Communication devices sometimes use auto-negotiation methods when setting up communication links. Such methods are typically used to determine communication capabilities that are supported by both sides of the link, in order to agree on mutually-supported capabilities that may be used for communication. In particular, speed auto-negotiation methods are used to negotiate and resolve a communication speed at which the devices may communicate with one another.
Speed auto-negotiation methods in Ethernet™ links are described, for example, in the IEEE 802.3-2005 standard entitled “Information Technology—Telecommunications and Information Exchange between Systems—Local and Metropolitan Area Networks—Specific Requirements—Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications,” which is incorporated herein by reference. Clause 28 of the standard describes auto-negotiation methods for physical layer link signaling over twisted-pair links for 10 Mbps, 100 Mbps and 1000 Mbps. Speed auto-negotiation is also defined for backplane Ethernet applications, in clause 73 of the emerging IEEE 802.3ap standard. Information regarding backplane Ethernet is available at grouper.ieee.org/groups/802/3/ap.
Speed negotiation is also sometimes used in Fibre Channel (FC) links. FC has been standardized by working group T11 of the International Committee for Information Technology Standards (INCITS), and FC standards are available at www.t11.org. Section 26 of INCITS Standard FC-FS-2, entitled “Fibre Channel Framing and Signaling 2,” revision 1.01, Aug. 8, 2006, which is incorporated herein by reference, describes methods for speed negotiation in FC links.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: