To improve the reliability and scalability that are very important for large-scale all optical fiber sensor networks
(AOFSN), three-level hierarchical sensor network architectures are proposed. The first two levels consist of active
interrogation and RNs, respectively. The third level called sensor subnet (SSN) consists of passive FBGs and a few
switches. As AOFSN is mainly multiplexed by wired and passive FBGs, the routing algorithm for scanning sensors is
determined by the virtual topology of SSN due to the passivity. Therefore, the research concentrates on the construction
of SSN and aims at proposing regular and unicursal virtual topology to realize reliable and scalable routing schemes.
Two regular types of SSNs are proposed. Each type consists of several sensor cells (SC), square-based SC (SSC) or
pentagon-based SC (PSC) and is scaled several times from the SCs. The virtual topologies maintain the self-similar
square- or pentagon-like architecture so as to gain simple routing. Finally, the switch architecture of RN is proposed for
the reliability of the first two levels; and then, the reliability and scalability of SSN are discussed in view of how much
link failures can be tolerant, and how each SC is scaled to maintain the self-similarity, respectively.