(Cellular Digital Packet Data) A low-speed, digital, wireless data network that is an enhancement to an existing analog cellular network. Based on IBM's CelluPlan II, CDPD provides a packet overlay onto the AMPS network and moves data at 19.2 Kbps over ever-changing unused intervals in the voice channels. If all the channels are used, the data are stored and forwarded when a channel becomes available. CDPD is used for applications including police data networks, public safety, point of sale, mobile positioning and other business services. Since it works under the analog cellular system, CDPD usage is on the decline.

Wireless IP
Developed as a wireless extension to an IP network, CDPD uses the four octet (0.0.0.0) address for connections. CDPD networks cover most of the major urban areas in the U.S. and has been deployed by AT&T, Ameritech, GTE, BellAtlantic Mobile and other carriers. By the late 1990s, incompatibility issues had been worked out, and roaming agreements and interoperability between carriers became nationwide. CDPD modems are available on PC Cards for laptops and popular PDAs. See DataTAC, Velocita Wireless and Ricochet.