November 2002

The Building Block's Building Block

BY JIM MACHI

At any rate, it’s a daunting task to write about all building blocks in a single column. So I’ll concentrate on what I call the building block’s building block -- the “hosts” for the IP telephony software algorithms. I’m talking chips, my friend. 

There are three main types of chips used to run the IP telephony software algorithms: digital signal processors (DSPs), microprocessors, and network processors. Two years ago I wrote another building block article that discussed DSPs and some of the call control options. Back then, the DSP was the primary chip-level building block. In the ensuing two years, microprocessors themselves and network processors have become increasingly important as IP telephony building blocks. But before we discuss chips and why they have taken a more prominent role, let’s get some DSP grounding.

When IP telephony products first came out, the DSP stood front and center. Since DSPs digitize and process analog (and already-digital) signals, they are critical in computer telephony tasks. For instance, features such as conferencing, speech recognition, play/record, and echo cancellation have been done primarily with DSPs. And while these have become important in the IP telephony world, the first real DSP requirements included transcoding, jitter buffer management, and packet redundancy (that is, either putting the phone call into a G.711, G.723.1, G.729a, etc. codec for IP packet transmission, or putting the codecs “back together” into an analog or TDM signal). All of these feature requirements (and others) are why you will see DSP “farms” on any IP telephony board.

Do we still need these functions today? Yes, because all those functions are still required. But two other building blocks at this level are becoming increasingly important. First, there is the matter of the host processor itself. As these processors gain processing capability via Moore’s Law, the host processors can potentially do more processing. Makes sense, right? Essentially, some of the DSP functions can be moved to the host processor by porting the DSP software, thus making the host processor a critical building block. This is not a new idea in the computer telephony world, where speech recognition and fax algorithms have, within the last few years, been at least partially architected to run on the host processor. So that migration is underway. 

In IP telephony, the complex and MIPS-intensive transcoder algorithms have traditionally been better served by DSPs. But now, with increased processing power, it’s possible to move IP telephony algorithms to the host, especially for lower-density cards where a wide variety of tasks need to be performed. It should be noted that high-density cards requiring many specific algorithms to be performed at a high rate would still be more cost effective with a DSP approach, which is why you still see (and want) these cards on the market.

Another important type of new silicon-level building block is the network processor. Since network processors are built to handle packet processing, as we move toward an “all-IP” world that won’t demand as much TDM-to-IP transcoding, the ability to handle packets will become increasingly important. The network processors can also deal well with packet analysis, packet classification, packet modification, and packet forwarding -- all required in IP telephony. And since these functions are especially important for quality of service (QoS) improvements, these building blocks will undoubtedly be more important in the future. So you may first see some boards using network processors as “packet assist” functions on the boards, then moving to all network-processor-based boards as the “all-IP” world evolves.

Depending on what you want to do, there are more options than ever at the chip level. Maybe next time, I’ll even write an article about that sand…

Jim Machi is director, Product Management for the Network Processing Division of the Intel Communications Group. Intel, the world’s largest chip maker, is also a leading manufacturer of computer, networking, and communications products. For more information, visit www.intel.com.

*Other names and brands may be claimed as the property of others.

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