11.7 IP Multicast access

29.0613GPPInterworking between the Public Land Mobile Network (PLMN) supporting packet based services and Packet Data Networks (PDN)Release 17TS

NOTE: This section is applicable only to GERAN and UTRAN.

The Packet Domain could allow access to IP Multicast traffic coming from an external network. The support of IP‑Multicast in the Packet Domain is optional.

In order for the Packet Core Network to support Multicast traffic that will allow the MS/UE to subscribe to multicast groups from outside the PLMN, the GGSN/P-GW shall support IGMP (IPv4) and/or MLD (IPv6) and one or more Inter-Router Multicast protocols, such as DVMRP, MOSPF, or PIM-SM.

IGMP/MLD is an integral part of IP. All hosts wishing to receive IP multicasts are required to implement IGMP (or equivalent) and class-D IPv4 addresses or MLD and IPv6 multicast according to RFC 2710 [48]. IGMP/MLD messages are encapsulated in IP datagrams.

To be able to deliver IP-Multicast packets to the appropriate Tes, the GGSN/P-GW may have an IP-Multicast proxy functionality.

The IP-Multicast proxy will perform the following tasks:

NOTE: In this example it is assumed that IGMP/MLD is used as a Host-Router Multicast protocol.

– maintain a list of mobiles that joined one or more Multicast groups. This list is built/updated each time the GGSN/P-GW receives an IGMP Join or MLD Report message from the mobile;

– send, based on this maintained list of mobiles, multicast routing information to the routers attached to the Packet Domain, allowing them to route multicast packets;

– upon reception by the GGSN/P-GW of multicast packets, make and send a copy as Point-to-Point packets, to each mobile of the group.

IP-Multicast traffic can only be handled after an MS/UE has attached to the Packet Domain, and a bearer (e.g. Activated PDP context(s)) (including possibly authentication) pointing to the preferred ISP/external network for this purpose. The Multicast traffic is handled at the application level from a Packet Domain perspective and is sent over UDP/IP.

Figure 12 depicts the protocol configuration for handling Multicast traffic (control plane) for the non-EPC based domain case. The Multicast traffic handling affects the GGSN by the introduction of the IP-Multicast proxy and the support for an Inter-Router Multicast protocol and a host-router multicast protocol. If the protocol configuration for handling Multicast traffic (control plane) is applied for Sgi (i.e EPC based packet domain), the P-GW has the functionality of GGSN and Sgi corresponds to the Gi in Figure 12.

Figure 12: Protocol configuration for IP-Multicast handling (control plane)