Cellular Digital Packet Data.
An open wireless transmission standard allowing two-way 19.2-Kbps packet data transmission over existing cellular telephone channels (AMPS with CDPD capability.) In essence, CDPD technology uses idle network capacity caused by pauses in phone conversations and gaps between calls placed, etc. to transmit data. Because it is packet-based, it does not require a continuous circuit, (connection,) like a voice call.
CDPD is an older technology that has mostly been replaced by newer GPRS and CDMA 1xRTT networks.