Downstream Multicast Forwarding

This section outlines the DPoE System and D-ONU requirements for downstream multicast forwarding. In the DOCSIS Network [MULPIv3.0], the DSID is used to restrict forwarding of multicast sessions through CMs with multicast clients that have joined the session, in a DPoE Network, the DSID is replaced by the mLLID.

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The DPoE System MUST assign mLLIDs to GSFs. The DPoE System MUST assign mLLIDs uniquely per MAC Domain.

In order to reach all of the members of an IP multicast session, the DPoE System MUST replicate the packet on the downstream channels of a MAC Domain. The DPoE System MUST forward IP multicast packets if the session has active group membership. Active group membership is determined by the presence of a multicast listener (client) behind a D-ONU.

8.2.2.1 Labeling Multicast Packets with mLLIDs

The DPoE System MUST tag all downstream multicast packets with an mLLID. The DPoE System signals the needed mLLIDs to the appropriate D-ONU. Packets with a known mLLID are received by the D-ONU and further filtered and forwarded to the set of CMIM-Interfaces (S interfaces) associated with this multicast session. Packets with an unknown mLLID are discarded by the D-ONU.

In [MULPIv3.0], each replication of an (S,G) IP multicast session to a particular Downstream Channel Set is assigned a unique DSID label within a MAC Domain. In DPoE Networks each GSF is assigned a unique mLLID within a MAC Domain. This is an important difference. In DOCSIS Networks, the DSID is unique to an individual (S,G) IP multicast session and in DPoE Networks, the mLLID is unique to the GSF. A GSF and the assigned mLLID can be used to forward one or many IP multicast sessions downstream.

8.2.2.2 Communicating mLLIDs, filtering and forwarding attributes to a D-ONU

The DPoE System is responsible for signaling to the D-ONU the required parameters for filtering and forwarding multicast traffic. This includes the mLLID and all of the associated filtering and forwarding parameters associated with each GSF. The process for communicating the required parameters for dynamic multicast sessions and static multicast sessions is described below.

After the DPoE System successfully authorizes an IP multicast session, the DPoE System MUST communicate the mLLID and required filtering and forwarding parameters to the D-ONU. The DPoE System MUST configure the D- ONU as defined in [DPoE-OAMv2.0] with the following filtering and forwarding parameters: mLLID, Source Address, IP multicast group address and client MAC Address. The client MAC Address sent by the DPoE System is based on the IGMP/MLD join messages for a particular IP Multicast session. The D-ONU uses this information to deduce the set of CMIM interfaces to which the multicast sessions is forwarded.

When a dynamic session is no longer active the DPoE System MUST communicate the mLLID, IP multicast group address and client MAC address for the inactive session as defined in [DPoE-OAMv2.0]. If the dynamic IP multicast session is no longer active on any of the CPE devices attached to the D-ONU, the DPoE System MUST direct the D-ONU to remove the mLLID and all associated filtering and forwarding parameters as defined in [DPoE- OAMv2.0].

For static multicast sessions, the DPoE System MUST configure the D-ONU as defined in [DPoE-OAMv2.0] with the following filtering and forwarding parameters: mLLID, Source Address, IP multicast group address and CMIM Interface. The CMIM interface sent by the DPoE System is specified in the configuration of the static multicast session. The D-ONU uses this information to identify the set of CMIM interfaces used to forward the multicast traffic associated with an mLLID. When a static session is removed the DPoE System MUST communicate the mLLIDID, IP multicast group address and CMIM interface for the inactive session as defined in [DPoE-OAMv2.0] mLLID based Filtering and Forwarding by a D-ONU The D-ONU filters the downstream IP multicast packets based on the mLLID, Source Address and IP Multicast Group Address that it has been configured to process. The D-ONU MUST discard all multicast packets that do not match a configured mLLID, source address and IP multicast group address.

The D-ONU MUST replicate filtered IP multicast packets only once on each based on the D-ONU’s CMIM interface map. The D-ONU CMIM interface map is the union of CMIM interfaces with active multicast session members based on the configured static and dynamic multicast sessions. If the D-ONU does not have any CMIM interfaces associated with the filtered IP Multicast packet, the D-ONU MUST discard the received multicast packets.

The DPoE System determines which GSF to transmit downstream local network control [DPoE-IPNEv2.0] and link- local multicast packets based on the destination multicast address.

Downstream local network control packets addressed to the all hosts multicast address and link-local multicast packets addressed to the all nodes address MUST be transmitted by the DPoE System on the multicast control traffic GSF and the associated mLLID for each IP(HSD) and multicast serving group. The DPoE System MUST support the downstream forwarding of the local network control and link-local multicast control protocols on the multicast control GSF based on the serving group configuration as specified in [DPoE-IPNEv2.0].

For packets that are destined to a multicast group specific address, the DPoE System MUST signal the appropriate mLLID to only the D-ONUs with active membership in the associated multicast group. The DPoE System MUST forward all downstream local network control and link-local multicast packets addressed to specific multicast group addresses on the same mLLID assigned by the DPoE System for the multicast data for this group address.

Downstream local network control and link-local multicast packets addressed to a specific multicast group address are not transmitted on the multicast control traffic GSF or the associated mLLID.