Brocade Converged Enhanced Ethernet Administrator's Guide v6.1.2_cee (53-1001258-01, June 2009)

Converged Enhanced Ethernet Administrator’s Guide 9
53-1001258-01
Layer 2 Ethernet overview
1
Queuing features are described as follows:
• RED—RED increases link utilization. When multiple inbound TCP traffic streams are switched to
the same outbound port, and some traffic streams send small frames while other traffic
streams send large frames, link utilization will not be able to reach 100 percent. When RED is
enabled, link utilization approaches 100 percent.
• Classification—Setting user priority.
- Inbound frames are tagged with the user priority set for the inbound port. The tag is visible
when examining the frames on the outbound port. By default, all frames are tagged to
priority zero.
- Externally tagged Layer 2 frames—When the port is set to accept externally tagged Layer 2
frames, the user priority is set to the Layer 2 CoS of the inbound frames.
• Queuing
- Input queuing—Input queuing optimizes the traffic flow in the following way. Suppose a CEE
port has inbound traffic that is tagged with several priority values, and traffic from
different priority settings is switched to different outbound ports. Some outbound ports
are already congested with background traffic while others are uncongested. With input
queuing, the traffic rate of the traffic streams switched to uncongested ports should
remain high.
- Output queuing—Output queuing optimizes the traffic flow in the following way. Suppose
that several ports carry inbound traffic and that each port has a different priority setting.
Traffic from all ports is switched to the same outbound port. By varying the traffic rate from
the inbound ports, some outbound priority groups will be congested while others can
remain uncongested. With output queuing, the traffic rate of the traffic streams that are
uncongested should remain high.
- Multicast rate limit—A typical multicast rate limiting example is where several ports carry
multicast inbound traffic that is tagged with several priority values. Traffic with different
priority settings is switched to different outbound ports. Some outbound ports are already
congested with background traffic while others are uncongested. The multicast rate limit
and burst size are set so that the total multicast traffic rate on output ports is less than the
specified set rate limit.
- Multicast input queuing—A typical multicast input queuing example is where several ports
carry multicast inbound traffic that is tagged with several priority values. Traffic with
different priority settings is switched to different outbound ports. Some outbound ports
are already congested with background traffic while others are uncongested. The traffic
rate of the traffic streams switched to the uncongested ports should remain high. All
outbound ports should carry some multicast frames from all inbound ports. You can set
the multicast packet expansion tail drop threshold for each of the four multicast traffic
classes. This enables multicast traffic distribution relative to the set threshold values.
- Multicast output queuing—A typical multicast output queuing example is where several
ports carry multicast inbound traffic. Each port has a different priority setting. Traffic from
all ports is switched to the same outbound port. By varying the traffic rate from the
inbound ports, some outbound priority groups will be congested while others remain
uncongested. The traffic rate of the traffic streams that are uncongested remains high.
The outbound ports should carry some multicast frames from all the inbound ports.