Decode & Understand 3GPP Protocol Messages
Paste any RRC or NAS hex dump, get instant decoding with human-readable explanations of what the network is doing and why.
Human explanations hand-crafted by telecom protocol engineers. References exact 3GPP TS sections for every message type.
Try an Example
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Frequently asked questions
Which protocols are supported?
What is channel auto-detection?
Is NAS decoding free?
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Common Messages Explained
Select any message below to load it as an example and see the full explanation. Each entry references the exact 3GPP TS section.
RRC Connection Setup (4G)
TS 36.331 Β§6.2.2Grants the UE a dedicated connection and configures SRB1.
RRC Reconfiguration (4G)
TS 36.331 Β§6.2.2Modifies bearers, triggers handover, or activates EN-DC.
RRC Release (4G)
TS 36.331 Β§6.2.2Moves the UE to RRC_IDLE with optional redirection.
Measurement Report (4G)
TS 36.331 Β§6.2.2UE reports serving and neighbor cell RSRP/RSRQ.
UE Capability Information (4G)
TS 36.331 Β§6.2.2Reports supported bands, CA combos, and NR capability.
Security Mode Command (4G)
TS 36.331 Β§6.2.2Activates RRC integrity protection and ciphering.
RRC Setup (5G NR)
TS 38.331 Β§6.2.2NR equivalent of RRC Connection Setup, establishes SRB1.
RRC Reconfiguration (5G NR)
TS 38.331 Β§6.2.2Modifies bearers, switches BWPs, or adds secondary cells.
RRC Release (5G NR)
TS 38.331 Β§6.2.2Releases or suspends the NR connection (RRC_INACTIVE).
Measurement Report (5G NR)
TS 38.331 Β§6.2.2UE reports NR cell measurements including RSRP and RSRQ.
UE Capability Information (5G NR)
TS 38.331 Β§6.2.2Reports NR band support, MIMO, FR2, and feature sets.
Security Mode Command (5G NR)
TS 38.331 Β§6.2.2Activates 5G NR AS security with 5G algorithms.
Attach Request (NAS)
TS 24.301 Β§8.2.4UE requests EPS attach with identity and capabilities.
Attach Accept (NAS)
TS 24.301 Β§8.2.1MME confirms attach with GUTI, TAI list, and default bearer.
Authentication Request (NAS)
TS 24.301 Β§8.2.7MME sends RAND/AUTN to authenticate the UE via EPS AKA.
PDN Connectivity Request (NAS)
TS 24.301 Β§8.3.18UE requests a PDN connection to a specific APN.
Registration Request (5G NAS)
TS 24.501 Β§8.2.6UE registers with 5GC using SUCI or 5G-GUTI.
PDU Session Establishment (5G NAS)
TS 24.501 Β§8.3.2UE requests a PDU session with DNN, slice, and SSC mode.
Frequently Asked Questions. Protocol Explainer
What does the Protocol Explainer do?
It decodes raw 3GPP protocol messages (RRC, NAS) and adds human-readable explanations of what each message means, which IEs are critical, and what the network is doing.
Which protocols are supported?
RRC for 2G GSM, 3G UMTS, 4G LTE (TS 36.331) and 5G NR (TS 38.331). NAS for 4G LTE (TS 24.301) and 5G NR (TS 24.501). Decoding engine uses ASN.1 UPER/APER up to Release 17.
How is this different from the L3 Decoder?
The L3 Decoder shows the raw decoded tree. The Protocol Explainer adds a human-readable explanation layer: what the message means in plain language, which IEs matter, and practical field implications.
Are the explanations generated by AI?
No. Each explanation is hand-crafted by telecom protocol engineers based on 3GPP specifications. We reference the exact TS section for every message type.
Is the Protocol Explainer free?
Yes. You get 20 free decodes per day and 5 free explanations per day with no signup required. Pro subscribers get unlimited access.
Where do hex frames come from?
Hex frames come from QMDL captures, DIAG logs, PCAP exports, Wireshark, QCAT, TEMS, Nemo, or the HiCellTek Android app.
Can I decode NAS messages?
NAS decoding (EMM, ESM for 4G; 5GMM, 5GSM for 5G) is available with a Pro subscription.
What if my message type has no explanation?
The decoder will still decode the message and show the full tree. A notice will indicate that the human explanation is coming soon for that message type.
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