e fan-out network of packet links is going to become a collec- tion of smaller fan-out networks gathering at several POPs. Generally, network plan- ning is more than proportionally simpler for smaller networks: It takes less than half the effort to design a network half the size. Thus we expect the planning effort for a piecemeal network with a backbone to be simpler, overall, than the full fan-out back- haul problem we saw earlier. We should make sure, however, that there is room on the backbone network for our wireless telephone transport. This may sound obvious, but it is possible to plan on us- ing the backbone for transport, to design the network with this expectation, and to find ourselves scrambling to find alternative transport from POP to POP because the back- bone is completely sold out. There also can be problems if the terminal equipment at the POP nearest our base station is completely full and does not have the ability to ac- cept new pipes. We know of one case where this actually happened during a major up- grade of an urban backhaul network. The backhaul network design with a transport backbone is still a fan-out network. The backbone gives us more structure and we can use that structure, to find simpler and faster heuristics. In this case, most of the simplicity is that the smaller subnet- works are easier to solve than one big fan-out network. We can use a heuristic for a backbone backhaul network. From each base station, find the cheapest link to a POP. As before, what is cheap depends on how we evaluate costs, as we discussed in Sec. 35.1. We add transport hops to the list of links for neigh- boring base stations and hops of one or two cells as before. We certainly do not need consider any link from a base station that costs more than the hop to a POP. We start our heuristic with the feasible solution of having every base station connected to the cheapest POP. As before, this is a reasonable solution by itself, and it is easy to ad- minister. Some providers may stop right here and decide that 