s real-time voice or video, delayed packets are no better than lost packets. The requirement of adequate backhaul capacity still leaves room for some traffic en- gineering on the packet links. Unlike conventional reuse systems (FDMA or TDMA), a Station Figure 26.1 Backhaul base station-to-MSC network. Downloaded from Digital Engineering Library @ McGraw-Hil (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. Capacity Calculations for Cellular Networks Capacity Calculations for Cellular Networks CDMA cell cannot use all the capacity of all the sectors. 1 Even at maximum CDMA power levels, full capacity, there is a statistical distribution of backhaul data load, and we can do some packet data traffic engineering to manage the cost of backhaul trans- port. We want to make sure that the backhaul link is engineered for very low packet delay. For real-time voice-link packets, we want to see almost real-time service because packets delayed more than a few milliseconds are treated as blocked. This blocking rate should be kept down in the range of 0.02 percent, far lower than the blocking levels in deploying base stations and radio links. Once the packet pipe sizes are determined for each base station, we have the more complex problem of building a transport network to get all these packets to the common MSC. 26.1.2 Graph theory We model a transport network as a set of nodes or vertices2 connected by arcs or edges. Such a collection of nodes and arcs is called a graph. 3 The study of these graphs called graph theory, and this is part of a bigger field called combinatorial mathematics, or combinatorics for short. Graph theory is a field of mathematics rich in useful optimization insights. Modeling a practical problem as a mathematical graph allows us to use these theoretical insights to find practical solutions. The variables in these problems can number in the millions, and combinatorial optimization is a power