Scenario A: A host joins a multicast group (TV channel) which is not yet being received by other hosts on the router, and therefore, is not yet present in the proxy database. The 7450 ESS or 7750 SR adds the group to the proxy database and sends a new IGMP Join group-specific membership report upstream to the multicast router.
Scenario B: A host joins a channel which is already being received by one or more hosts on the router, and is already present in the proxy database. No upstream IGMP report is generated by the router.
Scenario C: The multicast router periodically sends IGMP queries to the router, requesting it to respond with generic membership reports. Upon receiving such a query, the router compiles a report from its proxy database and send it back to the multicast router.
In addition, the router floods the received IGMP query to all hosts (on SAPs and spoke SDPs), and updates its proxy database based on the membership reports received back.
Scenario D: A host leaves a channel by sending an IGMP leave message. If fast-leave is not enabled, the router first checks whether there are other hosts on the same SAP or spoke SDP by sending a query. If no other host responds, the 7450 ESS or 7750 SR removes the channel from the SAP. In addition, if there are no other SAPs or spoke SDPs with hosts subscribing to the same channel, the channel is removed from the proxy database and an IGMP leave report is sent to the upstream Multicast Router.
Scenario E: A host leaves a channel by sending an IGMP leave message. If fast-leave is not enabled, the router checks whether there are other hosts on the same SAP or spoke SDP by sending a query. Another device on the same SAP or spoke SDP still wants to receive the channel and responds with a membership report. The router does not remove the channel from the SAP.
Scenario F: A host leaves a channel by sending an IGMP leave report. Fast-leave is enabled, so the router does not check whether there are other hosts on the same SAP or spoke SDP but immediately removes the group from the SAP. In addition, if there are no other SAPs or spoke SDPs with hosts subscribing to the same group, the group is removed from the proxy database and an IGMP leave report is sent to the upstream multicast router.