How are data packets transmitted in a mobile radio system?
Data packets are transmitted in a mobile radio system using Cellular Digital Packet Data or CDPD. This optimizes the use of cellular frequencies by transmitting data on idle voice channels. There are several items required for a CDPD network to be functional. The mobile CDPD user needs a subscriber unit which consists of a cellular radio, a modem, and a computer that creates and receiver of packets. This set ups is also called CDPD-speak as a Mobile End System or M-ES. Unlike a standard modem, a CDPD subscriber unit uses the channel only intermittently to transmit short bursts of data called packets. These packets have a constant or fixed amount of space called the payload. This is where used data may be placed. This packet also contains addressing information that identifies the source and destination of the data. In every cell site, a Mobile Data Base Station (MDBS) retrieves packets from the M-ES and creates packets to be transmitted back to the mobile unit. The Mobile Data Intermed
