P25 uplink decoding (inbound signal packets)

[kv6o]

I am looking for software that can decode and display the Inbound Signal Packets for a P25 Phase I (FDMA) system. I am playing with Unitracker, but it appears to log the inbound packets only - I have to stop the decoder and open the log to see what it decoded.

Anyone know of anything?

Thanks!

Steve

 

[Mobby1-Kenobby]

There isn't any software available to decode the P25 inbound messages sent from the SUs.

Unitrunker 2.2 decodes some of the ISP messages seen in the logging files but they tend to be incorrectly labeled as outbound messages.

Most ISP messages are just requests, along with data that is usually encrypted.

Post your unknown ISP messages, and there are some members here that can tell you what some of them are used for.
ISP messages must all be decoded the hard way.

Cheers

 

[boatbod]

Generally speaking it's not particularly useful to decode ISPs because your sdr hardware has to be close enough to the transmitter to pick them up, and (in the case of phase 2) they can encoded with a different modulation scheme that almost nobody has taken the time to write software for.

 

[kv6o]

I do have a use case that hopefully in the future I can elaborate on. Unitrunker does dump what I want to a file - looking for it in a realtime display. The specific packets I am looking to decode do get recorded.

Thanks!

Steve

 

[boatbod]

I do have a use case that hopefully in the future I can elaborate on. Unitrunker does dump what I want to a file - looking for it in a realtime display. The specific packets I am looking to decode do get recorded.

Thanks!

Steve

I can tell you that op25 won't do it because the uplink is true tdma (bursts) which the demodulator won't lock in time to properly decode.

 

[hrh17]

Since data is phase 1 just sit dsdplus on the input of the data channel and it should decode the packet data if the tx is in close enough proximity.

 

[kb5udf]

i’ve decoded subscribers with dsdplus. That is, sitting on the input of the control channel, DSD plus would happily display a log of what they were sending to the control channel.

 

[CanesFan95]

If you all figure out the meaning of any ISPs, let the DSD+ developers know dsdplusfastlane@gmail.com and hopefully they can update the software:

 

[kv6o]

Thanks! I'll give DSD+ a try.

 

[Mobby1-Kenobby]

The uhandled TDSU is:

Opcode A4 is extended function radio check command response sent from RID 4431266 to FNE ID 16777213.

I see these on a Harris system.

 

[kb5udf]

I was monitoring a P25Phase 1 system by running dsdplus directly on that control channel input (pied over virtual audio cable from SDR#), and using an older version of the software and no Log decoder menu. I don't recall seeing a bunch of unhandled issues on that system, but I may need to check again, its been a long time.

 

[Mobby1-Kenobby]

Yes, the A4 EFRCCR messages are seldom seen on my P25 system.
I see them when a Harris SU travels out of its home zone and into another zone.

When a P25 radio site goes.
back into service after being taken off-line by a radio tech all the Harris SUs within the range of that site will send the A4 message.