MPLS-Enabled Applications: Emerging Developments and New Technologies

10.3. mVPN - PROBLEM DECOMPOSITION

Figure 10.1 shows the conceptual model of multicast in a VPN. Two VPNs, VPN A and VPN B, are shown. For simplicity, we assume that PIM-SM in the SSM mode is used within each VPN. A multicast source in site S of VPN A is sending traffic to receivers in sites R1 and R2 of the VPN. This delivery of traffic can be decomposed into three stages. First, the traffic must be delivered from the source to PE1. Then, it must be delivered from PE1 to PE2 and PE3, and finally from there to the appropriate CEs, CE4 and CE3. The same decomposition applies when a source in site S of VPN B is sending traffic to receivers in sites R1 and R2 of VPN B.

In order for the source in site S to send multicast traffic to receivers in sites R1 and R2, receivers in sites R1 and R2 must inform the source about their desire to receive the multicast traffic from the source. Propagation of this information from the receivers towards the source could be decomposed into three steps. First, this information must be delivered from the receivers to the PEs connected to the sites that contain the receivers - PE2 and PE3 in our example. Then, this information has to be propagated to the PE connected to the site that contains the source, PE1 in our example. Finally, this information has to be propagated from that PE to the source itself.

Figure 10.1. Forwarding multicast traffic in a VPN

From a routing point of view, the first and the third (last) step in the above decompositions ...