italengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Adding Transport Adding Transport ages at the press of a button. These services send their packets along a route from the base stations through the MSC to the public packet data network (PPDN). The size of the MSC-to-PPDN link depends on the sizes of the markets for these features. The big selling point of 3G is data service, particularly high-rate data service. If the market develops as the 3G promoters say it will, then the packet data flow from the MSC to the PPDN is going to grow very rapidly as subscribers sign up for data service. Along with an interest in wireless data, the current interest in short message service (SMS) could migrate into a similar interest in MMS, and the packet data link could start carrying a lot of cell phone snapshot image files. It is not at all clear that there is a big market for these features. Landline data pop- ularity has relied on the low cost of data service, particularly the low incremental cost. The home data user typically pays a flat monthly fee and no extra money for more data activity. People pay a premium for wireless telephone service so that they can make and receive telephone calls in a lot of different places. We will have to wait to see if peo- ple have a similar desire to use data service in enough different places to pay a pre- mium for wireless. For wireless data service to succeed, it must offer its subscribers high enough quality of service (QoS) that they continue to use it. If the data market develops, then we want to make sure that the MSC-to-PPDN packet pipe has enough capacity. Few things dampen subscriber enthusiasm for a new, premium service than not being able to use it. The rush can come fast as people find out their neighbors have wireless laptops and they run out to buy their own. The wire- less service provider has to watch the market and be prepared to add packet capacity on short notice. As