Converged Networks and Fibre Channel over Ethernet

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The benefits of convergence are clear: Converged networking reduces the number of required I/O ports. This means that
smaller servers (including blades) with fewer available option card slots are ideally suited for taking advantage of
converged networks and the reduced requirement for I/O ports for full connectivity. Furthermore, the savings from not
purchasing and operating several fabric types and their server connections is substantial. Access to any and all
resources in the data center using simple wire-once servers reduces deployment, diagnosis, management, and
operating costs.
Data Center Bridging
An informal consortium of network vendors originally defined a set of enhancements to Ethernet to provide enhanced
traffic management and lossless operation. The consortium’s proposals have become a standard from the Data Center
Bridging (DCB) task group within the IEEE 802.1 Work Group.
The DCB standards define four new technologies:
• Priority-based Flow Control (PFC): 802.1Qbb allows the network to provide link level flow control (priority based
pause) for different traffic classes.
• Enhanced Transmission Selection (ETS): 802.1Qaz defines the scheduling behavior of multiple traffic classes,
including strict priority and minimum guaranteed bandwidth capabilities. This should enable fair sharing of the link,
better performance, and metering.
• Data Center Bridging Exchange Protocol (DCBX): 802.1Qaz supports discovery and configuration of network devices
that support PFC and ETS parameter negotiation between link partners. DCBX is specified as part of the same
standard as ETS.
• Quantized Congestion Notification (QCN): 802.1Qau supports end-to-end flow control in a switched LAN
infrastructure and helps eliminate sustained, heavy congestion in an Ethernet fabric. Before the network can use QCN,
you must implement QCN in all components in the DCB data path (CNAs, switches, and so on). QCN enabled networks
work with PFC to avoid dropping packets and ensure a lossless environment.
The DCB task group completed standards ratification in 2011.
Fibre Channel over Ethernet (FCoE)
FCoE is a protocol that wraps Fibre Channel frames in Ethernet frames for transporting them over Ethernet links. FCoE is
widely accepted as an enabler of converged I/O in servers. FCoE involves minimal changes to the Fibre Channel protocol.
FCoE packets encapsulate Fibre Channel frames inside Ethernet frames (Figure 2).
Figure 2: The FCoE protocol embeds FC frames within Ethernet frames.
FCoE on a DCB network mimics the lightweight nature of native Fibre Channel protocols and media. It does not
incorporate TCP or even IP protocols. This means that FCoE is a layer 2 (non-routable over IP) protocol just like Fibre
Channel. FCoE is primarily focused on local communication within a data center. The main advantage of FCoE is that
switch vendors can easily implement logic for converting FCoE on a DCB network (FCoE/DCB) to native Fibre Channel in
high-performance switch silicon.