AMPRnet

The Amateur Radio Internet

What is AMPRnet?

Radio amateurs have long used their radio equipment for digital communications - commonly known as packet radio. In recent years that here has been a growth in the use of the TCP/IP protocols over these radio links. The world-wide network of ham radio stations linked this way is called AMPRnet (AMateur Packet Radio network).

Is it part of the Internet?

Formally, yes. AMPRnet has the Class A internet address 44.0.0.0. However due to legal restrictions in many countries there are no direct links between AMPRnet and the rest of Internet. Some gateways do exist, mainly in the US, but are usually restricted so that access (from either side) is only by persons holding an amateur radio licence.

How does the addressing work?

The Class A net 44.0.0.0 is sub-divided into sub-nets, for example 44.131.0.0 is used in the UK. Further sub-netting is done on a regional basis, so that southern Oxfordshire is 44.131.154.0 (with a sub-net mask 255.255.255.0).

Hostnames use a domain name ampr.org, so for example the station with callsign G8EQX is named g8eqx.ampr.org, and its IP address is 44.131.154.147.

What services are available?

Just about everything you find on the "real" internet. SMTP mail, including POP3 mail collection, telnet, ftp, NNTP newsgroups, Domain Name Servers, Gopher, HTTP (Web) servers etc., etc. In addition to IP routing, in some areas routing via other radio network protocols, such as Net/Rom. In the dynamic environment of amateur radio, with stations (and therefore routers) switching on and off, some areas apply dynamic routing techniques such as RIP or RSPF.

What software is used?

There's a variety of software used to run the networking, but most of it is derived from NOS, written by Phil Karn, whose amateur radio callsign, KA9Q, is familiar to many Internet users as the name of the software they use. Popular varieties for ham radio use include JNOS, WNOS and TNOS, all of which are under continued active development. There are versions of NOS for most computer platforms and operating systems.

What equipment is needed?

Fairly simple radio equipment, running on a VHF or UHF frequency using frequency modulation, and a simple antenna. A computer, of course. And something to connect the two: a modem. This is normally something a bit more sophisticated than an ordinary phone modem, a thing called a Terminal Node Controller (TNC) which contains a Z80 processor (it was designed a long time ago!). However, you can get by with a simple modem, although it does need to be one specifically designed for packet radio, not an ordinary phone modem.

What data speeds are used?

OK I left the worst news till last. The commonly used data rate is 1200 bps. This is for historical reasons - it became widespread for packet radio a decade or so ago, because it can easily be used with radio transceivers which were designed for speech. In fact most of this radio equipment could also handle 9600 bps, but growth of the use of this speed is disappointing (at least here in the UK). Using specially built or modified radios, much higher speeds, even up to 64 kbps, have been used.

However there is one benefit from the use of 1200 bps: at this graceful speed you can really see what's going on. Personally, I had been using TCP/IP networks for several years at work, but only started to really understand it when I set up my amateur radio TCP/IP system at home.

South Oxfordshire

In the UK the AMPRnet network is a static one (i.e. we don't use RIP or RSPF), with permanent links between routers to "hubs" which provide a central point for all the hosts in a region to connect to.

The southern Oxfordshire region is known as soxon-uk.ampr.org [44.131.154.0]. It comprises all of Oxfordshire south of a line running roughly East-West through the City of Oxford, including the City itself. The hub station is g6lnu.ampr.org located at Wantage, IP address 44.131.154.112, and also has an alias (canonical name) of soxon-hub-uk.ampr.org.

All other AMPRnet hosts in South Oxordshire route through the hub on one of the user access frequencies, 144.925 MHz or 433.625 MHz.

The hub links to the rest of the world on 433.625 MHz via at experimental router located at Woodcote, near Reading. The intention is to upgrade this link to 9600 bps (on a different UHF frequency).

Services provided by g6lnu to users include:

The Voluntary Service Provider for this South Oxfordshire hub is John Durban, G6LNU.

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