Feature Description

AMF supports the following timers:

  • T3346 (t3346): It operates in NAS-CONGESTION state. AMF uses this timer value to encode t3346 IE in Registration / Service reject, and to encode back-off timer IE for rejection of session management message.

  • T3502 (t3502): It operates in the 5GMM-DEREGISTERED and 5GMM-REGISTERED states. AMF provides this timer value to UE in the Registration Accept and Registration Reject messages.

  • T3512 (t3512): It operates in the 5GMM-REGISTERED state. AMF provides this timer value to UE in the Registration Accept message.

  • T3513 (t3513): It operates in the 5GMM-REGISTERED state. It starts when the Paging procedure is initiated (with default paging algorithm) and stops when the Paging procedure ends (with the reception of paging response).

  • T3522 (t3522): It operates in the 5GMM-DEREGISTERED-INITIATED state. It starts with the transmission of Deregistration Request message and stops after receiving Deregistration Accept message.

  • T3550 (t3550): It operates in the 5GMM-COMMON-PROCEDURE-INITIATED state. It starts with the transmission of Registration Accept message and stops after receiving the Registration Complete message.

  • T3555 (t3555): It operates in the 5GMM-REGISTERED state. It starts with the transmission of Configuration Update Command message with the ACK bit set in the Configuration Update Indication IE. Stops with the Configuration Update complete message

  • T3560 (t3560): It operates in the 5GMM-COMMON-PROCEDURE-INITIATED state. It starts with the transmission of Authentication Request message and Security Mode Command. Stops after receiving the following messages:

    • Authentication Response

    • Authentication Failure

    • Security Mode Complete

    • Security Mode Reject

  • T3570 (t3570): It operates in the 5GMM-REGISTERED state. It starts with the transmission of Identity Request message and stops after receiving the Identity Response message

  • 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.

  • 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.

  • HO Supervisory (ho-supervisory): It supervises PDU responses from SMF during N2, N26, and Xn handovers.

  • Tidt (tidt): It starts after four minutes of T3512 timer expiry. The subscriber gets Deregistered implicitly upon this timer expiry.

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

  • Tpurge (tpurge): It starts when the Tidt timer expires. AMF sends a request to the UDM to Deregister (purge) the UE from the UDM for 3GPP access upon this timer expiry.

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

For information on the timer configurations, refer to Feature Configuration.