3.7 Functional Levels

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Fibre Channel Protocol (FCP) functional levels are FC-0 through FC-4. The FC-3 and FC-4 levels are outside the port level, permitting the sharing of resources of several ports in the event of future extensions. Applications lie above the FC-4 level. For example, the peripheral drivers for a SCSI application that typically communicates with Host Bus Adapters (HBAs) will communicate with the FC-4 level.

3.7.1 Placement in a Topology

As shown in Figure 3-8, FC-0, FC-1, and FC-2 are implemented at the port level. FC-3, FC-4, and the Upper Level Protocols (ULPs) are implemented at the node level. Fibre Channel considers that which is not visible on the link (above the FC-0 physical level) to be system dependent, and simply identifies the functions to be performed. It does not require allocation or placement.

Figure 3-8. Placement in a Topology

Figure 3-8 shows an example of a simple point-to-point ( two-node loop) topology to identify where the functionality of each level resides. FC-0, FC-1, and FC-2 are all implemented at the Port level. This means that each Port has the functionality of these levels. FC-3, FC-4, and ULPs are all implemented at the Node level.

Figure 3-9 shows another way to demonstrate this. The horizontal line in the middle divides the Node from the Port. You will see something new in this figure. Where there are multiples of FC-0, FC-1, and FC-2, there is only one FC-3, the common services level. That is because the FC-3 functionality may interact with multiple ports on a node. And then again above the FC-3 level, there are multiple FC-4s and ULPs. That is because there may be multiple ULPs within a node that map through multiple FC-4s.

Figure 3-9. Functional Levels

Figure 3-10 shows yet more detail. This figure shows that there are five levels used by Fibre Channel, (FC-0 through FC-4) separating the Upper Level Protocols into the system interface. Also, you can see that FC-4 can accommodate not only the channel protocols of SCSI, IPI, and others, but can also accommodate network protocols like IEEE 802.2.

Figure 3-10. Fibre Channel Framing Levels

Now you have a good overview of the different functional levels within Fibre Channel. Continue on to the next section to read about the detailed characteristics of each level.

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