s use to determine how many seats they should sell at a discount and still have enough for the expected last-minute, high-price passengers. Minutes per Day Break Even Usage DS-1 Links Figure 26.6 Facilities capacity usage. 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. Capacity Calculations for Cellular Networks Capacity and Quality Principles The erfc function is the statistical cumulative distribution of the positive half of the normal distribution, the integral in Eq. (26.4): erfc(x) (26.4) This simplification ignores usage patterns by day of week and time of day. The aver- age demand for the connection may be two DS-1 links, but most of those calls are hap- pening during the 8-hour business day. It is the time-of-day concentration of traffic that makes the sixth dedicated DS-1 economical. 26.3.1 Capacity for roamer termination Termination of roamer calls is a busy time for a wireless telephone system. The ANSI- 41 signaling system sends messages, the HLR and VLR update their data records, the base station sends paging messages, and the user terminal responds so that the call can start. The signaling system, HLR, VLR, and MSC have all been designed to han- dle the workload of a roamer termination. The final stage is establishing a connection between the two MSCs for the call. It is the MSC-to-MSC connection where we may derive some economy from dedicated transport links. The wireless system engineer should identify MSC-to-MSC links with enough traffic to justify dedicated transport. While there may be large wireless sub- scriber communities in Bogota and Dhaka, few Bogota subscribers are going to be in Dhaka when somebody calls them. It does not make sense to maintain a dedicated transport link from Columbia to Bangladesh for the tiny traffic it would support. How- ever, a large wireless system in Chicago may have three or four MSCs serv