ged. How- ever, the 3x and multicarrier standards need to be fully developed and then tested in real-world situations. W-CDMA services at a bandwidth of 4.8 MHz or higher will be able to offer flexible higher data rate services up to 1.92 Mbps in increments of only 100 bits per second. 21.1.2 Data There are two challenges in developing data capacity. The first is to manage the ca- pacity of individual data channels to meet the data-rate requirements of subscribers while maintaining an acceptable error rate. With the data services supported by the Transmission Control Protocol/Internet Protocol (TCP/IP), the bit error rate (BER) can be relatively high because retransmission is acceptable. However, retransmission adds delay, and total delay limits may preclude a lot of retransmission even when TCP/IP is being used. See Chap. 29 for more on this tradeoff. Even so, maximum data rates are achieved in current technology only by creating DO carriers. This solution is far from optimal because it means reserving fixed bandwidth for data and different carriers' bandwidth for voice (or voice plus low-speed data). This misses the whole point of con- vergence, which is to obtain optimal capacity through the ability to allocate resources dynamically to either voice or data as needed. High-speed data services push the en- velope of the theoretical capacity of both CDMA and time division multiple access (TDMA). For this reason, the 3G standards allowed that the highest data rates would only be available within a limited radius of the base station and for stationary or slow- moving users, that is, users who are walking and not riding in a vehicle. Early 2G cel- lular systems offered data rates comparable with slow modems, under 9.6 kbps. 2.5G systems offered data rates approaching 64 kbps. The minimum speed that can be certified as 3G is significantly higher, at 144 kbps. As of summer 2002, the only detail standard that has attained this certification and is being deployed is cdma2000 1x EV-DO, which uses a DO channel. If the hig