==Phrack Magazine== Volume Four, Issue Forty-Four, File 9 of 27 **************************************************************************** The Amateur Radio Packet Network by Larry Kollar, KC4WZK ... As a low-orbit satellite comes into range, Jim's system automatically goes into action. The computer downloads the last half of an image taken by the satellite's CCD camera, the first half having been taken on the previous pass. That done, the computer gets a list of new files on the satellite's BBS and downloads Jim's email... It's legal. ... Her mother is on the phone, but Rhonda accesses the local BBS by radio. She logs in to read postings from a world-wide network and her email from a penpal in Great Britain... It's not Internet. ... 11:30 p.m., and the local conference node is jumping. Two people were trying to work out a computer problem, when the local expert checked in with some ideas. Before long, three more people checked in and a freewheeling discussion got under way... It's happening now. While the Internet has been growing fast and with great hoopla, amateur radio operators (or "hams") around the world have been quietly building a network of their own -- the Amateur Radio Packet Network. Like Internet, the packet network has a large TCP/IP component and is available to anyone who can get access. Unlike Internet, getting access is very easy for nearly anyone who already has a ham license. The packet network is rather loosely organized, and is built and maintained by volunteer work. It's basic building block is the LAN (actually a MAN, or Metro Area Network, but terminology is never 100% accurate), which are coordinated by local or regional clubs. A LAN occupies a specific radio frequency (or channel, if you want to be crude about it :-), usually VHF or UHF, within a given area. Individuals and the regional organizations provide links between LANs for communications outside the local area. LAN operations work much like Ethernet -- your radio waits for the frequency to be clear, then transmits a packet. This allows several connections to run at once. Most packet systems can themselves maintain up to 10 simultaneous connections, but this feature is used only rarely. ---------------------- Packet Radio Equipment ---------------------- Hams to want to use packet radio need three pieces of equipment: - A radio (of course). Most LANs are found on the 2-meter band (144-148 MHz, with packet concentrated around 145.0 MHz and 145.6 MHz. Many hams dedicate older crystal-controlled commercial or ham radios to packet work. - A TNC (Terminal Node Controller). This is an intelligent box that contains a packet modem much like the guts of a landline (telephone) modem, and a micro- computer that handles the network interface. Other alternatives are available, including a dumb radio modem that plugs into a PC (software on the PC then handles the network interface), and multimode controllers that can handle other digital communication methods popular among hams. However, most hams use TNCs since they are cheap (just over $100) and readily available. - A terminal, or a PC running a terminal or packet program. Since TNCs are smart devices, a simple terminal or terminal emulator is all that's required: if it has a keyboard, a display, and an RS-232 port, you can use it with a TNC. However, many features (multiple connections, for example) are more useful if you have a computer running special packet software. Currently, most hams use 1200 baud on 2 meters. This is the lowest (very) common denominator in packet radio. However, large urban areas are starting many new LANs in the 420-450 MHz amateur band; most of these use 9600 baud as a minimum. As time goes on, and packet radio becomes more popular, 9600 baud will become the entry level. When many inter-LAN links use 56K baud, and some go as high as 2M baud, why are the vast majority of hams still using 1200 baud? Part of the answer is technical: to get reliable performance at better than 2400 baud, you have to tap into the guts of the radio, bypassing the audio stages for both transmit and receive. The other part is social: everybody else is using 1200 baud, why spend extra money for stuff you can't use? The technical problem has been solved -- you can buy "data radios" in kits and pre-built models that come with the audio bypasses already in place -- but it will take a few years or a good reason for hams to abandon their old gear and move up. -------------------- Local Communications -------------------- There is lots of local action to be found on the LANs. People and clubs run BBSes, conference nodes, and many personal mailboxes. Most BBSes are set up so they can send email and specified bulletins (equivalent to Usenet newsgroup articles) to personal mailboxes during late night hours when usage is light. A ham using this setup simply accesses his personal mailbox to get his feed for the day, not worrying about noise and propagation delays. In general, a ham who wants to add a component to a LAN just puts it up and advertises it on the local BBSes. For example, a friend in my area recently set up a "QUOTES" BBS dedicated to sharing quotes and funny stories. Perhaps by time this issue of Phrack is published, I will have a Xenix system available for logins over the air. In most areas, the local networks use AX.25 (a subset of X.25 designed by hams especially for packet radio), although TCP/IP is getting popular in some places. I'll talk more about this later. ----------------------- Linking It All Together ----------------------- A single LAN is useful, but the REAL power comes from hooking them together. Linking LANs into a wide-area network gives the Internet its power; so it goes with the packet network. With inter-LAN links, we can send email nationwide (and to many foreign countries), post articles (bulletins) for general reading, and even make distant keyboard-to-keyboard contacts -- with some limitations. So how is it done? Since many metro areas support a dozen or more LANs, these are usually linked together with high-speed UHF equipment using TCP/IP. An Atlanta-based group called GRAPES has developed a 56K bps system; some experimental links in the microwave bands run as fast as 2 MEGA bps! For long-haul links, many areas rely on HF (shortwave) frequencies. Since the FCC limits HF packet to 300 baud (yes, you read that right -- 300 baud), and the HF frequencies are often very noisy, this is a slow and painful process. The amazing thing is not how slow it is, but that it works at all! For this reason, many forward-looking hams are turning to packet satellites for long-haul links. The advantages include relatively quiet frequencies, 9600 baud data rates, and predictability; the major disadvantage is that there are simply not enough satellites to handle all the traffic that needs to be handled -- yet. I'll talk more about packet satellites later. ------------------------------- AX.25, TCP/IP, and All the Rest ------------------------------- The packet network grew from a handful of different experiments with radio networking, which has left us with several networking protocols. Far and away the most popular protocol is AX.25, which is built into thousands and thousands of TNCs and other packet controllers. AX.25, as implemented in most ham gear, offers up to 10 simultaneous connections and the ability to "digipeat" packets. Digipeating (DIGItal rePEATING) is one way to extend the range of a packet station -- if you can't reach the station you want to talk with directly, you can often digipeat through a station between you and the other person. One problem is that you have to manually construct a route each time you want to contact a distant station. The other problem is that the send-acknowledge sequence has to run all the way across the link. Digipeating through more than one or two stations is a good way to annoy other LAN users, and unreliable to boot. The connection works as follows: ---send---\ /--------> station1 digi station2 <---------/ \-- ack -- One popular improvement on the digipeater is the K-node, developed by Kantronics (a vendor of packet equipment). The K-node establishes two links -- one between you and the node, the other between the node and the other station. Each link has its own send-acknowledge loop, so a problem in one leg of the connection doesn't require re-sending packets through the entire end-to-end connection -- only through the leg where the packet got garbled. This connection works as follows: ---send---\ /--send--> station1 K-node station2 <--ack----/ \-- ack -- The K-node shares one disadvantage with the digipeater -- you still have to manually construct your own connection. This is where the higher-level protocols come in. I've already mentioned TCP/IP. Yes, we have it. The 44.*.*.* network is assigned exclusively to amateur packet operations. The network name is "ampr.org." Since TNCs do not have TCP/IP in ROM, some kind of personal computer is required. Most of them work -- PCs, Macs, Amigas, Ataris all have TCP/IP networking software. If you've ever used the free KA9Q NOS software (or one of its derivatives), you have software that was developed by hams for hams. TCP/IP lets amateurs create all sorts of interesting experiments, such as setting up "wormholes" through the Internet to relay traffic between distant LANs. Some parts of the country have Internet/packet email access as well. There are other "smart" networking protocols in wide use. NET/ROM is one highly popular protocol. Each NET/ROM node keeps a table of nodes heard and how to reach each one, eliminating the hassles of manual routing. One problem with NET/ROM is that during band openings, VHF and UHF signals can carry for hundreds of miles beyond their normal range. ("Line of sight?" Yeah right -- a friend of mine in north Georgia has made contacts with people as far away as Lincoln, Nebraska on 2 meters using the stuff he carries around in his truck.) After a band opening, NET/ROM nodes find themselves stuffed with faraway nodes that they can't hear anymore. The phreakers in the audience may find ROSE interesting. ROSE bases addresses on the NANP area code/prefix scheme. If a person uses ROSE, and you know her call sign and phone number, you contact her at the address " VIA AAAPPP." Unfortunately, ROSE does not have the widespread use necessary to make it a nationwide network. There are several other networking protocols in use, such as TheNet and a few others. However, I expect TCP/IP to replace most if not all competing protocols in a few years. ----------------- Packet Satellites ----------------- Here's something you won't see on Internet. Maybe some of Internet's traffic goes over satellites, but direct contact? Since 1959, amateurs have launched nearly 30 satellites into orbit. Nearly 20 of these are still in service -- and most of them are dedicated at least part-time to packet operation. >From a user's standpoint, there are two different types of packet satellite -- one type using 1200 bps FSK (frequency-shift keying) and the other using 9600 bps FM. The current population is split, with about a half dozen of each type. Most packet satellites, or pacsats, are based on a design from University of Surrey in Great Britain -- they're small and lightweight, keeping launch costs to a minimum. Pacsats are always launched as secondary payloads, and often ride as ballast to reduce launch costs even further. Many pacsats have on-board CCD cameras that can take pictures of Earth or space, and make the pictures available for downloading from the on-board BBS. Other pacsats carry equipment that allow them to be switched into a transponder mode, such as the Japanese FujiSat that carries SSB and CW (Morse code) contacts on Wednesdays, or can even be converted into an FM repeater such as AO-21. Some special software has been developed to make the most of the limited bandwidth. For example, pictures can take more time to download than is available during a single pass (normally 10-20 minutes), especially if other users are sending and downloading other files at the same time. The software, called PB, lets you download and upload as much of a file as possible during one pass, then gets the rest of the file on subsequent passes. Other software lets you automate the entire process, so you can get new files as they arrive without having to get up early for that 4 a.m. pass. PB also lets you download files by listening in -- if another person is downloading the file you want, you can simply listen to the downlink and let PB construct the file for you. This is a good way to save bandwidth; if two people want the same file, only one of them has to actually download it. If there are holes in the file, you can fill them in later. -------------------------------- Getting an Amateur Radio License -------------------------------- There are five grades of amateur radio licenses in the U.S.; from lowest to highest, they are Novice, Technician General, Advanced, and Extra. Each grade of license has a test on theory and regulations, with a Morse code "element" required for several of them. The good news is that 99% of what packet radio has to offer is available to the Technician. The better news is that the Technician license, as of January 1991, no longer requires you to learn Morse code. The "codeless Tech" has brought a great deal of new blood into ham radio, including many hackers and mainstream computer people. Study guides are available from Radio Shack and the American Radio Relay League (ARRL); the ARRL's guides are the better of the two, in my opinion. You can get ARRL study guides at most ham radio stores or directly from the ARRL. If you want to get a codeless Technician license, you'll need the Novice and the Technician study guides. The material isn't very hard to learn; anyone who can navigate the guts of Ma Bell will have no trouble with the Novice or Technician exams. :-) The ARRL can also provide you with a free schedule of exams in your area. The FCC some years ago turned over all testing to accredited amateur groups, so you should be able to find an exam at a time and place convenient to you. Many other ARRL services are available through an Internet mail server; send mail to info-server@arrl.org containing the line "send index" in the body of your message. If there's any bad news, it's that a group of diehards can't stand the idea of a code-free ham license. Some of these folks will go out of the way to hassle code-free hams. Fortunately, most of them are afraid of computers and don't do packet. Other things to watch out for -- the FCC frowns on profanity, intentional jamming, and encrypted data sent over the air. A small price to pay, in my opinion, for the opportunity to build and explore a worldwide network without the Secret Service breathing down your neck. -- end --