Dcb Exchange Protocol; Enhanced Ethernet Features; Enhanced Transmission Selection; Priority-Based Flow Control - Brocade Communications Systems Brocade 8/12c User Manual

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Enhanced Ethernet features

DCB exchange protocol

DCB Exchange (DCBX) protocol allows enhanced Ethernet devices to convey and configure their
DCB capabilities and ensures a consistent configuration across the network. DCBX protocol is used
between data center bridging (DCB) devices, such as a converged network adapter (CNA) and a
FCoE switch, to exchange configuration with directly-connected peers.
NOTE
When DCBX protocol is used, any other LLDP implementation must be disabled on the host systems.

Enhanced Ethernet features

Data Center Bridging (DCB) is a set of IEEE 802 standard Ethernet enhancements that enable Fibre
Channel convergence with Ethernet. The two basic requirements in a lossless Ethernet
environment are Enhanced Transmission Selection (ETS) and priority-based flow control. These
capabilities allow the Fibre Channel frames to run directly over 10 Gbps Ethernet segments without
adversely affecting performance.

Enhanced transmission selection

Enhanced transmission selection (ETS) allows lower priority traffic classes to use available
bandwidth that is not be used by higher priority traffic classes and maximizes the use of available
bandwidth.
ETS allows configuration of bandwidth per priority group.
Priority group ID usage is defined as follows:
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•
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The configured priority group percentage refers to the maximum percentage of available link
bandwidth after PGID 15.0 to 15.7 is serviced, assuming all priority groups are fully subscribed. If
one of the priority groups does not consume its allocated bandwidth, then any unused portion is
available for use by other priority groups.

Priority-based flow control

Priority-based flow control allows the network to selectively pause different classes of traffic and
create lossless lanes for Fibre Channel, while retaining packet drop congestion management for IP
traffic. A high-level pause example follows:
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PGID = {0, 7} is used when the priority group is limited for its bandwidth use.
PGID = {8, 14} is reserved.
PGID = {15.0 - 15.7} is used for priorities that are not limited for their bandwidth use.
During periods of heavy congestion, the receive buffers reach high threshold and generate a
pause.
The pause tells transmission (Tx) queues to stop transmitting.
After the receive (Rx) buffers reach low threshold, a zero pause is generated.
The zero pause signals the Tx queues to resume transmitting.
Brocade Network Advisor SAN User Manual
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