made up of three or more sites, another term comes in to play called meshing. Networks are either fully meshed or 5 NETWORK ARCHITECTURE, FACILITIES, AND SERVICES partially meshed. The four-site network depicted in Figure 5-5 is classified as partially meshed because there is no direct path or link between sites 1 and 3 or between sites 2 and 4. Figure 5-6 shows a fully meshed four-site network. The difference in meshing has implications in terms of economics, reliability, and robustness. Economically, the partially meshed net- work connected in a round-robin fashion requires four links. A fully meshed network would require six links. The two additional links might increase the monthly charges for leased private line facilities by 50% when comparing a fully meshed, four-site network to a partially meshed network. Such a choice or decision is the eternal dilemma of network architects and designers. The way out of the woods requires economic analysis and judgment to resolve. Chapters 11 and 12 provide a process and tools for resolving tech- nical dilemmas with financial approaches. For now, simply note that two-site networks need not be concerned about meshing issues. Three-site networks require four links to be fully meshed, four- site networks require six links to fully mesh, and a five-site network requires 10 links. Figure 5-7 shows a five-site fully meshed network. As the number of sites in a network increase, the number of links soars, dramatically increasing complexity. The more complex network Site 1 Site 2 Site 4 Site 3 FIGURE 5-6 Four-Site Fully Meshed Network PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS Site 2 Site 3 Site 1 Site 4 Site 5 FIGURE 5-7 Five-Site Fully Meshed Network architecture becomes, the greater the need for more detailed documen- tation required to manage cost, reliability, robustness, and network performance. Another factor mitigating the need for fully meshed networks is use. For example, consider that when one site connects to another, it is for the purpose of pa