Round Robin; Hash - Avaya P330 User Manual

Round Robin

Hash

Avaya P330 Load Balancing Manager User Guide
Using Round Robin, the load balancer issues sessions to each RS in turn.
The first RS in the group receives the first session, the second RS receives
the next session, and so on. When all the RSs receive a session, the
issuing process starts over with the first RS. Round Robin ensures that
each RS receives an equal number of sessions.
Using the Hash metric, sessions are distributed to RSs using a predefined
mathematical hash function. The hash function is performed on a
specified parameter. The source IP address, destination IP address, or
both are used as the hash function input.
The load balancer creates a list of all the currently available RSs. The
result of the hash function is used to select an RS from the list. Any
given parameter always gives the same hash result, providing natural
persistency.
If an RS is removed or added to the group, persistency is broken. This
occurs since the order of the RSs in the list changes, but the hash still
points to the same list entries. The following figure illustrates how a loss
of persistency occurs when an RS becomes non-operational:
Figure 1-8. Hash Metric - Loss of Persistency
In the above figure, when Server 2 becomes non-operational, the list of
available servers is readjusted, causing a lack of persistency. However, if
Server 2 becomes operational again, the list of available servers is
restored to its original order, and persistency is recovered.
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