5G NR SDAP Layer Failures: Root Causes and Solutions

The following outlines common 5G NR test cases at the SDAP layer, including potential failures, their root causes, and proposed solutions.

Failure Case #1: QoS Flow Establishment/Modification Failure

This failure occurs when the network is unable to establish or modify a Quality of Service (QoS) flow as requested by the User Equipment (UE).

Root Causes:

• Incorrect QoS parameters or mappings between the UE and the core network.
• PDU (Protocol Data Unit) session setup failures.
• Incompatibility in QoS settings between the UE and the core network.

Solutions/Rectifications:

• Verify correct QoS mapping and configuration between the UE and the core network to ensure consistency and accuracy.
• Optimize QoS flow management to ensure efficient resource allocation and the correct application of QoS parameters based on the service requirements.
• Implement robust signaling procedures for PDU session establishment and modification to minimize errors and ensure successful setup.

Failure Case #2: SDAP PDU Loss or Reordering

This failure manifests as the loss of SDAP PDUs or their arrival out of the intended order at the receiver.

Root Causes:

• Congestion in the lower layers of the protocol stack, leading to packet drops.
• Buffer management issues, such as buffer overflows, causing PDUs to be discarded.
• Improper QoS handling, resulting in prioritization issues and potential loss of certain types of traffic.

Solutions/Rectifications:

• Ensure proper handling of QoS flows to prioritize latency-sensitive traffic and minimize the impact of congestion.
• Optimize reordering and duplication management procedures to minimize the impact on high-priority traffic, ensuring timely delivery.
• Balance load across multiple paths or bearers to avoid congestion and loss, distributing traffic to alleviate bottlenecks.