Default-Bearer QoS Handling for 5G Sessions
The following procedure explains how the SMF handles the modification of authorized QoS for the default bearer in a 5G session.
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The SMF receives SmPolicyUpdateNotify from PCF with changed 5QI in AuthorizedDefaultQoS and/or a different session AMBR value.
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The SMF initiates N1N2MessageTransfer procedure with AMF to send N1 PDU Session Modification Command and N2 PDU Session Resource Modify Request Transfer IE in this message.
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In the N1 message, the default QoS flow is modified in Authorized QoS Flow Description IE to update the 5QI value.
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In the N1 message, the Mapped EPS Bearer Context IE is modified to update the QCI of the default bearer.
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In the N2 message, the QoS flow level QoS parameter for the default flow is modified to update the 5QI value.
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The SMF accepts the SMContextUpdate Request from AMF with the responses for the N1 and N2 requests sent in N1N2Message Transfer message.
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On the N4 interface, the following changes are done:
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New instance of the BearerLvlInfo IE is included with the changed 5QI to QFI mapping.
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Update PDR is sent for all PDRs which are a part of default flow to reflect the association with the new BearerLvlInfo IE.
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Forwarding Action Rule (FAR) associated with all PDRs in the default flow is updated with the new DSCP marking value if the 5QI-DSCP mapping configuration has a different value for the changed 5QI.
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