Functionality of Fibre Channel

FCoE maps Fiber Channel directly over Ethernet while being independent of the Ethernet forwarding scheme. The FCoE protocol specification replaces the FC0 and FC1 layers of the Fiber Channel stack with Ethernet. By retaining the native Fiber Channel constructs, FCoE was meant to integrate with existing Fiber Channel networks and management software.

Many data centers use Ethernet for TCP/IP networks and Fiber Channel for storage area networks (SANs). With FCoE, Fiber Channel becomes another network protocol running on Ethernet, alongside traditional Internet Protocol (IP) traffic. FCoE operates directly above Ethernet in the network protocol stack, in contrast to iSCSI which runs on top of TCP and IP. As a consequence, FCoE is not routable at the IP layer, and will not work across routed IP networks.

Since classical Ethernet had no priority-based flow control, unlike Fiber Channel, FCoE requires enhancements to the Ethernet standard to support a priority-based flow control mechanism (this prevents frame loss). The IEEE standards body is working on this in the Data Center Bridging Task Group.

Fiber Channel required three primary extensions to deliver the capabilities of Fiber Channel over Ethernet networks:

Encapsulation of native Fiber Channel frames into Ethernet Frames.

Extensions to the Ethernet protocol itself to enable an Ethernet fabric in which frames are not routinely lost during periods of congestion.

Mapping between Fiber Channel N_port IDs (aka FCIDs) and Ethernet MAC addresses.

July 4, 2011

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