LCR(Least Cost Routing) Module

Juha Heinanen

Edited by

Juha Heinanen


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. db_url (string)
1.3.2. gw_table (string)
1.3.3. gw_name_column (string)
1.3.4. ip_addr_column (string)
1.3.5. port_column (string)
1.3.6. uri_scheme_column (string)
1.3.7. transport_column (string)
1.3.8. grp_id_column (string)
1.3.9. lcr_table (string)
1.3.10. strip_column (string)
1.3.11. prefix_column (string)
1.3.12. from_uri_column (string)
1.3.13. priority_column (string)
1.3.14. gw_uri_avp (string)
1.3.15. ruri_user_avp (string)
1.3.16. contact_avp (string)
1.3.17. fr_inv_timer_avp (string)
1.3.18. fr_inv_timer (integer)
1.3.19. fr_inv_timer_next (integer)
1.3.20. rpid_avp (string)
1.3.21. db_mode (integer)
1.4. Exported Functions
1.4.1. load_gws(), load_gws(group-id)
1.4.2. next_gw()
1.4.3. from_gw(), from_gw(group-id)
1.4.4. to_gw(), to_gw(group-id)
1.4.5. load_contacts()
1.4.6. next_contacts()
1.5. FIFO Commands
1.5.1. lcr_reload
1.5.2. lcr_dump
1.6. Known Limitations
1.7. TODO
2. Developer's Guide
3. Frequently Asked Questions
List of Examples
1-1. Setting db_url module parameter
1-2. Setting gw_table module parameter
1-3. Setting gw_name_column module parameter
1-4. Setting ip_addr_column module parameter
1-5. Setting port_column module parameter
1-6. Setting uri_scheme_column module parameter
1-7. Setting transport_column module parameter
1-8. Setting grp_id_column module parameter
1-9. Setting lcr_table module parameter
1-10. Setting strip_column module parameter
1-11. Setting prefix_column module parameter
1-12. Setting from_uri_column module parameter
1-13. Setting priority_column module parameter
1-14. Setting gw_uri_avp module parameter
1-15. Setting ruri_user_avp module parameter
1-16. Setting contact_avp module parameter
1-17. Setting fr_inv_timer_avp module parameter
1-18. Setting fr_inv_timer module parameter
1-19. Setting fr_inv_timer_next module parameter
1-20. Setting rpid_avp module parameter
1-21. Setting db_mode module parameter
1-22. load_gws usage
1-23. load_gws usage with group-id
1-24. next_gw usage from a route block
1-25. next_gw usage from a failure route block
1-26. from_gw usage
1-27. from_gw usage with group-id
1-28. to_gw usage
1-29. to_gw usage with group-id
1-30. load_contacts usage
1-31. next_contacts usage from route block
1-32. next_contacts usage from failure route block

Chapter 1. User's Guide

1.1. Overview

Least cost routing (LCR) module implements two related capabilities:

  • sequential forwarding of a request to one or more gateways (functions load_gws and next_gw)

  • sequential forwarding to contacts if they don't share the the same qvalue (functions load_contacts and next_contacts).

Gateway selection is based on caller's RPID URI (if available in caller's RPID AVP after authentication) or From URI and user part of Request-URI (telephone number). A gateway matches a request if user part of Request-URI and "From" URI match the prefix and From pattern of the gateway. Matching gateways are then ordered for forwarding purpose (1) according to longest user part match, (2) according to gateway's priority, and (3) randomly.

Each gateway belongs to a gateway group either alone or among other gateways. All gateways in a group share the same priority.

Gateway and routing information is kept in two tables: gw and lcr.

When a gateway is selected, the Request-URI user part is stripped by the number of digits specified in the strip parameter. Subsequently, the Request-URI is rewritten with information from gw table: URI scheme, prefix, IP address, port, and transport protocol. Valid URI scheme values are NULL = sip, 1 = sip and 2 = sips. Prefix is appended in front of Request-URI user part. Currently valid transport protocol values are NULL = none, 1 = udp, 2 = tcp, and 3 = tls.

Table lcr contains prefix of user part of Request-URI, From URI, gateway group id, and priority. From URI can contain special characters % and _ matching any number of any characters and any one character, respectively, if db_mod parameter is set to 0. If db_mod parameter is set to 1, then From URI is a regular expression.

In addition to gw and lcr tables there is third table gw_grp that is used to associate names with gateway group ids.


1.2. Dependencies

1.2.1. OpenSER modules

The following modules must be loaded before this module:

  • TM module

  • A database module like mysql, postgres or dbtext.


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. db_url (string)

URL of the database table to be used.

Default value is "mysql://openserro:openserro@localhost/openser".

Example 1-1. Setting db_url module parameter

...
modparam("lcr","db_url","mysql://muser:pwd@localhost/openser")
...

1.3.2. gw_table (string)

Name of the table holding the gateways definitions.

Default value is "gw".

Example 1-2. Setting gw_table module parameter

...
modparam("lcr","gw_table","gw")
...

1.3.3. gw_name_column (string)

Name of the column holding the gateway name.

Default value is "gw_name".

Example 1-3. Setting gw_name_column module parameter

...
modparam("lcr","gw_name_column","gw_name")
...

1.3.4. ip_addr_column (string)

Name of the column holding the IP address of the gateway.

Default value is "ip_addr".

Example 1-4. Setting ip_addr_column module parameter

...
modparam("lcr","ip_addr_column","ip_addr")
...

1.3.5. port_column (string)

Name of the column holding the port number of the gateway.

Default value is "port".

Example 1-5. Setting port_column module parameter

...
modparam("lcr","port_column","port")
...

1.3.6. uri_scheme_column (string)

Name of the column holding the uri scheme of the gateway.

Default value is "uri_scheme".

Example 1-6. Setting uri_scheme_column module parameter

...
modparam("lcr","uri_scheme_column","scheme")
...

1.3.7. transport_column (string)

Name of the column holding the transport type to be used for the gateway.

Default value is "transport".

Example 1-7. Setting transport_column module parameter

...
modparam("lcr","transport_column","transport")
...

1.3.8. grp_id_column (string)

Name of the column holding the group ID.

Default value is "grp_id".

Example 1-8. Setting grp_id_column module parameter

...
modparam("lcr","grp_id_column","grp_id")
...

1.3.9. lcr_table (string)

Name of the table holding the LCR rules.

Default value is "lcr".

Example 1-9. Setting lcr_table module parameter

...
modparam("lcr","lcr_table","lcr")
...

1.3.10. strip_column (string)

Name of the column holding the number of digits to strip from the RURI before applying the prefix.

Default value is "strip".

Example 1-10. Setting strip_column module parameter

...
modparam("lcr","strip_column","strip")
...

1.3.11. prefix_column (string)

Name of the column holding the RURI(destination) prefix.

Default value is "prefix".

Example 1-11. Setting prefix_column module parameter

...
modparam("lcr","prefix_column","prefix")
...

1.3.12. from_uri_column (string)

Name of the column holding the FROM (source) URI.

Default value is "from_uri".

Example 1-12. Setting from_uri_column module parameter

...
modparam("lcr","from_uri_column","from_uri")
...

1.3.13. priority_column (string)

Name of the column holding the priority of the rule.

Default value is "priority".

Example 1-13. Setting priority_column module parameter

...
modparam("lcr","priority_column","priority")
...

1.3.14. gw_uri_avp (string)

Overrides the name of the AVP containing URI scheme, host, port, and transport of a gateway. If the string name of the AVP contains only digits, the name of the AVP is integer value of the string.

Default value is "1400".

Example 1-14. Setting gw_uri_avp module parameter

...
modparam("lcr","gw_uri_avp","1400")
...

1.3.15. ruri_user_avp (string)

Overrides the name of the AVP containing user part of Request-URI after the first next_gw() call. If the string name of the AVP contains only digits, the name of the AVP is integer value of the string.

Default value is "1402".

Example 1-15. Setting ruri_user_avp module parameter

...
modparam("lcr","ruri_user_avp","500")
...

1.3.16. contact_avp (string)

Overrides the name of the AVP containing the contact. If the string name of the AVP contains only digits, the name of the AVP is integer value of the string.

Default value is "1401".

Example 1-16. Setting contact_avp module parameter

...
modparam("lcr","contact_avp","1401")

...

1.3.17. fr_inv_timer_avp (string)

Overrides the name of the AVP carrying the Final Response timeout for INVITEs.

Default value is "fr_inv_timer_avp".

Example 1-17. Setting fr_inv_timer_avp module parameter

...
modparam("lcr","fr_inv_timer_avp","fr_inv_timer_avp")
...

1.3.18. fr_inv_timer (integer)

Sets the value of the fist INVITE's Final Response timeout to be used during sequential forwarding:

Default value is 90.

Example 1-18. Setting fr_inv_timer module parameter

...
modparam("lcr","fr_inv_timer",90)
...

1.3.19. fr_inv_timer_next (integer)

Sets the value of the next INVITE's Final Response timeouts to be used during sequential forwarding:

Function next_contacts() sets tm fr_inv_timer to fr_inv_timer_next value if, after next contacts, there are still lower qvalue contacts available, and to fr_inv_timer value if next contacts are the last ones left.

Default value is 30.

Example 1-19. Setting fr_inv_timer_next module parameter

...
modparam("lcr","fr_inv_timer_next",30)
...

1.3.20. rpid_avp (string)

Sets the string name of the AVP containing the RPID.

Default value is "rpid".

Example 1-20. Setting rpid_avp module parameter

...
modparam("lcr","rpid_avp","rpid")
...

1.3.21. db_mode (integer)

Sets the database mode of operating:

  • 0 : no-caching - a db lookup is performed during each load_gws()

  • 1 : regexp are used for from_uri; no db lookup is performed during load_gws(), the DB content is cached into memory;

Default value is "1".

Example 1-21. Setting db_mode module parameter

...
modparam("lcr","db_mode",0)
...

1.4. Exported Functions

1.4.1. load_gws(), load_gws(group-id)

Loads URI schemes, addresses, ports, and transports of gateways that match user part of Request-URI to gw_uri_avp AVPs (see Overview section). If an optional group-id is specified, only gateways belonging to this group are loaded. Returns 1 or -1 depending on success.

This function can be used from REQUEST_ROUTE.

Example 1-22. load_gws usage

...
if (!load_gws()) {
	sl_send_reply("500", "Server Internal Error - Cannot load gateways");
	exit;
};
...

Example 1-23. load_gws usage with group-id

...
if (!load_gws("1")) {
	sl_send_reply("500", "Server Internal Error - Cannot load gateways from group 1");
	exit;
};
...

1.4.2. next_gw()

If called from a route block, replaces URI scheme, host, port, and transport of Request-URI by the values stored in first gw_uri_avp AVP and destroys that AVP. Saves user part of Request-URI into ruri_user_avp AVP for use in subsequent next_gw() calls.

If called from a failure route block, appends a new branch to request, where URI scheme, host, port, and transport of Request-URI is replaced by the values stored in the first gw_uri_avp AVP and destroys that AVP. Request-URI user is taken from ruri_user_avp AVP.

Returns 1 on success and -1 if there were no gateways left or if an error occurred (see syslog).

Must be preceded by successful load_gws() call.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1-24. next_gw usage from a route block

...
if (!next_gw()) {
	sl_send_reply("503", "Service not available - No gateways");
	exit;
};
...

Example 1-25. next_gw usage from a failure route block

...
if (!next_gw()) {
	t_reply("503", "Service not available - No more gateways");
	exit;
};
...

1.4.3. from_gw(), from_gw(group-id)

Checks if request came from IP address of a gateway. If an optional group-id is given, only gateways belonging to this group are checked.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, ONREPLY_ROUTE.

Example 1-26. from_gw usage

...
if (from_gw()) {
	...
	exit;
};
...

Example 1-27. from_gw usage with group-id

...
if (from_gw("1")) {
	...
	exit;
};
...

1.4.4. to_gw(), to_gw(group-id)

Checks if in-dialog request goes to a gateway. If an optional group-id is given, only gateways belonging to this group are checked.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1-28. to_gw usage

...
if (to_gw()) {
	...
	exit;
};
...

Example 1-29. to_gw usage with group-id

...
if (to_gw("1")) {
	...
	exit;
};
...

1.4.5. load_contacts()

Loads contacts in destination set in increasing qvalue order as values of lcr_contact AVP. If all contacts in the destination set have the same qvalue, load_contacts() does not do anything thus minimizing performance impact of sequential forking capability when it is not needed. Returns 1 if loading of contacts succeeded or there was nothing to do. Returns -1 on error (see syslog).

This function can be used from REQUEST_ROUTE.

Example 1-30. load_contacts usage

...
if (!load_contacts()) {
	sl_send_reply("500", "Server Internal Error - Cannot load contacts");
	exit;
};
...

1.4.6. next_contacts()

If called from a route block, replaces Request-URI with the first lcr_contact AVP value, adds the remaining lcr_contact AVP values with the same qvalue as branches, and destroys those AVPs. It does nothing if there are no lcr_contact AVPs. Returns 1 if there were no errors and -1 if an error occurred (see syslog).

If called from a failure route block, adds the first lcr_contact AVP value and all following lcr_contact AVP values with the same qvalue as new branches to request and destroys those AVPs. Returns 1 if new branches were successfully added and -1 on error (see syslog) or if there were no more lcr_contact AVPs.

Must be preceded by successful load_contacts() call.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1-31. next_contacts usage from route block

...
if (!next_contacts()) {
	sl_send_reply("500", "Server Internal Error");
	exit;
} else {
	t_relay();
};
...

Example 1-32. next_contacts usage from failure route block

if (next_contacts()) {
	t_relay();
};

1.5. FIFO Commands

1.5.1. lcr_reload

Causes lcr module to re-read the contents of gateway table into memory.


1.5.2. lcr_dump

Causes lcr module to dump the contents of its in-memory gateway table.


1.6. Known Limitations

There is an unlikely race condition on lcr reload. If a process uses in memory gw table, which is reloaded at the same time twice through FIFO, the second reload will delete the original table still in use by the process.


1.7. TODO

Function load_gws() currently makes an SQL query for the matching gateways. In order to avoid the query, also lcr table should be read into memory and the corresponding query should be rewritten in C.


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:

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.