5G NR PDCP Layer Failures: Root Causes and Solutions

Here’s a breakdown of common 5G NR test cases at the PDCP layer, including typical failure scenarios, their underlying causes, and suggested solutions.

Failure Case #1: PDCP PDU Loss

Root Causes:

• Improper handling of packets during ciphering/deciphering processes. Think of this as a garbled message that can’t be understood.
• Packet drops due to network congestion, like cars getting stuck in a traffic jam.
• Improper reordering and duplication management, leading to packets arriving out of order or being discarded incorrectly.

Solutions/Rectifications:

• Optimize PDCP reordering and duplication procedures. Make sure the system can effectively handle packets that arrive out of sequence, like a good postal service that can sort mail correctly even if it arrives in a mixed-up order.
• Ensure robust ciphering and deciphering algorithms. Prevent packet corruption, so the message remains intact.
• Improve flow control between PDCP and lower layers to prevent packet drops. This ensures smooth delivery of data packets without bottlenecks.

Failure Case #2: Security Mode Command (SMC) Failure

Root Causes:

• Mismatched ciphering or integrity algorithms between the UE (User Equipment) and the network (gNB). Imagine trying to use different languages to communicate – you won’t understand each other!
• Failure in key derivation procedures, preventing the establishment of a secure connection.
• Timer expiry during security mode procedures, indicating a delay or problem in the security setup.

Solutions/Rectifications:

• Ensure correct configuration and compatibility of ciphering and integrity protection algorithms between the UE and gNB. Both sides need to speak the same language.
• Use fallback mechanisms to revert to previously working security algorithms if needed. Having a backup plan can keep things running smoothly.
• Optimize the security key derivation procedures and verify correct key management. Double-check that the encryption keys are properly generated and handled.

Failure Case #3: PDCP Duplication Failure

Root Causes:

• Incorrect duplication settings for URLLC (Ultra-Reliable Low Latency Communication) traffic, where data is sent multiple times for extra reliability.
• Software bugs in the duplication handling logic, causing errors when trying to duplicate and manage packets.
• Mismatch in duplication configuration between UE and gNB, leading to one side duplicating packets while the other isn’t expecting them.

Solutions/Rectifications:

• Implement proper duplication configuration and synchronization between UE and gNB for URLLC traffic. Make sure both sides are on the same page regarding duplication.
• Ensure correct handling of duplication in software logic to avoid inconsistencies. Iron out any software bugs that might cause duplication errors.
• Test the duplication feature comprehensively in various network conditions. Thoroughly test to catch any potential issues under different circumstances.