Common LTE Failure Response Codes by Procedure?

RACH Failures:-

RRC Connection Setup:-

Authentication & Security Failures:-

(0XB0F3)EMM Cause #20 "MAC failure" occurs when the integrity check of the NAS message fails due to a mismatch in the Message Authentication Code (MAC). This issue can arise due to several reasons in an LTE network:

Possible Causes & Fixes:

1. Incorrect NAS Security Key (K_ASME / K_NAS_INT)
• Cause: If there is a mismatch in the security keys (e.g., due to incorrect key derivation or reusing an old key), the UE and MME will not authenticate properly.
• Fix:
• Ensure correct key derivation from K_ASME.
• Verify that the MME and UE use the same security context.

EMM Cause #26: "Non-EPS authentication unacceptable" occurs when the LTE network (MME) requests an authentication procedure that the UE does not support or accept. This issue is related to authentication failures in EPS (Evolved Packet System) networks, typically involving 2G/3G fallback scenarios or security policy mismatches.

Possible Causes & Fixes:

1. UE Does Not Support Non-EPS Authentication

• Cause: The MME may attempt to use a non-EPS authentication method (e.g., GSM AKA or UMTS AKA) when the UE only supports EPS-AKA.
• Fix:
• Ensure that the MME is configured to use EPS-AKA (LTE authentication).
• Check if the UE supports fallback to non-EPS authentication (e.g., GSM/UMTS authentication).

(0XB0A1)EMM Cause #21: "Sync Failure"

This error occurs when the UE (User Equipment) and the network (MME) fail to synchronize during the EPS-AKA (Authentication and Key Agreement) process. The failure is typically due to a mismatch in the sequence numbers (SQN) used for authentication.

Possible Causes & Fixes

1. SQN Mismatch Between UE and HSS

• Cause: The Home Subscriber Server (HSS) maintains a sequence number (SQN) for each UE. If the UE and HSS are out of sync, the authentication will fail.
• Fix:
• Resynchronize the SQN in the HSS.
• Enable AUTS (Authentication Synchronization Failure) handling on the network side.
• If the issue persists, reset the subscriber profile in the HSS.

EPS Bearer failure- NAS Layer:

EPS Bearer Setup  failures -NAS Layers

Paging & Call Drop failures- NAS/RRC Layer