oud as well as the virtualized applications mature, VF architectures will migrate toward cloud-optimized implementations. This will result in more cost-optimized VFs with higher availability. 5.4.1 EXAMPLE: STATEFUL NETWORK ACCESS SERVICES Consider the example of a stateful function that might be typical of a layer 2/3 access or trans- port service, such as switched Ethernet or managed Internet services. Such services could consist of customer-managed premises equipment (CPE) connected through a metro mesh network to a Building the Network of the Future TABLE 5.2 VF Categorization Expected Typical VF Category Characteristics of High Availability Solution Availability Range No site failover, no Limited by availability of a single availability zone within a site; <3-9s local redundancy availability bound by worst-case physical infrastructure, compute, and store availability Improvements to infrastructure availability may be required to achieve target availabilities Local redundancy Takes advantage of local redundancy 3- to 4-9s with no site Availability bounded by physical infrastructure and the degree of failover redundancy and replication for compute/store within a site May be able to take advantage of dual control planes and multiple availability zones within a site Stateful function VFs designed to operate using georedundancy 4- to 5-9s with site failover Data replication solutions to maintain state across multiple instances within and across sites Failure detection and failover often addressed by the VF (do not rely on Cloud or ONAP capabilities) Stateless function VFs can be easily distributed across multiple sites >-5-9s with site failover Load balancers and protocol-level retries can be used to mitigate the impact of site failures Can achieve extremely high availability even when infrastructure availability is low provider-managed edge router (PER). A common way to implement these L2/3 services is to home the CPE to a particular PER port. These services fall into the category of "no site failover with local