Section: 5.4.3.2 Paging Policy Differentiation
Content: Paging policy differentiation is an optional feature that allows the AMF, based on operator configuration, to apply different paging strategies for different traffic or service types provided within the same PDU Session. In this Release of the specification this feature applies only to PDU Session of IP type. When the 5GS supports the Paging Policy Differentiation (PPD) feature, the DSCP value (TOS in IPv4 / TC in IPv6) is set by the application to indicate to the 5GS which Paging Policy should be applied for a certain IP packet. For example, as defined in TS 23.228[ IP Multimedia Subsystem (IMS); Stage 2 ]  [15], the P-CSCF may support Paging Policy Differentiation by marking packet(s) to be sent towards the UE that relate to a specific IMS services (e.g. conversational voice as defined in IMS multimedia telephony service). NOTE 1: This PPD feature may be used to determine the Paging Cause Indication for Voice Service, as described in clause 5.38.3. It shall be possible for the operator to configure the SMF in such a way that the Paging Policy Differentiation feature only applies to certain HPLMNs, DNNs and 5QIs. In the case of HR roaming, this configuration is done in the SMF in the VPLMN. NOTE 2: Support of Paging Policy Differentiation in the case of HR roaming requires inter operator agreements including on the DSCP value associated with this feature. In the case of Network Triggered Service Request and UPF buffering downlink packets, the UPF shall include the DSCP in TOS (IPv4) / TC (IPv6) value from the IP header of the downlink packet and an indication of the corresponding QoS Flow in the Downlink Data Report sent to the SMF. When PPD applies, the SMF determines the Paging Policy Indicator (PPI) based on the DSCP received from the UPF. In the case of Network Triggered Service Request and SMF buffering downlink packets, when PPD applies, the SMF determines the PPI based on the DSCP in TOS (IPv4) / TC (IPv6) value from the IP header of the received downlink packet and identifies the corresponding QoS Flow from the QFI of the received downlink packet. The SMF includes the PPI, the ARP and the 5QI of the corresponding QoS Flow in the N11 message sent to the AMF. If the UE is in CM IDLE, the AMF uses this information to derive a paging strategy, and sends paging messages to NG-RAN over N2. NOTE 3: Network configuration needs to ensure that the information used as a trigger for Paging Policy Indication is not changed within the 5GS. NOTE 4: Network configuration needs to ensure that the specific DSCP in TOS (IPv4) / TC (IPv6) value, used as a trigger for Paging Policy Indication, is managed correctly in order to avoid the accidental use of certain paging policies. For a UE in RRC_INACTIVE state the NG-RAN may enforce specific paging policies in the case of NG-RAN paging, based on 5QI, ARP and PPI associated with an incoming DL PDU. To enable this, the SMF instructs the UPF to detect the DSCP in the TOS (IPv4) / TC (IPv6) value in the IP header of the DL PDU (by using a DL PDR with the DSCP for this traffic) and to transfer the corresponding PPI in the CN tunnel header (by using a QER with the PPI value). The NG-RAN can then utilize the PPI received in the CN tunnel header of an incoming DL PDU in order to apply the corresponding paging policy for the case the UE needs to be paged when in RRC_INACTIVE state. In the case of Home-Routed roaming, the V-SMF is responsible of controlling UPF setting of the PPI. In the case of PDU Session with I-SMF, the I-SMF is responsible of controlling UPF setting of the PPI.