PHILA & DFAST: Two Licenses That Have Wide Impact


We interrupt the ongoing translations of the plug-and-play agreement, related Federal Communications Commission rules, down-rez and selectable output controls to delve into the wonkery of security licenses.

From a technology standpoint, the starting point for this discussion is at the corner of "CableCARD" and "host device," like a TV outfitted with a CableCARD slot.

Right there, where the card parks into the slot and digital bits representing the wares of one industry (movie studios and copyright holders) walk across the pins of a second industry (cable) to a third industry (consumer electronics).

From a strategic standpoint, the intersection matters because it's an early hot spot for larger, feistier, cross-industry debates — like who gets better content deals based on their ability to "down-rez" copy-protected content, if asked, on high-definition analog outputs.

The It Coalition

There's also the debate over who gets damaged or rewarded because their stuff (TVs) was built without down-rez capabilities, before the FCC articulated its position on the matter.

And there's another multibillion-dollar industry tugging on the licenses for removable security. Calling themselves the "IT Coalition" — where "IT" means "information technology" — the personal-computer posse includes names like Dell Computer Inc., Intel Corp., Hewlett-Packard Corp., and Microsoft Corp.

Their harrumph: Security deliberations should include their stuff, which falls under the general category of "digital rights management."

At the heart of this arcane-but-relevant security discussion are two Cable Television Laboratories Inc. licenses, known by the acronyms "PHILA" and the "DFAST Technology License Agreement." Both involve the techniques that encrypt and protect digital video.

PHILA stands for "POD Host Interface Licensing Agreement." Most people pronounce it "fie-luh," or "fee-lah." It's especially wonky because of that embedded acronym – "POD" – which stands for "point of deployment" module. POD equals "CableCARD." So, PHILA is a permission mechanism to build and test things with a CableCARD slot.

Standing DFAST

DFAST stands for "Dynamic Feedback Arrangement Scrambling Technique."

No, really. It does.

An anecdotal aside about how these techniques wind up with such densely technical names: I once had an engineering friend who, over dinner one night, expressed his desire to date a woman at his place of work. I asked him how he planned to go about it.

He explained that he had been observing the types of people she seemed to like, and concluded, in an endearingly earnest way: "I can emulate that protocol."

It is the people who refer to interpersonal skills as "emulating that protocol" who are occasionally asked to name their work. Usually, they name it by describing what it does. DFAST describes how to re-scramble the bits of a TV show, for handoff to a "host" device, such as a TV.

In part, it prevents a flourish of "imposter hosts."

Two Licenses

Why are there two licenses, PHILA and DFAST? In short, PHILA was first. It sufficed for licensing the industry's incumbent suppliers. But in the work of engaging a whole new industry of suppliers — CE manufacturers — things changed.

Mostly, the CE side found PHILA to be too specific, especially about their side of the deal — the "host" devices. A less-explicit specification for "host" devices gave them room to be more innovative and competitive. (This spawned cable worries that more interpretive room would mean more corners cut — or, as some quip, "the right to build crap.")

That's what begat DFAST, which applies a minimal level of requirements to host devices.

There are similarities between PHILA and DFAST. In essence, DFAST is a subset of PHILA. It defines how to license the "secret sauce" of the security that moves bits across the pins of the CableCARD, to the host device. PHILA references the same security mechanisms as DFAST. It also defines requirements for the host device.

Lastly, PHILA defines a mechanism for testing products — much like how cable modems are tested for interoperability at CableLabs.

CableLabs Hook

DFAST, by contrast, allows CE companies to certify products once at CableLabs, then to self-certify after that.

DFAST emerged last December as an appendix to the joint filing made by cable and the CE industry to the FCC, which became known as "the plug and play agreement." In the filing, DFAST was a draft, submitted for consideration.

After the FCC's Report and Order on plug-and-play, CableLabs issued a finalized version of a DFAST license. (They didn't issue DFAST licenses earlier, they submit, because they didn't know how the FCC would rule on things like down-resolution, which mattered to the license.)

Boil all of it down, and it means this: TVs complying to DFAST will arrive in cable systems. They will be capable of down-resolution on analog outputs. They'll be built using inevitably different interpretations of the involved technical specifications. Most of them will not be tested at CableLabs, after the first one.

If any of that matters to you, it's probably best to pay attention to this one.

Still stumped by gibberish? See all of Leslie Ellis's translations at