P25 OTA alias
- Thread starter KevinC
- Start date
I have only seen OTA alias with D Star and NXDN in DSDPlus.
Just curious, how would someone know (without an APX) if their system is using OTA alias?
Just curious, how would someone know (without an APX) if their system is using OTA alias?
Not that i know of. But @lwvmobile has implemented this for Harris P25. IF you know for a fact there are OTA aliases on your system, maybe if you capture the raw audio in the format that he needs to look at it, he might be able to determine if he is able to pull talker aliases out for that particular system.
I know for a fact. I’ll look into capturing raw audio.
I'd give you a link to where he indicates the audio that he can make use of / how to grab it. But it's in the huge DSD-FME thread somewhere and would take forever to find it. You could always just shoot him a PM.
If you get raw, you could also send to DSDPlus, Denny and Rick.
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lwvmobile
DSD-FME
If you want to send samples, usually I just tell people to send me DSDPlus Raw Audio files of the signal, since most people use that. If not, then you can record with and send from SDR++. For P25, use 12,000 BW and the Low Pass Filter only, if using SDR++. Just don't kill me with 4 hours of recordings, I usually just need some calls where you suspect the activity is happening, or the talker alias. Also, if its Phase 2, let me know what the wacn/sys/nac should be in case there is no net_sts_bcst on the recordings.
Currently, I have support for, but could always use extra samples for validation on:
DMR Embedded Talker Alias (FLCO 8)
NXDN Alias
P25p2 Harris Talker Alias (MFID A4 Opcode 0x28)
P25p1 APX/Moto 'Soft ID' (LSD when not encrypted voice)
and all the usual callsign data found in DSTAR, YSF, M17.
I don't know if Harris has Talker Alias on Phase 1, but if they do, I don't have support for it yet, but would assume its probably similar format to the Phase 2 vPDU.
If you want to use DSD-FME, not going to lie, its not beginner friendly, and usually the people who struggle the most to get a grasp on it are the ones who are used to DSDPlus, since there is a lot of assumptions that the two use the same swtiches, configuration, etc. Starting at the Github is a good place, particularly either here if you need a windows release (make sure to use the aw patch), or here if you need to see examples and readmes on things. I do tend to ramble a lot, so if you can cut through all of that, then you can probably figure out how to set it up.
Currently, I have support for, but could always use extra samples for validation on:
DMR Embedded Talker Alias (FLCO 8)
NXDN Alias
P25p2 Harris Talker Alias (MFID A4 Opcode 0x28)
P25p1 APX/Moto 'Soft ID' (LSD when not encrypted voice)
and all the usual callsign data found in DSTAR, YSF, M17.
I don't know if Harris has Talker Alias on Phase 1, but if they do, I don't have support for it yet, but would assume its probably similar format to the Phase 2 vPDU.
If you want to use DSD-FME, not going to lie, its not beginner friendly, and usually the people who struggle the most to get a grasp on it are the ones who are used to DSDPlus, since there is a lot of assumptions that the two use the same swtiches, configuration, etc. Starting at the Github is a good place, particularly either here if you need a windows release (make sure to use the aw patch), or here if you need to see examples and readmes on things. I do tend to ramble a lot, so if you can cut through all of that, then you can probably figure out how to set it up.
Unitrunker shows a site alias for the Motorola systems, it might show up for now til it changes to phase 2 on the UCA sites right now its phase one. Is this the alias u mean?
No. RID aliases
MSI's implementation for OTA user aliases on ASTRO 25 systems (aka Group Services) appears to be proprietary, as far as I'm aware. I believe OTA aliases have been or will be added to the P25 standard, which is likely what Harris has implemented if that's what someone else in this thread was claiming is happening on Harris P25 systems. I recall a recent conversation about it, but my memory is fuzzy on the details.
Four years ago I sent some raw traffic channel recordings to the DSD+ author along with which aliases he should've seen, however that was fruitless, as he was not able to extract the aliases.
The reply was as follows:
We have not been able to reverse engineer the encoding scheme that Motorola has used. We can provide raw data if you wish to seek assistance from third parties.
The attached file shows the encoded data for alias length plus the first six characters for about 70 radio aliases. The encoding scheme roughly doubles the size of the data. A four bit length value is encoded as eight bits. Each eight bit alias character is encoded as sixteen bits. An eight bit value follows the last character. Encoding of characters is "modulated" by the preceding data - see the different encoding used for 'M' in aliases of differing lengths. All of this suggests an encoding scheme similar to non-systematic convolutional encoding, which is used in forward error correction schemes. Another possibility is the use of an LFSR, or a combination of both. The only purpose of this encoding appears to be for obfuscation, perhaps to mess with Harris, as these schemes are normally used to provide a level of forward error correction, but the data is already packaged in FEC- and CRC-protected OSPs. There is also the possibility that someone at Motorola had no clue what they were doing when they chose to implement radio alias encoding in this fashion. The cost of this encoding scheme is high - depending on length, it takes two to four OSPs to send a radio alias. Frankly, that is ridiculous.
Who knows, maybe some fresh ASTRO 25 traffic channel recordings sent to the authors of DSD+, SDRTrunk, Op25, etc. will be fruitful this time.
Four years ago I sent some raw traffic channel recordings to the DSD+ author along with which aliases he should've seen, however that was fruitless, as he was not able to extract the aliases.
The reply was as follows:
We have not been able to reverse engineer the encoding scheme that Motorola has used. We can provide raw data if you wish to seek assistance from third parties.
The attached file shows the encoded data for alias length plus the first six characters for about 70 radio aliases. The encoding scheme roughly doubles the size of the data. A four bit length value is encoded as eight bits. Each eight bit alias character is encoded as sixteen bits. An eight bit value follows the last character. Encoding of characters is "modulated" by the preceding data - see the different encoding used for 'M' in aliases of differing lengths. All of this suggests an encoding scheme similar to non-systematic convolutional encoding, which is used in forward error correction schemes. Another possibility is the use of an LFSR, or a combination of both. The only purpose of this encoding appears to be for obfuscation, perhaps to mess with Harris, as these schemes are normally used to provide a level of forward error correction, but the data is already packaged in FEC- and CRC-protected OSPs. There is also the possibility that someone at Motorola had no clue what they were doing when they chose to implement radio alias encoding in this fashion. The cost of this encoding scheme is high - depending on length, it takes two to four OSPs to send a radio alias. Frankly, that is ridiculous.
Who knows, maybe some fresh ASTRO 25 traffic channel recordings sent to the authors of DSD+, SDRTrunk, Op25, etc. will be fruitful this time.
"MSI has declined standardization"
imagine that.
imagine that.
ScannerDude244
Member
My local system started doing this it's a l3harris
