LCR (Least Cost Routing) Module

Least cost routing (LCR) module implements capability to serially forward a request to one or more gateways so that the order in which the gateways is tried is based on admin defined "least cost".

For the purpose of facilitating least cost routing of requests, each gateway belongs to a gateway group and each gateway group is associated with one or more <prefix, from pattern, priority> tuples. A gateway matches a request if user part of Request URI matches a prefix and caller's URI matches a from pattern in a tuple that belongs to the group of the gateway.

When function load_gws() is called, matching gateways are ordered for forwarding purpose (1) according to longest user part match, (2) according to tuple's priority, and (3) gateway's randomized weight within its group. Prefix is a string of characters or NULL. From pattern is a regular expression (see 'man pcresyntax' for syntax), an empty string, or NULL. Empty or NULL from pattern or prefix matches anything. Smaller priority value means higher priority (highest priority value being 0). Weight is an integer value from 1 to 254.

Function next_gw() can then be used to select one gateway at a time for forwarding. Upon each call, user part of original Request URI is first stripped by the number of characters as specified by the gateway's strip count and then prefixed by gateway's tag. Upon first call, if gateway's hostname is NULL, Request URI is rewritten based on gateway's URI scheme, IP address, port, and transport protocol. If hostname is not NULL, Request-URI is rewritten based on gateway's URI scheme and hostname, and destination URI is set based on gateway's URI scheme, IP address, port, and transport protocol. Upon subsequent calls, the same is done, but instead of rewriting Request URI, a new branch is added.

Valid URI scheme values are NULL = sip, 1 = sip and 2 = sips. Currently valid transport protocol values are NULL = none, 1 = udp, 2 = tcp, 3 = tls, and 4 = sctp.

As a side effect of gateway selection, gateway's flags (that may contain information about capabilities of the gateway) are stored into an AVP.

1.2. Dependencies

1.2.1. Kamailio 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 Kamailio 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","dbdriver://username:password@dbhost/dbname")
...

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. `grp_id_column` (string)

Name of the column holding the group ID of gateway both in gw and lcr tables.

Default value is “grp_id”.

Example 1.4. Setting grp_id_column module parameter

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

1.3.5. `ip_addr_column` (string)

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

Default value is “ip_addr”.

Example 1.5. Setting ip_addr_column module parameter

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

1.3.6. `hostname_column` (string)

Name of the column holding gateway's hostname that is used in Request-URI, when request is sent to the gateway. Note that request is not forwarded based on hostname, but based on gateway's IP address in destination uri.

Default value is “hostname”.

Example 1.6. Setting hostname_column module parameter

...
modparam("lcr", "hostname_column","host")
...

1.3.7. `port_column` (string)

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

Default value is “port”.

Example 1.7. Setting port_column module parameter

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

1.3.8. `uri_scheme_column` (string)

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

Default value is “uri_scheme”.

Example 1.8. Setting uri_scheme_column module parameter

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

1.3.9. `transport_column` (string)

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

Default value is “transport”.

Example 1.9. Setting transport_column module parameter

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

1.3.10. `strip_column` (string)

Name of the column holding the number of characters to be stripped from the front of Request URI user part before inserting tag.

Default value is “strip”.

Example 1.10. Setting strip_column module parameter

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

1.3.11. `tag_column` (string)

Name of the column holding gateway specific tag string.

Default value is “tag”.

Example 1.11. Setting tag_column module parameter

...
modparam("lcr","tag_column","gw_tag")
...

1.3.12. `weight_column` (string)

Name of the column holding gateway's weight within its group.

Default value is “weight”.

Example 1.12. Setting weight_column module parameter

...
modparam("lcr","weight_column","gw_weight")
...

1.3.13. `flags_column` (string)

Name of the column holding gateway specific flag values.

Default value is “flags”.

Example 1.13. Setting flags_column module parameter

...
modparam("lcr","flags_column","gw_flags")
...

1.3.14. `lcr_table` (string)

Name of the table holding the LCR rules.

Default value is “lcr”.

Example 1.14. Setting lcr_table module parameter

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

1.3.15. `prefix_column` (string)

Name of the column holding prefix of Request URI user part.

Default value is “prefix”.

Example 1.15. Setting prefix_column module parameter

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

1.3.16. `from_uri_column` (string)

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

Default value is “from_uri”.

Example 1.16. Setting from_uri_column module parameter

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

1.3.17. `priority_column` (string)

Name of the column holding the priority of the rule.

Default value is “priority”.

Example 1.17. Setting priority_column module parameter

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

1.3.18. `gw_uri_avp` (AVP string)

Internal AVP that load_gws function uses to store information of matching gateways.

There is NO default value, thus this variable must be defined in kamailio.cfg.

Example 1.18. Setting gw_uri_avp module parameter

...
modparam("lcr", "gw_uri_avp", "$avp(i:709)")
...

1.3.19. `rpid_avp` (AVP string)

An AVP that contains caller's RPID (if any).

There is NO default value, thus this variable must be defined in kamailio.cfg.

Example 1.19. Setting rpid_avp module parameter

...
modparam("^auth$|lcr", "rpid_avp", "$avp(i:302)")
...

1.3.20. `ruri_user_avp` (AVP string)

Internal AVP that next_gw function uses to store Request-URI user for subsequent next_gw calls.

There is NO default value, thus this variable must be defined in kamailio.cfg.

Example 1.20. Setting ruri_user_avp module parameter

...
modparam("lcr", "ruri_user_avp", "$avp(i:500)")
...

1.3.21. `flags_avp` (AVP string)

An AVP where successful next_gw and from_gw functions store gateway's flags.

There is NO default value, thus this variable must be defined in kamailio.cfg.

Example 1.21. Setting flags_avp module parameter

...
modparam("lcr", "flags_avp", "$avp(i:712)")
...

1.3.22. `lcr_hash_size` (integer)

Defines the size of hash table used to store <prefix, from_pattern, priority> tuples. Hashing is done based on prefix. Larger value means less collisions with other prefixes. Hash size value should be a power of 2.

Default value is 128.

Example 1.22. Setting lcr_hash_size module parameter

...
modparam("lcr", "lcr_hash_size", 1024)
...

1.3.23. `fetch_rows` (integer)

The number of the rows to be fetched at once from database when loading data from lcr table. This value can be used to tune the load time at startup. For 1MB of private memory (default) it should be below 3750. In order for this parameter to have effect, database driver must support fetch_result() capability.

Default value is “2000”.

Example 1.23. Set fetch_rows parameter

...
modparam("lcr", "fetch_rows", 3000)
...

1.4. Exported Functions

1.4.1. `load_gws([pvar])`

Loads URI schemes, IP addresses, hostnames, ports, and transports of matching gateways to gw_uri_avp (see Overview section). If optional pseudo variable argument is included, caller's URI is taken from it. If pseudo variable argument is not included, caller's URI is taken from rpid_avp or, if rpid_avp value is empty, from From URI. Returns 1 or -1 depending on success.

Execution time of load_gws() function is O(N) * O(M), where N is number of different prefix lengths and M is number of collisions for matching prefix(es) in lcr hash table.

This function can be used from REQUEST_ROUTE.

Example 1.24. load_gws usage

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

1.4.2. `load_gws_from_grp(group-id)`

Loads URI schemes, IP addresses, hostnames, ports, and transports of gateways that belong to a given group to gw_uri_avp. group-id argument is a string that may contain pseudo-variables. Its value must be a a string of digits that are converted to an integer group id. Returns 1 or -1 depending on success.

Execution time of load_gws_from_grp() function is O(N), where N is number of gateways.

This function can be used from REQUEST_ROUTE.

Example 1.25. load_gws_from_grp usage

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

if (!load_gws_from_grp("$avp(s:gateway_group)")) {
	sl_send_reply("500", "Server Internal Error - Cannot load gateways");
	exit;
};
...

1.4.3. `next_gw()`

Upon first call, replaces URI scheme, host, port, and transport of Request-URI by the values stored in first gw_uri_avp and destroys that AVP (see Overview section). Saves user part of Request-URI into ruri_user_avp for use in subsequent next_gw() calls.

Upon subsequent calls, appends a new branch URI to the request, where URI scheme, host, port, and transport of are taken from values stored in the first gw_uri_avp and destroys that AVP. URI user is taken from ruri_user_avp.

As a side effect, stores gateway's flags to flags_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 1.26. next_gw usage from a route block

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

Example 1.27. next_gw usage from a failure route block

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

1.4.4. `from_gw([pvar])`

Checks if request came from IP address of a gateway. IP address to be checked is either taken from source IP address of the request or (if present) from pseudo variable argument. As a side effect, stores gateway's flags to flags_avp.

Execution time of from_gw() function is O(log N), where N is number of gateways.

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

Example 1.28. from_gw usage

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

Example 1.29. from_gw usage with pseudo variable argument

...
if (from_gw("$si")) {
	...
};
...

1.4.5. `from_gw_grp(group-id)`

Checks if request came from IP address of a gateway that belongs to the given group (integer string). Sets or resets a message flag depending on whether the gateway supports directed media.

Execution time of from_gw_grp() function is O(log N), where N is number of gateways.

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

Example 1.30. from_gw_grp usage

...
if (from_gw_grp("1")) {
	...
};
...

1.4.6. `to_gw([group-id])`

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

Execution time of to_gw() function is O(log N), where N is number of gateways.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1.31. to_gw usage

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

Example 1.32. to_gw usage with group-id

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

1.5. Exported MI Commands

1.5.1. `lcr_reload`

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

Name: lcr_reload

Parameters: none

MI FIFO Command Format:

		:lcr_reload:_reply_fifo_file_
		_empty_line_

1.5.2. `lcr_gw_dump`

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

Name: lcr_gw_dump

Parameters: none

MI FIFO Command Format:

		:lcr_gw_dump:_reply_fifo_file_
		_empty_line_

1.5.3. `lcr_lcr_dump`

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

Name: lcr_lcr_dump

Parameters: none

MI FIFO Command Format:

		:lcr_gw_dump:_reply_fifo_file_
		_empty_line_

1.6. Known Limitations

In-memory gateway and in-memory lcr table are switched by two consecutive machine instructions. If lcr reload process is interrupted after the first one, in-memory gateway table does not match in-memory lcr table until execution of lcr reload process is resumed.

LCR (Least Cost Routing) Module

Juha Heinanen

Edited by

Juha Heinanen

Chapter 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. db_url (string)

1.3.2. gw_table (string)

1.3.3. gw_name_column (string)

1.3.4. grp_id_column (string)

1.3.5. ip_addr_column (string)

1.3.6. hostname_column (string)

1.3.7. port_column (string)

1.3.8. uri_scheme_column (string)

1.3.9. transport_column (string)

1.3.10. strip_column (string)

1.3.11. tag_column (string)

1.3.12. weight_column (string)

1.3.13. flags_column (string)

1.3.14. lcr_table (string)

1.3.15. prefix_column (string)

1.3.16. from_uri_column (string)

1.3.17. priority_column (string)

1.3.18. gw_uri_avp (AVP string)

1.3.19. rpid_avp (AVP string)

1.3.20. ruri_user_avp (AVP string)

1.3.21. flags_avp (AVP string)

1.3.22. lcr_hash_size (integer)

1.3.23. fetch_rows (integer)

1.4. Exported Functions

1.4.1. load_gws([pvar])

1.4.2. load_gws_from_grp(group-id)

1.4.3. next_gw()

1.4.4. from_gw([pvar])

1.4.5. from_gw_grp(group-id)

1.4.6. to_gw([group-id])

1.5. Exported MI Commands

1.5.1. lcr_reload

1.5.2. lcr_gw_dump

1.5.3. lcr_lcr_dump

1.6. Known Limitations

1.3.1. `db_url` (string)

1.3.2. `gw_table` (string)

1.3.3. `gw_name_column` (string)

1.3.4. `grp_id_column` (string)

1.3.5. `ip_addr_column` (string)

1.3.6. `hostname_column` (string)

1.3.7. `port_column` (string)

1.3.8. `uri_scheme_column` (string)

1.3.9. `transport_column` (string)

1.3.10. `strip_column` (string)

1.3.11. `tag_column` (string)

1.3.12. `weight_column` (string)

1.3.13. `flags_column` (string)

1.3.14. `lcr_table` (string)

1.3.15. `prefix_column` (string)

1.3.16. `from_uri_column` (string)

1.3.17. `priority_column` (string)

1.3.18. `gw_uri_avp` (AVP string)

1.3.19. `rpid_avp` (AVP string)

1.3.20. `ruri_user_avp` (AVP string)

1.3.21. `flags_avp` (AVP string)

1.3.22. `lcr_hash_size` (integer)

1.3.23. `fetch_rows` (integer)

1.4.1. `load_gws([pvar])`

1.4.2. `load_gws_from_grp(group-id)`

1.4.3. `next_gw()`

1.4.4. `from_gw([pvar])`

1.4.5. `from_gw_grp(group-id)`

1.4.6. `to_gw([group-id])`

1.5.1. `lcr_reload`

1.5.2. `lcr_gw_dump`

1.5.3. `lcr_lcr_dump`