Wednesday, November 07, 2012

Packet Radio


That's not a typo, I mean packet radio, not pocket radio.  Packet radio is one of the major categories of digital radio communication modes. It is a form of packet switching technology used to transmit data by radio. It transmits datagrams which are a fundamental component of internet communications. They are unlike prior data modes like telegraphy (Morse Code), teleprinter (Baudot) or facsimile (Fax). Like early modes datapackets were intended to transmit text with improved speed but it has developed into much more. We now use it to send file, programs, commands and more.

Datagram concepts are fundamental to communications via the Internet. I'll start there. It's a transfer unit, comprised of two main parts a header and a data payload. The payload is the data you are sending, or more accurately a tiny piece of the data. The header contains all the information the packet needs to route itself through the internet from your point of transmission to your point of reception.now usually this is discussed in terms of the wired world, T1, fiber optics, Ethernet, etc; that is the internet as we see it in a server cabinet. but increasing the the networked world is wireless so this packet data can also be broadcast.  RFC 1594 defines the term Datagram as follows:
“A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.”

The "datagram" was first developed as part of the CYCLADES project which was an early, experimental  packet switching network created in the early 1970s. the word was coined by software pioneer Louis Pouzin. CYCLADES was the first network that made the hosts responsible for the reliable data delivery, rather than the network itself. Everything today is based on his idea because he was right.

By the late 70s Amateur packet radio had begun it's own experimentation. Several Canadian ham radio enthusiasts began transmitting ASCII data over VHF frequencies. In 1980 the FCC executed a rule change to permit the use of packet radio in the US. AMPRNet was born shortly thereafter. Commercial packet radio developed in the mid 1980s and remains integral to many wireless networks including US and European standards like Mobitex, MDI, DCS, DRN, ARDIS and many others.


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