To answer the question, you don't really need to change the modem, but you
need to add a protocol on top. Use the 1600 codec (no FEC) and add a
superframe.
+-----------------------------------------------------------------------+
| CODEC2 1600 (8 Bytes) |
+-----------------------------------------------------------------------+
| VOICE FRAME |
+-----------------------------------------------------------------------+
64 Bits per Frame
40 ms
+--------+--------+--------+--------+--------+--------+--------+--------+
| BYTE 1 | BYTE 2 | BYTE 3 | BYTE 4 | BYTE 5 | BYTE 6 | BYTE 7 | BYTE 8 |
+--------+--------+--------+--------+--------+--------+--------+--------+
| DATA FRAME (Data, Text, Image) |
+-----------------------------------------------------------------------+
64 Bits per Frame
40 ms
40 ms 40 ms 40 ms 40 ms 40 ms
64 Bits 64 BITS 64 BITS 64 BITS 64 BITS
+---------------+---------+---------+---------+-- --- --+---------+
| HEADER FRAME | FRAME 1 | FRAME 2 | FRAME 3 | | FRAME 9 |
+------+--------+---------+---------+---------+-- --- --+---------+
| SYNC | PDW | VOICE/DATA FRAME (360 ms) |
+------+--------+-------------------------------- --- ------------+
| SUPERFRAME |
+------------------------------------------------ --- ------------+
640 Bits
400 ms
+---------+---------+---------+---------+
| 0x1A | 0xCF | 0xFC | 0x1D |
+---------+---------+---------+---------+
| SYNC WORD |
+---------------------------------------+
32 bits
20 ms
4 Bits 4 Bits 8 Bits 16 Bits
+-------+-------+----------+------------+
|VERSION| MODE | ROLLOVER | SEQUENCE # |
+-------+-------+----------+------------+
| PACKET DEFINITION WORD |
+---------------------------------------+
32 Bits
20 ms
Version = 0000
Mode = 0001 Voice Frame
Mode = 0010 Data Frame
------------------------------------------------------------------------------
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