Your Environment

• Version: 1.5
• Affected Component: Access Gateway
• Affected Subcomponent: MME
• Deployment Environment: Bare-metal (AGW), Vagrant (AGW)

Describe the Issue

During testing of S1 handover with a two physical eNBs and a UE, the UE fails to successfully complete the handover procedure, with no HandoverNotify message generated by the target eNB.

To Reproduce

1. Set up two eNBs such that handover can occur between them (i.e., configure neighbor tables, ensure both are connected to the same MME)
2. Attach a UE to the source eNB.
3. Trigger a handover to the target eNB (e.g., by reducing signal strength of the source eNB with attenuators)
4. Observe UE perform a reconnect to the target eNB, rather than a clean handover, and fail to receive a HandoverNotify at the MME from target eNB.

Expected behavior
Handover should complete successfully, and the target eNB should generate a HandoverNotify message towards the MME.

Additional context
We performed two sets of tests. The first used a Baicells Nova 227 (firmware: RTS 3.6.6) as both source and target eNB. The second used a Baicells Nova 227 as source eNB and Airspan AirVelocity 1500 (15.17.00.1049) as a target eNB. In both cases, we used a Pixel 3 as the UE. Logs and packet traces are attached, a description is below:

• Nova 227 > Nova 227.
  • handover_nova227_nova227_pixel3_20210426_2117_s1ap_rrc.pcapng: Contains RRC trace messages from both source eNB (192.168.60.249) and target eNB (192.168.60.245), along with S1AP messages.
  • Nova 227 debug logs exported from target eNB.
  • Note that in this test, we receive an RRCConnectionReconfigurationComplete message in the RRC trace from the target eNB, indicating the UE reported it had successfully completed handover to the target eNB.
• Nova 227 > AirVelocity 1500
  • s1_handoff_airspan_target_1323.pcapng: Source eNB 10.0.2.10, Target eNB 10.0.2.20
  • RRC tracing was not available for this test.