Message Sequence Charts (MSC)

Introduction

Message Sequence Charts (MSC) is a standardized notation used for the description of typical or exceptional message exchanges between entities. MSC diagrams provide a clear description of system communication in the form of message flows.

Originally standardized as a 'sister language' to SDL, it is developed and maintained by the ITU-T as ITU Recommendation Z.120.

MSCs and SDL descriptions should be regarded as different but complementary views of a system. SDL provides behaviour descriptions of individual communicating entities, but there is no direct description of communication between several entities. By contrast, MSCs provide a clear description of system traces in the form of message flows. Despite their simplicity, MSCs are a powerful notation, with built-in mechanisms to portray timers, loops, optional, alternative and exceptional system behaviour, as is necessary in any protocol description.

Our Role & Activities

MSCs have long been used in standardization and in industry for visualization of selected message traces within communication systems. Its simplicity and intuitive understanding have made the notation popular.

A set of MSC diagrams normally covers partial system behaviour. Each MSC diagram represents one scenario of either a typical or an exceptional exchange of messages between system parts. The language is particularly useful when distributed processing must be managed at several interfaces. For instance, it can be used effectively in describing basic scenarios of calls and the establishment of connections. MSCs may be used for requirement specification, displaying simulation and validation results, test purpose description and documentation of real-time systems.

Use of MSC tools

MSC diagrams can be developed using any computer application capable of handling simple graphics. However, the use of specialized MSC tools improves all aspects of their development and use. It enforces the use of standardized MSC language elements, while permitting rapid development and maintenance of diagrams. Including MSC diagrams into the text of the standard is very straightforward.

High Level Message Sequence Charts (HMSC)

The Z.120 standard also defines High Level Message Sequence Charts (HMSCs). HMSC diagrams are used to specify more complex patterns of message flows by showing sequences or alternatives of atomic MSC scenarios, shown only as MSC references. HMSC diagrams specify what communication activities are needed while the referenced MSC diagrams show how the communication is done in terms of message sequences. HMSC diagrams can conveniently express options and alternatives in using parts of a complex procedure. Expressing the same thing only in MSC diagrams is possible but less straightforward.

ETSI Guidance on the use of MSC

A guideline for the use of MSC in communication standardization is available within the guidelines for SDL, EG 202 106, published by ETSI technical committee Methods for Testing and Specification (MTS).

Standards

The following is a list of the latest published ETSI standards on MSC.

A full list of related standards in the public domain is accessible via the ETSI standards search. Via this interface you can also subscribe for alerts on updates of ETSI standards. 

For work in progress see the ETSI Work Programme on the Portal.

Standard No. Standard title.
ES 201 873-3 Methods for Testing and Specification (MTS); The Testing and Test Control Notation version 3; Part 3: TTCN-3 Graphical presentation Format (GFT)
ES 201 873-3 Methods for Testing and Specification (MTS); The Testing and Test Control Notation version 3; Part 3: TTCN-3 Graphical presentation Format (GFT)
EG 202 106 Methods for Testing and Specification (MTS); Guidelines for the use of formal SDL as a descriptive tool
ES 201 873-3 Methods for Testing and Specification (MTS); The Testing and Test Control Notation version 3; Part 3: TTCN-3 Graphical presentation Format (GFT)
ES 201 873-3 Methods for Testing and Specification (MTS); The Testing and Test Control Notation version 3; Part 3: TTCN-3 Graphical presentation Format (GFT)
TR 101 873-3 Methods for Testing and Specification (MTS); The Testing and Test Control Notation version 3; Part 3: TTCN-3 Graphical presentation Format (GFT)
TR 101 873-3 Methods for Testing and Specification (MTS); The Tree and Tabular Combined Notation version 3; Part 3: TTCN-3 Graphical Presentation Format (GFT)
EG 201 872 Methods for Testing and Specification (MTS); Methodological approach to the use of object-orientation in the standards making process
TR 101 873-3 Methods for Testing and Specification (MTS); The Tree and Tabular Combined Notation version 3 Part 3: TTCN-3 MSC Presentation Format
TR 102 105 Methods for Testing and Specification (MTS); Methodological approach to the use of object-orientation within the standards making process; Initial study
EG 201 015 Methods for Testing and Specification (MTS); Specification of protocols and services; Validation methodology for standards using Specification and Description Language (SDL); Handbook
EG 201 015 Methods for Testing and Specification (MTS); Specification of protocols and services; Validation methodology for standards using SDL; Handbook
TCRTR 050 Methods for Testing and Specification (MTS); Specification of protocols and services; Handbook for SDL, ASN.1 and MSC development [ETR 298 (1996)]
ETR 298 Methods for Testing and Specification (MTS); Specification of protocols and services; Handbook for SDL, ASN.1 and MSC development