DSD-FME Tone frame, Erasure Frame in vocoder Ambe

[SantiagoRC]

Good afternoon,
I have activated the vocoder data dump (cleaned up a bit), and I see that in a DMR transmission with RC4 encryption, tone and erasure frames occasionally appear, in addition to the silence frames. What is the purpose of these types of frames?

Slot 1 DMR PI H- ALG ID: 21; KEY ID: 01; MI(32): 1A9FFB3C; DMRA RC4;
DMR PDU Payload [21][10][01][1A][9F][FB][3C][00][05][DC][5E][17]
Activity Update TS1: Group Voice; Hash: 91; TS2: Idle; Hash: 0;
SLCO Completed Block [18][05][B0][08][60]

19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC1*
[VOCODER] BIT1 = 62 BIT2 = 4 Silence Frame AMBE F801A99F8CE200 err = [0] [1]
[VOCODER] BIT1 = 62 BIT2 = 10 Silence Frame AMBE F801A99F8CE500 err = [0] [0]
[VOCODER] BIT1 = 62 BIT2 = 11 Silence Frame AMBE F801A99F8CE580 err = [0] [0]
19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC2
[VOCODER] BIT1 = 62 BIT2 = 10 Silence Frame AMBE F801A99F8CE500 err = [0] [0]
[VOCODER] BIT1 = 62 BIT2 = 12 Silence Frame AMBE F801A99F9CE600 err = [0] [0]
[VOCODER] BIT1 = 62 BIT2 = 0 Silence Frame AMBE F801A99F8CE000 err = [0] [1]
SLCO CRC ERR
19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC3
[VOCODER] BIT1 = 62 BIT2 = 15 Silence Frame AMBE F801A99F8CE780 err = [0] [0]
[VOCODER] BIT1 = 62 BIT2 = 14 Silence Frame AMBE F801A99F8CE700 err = [0] [1]
[VOCODER] BIT1 = 62 BIT2 = 6 Erasure Frame b0 = 120 AMBE F801A99F886300 err = [0] [0]
19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC4
[VOCODER] BIT1 = 38 BIT2 = 8 AMBE 9802B94FA4D400 err = [0] [0]
[VOCODER] BIT1 = 43 BIT2 = 11 AMBE AC810DC24FF580 err = [0] [0]
[VOCODER] BIT1 = 38 BIT2 = 6 AMBE 983F43302AF300 err = [0] [0]

Activity Update TS1: Group Voice; Hash: 91; TS2: Idle; Hash: 0;
SLCO Completed Block [18][05][B0][08][60]
19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: DMR slot1 [SLOT2] | Frame Sync Err: 7
19:39:32 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:39:32 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC5
[VOCODER] BIT1 = 34 BIT2 = 0 AMBE 88C7B439A8F000 err = [0] [0]
[VOCODER] BIT1 = 57 BIT2 = 3 AMBE E6753CE2F54980 err = [0] [0]
[VOCODER] BIT1 = 2 BIT2 = 11 AMBE 0BEF283F1FCD80 err = [0] [0]


Tone Frame:


Activity Update TS1: Group Voice; Hash: 91; TS2: Idle; Hash: 0;
SLCO Completed Block [18][05][B0][08][60]
19:54:22 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:54:22 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC3
[VOCODER] BIT1 = 50 BIT2 = 6 AMBE CB380ED91BBB00 err = [0] [0]
[VOCODER] BIT1 = 32 BIT2 = 8 AMBE 82CBC3AC2A5400 err = [0] [0]
[VOCODER] BIT1 = 49 BIT2 = 0 AMBE C581A858627800 err = [1] [2]
19:54:22 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:54:22 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC4
[VOCODER] BIT1 = 30 BIT2 = 9 AMBE 7A826646F7B480 err = [0] [0]
[VOCODER] BIT1 = 49 BIT2 = 7 AMBE C77E3266FCCB80 err = [0] [0]
[VOCODER] BIT1 = 15 BIT2 = 9 AMBE 3FC5DF14AEAC80 err = [0] [0]

Activity Update TS1: Group Voice; Hash: 91; TS2: Idle; Hash: 0;
SLCO Completed Block [18][05][B0][08][60]
19:54:22 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:54:22 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC5
[VOCODER] BIT1 = 7 BIT2 = 13 AMBE 1DE0CEAD33BE80 err = [0] [0]
[VOCODER] BIT1 = 62 BIT2 = 0 Tone Frame 1 AMBE F9C458C4EEF000 err = [0] [1]
[VOCODER] BIT1 = 1 BIT2 = 14 AMBE 058F34F88FCF00 err = [0] [0]
19:54:22 Sync: +DMR slot1 [slot2] | Color Code=10 | IDLE
19:54:22 Sync: +DMR [SLOT1] slot2 | Color Code=10 | VC6
SLOT 1 TGT=1500 SRC=16448250 FLCO=0x00 FID=0x10 SVC=0x40 Group Encrypted Call Key 2225410000
DMR PDU Payload [00][10][40][00][05][DC][FA][FA][FA]
[VOCODER] BIT1 = 44 BIT2 = 5 AMBE B13C43955CE280 err = [0] [0]
[VOCODER] BIT1 = 34 BIT2 = 9 AMBE 8BFBADA7EE5C80 err = [0] [0]
[VOCODER] BIT1 = 16 BIT2 = 3 AMBE 4294713D8F8980 err = [0] [1]
SB: 00000001001 - 009;
SLOT 1 SB/RC (FEC ERR) E:1; I:05020A03 D:009;


Thanks a lot,

 

[boatbod]

Tone frames are the AMBE way of encoding tones & dtmf without having to perform traditional sampling/quantization. They ensure more accuracy when the tone is regenerated.

Erasure frames are caused by errors, and based on procedures defined in TIA-102.BABA they result in either a frame repeat or a discard.

Silence frames are just that - periods of silence, usually at the beginning or end of a transmission. Typically each manufacturer has their own specific silence frame sequence. Much watched by the crypt community...

 

[SantiagoRC]

Thanks for the response, the purpose of the tone and erasure frames is now clear.

Regarding silence frames, even though each manufacturer defines their own silence frame, I assume it must always conform to the bit pattern defined by the vocoder in order to be interpreted as a silence frame—right?

 

[boatbod]

Thanks for the response, the purpose of the tone and erasure frames is now clear.

Regarding silence frames, even though each manufacturer defines their own silence frame, I assume it must always conform to the bit pattern defined by the vocoder in order to be interpreted as a silence frame—right?

Yes, BABA Table 14 says silence frames must have Frame Type (b0) = 124-125, but then in the actual text it says silence frames are always b0=124

 

[SantiagoRC]

Yes, BABA Table 14 says silence frames must have Frame Type (b0) = 124-125, but then in the actual text it says silence frames are always b0=124

Could this be a valid method to locate the silence frame regardless of the manufacturer?

 

[boatbod]

Could this be a valid method to locate the silence frame regardless of the manufacturer?

Well that's what the TIA-102 spec says defines a silence frame.

Just for grins, I hacked a log message into p25p2_tdma that checked b0 and printed when it found a silence frame. The logger did appear to go off at the expected points in a call, so I'd say it works.

 

[SantiagoRC]

Yes, it seems to work well, but I don't have samples from another manufacturer to confirm it 100%.

Thanks

 

[boatbod]

Yes, it seems to work well, but I don't have samples from another manufacturer to confirm it 100%.

Thanks

Various mfr silence frame codeword sequences are already well known, so it should be trivially easy to look at that data, unpack it and confirm the value of b0