s. Reprinted with permission of John Wiley & Sons, Inc. Ron Nadiv the VP of Technology and Systems Engineering at Ceragon has written comprehensive book on Wireless Wireline and Photonic Networks published by John Wiley4 that treats the topic of microwave backhaul in substantially greater detail than attempted here. A supporting White Paper5 covers some of the same topics. A summary of some of the points made about topology is, however, useful and relevant. Most radio networks have a backhaul topology that is a combination of trees and rings, the tree being a combination of chain and star topologies, as shown in Figure 13.1. Star topologies use a separate link from a hub to each site, which is simple but requires longer radio links and line-of-sight for each link that may or may not be possible. Interference is also more likely as all links originate at the same point SO opportunities to achieve frequency reuse are limited. Chain topologies don't have these problems but if one link goes they all go, just like those cheap Christmas lights you bought last year. Putting the chain and star together produces a tree. In a tree topology fewer links will cause a major network failure and therefore fewer links require protection schemes (hardware duplication for example). Closing the chain produces the ring that provides the most protection. Ceragon then develop a test case in which ten cell sites each requiring 50 Mbps aggregate to a total of 400 Mbps with every link that supports more than one site being protected. The options are shown in Figure 13.2. The trade offs are as follows. The ring topology requires fewer microwave links but the links have to be higher capacity and use more spectrum, though since the ring has no more than two links to every node good frequency reuse can probably be achieved. The ring also requires some additional antennas but has inherently good availability due to the fact that a service failure would only occur when both paths fail. However, a ring will introduce additional latency and delay