Cẩm nang dữ liệu không dây P4

PUBLIC TERRESTRIAL PACKET SWITCHED NETWORKS MESSAGING/DISPATCH ORIENTATION Amateur packet radio has been active in the 2- and 20-meter bands since the early 1980s. But recognizable pay-for-service packet switched offerings began in Chicago in 1986 with Motorola’s DRN. With coverage in only three cities and weak marketing, DRN struggled for three years. In 1990 it was folded into a joint venture that also embraced IBM’s .ield Service System. The result was ARDIS, a truly nationwide public packet data network. The formation of ARDIS was quickly followed by an alternative carrier: RAM Mobile Data. With extremely limited geographic coverage, RAM’s early struggles were...