Questions about PFCP Session Establishment Request

Q/A
,
#1

I think it is possible to configure multiple UPFs in the up_nodes of userplane_information in smfcfg.conf.
When establishing a PDU session, am I correct that the PFCP Session Establishment Request is sent only to the UPF listed at the beginning of the list of up_nodes?
In my smfcfg.conf, I think that a PFCP Session Establishment Request is sent to UPF1 only.

My smfcfg.conf is configured as follows:

userplane_information:

  • up_nodes:
    • gNB1:
      • type: AN
      • an_ip: 192.188.2.3
    • UPF1:
      • type: UPF
      • node_id: 192.168.1.2
      • up_resource_ip: 192.188.2.2
    • UPF2:
      • type: UPF
      • node_id: 192.168.1.3
      • up_resource_ip: 192.188.2.23
  • links:
    • A: gNB1
    • B: UPF1
    • A: gNB1
    • B: UPF2
#2

PFCP Session Establishment will be sent if PDU Session Establish is trigger by UE.

As of SMF, it will check which UPF the UE’s PDU Session goes through in Establishing the PFCP Session. So that, the PDU Session can able to cross multiple UPF if needed.

#3

Hi, @free5GC.
In other words, are the following questions wrong?
Am I correct that the PFCP Session Establishment Request is sent only to the UPF listed at the beginning of the list of up_nodes?

Which parameter does the SMF use to check which UPF the UE PDU session passes through?

#4
  1. Yes, smf will only know the UPF list on smfcfg.conf 's up_node. But the message will send after the UE have sent PDU Session Setup.
  2. If you have complicate UPF topologie, you may want to use uerouting.yaml to assigned the ULCL path. Or the smf will calculate itself.