LDU Data

[LubeckTech]

Please move this if it is not the proper forum in which to ask this question.
Can anyone tell me what the LDU1 & LDU2 data fields mean.
I am monitoring a P25 repeater with DSD+ 2.228 software.

 

[slicerwizard]

I'd take a shot at it if you were more specific.

 

[riccom]

Is it trunked?? Or conventional?

 

[LubeckTech]

I will try to provide a screen shot.

 

[LubeckTech]

It is P25 conventional.

 

[katt02]

I believe LDU stands for Link Data Unit. It is basically a voice packet from my understanding. It should be alternating between LDU1 and LDU2 when it is decoding voice packets.

https://www.dvsinc.com/papers/p25_training_guide.pdf

Page 47 has some information on it, however this document is very advanced into the theory of p25. It is definitely worth a read.

 

[LubeckTech]

This is what it looks like.
(if the link works)

 

[u2brent]

More information..

SDRTrunk -- first 1-2 secs of transmissions are constantly clipped

I'm having constant trouble with SDRTrunk where the first 1 to 2 seconds of incoming radio traffic does not produce any audio. When I finally do hear audio it starts in mid-conversation, usually one PD unit in the middle of addressing another. Other times they are missed altogether. I thought...

forums.radioreference.com

 

[LubeckTech]

How about TDU?

 

[wgbecks]

LDU is "Link Data Unit". A P25 term refereeing to the voice calls. You'll see alternating LDU1 and LDU2 frames that encapsulate the voice
data from the vocoder for transmission over the air via the Common Air Interface (CAI) specification. TDU is "Terminator Data Unit" that is sent at the end of each transmission. It's all part of the P25 protocol.

 

[u2brent]

How about TDU?

Terminator Data Unit

 

[slicerwizard]

This is what it looks like.
(if the link works)

That indicates that it's a group call and it shows the source radio ID and the target talkgroup ID.