Technical reference hub for telecom engineers

Structured protocol references, message databases, call flows, troubleshooting guides, releases, and engineering tools for wireless and telecom engineers.

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Initial Context Setup Failure NGAP Downlink NAS Transport RRC Connection Setup PDU Session Establishment Failure

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5G

Architecture, interfaces, protocols, procedures, and technical reference pages for NR.

LTE

LTE protocol references, mobility procedures, messages, and engineering lookup pages.

6G

Early-stage 6G concepts, standardization status, and next-generation wireless reference material.

Troubleshooting Guides

5G Initial Access Troubleshooting

Isolate failures in cell search, PBCH decode, SIB1 acquisition, suitability checks, camping, and pre-random-access gating.

TAI and Tracking Area Mismatch Troubleshooting

Troubleshoot TAC broadcast errors, tracking-area restrictions, roaming-area mismatch, and area-related registration reject causes.

AMF Selection and GUAMI Issues

Troubleshoot wrong AMF targeting, stale GUAMI or 5G-GUTI context, and broken AMF-selection hints across RRC and NGAP.

5G Registration Failure Troubleshooting

End-to-end guide for registration reject, incomplete registration, AMF selection issues, and first-access failures.

Initial Context Setup Failure Analysis

Diagnose failures during Initial Context Setup and isolate core, policy, or radio-side blockers.

PDU Session Establishment Failure

Diagnose failed session setup, 5GSM reject causes, policy gaps, and missing path creation.

Latest Updates

Protocol 5G Sidelink SDAP Overview and SL-DRB Mapping

5G SDAP reference covering sidelink SDAP over PC5, SDAP entity model per destination and cast type, PC5 QoS flow to SL-DRB mapping, default SL-DRB behavior, and sidelink limits such as no Reflective QoS over PC5.

Protocol 5G Sidelink SDAP Data PDU Format and PQFI

5G sidelink SDAP reference covering SL SDAP data PDU format, PQFI, unicast header-bearing SDAP, headerless groupcast and broadcast handling, and the relationship to SL-SDAP-Config-r16.

Protocol 5G SL-SDAP-Config and Cast Types

5G NR sidelink RRC reference covering SL-SDAP-Config-r16, sl-SDAP-Header-r16, sl-DefaultRB-r16, sl-MappedQoS-FlowsToAddList-r16, sl-MappedQoS-FlowsToReleaseList-r16, and sl-CastType-r16 for unicast, groupcast, and broadcast.

Protocol 5G SDAP Architecture, Services, and Functions

5G SDAP architecture reference covering SDAP entities, protocol placement, services to upper layers, lower-layer expectations, QoS flow mapping, reflective QoS, MRB handling, and sidelink functions.

Protocol 5G SDAP End-Marker Control PDU and Flow Remapping

5G SDAP reference covering End-Marker Control PDU format and procedure, QoS flow to DRB remapping, reflective mapping updates, old bearer termination, and PC5 QoS flow to SL-DRB remapping.

Protocol 5G SDAP Entity Handling and Data Transfer

5G SDAP procedure reference covering SDAP entity establishment and release, uplink and downlink data transfer, default DRB behavior, MRB reception, and sidelink transmission and reception.