SL module
Admin Guide
Section titled “Admin Guide”Overview
Section titled “Overview”The SL module allows OpenSIPS to act as a stateless UA server and generate replies to SIP requests without keeping state. That is beneficial in many scenarios, in which you wish not to burden server’s memory and scale well.
The SL module needs to filter ACKs sent after a local stateless reply to an INVITE was generated. To recognize such ACKs, OpenSIPS adds a special “signature” in to-tags. This signature is sought for in incoming ACKs, and if included, the ACKs are absorbed.
To speed up the filtering process, the module uses a timeout mechanism. When a reply is sent, a timer is set. As time as the timeout didn’t hit, the incoming ACK requests will be checked using TO tag value. Once the timer expires, all the ACK are let through - a long time passed till it sent a reply, so it does not expect any ACK that have to be blocked.
The ACK filtering may fail in some rare cases. If you think these matter to you, better use stateful processing (tm module) for INVITE processing. Particularly, the problem happens when a UA sends an INVITE which already has a to-tag in it (e.g., a re-INVITE) and OpenSIPS want to reply to it. Than, it will keep the current to-tag, which will be mirrored in ACK. OpenSIPS will not see its signature and forward the ACK downstream. Caused harm is not bad—just a useless ACK is forwarded.
Dependencies
Section titled “Dependencies”OpenSIPS Modules
Section titled “OpenSIPS Modules”The following modules must be loaded before this module:
- No dependencies on other OpenSIPS modules.
External Libraries or Applications
Section titled “External Libraries or Applications”The following libraries or applications must be installed before running OpenSIPS with this module loaded:
- None.
Exported Parameters
Section titled “Exported Parameters”enable_stats (integer)
Section titled “enable_stats (integer)”If the module should generate and export statistics to the core manager. A zero value means disabled.
SL module provides statistics about how many replies were sent ( splitted per code classes) and how many local ACKs were filtered out.
Default value is 1 (enabled).
modparam("sl", "enable_stats", 0)Exported Functions
Section titled “Exported Functions”sl_send_reply(code, reason)
Section titled “sl_send_reply(code, reason)”For the current request, a reply is sent back having the given code and text reason. The reply is sent stateless, totally independent of the Transaction module and with no retransmission for the INVITE’s replies. ‘code’ and ‘reason’ can contain pseudo-variables that are replaced at runtime.
Meaning of the parameters is as follows:
- code (int) - Return code.
- reason (string) - Reason phrase.
This function can be used from REQUEST_ROUTE, ERROR_ROUTE.
...sl_send_reply(404, "Not found");...sl_send_reply($err.rcode, $err.rreason);...sl_reply_error()
Section titled “sl_reply_error()”Sends back an error reply describing the nature of the last internal error. Usually this function should be used after a script function that returned an error code.
This function can be used from REQUEST_ROUTE.
...sl_reply_error();...Exported Statistics
Section titled “Exported Statistics”1xx_replies
Section titled “1xx_replies”The number of 1xx_replies.
2xx_replies
Section titled “2xx_replies”The number of 2xx_replies.
3xx_replies
Section titled “3xx_replies”The number of 3xx_replies.
4xx_replies
Section titled “4xx_replies”The number of 4xx_replies.
5xx_replies
Section titled “5xx_replies”The number of 5xx_replies.
6xx_replies
Section titled “6xx_replies”The number of 6xx_replies.
sent_replies
Section titled “sent_replies”The number of sent_replies.
sent_err_replies
Section titled “sent_err_replies”The number of sent_err_replies.
received_ACKs
Section titled “received_ACKs”The number of received_ACKs.
Contributors
Section titled “Contributors”By Commit Statistics
Section titled “By Commit Statistics”Top contributors by DevScore(1), authored commits(2) and lines added/removed(3)
| # | Name | DevScore | Commits | Lines++ | Lines— |
|---|---|---|---|---|---|
| 1. | Bogdan-Andrei Iancu (@bogdan-iancu) | 77 | 54 | 973 | 808 |
| 2. | Jiri Kuthan (@jiriatipteldotorg) | 42 | 32 | 674 | 241 |
| 3. | Daniel-Constantin Mierla (@miconda) | 23 | 16 | 307 | 184 |
| 4. | Andrei Pelinescu-Onciul | 16 | 14 | 52 | 52 |
| 5. | Liviu Chircu (@liviuchircu) | 13 | 10 | 46 | 80 |
| 6. | Jan Janak (@janakj) | 13 | 8 | 364 | 30 |
| 7. | Razvan Crainea (@razvancrainea) | 8 | 6 | 14 | 13 |
| 8. | Henning Westerholt (@henningw) | 7 | 5 | 12 | 12 |
| 9. | Stefan Darius (@dariusstefan) | 7 | 4 | 226 | 31 |
| 10. | Vlad Patrascu (@rvlad-patrascu) | 7 | 4 | 31 | 84 |
All remaining contributors: Maksym Sobolyev (@sobomax), Elena-Ramona Modroiu, Jeffrey Magder, Andreas Heise, Anca Vamanu, Konstantin Bokarius, Peter Lemenkov (@lemenkov), Ionut Ionita (@ionutrazvanionita), Edson Gellert Schubert.
(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)
(2) including any documentation-related commits, excluding merge commits
(3) ignoring whitespace edits, renamed files and auto-generated files
By Commit Activity
Section titled “By Commit Activity”| # | Name | Commit Activity |
|---|---|---|
| 1. | Stefan Darius (@dariusstefan) | Jun 2026 - Jul 2026 |
| 2. | Razvan Crainea (@razvancrainea) | Feb 2012 - Jun 2026 |
| 3. | Liviu Chircu (@liviuchircu) | Mar 2014 - May 2024 |
| 4. | Maksym Sobolyev (@sobomax) | Oct 2020 - Feb 2023 |
| 5. | Bogdan-Andrei Iancu (@bogdan-iancu) | Feb 2002 - Nov 2019 |
| 6. | Vlad Patrascu (@rvlad-patrascu) | May 2017 - Apr 2019 |
| 7. | Peter Lemenkov (@lemenkov) | Jun 2018 - Jun 2018 |
| 8. | Ionut Ionita (@ionutrazvanionita) | Nov 2014 - Nov 2014 |
| 9. | Anca Vamanu | Nov 2010 - Nov 2010 |
| 10. | Henning Westerholt (@henningw) | Aug 2007 - Jun 2008 |
All remaining contributors: Daniel-Constantin Mierla (@miconda), Konstantin Bokarius, Edson Gellert Schubert, Andreas Heise, Elena-Ramona Modroiu, Jeffrey Magder, Jiri Kuthan (@jiriatipteldotorg), Jan Janak (@janakj), Andrei Pelinescu-Onciul.
(1) including any documentation-related commits, excluding merge commits
Documentation
Section titled “Documentation”Contributors
Section titled “Contributors”Last edited by: Razvan Crainea (@razvancrainea), Vlad Patrascu (@rvlad-patrascu), Peter Lemenkov (@lemenkov), Liviu Chircu (@liviuchircu), Bogdan-Andrei Iancu (@bogdan-iancu), Henning Westerholt (@henningw), Daniel-Constantin Mierla (@miconda), Konstantin Bokarius, Edson Gellert Schubert, Elena-Ramona Modroiu, Jan Janak (@janakj).
License
Section titled “License”All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0