Standards families
MSC / HMSC message sequence chart
ITU message sequence charts: instances as vertical axes, messages as arrows between them, with an HMSC referencing sub-charts.
msc.basic@1New DDN source
Why use it?
Protocol reviews need the exact interleaving on paper; MSC is the telecom-standard way to draw it.
When it helps
Protocol specification, inter-system message contracts, telecom and embedded documentation.
How to read it
- Each vertical line is an instance axis; time runs downward.
- Arrows between axes are messages; the variant shows a high-level MSC referencing the details.
What you need
- The instances
- The ordered messages
- Conditions and references
Things to check
- Do not cross arrows casually — crossing is a claim about overtaking.
- A referenced sub-chart must exist; a dangling ref fails review.
Scope of this diagram
Declared charts with MSC structural validation; no conformance test against an implementation is run.
Work with the converted example
- Open the viewer and select
chart. Inspect the rendered view and its source. - Open the designer. Keep the selected profile and inspect its legal palette and property controls.
- Change one displayed title or an appropriate data value. Apply the edit and check the resulting diagram.
- Run the verifier and review its diagnostics before moving complete content into review.
- Download your edited DDN source to retain the change.
The example uses the indentation-based ddn-next-1 dialect. The language guide explains reusable definitions, dotted data rows and explicit property blocks.