As broadband access becomes more available in homes, new possibilities exist for services that can be provided to the consumer using that access. Chief among those is the ability to aggregate multiple digital services into a handful of packages. The key services that will drive consumer interest in this area are low-cost digital telephony, streaming video and audio, interactive gaming and communication, and Internet access.
Semiconductor vendors have also identified this market as a key segment for driving current and upcoming chip product lines. OEMs are looking for cost-effective solutions that can evolve along with the needs of their equipment. This article outlines the key drivers for the hardware and software solutions needed to build effective broadband residential gateways. In particular, it examines the need for a coherent hardware/software platform that can not only address current market needs but can also evolve to meet future demands for such equipment. Key to this platform is the broad use of programmable, configurable and scalable digital signal processors (DSPs) coupled with stable embedded microprocessors.
The content of the new semiconductor devices falls into three categories: control and signaling, interfacing and functional services. Control and signaling functions are handled using the combination of a microprocessor and extensive software including protocol and signaling stacks.
Stability a priority
In addition to a minor requirement to support the user interface to the equipment, the primary goal of the control processor is stability, since the protocol and signaling stacks are there to provide communication to external equipment. This means the ideal control processor is fixed; the instruction set and the implementation should not be changed. For that reason, configurable microprocessors are not suitable.
There are a number of interfaces that need to be supported: a wide-area network interface, a local-area network interface and direct connection to other equipment and/or human interfaces. The WAN interface to the home will be a digital subscriber line (DSL), cable or a broadband wireless modem. The LAN interface will be Ethernet, power line or wireless LAN.
Other required interfaces include USB (for direct connection to a PC), subscriber line interface circuits/subscriber line audio-processing circuits for direct connection to the home telephony network and 1394 for direct connection to consumer equipment.
Some of those interfaces are well-defined standards-such as USB, 1394 and Ethernet-that can be readily addressed using fixed intellectual-property (IP) blocks. On the other hand, some of those blocks either have standards that continue to evolve-different DSL options, for instance-or the selection of the interface is not clear, as is the case with HomePNA vs. 802.11b. In those situations, a soft solution that combines a custom processor with a software implementation of the functionality is appropriate. The processor should be specifically configured for the requirements of the functionality, but should be general enough to handle different flavors or even different programs.
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Two very interesting interfaces for software solutions are the WAN and LAN interfaces. Currently, the broadband WAN access market is unclear. There has been a major push to leverage the current wired and wireless lines into the home, via copper, satellite and cable, to provide broadband data access in addition to their traditional services.
While it is beyond the scope of this article to investigate the different issues and trade-offs associated with each of those solutions, semiconductor vendors must look at the different requirements presented by these solutions and consider how to address them. Configurable DSP processors can provide significant advantages in that area. While the physical interfaces are different and do not lend themselves to programmable solutions, the different transport and modulation schemes do. By implementing those aspects in an optimized, programmable DSP, significant complexity and cost can be cut out of the solution.
The full power of configurable processors coupled with optimized software is revealed in the functional services provided by a semiconductor device targeted at the broadband residential-gateway market. The key services provided by a residential gateway will include telephony, media processing and security. The functional requirements for the different services are extremely broad and can change dramatically for different equipment scenarios and market directions.
After broadband access, digital telephony is the next driver for equipment in the broadband residential-gateway market. There is a clear market for adding residential telephone and fax services without putting more lines into the home. A semiconductor solution must provide support for four lines of telephony/fax channels. In addition, a large number of features must be supported, including comfort noise generation, voice activity detection, dial-tone handling and so forth.
The primary functions are voice compression to reduce the bandwidth requirements for the lines, and line echo cancellation to minimize the crossover effects of moving the voice data from the two-wire phone connections onto the four-line phone network. The main processing for this support resides in a DSP solution. Currently, there are a number of voice-compression algorithms that must be supported that provide different compression ratios and latencies, including G.711, G.723.1, G.726, G.728 (a and i) and G.729 (a and e). The best DSP for the job is one that has been optimized for voice processing and echo cancellation and that has been customized to provide a small footprint while using little power.
Turning to the media-processing side, there are four different uses for video within a broadband residential gateway. These are digital TV, interactive gaming, videoconferencing and streaming video. In order to decrease bandwidth requirements, almost all video coming through the gateway will be compressed into some format. For digital TV, the format is MPEG-2. There is still much uncertainty about the other formats, although MPEG-4 is also emerging as a reasonable candidate for the other three categories. Each of those video functions has very different requirements for frame sizes, frame rates and picture quality. In addition to traditional video, there is a growing need for graphics support outside of the traditional PC market. Audio capabilities are similar, as the market evolves to support digital radio, streaming audio and advanced audio equipment like surround-sound.
Security is the another key factor to consider. Security functions can be separated into controlled access-firewalls and VPN-and data encryption. The former is typically implemented in software running on the control processor, while the latter is implemented using custom DSP blocks. Data encryption is a rapidly evolving area and there are many different approaches being considered.
It is a daunting task to tie all this together into a coherent hardware/software platform. As we have seen, however, the effective application of configurable DSP technology can significantly simplify the platform and provide a basis for short-term products that can evolve as the needs of the market change and mature. An integrated platform that is ideally suited for that market would contain a socket for a standard microprocessor to handle the control and signaling capabilities; a combination of hardwired and programmable, configured peripherals; and a DSP structure that can handle the wide range of requirements presented here. Such a platform has been designed using existing IP, including optimized configurations of Improv's Jazz Processor for the critical DSP sections.