Which of the following best describes CDPD?

The correct choice accurately reflects that CDPD, or Cellular Digital Packet Data, is primarily focused on a method for cellular data transfer. This technology was designed for the transmission of data over existing cellular networks, enabling packet-switched communication.

CDPD technology allows for efficient use of the bandwidth, enabling mobile devices to send and receive data while maintaining voice communication simultaneously. It marked a significant advancement in mobile data services by allowing mobile computers and devices to connect to the internet and transmit data without needing a dedicated line. This capability fostered the growth of mobile internet access long before the widespread adoption of more advanced data standards such as 3G and 4G.

In contrast, the other options do not accurately define CDPD. Voice communication, satellite communication, and video transmission each refer to different technologies and applications that do not align with the primary function and purpose of CDPD as a data transfer method.