ocks (FTBBs). Building the Network of the Future Geo-distributed Zones / DCP Strategy Virtual Machine DCP Multiple Geo Geo Location 1 Locations Load LCP Compute Balanced Host (Server) LCP Rack of Compute LCP Control Hosts (LCP) Datacenter / Central Office Geo Location 2 FIGURE 4.5 Fault-tolerant design of AIC zones. 4.4.3 INFRASTRUCTURE RESILIENCY As mentioned previously, the geographic dispersal of cloud zones is essential to provide the resil- iency needed to guarantee a constantly accessible network. This is done in large part to have the physical infrastructure deployed in close proximity to customers, to ensure best network experience and lowest latency. Aside from the geographical locations of the NFVI zones, the network design and physical infrastructure itself plays a large part in creating a resilient infrastructure. This starts with the use of fault-tolerant hardware, that is, redundant network cabling from the servers to the switches, dual power supply for the servers' multiple NIC cards, and Redundant array of independent disks (RAID) internal drive configuration in the servers. RAID is a method of pairing multiple drives together virtually, to improve performance, redundancy, or both. It is critical to have an "active-active" VNF configuration across zones. It is even better to have an active-active-active VNF configuration across zones. Active-active configuration uses data rep- lication built into the infrastructure to increase resiliency. The data are written to a data store and automatically replicated to two other geographic locations SO that it is simultaneously live in both zones and minimal latency would exist with the failover of single zone. A service provider can also deploy the core infrastructure software in a fault-tolerant manner. For example, OpenStack components, such as Nova, Cinder, Swift, Keystone, and Neutron, are deployed on different servers in the event that either the server or software component fails. In addition, other software such as network load balancers and continuous