PDF of this tutorialThe Importance of Signaling
With each new level of signaling sophistication, the ability to efficiently emulate previous signaling schemes has always been a fundamental requirement in order to ensure seamless compatibility with the full range of previously deployed equipment. In addition, the public at large has become entrenched with a very high level of expectation from the plain old telephone service (POTS) system. The public demands nothing less than “always-there,” on-demand, connections with flawless quality when dialing any number from any location. Therefore, every new step in the evolution of signaling also has been rigorously designed to withstand the most extreme conditions possible with regard to peak loads, equipment variability, marginal line conditions, emergency reroute demands, etc. In essence, every advance in signaling methodology served to reliably extend and expand the basic bedrock that underlies the entire worldwide telephone system.
The Voice-over–DSL (VoDSL) Opportunity
Today, the widening availability, higher bandwidths, and low-latency performance capabilities of broadband network connections such as digital subscriber line (DSL) have made the provision of voice over broadband an increasingly attractive service offering. For instance, for an integrated communications provider (ICP), the ability to offer customers multiple voice lines over a single DSL connection greatly leverages the provider’s competitive position by packing more service capacity across the “final mile of copper” that the ICP typically has to lease from incumbent carriers. By enabling 16 or more voice connections plus high-speed Internet access over a single DSL connection, ICPs are now able to cost-effectively address the needs of the huge market for small- and mid-size businesses.
Although VoDSL represents a major new and immediate revenue opportunity for ICPs, as this new market takes off, their ultimate success invariably hinges upon the robustness and adaptability of their initial engineering and deployment choices. The signaling methodology incorporated in these new VoDSL system implementations will play a strategic role in laying a solid foundation for achieving the required levels of system-wide compatibility, reliability, and extensibility. Likewise, a wrong choice of signaling methodology can lead to unacceptable line failures at the customer end and, ultimately, to a lack of competitive viability for the service.
While it certainly is possible to shortcut the implementation of signaling methods within VoDSL systems by stepping backward to a previous level of signaling evolution, shortcuts can extract a huge cost in service failures, management costs, and an inability to offer advanced and emerging services. As the discussion that follows demonstrates, modern message-based digital signaling techniques currently represent the highest point of the signaling evolution as well as offering the best combination of efficiency, robustness, and extensibility for implementing carrier-class VoDSL systems.
