When end users employ broadband, they expect to have seamless and reliable accessibility to any application or service, no matter the system or software provider. Most users do not understand that broadband is actually a complex collection of specialized technologies and protocols that must cohesively interact together and are constantly evolving to meet the consumer's vision of a broadband empowered world.

Interoperability makes this happen. It is the ability to connect hardware and software elements of both infrastructure and customer premises equipment (CPE), all of which originate from different broadband systems suppliers, to seamlessly work together. Interoperability is a key and crucial consideration for manufacturers because it plays a vital role in whether broadband meets the end user's expectations and how quickly they adopt broadband technology, products and services.

Both DSL and cable have different procedures for ensuring interoperability across equipment platforms from multiple suppliers, in addition to industry-specific testing and standards compliance. In some cases, such as the cable industry, standards bodies certify products as interoperable, while others, such as DSL, rely on individual broadband systems manufacturers and their suppliers to meet industry requirements. However, the ultimate goal for the end user is seamless accessibility and, therefore, faster adoption, is the same for both.

Interoperability in the cable broadband industry has long been a high priority of the Multiple System Operators (MSOs). In fact, the industry consortium Cable Television Laboratories, or CableLabs®, was created by the MSOs to centralize the definition and execution of the standards required to achieve multiple vendor interoperability.

CableLabs, in close partnership with many industry-leading suppliers, defines requirements and then certifies every piece of cable broadband equipment that goes to market. CableLabs offers multiple certification opportunities per year, giving modem manufacturers the opportunity to prove their equipment can pass the test for certification.

Before cable modems are released to the market, they first must achieve certification status. Due to the limited number of certification opportunities each year, the importance of success on the first attempt is high. Silicon suppliers play an important role in maximizing certification success by performing extensive testing prior to the certification wave.

For example, prior to its CableLabs submission, Texas Instruments will perform its own tests which includes several complete execution cycles of the test execution plan (TEPs) that have been defined and developed at CableLabs. It is this complete test coverage that removes the mystery and dramatically increases the likelihood of certification success. During this pre-certification testing, to be complete, vendors must verify and prove compliancy to more than 5000 conformance checklist items - the items that will be formally tested at CableLabs.

Thorough interoperability testing and validation of a cable modem includes running test suites that cover the physical layer performance, MAC layer messaging, modem management compliance, privacy and encryption methodologies, quality of service functionality, home interface functionality and long term stability and reliability. This task requires large, automated validation labs, a large amount of network equipment including all of the commonly deployed CMTS units, thousands of person-hours of automation and an acute attention to thoroughness, process and detail.

As part of these complex system tests, suppliers must verify the compliancy of the new cable modem with other legacy modems and with a large variety of Cable Modem Termination Systems (CMTS), or cable head end units which aggregate traffic from cable modems. This verifies that cable modems are interoperable with one another as well as with the CMTS against which they are deployed. This is essential since the cable modems in a neighborhood are connected to the same cable.

Open to interpretation

Within ADSL, the challenges to achieving and ensuring interoperability began when the initial ANSI T1.413 issue 2 standard was created. Though this standard provided a base for the ADSL industry, it was open to various interpretations by broadband system suppliers who implemented their solutions differently. In addition, unlike in the cable industry, the DSL industry does not have certification labs, so there is no rigorous process to verify that modems met the standards or interoperability requirements.

This has led to a deployed base of proprietary solutions with different interpretations and implementations of key systems parameters (e.g. allowable power spectral densities, FFT sizes, noise margins, and messaging protocols). It is currently left to the service providers to certify equipment that can be deployed in the network.

There are dozens of equipment manufacturers and software providers, each with slightly different interpretations of the ADSL standards and requirements. As a result interoperability is an issue that has hindered the deployment of ADSL.

In order to achieve leadership in interoperability, and maximize the likelihood of certification success at service providers, it has become a requirement for ADSL systems vendors to establish their own comprehensive interoperability test and validation laboratories.

Thorough interoperability testing of ADSL modems consist of three major components: verification of connectivity and the ability to exchange parameters; verification of the ability to achieve specified or expected performance and bit error rates under various loop and noise conditions; and verification of stability and robustness under changing loop and noise conditions.

This extensive testing and validation against the large number of deployed infrastructure and CPE solutions requires a significant investment in an all encompassing and extensive, automated lab. The thousands of person-hours of testing needs to be complemented not only with thorough processes, tools and databases to archive and mine the vast amount of data, but also a broad systems knowledge to be able to correlate results and dissect interoperability problems.

The overall DSL community is working to fix the interoperability problems that have plagued it in the past. The newly ratified ADSL2 (or G.dmt.bis) standard is designed to tighten the messaging protocols and initialization sequence.

There are also better defined and more widely accepted performance requirements such as TR-048 from the DSL Forum. New requirements under discussion (TR-085) will potentially consolidate even more requirements from the different regions in the world. In addition, there are proposals to add more comprehensive test requirements that would better validate the accuracy of key systems parameters (e.g. noise margin).

In addition to these standardization and certification efforts, it continues to be vital for ADSL systems vendors to design solutions that are flexible and have a high degree of programmability. This allows products to be quickly adapted to ensure the highest levels of performance and interoperability, allows equipment to be upgraded to meet evolving standards, and to maintain interoperability with legacy equipment.

The responsibility for interoperability is clearly shared between industry consortiums, standards bodies, broadband systems manufacturers and their suppliers. The most successful companies will be those who work together to meet the challenge of interoperability by investing in laboratories, automation and systems expertise necessary to ensure that robust and interoperable devices will be deployed. Broadband silicon and software suppliers who make interoperability and validation a key part of their business strategy will be able to provide OEMs with quality products that in turn make everyone successful in the market and increases the end user adoption of broadband.