B.2 Enabling of IP Flows

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

B.2.1 General

Prior to the completion of the SIP session set-up, i.e. until the 2xx response to the INVITE request is received, the P-CSCF may enable or disable media IP flows depending on operator policy, thus allowing or forbidding early media in forward and/or backward direction. The P-CSCF may set the values of the "fStatus" attribute derived from the SDP direction attributes as defined in 3GPP TS 29.513 [7] clause 7.3.3 or set the values of the "fStatus" attributes considering the em-param of the P-Early-Media header field according to clause B.2.2 or downgrade the values of the "fStatus" attribute derived from the SDP direction attribute based on the configuration in the P-CSCF according to clause B.2.3. However for multiplexed RTP/RTCP flows (as negotiated using the "a=rtcp-mux" SDP attribute defined in IETF RFC 5761 [31]), a P-CSCF supporting RTP/RTCP transport multiplexing shall set the "fStatus" attribute to "ENABLED" to prevent that RTCP is blocked. If the P-CSCF chooses to modify the values of the "fStatus" as received from the SDP direction attribute, the P-CSCF shall store the last received SDP.

When a 2xx response is received, the P-CSCF shall enable all media IP flows according to the direction attribute within the last received SDP, as specified in 3GPP TS 29.513 [7] clause 7.3.3. When a 2xx response is received and the P-CSCF previously provided the values of the "fStatus" attributes different from the value derived from the SDP direction attribute in the session information, the P-CSCF shall provide service information with values of the "fStatus" attributes corresponding to the last received SDP.

NOTE: In most cases a 2xx response is a 200 (OK) response.

If the P-CSCF receives SDP answers after the completion of the SIP session set-up, i.e. after the 2xx response to the INVITE request is received, the P-CSCF shall provide the "fStatus" attribute, based on the last received SDP answer. The "fStatus" attribute shall be derived from the SDP according to 3GPP TS 29.513 [7] clause 7.3.3.

B.2.2 Gate control procedures considering the P-Early-Media header field

Prior to the completion of the SIP session set-up, the P-CSCF may use the em-param of the P-Early-Media header field defined in IETF RFC 5009 [35] in order to enable or disable early media in forward and/or backward direction. If the P-CSCF uses the em-param of the P-Early-Media header field for the gate control of early media, the P-CSCF shall perform the following procedures.

In the terminating P-CSCF, when a SIP message with the P-Early-Media header field is received from the UE and the policies configured in the P-CSCF indicate that the UE is authorized to send early media, then:

1) the P-CSCF shall set the "fStatus" attribute to "ENABLED" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the UE is "sendrecv" or no SDP direction attribute has been received; or

2) the P-CSCF shall set the "fStatus" attribute to "ENABLED-UPLINK" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the UE is "sendonly"; or

– the received em-param(s) in the P-Early-Media header field includes "sendonly" and the last received SDP direction attribute from the UE is "sendrecv" or "sendonly" or no SDP direction attribute has been received; or

3) the P-CSCF shall set the "fStatus" attribute to "ENABLED-DOWNLINK" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the UE is "recvonly"; or

– the received em-param(s) in the P-Early-Media header field includes "recvonly" and the last received SDP direction attribute from the UE is "sendrecv" or "recvonly" or no SDP direction attribute has been received; or

4) the P-CSCF shall set the "fStatus" attribute to "DISABLED" if either the received em-param(s) in the P-Early-Media header field or the last received SDP direction attribute from the UE includes "inactive"; or

5) the P-CSCF may set the "fStatus" attribute to "DISABLED" or apply the rules defined in clause B.2.2 if the received em-param(s) in the P-Early-Media header field includes "sendonly" or "recvonly" and the last received SDP direction attribute from the UE is "recvonly" or "sendonly" respectively.

NOTE 1: If the UE is authorized to send early media, the P-CSCF will not remove or modify the P-Early-Media header field according to 3GPP TS 24.229 [32].

When a SIP message with the P-Early-Media header field is received from the functional entity within the trust domain, and if:

– the P-Early-Media header field includes the "gated" parameter, then the P-CSCF may decide not to perform the gate control of early media; or

– the P-Early-Media header field does not include the "gated" parameter, then the P-CSCF shall perform the following procedures:

1) the P-CSCF shall set the "fStatus" attribute to "ENABLED" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the functional entity is "sendrecv" or no SDP direction attribute has been received; or

2) the P-CSCF shall set the "fStatus" attribute to "ENABLED-DOWNLINK" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the functional entity is "sendonly"; or

– the received em-param(s) in the P-Early-Media header field includes "sendonly" and the last received SDP direction attribute from the functional entity is "sendrecv" or "sendonly" or no SDP direction parameter has been received; or

3) the P-CSCF shall set the "fStatus" attribute to "ENABLED-UPLINK" if:

– the received em-param(s) in the P-Early-Media header field includes "sendrecv" and the last received SDP direction attribute from the functional entity is "recvonly"; or

– the received em-param(s) in the P-Early-Media header field includes "recvonly" and the last received SDP direction attribute from the functional entity is "sendrecv" or "recvonly" or no SDP direction parameter has been received; or

5) the P-CSCF may set the "fStatus" attribute to "DISABLED" or apply the rules defined in clause A.2.2 if the received em-param(s) in the P-Early-Media header field includes "sendonly" or "recvonly" and the last received SDP direction attribute from the functional entity is "recvonly" or "sendonly" respectively.

NOTE 2: According to IETF RFC 5009 [35], the non-direction parameter "gated" can be included after the direction parameter (e.g. "sendrecv") in the parameter list. The proxy performing gating of early media can add the parameter before forwarding the SIP message.

When a SIP message without the P-Early-Media header field is received from either the functional entity within the trust domain or the UE that is authorized to send early media, then the P-CSCF may set the "fStatus" attribute to "DISABLED" or apply the rules defined in clause B.2.3 or apply the rules defined in 3GPP TS 29.513 [7] clause 7.3.3.

NOTE 3: As indicated in IETF RFC 5009 [35] the applicable preconditions need to be met in order to allow early media in a particular direction.

When a SIP message is received from the functional entity other than the functional entity within the trust domain or the UE that is authorized to send early media, then the P-CSCF shall not use the received em-param(s) in the P-Early-Media header field and may apply the rules defined in clause B.2.2 or apply the rules defined in 3GPP TS 29.513 [7] clause 7.3.3.

NOTE 4: The P-CSCF will remove or modify the P-Early-Media header field in the above case.

B.2.3 Gate control procedures based on the configuration in the P-CSCF

Prior to the completion of the SIP session set-up, the P-CSCF may downgrade the values of the "fStatus" attributes derived from the SDP direction attributes based on the configuration in the P-CSCF. If the P-CSCF has the configuration for the gate control of early media, the P-CSCF shall perform the following procedures.

NOTE: The gate control of early media can be configured in the P-CSCF per UE basis.

When the "fStatus" attribute derived from the SDP direction attribute is "ENABLED", then the P-CSCF may downgrade the value of the "fStatus" attribute to the value "DISABLED", "ENABLED_UPLINK", or "ENABLED_DOWNLINK" based on the configuration in the P-CSCF.

When the "fStatus" attribute derived from the SDP direction attribute is "ENABLED_UPLINK" or "ENABLED_DOWNLINK", then the P-CSCF may downgrade the value of the "fStatus" attribute to the value "DISABLED" based on the configuration in the P-CSCF.