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DOCSIS 1.1: What It Is, and What It Isnt

With little fanfare, the first batch of DOCSIS 1.1-based cable modems entered CableLabs' test queue late last month-the week after Diversity Week, to be exact. The testing mile-marker seemed like a sensible enough reason to translate what those boxes will, and will not, be able to do for cable.

There are three main areas in which the new, 1.1-based modems differ from the millions of 1.0-based cable modems deployed in this country as of June 30. They are: quality of service, data fragmentation and enhanced security.

Let's look at quality of service first. It's abbreviated "QoS," and pronounced "Q-oh-S."

Really, QoS is the high-speed-data equivalent of basic and premium TV differentiation. It lets you add "grades," or "tiers," of data services, characterized by speed or transit timeliness.

In today's cable modems, MSOs generally cap the downstream (headend-to-home) and upstream (home-to-headend) speeds at the time of installation, or earlier. Technologists call this "rate limiting," and use it to preserve bandwidth, which is especially precious in the upstream signal path.

As explained in the Sept. 18 "Translation Please," bandwidth isn't unlimited, and needs to be monitored carefully. Most MSOs set a maximum of between 1.5 to 2 megabits per second downstream, and about 384 kilobits per second upstream.

It's a best-effort thing: First come, first served. Last on, you get what you get. Usually, the capping works to ensure that everyone gets speedy services.

With 1.1 and QoS, operators can vary maximum data rates, on the fly. Technologists call this "committed information rate," meaning they can nail up different data rates to different customers, depending on their needs (and willingness to pay).

Example: User Jane wants to watch a movie on her PC. She clicks to stream it. With QoS, the modem sees that Jane is streaming video, and pops her up to a sustained and higher bandwidth for a certain amount of time.

If the equipment spoke, it'd say, "Oh, Jane's watching a movie. I'll fix her at 1.5 Mbps while she needs it."

They can do this because DOCSIS 1.1 comes with 16 different "service identifiers," or "SIDs" (pronounced "sihds"). SIDs are a way to stripe packets that flow to and from a modem, to make each different and distinct from another.

There's a second part to QoS, called "data fragmentation." It helps services like voice, which are intrinsically isochronous. Isochronous is a fancy way of saying "equally timed to and from destination, without delays."

Think of it this way: When you're talking on the phone, it matters more that the packets get there without hiccups than it does that they get there over a fat, dedicated pipe. Think of it as the converse of electronic mail.

You write a note. You hit "send." The note gets broken up into small pieces; often, the pieces are sent over different routes. It doesn't matter, because everything gets reassembled at the other end.

If one packet is a few milliseconds late, it's not the end of the world. Your note still arrives.

Voice has to work differently. If a packet is a few seconds late, and you're talking live, it's the equivalent of saying, "This ridiculous is."

What really matters in voice is that packets travel smoothly and without delays. That's what the data fragmentation portion of DOCSIS 1.1 does.

The third thing DOCSIS 1.1 brings is better security-which is not to say existing 1.0 gear is vulnerable.

DOCSIS 1.0 uses what's called "link layer" encryption to secure all communications between the cable modem and the headend. CableLabs licenses the technique from RSA, and it's not yet been cracked in a cable-modem environment.

DOCSIS 1.1 builds on that with a military-grade type of encryption known as "triple DES" (pronounced "triple dehz")-which is generally acknowledged as impenetrable. Spies use triple-DES.

In addition to QoS and privacy, DOCSIS 1.1 is notable for one other reason: It's the foundation for PacketCable. The third leg of CableLabs' trio of major projects, PacketCable is building up lots of other packet-style services, starting with lifeline telephony and streaming media.

DOCSIS 1.1 is not a cure-all for the myriad technical and operational issues that comprise open access. While 1.1-based equipment does help, it isn't the total answer. It helps because MSOs can use some of the SIDs to identify outside ISPs-although this usage is debated in engineering circles.

It'll likely be another couple of testing rounds before CableLabs certifies any 1.1-based cable modems, or qualifies any 1.1-based headend gear (known as "Cable Modem Termination Systems," or "CMTS.") After that, upgrades begin.

Silicon and equipment suppliers have promised operators they can shift from 1.0 to 1.1 with software downloads. However, some MSOs are already starting to wonder if that will remain true, should they want to provide "carrier-class" telephony services.

Going to carrier class means a lot of software and systems in the back office (the stuff of PacketCable), and resolution of plant issues, like how to juice a modem or phone when utility power is out. That requires a whole new set of translations.

Stumped by jargon? Heard a gibberish tech term? Ask Ellis. She loves this stuff. Send questions to, with "Translation Please" in the header.