ibed in Chapter 4. In this architecture what was a vertically integrated packet edge is now dis- aggregated into three major modular subsystems: (1) network fabric hardware, (2) edge VNF service software running on servers, and (3) control software. This will be covered in more detailed in the following three subsections. 12.4.2 NETWORK FABRIC The first major component in the disaggregated packet edge platform is the network fabric. The most common network fabric topology is the Clos architecture (Clos 1953). The premise of this Building the Network of the Future Central Office / Data Center vEdge Soltware A'C Platform IPDSLAM (x86) Access Ethernet Fabric Gray/ ROADM/OA Aggregation Cilicont Ontics Metro/ Intercity Core FIGURE 12.3 Disaggregated network function. Northbound API Orchestration & Traditional Control (ONAP) Evolution Proprietary Network API Open Standard Proprietary Control & Services Open Standard Mgmt. (VNFs) (including data models) os & Network Proprietary Control Software Swappable Open Standard Proprietary Hardware Merchant Silicon Switch, x86 FIGURE 12.4 Moving to open standards for the network cloud. architecture is to optimally synthesize very large switches by using multiple stages of smaller switch components. This architecture is named after Charles Clos, a Bell Labs researcher, who in 1952 established the mathematical theory behind optimal multistage switches. It has been used in tra- ditional voice, private line, frame relay, ATM, Ethernet switches, and IP routers. Clos is also the primary architecture used in modern intra-data center switching to interconnect servers/storage and is central to the concept of the "scale out," or pay as you grow, networking strategy to scale existing network fabrics to achieve higher packet throughput requirements over time. While Clos is used for intra-platform and intra-data-center, it is not well adapted to inter-data-center or inter-central-office due to outside plant fiber topologies and layer 1 wavelength cost structures where partial mesh topologies 