Motorola TETRA Talk Group Names Broadcast

[Erik211]

I remember reading that some Motorola TETRA networks broadcast talk group names in clear text, but for example the TELIVE software can't decode this. I have been searching like crazy for information on this without being able to find it.
It would be very useful to decode this TG information (of course there's a charm finding out the user of each TG and alpha-tagging it yourself, but I think there's are also a charm having the TG names exactly as the actual users have it on their radios )

Thanks in advance for any info!

 

[Ubbe]

For the Stockholm ABSL Tetra system it is sent out as text messages that programs a vehicle computer with a text tag for the TG. The vehicle computer looks at the text that start with the # symbol.

When a driver of a vehicle logs into his computer it sends a message with the login credentials and the system looks in its database what TG's that vehicle will need and sends the # text strings to the computer that then programs those TG's and text tags to the radio. With each logout and login those text messages are sent to reset and set the TG's in the radio.

I haven't used Telive for many years but it used to show all those text messages.

/Ubbe

 

[Erik211]

Great information! This is exactly what I was looking for, although I didn't remember it correctly.
Now I just need to hassle to decode SDS. I haven't been running Telive for very long either, I might check the SDS feature in TTT first. Or any other good tools out for decoding SDS to clear text?

Tack så mycket

 

[Ubbe]

I've only captured those # messages in Telive, and post them at scanner.nu, and never seen them in TTT, but then I'm probably using a too old version of both TTT and SDR#. I only see 16 characters of a text and sometimes it's followed by some random thrash characters with some of the first 16 characters jumbled in between them. I might try and do a clean install of the latest versions of the programs to see if it makes a change.

Textdata:'!Hej kollegor. Vi ???? ~f*?Ã' >ºÀ??!Hej kollegor'

/Ubbe

 

[Erik211]

I'm trying the lastest TTT since yesterday (clean install) and I get clear text messages, like your's above but with correct Swedish å, ä, ö, and also the full string. However the only messages I've seen so far are "real" text, and only for buses. I get alot of user defined data. These could very well be the talk group text tags, but in TTT I only get the binary data strings.

 

[hamradionl]

There are also short SDS contain HEX who TTT not shown. Seen in other linux version (not Telive).

 

[Ubbe]

Latest version have full text messages. But SDR# has audio issues and I need to reduce the volume 10 steps, or disable AGC which will lower the volume the same amount, to get clean audio. The spectrum history of SDR# are gone after 3 sec at slowest setting which makes it pretty much useless. The whole GUI are clunky and difficult to get used to. SDR# crashes each time I close it. I will go back to the old versions as they work fine for me, except for the text messages.

I never notice any # talkgroup config messages in the log. I think I have Telive on a stick somewhere and can check if they still use the same method. It used to be 2 different SDS servers but now there's 5 or 6 sending all sorts of data messages, so could be that they changed how they configure talkgroups.

/Ubbe

 

[Erik211]

Yes, I also have some troubles with the latest version of TTT, it seems SDR# is either crashing or the audio stops after a little while.
I tried to run Telive for a few hours today. I only got binary SDS strings, and no clear text at all, at least on the LA I was monitoring today. So pretty much the same as on TTT in other words. But it could be that I missed something - it was a really long time since I ran Telive.

If you find something out I'm very curious to know

 

[masve179]

First of all I'm no expert, neither on the Swedish Storstockholms Lokaltrafik TETRA system or TETRA in general. But actually there are two ways I know of to get to these group names in the previously named system.

One way is what Ubbe describes and can be seen below with the actual text in the bold red bits (yes you need both the start and the fragment). This is just standard 8-bit coded letters. To make life easy for you this decodes to >>> Line-tg:69:#L 69:#H S-CITY:0; <<<

The biggest issue with Telive, well not exactly Telive but the attached osmo-tetra source, is that the experimental support for fragmented data is broken. To make life more complicated TETRA also can make use of PDU association, which needs to be disassociated before the individual PDUs can be processed from that MAC block. So there is also a chance to miss or mix up data parts in these fragmented SDS data with the Telive version of osmo-tetra. Newer official versions of osmo-tetra had these issues fixed, but instead are not plug-n-play compatible with Telive. TTT should overcome both these problems and get the full data, disassociated and defragmented. Haven't used TTT in a few years though so I can't comfirm. But also this SDS data is not standard "Text Messaging" but instead as "User application defined". Therefore it still won't decode despite being plain text. There are also a few different types of SDS data, where some contain these talk group names. You can copy-paste the red data bits to for instance this decoder and test the data yourself.

Oh right, I said two ways do get the names.. The other one is by the mnemonic element in the D-FACILITY PDU, but for now I'll leave that one for you to figure out yourself.

---------
MAC-RESOURCE (fragmented), TM-SDU , TL-SDU
[0000000111111001000011110111110000111100000 01010 01001111010000000000000001111101001100100000000111101100000001001111001 01001100011010010110111001100101001011010111010001100111001110100011011000111001001110100010001101001100001000000011011000111001001110100010001101001]

MAC-FRAG, TM-SDU, FCS (32-bit CRC)
[0101 00000100000010100110010110101000011010010010101010001011001001110100011000000111011 0 00101100001010000010101101101100 1000]

MAC-END
[011100000111000000000100]
---------

 

[Erik211]

Many thanks @masve179, this is very interesting! If you're no expert, then I don't know where this puts me
I have a decent understanding of the radio side of the system, but very limited to the data side. I guess I'll have to find time for some reading up.

The strings you isolated are making sense together as you say. But right now, to be honest, I have no clue to the logic of finding the right fragments.

 

[Ubbe]

Latest TTT allows decoding of the user define protocols.

The line entry format for 'TETRA_sds_unknown_protocol.txt' is as follows:
MCC;MNC;procotolID;bin_parameters
The above entry is required to be delimited by “ ; ”
MCC – “123” country code for where unknown protocol id seen
MNC – “4” Your network code for where unknown protocol id seen
procotolID – “User_Defined_111” **
bin_parameters – “e8,s40,r0” parameters to handle binary string. (Usage explained further down

Another example of entry is as follows: 123;4;User_Defined_111;e8,s16,r0 binary string = '010101010101010101010101010101010101010101010101' This would remove the last 8 bits (yellow) then skip the first 16 bits (blue) then the remainder binary string (the green) is converted to text.

When I now start the latest SDR# to try and see if I can successfully configure the SDS decoder I get an error in tetra plugin panel. If I remove the magic line in plugin the SDR# works fine. I have received a Windows upgrade so that might have disturbed something. I probably have to reinstall SDR# again.

/Ubbe