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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()
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.
Meaning of the parameters is as follows:
* code - Return code.
* reason - Reason phrase.
This function can be used from REQUEST_ROUTE.
Example 1-2. sl_send_reply usage
...
sl_send_reply("404", "Not found");
...
_________________________________________________________
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();
...
_________________________________________________________
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://openser.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:
* User Mailing List -
http://openser.org/cgi-bin/mailman/listinfo/users
* Developer Mailing List -
http://openser.org/cgi-bin/mailman/listinfo/devel
E-mails regarding any stable OpenSER release should be sent to
<users@openser.org> and e-mails regarding development versions
should be sent to <devel@openser.org>.
If you want to keep the mail private, send it to
<team@openser.org>.
3.3. How can I report a bug?
Please follow the guidelines provided at:
http://sourceforge.net/tracker/?group_id=139143.
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