Beyond Gigabit Ethernet
While Gigabit Ethernet (VITA 41.3) offers a lot of advantages, as a VXS fabric choice it still has one huge disadvantage: raw speed. Because VITA 41.3 uses 1.25 Gbps links, the theoretical throughput of a fully implemented system is only 40% of what can be achieved with Serial RapidIO or Aurora.
In addition, while it allows payload cards to implement up to eight Gigabit Ethernet links, in reality the overhead of multiplexing separate links makes this option unrealistic. Typical implementations include two links per payload slot, resulting in throughput that is 10% of other fabric options.
10 Gigabit Ethernet, which is being standardized for VXS as VITA 41.8, leverages commercially available 10 Gigabit technology to fully address the limitations of Gigabit Ethernet.
- VITA 41.8 is based on the 10GBASE-KX4 standard, which uses a raw serial bit rate of 3.125 Gbps which is as fast or faster than RapidIO-based VXS implementations.
- 10 Gigabit Ethernet link uses four serial pairs for each link, resulting in two logical links per payload card instead of eight Gigabit links. This allows systems to easily use both single and dual star topologies without any unnecessary overhead on the payload card.
Effective use of 10 Gigabit speeds depends on an ecosystem of solutions that provide efficient solutions for both switches and endpoints. In this area, 10 Gigabit Ethernet potentially offers significant advantages due to the need within the commercial marketplace for the high performance features that are critical for embedded applications such as TCP offload and RDMA support. Native 10 GbE support is currently available for both embedded and x86 class processors, and FPGA IP cores are available for FPGA-based endpoints. Over time, it seems clear that 10 GbE endpoints and switches will become as ubiquitous as Gigabit Ethernet is today, allowing board vendors to leverage a broad ecosystem for 10 GbE solutions that are both power and space efficient.
10 GbE technology will be a more network-centric view of embedded VXS-based systems. Control and data traffic can be intermixed using intelligent switching to achieve throughput and low latency, and the system architecture easily scales to include external sensor inputs and processing outputs all using common network interfaces. This enables future VXS systems to easily fit into a more network-centric architecture within the deployed platform.
The availability of Gigabit Ethernet offers a low cost bandwidth solution for many developers already familiar with the protocol. As a switched fabric, Gigabit Ethernet offers a simple, efficient option for communication. Operating independently over the P0 connector, the VITA 31.1 standard provides a 10/100 or Gigabit link between any VITA 31.1-compatible boards within the chassis. This enables a tried and tested method of implementing a Local Area Network-based multiprocessor architecture by using easily available Ethernet hardware, TCP/IP software and clustering, and other network management tools.