Y.2 QoS related concepts

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

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

Y.2.1 Application Level Signalling for IMS

Y.2.1.0 General

When the UE uses 5GS-access for IMS services, it shall be possible to establish at least one QoS flow identified by a QFI for IMS signalling.

Y.2.1.1 QoS Requirements for Application Level Signalling

It shall be possible to request prioritised handling over the 5GS system for IMS signalling by applying the appropriate 5QI for the established QoS flow for the IMS signalling, see TS 23.501 [93], clause 5.7.

Y.2.1.2 Void

Y.2.2 The QoS requirements for an IMS session

Y.2.2.0 General

The selection, deployment, initiation, and termination of QoS signalling and resource allocation shall consider:

– The general requirements described in clause 4.2.5.

– The QoS handling is described in TS 23.501 [93], TS 23.502 [94] and TS 23.203 [54] and TS 23.503 [95].

Y.2.2.1 Relation of IMS media components and 5GS QoS flows carrying IMS media

All associated media flows (such as e.g. RTP / RTCP flows) used by the UE to support a single media component are assumed to be carried within the same 5GS QoS flow.

Y.2.3 Interaction between 5GS QoS and session signalling

Y.2.3.0 General

The generic mechanisms for interaction between QoS and session signalling are described in clause 5.4.7. The mechanisms described there and the related procedures througout the present specification are applicable to 5GS-accesses as well with the following clarifications:

– An IP-CAN bearer in this specification shall be interpreted as a 5GS QoS flow.

– An IP-CAN session in this specification shall be interpreted as a 5GS PDU session of type IP.

– The negotiation of the bearer establishment mode does not apply for the 5GS.

– The PCEF corresponds to the combination of SMF and UPF.

Y.2.3.1 Resource Reservation with PCF

The UE or 5GC can initiate the resource reservation request for the media parameters negotiated over SDP using PDU session modification procedure, see TS 23.502 [94], clause 4.3.3. However, for IMS. the network shall initiate the establishment, modification and termination of 5GS QoS flows triggered by negotiated SDP.

Y.2.4 Network initiated session release – P-CSCF initiated

Y.2.4.0 General

In the event of loss of coverage for 5GS radio access, TS 23.502 [94], clause 4.2.6, defines the N2 release procedure. This procedure releases the QoS flows. This is indicated to the P‑CSCF as shown in figure Y.3.

Y.2.4.1 Network initiated session release – P-CSCF initiated

Covers radio coverage loss and that GFBR cannot be maintained by the radio access.

Figure Y.3: Network initiated session release – P‑CSCF initiated after loss of radio coverage

1. In the case of loss of radio coverage or that GFBR cannot be retained in NG-RAN, the 5GC may release the related GBR QoS flow and PCF and P-CSCF are notified appropriately.

2. The P‑CSCF decides on the termination of the IMS session. In the event of the notification that the signalling transport to the UE is no longer possible, the P‑CSCF shall terminate any ongoing IMS session with that specific UE. If the P‑CSCF decides to terminate the IMS session, it indicates this to PCF, which removes the authorization for resources that had previously been issued for this endpoint for this session. (see TS 23.503 [95]).

The following steps are only performed in the case the P‑CSCF has decided to terminate the session.

3. The P‑CSCF generates a Release (Bye message in SIP) to the S‑CSCF of the releasing party.

4. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. The S‑CSCF of the releasing party forwards the Release to the S‑CSCF of the other party.

5. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. The S‑CSCF of the other party forwards the Release on to the P‑CSCF.

6. The P‑CSCF of the other party removes the authorization for resources if they have previously been issued for this endpoint for this session. The P‑CSCF forwards the Release to the UE.

7. The UE of the other party responds with a SIP OK to the P‑CSCF

8. Depending on the Bearer Control Mode selected for the IP‑CAN session, the release of previously reserved resources shall be initiated either by the UE or by the IP‑CAN itself. The SIP OK message is sent to the S‑CSCF of the other party.

9. The S‑CSCF of the other party forwards the OK to the S‑CSCF of the releasing party.

10. The S‑CSCF of the releasing party forwards the OK to the P‑CSCF of the releasing party.