PLANET EPL-1000 - Manual (Page 77)

„ Group Removal Process:
General Query Issued
The OLT will periodically issue General Queries every Query Interval units. The use of the
General Query in IGMPv2 is very different from the way it was used in IGMPv1. In IGMPv2
the General Query is used for failure detection only. In IGMPv1 the General Query was the
only mechanism used to detect a leave. Because failures are extremely rare in modern
networks the Query Interval may be provisioned to a very large value. Query Response
Timeout units after the OLT issues the General Query the OLT will decrement the
robustness variable for each group joined for which the OLT has not received a report.
When the robustness for a particular group is 0, the OLT will assume that an implicit leave
has occurred and start the same process as described above. Since IGMPv2 has a
different mechanism than IGMPv1 to guarantee robustness - the Group Specific Query
Count - it is probably not necessary to provision the Robustness Count to a large value.
The value recommend by the standard for backwards compatibility with IGMPv1 is 2,
however, if the target system will only have IGMPv2 capable clients, a robustness count of
1, is probably a better choice.
The protocol description assumes that IGMP snooping and proxy are enabled. If these
functions are disabled, IGMP multicast data packets will be forwarded based on the Host
provisioned classification scheme and bridging mode(s).
If faster leave operation is desired, the GSQC may be set to 1, and the Last Member Query
Max Response Time provisioned to a smaller value than the default.
The ONU Snooping and OLT Proxy functions MUST be configured identically. Otherwise
multicast traffic will NOT be forwarded as expected.
The number of IGMP multicast data FIFOs used MUST NOT be changed when the OLT
PON Plant is enabled.
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