Power Core User Manual Version: 6.6.0/3 91/539
9. Audio IO
IGMP
The Internet Group Management Protocol (IGMP) is used in IPv4 networks to establish multicast group
memberships.
There are three versions of IGMP: v2 improves upon v1 by adding the ability for a host to leave a multicast
group; v3 improves upon v2 by supporting Source Specific Multicast (SSM). SSM is a method of delivering
multicast packets in which the only packets delivered to a receiver originate from a specific source address.
Thus, SSM reduces demands on the network and improves security.
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Setting the IGMP Scheme
The SSM Enable (IGMP v3 only) and IGMP v1/2 Disable options determine how IGMP Joins are transmitted.
There are two possibilities: Any Source Multicast (ASM) or Source Specific Multicast (SSM). The table below
describes what happens when the options are combined.
SSM Enable
(IGMP v3 only)
IGMP Joins are sent as IGMP v2 (Any Source Multicast).
IGMP Joins are sent, by default, as IGMP v3 (Source Specific Multicast).
If Power Core receives queries in v2, it reverts to v2 and keeps sending in v2.
IGMP Joins are sent as IGMP v2 (Any Source Multicast).
IGMP Joins are sent as IGMP v3 (Source Specific Multicast).
There is no fallback to v2 and so Power Core keeps sending IGMP v3 only.
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Configuring the IGMP Behavior
The following options are active by default and can be deactivated as required. This is sometimes necessary,
depending on the type of network switch in use. If in doubt, leave both options enabled.
·
IGMP Legacy Suppression (sysctl: net.inet.igmp.legacysupp)
If this variable is non-zero, then IGMP v1 and v2 membership reports received on a link are allowed to suppress
the IGMP v3 state-change reports which would otherwise be issued.
·
IGMP Router Alert option (sysctl: net.inet.igmp.sendra)
If this variable is non-zero, then IGMP v2 and v3 reports contain the IP Router Alert option.
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Receiving single streams as ASM in a SSM environment
It is also possible to connect individual streams as ASM in a SSM environment if:
·
The SDP received via Ember+ has the source IP address omitted from the source-filter field.
·
A RAVENNA Static Stream is configured where the multicast source IP address field is left blank.
Example SDP (with source IP Address omitted)
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