Adaptive Rate Limiting; Fspf Link Cost Calculation When Arl Is Used - Brocade Communications Systems 8 Administrator's Manual

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Adaptive Rate Limiting

Adaptive Rate Limiting

Adaptive Rate Limiting (ARL) is performed on FCIP tunnel circuits to change the rate in which the
FCIP tunnel transmits data through the IP network. ARL uses information from the TCP connections
to determine and adjust the rate limit for the FCIP circuit dynamically. This allows FCIP connections
to utilize the maximum available bandwidth while providing a minimum bandwidth guarantee. ARL
is configured on a per circuit basis because each circuit may have available differing amounts of
bandwidth.
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. ARL never attempts to exceed
the maximum configured value and reserves at least the minimum configured value. The aggregate
of the minimum configured values cannot exceed the speed of the Ethernet interface, which is 1
Gbps.
The maximum configured committed rate can be no larger than 5 times the minimum committed
rate. In V6.4.0 this is enforced in the CLI. When upgrading to v6.4.0 from an earlier version, if there
is a circuit configured with a maximum committed rate greater than 5 times the minimum
committed rate, the configuration will need to updated so the maximum is no larger than 5 times
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:
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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
1,000,000 divided by the bandwidth in Mbps.
If the bandwidth is less than 1 Gbps, the link cost is 2000 minus the bandwidth in Mbps.
Fabric OS FCIP Administrator's Guide
53-1001766-01