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The Internet Radio Linking Project


Forest Whitaker. Phenomenon. Dennis Quaid. non-Celebrity Hams. Amateur Radio Activities ... Los Angeles Area Nodes. IRLP is based on Speak Freely for Linux. ... – PowerPoint PPT presentation

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Title: The Internet Radio Linking Project

The Internet RadioLinking Project
  • Presentation for the Triangle Linux Users
    Groupby Jim Price WW4M
  • April 10, 2003

Portions of this presentation courtesy of KD4RAA,
  • What is Amateur Radio?
  • Ham Radio Activities
  • IT and Amateur Radio
  • Ham Radio Internet Linking
  • The IRLP Network
  • IRLP Hardware
  • IRLP Software
  • Using IRLP
  • Listening
  • For More Info...
  • Demonstration

What is Amateur Radio?
  • Licensed as a public service by the Federal
    Communications Commission
  • voluntary non-commercial communications, with an
    emphasis on providing emergency communications
  • advancement of the radio art
  • advancing communication and technical skills and
    provide trained operators, technicians and
    electronics experts
  • promote international goodwill
  • 680,000 hams in the U.S., 18,000 in NC

Celebrity Hams
Entertainers Chet Atkins WA4CZD, Ronnie Milsap
WB4KCG, Marlon Brando FO5GJ, Patty Loveless
KD4WUJ, Gary Shandling KD6OY, Burl Ives KA6HVA,
Arthur Godfrey K4LIB, Priscilla Presley N6YOS
Joe Walsh WB6ACU
. A huge number of politicians and royals
including Gov. George Pataki N2ZCZ, Sen. Barry
Goldwater K7UGA, Spains King Juan Carlos EA0JC,
Jordan's King Hussein JY1 and Queen Noor JY2,
Argentinas Pres. Carlos Menem LU1SM, Indias
Rajiv Gandhi VU2RG
Famous and infamous hams most astronauts,
Hugh Downs KD6WUS, Art Bell W6OBB, Kevin Mitnick
N6NHG, and the author of The Joy of Sex, Dr. Alex
Comfort KA6UXR
Walter Cronkite KB2GSD
Celebrity non-Hams
Forest WhitakerPhenomenon
Dennis Quaid
non-Celebrity Hams
Amateur Radio Activities
  • HF (shortwave)
  • VHF/UHF and repeaters
  • Morse code, analog voice
  • Public Service/ Emergencies
  • Home-building equipment
  • Dxing (long distance contacts)
  • Contesting
  • Amateur Radio Satellites
  • Digital Modes

IT and Amateur Radio
  • Computer-Controlled Modes
  • Packet Radio
  • Narrow Band Teletype (e.g. PSK-31)
  • Amateur Television
  • IEEE 802.11b WiFi / HSMM
  • Amateur Radio Satellites
  • Internet Radio Linking
  • Remote Bases and Web Radio
  • Digital Signal Processing
  • Software Defined Radio
  • Spread Spectrum Technology
  • Contact Logging Software
  • Antenna Design

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  • Repeater A station that simultaneously
    retransmits the transmission of another station
    over a wider area on another frequency

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Coverage from 320-ft in West Raleigh
Ham Radio - Internet Linking
  • Radio-only Access
  • IRLP (linux)
  • PC -or- Radio Access
  • eQSO (Windows)
  • iLink (Windows)
  • WIRES (Windows)
  • EchoLink (Windows or linux)

The Internet Radio Linking Project (IRLP)
  • Uses the Internet to link distant radio sites
  • Gives global coverage to normally localized VHF
    and UHF frequencies
  • Enables minimally equipped stations to
    communicate globally
  • Allows end user control of links via their
    radios DTMF (Touchtone) keypad

The Internet Radio Linking Project (IRLP)
Created by Dave Cameron VE7LTD of Vancouver, BC  
Dave was frustrated with the unreliable
operation of Windows-based Iphone and turned to
linux. Iphone and other systems use VOX. IRLP
uses COS.IRLP is radio-access only.
Dave VE7LTD and Pete VK2YX
IRLP Growth
November 1998 - 2 December 1999 10 12June 2000
20 32December 2000 29 61June 2001 61
122December 2001 199 321June 2002 236
557 December 2002 263 820
database records 1/1/03
IRLP Network
445 United States154 Canada 54
Australia New Zealand 49 Europe 12
Caribbean Bermuda 6 Japan 3
Southern Africa 2 Ecuador, Mexico 1
India 1 Antarctica
active nodes 4/1/03

Australia and New Zealand

North America
ExampleLos Angeles Area Nodes
IRLP is based on Speak Freely for Linux. Speak
Freely for linux is Open Source, while Speak
Freely for Windows is GPL. Linux offered the best
in reliability, programmability, efficiency, and
functionality.  IRLP currently ships with RH 7.3
and will run on a 486 DX100 or better computer
Typical IRLP Node
  • Standard PC, P100 or better
  • Linux (Red Hat 7.3)
  • SB16 ISA soundcard
  • Custom IRLP computer/radio control interface
  • Radio
  • Dedicated internet connection

Custom Red Hat CD-ROM Boot Diskette Custom
IRLP Software
IRLP Control Board Does COS, PTT DTMF DB9
IRLP to Radio Interface LPT1 to IRLP Jumper
v.2 IRLP card
Indicators on v.2 Control Board
DTMF Decode Sense Carrier
Operated Squelch Sense PTT out to Link
Radio or Controller
v.3 IRLP card features surface-mount components
100MB Switch 10MB HubLinksys Router
DualBand 2M/440Control Xcvr
KD4RAANode 4260 / 4270Configuration
4270 Link Radio 4260 Link Radio Audio
Equalizer and Broadcast Leveling
(No Transcript)
What Happens During a Call?
  • Notes from Dave Cameron, VE7LTD

DTMF Decode
  • DTMF program monitors COS and DTMF
  • Once detected DTMF sequence passed to the decode
  • Decode script checks custom_decode for matches
  • Assuming a call is decoded, call script is
    started with the node number as the argument

Call Script
  • Best server is determined by using
    find_best_server script
  • Best server is asked for latest IP of node being
  • If IP received is different from IP in hosts
    file, a new hosts file is d/l from best server
  • Irlp_call is started, and a TCP connection is
    made to the called node on port 15425

  • Remote node starts irlp_answer in response to TCP
    call on port 15425
  • PGP security performs a dual challenge to ensure
    calling node is an IRLP node
  • Codec (GSM/ADPCM) is determined
  • Irlp_call and irlp_answer start speak freely
    software on UDP ports 2074 and 2075

During the Call
  • Irlp_call and irlp_answer send keepalives in the
    background. If keepalive fails, the connection
    drops (every 15 sec)
  • Irlp_call and irlp_answer keep open info channel
    to pass dtmf regeneration info,
    disconnect/timeout message

  • Disconnecting node uses TCP info channel to send
    disconnect message. Both nodes run the off script
  • Unexpected drop in the TCP connection prompts
    reset of IRLP node
  • If the timeout elapses, disconnect is sent

NCSU Bookstores
Sending Audio
Audio streaming is enabled when the link radio
receives a signal with COS and keys the IRLP
interface card. The sound card receives the
radios audio and creates a continuous mono 8-bit
digital stream of raw audio at 8000Hz (64k
bps). Speak Freelys sfmike program compresses
the audio stream by a factor of two (32k bps)
using an audio compression algorithm (codec).
NCSU Bookstores
The audio is split into packets, which are
transmitted over port 2074 using a User Datagram
Protocol (UDP) stream. UDP does NOT confirm the
reception of packets - it "fires and forgets"
NCSU Bookstores
Receiving Audio
Speak Freelys sfspeaker receives the packets on
port 2075 and rejoins them into an 8-bit ULAW
stream. . Next the ULAW stream is uncompressed
back into an 8-bit raw stream of audio. . The raw
audio is streamed through the digital to analog
(D/A) converter (the output device of your sound
card). . The IRLP interface card keys the radio
when the audio stream is present (live -- no
NCSU Bookstores
Audio Compression
Jason Woodard, http//
NCSU Bookstores
  • ADPCM(Adaptive Differential Pulse Code
  • only 32 kb/s - more efficient than the PCM codec
    used by WAV, AIFF and CD audio (and is used on
    the Sony Mini Disc)
  • cuts the data rate from 8000 to 4000 bps
  • superior sound quality vs. GSM

NCSU Bookstores
  • GSM(Global System for Mobile Communications)
  • requires only 13 kb/s bandwidth
  • reduces the data rate from 8000 to 1650 bps,
    which makes a 28.8 Kb modem usable
  • serves 71 of the total digital wireless market
    and provides good quality speech

NCSU Bookstores
ADPCM quantizes the difference between the
sampled signal and a prediction. If the
prediction is accurate, the difference between
the real and predicted samples will have a lower
variance than the real speech samples and will be
accurately quantized with fewer bits than needed
for the original. At the decoder the quantized
difference signal is added to the predicted
signal to give the reconstructed speech signal.
Performance is aided by using adaptive prediction
and quantization, so that the predictor and
difference quantizer adapt to the changing
characteristics of the sampled speech.
NCSU Bookstores
GSM uses a Regular Pulse Excited (RPE) codec.
Input is split into 20ms frames, each with 8
short term predictor coeffiecients. Frames are
further split into four 5ms sub-frames, each with
a delay and gain for a long term predictor.
After short and long term filtering, the residual
signal for each sub-frame is decimated into three
possible excitation sequences, each 13 samples
long. The sequence with the highest energy is
chosen as the best rep-resentation of the
excitation sequence, and each pulse in the
sequence has its amplitude quantized with three
bits. At the decoder the reconstructed
excitation signal is fed through the long term
and short term synthesis filters to reconstruct
the speech. A postfilter improves perceptual
Ports Required
2074 - 2093 Audio (bi-directional UDP) 15425-7
IRLP Control/Update (TCP) Outbound ports used
80 (http) for updates 873 or 8873 (rsync) for
downloading updates 10000 (for IP
determination) parallel port set to "standard"
or "compatible" mode, not to ECP, EPP or
Some IRLP Details 512-bit bi-directional PGP
authentication ensures connections only with
other IRLP nodes. Redundant servers support
IRLP-BIND(DHCP isnt a problem) as well as
download of pgp key rings, software updates, and
station ID wavfiles. IRLP accepts commands from
keyboard or via DTMF (dual tone multi frequency,
i.e. Touchtones)
IRLP and the GPL I had released code under the
GPL, and it led to nothing but 1000's of emails
criticising my code, asking for features,
wondering why I built this that way, etc... I got
tired of answering questions. There is a
strong commercial potential for this product, and
I did not want to hand several 1000 hours worth
of code to the private sector just to be
replicated. Closed code maintains a standard,
which open releases would compromise. VE7LTD
IRLP Admin
  • FCC regulations prohibit unlicensed people using
    amateur frequencies.
  • IRLP links are accessible only on amateur radio
    frequencies within range of a node. No direct
    Internet access.
  • OpenSSH used for remote administration.
  • Linux packages updated automatically (up2date,
    autorpm, apt).
  • Cron jobs to automate functions

IRLP Scripting
  • The IRLP software is composed largely of bash
    shell scripts.
  • Flexible easily customized to suit local needs.
  • Almost anything that can be run from the console
    can be controlled via radio.
  • Morse Code ID using MIDI or wav (per FCC legal
  • Node status (link off/on and where linked to)
  • Time of day (talking clock)
  • Weather reports, Amber Alerts
  • Local Announcements
  • Download and play radio news programs from
  • Random dialing
  • 69 / Call Waiting

IRLP Advantages
  • User Flexibility - Custom Scripts
  • Accessible only by radio
  • Security
  • Stability of linux OS
  • Superior audio COS (not VOX)
  • Cost linux is free, will run on old PCs
  • Continues to function if servers fail

Two ways to make contacts
Point-to-Point and Reflectors(like chat rooms
-- multiple nodes connected together, hearing
audio from one node at a time)
IRLP Reflectors
  • Enable multiple nodes to link together into a
    network number limited only by bandwidth.
  • Running a reflector requires bandwidth (32 kbps
    per connected node) to handle the multiple data
    streams. Most reflectors are hosted by ISPs
    (like Inflow) who often donate the bandwidth.

Raleigh Reflector
Established for coordinated response to severe
weather events and for public service Links NC
repeaters beyond the range of conventional RF
linking systems During Hurricane Lily, linked
stations in Louisiana with the National Hurricane
Center in Florida Has linked stations from
Georgia to Maryland to track several winter
storms Simulcast a ham radio contact between
the International Space Station and Chapel Hill
middle school students Participated in the Boy
Scouts JOTA event
Impact of Internet Linking on Amateur Radio
  • Level of amateur activity has increased
  • Amateurs who have been inactive for a long time
    are coming back on the air
  • Amateur Radio is becoming more appealing to
    todays Internet-oriented youth
  • New opportunities for experi-mentation.

The Future
  • Internet linking is already becoming commonplace
    over 800 IRLP nodes on the air.
  • Advances in technology will improve performance
    of links.
  • Technology can be ported to high-speed microwave
    and satellite links.
  • Enhanced global slack.

Listening to IRLP
  • Live Demonstration
  • Monitoring IRLP Reflector 2 via Live365 streaming
    audio (linked from
  • Recorded conversation with Antarctica, and
  • Recorded school contact with the International
    Space Station (linked from
  • local frequencies via radio or scanner

How to Become a Ham Radio Operator
  • Radio amateurs are licensed by the FCC, after
    passing examinations in radio theory,
    electronics, regulations, and optionally, Morse
  • Examinations are conducted locally by individuals
    or clubs almost every week and cost about 12
    (10-year renewals are free)
  • Many radio clubs run study courses. 1-on-1
    tutoring, book and online stuyding, and taking
    mock online exams are other study options.

More Info
  • IRLP in Raleigh
  • -
  • IRLP in General -
  • What is Amateur Radio? -
  • Raleigh Amateur Radio Society -
  • American Radio Relay League -

Thank You