Data Center Fabric Manager Enterprise User Manual v10.3.X (53-1001357-01, November 2009)

398 DCFM Enterprise User Manual
53-1001357-01
Enhanced Ethernet features
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Enhanced Ethernet features
Converged Enhanced Ethernet (CEE) 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:
• PGID = {0, 7} is used when the priority group is limited for its bandwidth use.
• PGID = {8, 14} is reserved.
• PGID = {15} is used for priorities that are not limited for their bandwidth use.
The configured priority group percentage refers to the maximum percentage of available link
bandwidth after PGID 15 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:
• 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.