How to Join Flow

This section considers IGMPv2 proxy as an example to describe the Join Flow.

Join Flow [OLT]

Figure 1 Join flow

1. The multicast user switches a channel and sends a join message for demanding a new program GIP1.
   
2. After receiving the join message, the service board enters the IGMP protocol stack of the multicast user. After multicast control is implemented (for details, see "Multicast CAC"), the following group membership table is generated on the service board.
   

   Index	Online Member
   MVLAN1+GIP1	Multicast user 1

   • At the same time, the following multicast forwarding table is generated on the service board (for details on how to map GIP1 to GMAC1, see "Basic Concepts").

   Index	Duplication Destination
   MVLAN1+ GMAC1	GPON port 1

   • According to MVLAN1 corresponding to the program, the service board serves as the proxy of multicast user 1 and sends a join message to the control board.
3. After receiving the join message, the control board enters the IGMP protocol stack of MVLAN1 and generates the following group membership table.
   

   Index	Online Member
   MVLAN1+GIP1	Service board 1

   • At the same time, the control board generates the following multicast forwarding table.

   Index	Duplication Destination
   MVLAN1+ GMAC1	Port corresponding to service board 1

4. The control board then sends a join message to the multicast router through the multicast upstream port of MVLAN1.
   
5. After receiving the multicast stream, the device first duplicates the stream to service board 1 according to the multicast forwarding table of the control board, and then duplicates the stream to GPON port 1 according to the multicast forwarding table of the service board.

NOTE:

1. Though the SVLAN of a multicast user is different from the MVLAN, the device can still implement the mapping to the MVLAN according to the multicast member configuration relationship. In this way, cross-VLAN multicast is supported without requiring additional configuration.
2. The join flow for boards supporting the group filter mode is similar and only the forwarding entry index is different.

Join Flow [DSLAM]

Figure 2 Join flow

1. The multicast user switches a channel and sends a join message for demanding a new program GIP1.
   
2. After receiving the join message, the control board enters the IGMP protocol stack of the multicast user. After multicast control is implemented (for details, see "Multicast CAC"), the following group membership table is generated on the control board.
   

   Index	Online Member
   MVLAN1+GIP1	Multicast user 1

   At the same time, the following multicast forwarding tables are generated on the control board and the service board (for details on how to map GIP1 to GMAC1, see "Basic Concepts").
   

   Table 1 Multicast forwarding table on the control board

   Index	Duplication Destination
   MVLAN1+ GMAC1	Corresponding port on service board 1

   Table 2 Multicast forwarding table on the service board

   Index	Duplication Destination
   MVLAN1+ GMAC1	User port 1

   • According to MVLAN1 corresponding to the program, the service board serves as the proxy of multicast user 1 and sends a join message to the control board.
3. The control board then sends a join message to the multicast router through the multicast upstream port of MVLAN1.
   
4. After receiving the multicast stream, the device first duplicates the stream to service board 1 according to the multicast forwarding table of the control board, and then duplicates the stream to user port 1 according to the multicast forwarding table of the service board.

NOTE:

1. Though the SVLAN of a multicast user is different from the MVLAN, the device can still implement the mapping to the MVLAN according to the multicast member configuration relationship. In this way, cross-VLAN multicast is supported without requiring additional configuration.
2. The join flow for boards supporting the group filter mode is similar and only the forwarding entry index is different.
3. If the traffic with a high priority is suddenly overloaded and the service with a low priority is affected, IGMP packets are not discarded. The device processes and sends the IGMP packets first.

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