 all those costs into a mathematical program and get an optimal solution for fan-out backhaul, at least one optimal for the specific base station layout being considered. Once the system grows and adds base stations, the solution needs to be reevaluated. We probably can afford to be a little more relaxed and consider only the more eligible hops. Connections between neighboring base stations should be on the fan-out candidate list along with connections two and three cells away. The list of fan-out backhaul con- nections also should include a direct connection from every base station to the MSC. Once all the possible hops are cataloged, we need to find out how much each hop costs. Because we expect to be bundling the packet links together as we get closer to the MSC, we need to know the link costs as a function of their capacity. As we discussed in Sec. 35.1, getting well-defined cost values for transport may be a difficult problem all by itself. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Backhaul Planning Backhaul Planning The idea is to form a daisy chain of packet links from base stations to the MSC. We can visualize a fan-out network as streams and tributaries merging into rivers, and we can visualize the transport network as packet flows from the base stations to the MSC. These are two-way packet pipes, of course, but we can visualize a one-way flow from base stations to MSC to see the design process more clearly. Each base station node in the fan- out network has a next node where all its packets are sent on their way to the MSC. We can approximate the mathematical optimum using a heuristic approach to solv- ing the fan-out problem. We tend to call a solution technique a heuristic instead of an algorithm when it is more like an approximation that gradually improves rather than a full solution for a large problem. In the case of a f