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Content for  TS 23.548  Word version:  19.1.0

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6.10 Support of the Local Offloading Management  6.10.1 General  6.10.2 Procedure  6.10.2.1 General  6.10.2.2 I-SMF insertion during the PDU Session establishment  6.10.2.3 EAS Discovery Procedure with EASDF for Local Offloading Management  6.10.2.4 UE mobility for PDU session supporting Local Offloading Management  6.10.3 Policy provisioning for Local Offloading Management  6.10.3.1 General  6.10.3.2 Local offloading management policy handling for Local Offloading Management 
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6.10  Support of the Local Offloading Management |R19|  p. 75

6.10.1  General  p. 75

In edge computing deployment, to reduce the impact on a centrally deployed SMF on management of the edge computing related information, 5GS may support the Local Offloading Management.
In Distributed Anchor Point and Multiple PDU Sessions connectivity models (see clause 4.3), the existing means such as URSP and SSC mode are used to support Local Offloading Management.
In Session Breakout connectivity model, the Local Offloading Management only applies to the non-roaming PDU session. For Session Breakout connectivity model, if the AMF determines that the UE is within the Local Offloading Management service area and Local Offloading Management is allowed in the SMF selection subscription data, AMF selects/re-selects an I-SMF to support Local Offloading Management. This also includes the case when the UE is within the SMF service area. For the Local Offloading Management, the I-SMF is in charge of edge computing handling and supports following functionalities:
  • EASDF configuration and DNS message handling, as defined in clauses 6.2.1 and 6.2.3, instead of SMF.
  • EASDF discovery and selection is performed by the I-SMF instead of SMF as described in clause 6.3.23 of TS 23.501.
  • Management and retrieval of EDI from NEF as described in clause 6.2.3.4.
  • Receiving of the Local Offloading Information from PCF via SMF, which indicates IP range(s) and/or FQDN(s) allowed to be routed to the local part of DN.
When the I-SMF is inserted for the Local Offloading Management, i.e. the inserted I-SMF providing Local Offloading allowed indication to SMF, the SMF does not discover, select and configure EASDF. as well as DNS message handling for the locally offloaded traffic towards the local part of DN.
The UE is unaware of whether the Local Offloading Management is applied or not for a PDU Session.
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6.10.2  Procedure  p. 76

6.10.2.1  General  p. 76

This clause describes EAS (re)discovery procedure within PDU session applied for Local Offloading Management.

6.10.2.2  I-SMF insertion during the PDU Session establishment  p. 76

Reproduction of 3GPP TS 23.548, Fig. 6.10.2.2-1: Procedure for PDU Session establishment supporting Local Offloading Management
Figure 6.10.2.2-1: Procedure for PDU Session establishment supporting Local Offloading Management
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Step 1.
During the Registration procedure, the AMF receives the Local Offloading Management allowed indication per DNN/S-NSSAI as part of SMF selection subscription data from the UDM in the step 14b of the procedure in the clause 4.2.2.2.2 of TS 23.502.
If Local Offloading Management is allowed for the requested DNN/S-NSSAI in the step 1 of clause 4.3.2.2.1 of TS 23.502, during the PDU session establishment procedure the AMF selects a SMF that supports Local Offloading Management. For the selected SMF, the AMF executes as follows:
  • If the UE is not within the local offloading management service area , then the I-SMF for local offloading management is not needed and step 2a is executed.
  • If the UE is within the local offloading management service area, then the I-SMF for local offloading management is needed and step 2b is executed.
Step 2a.
Same as the step 1-6 defined in Figure 6.2.3.2.2-1, the SMF selects an EASDF and instructs the EASDF to create DNS context for PDU session. Step 3-4 are skipped.
Step 2b.
The AMF selects an I-SMF that serves the UE location and supports Local Offloading Management. The PDU Session Establishment procedure as described in clause 6.7.2.2 is used with the following differences and additions:
  • This procedure applies for non-roaming PDU session and all NFs are located in HPLMN.
  • The V-SMF and V-UPF are replaced by I-SMF and I-UPF, respectively.
  • The H-SMF and H-UPF are replaced by SMF and UPF(PSA), respectively.
  • The AMF sends a Local Offloading Management allowed indication to the I-SMF in the step 3a of clause 4.3.2.2.2 of TS 23.502 with V-SMF replaced by I-SMF.
If the I-SMF receives the Local Offloading Management allowed indication from AMF, the I-SMF:
  • Selects UL CL/BP UPF and L-PSA UPF based on UE location information.
  • Selects an EASDF.
  • Obtains the EASDF IP address based on local configuration.
  • May obtain EASDF DNS security information based on local configuration or via interaction with EASDF.
  • Sends the request for the establishment of the PDU Session, Local Offloading Management support indication, IP address and (if exists) DNS security information of EASDF and I-SMF supported DNAI(s) to the SMF in the Nsmf_PDUSession_Create Request in the step 6 of the procedure in Figure 4.3.2.2.2-1 of TS 23.502 with V-SMF, H-SMF replaced by I-SMF, SMF respectively.
When the SMF receives the Local Offloading Management support indication and allows I-SMF to perform Local Offloading Management based on SM subscription data, the SMF:
  • Skips the EASDF Discovery and Selection procedure and DNS message handling.
  • Retrieves the Local Offloading Management Policy (i.e. FQDN/IP range allowed to be routed to the local part of DN as described in clause 6.4 of TS 23.503) from PCF by providing local offloading support indication. Each Local Offloading Management Policy is provided with an Offload Identifier which is assigned by PCF.
  • Sends the retrieved Local Offloading Management Policy or Offload Identifier to the I-SMF.
  • Sends IP address and optional DNS security information of the EASDF received from the I-SMF to the UE via PCO.
  • Sends Local Offloading Management Allowed indication to the I-SMF.
Step 3.
The I-SMF configures the EASDF with the DNS handling rules using the Local Offloading Control Information received from SMF.
If the I-SMF obtains the EASDF IP address based on local configuration, the I-SMF invokes Neasdf_DNSContext_Create Request to configure the EASDF.
The I-SMF configures the UL CL UPF and local PSA UPF selected in the step 2 to forward DNS messages to EASDF.
Step 4.
EAS Discovery procedure with EASDF is performed as described in clause 6.10.2.3.
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6.10.2.3  EAS Discovery Procedure with EASDF for Local Offloading Management  p. 78

The EASDF is selected and configured by the I-SMF and the DNS query of the UE is routed to the EASDF directly or via UL CL as defined in clause 6.7.2.3.

6.10.2.4  UE mobility for PDU session supporting Local Offloading Management  p. 78

For a PDU session supporting Local Offloading Management, during mobility events, e.g. Hand-Over or AMF change, the mobility handling is executed same as the respective mobility handling defined in clause 4.23 of TS 23.502 with the following difference:
  • The retrieval of the Local Offloading Management Allowed indication as part of the SMF selection subscription data from UDM, the new AMF determines the new I-SMF as follows:
    • If the service area of SMF includes the new UE location and the UE location is out of local offloading management service area, the AMF removes the old I-SMF (if available).
    • If the service area of SMF include the new UE location and the UE location is within local offloading management service area, the AMF selects a new I-SMF unless the existing I-SMF can serve the new UE location. If there is an old I-SMF which cannot serve the new UE location, the AMF also removes the old I-SMF.
    • To support the local offloading management, the selected I-SMF need to support Local Offloading Management, serves the new UE location; and support the DNN and S-NSSAI associated with the PDU session.
  • For I-SMF insertion and relocation case, the target I-SMF and SMF interacts as follows:
    • The target I-SMF sends new selected EASDF IP address and Local Offloading Management allowed indication to the SMF.
    • The SMF sends the new selected EASDF IP address to the UE via PCO.
  • For I-SMF removal case, the SMF performs as follows:
    • A new EASDF is selected by the SMF and the SMF sends the new selected EASDF IP address to the UE via PCO.
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6.10.3  Policy provisioning for Local Offloading Management  p. 78

6.10.3.1  General  p. 78

For Local Offloading Management, traffic routing related policy (e.g., local offloading management policy) need be provided to the I-SMF.
Based on the received policy information and EAS Deployment information, the I-SMF may (re)discover and (re)select ULCL and local PSA UPF for routing the traffic locally.

6.10.3.2  Local offloading management policy handling for Local Offloading Management  p. 79

The Local Offloading Management Policy is generated by PCF and retrieved by SMF for Local Offloading Management as described in clause 6.10.2. The Local offloading Management Policy may also be provided with a Offload Identifier. The Offload Identifier is assigned by PCF, and is unique within the PLMN. The SMF and I-SMF for Local Offloading Management may also be preconfigured with Local Offloading policy and tagged with related Offload Identifier(s). In this case, the PCF only provides the Offload Identifier to the SMF.
The detailed information of Local Offloading Management Policy is described in clause 6.4 of TS 23.503.The SMF forwards the received Local Offloading Management Policy or Offload Identifier to the I-SMF transparently.
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