 switch to something else. The MSC has links to base stations, the public switched telephone network (PSTN), the public packet data network (PPDN), private networks, the ANSI-41 signaling network, other MSCs, and itself via loopback trunks. This is a deterministic calculation, the total of all the links compared with the total communi- cation capacity of the switch, as discussed in Sec. 24.2. We can take the total of all of these, with some proportional estimate for inter-MSC transport, and divide that by the maximum transport capacity of one MSC. This gives us another lower bound for the number of MSCs we need. 34.1.3 Circuit switching The circuit-switching load of a telephone switch is the number of voice call actions de- scribed in Sec. 24.3. The total voice call activity divided by the maximum voice call ac- tivity for one MSC gives a lower bound for the MSC count. If 3G realizes its promise of an increasing share of data service calls, then the circuit-switching limitation of an MSC should recede in importance. Real-time video may be circuit switched at the MSC, but the high data rates required for it should keep the number of real-time video calls small compared with voice calls. For example, it is the number of calls being switched 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. Mobile Switching Center (MSC) Planning Mobile Switching Center (MSC) Planning that taxes the circuit-switching resources of an MSC, not the quantity of data in each call. 34.1.4 Speech coding The speech-coding load described in Sec. 24.5 is another load we must consider in esti- mating the number of MSCs required. We divide the total speech-coding load by maximum number of speech coders at one MSC. 1 We should add a small fraction quotient for the Erlang-B traffic engineering required for the speech coders to get a speech-coding lower bound for the MSC count. 