DCB and FCoE

Since its inception, Brocade has been a driving force behind open industry standards for data center networking technologies. Today, Brocade continues to lead the creation of open standards for converged data center technologies:

• Fibre Channel over Ethernet (FCoE)
• Data Center Bridging (DCB)
• Transparent Interconnection of Lots of Links (TRILL)

Brocade also leads the industry in high-performance solutions that streamline server I/O consolidation and enable converged data centers. Today, the unified, end-to-end Brocade DCB/FCoE solution integrates seamlessly into existing data center environments and includes:

• Brocade Converged Network Adapters (CNAs)
• Top-of-rack FCoE switches
• End-of-row FCoE blades for backbone platforms
• Data center management applications

The FCoE protocol was developed by the INCITS Technical Committee T11 as part of the T11 FC-BB-5 project. The FCoE protocol and the FCoE Initialization Protocol (FIP) are defined in FC-BB-5, which describes how other protocols are transported and mapped over a Fibre Channel network. The T11 committee completed its technical work for FC-BB-5 in June 2009, and forwarded the draft standard to INCITS for approval and publishing. The INCITS public review was completed with no comments, which means that the standard will soon be published by INCITS as an industry standard.

FCoE Encapsulation
FCoE is a new industry-standard protocol that enables the transport of Fibre Channel storage traffic over new enhanced lossless Ethernet links. To achieve that goal, FCoE simply encapsulates, or wraps, Fibre Channel frames into Ethernet frames (see Figure 1) and prepares them for transport over Data Center Bridging (DCB) links. It is important to note that FCoE simply wraps the entire Fibre Channel frame as-is without any modifications.

The fact that the Fibre Channel payload remains intact throughout its FCoE journey means that FCoE preserves the Fibre Channel constructs and services and enables FCoE solutions to utilize existing management applications. As a result, FCoE solutions are designed to integrate seamlessly into existing Fibre Channel environments without introducing incompatibilities or disrupting existing infrastructures. Note, however, that FCoE will not alleviate existing incompatibilities in existing Fibre Channel products or environments.

As an encapsulation protocol, FCoE builds on the success of Fibre Channel in the data center and serves to extend its presence. Contrary to some beliefs, FCoE does not compete with Fibre Channel, as encapsulation protocols tend to supplement rather than compete with storage interface or networking protocols such as Fibre Channel.

The FCoE protocol stack (see Figure 2) is constructed by taking Fibre Channel upper services (Layers FC 2, FC 3, and FC 4) and placing them on top of Ethernet physical and Data Link layers (Layer 2). Note that the layer labeled DCB is the Ethernet Link Layer (Layer 2) where DCB enhancements aimed at making Ethernet lossless are being added. Sandwiched between the Fibre Channel and Ethernet layers is the FCoE layer. The FCoE layer encapsulates Fibre Channel to DCB traffic and performs the reverse function on DCB-to-Fibre Channel traffic. Ethernet frames carrying Fibre Channel traffic are assigned a new EtherType code to distinguish FCoE traffic. FCoE also requires a new larger Ethernet frame size called "baby jumbo frame" that accommodates the Fibre Channel frame and the associated Ethernet and FCoE headers.

Figure 1. Ethernet frame with Fibre Channel frame insertion.




Figure 2. FCoE stack.

FCoE Initialization Protocol (FIP)
FIP is the control plane protocol that is used in the discovery and initialization stages of establishing links among the elements of the fabric. Once discovery and initialization are established and the nodes have successfully performed fabric login, the FCoE data plane frames are used for data transmission operations. Unlike FCoE frames, FIP frames do not transport Fibre Channel data, but contain discovery and Login/Logout parameters. FIP frames are assigned a unique EtherType code to distinguish them from FCoE frames with Fibre Channel storage data.