VXS (VITA 41) Switched Serial Specification

VXS (VITA 41-2005) is a specification which defines an open standard for supporting high-speed, switched interconnect protocols on VME P0. This standard is the base for defining physical features of VXS and is used in combination with protocol layer standards to define specific serial interconnects for system implementations.

VXS or VITA-41 or VMEbus Switched Serial is an extension of VMEbus which extends the capabilities of VME's traditional 6U Eurocard form factor by offering a standard method of employing high-speed switched serial fabrics in the VME context. This ANSI standard that combines parallel VMEbus with enhancements to support high speed serial communications. The VXS (VITA-41) specification can therefore run point-to-point (including Serial FPDP and Aurora) or switched serial protocols (including PCI Express, RapidIO, StarFabric and InfiniBand) over a new high speed P0 connector. Backward compatibility is maintained with existing backplanes that do not have a conflicting P0 scheme.

Under the VITA 41 (VXS) specification, VMEbus cards (now called “payload cards”) are connected via a high-speed P0 connector. Each payload card has two 4x VXS ports (port A and port B) to connect to other boards in the system. Each VXS port is comprised of 4 HSS links running at speeds up to 2.5Gbps or 3.125Gbps. The VXS specification also defines switch cards. The switch cards provide the interlinks between each VXS port on one payload card to another.

The VXS Standard does not mandate a specific backplane topology. Therefore, multiple topologies are available for configuring VXS systems: star, dual star, mesh, daisy chain, and custom topologies. In a dual-star configuration, each payload card can connect to one of two switch cards. Incorporating both switch cards ensures optimal performance. The second switch may be used for high availability standby or active load balancing. Each one of the links in the 4x pair has been simulated and tested by the VITA 41 working group to run at data rates as high as 6.25Gbaud to ensure a development road map - current protocols support rates up to 3.125Gbps.

While VXS requires a new backplane for applications migrating from VME, VXS provides compatibility with existing VMEbus products. Existing VMEbus cards will plug into a VXS payload slot if the card does not have a VME64x (2mm) P0 connector or some other obstruction in the P0 area. Conversely, VXS payload cards will plug into a traditional backplane slot if the backplane does not have a VME64x (2mm) P0 connector or some other obstruction in the P0 area.

The VXS specifications include:

VITA 41.1: 4x InfiniBand Link
VITA 41.2: 4x Serial RapidIO Link
VITA 41.3: 1/10 Gigabit Ethernet Link
VITA 41.4: 4x PCI Express Link
VITA 41.5: 4x Aurora Link
VITA 41.6: 1x Gigabit Ethernet Control Channel Layer
VITA 41.7: Redundant Processor Mesh for VXS
VITA 41.10: Live Insertion
VITA 41.11: Rear Transition Module