thumb|terminal node controller 2400 packet radio modem packet radio is a form of packet switching technology used to transmit digital data via radio or wireless communications links. it uses the same concepts of data transmission via datagram that are fundamental to communications via the internet, as opposed to the older techniques used by dedicated or switched circuits. ==purpose and advantages== packet radio is a digital radio communications mode. earlier digital modes were telegraphy (morse code), teleprinter (baudot) and facsimile. like those earlier modes, packet was intended as a way to reliably transmit written information. the primary advantage was initially expected to be increased speed, but as the protocol developed, other capabilities surfaced. by the early 1990s, packet radio was recognized as a way not only to send text, but also to send files (including small computer programs), handle repetitive transmissions, control remote systems, etc. the technology itself was a leap forward, making it possible for nearly any packet station to act as a digipeater, linking distant stations with each other through ad hoc networks. this makes packet especially useful for emergency communications. in addition, mobile packet radio stations can automatically transmit their location, and check in periodically with the network to show that they are still operating. the most common use of packet is in amateur radio, to construct wireless computer networks. packet radio uses the ax.25 (amateur x.25) data link layer protocol, derived from the x.25 protocol suite and adapted for amateur radio use. ax.25 was developed in the 1970s and is based on the wired network protocol x.25. ax.25 includes a digipeater field to allow other stations to automatically repeat packets to extend the range of transmitters. one advantage is that every packet sent contains the sender's and recipient's amateur radio callsign, thus providing station identification with every transmission. ==timeline== === aloha and prnet === since radio circuits inherently possess a broadcast network topology (i.e., many or all nodes are connected to the network simultaneously), one of the first technical challenges faced in the implementation of packet radio networks was a means to control access to a shared communications channel. professor norman abramson of the university of hawaii developed a packet radio network known as alohanet and performed a number of experiments around 1970 to develop methods to arbitrate access to a shared radio channel by network nodes. this system operated on uhf frequencies at 9600 baud. from this work the aloha multiple access protocol was derived. subsequent enhanceme
Packet_radio