sl Module

Bogdan Iancu

voice-system.ro

Edited by

Bogdan Iancu

Copyright © 2003 FhG FOKUS

Table of Contents
1. User's Guide
1.1. Overview
1.2. Dependencies
1.2.1. OpenSER Modules
1.2.2. External Libraries or Applications
1.3. Exported Parameters
1.3.1. enable_stats (integer)
1.4. Exported Functions
1.4.1. sl_send_reply(code, reason)
1.4.2. sl_reply_error()
1.5. Exported Statistics
1.5.1. 1xx_replies
1.5.2. 2xx_replies
1.5.3. 3xx_replies
1.5.4. 4xx_replies
1.5.5. 5xx_replies
1.5.6. 6xx_replies
1.5.7. sent_replies
1.5.8. sent_err_replies
1.5.9. received_ACKs
2. Developer's Guide
3. Frequently Asked Questions
List of Examples
1-1. enable_stats example
1-2. sl_send_reply usage
1-3. sl_reply_error usage

Chapter 1. User's Guide

1.1. Overview

The SL module allows OpenSER 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, OpenSER 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 OpenSER want to reply to it. Than, it will keep the current to-tag, which will be mirrored in ACK. OpenSER will not see its signature and forward the ACK downstream. Caused harm is not bad--just a useless ACK is forwarded.

1.2. Dependencies

1.2.1. OpenSER Modules

The following modules must be loaded before this module:

  • No dependencies on other OpenSER modules.

1.2.2. External Libraries or Applications

The following libraries or applications must be installed before running OpenSER with this module loaded:

  • None.

1.3. Exported Parameters

1.3.1. 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).

Example 1-1. enable_stats example

modparam("sl", "enable_stats", 0)

1.4. Exported Functions

1.4.1. 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 - Return code.

  • reason - Reason phrase.

This function can be used from REQUEST_ROUTE, ERROR_ROUTE.

Example 1-2. sl_send_reply usage

...
sl_send_reply("404", "Not found");
...
sl_send_reply("$err.rcode", "$err.rreason");
...

1.4.2. 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.

Example 1-3. sl_reply_error usage

...
sl_reply_error();
...

1.5. Exported Statistics

1.5.1. 1xx_replies

The number of 1xx_replies.

1.5.2. 2xx_replies

The number of 2xx_replies.

1.5.3. 3xx_replies

The number of 3xx_replies.

1.5.4. 4xx_replies

The number of 4xx_replies.

1.5.5. 5xx_replies

The number of 5xx_replies.

1.5.6. 6xx_replies

The number of 6xx_replies.

1.5.7. sent_replies

The number of sent_replies.

1.5.8. sent_err_replies

The number of sent_err_replies.

1.5.9. received_ACKs

The number of received_ACKs.

Chapter 2. Developer's Guide

The module does not provide any API to use in other OpenSER modules.

Chapter 3. Frequently Asked Questions

3.1. Where can I find more about OpenSER?
3.2. Where can I post a question about this module?
3.3. How can I report a bug?

3.1. Where can I find more about OpenSER?

Take a look at http://www.openser-project.org/.

3.2. Where can I post a question about this module?

First at all check if your question was already answered on one of our mailing lists:

E-mails regarding any stable OpenSER release should be sent to and e-mails regarding development versions should be sent to .

If you want to keep the mail private, send it to .

3.3. How can I report a bug?

Please follow the guidelines provided at: http://sourceforge.net/tracker/?group_id=139143.