PDN_CONNECTIVITY_REJECT with "Cause #27 – Missing or unknown APN"

Hello Experts.

Someone know why in the procedure of Attach, the MME send to the UE PDN_CONNECTIVITY_REJECT with “Cause #27 – Missing or unknown APN”?

Admin note: this post was updated with image below.

  • Cause #27 – missing or unknown DNN

    • SMF sends this cause when DNN is not present in SmContextCreateData even though it is required and not configured in SMF (SMF stands for Session Management Function).

Simply put, it collects all the informations related to PDU session management from various network components (e.g, UPF, PCF, UDM) and controls / orchastrates those network components based on request from AMF ) ( The SMF is the control function that manages the user sessions including establishment, modification and release of sessions, and it can allocate IP addresses for IP PDU sessions.

The SMF communicates indirectly with the UE through the AMF that relays session-related messages between the devices and the SMFs )

Check the allocated IP connevtivitiy for E2E for problematic sites or area

Thank you, but this I suppose is for 5G.

Do you know if is the same in NB IoT?

The problem I describe is for NB IoT.

Totally. Should be the same, because of network architecture flows.

These CN / Backpone parts are mandatory equipment and function, doesn’t matter if BTS is 4G / 5G / IoT etc.