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.

Step | Description |
---|---|
1 | HSS 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. |
2 | If the subscribed UE-AMBR is modified, the MME calculates a new UE-AMBR value and sends the Modify Bearer Command to SGW. |
3 | SGW 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. |
4 | SMF or PDN GW sends the updated APN-AMBR to PCF. |
5 | PCF 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. |
6 | SMF sends the Update Bearer Request to SGW. |
7 | SGW sends the Update Bearer Request to MME. This request message includes the details on EBI, EPS Bearer QoS, TFT, and APN-AMBR. |
8 | MME sends the Update Bearer Response to SGW. |
9 | SGW 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. |
10 | UPF 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. |
11 | UPF 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. |
12 | SMF or PDN GW notifies PCF on the requested PCC decision whether it was enforced or not. |
13 | PCF sends the “200 OK” acknowledgment to SMF or PDN GW. |