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What data center bridging is

Data center bridging (DCB) is a collection of extensions to the existing Ethernet standard that provides a lossless transport layer for FCoE traffic.

FC provides a reliable, dedicated fabric with no packet loss. Ethernet, however, is inherently lossy, which poses problems for transmitting FC traffic. The DCB standard resolves this problem by implementing the following technologies:
Per-priority pause (priority-based flow control)
Enables a device to only inhibit the transmission of frames based on user-defined priorities.
Enhanced transmission selection
Allows administrators to allocate bandwidth on a percentage basis to different priorities.
Congestion notification
Transmits congestion information.
DCB Exchange (DCBX) protocol
Exchanges connection information with directly connected peers and detects misconfigurations.

Although these technologies possess their own independent functions, they operate together to provide an enhanced Ethernet standard that eliminates packet loss due to traffic congestion. For more information about FCoE deployment, see TR-3800.