# Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency
## 1 Introduction  
The fortified multimedia applications, in addition to wider bandwidth appeal and real-time service, request immense rise in the intercommunication area. This incites service suppliers to find a highly effective method to meet the access arena requirements, which eradicates network failure and distance. Previous research has been interested in the passive optical network (PON) to address the \"last mile\" obstruction matter in the future generation of fiber access networks. PON does not incorporate active components with the signal pathway and is designed for point-to-multipoint. PON supplies the privilege, comprising coverage to long-reach transmission, wider bandwidth and reduced fiber deployment within the loop and local exchange. Moreover, PON network incorporation permits several splitting points that offer various customers access to the flexible topology. The hybrid topology is based on wavelength division multiplexing (WDM), time division multiplexing (TDM), optical code division multiple access (OCDMA) and orthogonal frequency division multiplexing (OFDM) [1,2]. Recently, TDM-based PON standards, such as gigabit ethernet PON (GE-PON) and gigabit PON (G-PON), are major in distinct countries. However, due to the whole bandwidthrange being shared among different customers in the system, every customer receives access to a restricted transmission rate, frequently condensed to Mbit/s. Presently, the request for large bandwidth is growing quickly because of the advent of modern multimedia apps such as video-on-demand services with online gaming. Thus, upgrading and developing the latest technologies is essential to adapt to the latest applications. Amongst the several PON technologies, time and wavelength division multiplexing PON (TWDM-PON) has been chosen as the preferred topology for next-generation PON (NG-PON) as it sustains backward compatibility, static sharing and flexibility. Additional advantages consist of a high transmission rate, stability, protocol transparency, cost-effectiveness and dedicated connectivity [3; 4]. Though, multipoint transmission is handled by some addressing prime factors such as network resilience and failure management. Several approaches were presented for TWDM-PON to form possible communication, such as tree, bus, ring and wheel-based structures. Conventionally, the TWDM-PON is utilized in a tree or bus fashion. However, a link break or failure can interrupt the whole network by deactivating the optical line terminal (OLT) from optical network units (ONUs). The majority of limitations emerge from the topology of the network and be unsuccessful to employ the possible network resources effectively from mildly loaded, idle channels or customers to the highly loaded channels in the PON network. Additionally, the growing demands for huge bandwidth to handle upcoming heavy data traffic of the network access domain cannot be obtained along with the incorporation of conventional tree-based TWDM-PON. Furthermore, mapping a multi-star architecture in TWDM-PON is accessible by implanting a sequence of power splitters. The primary disadvantage of utilizing single star-based TWDM-PON is high preliminary installation expenditure because of the integration of multiplexer (MUX) and de-multiplexer (DEMUX) for each star. Moreover, ring topology was presented to reduce the cost of settling superfluous paths in conventional PONs. However, ring-based TWDM-PON generates needed reliability at average costs, and the inclusion of passive optical couplers between OLT and various ONU units raises critical power problems which inhibit the network capacity. Additionally, the hybrid topologies, i.e., the mixture of tree-star, tree-ring, ring-star or star-tree-ring, improvised TWDM-PON network capacity, redundancy and credibility while strengthening the network complexity. The recent work focuses on investigating and profiting from reliable topologies, especially for TWDM-PON, to build reliability in fast access networks.