IRLP is an abreviation for "Internet Radio Linking Project", a system which uses the internet as a means
of linking or networking computers together, each linked computer has a radio which is interfaced to it.
The radio is connected to the sound card and to the computer's parallel port, the sound card provides the
audio in and out from the computer to the radio, while the parallel port provides the control of the radio,
which consists of a carrier sense, to tell the computer if the radio is hearing traffic on the channel, and
control of the radio's PTT line, to key up the transmitter so that the computer can feed an incoming audio
for transmission.
Each computer is connected to the internet, and in my case it is via LAN connection, to an ADSL modem and router.
At present, there are over 1200 nodes operational worldwide, on every continent.
How does IRLP work?.
The IRLP system runs on a standard off the shelf PC, nothing particularly fast, or high spec is needed in the PC
side of things. The computer itself is running on a Linux operating system, and is running software that is designed
for using Voice Over the Internet Protocol (VOIP).
The user of an IRLP node will be using a radio that is DTMF equipped, and to use the system, the operator will key up
their radio on the frequency of their local node, and "dial" a node number they wish to communicate with using the DTMF
keypad on their radio.
The software in the computer converts the audio from the radio into data packets (ananlogue to digital conversion) which
are then able to be delivered to the datastream on the internet, and takes the incoming data packets it receives from
the internet, and converts the data packets back into audio (digital to analogue), which is then fed out to the radio
for transmission.
Each individual node computer on the internet will have a specific Internet Protocol (IP) address, to which all
data for that particular node is sent. Each node computer is constantly "talking" to a central server, in order to
ensure that the server knows which nodes are currently active, in use, or offline, to direct any calls in between nodes.
The IRLP server will direct calls from one node to another, in much the same way as a telephone exchange is essentially
a router which directs calls to and from fixed telephone lines.
On the internet, each computer has a specific address, which is unique to that particular computer, however, this unique
address does change from time to time, mainly because there will be more computers which can connect to the internet than
there is possible IP addresses available. Because the IP address of your computer changes (dynamic IP address), the node
needs to be in contact with the central server constantly, so that the server is kept up to date when an address changes
otherwise an call would not be able to reach the node being called if it's address changes.
What sort of equipment does my node use?.
My IRLP node here uses a Pentium 200MHz MMX processor, 64MB Ram, 2.0GB Hard drive, and a SoundBlaster 32 sound card,
D-link 100Mbps Ethernet LAN card. This setup is dedicated to IRLP, and performs no other tasks.
What do I have on my network?.
My LAN here is running two computers, both the IRLP node and my normal PC for all my usual applications, we are
sharing an ADSL internet connection between about 4 computers, I have a port coming from the router/firewall,
to an 8 port switch at my end, and the two machines here are fed from the switch. My LAN is all 100Mbps.
What software does my node run?.
The IRLP system runs on Linux RedHat version 7.3, (IRLP Custom install version), and uses a version 3 IRLP interface
board, which is built into the computer case.
What sort of radio equipment does my node run?.
The radio equipment used by the node is an Alinco DR-435T UHF FM radio, running 10 Watts, continuously fan cooled.
For an antenna, I use a dual band vertical collinear type antenna, it's a GST-3, similar to a Diamond X-510.
The antenna is 8m above gound level at it's mounting point.
What do you need to do to access my node?.
My IRLP node is operating on UHF simplex, as opposed to many nodes which are running on an existing repeater,
the frequency it is operating on is 432.700 MHz. To access the node, you will need to enable the CTCSS encode
feature on your UHF radio, and set the tone frequency to 103.5 Hz.
As my node is operating as a simplex node, there is no tail. To use the node, key up and enter the number of the
node or reflector, and release the PTT. The node will then key up, and you will hear a message confirming that the
link is active to the node number that you have called. Simple as that!.
From any other IRLP node, simply dial my node number, 6493.
For more information on IRLP, check out: