 variation that might affect synchronisation signals and traffic latency. However, some of the tree links have lower bandwidth than those in the ring, which may introduce delay variation. Statistical multiplexing is more effective in a ring topology as the total capacity of the links in a ring is usually greater than the links in the branches of a tree. Rings are, however, more expensive to upgrade as each link needs an identical upgrade. A practical example is then given of a Latin American operator transitioning from a TDM network to an IP network. Each cell site requires 45 Mbps of bandwidth for Ethernet traffic with additional E1 lines (2.048 Mbit/s supporting 32 by 64 kilobit voice channels). All wireless links were required to have hardware redundancy. 4 http://onlinelibrary.wiley.com/doi/10.1002/9780470630976.fmatter/pdf. http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470543566,descCd-description.html http://www.ceragon.com/files/Ceragon_Wireless_Backhaul_Topologies_%20Tree_vs_%20Ring_%20White% 20Paper.pdf. Wireless Core Network Hardware Ring + Tree 50Mbps 100Mbps 200Mbps Ring 200Mbps all links 200Mbs 1+0 100Mbps 50Mbps 400Mbps 400Mbps 400Mbps Ring 400Mbps all links 400Mbs 1+0 50Mbps 200Mbps 100Mbps 200Mbps Ring all links 200Mbs 1+0 100Mbps 50Mbps 16 radio terminal pairs 12 radio terminal pairs 11 radio terminal pairs 4x 50 Mbps 12x 200 Mbps 11 X 400Mbps 8x 100 Mbps 4x 200 Mbps 20 antennas 24 antennas 22 antennas Maximum 3 radio hops Maximum 5 radio hops Maximum 10 radio hops Figure 13.2 Aggregation topologies test case. Reprinted with permission of John Wiley & Sons, Inc. An analysis suggested that the shift towards Ethernet improved the Capex and Opex eco- nomics of the ring topology compared to other options and offered better resiliency. The ring topology is combined with ring-based protection using the Rapid Spanning Tree Protocol. Apparently, this meets the Next Generation Mobile Network requirement of path restoration within a range of 50 to 250 milliseconds. The other wireless option briefly re