3GPP ASN.1 decoder: build vs buy for your telecom tool

If you are developing a mobile network diagnostic tool, a drive test application, or a chipset-level protocol analyzer, you will inevitably face the ASN.1 decoding problem. Every Layer 3 message in LTE and 5G NR — RRC, NAS, SIB — is encoded using ASN.1 PER (Packed Encoding Rules) as defined by 3GPP. Without a robust decoder, your tool cannot interpret what the modem is actually signaling.

This article examines the realistic trade-offs between building your own ASN.1 decoder and buying a production-ready library.

What ASN.1 does in telecom

ASN.1 (Abstract Syntax Notation One) is the serialization format used by 3GPP to define the structure of radio interface messages. In practice, this means:

• LTE RRC (TS 36.331): connection setup, handover commands, measurement reports, SIB broadcasts — all encoded in ASN.1 UPER
• 5G NR RRC (TS 38.331): similar scope but significantly larger specification surface, including NR-specific IEs like MeasResultNR, BWP-Config, and CellGroupConfig
• NAS (TS 24.301 for LTE, TS 24.501 for 5G): attach, authentication, PDU session management — partially ASN.1 encoded with TLV wrappers

When your tool captures raw DIAG frames from a Qualcomm modem, the payload is a binary blob. Without ASN.1 decoding, it is opaque. With decoding, you get structured fields: cell IDs, measurement values, configuration parameters, cause codes.

The scale of the 3GPP ASN.1 specifications

Many teams underestimate the sheer volume of the ASN.1 grammar they need to compile and maintain:

Specification	ASN.1 source size	Approximate IE count
LTE RRC (TS 36.331)	~25 MB of ASN.1 text	2,000+ IEs
5G NR RRC (TS 38.331)	~22 MB of ASN.1 text	2,500+ IEs
LTE NAS (TS 24.301)	Mixed TLV + ASN.1	200+ message types
5G NAS (TS 24.501)	Mixed TLV + ASN.1	250+ message types

These are not static. 3GPP publishes new releases quarterly, and each release can add, modify, or deprecate hundreds of IEs. A decoder built against Release 15 will miss critical fields from Release 17 or 18.

The real cost of building in-house

Building an ASN.1 UPER decoder for 3GPP telecom is not a weekend project. Here is what the development effort typically looks like:

Development timeline

• ASN.1 compiler: 2-4 months to build or adapt an open-source compiler (such as asn1c or asn1tools) to handle 3GPP-specific extensions and UPER encoding
• Schema integration: 1-2 months to parse and compile the full TS 36.331 and TS 38.331 grammars without errors
• NAS decoder: 1-2 months for the TLV+ASN.1 hybrid format used in EPS and 5GS NAS
• Testing and validation: 2-3 months to validate decoded output against reference tools (QCAT, Wireshark) across hundreds of message types
• Total: 6-12 months of focused engineering effort

Financial cost

For a team of 2-3 experienced C/C++ engineers with telecom protocol expertise:

Cost element	Estimated range
Engineering salaries (6-12 months)	100,000 - 250,000 EUR
ASN.1 tooling licenses (if commercial)	5,000 - 20,000 EUR
Testing infrastructure	5,000 - 15,000 EUR
Total Year 1	110,000 - 285,000 EUR

Ongoing maintenance burden

The cost does not end at v1.0. Every quarter, you must:

1. Download updated ASN.1 grammars from 3GPP
2. Recompile and resolve schema conflicts
3. Test against new message types and modified IEs
4. Fix regressions introduced by spec changes
5. Support new chipset variants that encode messages differently

This represents 1-2 full-time engineers dedicated to maintenance alone, or roughly 80,000-150,000 EUR per year in ongoing cost.

The alternative: buying a production-ready SDK

Instead of building from scratch, you can integrate a pre-compiled ASN.1 decoding library into your application. This is the approach HiCellTek offers with its Layer 3 SDK.

What the HiCellTek L3 SDK provides

• Pre-compiled shared libraries: libasn1c_lte_rrc.so and libasn1c_nr_rrc.so for ARM64 and Linux, plus .dll equivalents for Windows
• Full coverage of LTE RRC, NR RRC, and NAS message types up to the latest 3GPP release
• Structured output: decoded messages as JSON or structured C objects
• Quarterly updates aligned with 3GPP release cycles — no recompilation on your side
• Integration support: C/C++ API with headers, sample code, and documentation

Cost comparison

Approach	Year 1	Year 2	Year 3	3-year total
Build in-house	110-285K EUR	80-150K EUR	80-150K EUR	270-585K EUR
HiCellTek L3 SDK	4,990 EUR	4,990 EUR	4,990 EUR	14,970 EUR

The difference is not marginal — it is one to two orders of magnitude. Even for large organizations with dedicated R&D budgets, the build option is difficult to justify unless ASN.1 decoding is a core differentiator of your product.

When building in-house makes sense

There are legitimate reasons to build your own decoder:

• You are a chipset vendor (Qualcomm, MediaTek, Samsung LSI) and need deep integration with proprietary modem firmware
• You have regulatory requirements that mandate full source code control over every component
• ASN.1 decoding is your core product — you are selling the decoder itself

For everyone else — operators building internal tools, system integrators, startups developing drive test apps — buying a proven SDK is the rational choice.

Conclusion

The 3GPP ASN.1 decoding problem is well-defined but deceptively expensive to solve in-house. The specifications are massive, the maintenance is perpetual, and the engineering talent required is scarce and expensive. For most telecom tool developers, integrating a production-ready SDK eliminates months of development risk and hundreds of thousands of euros in cost.

HiCellTek’s Layer 3 SDK delivers compiled ASN.1 decoders for LTE and 5G NR, updated quarterly, at a fraction of the in-house development cost. Explore the full SDK capabilities on the product page or review licensing options on the pricing page. The Layer 3 decoder page shows the end-user application built on this SDK.