems and back,” he adds. “Today, with deeper fiber penetration and more bandwidth assigned to IP, it’s turning into a high-capacity, short-distance service environment. So there are other ways of doing it now.”
Timing and transition costs aside, a move beyond DOCSIS seems likely at some point, Chiddix suggests. “I’d have to guess in broad strokes that in ten or 15 years people will be getting Gigabit Ethernet kinds of services to their homes simply because Gigabit Ethernet is cheap,” he notes.
“It’s a ton of bandwidth bi-directionally,” he adds. “All the infrastructure and the equipment and so forth is very well understood and thoroughly commoditized. If you’ve got Cat 5 running around your house, you can go to Radio Shack and for thirty-five bucks you can get a Gigabit Ethernet switch and have that kind of speed two-way all around the house.”
But the momentum behind DOCSIS 3.0 shouldn’t be underestimated, he advises. “CMTSs (cable modem termination systems) are getting much bigger and much more dense. There’s a long way for DOCSIS 3 to go in terms of density and cost before it runs out of steam.”
Still, given the great variety of plant conditions and operational strategies across the cable industry, the fact that GigE offers an attractive, low-cost alternative to DOCSIS transport suggests there may be many situations where operators would opt to go this direction if a solution were available, even if there were no set standard for such an architecture on the HFC plant.
This is where Aurora’s focus would be in developing a solution, Dahlquist says. For Aurora it’s not a big stretch, given the firm some time back offered an Ethernet solution for HFC it called “BitCoax.” Introduced as a potential product in mid 2008, BitCoax was designed to provide operators a two-way Ethernet transport at 400 megabits-per-second in each direction using the RF spectrum on the coaxial plant above 1 GHz.
Such a solution would require that fiber be extended well into the network, in so-called “fiber-deep” configurations, so as to shorten the coaxial transport distances to where the Ethernet signals could survive the attenuation that inhibits use of the higher frequencies on today’s cable plant. Given the dearth of fiber-deep configurations, “we were ahead of our time with BitCoax,” Dahlquist acknowledges.
But with the industry now focused on migrating TV services to IP, which will require finding enough bandwidth to simulcast IP content with legacy MPEG-2 TV, the issue becomes how to use the freed up bandwidth with maximum efficiency, wherever it’s found either within the existing spectrum range or above. BitCoax was designed to allow cable operators to leverage their current HFC architecture to deliver new services without costly changes to their back office provisioning and operating systems.
Having achieved that OSS integration, Aurora is well positioned to develop a “BitCoax 2 type of product,” Dahlquist says. The idea would be to tap into some of the bandwidth operators would in any event be allocating to IPTV below 1 GHz and to leverage some of the bandwidth above, which will become more readily usable as operators drive fiber deeper to accommodate the surging requirements for unicast on-demand capacity.
There’s definitely been an increase in momentum toward deeper fiber penetration, Dahlquist notes. “One of the things we use as a leading indicator is the fact that our design backlog is up about 20 percent over last year,” he says. “The percentage is greater than that in terms of the number of designs, but the number of households represented by these projects is up about 20 percent. And the percentage of our designs that are fiber deep is increasing. These account for about twice as many projects as we’re seeing with segmented nodes.”
Significantly, this trend is based on demand for more bandwidth for current operations, where there’s a need for more VOD and HD capacity. “We’re probably one step removed from seeing the impact that will come with the migration to IPTV,” Dahlquist says
One of the technical strengths Aurora brings to the Gigabit Ethernet concept is the ability to deliver Ethernet in TDM (time division multiplexed) mode, a skill it developed in conjunction with producing a cellular backhaul solution for cable operators which is now in wide deployment. Operating a subscription video service over a gigabit Ethernet flow will require some means of tightly controlling performance parameters, which is what TDM is designed to do.
“What we’re looking at doing is resurrecting a TDM product that we’d run just over 1 GHz as far as center frequency goes, utilizing the same [RF] path for forward and downstream over coax,” Dahlquist says.
Aurora’s cellular backhaul solution for cable plant employs T1/E1 circuit emulation that allows operators to use Gigabit Ethernet transport over fiber to deliver signals through the legacy PDH (Packet Digital Hierarchy) T1/E1 connections of the cellular base stations and base station controllers. As a solution certified to be compliant with the Metro Ethernet Forum’s MEF 18 specification, the Aurora TDM-over-packet technology had to overcome limitations of traditional “pseudo-wire” solutions by assuring the jitter, wander, frame loss and packet delay metrics on a per-link and aggregate backhaul network basis are well within tolerance levels set for all generations of GSM, CDMA and WiMAX networks.
Such capabilities, along with synchronization of clock timing to coordinate performance across all end points, could offer cable operators a way to maintain rigorous performance requirements in the IPTV domain. In cellular operations such synchronization must extend across hundreds or even thousands of base stations connected to any one controller.
How close such thinking is to what’s taking shape behind the scenes in the advanced MAC and PHY discussions at CableLabs remains to be seen. Any MAC specification that emerges for the new architecture would serve as the interface between the data pipe and everything else to ensure that the specific quality-of-service parameters attending each type of service are maintained across the distribution network. The new MAC would have to “talk” to the traditional DOCSIS MAC, MPEG MACs and other data protocols and translate them into commands at the Ethernet MAC layer.
All the intelligence associated with user authentication, billing, operations support, usage policies, functioning of applications, advertising placements, security, etc. could be handled in the IP domain, allowing operators to position intelligence in support of such operations wherever they wish. These controls would all be passed transparently through the system to communicate with network and premises devices.
“We would incorporate as much of what’s taking shape [at CableLabs] as we can but go out there and see if the market isn’t ready for this type of product,” Dahlquist says. “We were ahead of ourselves with BitCoax because a couple of years ago people were tied up trying to implement DOCSIS 3.0, and we were trying to get mindshare for something radical. Maybe now it won’t seem so radical.”