PLX PCI Express Gen 2 Switches Support Access Control Service -- Required for I/O Virtualization

All PLX Gen 2 switches also support Alternative Routing-ID Interpretation (ARI), which increases the number of functions a device may support. Additionally, PLX PCIe Gen 2 switches support Multicast (MC), which allows a single ingress packet to be sent to multiple egress ports, delivering significant saving in CPU utilization.

ACS, ARI and MC were announced as engineering change notices (ECNs) by the PCI-SIG and later included in PCI Express Base Specification 2.1. ACS defines a set of control points within a PCIe topology to determine whether a packet should be routed normally, blocked or redirected. ACS is applicable to root complexes (RCs), switches and multi-function I/O devices.

In PCIe packets, routing IDs, requester IDs, and completer IDs are 16-bit identifiers traditionally composed of three fields: an 8-bit bus number, a 5-bit device number, and a 3-bit function number. With ARI, the 16-bit field is interpreted as two fields instead of three: an 8-bit bus number and an 8-bit function number; the device number field is eliminated. This new interpretation allows an ARI-enabled device to support up to 256 functions instead of eight, which allows higher device integration and provides better utilization of server CPU for virtual machines or system images.

Multicast defines the process for copying a single packet on an ingress port to multiple egress ports of a PCIe switch. Multiple groups of ingress/egress ports can be configured for MC, thus providing additional flexibility in moving traffic or storing information. PLX pioneered this idea in PCIe and helped define it for the PCI-SIG specification.

PLX anticipated the need for ACS, ARI and MC, which were defined by the PCI-SIG as optional, in our PCIe switches and included them in early designs, said Akber Kazmi, marketing director for PCIe switches at PLX. We are presently shipping production silicon with these important capabilities, while working with other industry leaders to create an eco-system providing end-to-end support that enables easy implementation and rapid deployment of I/O sharing and virtual computing.

PLX Technology today offers 20 PCIe Gen 2 switch devices, with more in development. These solutions include the industry's largest lane and port count switch -- 96 lanes and 24 ports -- and, for more mainstream applications, a four-lane, four-port switch. PLX was first to market with PCIe switches in 2004 and has continued to innovate product designs to address markets worldwide. The company is now investing in the development of products compliant with the Gen 3 specification and is working closely with key designers and manufacturers to meet their PCIe needs.