Cable Gets Ringed Up for Reliability


If you listen closely to what is going on in cable video-delivery strategies these days, you will hear a definite ring.

A fiber ring, that is. Long used by cable operators to funnel data services and even voice across their networks, fiber rings are now gaining ground as a transport conduit for video.

Not only are they attracted to fiber-ring architecture by the lower cost of transport in the era of Gigabit Ethernet, but more importantly by its failure-proof features — and that has become increasingly important as cablers line up against strong satellite competitors.

Cable's king of the rings is Cox Communications Inc., which has not only put fiber rings in its national backbone and metro transport infrastructures, but in its outer access network as well.

Less fiber, actually

So why does Cox have a thing about rings? Compared to the traditional video-star infrastructure, in which fiber lines run out from central hubs, ring designs within regional networks actually require less fiber, according to Dick Mueller, vice president of network planning, engineering and operations.

But its biggest advantage comes when things go wrong — in a ring with channels running in each direction, if there is a failure at any point in the system, traffic can be rerouted in the opposite direction, rather than simply dead-ending if it were trapped in a single line.

That's significant, given that Cox averages about 370 point failures across its networks each month. Without the ring architecture, that would mean service outages, Mueller said.

"The difference is very straightforward," he said. "In the ringed architecture, I can detect the switch — actually I have lost light on the primary route, but I did not lose service because I had the diverse route. From the star architecture I would not have a diverse route — I would only have one route out to the node and if the fiber got cut, my customers would be out of service."

While high reliability has been a watchword for telco networks — where fiber rings began and still dominate — it is becoming increasingly important for cable video operations. At a time when customers can choose between cable and satellite competitors, providing TV signals most of the time isn't good enough any more, according to Mark Davis, vice president of professional services at bandwidth management systems provider BigBand Networks.

Davis's resume included working at Cox, and up until recently, he was vice president of engineering for then AT&T Broadband's Atlanta division.

"People used to refer to video as, 'It's just video. It's not lifeline, like telephone is,' " Davis said. "But I will tell you when you've got a market with 600 or 700,000 basic subscribers and 400,000 set-top boxes — let one of those channels go out during prime time and you'll find out how lifeline the video is.

"So I think people are starting to revisit how they see video quality, video reliability and network availability when it relates to video," he added. "Some of the things that the phone guys and the data guys had to do early on are having to be applied to the video market, given the competition."

Another key driver is the development of video-on-demand services, which require a large amount of bandwidth delivered to the edge of the network and the flexibility to tap streams from either central archives or edge servers.

The potential for VOD was enough to lure Synchronous Optical Networking (SONET) telco-systems provider Fujitsu Network Communications Inc. into the cable-gear game with a line of products aimed at video delivery.

VOD's demands

"It's really the video-on-demand that is driving large amounts of bandwidth requirements on the core ring between the master headend and the primary hubs," said Randy Eisenach, Fujitsu's senior marketing manager. "That need was there with legacy systems, and it certainly grew with cable-modem termination. But once they go into video-on-demand, they are looking to distribute hundreds of DVB-ASI or IP-based channels across that primary ring, and that almost drives them into a metro DWDM architecture with a core ring and a fairly high-capacity SONET type rings off secondary rings."

The declining price of fiber capacity also comes into play. In years past, a single SONET OC-48 terminal cost $120,000 and could carry a maximum 16 channels of uncompressed video, Davis said. But the situation has changed with the advent of Gigabit Ethernet and Dense Wavelength Division Multiplexing — the latter a method of subdividing light wavelengths into as many as 80 channels, each able to provide 2.5 Gigabits per second capacity.

"These days, you can easily fit 300 channels of video to a single Gig E platform and move it around running at $8,000 an end (terminal)," Davis said.

'Just reliability'

For Cox meanwhile, the ring advantage for VOD services is "just reliability, and the ability to access different data stores," Mueller said. "If I'm in a market with nine hubs in it, and I had those ringed together, and I had storage devices in each of those nine hubs, I might be able to access different hubs than I normally would by having that ring."

VOD isn't the only video finding its way onto these fiber rings.

With the advent of low-cost Gigabit Ethernet, it is now possible to funnel 300 channels of digital video onto fiber rings in regional networks.

"The rings were in place, but the electronics that hang off the rings to do digital video transport was not affordable and available," Davis said. "So it is only recently, through the advent of very low-cost Gigabit Ethernet transport can you afford to move 300 channels of digital programming around a ring."

Another motivation is the idea that one day, cablers can consolidate voice, video and data delivery on a single unified system. In most cable systems, video, data and sometime voice traffic flows over their own separate fiber connections, some of which are leased from other carriers.

Getting all three on the same ring fiber transport system would make things easier and cheaper for cablers, Eisenach said.

"If you can roll that all onto a single platform that can consolidate those networks onto a single fiber pair, you can free up fiber pairs, and if you are lease them that's a huge cost savings," he said. "But it also is a big operational cost issue, because you are not having to track down out-of-plant issues, bit errors or things that are going wrong on six or seven different networks."

The seeds of that unification are beginning, according to Davis.

"The less operating systems you have to deal with the better off you are from a transport perspective," Davis said. "Although you still need that specialized processing to get it into that common platform – whether it be a video processing or voice processing or data processing –fortunately voice and data are becoming more converged quicker because of the IP platform. But you are starting to see video, thanks to VOD, getting mapped into IP packets."

Bandwidth aid

It also makes sense as growing VOD and HDTV services demand more bandwidth, Mueller noted.

"One of the benefits of fiber is the glass itself has incredible bandwidth," he said. "The limiting factor is the electronics that we can put on the end of it, and they evolve over time anyway. So with the infrastructure in place the fiber has tremendous capacity going forward."

At the outer edge, each coaxial network feeds into a fiber optic ring, which has two fibers running in each direction. Cox is using DWDM in the metro and national rings, but Mueller noted it could be used in the local access rings should it need the capacity.

"That's the point — we built the infrastructure, and the electronics on the end will change as we require more capacity," Mueller said. "And that's the beauty of having the fiber rings."