15 Interworking with DN (Multicast Routing Protocol)

29.5613GPP5G SystemInterworking between 5G Network and external Data NetworksRelease 17Stage 3TS

15.1 General

The 3GPP network support IPTV multicast packets transmission over PDU Session as specified in 3GPP TS 23.316 [43] clause 7.7.1. When support of multicast routing protocol is provided at the N6 interface, different techniques may be used.

15.2 DN interworking Model of UPF for PIM

If PIM (Protocol-Independent Multicast) is used as Multicast Routing Protocol, including PIM-SM (Protocol-Independent Multicast-Sparse Mode, IETF RFC 7761 [44]) and PIM-DM (Protocol-Independent Multicast- Dense Mode, IETF RFC 3973 [45]), are commonly used to efficiently routing multicast groups that may span wide-area (and inter-domain) internets.

UPF acts as the PIM router which is clostest to UE and receive multicast packets originated from multicast source via perform PIM function. Based on local policy, UPF support either PIM-SM or PIM-DM or both.

UPF shall acts as PIM router used for interworking with the IP network as illustrated in figure 15.2-1.

Figure 15.2-1: The protocol stacks for the N6 reference point for PIM

PIM function in UPF shall interacts with PIM routers in IP network.

– In case of PIM-SM, PIM router in UPF acts as DR (Designated Router) which is clostest to UE and send register message to RP (Rendezvous Point). It receive multicast packets over shared tree from RP. Refer to IETF RFC 7761 [44] for more details.

– In case of PIM-DM, PIM router in UPF sends Upstream Prune Messages to indicate that designated multicast traffic is not desired, It sends Upstream Graft message to re-join a previously pruned branch to the delivery tree. Refer to IETF RFC 3973 [45] for more details.