COM1? COM2? COM13? /dev/ttyUSB4? /dev/cu.USBtoSerial14?
USB Sound Device? USB Audio CODEC? Default Sound Output?
127.0.0.1:8001 or 127.0.0.1:8042? TCP or UDP?
PROPOSAL
2021-01-01 - added note on UTF-8 and further command line examples
2021-01-25 - added method to describe multiport TNCs
Heikki Hannikainen, OH7LZB
Most hams who have tried digital modes are quite familiar with the difficulties of getting modem software attached to the correct sound card, finding the correct virtual serial port device that's going to the radio, and connecting logging software to the modem software. It gets even more complicated when connecting to a device on the local network with dynamic DHCP-assigned IP addresses.
In 2021 it is time to make one of these things a bit easier, and start using DNS Service Discovery (RFC 6763 DNS-SD) over Multicast DNS (RFC 6762) for locating KISS TNCs attached to the local network.
DNS-SD libraries exist for all relevant operating systems. Finding DNS-SD capable TNCs is very easy on Android and iOS platforms, as well as desktop systems. To the end user, it feels like magic, when compared to the traditional hunting of dynamic IP addresses and weird port numbers. Easier than setting up a new printer, anyway.
User selects the correct TNC from a list, application connects to the TNC, and the user does not need to know which IPs or ports are being used.
Example code for the TNC side can be found in the references below.
KISS TNCs providing a TCP socket server on a LAN shall announce their presence, and the port being listened on, using mDNS DNS-SD with the "_kiss-tnc._tcp" service in the "local." domain.
As per RFC 6763, the instance name is an user-friendly UTF-8 encoded Unicode name of the TNC. Devices with some sort of configuration interface SHOULD allow configuration of the instance name and permit use of non-ASCII unicode characters. Client applications MUST handle devices having non-ASCII unicode characters in the instance name.
A TNC MAY publish symbolic names of ports using a TXT record of pn having a comma-separated list of UTF-8 encoded names. This is useful in case of a multi-port TNC. If a pn record does not exist, a client SHOULD assume that the TNC has a single port. If a comma-separated list for pn is available, the number of values indicates the number of ports.
"pn=144.800 1200 bit/s,433.425 9600 bit/s"
The instance name of each KISS TNC SHOULD be user-friendly, containing the name of the software or the model and manufacturer of the device. A few examples of good names:
- ACME SüperTNC in 日本
- WinDSPTnc on NameOfServer
- Dire Fox on raspberrypi
Note how the last two examples default to including the user-configured hostname of the computer as a part of the instance name.
As per RFC 6763 Appendix C, the name of the TNC SHOULD NOT, by default, contain random hexadecimal gibberish, such as serial numbers or MAC addresses, to make the name unique. RFC 6763 describes, in Appendix D, that when the device detects a naming conflict, it should add or increment a number in the end of the name, resulting an user-friendly name like "ACME SuperTNC (2)".
If possible, the adjusted name SHOULD be stored persistently, so that it will remain assigned to the correct device in case both devices remain on the same network, even if the device is turned off temporarily.
If the device has an user interface, it is also a good idea to make the name configurable, so that the user can have meaningful names for multiple TNCs attached to different radios on different frequencies.
If the device has a BLE KISS interface, the same name MUST be used for both BLE and DNS-SD.
Note that some APIs require you to pass the TCP port in network byte order when registering the DNS-SD announcement. On Mac dnssd, network byte order; on Linux Avahi, host byte order. Use htons() to do the conversion so that your code will work on both Big Endian and Little Endian computers.
On a Linux system with Avahi and avahi-utils installed, you can use avahi-browse to fetch currently discoverable TNCs from the cache. It'll also continue to print updates of newly added and removed TNCs.
$ avahi-browse -v _kiss-tnc._tcp
Server version: avahi 0.7; Host name: raspberrypi.local
E Ifce Prot Name Type Domain
+ eth0 IPv6 Dire Wolf on Hessu-mac-2 _kiss-tnc._tcp local
+ eth0 IPv4 Dire Wolf on raspberrypi _kiss-tnc._tcp local
+ eth0 IPv4 Dire Wolf on Hessu-mac-2 _kiss-tnc._tcp local
: Cache exhausted
: All for now
To resolve the IP addresses and ports on Linux:
$ avahi-browse -v -r _kiss-tnc._tcp
Server version: avahi 0.7; Host name: raspberrypi.local
E Ifce Prot Name Type Domain
+ eth0 IPv4 Dire Wolf on Hessu-mac-2 _kiss-tnc._tcp local
= eth0 IPv4 Dire Wolf on Hessu-mac-2 _kiss-tnc._tcp local
hostname = [Hessu-mac-2.local]
address = [10.11.0.106]
port = [8001]
txt = ["pn=144.800 1200 bit/s,434.125 9600 bit/s"]
On a Mac, the "dns-sd" tool will do the same.
$ dns-sd -B _kiss-tnc._tcp
Browsing for _kiss-tnc._tcp
DATE: ---Tue 29 Dec 2020---
9:31:26.959 ...STARTING...
Timestamp A/R Flags if Domain Service Type Instance Name
9:31:26.960 Add 3 6 local. _kiss-tnc._tcp. Dire Wolf on raspberrypi iGate 144.800
9:31:26.960 Add 3 1 local. _kiss-tnc._tcp. Dire Wolf on Hessu-mac-2
9:31:26.960 Add 2 6 local. _kiss-tnc._tcp. Dire Wolf on Hessu-mac-2
To resolve the hostname and TCP port (8001):
$ dns-sd -L "Dire Wolf on Hessu-mac-2" _kiss-tnc._tcp
Lookup Dire Wolf on Hessu-mac-2._kiss-tnc._tcp.local
DATE: ---Tue 29 Dec 2020---
9:32:49.275 ...STARTING...
9:32:49.275 Dire\032Wolf\032on\032Hessu-mac-2._kiss-tnc._tcp.local. can be reached at Hessu-mac-2.local.:8001 (interface 1) Flags: 1
9:32:49.275 Dire\032Wolf\032on\032Hessu-mac-2._kiss-tnc._tcp.local. can be reached at Hessu-mac-2.local.:8001 (interface 6)
And finally the IP address:
$ dns-sd -G v4 Hessu-mac-2.local.
DATE: ---Tue 29 Dec 2020---
9:33:13.662 ...STARTING...
Timestamp A/R Flags if Hostname Address TTL
9:33:13.662 Add 40000002 6 Hessu-mac-2.local. 10.0.0.42 120
If you have a TNC which does not yet know how to do the announcement, you can publish a service from the Linux command line. Alternatively, a service can be configured for announcement by placing a configuration file in /etc/avahi/services/.
# service running on this host
# avahi-publish [options] -s <name> <type> <port> <txt>
avahi-publish -s "My TNC" _kiss-tnc._tcp 8001 "pn=144.800 1200,434.125 9600"
#
# proxy announcement, service is running on another host instead of this
# one, so we provide its hostname
avahi-publish -H otherhosthost.local. -s "My Amazing TNC in Åland" \
_kiss-tnc._tcp 8001 "pn=144.800 1200,434.125 9600"
# and then announce the IP address for that host
avahi-publish -a another-host.local. 10.0.0.55
On a Mac, publishing a service from the command line:
# service running on this host
# dns-sd -R name type domain port txt
dns-sd -R "KISS TNC on the attic" _kiss-tnc._tcp local 8001 "pn=Port 1,Port 2"
#
# proxy announcement, service is running on another host instead of this
# one, so we provide its hostname and IP address
# dns-sd -P name type domain port host IP
dns-sd -P "KISS TNC on the attic" _kiss-tnc._tcp local 8001 \
otherhost.local. 10.0.0.55
- RFC 6762, mDNS / Multicast DNS: https://tools.ietf.org/html/rfc6762
- RFC 6763, DNS-SD: https://tools.ietf.org/html/rfc6763
- Pull Request to add DNS-SD support to Dire Wolf, example code for Linux and MacOS: wb2osz/direwolf#307
The aprs.fi iOS app supports KISS TNCs via WiFi, discovered using DNS-SD. BLE and TCP KISS TNCs can be connected by simply selecting them from a list.
