Historical project notes: This article describes an earlier version of my telecom projects. Interface steps, coverage counts and sample outputs may differ from the current 3GPP Pilot. The examples are engineering illustrations, not evidence of client deployments.
When a 5G or LTE network event fails — a registration drops, a handover fails, a PDU session doesn't establish — diagnosing the root cause requires knowing which 3GPP clause governs the expected behaviour and how the actual trace deviates from it. 3GPP Search on TejVox is built for exactly this: describe the failure in plain English, get the relevant spec clauses back in seconds, and optionally generate the expected procedure flow to compare against your trace.
How to use it as a fault analyser
Step 1 — Describe the failure, not the symptom
Don't search for error codes alone. Describe what was happening when the failure occurred:
- Bad: "RRC setup failure"
- Good: "UE sends RRCSetupRequest, gNB responds with RRCSetup, but UE never sends RRCSetupComplete — what causes this?"
The semantic search understands the procedure context and returns the specific sub-clauses covering UE actions after receiving RRCSetup, including timer T300 expiry and what happens if the UE loses the RACH channel during setup.
Step 2 — Filter to the right technology family
Use the spec family dropdown: NR (38-series) for 5G, LTE (36-series) for 4G, Core (23/24/29) for network-side failures. Mixing families in search results for a specific fault creates confusion — scope to the right generation first.
Step 3 — Generate the expected procedure flow
Click Generate Procedure Flow to get the normative message sequence for the procedure that failed. Use this as the "golden path" to compare against your protocol trace or log. Steps where your trace deviates are where the fault is.
Step 4 — Use AI Explain for root cause context
Click Explain with AI to get a structured breakdown of the failure conditions defined in the spec. For most procedures, the spec explicitly lists the error conditions — what the UE must do if no response is received, what timers apply, which state the entity falls back to. These are the clauses to cross-check against your observed behaviour.
Key fault categories and how to search for them
RRC failures (NR: 38.331, LTE: 36.331)
Most RRC failures are timer or state machine issues. Search for the specific procedure ("RRC setup", "RRC reconfiguration", "RRC re-establishment") followed by "failure conditions" or "UE actions on expiry".
Registration and attach failures (5G: 24.501, LTE: 24.301)
NAS-level failures involve reject cause codes. Search for the cause code directly: "5GMM cause #22 congestion" or "EMM cause #15 no suitable cells". The spec clause for that cause code tells you exactly what the network is signalling and what the UE must do next.
Handover failures (NR Xn: 38.423, LTE X2: 36.423)
Search for "handover failure" with the interface name: "Xn handover failure cause", "X2 handover preparation failure". The interface specs define the failure cause IEs and the recovery procedure.
PDU session / bearer failures (5G: 23.502, LTE: 23.401)
Search for "PDU session establishment failure" or "default bearer activation failure" plus the specific cause. The 23-series architecture specs define the AMF/MME-level error handling, while the 24-series NAS specs define what the UE sees.
Reading the output
Each result shows: spec ID (e.g. TS 38.331), clause number (e.g. §5.3.7), a relevance label, and an excerpt. For fault analysis, prioritise Top match results with content type procedure_step — these are the normative clauses that define exactly what should happen. Architecture overview clauses are useful for context but are not normative on behaviour.
Use 3GPP Search free with a TejVox account — no download, no PDF scrolling.
Comments
Loading comments…