Dedicated Bearer Activation

Dedicated Bearer Activation

The following diagram describes the steps the messages follow during the dedicated bearer activation procedure.

1. If the PDN-GW has local QoS policy, then this step does not apply. However, if dynamic PCC is deployed, either the PCRF initiates IP-CAN Session Modification procedure with the PCEF, or the PCEF initiates IP-CAN Session Modification procedure with the PCRF.

2. The PDN-GW uses the QoS Policy values i.e. QCI, ARP, GBR and MBR to assign to the EPS Bearer QoS. The PDN-GW sends a Create Bearer Request message to the S-GW with the identities - IMSI, PTI, EPS Bearer QoS, TFT, P-GW S5/S8 TEID, Charging ID, default EPS Bearer Identity and PCO.

3. The S-GW sends the Create Bearer Request message to the MME with the identities - IMSI, PTI, EPS Bearer QoS, S1 TEID of S-GW, TFT, default EPS Bearer ID and PCO.

4. The MME assigns a unique EPS Bearer Identity to the UE. The MME builds the Session Management Request (at the NAS layer) including PTI, TFT, EPS Bearer QoS, PCO, EPS Bearer Identity and default EPS Bearer ID. This message is encapsulated into a Bearer Setup Request message which includes EPS Bearer Identity, EPS Bearer QoS, Session Management Request and S1 TEID, and sends to the eNodeB.

5. The eNodeB maps the EPS Bearer QoS to the Radio Bearer QoS and signals an RRC Connection Reconfiguration message to the UE which includes the identities - EPS Radio Bearer Identity, Radio Bearer QoS, Session Management Request. At the NAS Layer, the UE stores the EPS Bearer ID and links the dedicated bearer to the default bearer. The UE also retrieves the Uplink TFT and uses it to determine the mapping of traffic flows to the radio bearer.

6. The UE acknowledges the radio bearer activation to the eNodeB using an RRC Connection Reconfiguration Complete message.

7. The eNodeB acknowledges the bearer activation to the MME using the Bearer Setup Response message which includes the EPS Bearer Identity and S1 TEID.

The UE also builds a Session Management Response message at the NAS Layer including the EPS Bearer Identity. The UE then sends a Direct Transfer message to the eNodeB which includes the Session Management Response message. The eNodeB sends an Uplink NAS Transport message to the MME which includes the Session Management Response message.

8. Upon receipt of Bearer Setup Response and Session Management Response messages, the MME sends Create Bearer Response (EPS Bearer Identity, eNodeB S1-TEID) message to the S-GW.

9. The S-GW sends Create Bearer Response (EPS Bearer Identity, S-GW S5/S8-TEID) message to the PDN-GW.

10. The PDN-GW responds to the PCRF allowing the completion of IP-CAN Session Modification procedure.