Converged networks with Fibre Channel over Ethernet and Data Center Bridging

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Figure 2: Multiple traffic types can share the same link using a multifunction adapter.
Network convergence with FCoE
Now that 10 GbE is becoming more widespread, FCoE is the next attempt to converge block storage
protocols onto Ethernet. FCoE takes advantage of 10 GbE performance and compatibility with existing
Fibre Channel protocols. It relies on an Ethernet infrastructure that uses the IEEE Data Center Bridging (DCB)
standards. The DCB standards can apply to any IEEE 802 network, but most often the term DCB refers to
enhanced Ethernet. We use the term DCB to refer to an enhanced Ethernet infrastructure that implements at
least the minimum set of DCB standards to carry FCoE protocols.
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 pause 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.
• 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 CEE data path (CNAs,
switches, and so on). QCN networks must also use PFC to avoid dropping packets and ensure a lossless
environment.
• Data Center Bridging Exchange Protocol (DCBX), 802.1Qaz supports discovery and configuration of
network devices that support PFC, ETS, and QCN.
Fibre Channel over Ethernet
In legacy Ethernet networks, dropped frames occur under collision or congestion situations. The networks
rely on upper layer protocols such as TCP to provide end-to-end data recovery. FCoE is a lightweight
encapsulation protocol and lacks the reliable data transport of the TCP layer. Therefore, FCoE must operate
on DCB-enabled Ethernet and use lossless traffic classes to prevent Ethernet frame loss under congested
network conditions.
FCoE on a DCB network mimics the lightweight nature of native FC protocols and media. It does not
incorporate TCP or even IP protocols. This means that FCoE is a layer 2 (non-routable) protocol just like FC.
FCoE is only for short-haul communication within a data center. The main advantage of FCoE is that switch