ted PLMN ID to the AMF as part of the tracking area identity (TAI) sent in the handover required message. The source AMF uses the TAI information supplied by the source NG-RAN to select the target AMF/ MME and to forward the selected PLMN ID to the target AMF/MME. The selected PLMN ID is signaled to the target NG-RAN/eNB SO that it can select target cells for future handovers. In a network slicing scenario, a network slice is defined within a PLMN. Network sharing is performed among different PLMNs and each PLMN sharing the NG-RAN defines and supports its PLMN-specific set of slices that are supported by the common NG-RAN [3]. 1.2 Reference Architectures 5G systems have been designed to support seamless user connectivity and to render new services/applications which would require deployment of networks that exploit innovative techniques such as NFV and SDN. A distinct feature of 5G system architecture is network slicing. The previous generation supported certain aspects of this with the functionality for dedicated core networks. In the context of 3GPP 5G system architecture, a network slice refers to the set of 3GPP defined features and functionalities that together form a complete PLMN for providing services to UEs. Network slicing allows controlled composition of a PLMN from the specified NFs with their specifics and provides services that are required for a specific usage scenario. The need for these new techniques is increasing due to the versatility of data services that are supported by 5G networks. Mobile networks were tradi- tionally designed as voice-centric and later data-centric systems; however, with 5G this design philosophy has changed as a result of proliferation of new use cases and applications. 112 Chapter 1 Having such requirements in mind, 3GPP attempted to maintain the premises of flat archi- tecture where the control-plane functions are separated from the user plane in order to make them scale independently, allowing the operators to exploit logical functional split for dimensioning in deplo