CDPD (Cellular Digital Packet Data) is a specification for supporting wireless access to the Internet and other public packet-switched networks. Cellular telephone and modem providers that offer CDPD support make it possible for mobile users to get access to the Internet at up to 19.2 Kbps . Because CDPD is an open specification that adheres to the layered structure of the Open Systems Interconnection (OSI) model, it has the ability to be extended in the future. CDPD supports both the Internet's Internet Protocol protocol and the ISO Connectionless Network Protocol (CLNP).
CDPD also supports IP multicast (one-to-many) service. With multicast, a company can periodically broadcast company updates to sales and service people on the road or a news subscription service can transmit its issues as they are published. It will also support the next level of IP, IPv6.
For the mobile user, CDPD's support for packet-switching means that a persistent link isn't needed. The same broadcast channel can be shared among a number of users at the same time. The user's modem recognizes the packets intended for its user. As data such as e-mail arrives, it is forwarded immediately to the user without a circuit connection having to be established.
There is a circuit-switched version, called CS CDPD, that can be used where traffic is expected to be heavy enough to warrant a dedicated connection.