DISPATCHER Module

Daniel-Constantin Mierla

voice-system.ro

Edited by

Daniel-Constantin Mierla

Copyright © 2004 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. list_file (string)
1.3.2. force_dst (int)
1.4. Exported Functions
1.4.1. ds_select_dst(set, alg)
1.5. Installation & Running
1.5.1. Destination List File
1.5.2. OpenSER config file
2. Developer's Guide
3. Frequently Asked Questions
List of Examples
1-1. Set the "list_file" parameter
1-2. Set the "force_dst" parameter
1-3. ds_select_dst usage
1-4. dispatcher list file
1-5. OpenSER config script - sample dispatcher usage

Chapter 1. User's Guide

1.1. Overview

This modules implements a dispatcher for destination addresses. It computes hashes over parts of the request and selects an address from a destination set. The selected address is used then as outbound proxy.

The module can be used as a stateless load balancer, having no guarantee of fair distribution.

1.2. Dependencies

1.2.1. OpenSER modules

The following modules must be loaded before this module:

  • none.

1.2.2. External libraries or applications

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

  • none.

1.3. Exported Parameters

1.3.1. list_file (string)

Path to the file with destination sets.

Default value is "/etc/ser/dispatcher.list" or "/usr/local/etc/ser/dispatcher.list".

Example 1-1. Set the "list_file" parameter

...
modparam("dispatcher", "list_file", "/var/run/ser/dispatcher.list")
...

1.3.2. force_dst (int)

If set to 1, force overwriting of destination address when that is already set.

Default value is "0".

Example 1-2. Set the "force_dst" parameter

...
modparam("dispatcher", "force_dst", 1)
...

1.4. Exported Functions

1.4.1. ds_select_dst(set, alg)

The method selects a destination from addresses set.

Meaning of the parameters is as follows:

  • set - the id of the set from where to pick up destination address. It is the first column in destination list file.

  • alg - the algorithm used to select the destination address.

    • "0" - hash over callid

    • "1" - hash over from uri.

    • "X" - if the algorithm is not implemented, the first entry in set is chosen.

Example 1-3. ds_select_dst usage

...
ds_select_dst("1", "0");
...

1.5. Installation & Running

1.5.1. Destination List File

Each destination point must be on one line. First token is the set id and next is destination address. The set id must be an integer value. Destination address must be a valid SIP URI. Empty lines or lines starting with "#" are ignored.

Example 1-4. dispatcher list file

...
# $Id: dispatcher.list,v 1.1.1.1 2005/03/22 17:23:49 bogdan Exp $
# dispatcher destination sets
#

# proxies
2 sip:127.0.0.1:5080
2 sip:127.0.0.1:5082

# gateways
1 sip:127.0.0.1:7070
1 sip:127.0.0.1:7072
1 sip:127.0.0.1:7074
...

1.5.2. OpenSER config file

Next picture displays a sample usage of dispatcher.

Example 1-5. OpenSER config script - sample dispatcher usage

...
# $Id: dispatcher.cfg,v 1.2 2005/06/09 09:32:02 daniel Exp $
# sample config file for dispatcher module
#

debug=9          # debug level (cmd line: -dddddddddd)
fork=no
log_stderror=yes  # (cmd line: -E)

children=2
check_via=no      # (cmd. line: -v)
dns=off           # (cmd. line: -r)
rev_dns=off       # (cmd. line: -R)
port=5060

# for more info: sip_router -h

# ------------------ module loading ----------------------------------

loadmodule "modules/maxfwd/maxfwd.so"
loadmodule "modules/sl/sl.so"
loadmodule "modules/dispatcher/dispatcher.so"

# ----------------- setting module-specific parameters ---------------
# -- dispatcher params --

modparam("dispatcher", "list_file", "../etc/dispatcher.list")
# modparam("dispatcher", "force_dst", 1)

route{
	if ( !mf_process_maxfwd_header("10") )
	{
	 	sl_send_reply("483","To Many Hops");
	 	drop();
	};
	
	ds_select_dst("2", "0");
	
	forward();
	# t_relay();
}

...

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. Does dispatcher provide a fair distribution?
3.2. Is dispatcher dialog stateful?
3.3. Where can I find more about OpenSER?
3.4. Where can I post a question about this module?
3.5. How can I report a bug?

3.1. Does dispatcher provide a fair distribution?

There is no guarantee of that. You should do some measurements to decide what distribution algorithm fits better in your environment.

3.2. Is dispatcher dialog stateful?

No. Dispatcher is stateless, although some distribution algorithms are designed to select same destination for subsequent requests of the same dialog (e.g., hashing the call-id).

3.3. Where can I find more about OpenSER?

Take a look at http://openser.org/.

3.4. 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 version should be sent to and e-mail regarding development versions or CVS snapshots should be send to .

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

3.5. How can I report a bug?

Please follow the guidelines provided at: http://openser.org/bugs