Digital Data on Digital Voice Systems

Status
Not open for further replies.

kb1ipd

Member
Joined
Feb 26, 2006
Messages
82
One thing you will notice about just about all the digital voice systems out there is they have the capacity to transmit non-voice data as well.

Apco P25, for example, has native support for binary transmissions of 4,800 baud, with possible additional capacity. Some of the early demonstration radios I saw had a serial port and could work as a TNC

D-Star has a data mode

Provoice has a data mode

even NXDN has a data only mode

In practice are these ever used for anything? Dispatch? Paging? Mobile data terminals?

My guess is that they were probably included with the idea that they would use the same system to power the MDT's as for voice, but once 4g came around, it was a nobrainer to go with that.

Are they used at all?

IF so, is there a way to decode them? Would DSD be smart enough to realize it was monitoring a mode that was not speech and then show the text or pipe it to something?
 

DSheirer

Member
Premium Subscriber
Joined
Feb 15, 2010
Messages
459
Location
Fulton, NY
One of the local P25 systems uses SNDCP for UDP/IP packets. sdrtrunk detects and decodes the UDP/IP packets--other IP protocols are logged, but not decoded.
 

Jay911

.
Joined
Feb 15, 2002
Messages
9,183
Location
Bragg Creek, Alberta
In practice are these ever used for anything? Dispatch? Paging? Mobile data terminals?

IF so, is there a way to decode them? Would DSD be smart enough to realize it was monitoring a mode that was not speech and then show the text or pipe it to something?
I am familiar with a P25 system which uses data transmissions as a means of sending 'text pages' - replacing old-style alpha pagers. A "data call" is made, which in terms the scanner hobby would be familiar with looks kind of like an I-call or private call but with data instead of voice being transferred. The radio asks for a channel for it to transmit its data on, the system assigns one, and then it (the sending radio) goes to work - same as a request for a voice call, but with data.

Both Unitrunker and PRO96COM see these data calls but do not indicate the destination, only the source (i.e. if radio 12345 is sending to 67890, you only see that radio 12345 has initiated a data call). I have looked in the P25 standards documents but I am unsure if the destination just isn't specified in that particular message or not.

I would be very surprised if the data being transmitted (in the data call itself) wasn't encrypted or proprietary in some form - I would hope that it wasn't in ASCII or hex. I think it would be in the P25 Common Air Interface if it was specified anywhere.
 
Status
Not open for further replies.
Top