IRLP Revisited

Article kindly submitted by Peter, VK3KG.

The Eastern and Mountain Districts Radio Club hosts an IRLP node on 70cm. This article is to assist those amateurs who wish to know how IRLP works, and how to use it.

The EMDRC IRLP node is available for all amateurs who are in access range to the repeater. You do not have to be a member of our Club, nor do you need to use any “secret” access tones.

The repeater through which this node can be accessed is:-

What is IRLP?

The concept of the IRLP is the brainchild of it’s designer, David Cameron VE7LTD.

The aim of the Internet Radio Linking Project (IRLP) is to provide a simple and easy system to link radio systems (repeaters) together using the Internet as the communications backbone.

Similar linking options exist, but they use expensive leased telephone lines or satellite equipment. It is not the goal of this project to compete with them, but to work along with other networks to improve the technology and improve radio linking for all involved parties. The people who benefit most from the IRLP are it’s users.

The software and hardware requirements for IRLP hosts are minimal, and the cost to set up a node is low. This brings the opportunity for smaller more remote locations, or small clubs, to experience national linking without the large capital cost of a satellite node or leased line.

For users, they only need to be able to access a local repeater node, using a handheld or their home equipment. The IRLP was started back in November of 1997 as an attempt to use the internet to link radio systems across Canada. The first full time link that was established ran from Vancouver, BC to Saint John, NB. The link had many problems and was shut down in March of 1998 due to the numerous computer crashes and repeater lockups it was causing, and the lack of user control over the system.

David set out to design a better way to use the same technology to perform the same task, while improving usability, user control, and sound quality. His first breakthrough was to replace the existing operating system, Windows, with a more stable and versatile language.
He chose Linux, an open source form of the operating system UNIX designed by Linus Torvalds, because of its superior networking characteristics, its reliability, and its ease of programming.

The IRLP uses a Voice-Over-IP (VoIP) streaming software called Speak Freely. Speak Freely is very similar to other VoIP software packages (such as Microsoft NetMeeting and VocalTec Iphone) with one difference... It runs under Linux.

How does it work?

The IRLP network comprises some nearly 600 nodes (computers) around the world, each of which is connected to the Internet, while at the same time, also connected to a two radio station via a sound card. These radio stations are mainly in the 2 metre or 70 cm amateur bands, with the odd one on the 6 metre, 1.5 metre, and 23 cm metre bands.

Some of these radio links are simplex, although many of them comprise a semi-duplex repeater operated by the local radio clubs.

In the latter case, the computer node linking to the Internet is not necessarily directly connected to the repeater, but rather to a trigger link which accesses the repeater in just the same manner as any other user. In addition to the “one-to-one” connections, which basically connect one city repeater to another city repeater, there are so-called “reflectors” which in fact have no radio connected to them but are a Linux computer which, via the Internet, can merge several connections together to form a large radio network.

Each node (or reflector) allocated by the IRLP manages its own four digit ID number.

In order to open a link to a remote repeater or reflector, you need to send via your radio the ID number of the remote node using DTMF tones. To disconnect at the conclusion of a QSO, you simply need to send the digits “73”, and the computers will disconnect the link.

The operation of the IRLP network is controlled by David Cameron, together with a group of enthusiastic and dedicated amateurs. Each individual node is operated and maintained by the sponsor of the node. In the case of Node 6360, this is the EMDRC.

How do I operate the IRLP to contact another station

First, you need to know the four digit ID code number of the node you wish to access. As new nodes are being added to the project all the time, you should update your list on a regular basis. These node numbers are kept up to date at the IRLP web site. This URL will give you the current node numbers, and their status:- http://status.irlp.net/statuspage.html

Because the Internet is a “packet” based data system, which routes data packets around the world according to a destination address, and taking into account that the “voice” signals from both ends are being digitised prior to transmission, and then “analogised” at the receiving end, there is an inevitable delay between one and the other.

For this reason there are some fairly important protocols which one should adhere to if you are going to enjoy the IRLP mode of operation. These are all related to “waiting” before performing certain actions. Unlike normal repeater access which is virtually instantaneous, the transmission delays mean that you should wait after or before each action to enable the “latency” of the system to elapse.

We ask that you follow the rules regarding IRLP operation which can be found on the following URL:- http://www.irlp.net/guidelines.html

A brief summary of the most important points of the protocol are given below.

“First of all listen on your local machine for at least 15 - 30 seconds before transmitting and then ask if the repeater is currently in use. Assuming all is clear, identify your self and give the node name or number you wish to call . Example: "VK3xyz for the Manchester node" - - then enter the ON code for the node and release your PTT. Your local repeater should come up with a carrier as it waits for the connection to be authenticated. This can take a few
seconds of dead-air so don't be concerned. When the connection is confirmed, the voice ID of the destination node will be transmitted back to you as well as your nodes voice ID to the other repeater.

NOTE: If your node is already connected to another node or reflector, a greeting will play saying; - "your node is currently connected to...(ID of the connection)”. In this case confirm if anyone desires the connection to remain up before dropping by using the OFF code..

Once connected and after hearing the confirming voice ID, wait at least 15 seconds before transmitting because.......

Press and hold the microphone PTT for a second and then announce your presence and your intention, such as you are calling someone specifically, or just looking for a QSO with another ham in that city.

If no response is heard, announce your call and your intent to drop the link and then touch- tone in the OFF code. Not a good idea to transmit touch-tone commands without first giving your call-sign. Not only is this courteous it is a regulatory issue in some countries which may be connected to the reflector.

Some nodes are configured so you cannot connect to them if that repeater is active. In this case you will receive the message "The node you are calling is being used locally" If you receive this message wait 5 or 10 minutes and then try again.

If you stay connected to a node and there is no activity on your repeater for 4 minutes, the connection will time out and automatically disconnect with a voice ID disconnect message on both nodes.”

What equipment do I need?

A hand held or base station transceiver capable of reliably contacting the repeater or transceiver through which you wish to contact another node, and a microphone which can generate DTMF codes, or another device which can generate DTMF tones. For example, some mobile phones create the DTMF tones when the keys are pressed. Simply place your mic. close to the phone’s speaker while holding the PTT down and dial the tones.

You can also download programs from the Internet which will generate the tones through your computer’s loudspeakers. The Club CD also has some programs which you can install on your computer to generate tone Other enterprising hams have taken the tone generating chip from a discarded telephone, and built their own tone generator.

What other IRLP nodes operate in Melbourne?

In addition to the IRLP node sponsored by the EMDRC, other nodes which may be active in Melbourne include:-