Content for TS 23.334 Word version: 17.2.0

1… 4… 5… 5.11… 5.12… 5.14… 5.18… 5.19… 5.20… 5.21… 6… 6.1.6… 6.1.11… 6.2… 6.2.10… 6.2.10.3.1.2 6.2.10.3.2 6.2.10.4… 6.2.10.4.3… 6.2.10.5 6.2.10.6… 6.2.10A… 6.2.13… 6.2.14… 6.2.14.3 6.2.14.4… 6.2.15… 6.2.17… 6.2.17.3… 6.2.17.5… 6.2.18… 6.2.20 6.2.21… 6.2.22… 6.2.22.3… 6.2.22.3.2 6.2.23 6.2.24 6.2.25 7 8… 8.3 8.4 8.5… 8.23…

6.2.14.4 PS to CS Access Transfer procedure with media anchored in IMS-AGW (ATGW) 6.2.14.5 ECN support during PS to CS Access Transfer procedure with media anchored in IMS-AGW (ATGW) 6.2.14.6 Support of generic image attributes 6.2.14.7 Handling of common codec parameters 6.2.14.8 EVS speech codec support
...

6.2.14.4 PS to CS Access Transfer procedure with media anchored in IMS-AGW (ATGW) p. 128

The signalling flow shown in Figure 6.2.14.4.1 gives an example for PS to CS access transfer with media anchored in the IMS-AGW (ATGW). In this case, the media has been anchored in IMS-AGW (ATGW) as specified in clause 6.2.14.3.

Copy of original 3GPP image for 3GPP TS 23.334, Fig. 6.2.14.4.1: PS to CS Access Transfer with transcoding in IMS-AGW (ATGW)

Figure 6.2.14.4.1: PS to CS Access Transfer with transcoding in IMS-AGW (ATGW)
(⇒ copy of original 3GPP image)

Step 1.

The IMS-ALG (ATCF) receives an SDP offer in SIP signalling from the MSC Server. The IMS-ALG (ATCF) checks whether transcoding is required.

Step 2.

The IMS-ALG (ATCF) sends a H.248 ADD request command to create the target access leg termination and to request IP resources to execute ATGW function. Topology is changed and media reconfigured to connect media between T2 and T3.

If no media transcoding is required this may be indicated by signalling "-" or by signalling the same media information on T3 as is configured on T2, following the principles specified in clause 6.2.14.3.

If media transcoding is required (as illustrated in this example), the IMS-ALG (ATCF) signals media related sub-fields in the media descriptor to the IMS-AGW (ATGW). The IMS-AGW (ATGW) determines from the media configuration whether transcoding is required on a stream between two terminations between which data flow is permitted.

Step 3.

The IMS-AGW (ATGW) creates the target access leg termination T3 and starts to apply transcoding between T2 and T3 (if required).

Step 4.

The IMS-AGW (ATGW) replies to IMS-ALG (ATCF) with a H.248 ADD reply command and provides the local address and port of the outgoing termination.

Step 5.

The IMS-ALG (ATCF) returns an SDP answer to the MSC Server; the IP address inside the SDP uses the information coming from IMS-AGW (ATGW).

Step 6.

Upon successful completion of the access transfer procedure, the IMS-ALG (ATCF) receives a BYE request from the SCC AS if there is no more media flows on the PS access.

Step 7.

The IMS-ALG (ATCF) sends a H.248 SUB request command to subtract the source access leg termination.

Step 8.

The IMS-AGW (ATGW) releases the source access leg termination.

Step 9.

The IMS-AGW (ATGW) replies to IMS-ALG (ATCF) with a H.248 SUB reply command.

6.2.14.5 ECN support during PS to CS Access Transfer procedure with media anchored in IMS-AGW (ATGW) p. 129

The signalling flow shown in Figure 6.2.14.4.1 gives an example for PS to CS access transfer with media anchored in the IMS-AGW (ATGW). The following additional actions are required if ECN is supported by the IMS-ALG/IMS-AGW:

-
1. If ECN was supported during the PS session transparently and the SDP offer received from the MSC Server does not indicate ECN support, it is not possible to maintain transparent ECN support to the IMS CN. The IMS-ALG (ATCF) shall modify the Termination T2 to act as an ECN endpoint toward the IMS CN (see Clause 5.12). Additionally the IMS-ALG (ATCF) shall disable ECN on the termination T3 (or T1).
2. If ECN was supported during the PS session transparently and the SDP offer received from the MSC Server does indicate ECN support and no transcoding is required (codec types and modes are aligned between ICS side and IMS CN), then the IMS-ALG (ATCF) shall request ECN transparent properties when seizing T3 and respond to the MSC Server with ECN supported in the SDP answer (step 5).
3. If ECN was supported during the PS session transparently and the SDP offer received from the MSC Server does indicate ECN support and transcoding is required between the CS leg and the IMS-CN, then the IMS-ALG (ATCF) shall request ECN endpoint properties when seizing T3 (or modify the termination T1 with ECN endpoint properties) and respond to the MSC Server with ECN supported in the SDP answer (step 5). Additionally the IMS-ALG (ATCF) shall modify the Termination T2 to act as an ECN endpoint toward the IMS CN (see Clause 5.12).
4. If ECN was not supported during the PS session and the SDP Offer received from the MSC Server indicates ECN support, the IMS-ALG (ATCF) shall not accept ECN support in the SDP answer (step 5).

6.2.14.6 Support of generic image attributes |R12| p. 130

6.2.14.6.1 General p. 130

The IMS-ALG (ATCF) and the IMS-AGW (ATGW) may support a media-level SDP image attribute "a=imageattr" defined in RFC 6236 to negotiate the image size for sending and receiving video.

The list of image sizes per payload type supported by the IMS-AGW (ATGW) shall be preconfigured in the IMS-ALG (ATCF). If the image sizes received within an SDP body on the Mw/Mx interface are not all supported by the IMS-AGW (ATGW) then the IMS-ALG (ATCF) shall only send the list of corresponding IMS-AGW (ATGW) supported image sizes to the IMS-AGW (ATGW). If no image size is supported by the IMS-AGW (ATGW), the IMS-ALG (ATCF) shall not send the generic image attribute parameter to the IMS-AGW (ATGW).

The signalling flow shown in Figure 6.2.14.3.1 gives an example for a PS session establishment with media anchored in the IMS-AGW (ATGW). The following additional actions may be performed if the negotiation of the image size is supported by the IMS-ALG/IMS-AGW:

upon receipt of an SDP offer containing the image attribute(s) and if the received image sizes are supported by the IMS-AGW (ATGW) then the IMS-ALG (ATCF) may send the generic image attribute parameters for the send and receive directions to the IMS-ALG (ATCF) (step 2 or step 8) when seizing or modifying an outgoing termination;

NOTE 1:
If the offered image attributes are not supported by the IMS-AGW (ATGW) then the IMS-ALG (ATCF) will not send the generic image attribute parameter to the IMS-AGW (ATGW).
the IMS-ALG (ATCF) shall include the SDP image attribute(s) "a=imageattr" indicating the supported image sizes in the modified SDP offer (step 5);
upon receipt of an SDP answer containing the generic image attribute(s) and if the received image sizes are supported by the IMS-AGW (ATGW) then the IMS-ALG (ATCF) may include the generic image attribute parameter to the IMS-AGW (ATGW) (step 11) when seizing an incoming termination; and
the IMS-ALG (ATCF) shall include the SDP image attribute(s) "a=imageattr" indicating the supported image sizes in the modified SDP answer (step 14).

NOTE 2:
The IMS-ALG (ATCF) not supporting the negotiation of generic image attributes will ignore the SDP image attribute received in the SDP offer and will send the SDP offer/answer without any associated SDP image attribute.

When sending the SDP body with image attribute(s) on the Mw/Mx interface the IMS-ALG (ATCF) shall include in the "a=imageattr":

"recv" keyword and corresponding image sizes which the IMS-AGW (ATGW) supports in the receiving direction; and
"send" keyword and corresponding image sizes which the IMS-AGW (ATGW) supports in the sending direction.

The signalling flow shown in Figure 6.2.14.4.1 gives an example for PS to CS access transfer with media anchored in the IMS-AGW (ATGW). The following additional actions may be performed if the negotiation of the image size is supported by the IMS-ALG/IMS-AGW:

if the image sizes were negotiated during the PS session and if the IMS-AGW (ATGW) applies the video transcoding (step 3) and if the IMS-AGW (ATGW) is configured with different image sizes on the receive direction of one termination and the send direction of another interconnected termination, then it shall adjust the frame sizes accordingly when forwarding video media streams and use the image size as described in TS 26.114 when sending media.

6.2.14.6.2 Indication of generic image attributes p. 131

The IMS-ALG (ATCF) may include the generic image attributes to the IMS-AGW (ATGW). The example sequence is shown in Figure 6.2.14.6.2.1.

Copy of original 3GPP image for 3GPP TS 23.334, Fig. 6.2.14.6.2.1: Request to reserve AGW connection point with generic image attribute

Figure 6.2.14.6.2.1: Request to reserve AGW connection point with generic image attribute
(⇒ copy of original 3GPP image)

6.2.14.7 Handling of common codec parameters |R12| p. 131

For PS session origination, Figure 6.2.14.3.1 shall apply with the handling of codec related parameters applicable to multiple codecs in Table 6.2.14.7.1, assuming that codec related information is signalled to the IMS-AGW(ATGW) at this stage. If no codec related information is signalled to the IMS-AGW at this stage, the common codec related parameters for the termination towards the SDP answerer in Table 6.2.14.7.1 shall be signalled towards the IMS-AGW during a PS to CS Access Transfer procedure.

Table 6.2.14.7.1: IMS-ALG handling of common codec related SDP parameters during PS session origination

Parameter	Handling in SDP offer	Handling in the SDP answer
ptime (NOTE)	If the ptime parameter is included in the received SDP offer, the IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor. If the value is supported by the IMS-AGW for receiving media, the IMS-ALG should keep the value from the received SDP offer unchanged in the SDP offer it sends. If the IMS-AGW only supports a lower ptime value, the IMS-ALG shall supply the ptime value according to configured preferences in the SDP offer it forwards. If no ptime value was contained in the received SDP offer, the IMS-ALG 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 IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the answerer in the remote descriptor. If the value is supported by the IMS-AGW for receiving media, the IMS-ALG should keep the value from the received SDP answer unchanged in the SDP answer it sends. If the IMS-AGW only supports a lower ptime value, the IMS-ALG shall supply the ptime value according to configured preferences in the SDP answer it forwards. If no ptime value was contained in the received SDP answer, the IMS-ALG may add the 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 IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor. If the value is supported by the IMS-AGW for receiving media, the IMS-ALG should keep the value from the received SDP offer unchanged in the SDP offer it sends. If the IMS-AGW only supports a lower maxptime value, the IMS-ALG shall supply the maxptime value according to the IMS-AGW capabilities in the SDP offer it forwards. If no maxptime value was contained in the received SDP offer, the IMS-ALG may add the parameter with a value according to the IMS-AGW capabilities to the SDP offer.	If the maxptime parameter is included in the received SDP answer, the IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the answerer in the remote descriptor. If the value is supported by the IMS-AGW for receiving media, the IMS-ALG should keep the value from the received SDP answer unchanged in the SDP answer it sends. If the IMS-AGW only supports a lower maxptime value, the IMS-ALG shall supply the maxptime value according to the IMS-AGW capabilities in the SDP answer it forwards. If no maxptime value was contained in the received SDP answer, the IMS-ALG may add the parameter with a value according to the IMS-AGW capabilities to the SDP answer.
NOTE: This SDP attribute is defined in RFC 4566. It applies to all codecs offered in an SDP media line.

For PS to CS Access Transfer, Figure 6.2.14.4.1 shall apply with the handling of codec related parameters applicable to multiple codecs in Table 6.2.14.7.2.

Table 6.2.14.7.2: IMS-ALG handling of common codec related SDP parameters during PS to CS Access Transfer

Parameter	Handling of common codec parameters received in the SDP offer	Common Codec parameters supplied in the SDP answer
ptime (NOTE)	If the ptime parameter is included in the received SDP offer, the IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	The IMS-ALG may add the 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 IMS-ALG shall supply the parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	The IMS-ALG may add the parameter with a value according to the IMS-AGW capabilities to the SDP answer.
NOTE: This SDP attribute is defined in RFC 4566. It applies to all codecs offered in an SDP media line.

6.2.14.8 EVS speech codec support |R12| p. 132

For PS session origination, Figure 6.2.14.3.1 shall apply with the EVS parameter handling in Table 6.2.14.8.1, assuming that EVS is "codec 1", which is selected, and that "codec 1" related information is signalled to the IMS-AGW(ATGW) at this stage. If no codec related information is signalled to the IMS-AGW at this stage, the EVS related parameters for the termination towards the SDP answerer in Table 6.2.14.8.1 shall be signalled towards the IMS-AGW during a PS to CS Access Transfer procedure.

Table 6.2.14.8.1: IMS-ALG handling of EVS related SDP parameters during PS session origination

For PS to CS Access Transfer, Figure 6.2.14.4.1 shall apply with the EVS parameter handling in Table 6.2.14.8.2, assuming that EVS is "codec 3", which is selected.

Table 6.2.14.8.2: IMS-ALG handling of EVS related SDP parameters during PS to CS Access Transfer

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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the evs-mode-switch parameter is contained in the SDP offer, the IMS-ALG shall include the evs-mode-switch parameter with unmodified value in the SDP answer. Otherwise, if EVS was used before the access transfer, the IMS-ALG should include the evs-mode-switch parameter with a value indicating the mode that was negotiated before the access transfer. Otherwise, if the IMS-ALG decides to transcode between AMR-WB and EVS (e.g. because AMR-WB was used before the access transfer), it shall include the evs-mode-switch with value 1. Otherwise the IMS-ALG shall not include the evs-mode-switch. If the IMS-ALG supplies the evs-mode-switch in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the hf-only parameter is contained in the SDP offer, the IMS-ALG shall include the hf-only parameter with unmodified value in the SDP answer. Otherwise, if the IMS-AGW is configured to negotiate using only the header-full EVS RTP payload format, the IMS-ALG shall include the hf-only parameter with a value 1. Otherwise, if EVS was used before the access transfer, the IMS-ALG should include the hf-only parameter with a value indicating the mode that was negotiated before the access transfer. If the IMS-ALG supplies the hf-only parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the dtx parameter is contained in the SDP offer, the IMS-ALG shall include the dtx parameter with unmodified value in the SDP answer. Otherwise, if the dtx-recv parameter is contained in the SDP offer, the IMS-ALG may include the dtx parameter in the SDP answer with the same value as the dtx-recv parameter in the SDP offer. Otherwise, if the usage of DTX is not desired (e.g. due to DTX capabilities of expected codecs to transcode with), the IMS-ALG shall include the dtx parameter with a value 0. Otherwise, if EVS was used before the access transfer, the IMS-ALG should include the dtx parameter with a value indicating the mode that was negotiated before the access transfer. If the IMS-ALG supplies the dtx parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the reception of DTX is not desired and the dtx parameter is not included, the IMS-ALG 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 IMS-ALG supplies the dtx-recv parameter in the SDP answer, it should also supply it to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the br parameter is contained in the SDP offer, the IMS-ALG shall select a bitrate value, which is either the received br value or a subset of it, based on IMS-AGW capabilities, possible configured policies, and the negotiated br range of an EVS codec used before the access transfer, and shall include the br parameter with the selected value that is also supplied towards the IMS-AGW in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities possible configured policies, and the negotiated br range of the EVS codec used before the access transfer, the IMS-ALG shall supply the br parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include this parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the br parameter in the SDP answer, it shall also supply to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the br-recv parameter is contained in the SDP offer, the IMS-ALG shall select a bitrate value, which is either the received br-recv value or a subset of it, based on IMS-AGW capabilities possible configured policies, and the negotiated br range of an EVS codec used before the access transfer, and the IMS-ALG shall include the br-send parameter with the selected value that is also supplied towards the IMS-AGW in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities and possible configured policies, it shall supply the br-send parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include the br-send parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the br-send parameter in the SDP answer, it shall also supply to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the br-send parameter is contained in the SDP offer, the IMS-ALG shall select a bitrate value, which is either the received br-send value or a subset of it, based on IMS-AGW capabilities, possible configured policies, and the negotiated br range of an EVS codec used before the access transfer, and the IMS-ALG shall include the br-recv parameter with the selected value that is also supplied towards the IMS-AGW in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities and possible configured policies, it shall supply the br-recv parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include the br-recv parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the br-recv parameter in the SDP answer, it shall also supply to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the bw parameter is contained in the SDP offer, the IMS-ALG shall select a sampling bandwidth value, which is either the received bw value or a subset of it, based on IMS-AGW capabilities, possible configured policies, and the negotiated bw range of an EVS codec used before the access transfer, and the IMS-ALG shall include the bw parameter with the selected value that is also supplied towards the IMS-AGW in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities, possible configured policies, and the negotiated bw range of the EVS codec used before the access transfer, the IMS-ALG shall supply the bw parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include this parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the bw parameter in the SDP answer, it shall also supply to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the bw-recv parameter is contained in the SDP offer, the IMS-ALG shall select a sampling bandwidths value, which is either the received bw-recv value or a subset of it, based on IMS-AGW capabilities, possible configured policies, and the negotiated bw range of an EVS codec used before the access transfer, and the IMS-ALG shall include the bw-send parameter with the selected value in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities, possible configured policies, and the negotiated bw range of the EVS codec used before the access transfer, the IMS-ALG shall supply the bw-send parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include the br-send parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the bw-send parameter in the SDP answer, it shall also supply to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW 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 IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type, it shall forward the bw-recv parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the bw-send parameter is contained in the SDP offer, the IMS-ALG shall select a sampling bandwidths value, which is either the received bw-send value or a subset of it, based on IMS-AGW capabilities, possible configured policies, and the negotiated bw range of an EVS codec used before the access transfer, and the IMS-ALG shall include the bw-recv parameter with the selected value in the SDP answer. Otherwise, if the IMS-ALG 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 IMS-AGW capabilities, possible configured policies, and the negotiated bw range of the EVS codec used before the access transfer, the IMS-ALG shall supply the bw-recv parameter in the SDP answer it sends. Otherwise the IMS-ALG shall not include the bw-recv parameter in the SDP answer. If the IMS-ALG 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 IMS-ALG supplies the bw-send parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the cmr parameter is contained in the SDP offer, the IMS-ALG shall include the cmr parameter with unmodified value in the SDP answer. Otherwise, if the IMS-AGW desires to disable codec mode requests within the RTP payload of the EVS primary mode (due to the IMS-AGW capabilities, possible configured policies, and the negotiated CMR mode of an EVS codec used before the access transfer), it shall include the cmr parameter with value -1 in the SDP answer it sends If the IMS-ALG supplies the cmr parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW supports the indicated mode in the send direction. If the indicated mode is not supported, the IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the IMS-ALG 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 IMS-AGW in the local descriptor for the termination towards the offerer with the same value. The IMS-ALG shall consider the capabilities of the IMS-AGW and the negotiated ch-aw-recv mode of an EVS codec used before the access transfer when it chooses an appropriate value.
number of channels (NOTE 2)	If the "number of channels" parameter is contained in the SDP offer the IMS-ALG shall check if the IMS-AGW supports the indicated number of channels. If the indicated number of channels is not supported, the IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the "number of channels" parameter is contained in the SDP offer, the IMS-ALG shall include the "number of channels" parameter with unmodified value in the SDP answer and shall also supply it to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW supports the indicated number of channels in the receive direction. If the indicated number of channels is not supported, the IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type for transcoding, the IMS-ALG shall forward the ch-send parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the ch-recv parameter is contained in the SDP offer, the IMS-ALG shall include the ch-send parameter with unmodified value in the SDP answer and shall also supply the ch-send parameter to the IMS-AGW 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 IMS-ALG shall check if the IMS-AGW supports the indicated number of channels in the send direction. If the indicated number of channels is not supported, the IMS-ALG shall not select the EVS payload type for transcoding. If the IMS-ALG selects the EVS payload type for transcoding, the IMS-ALG shall forward the ch-recv parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the ch-send parameter is contained in the SDP offer, the IMS-ALG shall include the ch-recv parameter with unmodified value in the SDP answer and shall also supply the ch-recv parameter to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If the mode-set parameter is contained in the SDP offer, the IMS-ALG shall include the mode-set parameter with unmodified value in the SDP answer. Otherwise, if EVS or AMR-WB was used before the access transfer, the IMS-ALG should include the mode-set parameter with a value indicating the mode that was negotiated before the access transfer (or omit it if no restrictions applied before). If the IMS-ALG supplies the mode-set parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If EVS or AMR-WB was used before the access transfer, the IMS-ALG should include the mode-change-period parameter with a value indicating the mode that was negotiated before the access transfer (or omit it if no restrictions applied before). the IMS-ALG should include the mode-change-period parameter for the EVS payload in the SDP offer it forwards. If the IMS-ALG supplies the mode-change-period parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG may forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	The IMS-ALG shall either include the mode-change-capability parameter with a value 2 or omit the parameter. If the IMS-ALG supplies the mode-change-capability parameter in the SDP answer, it may also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	If EVS or AMR-WB was used before the access transfer, the IMS-ALG should include the mode-change-neighbor parameter with a value indicating the mode that was negotiated before the access transfer (or omit it if no restrictions applied before). If the IMS-ALG supplies the mode-change-neighbor parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW for the termination towards the offerer in the remote descriptor.	The IMS-ALG 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 IMS-ALG shall consider the capabilities of the IMS-AGW and, If EVS or AMR-WB was used before the access transfer, the redundancy that was negotiated before the access transfer. If the IMS-ALG supplies the max-red parameter in the SDP answer, it shall also supply it to the IMS-AGW 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 IMS-ALG select the EVS payload type for transcoding, the IMS-ALG shall forward this parameter to the IMS-AGW the IMS-ALG shall forward this parameter to the IMS-AGW in the remote descriptor.	If the IMS-AGW supports RTCP APP based adaptation messages defined in TS 26.114, and the IMS-ALG has a policy to negotiate the usage of those messages, the IMS-ALG shall include the 3gpp_mtsi_app_adapt SDP attribute indicating the allowed APP messages in the SDP answer. If EVS was used before the access transfer, the IMS-ALG should consider the negotiated RTCP APP packet types the access transfer in addition to the IMS AGW capabilities when selecting the allowed RTCP APP messages.
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: This MIME parameter of the EVS RTP payload type is defined in RFC 4867. It is encapsulated within the SDP "a=fmtp" attribute defined RFC 4566.