can be aggregated into a single digital stream so that the subscriber can see data rates as high as 114 kbps. Packet services provide direct digital links through a service called cellular digital packet data (CDPD) from the subscriber to a public packet data network (PPDN) such as the Internet. The wireless telephone system conserves its air-interface resources by putting inactive packet users into dormant states where they temporarily cannot send or receive packets. Voice or circuit-switched data can be sent while the packet service is dor- mant. Simultaneous voice and data on the same traffic channel are supported for sub- scribers with user terminals equipped for this capability. These services are supported even when the user terminal is handed off to another mobile switching center (MSC). 10.1.2 cdmaOne speech coding The speech coder used in cdmaOne is the code excited linear prediction (CELP) de- scribed in Sec. 18.2.1. The standard IS-96A speech coding for cdmaOne is RS1, 8.55 kbps. Two enhanced modes are offered, the enhanced variable-rate codec (EVRC) using RS1 and the 13-kbps speech codec developed by the CDMA Development Group (CDG) using RS2. A codec is a speech coder and decoder the same way that a modem is a data modulator and demodulator. EVRC is a more sophisticated version of CELP that reduces the number of bits re- quired for its linear predictor coefficients and pitch synthesis, so it has higher voice quality at the same 8.55 kbps as the original IS-96A coding, as shown in Table 18.2. RS2 is a higher-quality, higher-bit-rate CELP speech coding system. While it sounds even better than EVRC, its higher bit rate of 13 kbps reduces the capacity of a cdmaOne system by 40 percent compared with IS-96A or EVRC. All these speech coders have multiple rates depending on the subscriber's speech pat- terns. When the speech pattern is less complex, they go to rate one-half. IS-96A and 2This process is repeated until the packet is error-free or the error continues beyond a prede- termined number of transmiss