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Content for  TS 23.548  Word version:  19.0.0

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6.7.2.4 EAS Discovery Procedure with Local DNS for HR-SBO  6.7.2.5 EAS discovery procedure with V-EASDF/Local DNS Server using IP replacement mechanism for supporting HR-SBO 
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6.7.2.4  EAS Discovery Procedure with Local DNS for HR-SBO  p. 58

Reproduction of 3GPP TS 23.548, Fig. 6.7.2.4-1: Procedure for EAS Discovery with local DNS for HR-SBO roaming scenario
Figure 6.7.2.4-1: Procedure for EAS Discovery with local DNS for HR-SBO roaming scenario
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The procedure in this clause assumes that the UL CL is able to detect FQDN(s) in traffic sent to the IP address of the local DNS Server. It is thus incompatible with usage of DoT (DNS over TLS) or DoH to protect the DNS traffic exchanged between the UE and the PLMN.
If the target FQDN of the DNS query is not part of the FQDN authorized by the H-SMF in step 2 of Figure 6.7.2.2-1, the UL CL/BP UPF is instructed to send the DNS request to the DNS server address provided by HPLMN via V-UPF (if it exists) and H-UPF (through N9), by modifying the packet's destination IP address (corresponding to local DNS Server) to the DNS server address provided by HPLMN on UL CL or H-UPF . For the corresponding DNS response received by H-UPF, the H-UPF or UL CL modifies the packets' destination IP address to that of the local DNS Server.
The steps 0 to 5 are the same as the steps 0 to 6 of Figure 6.2.3.2.3-1 with following differences:
  • SMF is replaced with V-SMF.
  • UE, (R)AN, AMF, UL CL/BP UPF, L-PSA UPF, V-SMF, Local DNS Resolver/Server are located in VPLMN.
  • UPF, H-SMF, C-DNS are located in HPLMN.
Step 0.
The HR-SBO PDU Session is established. See the procedure in clause 6.7.2.2.
Step 1.
UL CL/BP insertion. See the step 1 of the procedure in Figure 6.2.3.2.3-1.
Step 2.
After UL CL/BP insertion is performed, the V-SMF sends new local DNS server address to the UE by performing PDU Session Modification procedure as in clause 4.3.3.3 of TS 23.502 with following additions:
Step 3-5.
See the steps 4-6 of the procedure in Figure 6.2.3.2.3-1.
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6.7.2.5  EAS discovery procedure with V-EASDF/Local DNS Server using IP replacement mechanism for supporting HR-SBO  p. 59

Based on the operator's configuration and local regulations, the IP replacement mechanism may be used for EAS discovery supporting HR-SBO:
  • The H-SMF sends DNS server address provided by the HPLMN included in PCO to UE via V-SMF during PDU Session Establishment/Modification procedure. The DNS query related to the edge computing (corresponding to FQDNs) can be routed to V-EASDF/Local DNS server in the VPLMN using IP replacement mechanism.
To support IP replacement mechanism, in this clause the SMF shall instruct the UPF to use the FAR that contains Information elements of "IP Address and Port Number Replacement".
Reproduction of 3GPP TS 23.548, Fig. 6.7.2.5-1: EAS discovery procedure with V-EASDF/Local DNS Server using IP replacement mechanism for supporting HR-SBO
Figure 6.7.2.5-1: EAS discovery procedure with V-EASDF/Local DNS Server using IP replacement mechanism for supporting HR-SBO
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Step 0.
The Registration procedure is described in step 1 of clause 6.7.2.2.
Step 1.
The HR-SBO PDU Session Establishment is described in the step 2 of clause 6.7.2.2 with the following differences:
  • After step 3 in clause 4.3.2.2.2 of TS 23.502, the V-SMF selects a UPF in VPLMN supporting UL CL/BP and PSA functionalities based on UE location information.
  • The V-SMF sends the request for establishment of the PDU session supporting HR-SBO in VPLMN without the V-EASDF/Local DNS server IP address in the step 6 of clause 4.3.2.2.2 of TS 23.502.
  • If the Nsmf_PDUSession_Create Request received by the H-SMF does not include the V-EASDF/Local DNS server IP address, the H-SMF constructs PCO with DNS server address field set to DNS server address provided by the HPLMN and sends the PCO to UE via V-SMF in the step 13 of clause 4.3.2.2.2 of TS 23.502.
Step 2.
The V-SMF configures the UPF in VPLMN as described in step 3 of clause 6.7.2.2 with the following differences:
  • Based on the FQDN(s) received from the VPLMN Specific Offloading Information, the V-SMF indicates the UPF in VPLMN to route DNS queries for the FQDN (range) query to V-EASDF/Local DNS server. In the case of UL CL, the V-SMF configures the UPF in VPLMN with IP replacement information (i.e. DNS server IP address and port number of HPLMN, V-EASDF/Local DNS server IP address and port number). In uplink direction, UPF in VPLMN replaces the destination address of the DNS query targeting an FQDN eligible for HR-SBO related offload from DNS server IP address of HPLMN to V-EASDF/Local DNS server IP address; In downlink direction, UPF in VPLMN replaces the source address of the DNS response targeting an FQDN eligible for HR-SBO related offload from V-EASDF/Local DNS server IP address to DNS server IP address of HPLMN.
    If V-EASDF is used, the V-SMF also configures the V-EASDF as described in step 3 of clause 6.7.2.2.
Step 3.
UE sends DNS query to DNS server of HPLMN.
Step 4a.
If the DNS query does not match the FQDN range eligible for HR-SBO related offload, UPF in VPLMN delivers the DNS query via H-PSA through N9 and H-PSA delivers the DNS query to the DNS server of HPLMN.
Step 4b.
If the DNS query matches the FQDN range eligible for HR-SBO related offload, the UPF in VPLMN delivers the DNS query to V-EASDF/Local DNS server using IP replacement mechanism. The following EAS discovery procedure is based on step 4b.
Step 5.
The EAS discovery procedure described in steps 8-18 of clause 6.2.3.2.2 or steps 4-6 of clause 6.2.3.2.3 applies with the following differences:
  • This EAS discovery procedure with IP replacement is implemented in the VPLMN.
  • In step 16 of clause 6.2.3.2.2, the V-SMF may perform insertion or change of UL CL/BP and local PSA in VPLMN as described in the step 3 of clause 6.7.2.3.
Step 6.
The V-EASDF/Local DNS server sends the DNS response including FQDN to the UPF in VPLMN. The UPF in VPLMN replaces the source address from V-EASDF/Local DNS server to DNS server of HPLMN in the DNS response based on the V-SMF instructions and sends this DNS response to the UE directly or via UL CL/BP of VPLMN if existing in this PDU Session.
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