amr_mode_set.txt
Change-Id: If6cce37b37018ec0f138bd14fc5d3bdfb455ac04
This commit is contained in:
parent
f091db0f20
commit
788a47fe23
|
@ -0,0 +1,69 @@
|
|||
AMR bitrates
|
||||
============
|
||||
|
||||
AMR has 8 distinct bitrates that it can switch between.
|
||||
In GSM, only up to four rates can be selected; they are limited by the S bits.
|
||||
|
||||
In SDP:
|
||||
-------
|
||||
|
||||
m=audio 16010 RTP/AVP 112
|
||||
a=fmtp:112 mode-set=0,2,4,7
|
||||
|
||||
where
|
||||
|
||||
7 = 12k20
|
||||
6 = 10k20
|
||||
5 = 7k95
|
||||
4 = 7k40
|
||||
3 = 6k70
|
||||
2 = 5k90
|
||||
1 = 5k15
|
||||
0 = 4k75
|
||||
|
||||
On A-interface:
|
||||
---------------
|
||||
|
||||
"S-bits", S0 to S15, where each Sn defines a set of bitrates that are enabled.
|
||||
For example, S0 means: allow only 4k75.
|
||||
|
||||
A particular S bit, S1, has a special meaning: when on a half-rate channel,
|
||||
exclude 12k2 implicitly.
|
||||
|
||||
3GPP TS 28.062, Table 7.11.3.1.3-2
|
||||
|
||||
S0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
|
||||
12.20 (x) x x x
|
||||
10.20 x x x
|
||||
7.95 x x x
|
||||
7.40 x x x x
|
||||
6.70 x x x x x x
|
||||
5.90 x x x x x x x x x x
|
||||
5.15
|
||||
4.75 x x x x x x x x x x
|
||||
|
||||
OM F F F F F F F F F F F A F A F A
|
||||
|
||||
HR Y Y Y Y Y Y Y Y Y
|
||||
FR Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y
|
||||
|
||||
The immediate question is, are the S0-15 bits a combinatory bitmask,
|
||||
or a list of distinct rate selections?
|
||||
|
||||
Explained in an example:
|
||||
|
||||
Say S = 0x18 = S7 | S8
|
||||
|
||||
If it is combinatory, the SDP equivalent is a single resulting payload type:
|
||||
|
||||
m=audio 1234 RTP/AVP 96
|
||||
a=fmtp:96 mode-set=0,2,7
|
||||
|
||||
If a list of distinct selections, the SDP equivalent is two distinct payload
|
||||
types:
|
||||
|
||||
m=audio 1234 RTP/AVP 96 97
|
||||
a=fmtp:96 mode-set=7
|
||||
a=fmtp:97 mode-set=0,2
|
||||
|
||||
|
Loading…
Reference in New Issue