Feature Description

AMF supports the following non-3GPP timers:

  • UE Context Transfer (context-transfer-guard): AMF uses this timer to keep the individual UE Context resources until the timer expires. AMF starts this timer when UeRegStatusUpdateReqData message contains transferStatus as TRANSFERRED. Upon expiry, it clears the PDUs locally.

  • Procedural Timeout (proc-timeout): It starts when AMF receives Registration Request. After expiry, AMF sends the Registration Reject message to the UE.

  • Tidle (tidle): When the UE moves to the CONNECTED state, tidle timer is started and it's reset when any signalling occurs for the subscriber.

    On expiry of tidle timer, AMF checks:

    • If the UE Configuration Update is enabled and if new configuration is available to send to the UE, AMF triggers the UE Config Update Command to UE and resets the tidle timer.

    • If the UE Configuration Update isn’t enabled or there’s no configuration update to send the to UE, the UE is moved to the IDLE state. AMF triggers the Context Release Command towards the gNB and the SM Context Update towards the SMF accordingly.

  • Tn2 (tn2): It functions in AMF-initiated N2 messages, specifically for the AMF that waits for the response.

For more information, see the Session Timers chapter.