Brocade Communications Systems 415, Administrator'S Manual

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Brocade Adapters Administrator’s Guide 3
53-1001256-01
Enhanced Ethernet features
1
Priority-based flow control
Priority flow control pauses traffic based on the priority levels. A high-level pause algorithm follows:
•
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.
Ethernet jumbo frames
The basic assumption underlying FCoE is that TCP/IP is not required in a local data center network
and the necessary functions can be provided with Enhanced Ethernet. The purpose of an
“enhanced” Ethernet is to provide reliable, lossless transport for the encapsulated Fibre Channel
traffic. Enhanced Ethernet provides support for jumbo Ethernet frames and in-order frame delivery.
The Brocade FCoE 10 Gbps converged network adapter supports jumbo packets of up to 9 KB,
compared to the original 1,518-byte MTU for Ethernet. The frame size increase allows the same
amount of data to be transferred with less effort.
The frame data field size that you can set using the HCM GUI or BCU is for the storage side. You can
set the MTU using the OS interface, and this is for the network side. See
“Frame data field size” on
page 28 for information about setting the frame data field size.
NOTE
If a jumbo frame size is set for the CNA, the frame size setting on the attached FCoE switch must
match or it cannot accept jumbo frames.