Call Flows

This section describes the call flow for selecting and using SEPP.

The following types of requests are sent from a client to a server:

  • Requests to API roots - These requests are sent to the API root as defined in the YAML. The following headers are added to the request:

    • 3gpp-Sbi-Target-apiRoot - The value of this header is the FQDN of the NF that services the request. For requests sent to the hSMF, this is the hSMF FQDN.

    • Authority - The value of this header is the server SEPP to which the request is sent to by the client. When the request is sent by the vSMF, the value is vSEPP, and when the request is sent by the hSMF, it's hSEPP.

  • Callback Requests - These requests are callbacks that are invoked across PLMN boundaries. The values of the header field in such requests are defined in 3GPP TS 29.500, Annex B.

Call Flow with SEPP
Call Flow Description for Selecting a SEPP
Step Description
1 - 2 The vSMF initiates the procedure by sending an indication to hSMF about using a SEPP and the address of the SEPP. The call flow sequence for this forward messaging is as follows:
  • The vSEPP and hSEPP encrypts and decrypts the messages sent from the vSMF to hSMF respectively.

  • The AMF sends the hSMF FQDN to smf-service, which in turn sends it to rest-ep in all the messages.

  • The vSMF selects the vSEPP by reading the locally configured IP address and port number for the vSEPP and uses it to send messages to hSMF.

  • The rest-ep updates the 3gpp-Sbi-Target-apiRoot headers with the hSMF URI and Authority header with the IP address and port number of the vSEPP and then, sends the messages to vSEPP, which is further communicated to the hSEPP.

  • The hSEPP resolves the DNS (if required), decrypts the message and transmits it to the hSMF.

3 - 4 The hSMF responds with a callback header value. The call flow sequence for this return messaging is as follows:
  • The hSEPP and vSEPP encrypts and decrypts the messages sent from the hSMF to vSMF respectively.

  • The smf-service gets the FQDN for the vSMF from the notification URI that is received as apart of message from the vSMF and updates the 3gpp-Sbi-Target-apiRoot headers. The smf-service updates the 3gpp-sbi-callback enum value in all the messages.

  • The smf-service forwards the message to the rest-ep. The rest-ep updates the 3gpp-sbi-callback and 3gpp-Sbi-Target-apiRoot header values.

  • The rest-ep updates the Authority (pseudo header) with the locally configured IP address and port number of the hSEPP and forwards the message to the hSEPP, which is further communicated to the vSEPP.

  • The vSEPP resolves the DNS (if required), decrypts the message and transmits it to the vSMF.