For initial implementations, session data may be maintained in the state persistent database to enable maintenance of stable calls for intra- VNF CSCF failures only. Long-lived data are separated into a state persistence database for the VoLTE AS for better reliability. Service Platforms 14.4.1.3.4 Scalability at VNF Level An emphasis on N+K local redundancy is applied to enable horizontal scalability of VNFs, reduce the capital expenditure, and increase site-based reliability for VNFs where possible, including the CSCF and VoLTE AS. This also enables services to be massively scalable where a specific VNF can be scaled as needed, independent of other VNFs. 14.4.1.3.5 Resiliency An emphasis on N+K georesiliency is applied to reduce the capital expenditure and overprovision- ing of network functions. There is a heavy emphasis on software-based recovery of service VNFs from cloud failures. All VNFs support either 1 + 1 or N + K local redundancy. Locally at a site, the VNF VMs are distributed across multiple availability zones using anti-affinity rules for additional resiliency. In addition, the number of sites that a service is distributed at accounts for cloud hard- ware and software upgrade downtimes to ensure meeting the overall reliability needs of a service. As additional cloud sites become available, virtualized IMS service VNFs can be deployed in a much more distributed fashion at a greater number of sites. 14.4.1.3.6 Smaller Failure Domains Virtualized IMS service platforms will take advantage of broad cloud deployments to deploy smaller VNF pools or clusters at each site, SO that each site will support a smaller number of subscribers, thus limiting the impact of a site failure. It also enables the services to be massively scalable. 14.4.1.3.7 National Subscriber Provisioning Subscriber databases will implement a "National Subscriber Provisioning Distribution" model to minimize stranding of capacity and allow more efficient use of database resources. 14.4.1.3.8 Maintaining Quality of Service Differentiated s