Cellular digital packet data

Cellular digital packet data (CDPD) offers on-the-go users access to a low-cost, widespread, wireless data network. CDPD can be overlaid on existing analog cellular systems, and share their infrastructure equipment on a non-interfering basis. Basically, CDPD transmits packet data over idle cellular channels. It autonomously switches to another channel when the current channel is about to be assigned for voice usage. CDPD does not communicate with the underlining cellular network. However, CDPD does use its knowledge about the channel assignment algorithm of the cellular cell to predict the channels available for CDPD use. CDPD may serve as the wireless extension to other data networks (e.g., Internet) or public switched telephone networks. It supports connectionless network services which have packets called network protocol data units (NPDU). Every packet is routed individually based on the destination address of the packet and knowledge of the current network topology. Initially, CDPD provides two connectionless network services: the standard open systems interconnection connectionless network protocol and the Internet protocol