# 3GPP TR 26.501 Change Request - AF Requested Modification of Network Slices for UE

## Administrative Information

- **CR Number**: 0003 rev 2
- **Version**: 19.0.1 → Rel-20
- **Category**: B (addition of feature)
- **Work Item**: FS_AMD_Ph2
- **Source**: Samsung Electronics Co. Ltd.

## Reason for Change

TS 23.501 (Rel-19) introduced a new procedure for AF-influenced slice change for a UE. Document S4aI250082 addressed this topic in Rel-19, but SA4 MBS group decided to pursue this study topic in Rel-20 to complete network slicing features for 5G Media Streaming.

## Summary of Changes

This CR proposes:
1. A brief description of the new procedure for AF-requested modification of Network Slice(s) for a UE as specified in TS 23.501
2. A key issue description related to media delivery for study in Rel-20

## Technical Contributions

### CHANGE-1: Updates to Clause 4.2.2 - Network Slicing for Specific Applications

#### 4.2.2.1 Introduction
Minor editorial updates to existing text on network slicing procedures.

#### 4.2.2.2 Network Slice Replacement Without Application Influence
Editorial title change from previous version.

#### 4.2.2.3 AF-Requested Modification of Set of Network Slice(s) for a UE (NEW)

This new clause describes the procedure specified in TS 23.501 clause 5.15.5.2.2A:

**Key Procedure Elements:**
- An authorized AF (directly or via NEF) may request the PCF to replace a certain S-NSSAI (Replaced S-NSSAI) with another S-NSSAI (Alternative S-NSSAI) from the UE subscription
- The AF subscribes to notifications from PCF about the outcome of slice replacement
- PCF sends slice replacement management information to AMF in access and mobility management policies
- The slice replacement management policy includes:
  - Replaced S-NSSAI
  - Alternative S-NSSAI
  - Network Slice Replacement Type (indicating AF-requested replacement)
- AMF performs slice management operations:
  - Removes Replaced S-NSSAI from Allowed S-NSSAI
  - Adds Replaced S-NSSAI to Rejected S-NSSAI via UE Configuration Update
  - Releases PDU sessions using Replaced S-NSSAI
  - Reports outcome to PCF, which notifies AF
- Operator policies in PCF ensure UE is configured with URSP rule containing Alternative S-NSSAI
- AF/NEF may later request termination of slice replacement to switch back to original slice
- PDU Sessions are transferred as described in clause 4.2.2.1 during both forward and reverse transitions

### CHANGE-2: New Clause 6.X - Key Issue on AF-Requested Slice Change for UE

#### 6.X.1 Description

##### 6.X.1.1 Identification and Usage of Alternate S-NSSAI

**Context:**
- Describes procedure for AF-requested modification of Network Slice(s) for a UE
- AF interacts with PCF to modify current network slice (Replaced S-NSSAI) with Alternate S-NSSAI
- PCF interacts with AMF to facilitate slice modification and PDU session migration

**Use Case Applicability:**
- Provides dynamic update of network slice used by UE
- Preferable to 5GC-facilitated slice replacement (clause 4.2.2.2) for use cases requiring dynamic QoS treatment modification
- Supports premium gaming QoS use case (clause 5.3.2) where application traffic migrates to appropriate slice under Media AF direction

**Current Provisioning:**
- 5GMS Application Provider configures network slice information at 5GMS AF via M1 reference point using Provisioning API
- TS 23.501 clause 5.15.5.2.2A states that how AF obtains Alternate S-NSSAI information is out of scope

**Open Issues:**
1. When and how does 5GMS AF decide to trigger the AF-requested modification procedure?
2. How does 5GMS AF obtain information about S-NSSAI to be replaced and Alternate S-NSSAI?

#### 6.X.2 Candidate Solution

**Overview:**
Describes procedure for temporary upsell treatment of M4 application flows to be carried over premium network slice.

**Addresses Open Issues:**
1. UE application makes upsell treatment request; network API request sent at M5 (e.g., user purchases gaming slice treatment for desired duration)
2. Media Delivery AF obtains Alternate S-NSSAI information from Media Application Service Provider

**Assumptions:**
- Media Application Service Provider negotiates with MNO for both default/primary network slice and Alternate network slice

**Procedure Steps:**

**Initial Setup (Steps 1-3):**
1. Application Service Provider provisions Media Delivery session at Media AF via M1 using baseline downlink media delivery procedure (TS 26.501 clause 5.1), including Alternate S-NSSAI information
2. Media Delivery session setup with UE and 5G System components (TS 26.501 clause 5.1)
3. Media Access Function and Media AS perform media delivery at M4 using default/primary network slice

**Upsell Treatment Activation (Steps 4-7):**
4. User decides for temporary upsell treatment requiring dynamic QoS modification of M4 application flows
5. UE Application requests Media Session Handler for temporary upsell treatment at M6, including duration
6. Media Session Handler forwards request to Media AF at M5, including duration
7. Media AF requests PCF (directly if trusted AF, via NEF if untrusted) for Network Slice modification, replacing primary S-NSSAI with Alternate S-NSSAI per TS 23.501 clause 5.15.5.2.2a, including duration
8. PCF interacts with AMF to facilitate Network Slice modification per TS 23.501 clause 5.15.5.2.2a and TS 23.503 clauses 6.1.2.1 and 6.1.2.6; PCF ensures UE configured with URSP rule containing Alternate S-NSSAI; UE OS ensures use of Alternate S-NSSAI
9. Media Access Function and Media AS perform media delivery at M4 using Alternate S-NSSAI

**Upsell Treatment Termination (Steps 10-14):**
10. User decides to end upsell treatment
11. UE Application requests Media Session Handler to end upsell treatment at M6
12. Media Session Handler forwards request to Media AF at M5
13. Media AF requests PCF for Network Slice modification, replacing Alternate S-NSSAI with original primary S-NSSAI per TS 23.501 clause 5.15.5.2.2a
14. PCF interacts with AMF to revert to original Network Slice; PCF ensures UE configured with URSP rule containing primary S-NSSAI; UE OS ensures use of primary S-NSSAI
15. Media Access Function and Media AS perform media delivery at M4 using primary S-NSSAI

#### 6.X.3 Conclusions

**Identified Gaps:**
- Media Application Service Provider must provision Alternate S-NSSAI information required by 5G System Components
- Media Aware Application must request Media Session Handler over M6 for initiating/terminating temporary upsell treatment
- Media Session Handler must send request to Media AF over M5 for initiating/terminating upsell treatment

**Proposed Normative Changes:**

**1. TS 26.501 (Stage-2) Modifications:**
   - a. Modify domain model for dynamic policies (figure 4.0.6-2) to add Alternate S-NSSAI identifier property in Policy Template entity
   - b. Update clause 5.8.1 (Dynamic Policy based on Network Slicing for downlink): Update figure 5.8.1-1 call flow and add text describing design principles and procedure for AF-requested Network Slice replacement
   - c. Update clause 6.9.6 (Dynamic Policy based on Network Slicing for uplink): Update figure 6.9.6-1 call flow and add text describing design principles and procedure for AF-requested Network Slice replacement

**2. TS 26.512 (Stage-3) Modifications:**
   - a. Clause 4.8 (M6d UE Media Session Handling interface): Add procedure description for 5GMSd Aware Application requesting Media Session Handler for change of traffic treatment
   - b. Clause 5.8 (M6u UE Media Session Handling interface): Add procedure description for 5GMSu Aware Application requesting Media Session Handler for change of traffic treatment

**3. TS 26.510 (Stage-3) Modifications:**
   - a. Clause 8.7.3: Update PolicyTemplate resource data model to include Alternate S-NSSAI property
   - c. Clauses 5.2.7 and 5.3.3: Update Dynamic Policy provisioning and invocation interactions to describe interactions between Media Application Provider and Media AF, and Media Session Handler and Media AF
   - d. Clause 9.3.3: Update DynamicPolicy resource data model with additional property representing request from Media Session Handler to Media AF for different traffic treatment via AF-requested Network Slice modification

## Updated Conclusions and Recommendations (Clause 8)

**New Recommendation 4:**
To support the procedure for AF-requested modification of Network Slice(s) for a UE, adopt the following into media delivery specifications as described in clause 6.X.3:
- a. TS 26.501: Update domain model for dynamic policies and procedures for Dynamic Policy based on Network Slicing (downlink and uplink)
- b. TS 26.512: Add procedure descriptions for M6d and M6u for 5GMSd/5GMSu Aware Application requesting Media Session Handler for traffic treatment change
- c. TS 26.510: Update PolicyTemplate and DynamicPolicy resource data models, and Dynamic Policy provisioning/invocation interactions