We now have a new and powerful recruitment tool for the younger generation interested in technologies like the Internet, Linux and Ham Radio. By enabling our standard FM repeaters and simplex channels with this new IRLP technology, we can provide instant on-demand linking with one or more repeaters world-wide. And if you're concerned about cost, this entire project is definitely within a "Ham Approved" -cheap- budget of under US$188 including hardware and software.

IRLP is the brainchild of Dave Cameron, VE7LTD of Vancouver BC. IRLP is the abbreviation used for the Internet Radio Linking Project which Dave developed over the past several years. Back in 1998 Dave became frustrated with the unreliable operation of the Windows based Voice over IP software. All Windows based amateur linking software used VOX and were not secure from non-amateur access. The IRLP network uses a digital switching concept and produces an instant and secure link between licensed repeaters around the world.

Eight months after Dave started his design work in 1998, the IRLP network was born and is now on Version 2 of his hardware and software. As of this posting, IRLP is several thousand repeaters (nodes) and is growing in leaps and bounds.

How It Works

Dave's custom IRLP software - takes the audio from the receiver which is then fed into the sound card - where it is converted into ADPCM digital data. The Linux PC then converts this digital information into digital packets each assigned with IP addresses for the destination node. These packets now flow through the internet to the destination Linux PC where the packets are decoded then sent to the sound card and out to the transmitter microphone of the link radio which then transmits the audio out over the local repeater. The transmitter is keyed as soon as these TCP/IP (Internet Protocol) packets start to arrive. As soon as the data stops the link radio automatically un-keys and process reverses.

To assure security of the system, PGP keys are assigned to each node. When a connect request is made the connecting node exchange key challenges which must be correct or the connection is refused.

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Security From Hackers and Non-Amateur PC access

Unlike some systems that allow users access from a PC with minimal if any security, IRLP uses a 100% authentication system to assure the connecting nodes are authenticated and authorized to transmit on the amateur bands.

Here are some points on the IRLP connect request authentication

1. IRLP uses public/private key authentication (512 bit PGP keys)
2. The calling node has to authenticate against the node called
3. Once this is done, the called node has to prove to the calling node that he is who he claims to be.. So the authentication is bi-directional.. Ensures machines can't masquerade as another
4. The PGP key is created ONLY by the IRLP Installer and uploaded to the master IRLP server.

This method of authentications assures licensing agencies that all audio being repeated on a node in another country has originated from a radio and not a PC.

Even though the IRLP uses the internet it does MAXIMIZE the RF content . The philosophy behind IRLP is to have a radio as an entry and exit point in the system.

Under the Hood

The underlying audio processing technology in IRLP is a modified version of the UNIX freeware application called "Speak Freely". Speak Freely produces Voice-Over-IP (VoIP) audio streaming and is very similar to other VoIP software packages such as Microsoft NetMeeting and the VocalTec iPhone with one major difference - It runs under Linux not Windows. Linux was Dave's operating system of choice for the IRLP system as it allows the best in reliability, programmability, efficiency, and functionality. Since our repeaters don't need anything even close to MP3 audio quality, IRLP is using a low-bitrate VoIP to communicate. Most nodes use an encoding system that requires only 32KB/s of bandwidth, however some nodes with extremely limited bandwidth, use a GSM encoding method which only requires 17KB/s albeit at the cost of some audio quality. A full time internet connection with DSL, Cable modem or ISDN is required.

The control of the radio is performed using a small custom logic board which is connected to the computers parallel port. This board samples the received audio for DTMF audio, detects the link receiver COS for positive and instant remote keying, and generates the TX PTT line for the link radio. All of the command I/O between the PC and the IRLP board is handled by a connection to the PC's parallel port.

The whole system is DTMF (touch-tone) controllable. The control codes lie imbedded in a separate program that reads the DTMF tones from the decoder located on the interface controller board and activates various parts of the software. DTMF codes are used to enable/disable linking, open/close links and set identifiers. Every site has the ability to connect direct to any other site(s), either using direct connections or reflector sites.

Hosting an IRLP Node

To host an IRLP node you require:

1. a full time DSL, Cable modem or ISDN connection 
2. a dedicated Linux computer - a 486 DX100 or better is required, 
3. the IRLP custom software/hardware and 
4. a link radio or direct connection to the repeater controller. 

Each node on the IRLP network is assigned a four digit ID code and multiple redundant servers spread around the world manage the BIND process (DNS) IP address routing required to complete connections.

IRLP Reflectors and Super Reflectors

A reflector is a Linux server that allows unlimited multiple node (repeaters) to be linked together at the same time. Most reflectors are hosted by public service minded companies who offer lots of bandwidth to support the requirements of a reflector.

The new super reflectors, launched in October of 2002 provide 10 channels each boosting the number of reflectors to 65. The super reflectors are 9200, 9100, 9210, 9500 and 9250.

The bandwidth requirement for a reflector is directly related to the number of simultaneously connected nodes. During one Sunday evening net with 33 nodes connected, the bandwidth being used on the Denver reflector was just over 1mb. This reflector usually has a number of US, Canadian, Australian and Caribbean repeaters connected so any conversation that occurs on one is heard on all connected stations.

The super reflectors now each support two channels of GSM to allow dial-up nodes the ability to use multiple reflectors.

Using the IRLP Network

To connect to another repeater you simply dial a 4 digit on-code. (some node operators require a pre-access code much like an autopatch code) Within a few seconds that node will ID in plain voice with it's callsign and location. If the node is currently connected to another or to a reflector, you will receive a recording telling you which connection the other repeater is currently engaged with.

Before placing a call you can always check the status of any node in real time by going to http://www.irlp.net/status.html and look at the node you wish to connect with. This page updates in real-time and refreshes every minute so it is always current.

Just as with any linking system, IRLP is subject to some minor audio delays which are mostly radio related. These delays are caused by the amount of time it takes for numerous radios to decode the Tone Squelch information so the first thing to remember is to slow down and be patient. (to dispel internet delay myths, the audio delay over the internet is the same as you experience when using a digital cell phone)

When completed with a QSO, announce your call and dial the OFF code at which time a voice ID indicating the link is dropping will play. Since many repeaters are not heavily used, there are always a number of nodes left connected to the Denver CO Reflector allowing you to place a CQ, or ORZ type call with an excellent chance of speaking with someone somewhere in the world.

Refer to the following list of nodes (repeaters) and find one close to your QTH. If one of the members brings up one of the reflectors you will be able to simply key your microphone and talk but we do advise to contact the node operator and determine if local membership is required.

Active nodes around the World

New repeaters and new countries continue to join the IRLP family. Current countries that are active around the world include Canada, USA, United Kingdom, Dominica, Trinidad, Australia, Tasmania, New Zealand, South Africa, Sweden, India, Sweden, Belgium, Ecuador, Scotland, Japan and the Netherlands plus the node on Scott Island in Antarctica. Nodes are also under construction in other countries around the world.

Summary

This exciting new technology will be a tremendous catalyst to bring new young blood into our hobby. Where else can you witness an open world-wide VoIP wireless network using a free and open protocol like IRLP? As we all know there has been a real challenge for us to draw kids into our hobby as they could previously talk on their poor quality iPhone connections over the Internet. Now with a basic HT they can enjoy far superior audio and be talking with their friends across town and around the world.

73 KE5NZY