There is a Double S1 Alarm in 4G. Does anyone know the root cause of this issue? The problem occurs when we swap the MME to another vendor, and this counter stops pegging in Nokia BTS.
About the Counter (ERAB_REL_DOUBLE_S1)
This counter tracks the number of E-RAB releases initiated by the MME in a Double S1 scenario, except for cases where the ERAB Release Command was already sent for the same UE.
Updated Behavior:
The counter increments when the eNB detects a Double S1 scenario for a UE and logs the number of released E-RABs.
It is updated upon receiving the S1AP: UE CONTEXT RELEASE COMMAND from the MME to the eNB due to “Radio Connection With UE Lost”, without a prior S1: UE CONTEXT RELEASE REQUEST from the eNB to the MME.
Exception: ERABs are excluded if the ERAB Release Command was previously sent for the same UE.
Would appreciate any insights on why this counter stops pegging after the MME swap!
This issue could be linked to differences in how the new MME handles signaling and procedures. below are some thoughts:
MME Configuration Differences: The new MME might have different settings or features that affect how it interacts with the eNB (it might not send the S1AP: UE CONTEXT RELEASE COMMAND in the same way or under the same conditions as the previous MME).
Protocol Compatibility: There could be subtle differences in the implementation of S1AP protocols between the old and new MME vendors. These differences might lead to scenarios where the eNB does not detect a Double S1 situation as expected.
Counter Logic: The logic for incrementing the counter might rely on specific signaling patterns or sequences that are no longer occurring due to the MME swap.
Transport Layer Issues: If there are any transport layer mismatches or issues (e.g., MTU size, packet loss, or latency), it could affect the signaling flow and prevent the counter from being updated.
Vendor-Specific Features: Nokia BTS might have vendor-specific features or dependencies that are not fully compatible with the new MME’s behavior.
Way forward:
Configuration Review: Check the configuration of the new MME and ensure the mapping of the parameters between Old and New MME is correctly done, any you may check if it aligns with the requirements of the Nokia BTS.
Vendor Collaboration: Engage both New MME vendor and Nokia to identify any compatibility issues or required adjustments.
Transport Checks: Verify the transport layer settings and ensure there are no issues affecting signaling. Trace Analysis : if applicable perform a detailed signaling trace to compare the behavior of the old and new MME during Double S1 scenarios.
I hope the above assists you. and please keep us updated once the issue is resolved.