Cable Television Laboratories Inc.'s modem team issueddraft specifications for the next version of DOCSIS last week, opening the way for productdevelopment to begin as early as February.
Version 1.1 of the Data Over Cable System/InteroperabilitySpecification adds functionalities to the basic 1.0 standard that give operators far moreflexibility in managing and packaging data services than what is possible withfirst-generation gear.
The draft specs will go through a 30-day comment period,with the goal of achieving interim status by Jan. 29, said Andrew Sundelin, projectengineer for integrated-service technologies at CableLabs.
"Once they are released as interim specs, vendors canbegin building to the platform," Sundelin said.
"People have had a general idea of where we wereheaded since early this year, and now, they're getting the details," he added."How soon they'll be able to deliver product depends on how much workthey've done to date."
The good news for operators is that most of the 1.1 specsare software enhancements that vendors can add to headend CMTS (cable-modem-terminationsystems) and DOCSIS 1.0-compliant modems without waiting for development of new chips.
Moreover, many manufacturers will soon be shipping"1.1-ready" 1.0 modems that incorporate the one key hardware change included inthe 1.1 specs, thanks to the rapid industry embrace of a new chip set from Broadcom Corp.that incorporates the hardware-based function known as "fragmentation."
Nonetheless, the software improvements won't comeovernight. Because some elements must be implemented as firmware in modem chips, itremains to be seen how readily vendors will be able to upgrade 1.1-ready gear withouthaving to install the firmware at the factory.
"The hardware supporting 1.1 is going to come a lotsooner than the software," said David Berman, director of integrated-video solutionsfor Nortel Networks, which plans to begin shipping 1.1-ready modems by the end of thefirst quarter.
Vendors that have pushed ahead with developing firmwareimplementations that they felt would match the specs may be able to deliver 1.1 gearfairly early in 1999. But CableLabs does not anticipate reaching the point of certifyingequipment as compliant to the specs until sometime in the third quarter, said RouzbehYassini, executive consultant to the DOCSIS team. "We have a lot of work to do beforewe're ready to begin certification of 1.1," he added.
There are several elements to the 1.1 software extensionsthat pertain to setting quality-of-service parameters, especially in the upstream datachannels. While downstream communications can be controlled with QOS implementations inrouters, the upstream side has to be managed on a modem-by-modem basis throughcommunications generated by the CMTS.
The new QOS specs provide for RF MAC (media-access control)extensions that permit dynamic reservation of networking services tailored to userapplications, officials said. This means that the CMTS assigns QOS parameters on requestfrom a particular user, taking the user off the best-effort default mode that usuallygoverns upstream access rates.
These dynamically assignable upstream parameters includeconstant-bit-rate and guaranteed-bit-rate applications, like telephony, which have tightertiming requirements than Web browsing, e-mail or other traditional Internet applications.The specs provide the means by which these bit rates are triggered in the modem.
In addition, the QOS specs provide support for dynamicnetwork response to changing traffic loads. This is crucial to preventing QOS assignmentsfrom producing surges in upstream traffic that might overwhelm the available capacity.
On the hardware side, support for fragmentation in themodem chips permits the CMTS to instruct cable modems to fragment packets into smaller,uniform segments or cells before upstream transmission, increasing bandwidth efficiency byfilling all available free space in the transmission path. Fragmentation, working inconjunction with QOS, also improves support for constant-bit-rate and guaranteed-bit-rateservices.
The 1.1 specs also include support for IP(Internet-protocol) multicasting, which allows delivery of data from a live event or froma stored file to be streamed simultaneously to all session participants.
Version 2.0 of IP multicasting -- which is now nearingcompletion as an Internet standard -- is designed to support streaming of high-qualitymultimedia content to thousands of end-users via advanced routers that are equipped toperform such functions.
The cable industry wants to both exploit the capabilitiesof multicasting and to lessen the potential for saturation of its pipes that could occurfrom wide-scale use of the technology, as now appears likely.
The 1.1 multicast provisions define mechanisms forexercising dynamic control over modem access to IP multicast and ensure that theinfrastructure is in place to support new services over IP multicast, officials said.
While some vendors have already begun shipping 1.0 modemsusing the Broadcom 3220 chip set without fragmentation, others are waiting to include thenew 1.1-ready 3300 in their modems before shipping DOCSIS gear. Com21 Inc., for example,is holding off in anticipation that it can begin shipping 1.1-ready modems by the end ofthe first quarter, said Buck Gee, vice president of marketing at Com21.
"We don't think that we're going to missmuch of the market by going this route," Gee said.
Indeed, noted Berman, where operators have already deployedcable-modem services using proprietary gear, the inclination is to wait on transiting toDOCSIS until 1.1-ready gear is available.
But in instances where they're only now launchingservices, they want to go with DOCSIS 1.0 rather than waiting, he added.