Design Tips

Serial RapidIO Switching in Wireless Infrastructure

By Keri Zingle, Product Marketing Engineer, PMC-Sierra

Wireless infrastructure vendors are pursuing implementations using AdvancedTCA® and MicroTCA™ architectures with Serial RapidIO interconnect. Within these systems, Serial RapidIO can be implemented for card-to-card connections, or for intra-card local interconnect. Each of these interconnect applications requires a switch with specific features to meet the needs of the application.

For Wireless Basestations, vendors using standard hardware are choosing MicroTCA, because it provides a more compact, lower cost solution than the AdvancedTCA form factor. Basestations implement MicroTCA in a dual-star configuration, offering 1+1 protection for the switch fabric, i.e. working and protecting MicroTCA Carrier Hubs (MCH). Each basestation supports multiple DSP Advanced Mezzanine cards (AMC), which are treated as a pool of resources to be shared by all antennae.

On MCH cards, the Serial RapidIO switch needs to be a high density, high capacity device that can be implemented in a single stage, providing power, space, and cost savings over multi-chip solutions. For full connectivity, the switch should have 16 ports that can scale to address the bandwidth growth occurring between baseband processors and radio interfaces. Scaling from low link rate to high link rate, and from 1x to 4x links per port, provides expanded capacity as additional carriers and sectors get added. For traffic distribution, latency through the switch must be minimized, as I/Q samples are periodic and highly time-sensitive. Further, the switch should be configurable to allow higher priority to the ports connected to the Radio interface cards (biased arbitration).

For local interconnect on baseband processing cards, the Serial RapidIO switch should support 1x links for connection to DSPs, and 4x links for connection to the MCH. DSP connections are short and have no intervening connectors, while MCH connections go over a backplane across 2 connectors. Therefore, electrical characteristics of the switch ports must support short-range and long-range interconnect environments.

For higher capacity wireless applications such as 3G Radio Network Controllers (RNC) or Media Gateways, systems integrators are implementing AdvancedTCA in a dual-star configuration with 1+1 protection for the switch fabric. The AdvancedTCA carrier cards in these systems may house up to 4 AMC modules, or use the entire carrier area for a pool of DSPs. Each processor card will be connected to the working and protect core switch fabric.

In these high-capacity computing applications, fast protection cut-over is critical to ensure a robust system in the event of fabric failure. The Serial RapidIO switch should implement a hardware based cut-over trigger, such as device pins or a single register write, for immediate response to failure. Switches located at the AdvancedTCA carrier cards should treat the ports connected to the Working and Protect core fabric cards as a Port Pair. The routing tables should be configured only to the level of specifying the Port Pair. A control function can direct traffic to either port within the pair based on the operational status of the two fabric cards.

On the carrier cards, DSPs can be connected in a single stage, with switches located on the AdvancedTCA carrier card. The switch requires high density, low capacity ports (x1) to DSPs with high capacity ports (x4) to the central switch or other switches. Alternatively, a two level switch can be implemented, in which switches are located on the AMCs and on the carrier cards.

PMC Sierra’s PM6352 RSE 160 switch implements key features that address card-to-card and local interconnect applications. Connection between the core fabric to every card in an AdvancedTCA or a MicroTCA chassis can be implemented in a single device. The integrated high-performance SERDES ensures signal integrity across the backplane. For high availability, the device supports hardware-based APS cut-over, with biased arbitration for traffic selection, and low latency. For local interconnect the RSE 160 scales to support 1.25G, 2.5G or 3.125G over one or four links, depending on application requirements. Wireless infrastructure vendors can utilize the RSE 160 switch for end-to-end Serial RapidIO connectivity. For more information, visit www.pmc-sierra.com.