If you work with 2G, 3G, 4G or 5G networks, you have probably spent time staring at hex dumps of RRC and NAS messages. Whether you are a field engineer debugging an attach failure, an RF optimizer analyzing handovers, or a protocol analyst investigating VoLTE drops, decoding Layer 3 signaling is a daily task.
The traditional workflow involves QCAT (Qualcomm-specific, Windows-only, license required), Wireshark (needs full PCAP files), or expensive tools like TEMS and Nemo ($10K+/year). But what if you could decode a single hex frame in your browser, in under a second?
What is RRC and why decode it?
RRC (Radio Resource Control) is the Layer 3 protocol between the UE (phone) and the base station (eNB in LTE, gNB in 5G NR). It carries:
- Connection setup and release (RRCSetup, RRCRelease)
- Reconfiguration (RRCReconfiguration for handovers, bearer changes, CA/DC config)
- Measurement reports (MeasurementReport with RSRP, RSRQ, SINR from neighbor cells)
- System information (SIB1, SIB2 with cell parameters broadcast)
- UE capabilities (UECapabilityInformation with bands, features, MRDC support)
RRC messages are encoded in ASN.1 using UPER (Unaligned Packed Encoding Rules). You cannot read them without a decoder.
The online alternative
HiCellTek offers a free online decoder that handles both RRC and NAS for 2G, 3G, 4G and 5G:
- Go to hicelltek.com/en/decoder/
- Select the technology (LTE or 5G NR) and logical channel
- Paste your hex frame
- Click Decode
The engine is compiled C++ (asn1c) running server-side with 3GPP Release 17 support. It handles complex structures like CellGroupConfig and the LTE-to-NR tunnel (nr-SecondaryCellGroupConfig-r15).
How it compares to Wireshark
| Feature | Wireshark | HiCellTek Decoder |
|---|---|---|
| Install required | Yes | No (browser) |
| Input format | Full PCAP | Single hex string |
| Speed | File-dependent | Sub-second |
| NAS decoding | Yes | Yes (Pro plan) |
| Batch mode | Manual | Up to 1,000 frames |
| Export | PDML/JSON | .txt and .json |
| Cost | Free | Free (20/day) or Pro 29 EUR/mo |
| 5G NR R17 | Version-dependent | Full R17 |
The key advantage: no need to reconstruct a PCAP. Paste the hex, get the tree.
Real use case: debugging a 5G SA registration failure
A field engineer captures a Registration Reject from the AMF. The hex payload looks like this:
7e0046110000001001000000
Pasting this into the decoder reveals:
- Message type: Registration reject
- 5GMM cause: #17 (Network failure)
- Diagnosis: the issue is core-side (AMF/UDM), not radio
Without a decoder, this hex string is meaningless. With one, you have a diagnosis in 2 seconds.
Who is this for?
- RF engineers doing drive tests and cluster optimization
- Protocol analysts investigating signaling flows
- Network operators validating SIB and CellGroupConfig parameters
- Telecom students learning 3GPP protocol structures
- Anyone who has a hex frame and needs to know what it says
Try it
The decoder is at hicelltek.com/en/decoder/. 20 free RRC decodes per day, no signup required. The Pro plan (29 EUR/month) adds NAS, batch mode, JSON export and advanced filters.
If you work with telecom signaling, I would love to hear your feedback. What features would make your workflow easier?
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