Call Flows
This section describes the key call flow of EBI Allocation and Reallocation Support feature.
The EBIAssignment service operation is used during the following procedures (see 3GPP TS 23.502 [3], clause 4.11.1.4):
UE requested PDU Session Establishment including Request Types Initial Request and Existing PDU Session (Non-roaming and Roaming with Local Breakout (see 3GPP TS 23.502 [3], Section 4.3.2.2.1).
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UE requested PDU Session Establishment including Request Types Initial Request and Existing PDU Session (Home-routed Roaming (see 3GPP TS 23.502 [3], Section 4.3.2.2.2).
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UE or network requested PDU Session Modification (non-roaming and roaming with local breakout) (see 3GPP TS 23.502 [3], Section 4.3.3.2).
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UE or network requested PDU Session Modification (home-routed roaming) (see 3GPP TS 23.502 [3], Section 4.3.3.3).
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UE Triggered Service Request (see 3GPP TS 23.502 [3], Section 4.2.3.2) to move PDU Session(s) from untrusted non-3GPP access to 3GPP access.
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Network requested PDU Session Modification, when the SMF needs to release the assigned EBI from a QoS flow (see 3GPP TS 23.502 [3], Section 4.11.1.4.3).
The EBI Assignment service operation is sent by the SMF towards the AMF, to request the AMF to allocate EPS bearer ID(s) towards EPS bearer(s) mapped from QoS flow(s) for an existing PDU Session for a given UE. EBI allocation applies only to PDU Session(s) via 3GPP access supporting EPS interworking with N26. EBI allocation does not apply to PDU Session(s) via 3GPP access supporting EPS interworking without N26 or PDU Session(s) via non-3GPP access supporting EPS interworking.
SMF performs EBI Assignment service operation by invoking assign-ebi custom operation on the individual ueContext resource.
The following call flow shows the messaging that happens in the network. The components of the AMF are not specified here.

Step |
Description |
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1 |
SMF sends Assign-ebi request to AMF. |
2 |
AMF sends 200 OK message to AMF |