Adaptive Rate Limiting; Fspf Link Cost Calculation When Arl Is Used; Pp-Tcp-Qos Priorities Over An Fcip Trunk - Brocade Communications Systems StoreFabric SN6500B Administrator's Manual

Adaptive Rate Limiting

Adaptive Rate Limiting (ARL) is performed on FCIP 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 different amounts of
bandwidth.
For Fabric OS v7.0.0 and later, you can configure minimum and maximum rates for each circuit of a
tunnel using the XGE ports on the FX8-24 blade.
ARL applies a minimum and maximum traffic rate, and allows the traffic demand and WAN
connection quality to dynamically determine the rate. 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 for GbE ports or 10 Gbps for
10GbE ports. The configured maximum data rate can be no larger than five times the configured
minimum rate.
ARL is supported only if Fabric OS v7.0.0 and later is running on both ends of the FCIP tunnel.

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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PP-TCP-QoS priorities over an FCIP trunk

Per-Priority TCP QoS (PP-TCP-QoS) prioritizes FC traffic flows between initiators and targets within
an FCIP tunnel to optimize bandwidth and performance.
Each circuit has four TCP connections that manage traffic over an FCIP tunnel, as illustrated in
Figure 7
medium, and low priority traffic are assigned a percentage of available bandwidth based on priority
level.
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Fabric OS FCIP Administrator's Guide
53-1002748-01
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.
on page 24. Each circuit handles one of the following priority traffic types. Qos high,
F class - F class is the highest priority, and is assigned bandwidth as needed at the expense of
lower priorities, if necessary. This is referred to as strict priority.
QoS high - The default priority value is 50 percent of the available bandwidth.

Adaptive Rate Limiting

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