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Tips for Reading Specifications and Standards

3GPP specifications (TS) are enormous, and until you get used to them, just searching for "where is what written" is exhausting. Here we introduce practical tips for reading and looking them up efficiently.

Be Aware of the Difference Between TS and TR

  • TS (Technical Specification): A normative specification that implementations must follow. Requirements written with "MUST/SHALL".
  • TR (Technical Report): A report on the study background, investigations, and studies. It is not normative.

What you base implementation and testing on is the TS. TR is used to understand the background of "why this design was chosen".

The Division of Roles Among Stages 1/2/3

3GPP specifications are often structured in three layers, and knowing this lets you quickly choose "the document to read".

Stage Content Representative Example in 5GC
Stage 1 Requirements specification (what to realize as a service) TS 22 series
Stage 2 Architecture and procedures (how to realize it) TS 23.501 (architecture) / 23.502 (procedures)
Stage 3 Protocol details (bit-level, message definitions) TS 24.501 (NAS) / 29 series (SBI) / 38 series (NGAP, etc.)

Start from Stage 2 First

If you "want to know the overall picture of a procedure", go to TS 23.502; for "architecture and definitions of terms", go to TS 23.501. It is efficient to descend to Stage 3 (the 24/29/38 series) only once you actually need the fine-grained bit definitions of messages.

Quick Reference of Frequently Used Major TS

  • TS 23.501: 5G System architecture (the source of NF, reference point, and concept definitions)
  • TS 23.502: Procedures (the source of call flows such as Registration / PDU Session)
  • TS 24.501: NAS protocol (5GMM / 5GSM messages)
  • TS 33.501: Security (key hierarchy, authentication)
  • TS 29 series: The individual SBI services (e.g., 29.502 Nsmf, 29.503 Nudm, 29.518 Namf)
  • TS 38.413: NGAP, TS 29.244: PFCP

For a more comprehensive correspondence table, see the 3GPP Spec Dictionary.

Cautions When Following Section Numbers

Section Numbers Shift by Release

Even within the same TS, section numbers and the section structure can change depending on the Release (Rel-15/16/17/18). When referencing, be conscious not only of the TS number but also the Release and version. On this site as well, we clearly annotate with "to be confirmed" those cases where we cannot pin down the sub-number of a section.