Hard-state Protocol Independent Multicast—Source-Specific Multicast (HPIM-SSM)

Source-specific multicast is a key technology for multicast services such as IPTV broadcasting, which relies on IGMPv3/MLDv2 for source-group membership signalling and multicast routing protocols such as PIM-SSM for building and maintaining receiver-initiated source-based distribution trees across the network. The authors propose the Hard-state Protocol Independent Multicast—Source-Specific Multicast (HPIM-SSM), a novel multicast routing protocol that keeps the design principles of PIM-SSM but overcomes its limitations, such as slow convergence and the possibility of creating suboptimal trees. The state machines of HPIM-SSM were designed to react promptly to all network events susceptible to reconfiguring the multicast trees, avoiding the need for soft-state maintenance through the periodic transmission of control messages. Moreover, the authors eliminated the need for designated routers, which led to suboptimal trees, and introduced a control-driven assert protocol that operates per source, allowing for considerable memory savings. Finally, the protocol enables the coexistence of multiple unicast routing protocols. HPIM-SSM was implemented in Python, and its correctness was extensively validated through model-checking techniques. Furthermore, a comparison between HPIM-SSM and PIM-SSM was conducted, encompassing both theoretical analysis and experimental evaluation of convergence times. The results demonstrate clearly that HPIM-SSM outperforms PIM-SSM, exhibiting significantly faster convergence times and completely avoiding suboptimal trees.