- works); any application developed for CDPD can be adapted to run on any IP- based network. The complete network specification for CDPD-including archi- tecture, airlink, network interfaces, encryption, authentication, network manage- ment, and security-is defined. Throughput is nominally 19.2Kbps, but 9.6Kbps is more common. CDPD looks like TCP/IP, which gives it some advantages, but it does require a specialized subscriber unit. Figure 14.2 shows a CDPD network. A mobile user has a CDPD subscriber device, typically a proprietary modem provided by the network operator. Incorpo- rated into the base station are elements such as a CDPD mobile data base station and a CDPD mobile data intermediate system (i.e., a router). The voice calls are Chapter 14 Wireless WANs Circuit Cellular Cellular Phone Cellular Antenna Laptop Modem Cellular Traffic Switched Telco CDPD Mobile Cellular Network Data Base Telephone Station Base Station Laptop with CDPD CDPD Mobile Subscriber Device Data Intermediate Router System (router) Network Figure 14.2 The CDPD network architecture switched out over the telco network, and the data traffic is sent over the CDPD router network. Packet Radio Packet radio data networks are an offshoot of Specialized Mobile Radio (SMR). They use licensed bandwidth and are built specifically for two-way data, not for voice communications. The data rates supported by packet radio range up to 19.2Kbps, but the norm is 9600bps. The best applications for packet radio include sessions that are short, as in Short Messaging Service (SMS), transaction processing, and, in some cases, e-mail; packet radio is not a solution for bulk file transfers or client/ server interactions. The key applications for packet radio include dispatching, order processing, airline reservations, financial services and banking, lottery, remote database access, messaging, point-of-sale, and telemetry. In the packet radio data network configuration shown in Figure 14.3, the end user has a mobile unit, a laptop, and a proprietary packet modem