Content for  TS 23.228  Word version:  16.6.0

5.4.7.0  General |R6|

5.4.7.1  Authorize QoS Resources  Word‑p. 92

The Authorize QoS Resources procedure is used during an establishment and a modification of a SIP session. The P-CSCF shall use the SDP contained in the SIP signalling to derive the session information that is relevant for Policy and Charging Control and forwards it to the PCRF/PCF. The PCRF/PCF shall use the received information to calculate the proper authorization. This enables the PCRF/PCF to authorize the required QoS resources.

The authorization shall be expressed in terms of the IP resources to be authorized and shall include limits on media flows, and may include restrictions on IP destination address and port. The PCC shall authorize each SIP session independently (including additional parallel sessions, e.g. Call Waiting) and shall take into consideration the amount of IP resources the user's subscription allows.

5.4.7.1a  Resource Reservation with Policy and Charging Control

5.4.7.2  Enabling of Media Flows  Word‑p. 93

The PCRF/PCF makes policy decisions and provides an indication to the PCEF within the IP-CAN that the user is now allowed to use the allocated QoS resources for per-session authorizations unless this was done based on Policy and Charging Control at the time of the Resource Reservation procedure. If there is more than one response for the same session, indicating that the session has been forked in the network, the PCRF/PCF may authorize the "logical OR" of the resources requested in the responses. When the session established indication has been received, if the PCRF/PCF earlier have authorized the "logical OR" of the resources then the PCRF/PCF will modify the authorization and enable the corresponding media flows according to the session established indication.

The PCEF within the IP-CAN enforces the policy decisions. The IP-CAN shall restrict any use of the IP resources prior to this indication from the PCRF/PCF, e.g. by keeping the gate closed and disabling the use of resources for the media flow. Based on local policy, IP-CAN and/or IP resources may be allowed to be used by the user at the time they are authorized by the PCRF/PCF.

5.4.7.3  Disabling of Media Flows

5.4.7.4  Revoke Authorization for IP-Connectivity Access Network and IP Resources

5.4.7.5  Indication of IP-Connectivity Access Network bearer release

5.4.7.6  Authorization of IP-Connectivity Access Network bearer modification

5.4.7.7  Indication of IP-Connectivity Access Network bearer modification  Word‑p. 94

When an IP-CAN bearer is modified such that the maximum bit rate (downlink and uplink) is downgraded to 0 kbit/s or changed from 0 kbit/s to a value that falls within the limits that were authorized at IP-CAN bearer activation (or last modification) then the PCEF within the IP-CAN shall report this to the PCRF/PCF.

This indication is forwarded to the P-CSCF and may be used by the P-CSCF to initiate a session release towards the remote endpoint.

5.4.7.8  Sharing of Resources for Network Detected Concurrent Sessions |R13|

5.4.7.8.1  Network Detected Concurrent Sessions

The following scenarios for concurrent sessions are subject to resource sharing:

• The UE is engaged in a session, puts the session on hold, then initiates a new session to a new UE.
• The UE is engaged in a session and receives an incoming session, puts the ongoing session on hold to accept the incoming session.
• The UE is engaged in multiple sessions, puts all sessions on hold and creates a conferencing session.

For a UE engaged in multiple sessions, with only one active session at any time, the network may be able to share resources for media components of the same type and that are common to these multiple sessions.

Resource sharing shall only be indicated for concurrent sessions that employ resource reservation based on TS 23.203 or TS 23.503.

When a UE puts a session on hold, it may put all or a subset of the media components of the session on hold. In such a case, the resource sharing applies only to the media components that are on hold and not to the rest of media components belonging to this IMS session

An emergency session shall not share resources with any other session.

5.4.7.8.2  Initiating Resource Sharing for Network Detected Concurrent Sessions

If the P-CSCF is configured to apply resource sharing, it may at establishment of a new Rx session or a new Npcf_PolicyAutorization application session context with the PCRF/PCF, indicate that resources may be shared in uplink and/or downlink direction by assigning an uplink and/or downlink tag to each media component of an IMS session unless it is an IMS emergency session.

If this is the first IMS session of a UE, the P-CSCF shall assign new tags. Upon detection by the P-CSCF that a UE is engaged in multiple sessions, it shall determine if these sessions fulfil the criteria specified in clause 5.4.7.8.1 and have common media components that can share resources. If so, the P-CSCF may activate resource sharing by assigning the same existing tag to each media component whose resources can be shared amongst the IMS sessions. Otherwise, the P-CSCF shall assign new tags that are different from any tag previously assigned for this UE. The PCRF/PCF may then authorize resource sharing based on these tags. For further information, see TS 23.203.

Whenever resource sharing is active, the P-CSCF shall ensure that the UE can only receive the media flow for one session at a time by closing the gates for all other media flows that can share the same resource, i.e. having the same tag.

SIP AS may indicate to a supporting P-CSCF to apply resource sharing to each media lines included in SDP of an IMS session. When SIP AS is used, P-CSCF, based on the local policy, may follow the resource sharing policy from SIP AS. The interaction between P-CSCF and SIP AS for handling Resource sharing procedure is defined in TS 24.229.

5.4.7.8.3  Void

5.4.7.9  Priority sharing for concurrent sessions |R13|  Word‑p. 95

The P-CSCF may indicate to the PCRF/PCF that the resource allocation for a media flow is allowed to use the same priority as other media flows of the same media type for the UE engaged in multiple sessions by providing a priority sharing indicator and an optional pre-emption control information in addition to the application identifier and the service priority. For MCPTT, the service priority and the priority sharing indicator are defined in TS 23.179. The pre-emption control information is used to indicate to the PCRF/PCF how to perform pre-emption in accordance to TS 23.203 and TS 23.503.

The following scenario is subject to priority sharing:

• The P-CSCF receives a priority sharing indicator associated with the media flow from the Application Server.

Upon detection by the P-CSCF that a session includes a priority sharing indicator for a media flow and may optionally include pre-emption control information, the P-CSCF shall convey to the PCRF/PCF the priority sharing indicator and, when available, the pre-emption control information as described in TS 23.203 and TS 23.503.