ivision multiple access (CDMA) air-interface resource and comparatively little MSC processing, so an increase in MMS might relieve the MSC processor for the voice call traffic it is displacing. 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) Growth Increasing Capacity The total DS-1 or E-1 connections on the MSC are increasing as we add backhaul for more cells. Growing activity also increases the transport needs to the public switched telephone network (PSTN) for voice traffic and to the public packet data network (PPDN) for data traffic. It is also important to remember that higher traffic levels beget higher inter-MSC handoffs levels, and the transport links between MSCs also may have to expand to meet this need. Finally, we may want to increase inter-MSC trans- port for cost reasons when there is an increase in mobile-to-mobile calls or roamer ter- minations within the system, as described in Sec. 37.1.2. As we said in Sec. 34.1.2, transport is a relatively deterministic item. Once we have done the traffic engineering and determined how much transport we need, we can make sure that the MSC has the required equipment to support that transport. As the number of voice calls increases, so must the amount of circuit switching in the MSC. The introduction of third-generation (3G) services can push subscriber demand away from voice and actually might reduce the voice calling load. It is more likely that voice and data service will both grow, and it is up to us as planners to make sure that the MSC circuit-switching equipment can handle the voice calls. The number of speech coders in the MSC also increases with the amount of voice calling. There is a subtle dif- ference that could be affected by changing call patterns. The circuit-switching activity depends on the total number of calls, whereas the speech-coding usag