Content for TS 23.333 Word version: 17.1.0
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5.12 Audio Transcoding p. 30
5.12.1 General |R12| p. 30
The MRFP shall support audio transcoding between streams of two Terminations within the same context where the streams are encoded differently, in accordance with standard H.248.1 principles, see ITU-T H.248.1 [3]. As minimum requirement the MRFP shall support the default 3GPP audio codec AMR (narrowband), and optionally any other audio codecs as specified in TS 26.114.
5.12.2 Handling of common codec parameters |R12| p. 30
Table 5.12.2.1 describes the MRFC handling of codec related parameters applicable to multiple codecs when the MRFC sends an SDP offer.
| Parameter | Handling of common codec parameter in sent SDP offer | Handling of common codec parameter in received SDP answer |
|---|---|---|
| ptime (NOTE) | The MRFC may add the parameter with a value according to configured preferences to the SDP offer. | If the ptime parameter is included in the received SDP answer, the MRFC shall supply the parameter to the MRFP for the termination towards the answerer in the remote descriptor. |
| maxptime (NOTE) | The MRFC may add the parameter with a value according to the MRFP capabilities to the SDP offer. | If the maxptime parameter is included in the received SDP answer, the MRFC shall supply the parameter to the MRFP for the termination towards the answerer in the remote descriptor. |
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NOTE:
This SDP attribute is defined in RFC 4566. It applies to all codecs offered in an SDP media line.
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Table 5.12.2.2 describes the MRFC handling of codec related parameters applicable to multiple codecs when the MRFC receives an SDP offer.
| Parameter | Handling of common codec parameter in received SDP offer | Handling of common codec parameter in sent SDP answer |
|---|---|---|
| ptime (NOTE) | If the ptime parameter is included in the received SDP offer, the MRFC shall supply the parameter to the MRFP for the termination towards the offerer in the remote descriptor. | The MRFC may add the ptime parameter with a value according to configured preferences to the SDP answer. |
| maxptime (NOTE) | If the maxptime parameter is included in the received SDP offer, the MRFC shall supply the parameter to the MRFP for the termination towards the offerer in the remote descriptor. | The MRFC may add the maxptime parameter with a value according to the MRFP capabilities to the SDP answer. |
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NOTE:
This SDP attribute is defined in RFC 4566. It applies to all codecs offered in an SDP media line.
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The MRFP handling of codec related parameters applicable to multiple codecs shall follow Table 5.13.2.2 in TS 23.334.
5.12.3 Handling of the EVS speech codec |R12| p. 31
The Enhanced Voice Services (EVS) speech codec is defined in TS 26.441. Its RTP payload type is defined in TS 26.445, and procedures for its usage as IMS Multimedia Telephony speech codec are defined in TS 26.114.
The MRFC and the MRFP may support transcoding to and from the EVS speech codec. If they do so, the procedures in the present clause apply.
Table 5.12.3.1 describes the MRFC handling of EVS codec parameters when the MRFC sends an SDP offer for an EVS payload type, and that EVS payload type is selected in the SDP answer. In addition, rules for the parameter handling in TS 26.445 shall apply.
| Parameter | Handling for EVS payload type added to an SDP offer | Handling if offered EVS payload type is accepted in the SDP answer |
|---|---|---|
| evs-mode-switch (NOTE 1) | If the MRFC expects that interworking between AMR-WB and EVS is required, it shall include the evs-mode-switch with value 1. Otherwise the MRFC shall not include the evs-mode-switch. | If the evs-mode-switch parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP for the termination towards the answerer in the remote descriptor. |
| hf-only (NOTE 1) | If the MRFC is configured to negotiate using only the header-full EVS RTP payload format, the MRFC shall include the hf-only parameter with a value 1. | If the hf-only parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| dtx (NOTE 1) | If the usage of DTX is not desired in the sending and receiving direction (e.g. due to DTX capabilities of expected codecs to transcode with), the MRFC shall include the dtx parameter with a value 0. | If the dtx parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| dtx-recv (NOTE 1) | If receiving DTX is not desired and the dtx parameter is not included, the MRFC shall include the dtx-recv parameter with a value 0. If both the dtx and dtx-recv parameters are included, those parameters shall have the same value; however, inclusion of the dtx-recv parameter is not required if the dtx parameter is included. | If the dtx-recv parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| br (NOTE 1) | If the MRFC desires the same bit rate range for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range to match MRFP capabilities and possible configured policies, it shall supply the br parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. If the MRFC also supplies the bw, bw-send or bw-recv parameter, the value of the br parameter shall be compatible with the values of those parameters. | If the br parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| br-send (NOTE 1) | If the MRFC desires a different bit rate (range) for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range for the send direction to match MRFP capabilities and possible configured policies, it shall supply the br-send parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. If the MRFC also supplies the bw or bw-send parameter, the value of the br-send parameter shall be compatible with the values of those parameters. | If the br-send parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| br-recv (NOTE 1) | If the MRFC desires a different bit rate (range) for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range for the receive direction to match MRFP capabilities and possible configured policies, it shall supply the br-recv parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. If the MRFC also supplies the bw or bw-recv parameter, the value of the br-recv parameter shall be compatible with the values of those parameters. | If the br-recv parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| bw (NOTE 1) | If the MRFC desires the same sampling bandwidth(s) for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidths to match MRFP capabilities, sampling bandwidths of expected codecs EVS will be transcoded to, and possible configured policies, it shall supply the bw parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. | If the bw parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| bw-send (NOTE 1) | If the MRFC desires different sampling bandwidths for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidths in the send direction to match MRFP capabilities, sampling bandwidths of expected codecs EVS will be transcoded to and possible configured policies, it shall supply the bw-send parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. | If the bw-send parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| bw-recv (NOTE 1) | If the MRFC desires different sampling bandwidths for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidths in the receive direction to match MRFP capabilities, sampling bandwidths of expected codecs EVS will be transcoded to, and possible configured policies, it shall supply the bw-recv parameter in the SDP offer it sends. Otherwise the MRFC shall not include this parameter in the SDP offer. | If the bw-recv parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| cmr (NOTE 1) | If the MRFC desires to disable codec mode requests within the RTP payload of the EVS primary mode (due to the MRFP capabilities or policies), it shall include the cmr parameter with value -1 in the SDP offer it sends. | If the cmr parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| ch-aw-recv (NOTE 1) | The MRFC shall include the ch-aw-recv parameter in the SDP offer if it desires to control the channel-aware mode of EVS in the receive direction, e.g. to disable it with value -1. The MRFC shall consider the capabilities of the MRFP when it chooses an appropriate value. | If the ch-aw-recv parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| number of channels (NOTE 2) | The MRFC shall only include the "number of channels" parameter in the SDP offer if it desires to send or receive multiple channels. If the desired number of channels in the send and receive direction differs, the MRFC shall include the higher value. The MRFC should consider the number of channels of expected codecs EVS will be transcoded to. | If the "number of channels" parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| ch-send (NOTE 1) | The MRFC shall only include the ch-send parameter in the SDP offer if it desires to send multiple channels, with different numbers of channels in the send and receive direction. The MRFC should consider the number of channels of expected codecs EVS will be transcoded to. | If the ch-send parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| ch-recv (NOTE 1) | The MRFC shall only include the ch-recv parameter in the SDP offer if it desires to receive multiple channels, with different numbers of channels in the send and receive direction. The MRFC should consider the number of channels of expected codecs EVS will be transcoded to. | If the ch-recv parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| mode-set (NOTE 3) | The MRFC shall only include the mode-set parameter in the SDP offer if it desires to restrict the mode-set of AMR-WB IO mode. The MRFC should only restrict the mode-set if the expected codecs EVS will be interworked with is AMR-WB and has a restricted mode-set. | If the mode-set parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| mode-change-period (NOTE 3) | The MRFC shall only include the mode-change-period parameter with value 2 in the SDP offer if it desires to restrict the mode-change-period of received packets in AMR-WB IO mode. The MRFC should only restrict the mode-change-period if the expected codec EVS will be interworked with is AMR-WB and has such a restriction. | If the mode-change-period parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| mode-change-capability (NOTE 3) | The MRFC shall either include the mode-change-capability parameter with value 2 or omit the parameter in the SDP offer. | If the mode-change-capability parameter is contained in the SDP answer, the MRFC may forward this parameter to the MRFP in the remote descriptor. |
| mode-change-neighbor (NOTE 3) | The MRFC shall only include the mode-change-neighbor parameter in the SDP offer if it desires to restrict the mode-change within received packets of AMR-WB IO mode to neighboring modes. The MRFC should consider the mode-change-neighbor parameter of the expected codec EVS will be interworked with if this is AMR-WB. | If the mode-change-neighbor parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| max-red (NOTE 5) | The MRFC shall only include the max-red parameter in the SDP offer if it desires to restrict the maximum redundancy of received packets. MRFC shall consider the capabilities of the MRFP, and should consider a max-red parameter of the expected codec EVS will be interworked with if this is AMR-WB. | If the max-red parameter is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
| 3gpp_mtsi_app_adapt (NOTE 4) | If the MRFP supports RTCP APP based adaptation messages defined in TS 26.114, and the MRFC has a policy to negotiate the usage of those messages, the MRFC shall include the 3gpp_mtsi_app_adapt SDP attribute indicating the supported APP messages in the SDP offer. | If the 3gpp_mtsi_app_adapt attribute is contained in the SDP answer, the MRFC shall forward this parameter to the MRFP in the remote descriptor. |
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NOTE 1:
This MIME parameter of the EVS RTP payload type is defined in TS 26.445. It is encapsulated within the SDP "a=fmtp" attribute defined RFC 4566.
NOTE 2:
This number of channels are encoded as "encoding parameters" of the SDP "a=rtpmap" attribute defined in RFC 4566.
NOTE 3:
This MIME parameter of the EVS RTP payload type relates to AMR-WB IO mode and is defined in RFC 4867. It is encapsulated within the SDP "a=fmtp" attribute defined RFC 4566.
NOTE 4:
This SDP attribute is defined in TS 26.114. It applies to all codecs offered in an SDP media line. However, some values are specific to EVS.
NOTE 5:
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When receiving an SDP offer that contains an EVS codec payload type, the MRFC shall handle the EVS codec parameters as described in Table 5.12.3.2. In addition, rules for the parameter handling in TS 26.445 shall apply.
| Parameter | Handling of EVS payload type parameter received in the SDP offer | EVS payload type supplied in the SDP answer |
|---|---|---|
| evs-mode-switch (NOTE 1) | If the evs-mode-switch parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the evs-mode-switch parameter is contained in the SDP offer, the MRFC shall include the evs-mode-switch parameter with unmodified value in the SDP answer. Otherwise, if the MRFC decides to interwork between AMR-WB and EVS, it shall include the evs-mode-switch with value 1. Otherwise the MRFC shall not include the evs-mode-switch. If the MRFC supplies the evs-mode-switch in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| hf-only (NOTE 1) | If the hf-only parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the hf-only parameter is contained in the SDP offer, the MRFC shall include the hf-only parameter with unmodified value in the SDP answer. Otherwise, the MRFC may include the hf-only parameter with a value matching negotiated values of possible other EVS call legs in the conference. If the MRFC supplies the hf-only parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| dtx (NOTE 1) | If the dtx parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the dtx parameter is contained in the SDP offer, the MRFC shall include the dtx parameter with unmodified value in the SDP answer. If the dtx parameter is not contained in the SDP offer and if a dtx-recv parameter is contained in the SDP offer, the MRFC may include the dtx parameter in the SDP answer, and the value of the dtx parameter shall then be identical to that of the dtx-recv parameter in the SDP offer (e.g, if that value matches negotiated values of possible other EVS call legs in the conference). If the dtx parameter is not contained in the SDP offer and if the dtx-recv parameter is not contained in the SDP offer the MRFC may include in the SDP answer the dtx parameter with a value matching negotiated values of possible other EVS call legs in the conference. If the MRFC supplies the dtx parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| dtx-recv (NOTE 1) | If the dtx-recv parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If no dtx parameter is included in the SDP answer and if the reception of DTX is not desired, the MRFC shall include in the SDP answer the dtx-recv parameter with a value 0. If both the dtx and dtx-recv parameters are included, those parameters shall have the same value; however, inclusion of the dtx-recv parameter is not required if the dtx parameter is included. If the MRFC supplies the dtx-recv parameter in the SDP answer, it should also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| br (NOTE 1) | If the br parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated bitrates, or a subset of them, in EVS primary mode in the send and receive direction. If the indicated bitrates, and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the br parameter is contained in the SDP offer, the MRFC shall select a bitrate value, which is either the received br value or a subset of it, based on MRFP capabilities, possible configured policies, and the negotiated br range of possible other EVS call legs in the conference, and shall include the br parameter with the selected value that is also supplied towards the MRFP in the SDP answer. Otherwise, if the MRFC desires the same bit rate range for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range to match MRFP capabilities, possible configured policies, and the negotiated br range of possible other EVS call legs in the conference, the MRFC shall supply the br parameter in the SDP answer it sends. Otherwise the MRFC shall not include this parameter in the answer. If the MRFC also supplies the bw, bw-send or bw-recv parameter, the value of the br parameter shall be compatible with the values of those parameters. If the MRFC supplies the br parameter in the SDP answer, it shall also supply to the MRFP the br parameter in the local descriptor for the termination towards the offerer with the same value. |
| br-send (NOTE 1) | If the br-send parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated bitrates, or a subset of them, in EVS primary mode in the receive direction. If the indicated bitrates, and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the br-recv parameter is contained in the SDP offer, the MRFC shall select a bitrate value, which is either the received br-recv value or a subset of it, based on MRFP capabilities possible configured policies, and the negotiated br range of possible other EVS call legs in the conference, and the MRFC shall include the br-send parameter with the selected value that is also supplied towards the MRFP in the SDP answer. Otherwise, if the MRFC desires a different bit rate (range) for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range for the send direction to match MRFP capabilities and possible configured policies, it shall supply the br-send parameter in the SDP answer it sends. Otherwise the MRFC shall not include the br-send parameter in the SDP answer. If the MRFC also supplies the bw or bw-send parameter, the value of the br-send parameter shall be compatible with the values of those parameters. If the MRFC supplies the br-send parameter in the SDP answer, it shall also supply to the MRFP the br-send parameter in the local descriptor for the termination towards the offerer with the same value. |
| br-recv (NOTE 1) | If the br-recv parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated bitrates, or a subset of them, in EVS primary mode in the send direction. If the indicated bitrates, and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the br-send parameter is contained in the SDP offer, the MRFC shall select a bitrate value, which is either the received br-send value or a subset of it, based on MRFP capabilities, possible configured policies, and the negotiated br range of possible other EVS call legs in the conference, and the MRFC shall include the br-recv parameter with the selected value that is also supplied towards the MRFP in the SDP answer. Otherwise, if the MRFC desires a different bit rate (range) for the send and receive direction in EVS primary mode, and wants to restrict the bit rate range for the receive direction to match MRFP capabilities and possible configured policies, it shall supply the br-recv parameter in the SDP answer it sends. Otherwise the MRFC shall not include the br-recv parameter in the SDP answer. If the MRFC also supplies the bw or bw-recv parameter, the value of the br-recv parameter shall be compatible with the values of those parameters. If the MRFC supplies the br-recv parameter in the SDP answer, it shall also supply to the MRFP the br-recv parameter in the local descriptor for the termination towards the offerer with the same value. |
| bw (NOTE 1) | If the bw parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated sampling bandwidth(s), or a subset of them, in EVS primary mode in the send and receive direction. If the indicated sampling bandwidth(s), and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the bw parameter is contained in the SDP offer, the MRFC shall select a sampling bandwidth value, which is either the received bw value or a subset of it, based on MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, and the MRFC shall include the bw parameter with the selected value that is also supplied towards the MRFP in the SDP answer. Otherwise, if the MRFC desires the same sampling bandwidth(s) for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidth(s) to match MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, the MRFC shall supply the bw parameter in the SDP answer it sends. Otherwise the MRFC shall not include this parameter in the SDP answer. If the MRFC also supplies the br, br-send or br-recv parameter, the value of the bw parameter shall be compatible with the values of those parameters. If the MRFC supplies the bw parameter in the SDP answer, it shall also supply to the MRFP the bw parameter in the local descriptor for the termination towards the offerer with the same value. |
| bw-send (NOTE 1) | If the bw-send parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated sampling bandwidths, or a subset of them, in EVS primary mode in the receive direction. If the indicated sampling bandwidths, and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the bw-recv parameter is contained in the SDP offer, the MRFC shall select a sampling bandwidths value, which is either the received bw-recv value or a subset of it, based on MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, and the MRFC shall include the bw-send parameter with the selected value in the SDP answer. Otherwise, if the MRFC desires a different sampling bandwidths for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidths for the send direction to match MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, the MRFC shall supply the bw-send parameter in the SDP answer it sends. Otherwise the MRFC shall not include the br-send parameter in the SDP answer. If the MRFC also supplies the bw or bw-send parameter, the value of the br-send parameter shall be compatible with the values of those parameters. If the MRFC supplies the bw-send parameter in the SDP answer, it shall also supply to the MRFP the bw-send parameter in the local descriptor for the termination towards the offerer with the same value. |
| bw-recv (NOTE 1) | If the br-recv parameter is contained in the SDP offer, the MRFC shall check if the MRFP supports the indicated sampling bandwidths, or a subset of them, in EVS primary mode in the send direction. If the indicated sampling bandwidths, and even each subset of them, are not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, it shall forward the bw-recv parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the bw-send parameter is contained in the SDP offer, the MRFC shall select a sampling bandwidths value, which is either the received bw-send value or a subset of it, based on MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, and the MRFC shall include the bw-recv parameter with the selected value in the SDP answer. Otherwise, if the MRFC desires a different sampling bandwidths for the send and receive direction in EVS primary mode, and wants to restrict the sampling bandwidths for the receive direction to match MRFP capabilities, possible configured policies, and the negotiated bw range of possible other EVS call legs in the conference, the MRFC shall supply the bw-recv parameter in the SDP answer it sends. Otherwise the MRFC shall not include the bw-recv parameter in the SDP answer. If the MRFC also supplies the br or br-recv parameter, the value of the bw-recv parameter shall be compatible with the values of those parameters. If the MRFC supplies the bw-send parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| cmr (NOTE 1) | If the cmr parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the cmr parameter is contained in the SDP offer, the MRFC shall include the cmr parameter with unmodified value in the SDP answer. Otherwise, if the MRFP desires to disable codec mode requests within the RTP payload of the EVS primary mode (due to the MRFP capabilities, possible configured policies, and the negotiated CMR mode of possible other EVS call legs in the conference, it shall include the cmr parameter with value -1 in the SDP answer it sends. If the MRFC supplies the cmr parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| ch-aw-recv (NOTE 1) | If the ch-aw-recv parameter is contained in the SDP offer the MRFC shall check if the MRFP supports the indicated mode in the send direction. If the indicated mode is not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the MRFC it desires to control the channel-aware mode of EVS in the receive direction, e.g. to disable it with value -1, it shall include the ch-aw-recv parameter in the SDP offer and shall also supply the ch-aw-recv parameter to the MRFP in the local descriptor for the termination towards the offerer with the same value. The MRFC shall consider the capabilities of the MRFP and the negotiated ch-aw-recv mode of possible other EVS call legs in the conference when it chooses an appropriate value. |
| number of channels (NOTE 2) | If the "number of channels" parameter is contained in the SDP offer the MRFC shall check if the MRFP supports the indicated number of channels. If the indicated number of channels is not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the "number of channels" parameter is contained in the SDP offer, the MRFC shall include the "number of channels" parameter with unmodified value in the SDP answer and shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| ch-send (NOTE 1) | If the ch-send parameter is contained in the SDP offer the MRFC shall check if the MRFP supports the indicated number of channels in the receive direction. If the indicated number of channels is not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type, the MRFC shall forward the ch-send parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the ch-recv parameter is contained in the SDP offer, the MRFC shall include the ch-send parameter with unmodified value in the SDP answer and shall also supply the ch-send parameter to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| ch-recv (NOTE 1) | If the ch-recv parameter is contained in the SDP offer the MRFC shall check if the MRFP supports the indicated number of channels in the send direction. If the indicated number of channels is not supported, the MRFC shall not select the EVS payload type. If the MRFC selects the EVS payload type for transcoding, the MRFC shall forward the ch-recv parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the ch-send parameter is contained in the SDP offer, the MRFC shall include the ch-recv parameter with unmodified value in the SDP answer and shall also supply the ch-recv parameter to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| mode-set (NOTE 3) | If the mode-set parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the mode-set parameter is contained in the SDP offer, the MRFC shall include the mode-set parameter with unmodified value in the SDP answer. Otherwise, if EVS or AMR-WB is used on possible other call legs in the conference, the MRFC should include the mode-set parameter with a value indicating the mode that was negotiated on those other call legs (or omit it if no restrictions applied before). If the MRFC supplies the mode-set parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| mode-change-period (NOTE 3) | If the mode-change-period parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If the MRFC select the EVS payload type, the MRFC shall either include the mode-change-capability parameter with value 2 or omit it. If the MRFC supplies the mode-change-capability parameter in the SDP answer, it may also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| mode-change-capability (NOTE 3) | If the mode-change-capability parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC may forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If EVS or AMR-WB is used on possible other EVS call legs in the conference, the MRFC should include the mode-change-capability parameter with a value indicating the mode that was negotiated on those other call legs (or omit it if no restrictions applied before). If the MRFC supplies the mode-change-capability parameter in the SDP answer, it may also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| mode-change-neighbor (NOTE 3) | If the mode-change-neighbor parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | If EVS or AMR-WB was used on possible other EVS call legs in the conference, the MRFC should include the mode-change-neighbor parameter with a value indicating the mode that was negotiated on those other call legs (or omit it if no restrictions applied before). If the MRFC supplies the mode-change-neighbor parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| max-red (NOTE 5) | If the max-red parameter is contained in the SDP offer and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP for the termination towards the offerer in the remote descriptor. | The MRFC shall only include the max-red parameter in the SDP answer if it desires to restrict the maximum redundancy of received packets. When selecting the value of the max-red parameter, the MRFC shall consider the capabilities of the MRFP and, if EVS or AMR-WB is used on possible other EVS call legs in the conference, the redundancy that was negotiated on those call legs. If the MRFC supplies the max-red parameter in the SDP answer, it shall also supply it to the MRFP in the local descriptor for the termination towards the offerer with the same value. |
| 3gpp_mtsi_app_adapt (NOTE 4) | If the 3gpp_mtsi_app_adapt parameter is contained in the SDP answer, and the MRFC select the EVS payload type, the MRFC shall forward this parameter to the MRFP the MRFC shall forward this parameter to the MRFP in the remote descriptor. | If the MRFP supports RTCP APP based adaptation messages defined in TS 26.114, and the MRFC has a policy to negotiate the usage of those messages, the MRFC shall include the 3gpp_mtsi_app_adapt SDP attribute indicating the allowed APP messages in the SDP answer. If EVS is used possible other EVS call legs in the conference, the MRFC should consider the negotiated RTCP APP packet types on those call legs in addition to the MRFP capabilities when selecting the allowed RTCP APP messages. |
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NOTE 1:
This MIME parameter of the EVS RTP payload type is defined in TS 26.445. It is encapsulated within the SDP "a=fmtp" attribute defined RFC 4566.
NOTE 2:
This number of channels are encoded as "encoding parameters" of the SDP "a=rtpmap" attribute defined in RFC 4566.
NOTE 3:
This MIME parameter of the EVS RTP payload type relates to AMR-WB IO mode and is defined in RFC 4867]. It is encapsulated within the SDP "a=fmtp" attribute defined RFC 4566.
NOTE 4:
This SDP attribute is defined in TS 26.114. It applies to all codecs offered in an SDP media line. However, some values are specific to EVS.
NOTE 5:
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The MRFP handling of EVS codec parameters shall follow Table 5.13.3.3 in TS 23.334. The MRFP should support transcoding of EVS with bandwidths (sampling rates) which are supported by codec the MRFP is capable to transcode EVS to/from (e.g. NB for AMR, and WB for AMR-WB).
5.13 Video Transcoding p. 40
The MRFP shall support video transcoding between streams of two Terminations within the same context where the streams are encoded differently, in accordance with standard H.248 principles, see ITU-T H.248.1 [3].
