r the average dura- tion of a wireless data session as we do for the average voice telephone call. We have to guess, however, and base our signaling capacity on our forecast call-processing load for the mix of services we expect on a third-generation (3G) CDMA system. The call-processing estimate is the best estimate of the call-processing activity based on the mix of services. The signaling workload estimate for call processing is the num- ber of ANSI-41 messages generated by that activity. 36.3 Roamers Virtually any user terminal activity sends ANSI-41 messages to and from the HLR. Registration, call activity, and short messages all involve the HLR no matter where the user terminal is. When the user terminal is served by an MSC other than its home MSC, then most activity also generates messages to the visitor location register (VLR). When we do our calculations to estimate roaming traffic, we think of the subscribers far from home using another wireless telephone system. As far as ANSI-41 signaling is concerned, any user terminal served by an MSC other than its home MSC is a roamer. This population of roamers depends on the number of MSC regions and how they are laid out. As we have more MSCs and more MSC regions, it is more likely for a user ter- minal to register or place a call as a roamer. Once we have an estimate of how many roamers our system will be supporting, we can use the message counts from Sec. 25.2 to estimate the total signaling load from roamers. The signaling load occurs in three main areas, MSC to HLR, MSC to VLR, and VLR to HLR. Each of these routes has message flows when roamers register, call, and send short messages. We should spend some time analyzing the patterns of subscriber roaming. People have different calling patterns and use their wireless telephones at different times of day. Commuters, travelers, and shoppers have different calling patterns, and we should take some time to form a clear idea about how that affects roamer activity levels. If an MSC region contains a major airport 