hat a 30-second voice call and a stationary 30-minute high-speed data session use the same amount of HLR processing time. The mix of services tells us a lot about how busy the HLR is going to be. 34.6.2 Visitor location register (VLR) planning The VLR database size depends on where calls are actually happening. Some areas will have surges of roaming activity, whereas others should be steadier. We expect airports Superscript(3)In the United States, congressional districts are assigned to decide which communities are rep- resented by which seats in Congress. Politicians have chosen some very strange shapes for these regions to change congressional representation on key issues. This political process is called gerrymandering. 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 Planning for CDMA Capacity to have large surges of roaming activity when flights are late, we expect office build- ings to have medium-sized fluctuations at lunchtime or the end of the work day, and we expect shopping malls to have a fairly continuous stream of users from different places. Most of the VLR activity we envision is voice call activity, but a VLR may end up con- centrating on SMS or even data service. We have to look at the mix of services in the demand forecasts to form our best estimates of how much processing capacity a VLR needs. The VLR should be traffic engineered to serve its demand with very low blocking. When a VLR is slow, wireless service is slow. 34.6.3 Signal transfer point (STP) planning The signal transfer point (STP) required by Signaling System 7 (SS7) handles all sig- nal traffic from the public switched telephone network (PSTN) SS7 network, plus all traffic from all SMSCs and multimedia message switching centers (MMSCs) sending short messages, enhanced short messages, and multimedia messages. We need to es