Comparing tree and chain topologies for designing resilient backhaul access network

Abstract

Long-reach passive optical networks (LR-PONs) have been proposed as an economically viable solution for FTTH network architectures. The longer reach allows it to bypass local-exchange (LE) sites. This results in the elimination of the processing of electronic traffic at the metro nodes and the need for a dedicated metro network. Consequently the functionalities of metro and core nodes are merged into metro-core (MC) nodes. An MC node is connected to tens of thousands of end-users via local exchange (LE) sites. Thus any cable cuts or MC node failures can affect tens of thousands of customers. Therefore, each LR-PON is connected to two MC nodes. In this paper we compare two topologies, tree and chain, to interconnect MC nodes and LEs. The tree topology uses cable splicing and allows cable sharing to reduce the cost. In the chain topology a set of exchange-sites are part of a chain whose end-points are two MC nodes. We study these topologies by modelling each one of them as a combinatorial optimisation problem, and present our findings by analysing national networks for the UK and Italy.