MME-initiated Bearer Modification for EPS session on SMF Call Flow

This section describes the MME-Initiated Dedicated Bearer Modification for EPS session on SMF call flow.

MME-Initiated Bearer Modification for EPS session on SMF Call Flow
MME-Initiated Bearer Modification for EPS session on SMF Call Flow Description
StepDescription
1HSS sends an Insert Subscriber Data message to the MME. The subscription data includes the details on IMSI, EPS subscribed QoS (QCI and ARP), and the subscribed UE-AMBR and APN-AMBR.
2If the subscribed UE-AMBR is modified, the MME calculates a new UE-AMBR value and sends the Modify Bearer Command to SGW.
3SGW sends the Modify Bearer Command message to the SMF or PDN GW. This message includes the details on EPS Bearer Identity, EPS Bearer QoS, and APN-AMBR.
4SMF or PDN GW sends the updated APN-AMBR to PCF.
5PCF sends the updated PCC decision to the SMF or PDN GW. The PCF modifies the APN-AMBR that is associated with the default bearer in response to the SMF or PDN GW.
6SMF sends the Update Bearer Request to SGW.
7SGW sends the Update Bearer Request to MME. This request message includes the details on EBI, EPS Bearer QoS, TFT, and APN-AMBR.
8MME sends the Update Bearer Response to SGW.
9SGW sends the Update Bearer Response as acknowledgment for the bearer modification to the SMF or PDN GW. The response message includes the details on EBI and user location information.
10UPF sends the PFCP Session Modification Response to SMF. Based on the PCC decision provision message (QoS policy) that is received from the PCF, the SMF or PDN GW initiates the dedicated bearer modification procedure. SMF or PDN GW uses the QoS policy to determine if a service data flow is to be added or removed from an active bearer or if the authorized QoS of a service data flow is changed.
11UPF updates the PFCP parameters and sends a PFCP Session Modification Response to the SMF or PDN GW. UPF confirms the successful modification of the PFCP session.
12SMF or PDN GW notifies PCF on the requested PCC decision whether it was enforced or not.
13PCF sends the “200 OK” acknowledgment to SMF or PDN GW.