PACKET RADIO

Unfortunately packet radio seems to be in decline here in Ireland,most amateurs seem to use it only to connect to the dx-cluster,files and mail now can be passed more quickly via the Internet, however this I feel is a statement about amateur radio rather than a statement about the internet.Unfortunatly amateurs did not keep up with the technology they pioneered.When most landline modems connected to the forerunner of the Internet at 300 baud amateurs were using 1200 baud packet on vhf,that was nearly 20 years ago, the Internet has now moved on to the WWW we see today and most amateurs are still using 1200 baud packet,not for technical reasons but because of a failure to exploit fully the massive allocation of bandwidth they have at their disposal

.It is quiet practical to have a national radio backbone across a country the size of Ireland on 10ghz with high speed modems delivering speeds of 5 mbits plus with user access on 23 cms using 100khz channels to deliver data at speeds exceeding an ISDN Internet connection.Now we come to the bit where I will be excommunicated by the amateur radio community and exiled to dwell forever in a radio black spot,Amateur radio has failed to attract newcomers to its ranks because it has presented an" old fogy" image of itself ,that is when it has presented any image at all,why would any young person today sit down and study to gain an experimenters licence in order to make contact on a crackly radio channel using Morse code,when they can with far less effort blackmail their parents into buying them a PC ,we now have free Internet access apart from call charges so with e -mail,mirc chatgroups and I-phone they can communicate with the person of their choice,rather than a stranger plucked at random from the"ether".If they are technically minded and would have probably become an amateur radio operator 20 years age, today with a visit to a couple of websites to download the appropriate software they can start to fiddle at the cutting edge of technology ,which strangely enough brings me back to radio.The latest craze is WAP ,the Internet on your mobile phone,or should I call a spade a spade, your digital full duplex frequency agile transceiver, which if amateur radio operators were running the networks would be stuck at 1200 baud ax25 protocol packet instead of 48kbaud access with a radio which is packaged to look like a phone.If reading this has got you all fired up don't send me a nasty e-mail on the internet,use your energy to set up a TCP/IP radio/Internet gateway which is capable of radio access at 64 kbaud and then send me your comments via the amateur radio TCP/IP network which all the other annoyed parties will have established while you were doing your bit. In case anyone takes this seriously and I hope they do you can contact me at sysop@ei6cpb.ampr.org.

BASICS

Packet radio is a term used by amateur radio operators to describe a particular form of data communications,where information to be transmitted is broken into small binary units called packets.The information can come from many sources but the most common ones would be keyboard input or files stored on your PC which you wish to send to some one else,keyboard input could be two or more operators just "chatting" via packet,but this is not common as it is much quicker to speak than type,( at least for me it is)a much more common use would be in the form of mail or bulletins being sent to and fro by operators keeping each other up to date on news ,events and just plain old gossip.Files would come mainly in the form of text documents but any type of file can be sent,file size is a limiting factor as packet via radio is slower than an Internet connection

Without getting too technical packet can be divided into three main categories,H.F packet which is used on the h.f bands and is very slow (300 baud) but is very good at making contacts in adverse conditions because of the error correcting nature of packet radio.It is very similar to vhf packet as described below,some of the parameters are different ,mainly to cope with higher noise levels and more fading on the channel,it is used for more or less the same purposes as vhf packet.

AX25 ON VHF/UHF

V.H.F/U.H.F packet based on theAX25 protocol (follow this link for a description of the ax25 protocol,but be warned it is heavy stuff and is included really only for those of you who want to go a couple of steps further in understanding how protocols work) which is mainly used for passing mail,bullitons and files from station to station,operation on vhf is usually 1200 baud ,though 2400 baud is possible. On uhf 9600 baud is possible but unfortunately not much used in Ireland. ax25 is a term you will commonly hear if you become involved in packet ,you need not worry too much about its technicalities but very simply data is broken into small blocks , each block is then given a flag which contains information about the number of packets to be sent and their order, when a packet is received it is examined for this information for example it might say "i am packet 1 of 20" so now the receiving station knows how many packets to expect and which order to reassemble them in, if a packet is lost or corrupted during transmission the receiving station knows it has not received a packet and will request the transmitting station to resend only the packet it did not recieve.This is the main error correcting nature of packet and allows large files to be sent and received intact.it also allows many operators to share a radio channel without interfering with each other as a packet station can be set up to receive only packets intended for it.you can ,if you wish monitor the channel, and see packets intended for everyone but your station will respond only when it receives a request addressed to it.

The main items of equipment you will need for to get going on packet are a transceiver PC and a T.N.C. (terminal node controller) which is very similar to a modem but does a lot of the work involved in handling all the parameters needed for ax25 to work as well as modulating/demodulating the signal, it also controls the TX/RX switching of the radio. Most vhf radios are capable of being used for 1200 baud packet via a connection to their microphone socket.For uhf 9600 baud operation connection to the microphone socket will not suffice due to the higher bandwidth requirements but a lot of newer uhf and dual band transceivers are fitted with an accessory socket which is suitable for 9600 baud.

TCP/IP

The third main form of packet radio is based around TCP/IP,which is the protocol used to transmit data over the internet,you are using it now to download this page, To fully explain TCP/IP I would have to write a book (and if I was to do that I would sell it and make money!! rather than giving it away to all and sundry over the Internet) but seriously a full explanation of TCP/IP is outside the scope of this page,so I am only going to glance over the surface.For any of you who wish to look further into data protocols I have included a description of TCP/IP which you may wish to read. (be warned it is heavy going)

TCP/IP over packet radio is mainly based around a form of software called nos,there are several versions of this software the most commonly used versions being Jnos and Tnos .The equipment used is similar to that used for ax25.the main difference is at the software level, each node in a TCP/IP network has a unique IP address,a block of IP addresses all beginning with 44. was allocated to amateur radio and are not for use on the internet.In Ireland the unique country identifier is 155 and the country is then subdivided into regions region 1 being Dublin,each individual station then has a unique identifier in the range 1 to 254.My stations identifier is 252, so my full IP address is 44.155.1.252 which shows station 252 is a amateur radio address(44), located in Ireland(155) and is in the Dublin area(1).This allows each station to be identified as if they were part of a network with each region forming the equivalent of a LAN over radio.Amateur radio also has its own domain ampr.org(AMateur Packet Radio organization) and the normal convention is to place ones call sign ahead of ampr.org to form a full domain name,so my station is identified as 44.155.1.252 or ei6cpb.ampr.org. The translation from IP address to domain name is performed by a domain name server,the same way as it is on the internet,however as not all stations are on the air all the time most amateur radio TCP/IP stations store a list of domain names in a text file calleddomain.txt, which allows then to be their own domain server,this removes the problems caused if an external domain server was used and was not on the air translation would not be possible and stations would not connect to each other.A typical entry in this text file would look like

EI6CPB.AMPR.ORG. IN A 44.155.1.252 ,,, hugh,bray co wicklow

Each station you wish to connect to has an entry in the domain.txt file, a separate file contains routing information which specifies routes to be taken to each station you wish to connect to,whether they are local stations you can directly connect to or whether you have to route through an other station or stations to connect.This all sounds far more complicated in theory than it actually is in practice,Try it your self and see,I have included some links to freely available software for DOS,WINDOWS AND LINUX on the page dealing with NOS.

OTHERS

There are also other variants of packet radio in use based around the above protocols offering different functions or being tailored for specific purposes such as network switching or bulletin boards or mail handling have included a very brief description of some of the more commonly used ones.