As is well known, Fibre Channel (FC) is an American National Standards Institute (ANSI) standard specifying a bidirectional serial data channel, structured for high performance capability. Physically, the Fibre Channel may be viewed as an interconnection of multiple communication points, called N_Ports, interconnected by a link comprising a switching network, called a fabric, or a point-to-point link. Fibre is a general term used to cover all physical media types supported by the Fibre Channel, such as optical fibre, twisted pair, and coaxial cable.
The Fibre Channel provides a general transport vehicle for Upper Level Protocols (ULPs) such as Intelligent Peripheral Interface (IPI) and Small Computer System Interface (SCSI) command sets, High-Performance Parallel Interface (HIPPI) data framing, IP (Internet Protocol), IEEE 802.2, and others. Proprietary and other command sets may also use and share the Fibre Channel, but such use is not defined as part of the Fibre Channel standard.
Fibre Channel is structured as a set of hierarchical functions denoted FC-0, FC-1, FC-2, FC-3 and FC-4.
FC-0 defines the physical portions of the Fibre Channel including the fibre, connectors, and optical and electrical parameters for a variety of data rates and physical media. Coax and twisted pair versions are defined for limited distance applications. FC-0 provides the point-to-point physical portion of the Fibre Channel. A variety of physical media is supported to address variations in cable plants.
FC-1 defines the transmission protocol which includes the serial encoding, decoding, and error control.
FC-2 defines the signaling protocol which includes the frame structure and byte sequences.
FC-3 defines a set of services which are common across multiple ports of a node.
FC-4 is the highest level in the Fibre Channel standard. It defines the mapping, between the lower levels of the Fibre Channel and the IPI and SCSI command sets, the HIPPI data framing, IP, and other ULPs.
Additional details regarding these and other aspects of Fibre Channel can be found in the ANSI Fibre Channel standard documents, including the FC-PH, FC-FS, FC-AL, FC-PI, FC-DA and FC-LS documents, all of which are incorporated by reference herein.
In typical conventional practice, Fibre Channel links are designed to operate at data rates of 4.25 Gbps, 2.125 Gbps or 1.0625 Gbps. Although higher data rates are possible, the industry is reluctant to spend money upgrading existing hardware to implement these higher data rates. The problem is that as data rates increase, to the proposed Fibre Channel rates of 8 Gbps, 16 Gbps and higher, the existing hardware degrades the electrical signals to the extent that error-free operation cannot be achieved without electrical equalization.
Current implementations generally attempt to address this problem through the use of pure receive equalization. However, at high data rates, on the order of 8 Gbps or higher, this receive-only equalization approach is very complicated, and requires significant increases in size and power consumption for the associated hardware. Moreover, the receive-only equalization approach may fail to provide the desired error-free operation at the high data rates.
Accordingly, what is needed is an improved approach to equalization for Fibre Channel or other bidirectional serial data channels, which can accommodate higher data rates without the need for hardware infrastructure upgrades while also avoiding the drawbacks of conventional receive-only equalization.