Aiming at the problem that BitString can not represent all Bit-Forwarding Routers (BFRs) in large-scale Software Defined Networking (SDN) multicast based on Bit Index Explicit Replication (BIER) due to the limited length, this study designs a Hierarchical Domain (HD)-BIER model and devises its construction algorithm.

The HD-BIER model is a multi-layer BIER network composed of multiple small-scale Sub Domains (SD), which enables BIER to support a number of devices exceeding the capacity of the BitString representation in large-scale networks. The proposed HD-BIER construction algorithm takes into account the BitString Length (BSL) limitation, link lengths between nodes, and network connectivity. It leverages the concept of community partition algorithms and introduces a modularity function based on node similarity as an evaluation metric for BIER SD partitioning. The construction follows a bottom-up approach to dynamically build the HD-BIER network.

The simulation results show that the HD-BIER construction algorithm can effectively construct HD-BIER networks that exceed the BSL limit in either simple networks or the complex networks with a large number of nodes. Additionally, the resulting HD-BIER model not only ensures normal transmission of multicast service data flows through the gradual encapsulation and decapsulation of BitString layers but also maintains SDN multicast communication performance throughout this process.

The simulation results validate that the proposed HD-BIER model presents an effective multicast service support solution for even larger-scale networks.