Description
Specification and Description Language (SDL) is a formal, object-oriented, graphical modeling language standardized by the International Telecommunication Union (ITU-T) in the Z.100 series. Within the 3GPP standardization context, SDL is employed to provide rigorous, unambiguous specifications for communication protocols, system procedures, and state machine behaviors. Its primary role is to define the dynamic behavior of systems, focusing on the sequence of events, message exchanges, and state transitions that occur in response to stimuli. This formal approach eliminates the ambiguities inherent in natural language text, thereby reducing the risk of misinterpretation and implementation errors across different equipment vendors and network operators.
SDL models a system as a set of concurrent processes that communicate asynchronously via signals. The language uses a hierarchical structure, starting with a system block diagram that defines the overall system and its communication channels. This system is decomposed into blocks, which are further refined into processes. Each process is defined using Extended Finite State Machines (EFSMs), represented by SDL process diagrams. These diagrams consist of states, inputs (triggering signals), outputs (sent signals), tasks (internal actions), decisions, and procedures. The language supports data typing, variables, timers, and the creation of new signal instances, enabling the specification of complex, real-time interactions found in telecommunications protocols.
In 3GPP technical specifications (TS), SDL diagrams are often provided as normative annexes to complement the prose descriptions of protocols. For instance, SDL is extensively used in the specification of layer 3 signaling protocols in both the Core Network and the Radio Access Network, such as Non-Access Stratum (NAS) and Radio Resource Control (RRC) procedures. The language's ability to precisely define timers, message formats, and conditional behavior is crucial for interoperability testing and conformance certification. By providing a visual and formal model, SDL serves as a critical tool for protocol engineers, test developers, and system architects to understand, implement, and verify the correct operation of 3GPP systems.
Purpose & Motivation
The primary purpose of SDL within 3GPP is to achieve unambiguous and precise specification of complex, reactive systems. Telecommunications protocols involve intricate sequences of messages, timers, and state-dependent behaviors. Describing these solely in natural language can lead to multiple interpretations, causing interoperability failures between equipment from different manufacturers. SDL addresses this by providing a formal, graphical notation that defines behavior with mathematical rigor, ensuring all implementers derive the same logical model from the specification.
Historically, as mobile systems evolved from 2G to 3G (UMTS) and beyond, the complexity of protocols increased dramatically. The introduction of packet-switched domains, sophisticated mobility management, and quality of service mechanisms required a more robust specification methodology. SDL, being an ITU-T standard already used in other telecom domains, was adopted to bring this rigor to 3GPP. It solves the problem of specification ambiguity, which is a major source of bugs and delays in multi-vendor network deployments.
Furthermore, SDL models are not just documentation; they can be used for simulation, validation, and even as a basis for automated test generation. This allows standards bodies and equipment vendors to verify the logical consistency of a protocol specification before it is finalized and to develop comprehensive test suites. Thus, SDL's purpose extends beyond static specification to actively improving the quality, reliability, and time-to-market of 3GPP-compliant products.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (111 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SDL (Specification and Description Language) function was newly introduced into the 3GPP drafting rules to standardize its inclusion in specifications. The release provided normative instructions for preparing and inserting SDL diagrams into Word documents, mandating they be provided as SDT binary or CIF files while explicitly excluding headers and footers. This formalized SDL as a recognized method alongside TTCN for describing system behaviors and test sequences within 3GPP technical specifications.
- Introduction of SDL L-band into TS 36.113 TS 36.113CR0070
- CR to TS 38.104 Combined updates from RAN4 #90bis and RAN4#91 From RAN4 #90bis: - R4-1903105, "Draft CR to TS 38.104: Corrections on terminologies and editorial errors" - R4-1903319, "Draft CR to TS 38.104: removal of unused definition: "minimum EIRP level under extreme condition"" - R4-1903320, "Draft CR to TS 38.104: OSDD information correction" - R4-1903457, "Draft CR to TS 38.104: Removal of FFS for FR2 TDD OFF power level requirement in clause 9.5" - R4-1903499, "Draft CR to 38.104: Correction to unwanted emissions mask for bands n7 and n38" - R4-1903836, "Draft CR to TS 38.104: Correction on description on multi-band operation in section 4.8" - R4-1904024, "Draft CR to TS 38.104 Applicability rules for BS demodulation" - R4-1904234, "draftCR: Correlation matrix for 8Rx in TS 38.104" - R4-1904723, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1904726, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1904729, "Draft CR on PRACH performance requirements in TS38.104" - R4-1904734, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1904735, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1904739, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1904745, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1904799, "Draft CR to TS 38.104: FRC update for PUSCH FR1 mapping type B and FR2 DMRS 1+1" - R4-1904816, "Draft CR : Clarification on step 5 and step 6 for delay profiles calculation (38.104)" - R4-1904842, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1905126, "draft CR to 38.104 for TAE requirements" - R4-1905139, "draft CR to TS 38.104 on EVM measurement (Annex B and C)" - R4-1905140, "Draft CR: editorial correction on FR1 spurious emission requirement in TS38.104" - R4-1905143, "Draft CR for TS 38.104: Addition of NOTE for transmitter intermodulation requirements in certain regions" - R4-1905144, "Draft CR to TS 38.104: FRC reference corrections for the Rx requirements" - R4-1905145, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for ACS, blocking and intermodulation requirements" - R4-1905148, "Draft CR to TS 38.104: Corrections on out-of-band blocking requirement" From RAN4 #91: - R4-1906002, "Draft CR to 38.104: Subclause 6.7 and 9.8 transmitter intermodulation – correction of interfering signal type" - R4-1906096, "Draft CR to 38.104: Correction of frequency range for OTA spurious emissions" - R4-1906311, "Draft CR to 38.104: Correction on FRC (Annex A)" - R4-1906346, "Removal of n65 in Rel-15 38.104" - R4-1906915, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for OTA ACS, blocking and intermodulation requirements" - R4-1906918, "Draft CR to TS 38.104: Clarification on type of interfering signal for ACS, in-band blocking and ICS requirements" - R4-1907110, "Draft CR to TS 38.104: correction of the fundamental frequency limit of 2.55GHz for the spurious emissions" - R4-1907246, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1907249, "Draft CR to TS 38.104: Correction on the terminology in PUSCH FRC tables" - R4-1907252, "Draft CR to TS38.104: Updates of PRACH performance requirements" - R4-1907255, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1907258, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1907261, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1907266, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1907267, "Draft CR on TS 38.104 Performance requirement for multi-slot PUCCH format 1" - R4-1907272, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1907275, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1907277, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1907629, "Draft CR to 38.104: Term “reference signal” replacing by term “ideal signal” in EVM context" - R4-1907634, "Draft CR to 38.104: corrections to the EVM annex" - R4-1907659, "Draft CR to TS 38.104 on Spurious emission Category B in FR2" - R4-1907661, "Draft CR to 38.104 Definition of contiguous transmission bandwidth" - R4-1907662, "Draft CR to 38.104: BS TAE requirements" - R4-1907664, "Draft CR to 38.104: Clarification of interferer RB frequency for narrowband blocking" - R4-1907672, "Draft CR for TS 38.104: Correction on EVM" - R4-1907689, "Correction to CA carrier spacing" TS 38.104CR0029
- Completion of description of power saving TS 38.300CR0050
- Correction to description of bandwidth adaptation TS 38.300CR0051
- Description of RLM aspects TS 38.300CR0116
- Corrections on the descriptions of active BWP TS 38.300CR0127
+ 23 more changes
In Release 16, the primary update for the Specification and Description Language (SDL) function was not a new feature but a set of corrections and clarifications to existing descriptions. These included corrections to the HARQ description, the field description for ra-ResponseWindow, and the description of SRS-Config, among other miscellaneous procedural descriptions. The changes ensured the technical accuracy and clarity of the normative specifications that incorporate SDL diagrams, as mandated by the core drafting rules.
- CR to TS 38.104: Introduction of NR-U into BS core specification TS 38.104CR0239
- Adding FRC table description in Annex in TS38.104 v16.5.0 TS 38.104CR0257
- 4-step RA type figure description TS 38.300CR0214
- Various corrections to NR Mobility enhancements description TS 38.300CR0274
- Stage-2 description of MPE reporting TS 38.300CR0299
- Description of Multi-TRP operation TS 38.300CR0300
+ 25 more changes
In Release 17, the updates to the Specification and Description Language (SDL) function were focused on corrections and clarifications to field descriptions within the RAN protocol specifications, particularly for TS 38.331. These included refinements to parameters for procedures such as PUCCH Carrier Switch, RLM/RLF reporting, NTN timing, and QoE measurements. The changes ensured the SDL diagrams and associated textual descriptions accurately reflected the normative behavior of features like 2-step RACH power control and gNB ID length reporting.
- Pi/2-BPSK specification updates for the merger of 5Gi into 3GPP TS 38.306CR0667
- Correction on Stage-2 descriptions for NR NTN TS 38.300CR0611
- Corrections to description of RAN Visible QoE Measurements TS 38.300CR0614
- Correction of QoE stage-2 description TS 38.300CR0686
- Corrections to the description of gNB ID length reporting capabilities [gNB_ID_Length] TS 38.306CR0769
- Correction to the field description of usage-pdc TS 38.331CR3351
+ 19 more changes
In Release 18, the SDL function saw no new functional introductions or feature expansions. The work was limited to editorial corrections and clarifications of existing stage 2 descriptions, such as those for SON, Network-Controlled Repeaters, and QMC, as well as clean-up of UE capability descriptions for various features including eDSS and sidelink relay. These changes were purely for specification accuracy and alignment, maintaining the existing rules for SDL diagram preparation as defined in the normative annex.
- CR to 38.104: FRC number alignments among specifications TS 38.104CR0616
- Corrections on stage 2 descriptions for SON TS 38.300CR0826
- Clarification to Network-Controlled Repeaters Stage-2 description TS 38.300CR0808
- Clean-up corrections on stage 2 description of QMC TS 38.300CR0960
- Clarification of the chapter title to match the description of the UE History Information TS 38.300CR0969
- Correction to PDCP duplication description for L2 MP using SL relay or N3C indirect path TS 38.300CR0989
+ 18 more changes
In Release 19, the updates for the Specification and Description Language (SDL) function focused on providing corrections to procedural descriptions within the specifications. Specifically, this included corrections to the description of the NG Control Plane procedure and to the description of the ssb-Ncell procedure. These changes ensure the SDL diagrams and associated textual descriptions accurately reflect the technical behavior for these elements.
Explore further
Broader topics and technologies where SDL plays a role.
Defining Specifications
3GPP specifications that define or reference SDL, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.801 vj00 | 3GPP Specification Drafting Rules | Rel-19 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 29.078 vj00 | CAMEL Phase 4 CAP Specification | Rel-19 |
| TS 29.278 vj00 | CAMEL Application Part (CAP) for IMS Phase 4 | Rel-19 |
| TS 36.113 vj00 | EMC Requirements for E-UTRA Base Stations | Rel-19 |
| TS 36.761 vf00 | Extended-Band 12 Study Report | Rel-15 |
| TS 36.858 ve00 | LTE 2.6 GHz SDL Band Technical Report | Rel-14 |
| TS 36.895 vd00 | 700 SDL Band for LTE Carrier Aggregation | Rel-13 |
| TS 37.814 vc00 | L-band Supplemental Downlink for UTRA/E-UTRA | Rel-12 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.113 vj00 | NR Base Station EMC Specification | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.306 vj00 | NR UE Radio Access Capability Parameters | Rel-19 |
| TS 38.307 vj20 | NR UE Release Independent Requirements | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |