DSDPlus Trying to analyze the Packet Data of P25 in version DSD+ 2.441 (LRRP/Location)

[Red_Ice]

Thank you, it is a very good contribution, I did not know the reason for this variation of the token and this helps a lot to understand it.

 

[thewraith2008]

There are a few GitHub repos out there that can help with getting your head around some of these MOT services and putting the pieces together.

Sadly some programmers have a real problem adding meaningful comments to their code to help understand the structure of this type of data.
The other issue can be understanding some of the programming languages, especially when no comments exist or are vague.
For me, Java and Python make no sense to me.

 

[Red_Ice]

Although FL is written in C, I don't have too many problems understanding it, at least for the most part, since I program in C# and in many ways it is similar, until now my studies had been directed towards the result provided by the DSD and the ETSI , now I have started studying the TIA standards, I think I will have to visit GitHub more frequently so I can also cover that branch.

 

[hrh17]

Happy to provide some phase 1 P25 GPS wav files from Tait radio using NMEA formatting if required

 

[billy2047]

I've also logged a lot of data transmission on a conventional P25 repeater. Although I have no idea what it means other than RX OK and Aff'd TG.. Does anyone know how to decode the data? Thanks!

 

[noamlivne]

I've also logged a lot of data transmission on a conventional P25 repeater. Although I have no idea what it means other than RX OK and Aff'd TG.. Does anyone know how to decode the data? Thanks!View attachment 154891

A few pages ago in this thread (DSDPlus - Trying to analyze the Packet Data of P25 in version DSD+ 2.441 (LRRP/Location)) it was written that SAP=1 is encrypted. So probably nothing can be done with that

 

[adamfancher]

Hi all,

So I took a good look through this thread and it was a really good read.....That being said I'm still having a little trouble deciphering my data....
I've been capturing some data packets in my area and am trying to make heads or tails of them:


The first thing I'd like to be able to pick out is GPS coordinates, however from what I've gleaned not all packets have them.
My understanding from previous messages in the thread is that there are four bytes each for latitude and longitude which can be directly converted into a floating point calculation equal to the coordinates in degrees.

For my area, I'd be looking for a string of bytes starting with 0xC29 and another starting with 0x422, but am unable to locate these values in the packets I'm seeing.

I also took a look at the packets indicated in a previous post where certain bytes were highlighted in yellow and green denoting the bytes in a SAP=0 packet and those didn't yield real numbers.

If anyone can shed any light on GPS coordinates or any additional info on what data is shown it'd be much appreciated!

Thanks in advance.

 

[RaleighGuy]

If anyone can shed any light on GPS coordinates or any additional info on what data is shown it'd be much appreciated!

Thanks in advance.

Not all systems are setup to transmit GPS locations via packet data.

 

[noamlivne]

Hi all,

So I took a good look through this thread and it was a really good read.....That being said I'm still having a little trouble deciphering my data....
I've been capturing some data packets in my area and am trying to make heads or tails of them:
View attachment 155772

The first thing I'd like to be able to pick out is GPS coordinates, however from what I've gleaned not all packets have them.
My understanding from previous messages in the thread is that there are four bytes each for latitude and longitude which can be directly converted into a floating point calculation equal to the coordinates in degrees.

For my area, I'd be looking for a string of bytes starting with 0xC29 and another starting with 0x422, but am unable to locate these values in the packets I'm seeing.

I also took a look at the packets indicated in a previous post where certain bytes were highlighted in yellow and green denoting the bytes in a SAP=0 packet and those didn't yield real numbers.

If anyone can shed any light on GPS coordinates or any additional info on what data is shown it'd be much appreciated!

Thanks in advance.

It looks that you are monitoring the an output channel. If that is the case, you won't find LRRPs there. Monitor the input channel(s).

 

[avkghost]

In this other data packet, the ARS ports appear in the second IP addresses, although it is not indicated and they do have the same values for the SAP and the DPF but they do not transmit the three bytes of LRRP data indicators.

You are a little bit wrong with the packet. It's an ICMP reply (destination network unreachable) packet with an original IP packet, see below.
IP header
45 00 00 3c
58 46 00 00
40 - packet TTL
01 - protocol, ICMP
b3 4a - the header checksum
0c 00 27 11 - source
0c 00 30 24 - destination/target


ICMP header
03 - type, destination unreachable
00 - code, destination network unreachable
5d b7 - checksum

content
00 00 - unused
00 00 - next hop MTU?
IP header and first 8 bytes of original datagram's data
45 00 00 3c
00 4F 00 00
40 - TTL
11 - protocol, UDP
0a 42 - checksum
0c 00 30 24 - src
0d 00 27 11 - dst / tgt

UDP Header
0f a5 - src port, ARS
0f a5 - dst port, ARS
00 14 - data length
7f ea - UDP header checksum
53 7d 19 d9 - payload of UDP Packet

 

[avkghost]

In the third case we see the same SAP and DPF and ports 4001, with an LRRP indication, but it does not include that data, making it difficult to follow that theory.

Maybe someone had answered before, but there are my 2 cents.
It's LRRP Triggered Location Start Response.
0B - CMD
08 - data length
22 - identity token
04 - identity token length
00 00 26 86 - identity token payload
37 16 - looks like bearing