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

Abstract 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.