Going Deeper With IP
The Cable Converged Access Platform (CCAP) has become part of the cable industry's lexicon. But it's just one approach to next-generation infrastructure development, and it doesn't preclude the use of other technologies designed to increase network efficiency.
In a recent conversation with Cox Communications Inc. CTO Kevin Hart, Light Reading Cable learned that the third-largest US MSO operator is not only looking at CCAP implementations within its network, but also approaches that complement CCAP, and even some that "leapfrog" it. Among the strategies that Hart is considering, a remote PHY architecture (also known as distributed PHY) is high on the list.
What is remote PHY exactly?
Remote PHY is a way of distributing the functions of a traditional cable headend so that the signals are converted from IP to RF deeper in the cable network. Today, an edge QAM device in the headend is responsible for converting signals to RF, then splitting and recombining those signals per user group and sending them down to a cable fiber node. With remote PHY, the conversion process shifts out of the headend altogether. The IP portion of an edge QAM stays in the headend, while the QAM modules for converting signals to RF are separated out and pushed to the node site.
"We see it being distributed… so that operators, as they continue to expand their service capabilities, are able to reduce from our standpoint the amount of equipment that they put in headends and hub sites," says John Dahlquist, vice president of marketing for vendor Aurora Networks Inc..
There are several advantages to this approach. Moving signal conversion to the cable node saves space and decreases power consumption in the headend. It also reduces complexity in the headend because everything at that site stays in the IP domain.
Beyond operational advantages, however, a remote PHY architecture also has potentially significant performance benefits. When RF conversion gets pushed deeper into the network, the resulting RF signals don't have to travel as far to reach a cable customer. That shorter distance means fewer issues of signal loss.
"This gives them the advantage of space," says Dahlquist. "It also gives them the advantage of performance because we convert digital signals into RF signals only at the point where you really need them."
Where does CCAP fit in?
A CCAP architecture combines the functions of a cable modem termination system (CMTS) and an edge QAM device into a single chassis in the cable headend. The goal is to increase channel density and decrease costs while also integrating the management of data and video delivery. (See Major Cable Players Rally Around CCAP.)
In one sense, CCAP is an alternative to remote PHY.
"To use a word, I think it was coined by Mr. Ludington of Time Warner, he used the word densification; that is taking everything that you have in the headend today and doubling or quadrupling the capacity of one of the slots in the chassis," says Dahlquist, referring to James Ludington, who is EVP, National Network Operations and Engineering, Advanced Technology Group, at Time Warner Cable Inc. "That's one approach," Dahlquist says. "The other approach is more to look at the remote PHY approach, or distributed architecture."
In another sense, however, CCAP and remote PHY are complementary. One of the major tenets of a CCAP architecture is the combined management of both video and data delivery. The CCAP Operations Support System Interface (OSSI) is a framework for managing functions that have traditionally been separated across CMTS and edge QAM hardware. That framework still works even if the QAM modulators responsible for converting signals from IP to RF are moved down to the cable node. In other words, a cable operator could implement a version of CCAP while also deploying remote PHY.
There's no telling if or when remote PHY will achieve significant adoption. However, cable operators are seriously considering the option in light of necessary infrastructure upgrades.
At Cable Congress in London last March, none other than Jorge Salinger, VP of Access Architecture at Comcast Corp. and the so-called father of CCAP, described remote PHY as a subject worthy of great investigation. Cox CTO Hart is also adamant about the importance of evaluating remote PHY and says that Cox will plan its network upgrades on a market-by-market and node-by-node basis. A remote PHY approach may be the right choice in certain locations.
On the vendor side, Dahlquist suggests the cable industry will have new information on remote PHY in the very near future. Aurora's remote QAM products for a distributed PHY architecture are about to go into field trials. The company hopes to "have a lot of results to talk about at the SCTE show in Atlanta," he notes. Aurora has seen a lot of interest in remote PHY from just about all of the cable MSOs.
Interest, of course, is one thing, and deployment is another. Only time will tell if remote PHY proves to be both a viable and valuable approach. In the meantime, the technology looks to be a hot topic of discussion for the fall. Stay tuned for more.
— Mari Silbey, special to Light Reading Cable