Brocade Network Advisor SAN User Manual v12.3.0 - Manual (Page 994)

942 Brocade Network Advisor SAN User Manual
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Adaptive Rate Limiting
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Adaptive Rate Limiting
Adaptive Rate Limiting (ARL) is performed on FCIP tunnel connections to change the rate in which
the FCIP tunnel transmits data through the TCP connections. This feature is available only on the 8
Gbps Extension Switches and 8 Gbps Extension Blades. ARL uses information from the TCP
connections to determine and adjust the rate limit for the FCIP tunnel dynamically. This allows FCIP
connections to utilize the maximum available bandwidth while providing a minimum bandwidth
guarantee.
ARL applies a minimum and maximum traffic rate, and allows the traffic demand and WAN
connection quality to dynamically determine the rate. As traffic increases, the rate grows towards
the maximum rate, and if traffic subsides, the rate reduces towards the minimum. If traffic is
flowing error-free over the WAN, the rate grows towards the maximum rate. If TCP reports an
increase in retransmissions, the rate reduces towards the minimum.
FSPF link cost calculation when ARL is used
Fabric Shortest Path First (FSPF) is a link state path selection protocol that directs traffic along the
shortest path between the source and destination based upon the link cost. When ARL is used, The
link cost is equal to the sum of maximum traffic rates of all established, currently active low metric
circuits in the tunnel. The following formulas are used:
• If the bandwidth is greater than or equal to 2 Gbps, the link cost is 500.
• If the bandwidth is less than 2 Gbps, but greater than or equal to 1 Gbps, the link cost is
1000000 divided by the bandwidth.
• If the bandwidth is less than 1 Gbps, the link cost is 2000 minus the bandwidth
QoS SID/DID priorities over an FCIP trunk
QoS SID/DID traffic prioritization is a capability of Fabric OS Adaptive Networking licensed feature.
This feature allows you to prioritize FC traffic flows between hosts and targets.
Four internal TCP connections provide internal circuits for managing QoS SID/DID priorities over an
FCIP tunnel, as illustrated
Figure 427 . The priorities are as follows:
• F class - F class is the highest priority, and is assigned bandwidth as needed at the expense of
lower priorities, if necessary.
• QoS high - The QoS high priority gets at least 50% of the available bandwidth.
• QoS medium - The QoS medium priority gets at least 30% of the available bandwidth.
• QoS low - The QoS low priority gets at least 20% of the available bandwidth.
NOTE
The QoS high (50%), medium (30%), and low (20%) values are default values which you can change
using procedures under
“Configuring QoS Priorities” on page 943. These priorities are enforced only
when there is congestion on the network. If there is no congestion, all traffic is handled at the same
priority.