There are a number of documents available for download detailing the reverse engineered design of the Asterisk® ‘C’ language open source telephony software platform from Digium ®, Inc.

Overall, the set of documents provides a good insight into the structure of the Asterisk software. The documents available are as follows:

• SSDD – contains: overall inter-subsystem data flows and procedure call diagrams; metrics analysis outputs; subsystem interfacing details; and details of the function calls shown in the SSDD Appendicies.
• SSDD Appendices 1 to 7 – contain sequence diagrams of the function call interactions between the subsystems. The functions in each appendix are detailed in a table in the SSDD.
• SDDs - covering the main subsystems of interest in the Asterisk code.

Notes:

1. SDDs for the subsystems: agi; stman; include; stdtime; and tinycap are not available for download due to their relatively trivial content.
2. It will not be possible to read the text details on many diagrams when printed due to the complex nature of some of the diagrams. If the diagrams are really complex the details may even be difficult to read zoomed into on a pdf file viewer.
3. The most interesting document from “software structure insight” viewpoint is the “channels” SDD.

Total number of pages in the complete set of Asterisk documents available for download is approximately 4,000, although some pages may only contain a heading.