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Transmission Modes
WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0
Fig. 2 Traffic Channel Mode: Voice Channel
All these channel frames can be coded in 5 different types in Network Mode: Voice, Data, Random Access
Frames, Training Frame, SCH/TI Frames. Additionally, Direct Mode Emergency Frame can also appear in
Direct Mode.
Each frame is 120 bits, which is obtained by several steps: discriminator with CRC, channel encoding, in-
terleaving, scrambling with formatting, differential with encoding, and modulation. The precise structures
of these are described in the TETRAPOL Specifications Radio Air Interface.
The frames can be interpreted according to the protocol. Examples of decoded frames are shown below.
Data Frame
Each data frame is 74 bits. They can be combined according to the FN bits to form HDLC frame displayed
in Hex, with the FCS check in the last two bytes. The first 2 bytes in the HDLC frames contain the address
information as shown in the first line. The second line is the ‘command field’, which indicates the types of
the frame. The ‘command field’ can be: Information (I), Supervision (S), DACH (A) and Unnumbered (U)
format (as shown in this example). The following bytes are the information field. The lines beginning with
‘--’ are the header information of the user data, including: type, presence or not of user data to be car-
ried, segmentation or not. The following lines beginning with ‘----’ are contents in each bytes for the appli-
cation layer.
