sl Module

Bogdan Iancu

Edited by

Bogdan Iancu

Revision History
Revision $Revision: 4594 $$Date: 2008-08-06 12:08:33 +0200 (Wed, 06 Aug 2008) $

Table of Contents

1. Admin Guide
1.1. Overview
1.2. Dependencies
1.2.1. Kamailio Modules
1.2.2. External Libraries or Applications
1.3. Exported Parameters
1.3.1. enable_stats (integer)
1.3.2. bind_tm (integer)
1.4. Exported Functions
1.4.1. sl_send_reply(code, reason)
1.4.2. send_reply(code, reason)
1.4.3. 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

List of Examples

1.1. enable_stats example
1.2. bind_tm example
1.3. sl_send_reply usage
1.4. send_reply usage
1.5. sl_reply_error usage

Chapter 1. Admin Guide

1.1. Overview

The SL module allows Kamailio 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, Kamailio 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 Kamailio want to reply to it. Than, it will keep the current to-tag, which will be mirrored in ACK. Kamailio 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. Kamailio Modules

The following modules must be loaded before this module:

  • TM - transaction module, if you want to use the transactional send_reply functionality.

1.2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio 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)

1.3.2. bind_tm (integer)

If the module should use the transaction module for sending replies. Default is 1(enabled).

Example 1.2. bind_tm example

modparam("sl", "bind_tm", 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 1.3. sl_send_reply usage

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

1.4.2.  send_reply(code, reason)

For the current request, a reply is sent back having the given code and text reason. The reply is sent stateful or stateless, depending of the Transaction module: if the transaction for current request has created, then the reply is sent stateful, otherwise stateless.

Meaning of the parameters is as follows:

  • code - Return code.

  • reason - Reason phrase.


Example 1.4. send_reply usage

send_reply("404", "Not found");
send_reply("403", "Invalid user - $fU");

1.4.3.  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 1.5. sl_reply_error usage


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.