Eliminate intrusion on the software layer--Use a distributed architecture--Part I

Designing residential gateways to support multiple services, security and manageability can be a challenge. Different services require different throughput, latencies and processing power. Services like voice and gaming are very sensitive to latencies, while management application can be very tolerant. Video requires higher throughput and low latencies. Applying security policies and encryption can be a very central processing unit (CPU)-intensive task. Implementing various services on a centralized CPU architecture requires precise allocation of CPU across all the applications, which is proving to be extremely difficult, if not impossible.

Adding to the complexity is the fact that operating systems are usually provided by different companies than those who develop applications and services. While real time operating systems exist, there remains a big challenge in effectively utilizing the CPU for multiple applications while using the operating system effectively. Linux is increasingly being used in embedded applications for its rich set of applications, however it poorly handles real time operation.

Traditionally embedded systems are designed using a central CPU and several asynchronous, serial or PCI peripheral interfaces. Software running on the CPU configures the peripherals and manages data between them. Many system vendors use the same approach for a networking system, like a router or a gateway. As the type of services provided the gateway increases, the traditional centralized CPU architecture becomes a severe bottleneck. As a result, the system can not be scaled for higher performance or improved services.

By departing from a conventional centralized CPU architecture and using a distributed architecture, gateway processors solve the problem of implementing multiple services and eliminate operating system inefficiencies.

This article describes how a distributed architecture can overcome the limitations of centralized CPU architecture.

Residential gateway requirements
Residential gateways are increasingly complex as a result of advances in access technologies for broadband connections, local area networking (LAN) technologies for in-home distribution of data, and the introduction of advanced applications by service providers.

WAN and LAN choices
Today, residential aateways are available for a wide range of access mechanisms including ADSL, ADSL2+, VDSL, VDSL 2+, Cable, FTTH and wireless.

A typical residential gateway no longer provides just the standard 10/100 Ethernet interface for LAN. Instead, it provides several options for in-home data distribution using interfaces like wireless, Multimedia over Coax Alliance (MoCA), Home Phoneline Networking Alliance (Home PNA) and Power Line Communication.

Voice and video integration
A Residential Gateway is required to support 2 to 4 channels of voice using regular phones. In addition it is expected to support Bluetooth or Digital Enhanced Cordless Telecommunications (DECT)-based cordless phones. Similarly residential gateways are central to passing multiple channel Video streaming data. Both Voice and Video content call for effective quality of service engines to ensure seamless reception of media rich content.

Fixed mobile convergence
Adding to the complexity is the emerging trend of Fixed Mobile Convergence, which requires using a broadband connection provided by the Residential Gateway to make VoIP calls using a cellular phone when the user is at home.

Remote management and configuration
To minimize customer support calls and configure services based on user preferences, service providers prefer that Residential Gateways are fully configured and capable of being managed remotely from a centralized management station. The DSL Forum has defined its TR69 protocol for use by service providers not just for DSL"based customer premises equipment (CPE), but also for Passive Optical Network (PON)-based deployments.

The many features addressed above, and the required integration has increased the complexity of residential gateway design, which in turn poses a great challenge for a gateway processor design. Gateway processors are now required to support performance across different interfaces and are required to do so without effecting the services running on the main CPU.

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