Fibre Channel Layers

Fibre Channel does not follow the OSI model layering, but is split similarly into 5 layers, namely:

FC4 — Protocol Mapping layer, in which application protocols, such as SCSI or IP, are encapsulated into a PDU for delivery to FC2.

FC3 — Common Services layer, a thin layer that could eventually implement functions like encryption or RAID redundancy algorithms;

FC2 — Network layer, defined by the FC-PI-2 standard, consists of the core of Fibre Channel, and defines the main protocols;

FC1 — Data Link layer, which implements line coding of signals;

FC0 — PHY, includes cabling, connectors etc.;

Layers FC0 through FC2 are also known as FC-PH, the physical layers of Fibre Channel.

Fibre Channel routers operate up to FC4 level (i.e. they may operate as SCSI routers), switches up to FC2, and hubs on FC0 only.

Fibre Channel products are available at 1, 2, 4, 8, 10, 16 and 20 Gbit/s; these protocol flavors are called accordingly 1GFC, 2GFC, 4GFC, 8GFC, 10GFC, 16GFC, or 20GFC. The 16GFC standard was approved by the INCITS T11 committee in 2010, and those products are expected to become available in 2011. Products based on the 1GFC, 2GFC, 4GFC, 8GFC and 16GFC standards should be interoperable and backward compatible. The 1GFC, 2GFC, 4GFC, 8GFC designs all use 8b/10b encoding, while the 16GFC standard uses 64b/66b encoding. Unlike the 10GFC and 20GFC standards, 16GFC provides backward compatibility with 4GFC and 8GFC.

The 10 Gbit/s standard and its 20 Gbit/s derivative, however, are not backward compatible with any of the slower speed devices, as they differ considerably on FC1 level in using 64b/66b encoding instead of 8b/10b encoding, and are primarily used as inter-switch links.

June 30, 2011

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