4 Codecs and media handling for MCPTT
26.1793GPPCodecs and media handlingMission Critical Push to Talk (MCPTT)Release 17TS
4.1 MCPTT client
4.1.1 Codec
MCPTT clients shall support the AMR-WB codec as specified in 3GPP TS 26.171 [7], 3GPP TS 26.190 [9], 3GPP TS 26.173 [8] and 3GPP TS 26.204 [14], including all 9 modes and source controlled rate operation as specified in 3GPP TS 26.193 [12], voice activity detection as specified in 3GPP TS 26.194 [13], comfort noise generation as specified in 3GPP TS 26.192 [11] and error concealment as specified in TS 26.191[10]. The MCPTT clients shall be capable of operating with any subset of these 9 codec modes.
Based on operator / MCPTT service provider policy, MCPTT clients may additionally support the EVS codec in super-wideband mode.
If an operator / MCPTT service provider chooses to additionally use SWB according to its policy, then an MCPTT client that offers super-wideband speech communication shall support the EVS codec in SWB mode as defined in 3GPP TS 26.441 [15], 3GPP TS 26.445 [18], 3GPP TS 26.442 [16], 3GPP TS 26.452 [27], 3GPP TS 26.443 [17], discontinuous transmission 3GPP TS 26.450 [21], voice activity detection as specified in 3GPP TS 26.451 [22], comfort noise generation as specified in 3GPP TS 26.449 [20] and error concealment as specified in TS 26.447 [19].
NOTE: In evaluating the codec alternatives for MCPTT, two codecs; AMR-WB and EVS were considered in detail. The EVS codec was shown to provide statistically significant performance improvements relative to the AMR-WB codec for some of the MCPTT KPIs as studied and reported in the TR 26.989 [4]. After consideration of all factors in Release 13, as documented in TR 26.989 [4], the currently widely deployed and available AMR-WB codec meets the needs of MCPTT services and was decided upon as the mandatory codec for MCPTT.
4.1.2 Control plane protocol
General MCPTT client procedures for SDP offer-answer are specified in 3GPP TS 24.379 [5] and 3GPP TS 24.380 [6].
MCPTT clients shall support both "RTP/AVP" [25] and "RTP/SAVP" [26] profiles in SDP offer/answer. MCPTT clients shall not reject an SDP offer due to offered RTP profile being either "RTP/AVP" or "RTP/SAVP". MCPTT clients may, based on operator / MCPTT service provider policy, offer either "RTP/AVP" or "RTP/SAVP" RTP profiles.
MCPTT clients shall support and offer a payload type with AMR-WB.
If an operator / MCPTT service provider policy enables an MCPTT service using the EVS codec in SWB mode, then MCPTT clients may, based on operator / MCPTT service provider policy, additionally offer a payload type with the EVS codec in SWB mode.
The offer-answer protocol, setting of the codec preference order, and the generation of SDP offer and answer shall be configured according to operator / MCPTT service provider policy.
4.1.3 User plane protocol
MCPTT clients shall support both RTP [24] and SRTP [26] media transport.
An MCPTT client shall understand the payload formats and options as defined in RFC 4867 [23]. The MCPTT client does not have to support operating according to all the options defined in RFC 4867 but shall be capable of properly accepting or rejecting all options.
The following payload format options from RFC 4867 are defined as follows to ensure minimum interoperability:
– bandwidth-efficient shall be supported
– mode-set: shall support all modes and shall offer no particular mode set
– mode-change-period: both "1" and "2" shall be supported, "1" shall be offered (or not included)
– mode-change-capability: both "1" and "2" shall be supported, "2" shall be offered
– mode-change-neighbor: both "0" and "1" shall be supported, "0" shall be offered (or not included)
– channels: shall offer "1"
Other parameters:
– ptime: shall be supported, "20" shall be offered
– maxptime: shall be supported, "240" shall be offered
– max-red: shall be supported, "0" shall be offered
If, based on operator / MCPTT service provider policy, the MCPTT service additionally supports the EVS codec in SWB mode, then an MCPTT client that supports the optional EVS codec in SWB mode shall understand the EVS payload format as specified in 3GPP TS 26.445 [18] in order to support EVS in SWB mode. The MCPTT client does not have to support operating according to all the options defined in 3GPP TS 26.445 [18] but must be capable of properly accepting or rejecting all options.
4.1.4 De-jitter buffer
When MCPTT voice traffic is received on the MBMS bearer in MBMS/MBSFN, the traffic is scheduled to arrive at intervals of multiples of 40ms. The received traffic could also exhibit time-varying jitter introduced in the backhaul and the uplink transmission by the talker before being scheduled for transmission on the MBMS bearer. The MCPTT UE receiving traffic on an MBMS bearer shall support and use a de-jitter buffer that is able to manage this amount of jitter.
4.2 MCPTT network
4.2.1 Control plane protocol
MCPTT Server procedures are specified in 3GPP TS 24.379 [5] and 3GPP TS 24.380 [6].
MCPTT call media codec information shall include codecs according to MCPTT Client capabilities as specified in clause 4.1.1.
Annex A (informative):
Change history
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Change history |
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Date |
TSG # |
TSG Doc. |
CR |
Rev |
Cat |
Subject/Comment |
New version |
|
2016-03 |
SA#71 |
Approved at TSG SA#71 |
13.0.0 |
||||
|
2016-06 |
SA#72 |
SP-160265 |
0001 |
1 |
F |
Introduction and correction to scope and adjustment of references to TR 26.879 to reflect its renumbering |
13.1.0 |
|
2016-09 |
SA#73 |
SP-160593 |
0003 |
– |
F |
Addition of mandatory RTP profiles for MCPTT |
13.2.0 |
|
Change history |
|||||||
|
Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
|
2017-03 |
75 |
Version for Release 14 |
14.0.0 |
||||
|
2018-06 |
80 |
Version for Release 15 |
15.0.0 |
||||
|
2019-03 |
83 |
SP-190036 |
0004 |
– |
B |
Correction and addition of reference to Alt_FX_EVS implementation |
16.0.0 |
|
2022-04 |
– |
– |
– |
– |
– |
Update to Rel-17 version (MCC) |
17.0.0 |