Welcome VK2RQ's Ham Radio Page

AX.25 Packet on Linux

Recently I have been experimenting with setting up packet radio on an ASUS netbook running Debian Linux. There have been a few challenges with this, which I describe below.

Installation of AX25 Lib/Tools/Apps: the problem here is that the packages supplied with debian are a little old, and assume that the kernel has support for legacy BSD-style pseudo-terminals. However, in the standard kernel distributed with debian linux, support for the legacy ptys has not been compiled in. So, I had a choice of recompiling the kernel to support the legacy ptys, or else compile up newer versions of the ax25libs/tools/apps that support the new Unix98-style ptys. I chose the latter.
The AX.25 "call" program supplied in the ax25apps package was crashing when I resized the window, and didn't have support for any scrollback buffer. I found a patch on the web that addresses these issues, but it was built against ax25-apps-0.0.8-rc2, and wouldn't apply cleanly to the more recent version of call.c in CVS that supports the Unix98 PTYs. So, I updated the patch to make it compatible with the newer release, and you can download the updated patch here .

I had an issue with getting linux soundmodem to work at 300 baud. I found the fix was to use modem tones less than 4*300=1200 Hz. However, I wanted to cover the national APRS freqnency on 40 m and the frequency used by our local packet group around 1 kHz higher together at the same time with the same radio. I found a testing patch against soundmodem-0.16 that removes this restriction on the modem tones.
The aprsd packaged with debian doesn't support multiple TNCs, and you can only run one instance of it on the system. So, I looked to the APRX daemon instead. This does support multiple TNCs, but unfortunately kept dumping core on my system. I made a small patch to prevent this from happening.
I found a patch to provide Internode Protocol (INP3) Support for Linux on this page. However, the patch was written against linux kernel 2.6.4, and does not apply cleanly to the latest 2.6.32 kernel. So, I updated the patch . However, I found that the patch causes a soft lockup when taking an AX25 interface out of service, due to a deadlock with the spin_locks, so some additional work is needed to address this. Investigations so far indicate a problem with nr_del_node_found(), which removes neighbours and nodes that are no longer valid. When it is called, sometimes there is already a lock on the global neighbour list, and sometimes there is also a lock on the global node list. When removing a neighbours or node, an attempt will be made to acquire a lock on the global neighbour or node list, and if such a lock is already existing, there is a deadlock, and the CPU will just spin. Will need to think about the best way to clean up the code.

Packet Radio Resources

I have collected here some useful links in my search to learn about packet radio.

AMPRNet Portal to manage 44.0.0.0/8 IP allocations and ampr.org DNS resource records.
Packet Radio Overview at Complete.Org
Larry Kenney WB9LOZ packet radio information page, including his Introduction to Packet Radio series of articles
VK2DOT Packet Site, including his Packet Setup page
Linux AX.25 Page
DB0ANF BBS page, can view packet BBS via web
JNOS developer page (and KF8KK's JNOS Setup Guide
Soundcard Packet page by Ralph Miles NM5RM
IP-in-UDP encapsulation with JNOS
AMPR Gates covering packet radio gateways and AXIP encapsulation
Hosts and DNS Zone files for ampr.org domain and 44.0.0.0/8 net
N5VDA Packet page, with list of packet software
AMPR Gateways page
DX Cluster information page
Net/Rom Manual and Original NET/ROM Paper
Running Packet radio on Linux
Linux AX25 HOWTO
AGWPE Yahoo Group
AX.25 Protocol standard
Timewave manufacturer of PK232 TNC
FBB Main Page and FBB Setup fgor Dummies
AX25IP README
FPAC Mini-HOWTP
N8UR Packet pages
TAPR SW Library
Linux AX25 SW Suite and AX25SPY Page
The Problem with Digipeaters by Tom Clark W3IWI, 1986
Installing LinBPQ BPQ Node/Mail/Chat on Linux

Packet Activity in the Local Area

Freq/MHz	Callsigns	Comments
7.03717	VK2IO BBS, VK2WL, VK2SX, VK2TT, VK4ALN et al	LSB w 1600/1800 Hz tones: The VK2IO HF BBS is stand-alone, but VK2IO-1 node has connectivity via Internet
145.175	VK2MB-1, VK2BEN-1 et al	National APRS Frequency, lots of activity
144.875	VK2TGB	VK2TGB BBS in the Blue Mountains (part-time only)
147.575	VK2IO-1, VK2AMW-7, VK2DOT-1	VK2IO BBS/VK2IO-1 node is separate instance from VK2IO on HF; links to wider packet network with message forwarding (via RF only, no internet); I can connect from my QTH via VK2AMW-7 node/digipeater
439.150(out) 434.150(in)	VK2RAG data regenerator	Reception is too marginal from my QTH, need a better antenna :-) Would then be able to access VK2IO, VK2DOT.

There are some others I will check out listed on Steve VK2KFJ's Packet page, (the info is dated, so some of these systems may not be running anymore)

Channels on the VK2MB Packet Digipeater

On the radio used for packet digipeating at the MWRS club house, the following channels have been programmed:

Channel	Freq/MHz	Comments
1	147.575	Main Channel (default), access VK2IO-1, VK2DOT-1, VK2RQ-7, VK2AMW-7 nodes
2	144.425	VK2RSY beacon (for diagnostics/testing)
3	144.700	Backup port to VK2DOT-1 XRouter
4	144.875	Backup port to VK2IO & VK2TGB BBS systems
5	145.175	Primary APRS frequency in VK
6	145.200	Alternate local packet frequency
7	147.600	Alternate local packet frequency