The redundant
multicast sources feature supports up to four SSM/ASM multicast address pairs
per video session. However, only multicast traffic from one source is forwarded
to the output QAMs. When the active source fails, another source is chosen
automatically. Multicast sources must be unique within a redundant group and
cannot overlap across redundant groups.
The order of the sources is critical when multicast sessions are configured via GQI or VSRM. For a given group IP address, the source IP addresses must be specified in the same order.
For example: The group IP address 232.1.2.3 used with two sessions must have the source IP addresses specified in the same order.
Session A configured with group IP 232.1.2.3 source 174.2.3.4 source2 174.4.5.6 source3 174.7.8.9 and session B or any session created after session A configured using group IP 232.1.2.3, must have the source IP addresses in this same order as specified for session A. That is, source 174.2.3.4 source2 174.4.5.6 source3 174.7.8.9.
This ensures that all sessions switch to the same source IP address when a source switch occurs. Additionally, sessions configured via GQI have up to three sources available for redundancy, whereas multicast labels configured for table-based sessions have up to four sources available for redundancy.
Multicast labels
must use unique groups and S/G pairs. These pairs cannot be used by other
multicast labels or by multicast sessions that use S/G pairs. For example, when
one multicast session uses {[S1, G], [S2, G] and [S3, G]}, another session
cannot use {[S1, G], [S4, G]}.
Multicast source
change is based on the session state; INIT, IDLE, ACTIVE or OFF. A session
configured for the first time is in INIT state and stays in this state for a
brief time. If traffic starts before the INIT timer expires, it moves to the
ACTIVE state, otherwise to the IDLE state.
When traffic starts,
the session remains in ACTIVE state as long as traffic continues to flow. When
traffic stops for a time longer than the IDLE timer, the session moves to IDLE
state. During IDLE state, PAT and PMT of the session is retained as the output.
If traffic resumes in this state, the session moves to ACTIVE state again with
all its previous PSI and remapping information unaltered.
In IDLE state, if
traffic does not start or resume before the OFF timer expires, the session
transitions to OFF state. When traffic resumes for a session in OFF state, it
is treated as a new session.
Sessions that
transition from ACTIVE to IDLE have higher priority and will be moved to the
backup source than those that were newly created and have changed from INIT to
IDLE.