November 2003

SoC Integration Delivers on Promise of VoIP

BY MAJID FOODEEI, PRINCIPAL SYSTEM ENGINEER, CENTILLIUM COMMUNICATIONS, INC.

During the halcyon days of rapid network build-outs and robust infrastructure budgets, experts and pundits declared that VoIP was a technology destined to take the market by storm. They said that everything was in place for VoIP to post huge market share gains. Yet, even before economic realities set in and companies were forced to face capital expenditure cutbacks, early deployments of VoIP systems were plagued by high costs and poor voice quality causing companies to delay deployments.

Today, new deployments of next-generation VoIP systems are rapidly changing these old quality and cost perceptions. Designers have overcome these problems through system-on-a-chip (SoC) integration. Tasks that used to take scores of chips to accomplish are now done by a single system-on-a-chip (SoC) design. Now, a single SoC combines multiple specialized DSPs, discrete network processors (NPs), and software codecs and algorithms into a tightly integrated solution that delivers on the promise of VoIP � reduced equipment and operating costs, better than toll quality voice, and higher reliability.
Network designs have evolved too. New network models place an emphasis on combining voice and data onto a single converged network. In an effort to lower overall costs, service providers are turning to a collapsed Central Office (CO) model that shifts the functionalities of switching to Customer Premises Equipment (CPE). This shift results in a simplified CO and is speeding the deployment of softswitches in networks. These softswitches enable service providers to deploy new voice services that add value for their customer base without the considerable expense of rebuilding their switching centers.

Although legacy circuit-switched telephone networks are not yet being replaced on a wide-scale basis, service providers are evaluating and finding ways to capitalize on the advantages VoIP systems. Such equipment, based on SoC voice processors, deliver cost efficient, high-quality systems that are easy to test and upgrade to new services.

SoCs MAKE THE DIFFERENCE
To meet today�s market challenges, industry leaders are embracing efficient solutions that come from very high-density SoC-based VoIP systems. Advanced SoC designs process from 100 to 1,000 channels per chip with a full range of echo cancellation and telephony IP features (hundreds of channels for the most complex codecs) and a tightly integrated silicon and software bundle. This reduces part count and system complexity as well as power consumption � crucial advancements for systems deployed in harsh environments with high-reliability requirements.

Unlike SoC designs, multi-chip solutions place higher demands on DSP and NP building blocks. Advanced VoIP SoCs provide unprecedented capabilities (close to 30-giga-MAC DSP and one-giga-op/sec NP plus up to three to five times higher capacity than the alternative with close to three times lower power/channel consumption) on a single integrated chip with which system-level software is bundled.

The most flexible system-on-a-chip approach integrates high-performance digital signal processing and network processing on the same die. This is essential because the complexity of codecs has gone from less than 10-MIPS a few years ago to more than 40-MIPS for some of today�s complex codecs today. The DSP portion of the chip also handles tandem free operation, transcoding, voice quality enhancement algorithms, and echo cancellation required in cellular wireless networks.

Networking protocols are also growing from basic IP and ATM AAL1, AAL2 support, to a whole range of new layers for features such as MPLS or VLAN or RTCP with extensions for voice quality. Many of these protocols and voice quality enhancement algorithms run concurrently, which makes it essential that DSP and network-processing elements work in harmony. The SoC approach has proven to be the best way to achieve this.

EVOLUTION OF DSP PROCESSORS
Incorporating the myriad standards driving rich voice quality requires substantial processing power. Technology has changed vastly from the early days of VoIP processors. Every year, MIPS processing advances yet DSP providers have merely adapted their general-purpose products.

DSP performance increases have come through increased speed and the migration to more advanced process technologies on which the circuits are built. Additionally codec, network processing, and voice quality algorithms have been increasing in complexity and have, in some cases, surpassed the advances in DSPs. The bulk of the cost in early VoIP systems comes from boards that are populated with the general purpose DSPs. This approach does not result in systems that can meet today�s aggressive cost, density, power, and space constraints.

In the past four years, the model for VoIP SoCs has evolved, shifting the model toward overall system innovation, not just increases in core speeds and geometric process advances.

The innovation revolves around the tight integration of the DSP and network processing functions together with the firmware. In contrast, the general purpose DSP model and initial SoC model both rely on a single, front-end NP which can become bottlenecked while trying to perform deep packet processing and high throughput aggregation network processing.

In the advanced SoC approach within the distributed NP model, deep packet processing is provided in the components within the SoCs. This provides a more scalable solution in view of increasingly complex requirements placed on VoIP systems. The general purpose DSP approach utilizes more components creating complexity. More complexity results in lowered reliability and reduced capability for service providers.

The general purpose DSP approach also requires tedious programming and management of the software and the byzantine task of integrating the software with the other pieces of the system. The SoC approach provides a complete system with a large block of software. This integration allows the box vendor to concentrate on adding their own specific value to the system they are building, thus accelerating time-to-market.

When designers integrate software components from DSP and NP vendors, they face the arduous task of efficiently mating vastly different software approaches into a cohesive system. Even with bundled software components that work together, maintenance becomes cumbersome and there is the added cost.
All the benefits of an SoC approach offers tremendous advantages for equipment and service providers looking to gain an edge on competitors. First and foremost is reduced system cost. Next is reduced time-to-market and service providers� superior ability to meet the challenges of integrating next-generation services that address wireless, IP, ATM, interworking, transcoding, and several other important services. More DSP capability also means higher quality of services (e.g., adding voice enhancement algorithms, and the like).

CONCLUSION
Service providers concerned with revenue-bearing services, equipment, deployment costs, and operating expenses can benefit from all of the advantages presented by next-generation VoIP systems based on advanced SoC design. Moreover, systems built on advanced SoC voice processors provide the easiest and most cost effective migration path while keeping future operations and upgrade costs to a minimum.

Majid Foodeei is Principal System Engineer at Centillium Communications, Inc. Centillium designs and markets communications chipset solutions for central office equipment, digital subscriber line access multiplexer (DSLAM), digital loop carrier (DLC) line cards, and customer premises equipment for Digital Subscriber Line (DSL), Voice over Packet (VoP) and premises networking. For more information, visit www.centillium.com.

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