Networking

Standards propel cable modems into the big time

CIOs grappling with remote user connectivity issues and those at small enterprises should pay close attention to the evolving cable modem standards that are geared toward making cable modems more viable.


Three sets of cable modem standards are emerging that CIOs would be wise to learn about. All three are aimed, in different ways, at making cable modems viable as the main connectivity for small and medium-size businesses and as a primary means of remote connectivity for remote workers.

While the growth of cable modem adoption has brought some considerable security issues to light, as I explained in the first part of this two-part series on cable modem technologies, today’s tech leaders believe that the new specifications are advancing cable modems into the big leagues.

“For the first time, I feel there is a real opportunity for alternative service providers,” said Rouzbeh Yassini, CEO of YAS Broadband Ventures and a senior executive consultant to industry consortium Cable Television Laboratories Inc.

“Cable modems now have better quality and faster speeds than what’s offered by the T1 guys or the telecommunications companies....For the CIO, it’s a dream come true.”

A look at the standards
The standards, taken as a group, increase premise-to-headend (upstream) bandwidth, heighten security, and introduce the concept of quality of service to the last mile of a cable network.

“These allow some degree of service level agreements to be available on cable networks,” explained Dev Gupta, the founder, president, and CEO of Narad Networks Inc. “This SLA is kind of a minimum requirement that businesses need in order to buy datacom services from cable operators.”

Narad’s system radically expands two-way bandwidth on cable’s hybrid fiber-coaxial cable architecture (HFC) by opening latent spectrum above what is currently in use.

All three of the new standards are products of CableLabs. Two are versions of the existing Data Over Cable Service Interface Specification (DOCSIS), and the third is an application-creation offshoot called PacketCable.

Though cable modems were widely introduced less than 10 years ago, the evolution has been fast. The fact that there will soon be modems and apps following four different sets of standards—not to mention proprietary units—in the field is not quite as cumbersome as it seems.

Part of the grand plan was to make all the standards backward-compatible. So, for instance, a DOCSIS 1.0 modem can continue to work in a system upgraded to DOCSIS 2.0 operation. It’s important for CIOs to keep these specifications straight, since each has significantly different capabilities.

Cable modem evolution
The first generation, rushed to market to take advantage of the explosive growth of the Internet in the early 1990s, was prestandard. The aim was to gain market share as quickly as possible and win the hearts and minds of consumers who were tired of the long delays of dial-up.

Late in the decade, CableLabs released DOCSIS 1.0, a spec that standardized modems but offered few features that would make them viable for all but the most mundane corporate uses. DOCSIS 1.0 was an important event, however. It introduced portability, a new concept for cable operators. It enabled modems—unlike system-specific cable converter boxes—to be moved between systems and to be sold at retail outlets.

Last year, a third wave of cable modems—the second version of the DOCSIS standard (1.1)—was released. It is currently working its way into modems and the headend gear, known as cable modem termination systems (CMTSes).

DOCSIS 1.1 represents a big improvement over DOCSIS 1.0, according to Ehsan Rashid, senior vice president of marketing and strategic planning for modem vendor Com21 Inc.

“DOCSIS 1.1 was created essentially to give the ability to offer QoS for applications such as voice, where predictability is needed,” Rashid said. DOCSIS 1.1 also adds security and somewhat alleviates cable’s biggest problem, the scarcity of upstream bandwidth. DOCSIS 1.1 also roughly doubles the amount of data that can be transported from the customer premise to the cable headend.

The reality is, however, that doubling the amount of upstream data doesn’t really do the trick. That is addressed by the next standard—DOCSIS 2.0—which was finalized in January. It is designed with two sophisticated modulation techniques: Synchronous Code Division Multiple Access (S-CDMA) and Advanced Frequency Agile Time Division Multiple Access (A-TDMA). These use different approaches to both broaden the upstream capacity of networks and to make signals more resilient to noise contamination. The more resilient a network is, the more bits can safely be squeezed into a given amount of spectrum and the more data transferred.

Since cable networks were initially designed as one-way entertainment media, the upstream—end user to headend or central office—capacity is severely constrained. The industry has used extensive fiber rebuilding to confront this problem. However, in the area closest to end users, which is served by coaxial cable, the problem persists. The importance of meeting this challenge is evident in the growing number of revenue-producing, upstream-intensive applications, such as streaming, gaming, and other peer-to-peer networking applications. Thus, DOCSIS 2.0, a standard that provides symmetrical 30-Mbps service, was developed.

The third new standard, PacketCable, represents a move away from the underlying plumbing to work on applications. The initial PacketCable goal is to provide Voice over IP (VoIP) over cable networks. More advanced applications, such as streaming, multimedia conferencing, and interactive gaming, are down the road.

While the standards are a good start, they don’t go far enough, according to Narad’s Gupta. The advanced DOCSIS standards represent a good platform for VoIP services, he noted, but are inadequate for demanding applications—such as storage area networks (SANs)—being deployed by corporations.

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