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Getting ready for DOCSIS 1.1

Sun, 09/30/2001 - 8:00pm
Leslie Ellis, Technology Analyst

Just as the air turns cooler, the potential to add new features to existing high-speed Internet services is getting much, much warmer. As early as this November, CableLabs is expected to release positive certification results for cable modem gear based on the next-generation DOCSIS specification, known as "DOCSIS 1.1."

With DOCSIS 1.1 comes a lengthy list of useful and necessary service enhancements. Those enhancements, in turn, bring along a pile of necessary back-office upgrades and test procedures.

Following CableLabs certification, approved vendors need a cushion of time, perhaps a month or two, to spin up factories for production of the enhanced gear. (At press time, two certification waves remained for the year: One in late September, and one in mid-November.)

That means it could be as early as February 2002 when DOCSIS 1.1-based modems, and associated headend gear, are available for industrywide launch. That cushion of time affords about five months for cable's technical leaders to prepare for the upgrade–and, as involved technologists resolutely agree, the to-do list for the DOCSIS 1.1 upgrade deserves an early start. The changes that come with DOCSIS 1.1 impact cable modem termination systems (CMTSs), and at least six back office software systems (some extant, some new).

Lest that seem daunting, bear in mind that DOCSIS 1.1 is viewed by cable's corporate executives as not just a nice batch of enhancements, but crucial to overall financial objectives for 2002 and beyond. It brings, for example, the ability to offer grades of service, on the fly, in response to market pressures. If, for example, a local DSL (digital subscriber line) provider lowers its service price by a few dollars a month, a cable provider outfitted with 1.1 could match or exceed the offer immediately.

Or, on the other end of the scale, MSOs using 1.1 will be able to automatically create premium tiers, with premium monthly rates–in the range of $60 per month or more–for those subscribers who want the assurance of dedicated bandwidth, and top-shelf customer support.

What's new with DOCSIS 1.1?

Service tiering is perhaps the most visible of DOCSIS 1.1's many accoutrements, but there's actually a long list of new features. Among them:

  • Quality of Service (QoS)–The root enabler of service level tiering, quality of service (QoS) features available in DOCSIS 1.1 gear allow cable providers to augment what is currently a "best effort" class of service, per modem. That means operators can adjust service classes automatically and spontaneously, instead of hard-capping per-user bandwidth, upstream and downstream. Essentially, QoS is a bandwidth reservation system. It works by setting aside an appropriate number of packet slots, known as "mini-slots," on a per-modem basis. QoS is initiated by manipulating a configuration file editor associated with the newer, 1.1-based gear.
  • Dynamic (D-QoS)–Essentially bandwidth-on-demand, D-QOS uses a mechanism of service IDs, or "SIDs," to automatically pop a cable modem user up to a higher bandwidth, if the content that user is viewing warrants it. In essence, SIDs are a method of "striping" data packets that flow to and from modems. Consider, for example, the cable modem customer who chooses to surf a video stream. With D-QOS, the cable modem and CMTS work in lockstep to dynamically upshift that customer to a wider, faster bandwidth, for a finite period, until the streaming or other high-bandwidth event concludes. They do so by setting up an appropriate number of "striped" mini-slots for the duration of the event, then downshift at its conclusion. D-QOS, however, may be treated by some vendors as optional; best to check before buying.
  • Packet Fragmentation–Designed to assist isochronous applications–where transit timeliness matters more than brute-force bandwidth–data fragmentation is a sort of queuing mechanism, designed to better handle variable-sized data packets. For example, trying to slot a 64-byte voice packet into the data stream carrying a multi-megabyte e-mail attachment, without fragmentation, could require making the voice packet to wait its turn. But, because voice calls are live, latency is intolerable. (A latent voice packet that arrives at the receiver out of order is the symptomatic equivalent of saying, into the phone, "This ridiculous is.") That's why the DOCSIS 1.1 architects devised fragmentation: To chop up packets, as needed, to assure that voice and other isochronous traffic is handled without latency hits.
  • Enhanced Security–Two new DOCSIS 1.1 elements–secure software download (SSD) and baseline privacy plus (BPI+)–constitute the inner workings of DOCSIS 1.1 security advancements. Existing DOCSIS 1.0 modems use what's known as "link layer encryption," or "baseline privacy," to secure all communications between cable modems and the CMTS. DOCSIS 1.1 builds on that with a military-grade form of encryption known as "triple-DES." While it is beyond the scope of this piece to detail the security enhancements associated with 1.1, technologists familiar with DOCSIS advise finding out whether existing, 1.0-based modems are indeed using BPI, before upgrading to BPI+. If not, more steps may be associated with the 1.1 upgrade, they say.
  • Upstream Pre-Equalization–A big help in widening the skinny swath of upstream bandwidth in cable systems, upstream pre-equalization yields a shift to 16-QAM (quadrature amplitude modulation) speeds of 10 Mbps per 3 MHz upstream spectral slice. By contrast, today's QPSK-based modems (quadrature phase shift key) top out at about 5 Mbps per 3 MHz chunk.
  • Consumption Tracking–As third-party Internet service providers continue to place their subscribers onto cable-owned high-speed Internet networks, there comes a need to mutually sustain the business and technical arrangements that will define those partnerships. Watch for "service level agreements," or SLAs, to become the norm for those cable operators engaging in third-party ISP deals. Adhering to SLAs, in turn, means making sure everyone involved is coloring inside the lines: That cable operators provide the agreed-upon levels of bandwidth, and third-party ISP users don't over-step it. That necessitates mutual (cable and ISP) tracking of not just per-modem speeds, but per-modem bandwidth usage, too.

Clearly, there's a lot more to DOCSIS 1.1 than just service tiers–which makes vigilance the driving need in prepping, testing and devising operational processes to manage the DOCSIS 1.1 transition.


Figure 1: Migrating to DOCSIS v1.1 in five steps.

Making it so

Developing a DOCSIS 1.1 transition plan can vary widely, depending on system design and operation. The methods suggested here are but a glimpse into one plausible transition plan–out of many possible scenarios.

That said, there are at least five steps to carry out a successful transition to DOCSIS 1.1 (see Figure 1, page 58).

It starts with the back office–that churning maw of billing, care, trouble-shooting and maintenance servers that manage the day-to-day operations of contemporary cable systems. Most, if not all, existing servers will need some new software elements to handle DOCSIS 1.1.

Billing system links, for example, will need a tweak, particularly if service tiers or consumption-based billing is in the mix. Optionally, DOCSIS 1.1 brings the ability to communicate subscriber data in XML (extensible markup language, an Internet invention); if this is a design goal, make sure existing billing vendors can support it.

New servers will also enter the mix. For example, new authentication mechanisms, linked to the BPI+ security enhancements, must be installed. (It's probably wise to leave a lot of testing room on security tests–much of BPI+ is new and comprehensive.)

The next step, after outlining necessary back-office upgrades, is to hang a few 1.1-based (new) cable modems onto a 1.0-based (existing) CMTS. The 1.1-based modems were designed to behave in 1.0 or 1.1 mode, but MIB (management information base) configurations will need careful attention and testing.

Next, slip a few 1.0-based cable modems onto a 1.1-based CMTS. Doing so assures that the momentum machine known as DOCSIS 1.0–the tens of thousands of existing modems moving into U.S. homes each week–can be supported on new (1.1-based) headend gear. By testing in parallel with existing, 1.0-based CMTS gear, using separate upstream and downstream spectral paths, service interruptions are obviously (and happily) averted.

When convinced that the 1.1-based CMTS is stable over the existing (1.0) service footprint, add a few 1.1-based cable modems into the mix. It's probably wise to allow for ample test time at this stage, too, to flex-test as many of the new DOCSIS enhancements that will likely be launched.

Lastly–when launch plans are finalized, equipment stabilized, back-office servers queued up and ready, and operational procedures in place for the new services that come with 1.1–it's probably time to take the big leap. That means moving more, and eventually all, 1.0- and 1.1-based cable modems over to the new CMTS.

Getting ready for DOCSIS 1.1 is intricate, to be sure. But with it come the sorts of enhancements that retain existing subscribers, and attract new ones. And it doesn't hurt the career path to be the person who speaks DOCSIS 1.1. Knowing what to do, who to call, and how to proceed, technologically, to get to a DOCSIS 1.1 launch, is the language of advancement.

That's because DOCSIS 1.1 is the baseline technical foundation for the "next next" batch of advanced broadband services–home networking, packet telephony, residential gateways and more. Knowing it well is almost certainly a doorway to decades of professional growth.


Author Information
Leslie Ellis is a Denver-based columnist, author and researcher of broadband technologies.

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