Adaptive Rate Limiting; Fspf Link Cost Calculation When Arl Is Used - Brocade Communications Systems Brocade BladeSystem 4/24 User Manual

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Adaptive Rate Limiting

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:
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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
1000000 divided by the bandwidth.
If the bandwidth is less than 1 Gbps, the link cost is 2000 minus the bandwidth
DCFM Enterprise User Manual
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