The purpose of the Coding Decoding Processing information element is to transfer the information on voice compression applied within the preceding section to succeeding section by DSS1. This information element indicates whether the voice call has been compressed and, if so, the type of voice compression used as well.
The Coding Decoding Processing information element is coded as shown in Figure III.1 and Table III.2.
The nth octet (Note) of this information element shows the type of voice compression and enabling/disabling of compression/decompression regarding the n-2th pair(s) of DME(s) with LVC, and the maximum length of this information element is network dependent.
NOTE – n is greater than or equal to 3.
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
Octet |
Coding Decoding Processing information element identifier |
||||||||
0 |
0 |
0 |
1 |
1 |
0 |
1 |
1 |
1 |
Length of Coding Decoding Processing contents |
2 |
|||||||
Compression status indicator |
Type of voice compression |
|||||||
Compression status indicator |
Type of voice compression |
N |
||||||
Figure III.1/Q.931 – Coding decoding processing information element
Table III.2/Q.931 – Coding decoding processing information element
Compression status indicator (octet n) |
|
Bits |
|
8 |
|
0 |
Decompressed |
1 |
Compressed |
Type of voice compression (octet n) |
|
Bits |
|
7 6 5 4 3 2 1 |
|
0 0 0 0 0 1 0 |
Recommendation G.711 [10] m-law |
0 0 0 0 0 1 1 |
Recommendation G.711 A-law |
0 0 0 0 1 0 0 |
Recommendation G.726 32 kbit/s ADPCM |
0 0 0 1 0 1 0 |
Recommendation G.728 [98] LD-CELP |
0 0 0 1 0 1 1 |
Recommendation G.729 [99] CS-ACELP |
All other values are reserved. |
|