ny use is subject to the Terms of Use as given at the website. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Chapter Special Situations To wrap up our discussion of planning code division multiple access (CDMA) networks, we need to examine two more issues. In telephony, there is a traditional assumption that the demand is the same in both directions. However, with the advent of third- generation (3G) data services and future video services, we will encounter asymmetric demand that will require planning for different capacity requirements in each direc- tion. The second special situation is the case where a CDMA service provider is enter- ing a new market. The combination of startup costs, the need to gain and maintain competitive advantage, and the unpredictability of demand creates a real challenge for making the business case for a new network and then implementing that network profitably. 38.1 Asymmetric Demand Cellular voice traffic is symmetric traffic on the air interface. The number of bits in the forward and reverse directions should be nearly the same for a voice conversation. 1 Data services may not have the same symmetry. Consider a wireless Web surfer, for example. The reverse link sends a Uniform Resource Locator (URL), and the forward link sends a Web page. Eighty bytes are sent in the reverse direction, and 80 kilobytes come back in the forward direction-and then the process repeats itself. The flow of bits for subscribers using the Internet in this fashion is highly asymmetric, favoring the for- ward direction. The asymmetry can go the other way, however. Suppose that we have a community of wireless multimedia message service (MMS) subscribers sending pictures to their landline "cyberfriends" on the Internet. Or suppose that we have a Web server that is itself a wireless data terminal. Then the flow of bits would be similarly skewed, but 1We can scratch our heads and come up with some exceptions. For example, subscribers calling in for recorded messages of some sort would punch two or three Touch