Need More Than 10G per Channel or Better Traffic Control?
By Tom Cox, RapidIO Trade Association
- The growth in AdvancedTCA and MicroTCA applications is being driven by demand for cost effective, high performance systems. RapidIO is meeting the needs of current designs, but what about future projects with higher performance needs?
The RapidIO Trade Association started nine years ago to evolve, support, and promote the RapidIO standard, the only interconnect designed specifically to meet the embedded market’s high-performance needs. Since then, the standard has matured and is globally deployed across the communications, military/aerospace, storage, and industrial markets.
To support higher performance, the RapidIO Trade Association unveiled a new technology roadmap with details about Specification Rev. 2.0, and a preview of Rev. 3.0. Although Rev. 1.3 fully meets designers’ needs today, we see substantial system requirements for QoS and faster signaling to 6.25 Gb/s.
Serial RapidIO offers embedded fabric system designers more compelling features with the approval of Specification 2.0. System designers can now select link rates from 1.25 Gb/s up to 6.25 Gb/s and port widths from x1 to x16, providing high granularity to select the overall data rate best suited to individual applications. Beyond the physical layer enhancements with Specification 2.0 are many higher level features that offer more QoS control over traffic flow.
Specification 2.0 allows all types of traffic to be carried on one interconnect, resulting in substantially simpler boards, simpler components, lower power consumption, and lower cost. Specification 2.0 extends the hardware-based short- and medium-term flow control mechanisms of Specification 1.3 to include long-term and application level mechanisms. The nine virtual channels (VCs) defined in Specification 2.0 allow system designers to allocate bandwidth for particular traffic types, in essence turning each link into up to nine independently managed streams. The extension is backward-compatible, allowing users of Specifications 1.2 and 1.3 to leverage their investment with future devices. Long-term flow control is a backward-compatible extension to Type 9 Data Streaming packets, which enables simple XON/XOFF, rate-based, or credit-based flow control. These mechanisms allow system designers to control precisely the amount of traffic each endpoint injects into the fabric, enabling not just congestion management but also congestion avoidance.
Virtual channels provide the ability to aggregate traffic flows with similar characteristics, while separating them from ones with different characteristics, and guaranteeing bandwidth to each flow. The comprehensive flow control mechanisms in Specification 2.0 can ensure that the traffic in each virtual channel meets its quality of service (QoS) requirements, without interfering with any other traffic.
Specification 2.0 fabrics simplify the implementation of systems that have multiple traffic flows with different performance requirements. Multiple control and data flows can be carried using a single efficient, high-bandwidth fabric that guarantees QoS for each flow and application. Implementing a single fabric requires fewer components with fewer connections between them and produces systems that consume less power, are easier to test, and are faster to market. The robust Specification 2.0 fabric simplifies the implementation of complex systems, delivering an enhanced Quality of Experience for end users and system implementers alike.
For more information on RapidIO and technical comparisons of interconnect technologies, go to www.rapidio.org.
Tom Cox is Executive Director of the RapidIO Trade Association. You can reach him at tom.cox@rapidio.org.