Multicast Program Leave

To leave a multicast program, a user sends to an IGMP-capable BRAS an IGMP Leave message. Figure 1 illustrates the process of the multicast program leave. The key actions during this process are described in Table 1.

Session-based multicast replication is used in the following illustration of the multicast program leave process. Multicast program leave processes of other multicast replication modes are similar to that of session-based multicast replication.

Figure 1 Multicast program leave process
Click to enlarge

**Table 1** Key actions in each multicast program leave step
Step	Device	Key Action
	STB	To leave a multicast program, an STB user sends to an IGMP-capable BRAS an IGMP Leave message. Upon receipt of the message, the BRAS identifies the user and the multicast program that the user wants to leave.
	BRAS	The BRAS sends an IGMP Query message to members in the multicast group specified in the IGMP Leave message it received. (If IGMP Prompt-Leave is configured, this step is skipped.)
	BRAS	The BRAS deletes the multicast forwarding entry of the STB user only if there are other members in the same multicast group. (If IGMP Prompt-Leave is configured, this step is skipped.) NOTE: If the STB user is not a member of any multicast group, the BRAS stops sending IGMP Query messages to the STB user after the robustness variable value is reached.
	BRAS	The BRAS stops sending to the STB the multicast traffic of the corresponding multicast group it joined.
	BRAS	If there is no member in the multicast group after the STB user leaves, the BRAS sends a PIM Graft message to the RP or source's DR to stop the multicast traffic replication to the group.
	RP/source's DR	The RP or source's DR stops the replication of multicast traffic to the BRAS, ending the STB user leave process.