ber of calls. In such a case, what matters is that at least one of those calls gets through. However, there is a possibility that, simultaneously, there will be another emergency in the same area, perhaps a medical emergency inside a house, where only one caller is dialing 911. That call also must get through. In planning for capacity for emergency access, we also need to take two other factors into account: We must support all cellular telephone calls, even from unregistered user terminals, and we must ensure enough capacity to allow real calls to get through even while allowing for the possibility of prank or nuisance calls to emergency services. 37.2.2 Data transport to the PPDN The total data service traffic from the MSC is a little harder to predict than voice traf- fic because we do not have a 20-year history of wireless data service or other services, as we do with cellular voice service. However, the estimates we made earlier for count- ing cells and the assignment we made of base stations to MSCs should give us a good idea of the volume and quality-of-service (QoS) requirements of packet data services. We start with the real-time packet data services and add up their total rates. This list of services includes two-way video calling and any data service with a very low de- lay requirement. The low delay requirement may be in a service-level agreement (SLA), or it may be a planning decision to offer high-quality service. The top tier of packet ser- vices is defined by the services that require the lowest amount of delay. We want to 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. MSC Transport Planning Planning for CDMA Capacity count the services going from the MSC to the PPDN so that we can eliminate from con- sideration those services which we can offer directly from an Internet Protocol (IP) node in the base station, as described i