DISPATCHER Module

Daniel-Constantin Mierla

Edited by

Daniel-Constantin Mierla

Edited by

Carsten Bock

ng-voice GmbH

Edited by

Olle E. Johansson

Edvina AB

Edited by

Alessandro Arrichiello

Hewlett Packard

Edited by

Luis Martin

Edited by

Julien Chavanton


Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio modules
2.2. External libraries or applications
3. Parameters
3.1. list_file (string)
3.2. db_url (string)
3.3. table_name (string)
3.4. setid_col (string)
3.5. destination_col (string)
3.6. flags_col (string)
3.7. priority_col (string)
3.8. force_dst (int)
3.9. flags (int)
3.10. use_default (int)
3.11. dst_avp (str)
3.12. grp_avp (str)
3.13. cnt_avp (str)
3.14. dstid_avp (str)
3.15. attrs_avp (str)
3.16. sock_avp (str)
3.17. hash_pvar (str)
3.18. setid_pvname (str)
3.19. attrs_pvname (str)
3.20. ds_ping_method (string)
3.21. ds_ping_from (string)
3.22. ds_ping_interval (int)
3.23. ds_probing_threshold (int)
3.24. ds_inactive_threshold (int)
3.25. ds_ping_reply_codes (string)
3.26. ds_probing_mode (int)
3.27. ds_ping_latency_stats (int)
3.28. ds_latency_estimator_alpha (int)
3.29. ds_hash_size (int)
3.30. ds_hash_expire (int)
3.31. ds_hash_initexpire (int)
3.32. ds_hash_check_interval (int)
3.33. outbound_proxy (str)
3.34. ds_default_socket (str)
3.35. ds_timer_mode (int)
3.36. event_callback (str)
4. Functions
4.1. ds_select_dst(set, alg[, limit])
4.2. ds_select_domain(set, alg[, limit])
4.3. ds_select(set, alg [, limit])
4.4. ds_next_dst()
4.5. ds_next_domain()
4.6. ds_mark_dst([state])
4.7. ds_list_exist(groupid)
4.8. ds_is_from_list([groupid [, mode [, uri] ] ])
4.9. ds_load_update()
4.10. ds_load_unset()
4.11. ds_reload()
5. RPC Commands
5.1. dispatcher.set_state
5.2. dispatcher.list
5.3. dispatcher.reload
5.4. dispatcher.ping_active
6. Installation and Running
6.1. Destination List File
6.1.1. Special Attributes
6.1.2. File Format
6.2. Kamailio config file
7. Event routes
7.1. dispatcher:dst-down
7.2. dispatcher:dst-up
2. Frequently Asked Questions

List of Examples

1.1. Set the list_file parameter
1.2. Set db_url parameter
1.3. Set table_name parameter
1.4. Set setid_col parameter
1.5. Set destination_col parameter
1.6. Set flags_col parameter
1.7. Set priority_col parameter
1.8. Set the force_dst parameter
1.9. Set the flags parameter
1.10. Set the use_default parameter
1.11. Set the dst_avp parameter
1.12. Set the grp_avp parameter
1.13. Set the cnt_avp parameter
1.14. Set the dstid_avp parameter
1.15. Set the attrs_avp parameter
1.16. Set the sock_avp parameter
1.17. Use $avp(hash) for hashing:
1.18. Use combination of PVs for hashing:
1.19. Set the setid_pvname parameter
1.20. Set the attrs_pvname parameter
1.21. Set the ds_ping_method parameter
1.22. Set the ds_ping_from parameter
1.23. Set the ds_ping_interval parameter
1.24. Set the ds_probing_threshold parameter
1.25. Set the ds_inactive_threshold parameter
1.26. Set the ds_ping_reply_codes parameter
1.27. Set the ds_probing_mode parameter
1.28. accessing the metrics
1.29. Set the ds_ping_latency_stats parameter
1.30. Set the ds_hash_size parameter
1.31. Set the ds_hash_size parameter
1.32. Set the ds_hash_expire parameter
1.33. Set the ds_hash_initexpire parameter
1.34. Set the ds_hash_check_interval parameter
1.35. Set the outbound_proxy parameter
1.36. Set the ds_default_socket parameter
1.37. Set the ds_timer_mode parameter
1.38. Set event_callback parameter
1.39. ds_select_dst usage
1.40. ds_select_domain usage
1.41. ds_select usage
1.42. ds_mark_dst usage
1.43. ds_list_exist usage
1.44. ds_is_from_list usage
1.45. ds_load_unset usage
1.46. dispatcher list file
1.47. Kamailio config script - sample dispatcher usage

Chapter 1. Admin Guide

Table of Contents

1. Overview
2. Dependencies
2.1. Kamailio modules
2.2. External libraries or applications
3. Parameters
3.1. list_file (string)
3.2. db_url (string)
3.3. table_name (string)
3.4. setid_col (string)
3.5. destination_col (string)
3.6. flags_col (string)
3.7. priority_col (string)
3.8. force_dst (int)
3.9. flags (int)
3.10. use_default (int)
3.11. dst_avp (str)
3.12. grp_avp (str)
3.13. cnt_avp (str)
3.14. dstid_avp (str)
3.15. attrs_avp (str)
3.16. sock_avp (str)
3.17. hash_pvar (str)
3.18. setid_pvname (str)
3.19. attrs_pvname (str)
3.20. ds_ping_method (string)
3.21. ds_ping_from (string)
3.22. ds_ping_interval (int)
3.23. ds_probing_threshold (int)
3.24. ds_inactive_threshold (int)
3.25. ds_ping_reply_codes (string)
3.26. ds_probing_mode (int)
3.27. ds_ping_latency_stats (int)
3.28. ds_latency_estimator_alpha (int)
3.29. ds_hash_size (int)
3.30. ds_hash_expire (int)
3.31. ds_hash_initexpire (int)
3.32. ds_hash_check_interval (int)
3.33. outbound_proxy (str)
3.34. ds_default_socket (str)
3.35. ds_timer_mode (int)
3.36. event_callback (str)
4. Functions
4.1. ds_select_dst(set, alg[, limit])
4.2. ds_select_domain(set, alg[, limit])
4.3. ds_select(set, alg [, limit])
4.4. ds_next_dst()
4.5. ds_next_domain()
4.6. ds_mark_dst([state])
4.7. ds_list_exist(groupid)
4.8. ds_is_from_list([groupid [, mode [, uri] ] ])
4.9. ds_load_update()
4.10. ds_load_unset()
4.11. ds_reload()
5. RPC Commands
5.1. dispatcher.set_state
5.2. dispatcher.list
5.3. dispatcher.reload
5.4. dispatcher.ping_active
6. Installation and Running
6.1. Destination List File
6.1.1. Special Attributes
6.1.2. File Format
6.2. Kamailio config file
7. Event routes
7.1. dispatcher:dst-down
7.2. dispatcher:dst-up

1. Overview

This module offers SIP load balancer functionality and it can be used as SIP traffic dispatcher. There are many load balancing and traffic dispaching algorithms that you can choose from, for example: round-robin, weight based load balancing, call load distribution, and hashing over SIP message attributes.

The module can be used as a stateless load balancer; it does not depend on any call state tracking module. It requires the TM module if you enable auto-discovery of active/inactive gateways.

It is very lightweight, therefore suitable for handling heavy SIP traffic. As the module has a small footprint and the ability to load balancing rules from a plain text file, it is suitable for embedded systems.

2. Dependencies

2.1. Kamailio modules

The following modules must be loaded before this module:

  • TM - only if active recovery of failed hosts is required.

  • database engine - only if you want to load balancing routes from database instead of plain text file. .

2.2. External libraries or applications

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

  • none.

3. Parameters

3.1. list_file (string)

Path to the file with destination sets (destination groups).

Default value is /etc/kamailio/dispatcher.list or /usr/local/etc/kamailio/dispatcher.list.

Example 1.1. Set the list_file parameter

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

3.2. db_url (string)

If you want to load the list of gateways from the database you must set this parameter.

Default value is NULL (disable DB support).

Example 1.2. Set db_url parameter

...
modparam("dispatcher", "db_url", "mysql://user:passwb@localhost/database")
...

3.3. table_name (string)

If you want to load the list of gateways from the database you must set this parameter as the database name.

Default value is dispatcher.

Example 1.3. Set table_name parameter

...
modparam("dispatcher", "table_name", "my_dispatcher")
...

3.4. setid_col (string)

The column's name in the database storing the gateway's set (group) id.

Default value is setid.

Example 1.4. Set setid_col parameter

...
modparam("dispatcher", "setid_col", "groupid")
...

3.5. destination_col (string)

The column's name in the database storing the destination sip URI.

Default value is destination.

Example 1.5. Set destination_col parameter

...
modparam("dispatcher", "destination_col", "uri")
...

3.6. flags_col (string)

The column's name in the database storing the flags for the destination URI.

Default value is flags.

Example 1.6. Set flags_col parameter

...
modparam("dispatcher", "flags_col", "dstflags")
...

3.7. priority_col (string)

The column's name in the database storing the priority for destination URI.

Default value is priority.

Example 1.7. Set priority_col parameter

...
modparam("dispatcher", "priority_col", "dstpriority")
...

3.8. force_dst (int)

If set to 1, force overwriting of destination address (outbound proxy) when that is already set. If set to 0, will return error when the destination address is already set.

Default value is 1.

Example 1.8. Set the force_dst parameter

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

3.9. flags (int)

Various flags that affect dispatcher's behaviour. The flags are defined as a bitmask on an integer value. If flag 1 is set only the username part of the URI will be used when computing an URI based hash. If no flags are set the username, hostname and port will be used. The port is used only if different from 5060 (normal sip URI) or 5061 (in the sips: case).

If flag 2 is set, then failover support is enabled. The functions exported by the module will store the rest of addresses from the destination set in the AVP, and use these AVPs to contact next address if the current-tried destination fails.

Default value is 0.

Example 1.9. Set the flags parameter

 ...
 modparam("dispatcher", "flags", 3)
 ...

3.10. use_default (int)

If the parameter is set to 1, the last address in destination set is used as a final option to send the request to. For example, it is useful when wanting to send the call to an anouncement server saying: "the gateways are full, try later".

Default value is 0.

Example 1.10. Set the use_default parameter

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

3.11. dst_avp (str)

The name of the avp which will hold the list with addresses, in the order they have been selected by the chosen algorithm. If use_default is 1, the value of last dst_avp_id is the last address in destination set. The first dst_avp_id is the selected destinations. All the other addresses from the destination set will be added in the avp list to be able to implement serial forking.

Note

You must set this parameter if you want to do load balancing fail over.

Default value is null - don't add AVPs.

Example 1.11. Set the dst_avp parameter

 ...
 modparam("dispatcher", "dst_avp", "$avp(dsdst)")
 ...

3.12. grp_avp (str)

The name of the avp storing the group id of the destination set. Good to have it for later usage or checks.

Note

You must set this parameter if you want to do load balancing fail over.

Default value is null - don't add AVP.

Example 1.12. Set the grp_avp parameter

 ...
 modparam("dispatcher", "grp_avp", "$avp(dsgrp)")
 ...

3.13. cnt_avp (str)

The name of the avp storing the number of destination addresses kept in dst_avp AVPs.

Note

You must set this parameter if you want to do load balancing fail over.

Default value is null - don't add AVP.

Example 1.13. Set the cnt_avp parameter

 ...
 modparam("dispatcher", "cnt_avp", "$avp(dscnt)")
 ...

3.14. dstid_avp (str)

The name of the avp storing the destination unique ID used for call load based dispatching.

Note

You must set this parameter if you want to do load balancing on call load (alg 10).

Default value is null - don't add AVP.

Example 1.14. Set the dstid_avp parameter

 ...
 modparam("dispatcher", "dstid_avp", "$avp(dsdstid)")
 ...

3.15. attrs_avp (str)

The name of the avp storing destination's attributes value.

Note

Default value is null - don't add AVP.

Example 1.15. Set the attrs_avp parameter

 ...
 modparam("dispatcher", "attrs_avp", "$avp(dsattrs)")
 ...

3.16. sock_avp (str)

The name of the avp which will hold the list with the sockets associated to the addresses stored in dst_avp avp.

Note

If you want to do load balancing fail over, you have to set this parameter to use the correct socket for each gateway.

Default value is null - don't add AVPs.

Example 1.16. Set the sock_avp parameter

 ...
 modparam("dispatcher", "sock_avp", "$avp(dssocket)")
 ...

3.17. hash_pvar (str)

String with PVs used for the hashing algorithm 7.

Note

You must set this parameter if you want do hashing over custom message parts.

Default value is null - disabled.

Example 1.17. Use $avp(hash) for hashing:

 ...
 modparam("dispatcher", "hash_pvar", "$avp(hash)")
 ...

Example 1.18. Use combination of PVs for hashing:

 ...
 modparam("dispatcher", "hash_pvar", "hash the $fU@$ci")
 ...

3.18. setid_pvname (str)

The name of the PV where to store the set ID (group ID) when calling ds_is_from_list() with no parameter.

Default value is null - don't set PV.

Example 1.19. Set the setid_pvname parameter

 ...
 modparam("dispatcher", "setid_pvname", "$var(setid)")
 ...

3.19. attrs_pvname (str)

The name of the PV where to store the attributes of matching address when calling ds_is_from_list().

Default value is null - don't set PV.

Example 1.20. Set the attrs_pvname parameter

 ...
 modparam("dispatcher", "attrs_pvname", "$var(attrs)")
 ...

3.20. ds_ping_method (string)

With this method you can define, with which method you want to probe the gateways. Pinging gateways feature depends on ds_ping_interval parameter.

Default value is OPTIONS.

Example 1.21. Set the ds_ping_method parameter

 ...
 modparam("dispatcher", "ds_ping_method", "INFO")
 ...

3.21. ds_ping_from (string)

With this Method you can define the "From:"-Line for the request, sent to the failed gateways. This method is only available, if compiled with the probing of failed gateways enabled.

Default value is sip:dispatcher@localhost.

Example 1.22. Set the ds_ping_from parameter

 ...
 modparam("dispatcher", "ds_ping_from", "sip:proxy@sip.somehost.com")
 ...

3.22. ds_ping_interval (int)

With this parameter you can define the interval for sending a request to a gateway marked as inactive upon a failed request routing to it. This parameter is only used, when the TM-Module is loaded. If set to 0, the pinging of inactive gateway is disabled.

Default value is 0.

Example 1.23. Set the ds_ping_interval parameter

 ...
 modparam("dispatcher", "ds_ping_interval", 30)
 ...

3.23. ds_probing_threshold (int)

If you want to set a gateway into inactive mode, there can be a specific number of failed requests until it will change from "active" to "inactive". It is using the state "trying", that allows selection of gateway but indicates there was a failure previously with the gateway. The number of attempts can be set with this parameter. This parameter can be modified via ser config framework.

Default value is 1 (set inactive with first failure).

Example 1.24. Set the ds_probing_threshold parameter

 ...
 modparam("dispatcher", "ds_probing_threshold", 10)
 ...

3.24. ds_inactive_threshold (int)

If you want to set a gateway into active mode (after being inactive), there can be a specific number of successful requests until it will change from "inactive" to "active". The number of attempts can be set with this parameter. This parameter can be modified via ser config framework.

Default value is 1 (set active with first success).

Example 1.25. Set the ds_inactive_threshold parameter

 ...
 modparam("dispatcher", "ds_inactive_threshold", 10)
 ...

3.25. ds_ping_reply_codes (string)

This parameter defines the valid response codes, which are accepted as a valid reply to the PING-Method. It is a list separated by colons, whery you may define either a single code (e.g. "code=202" would accept 202 as an additional, valid response) or a class of responses, you want to accept (e.g. "class=2" would accept everything from 200 to 299 as valid response). This parameter can be modified via config framework.

Please note that the response codes the module accepts as valid reply to the PING-Method are not only the ones generated from the remote servers, but also those that are generated locally. E.g.: setting code=408 or class=400 will never set a backend down even if it is, because internally the Kamailio transaction layer generates a 408 in the case of no response from the remote server, and this internal code 408 is accepted as valid value.

Default value is (only 200 OK is accepted).

Example 1.26. Set the ds_ping_reply_codes parameter

 ...
 modparam("dispatcher", "ds_ping_reply_codes", "class=2;code=403;code=488;class=3")
 ...

3.26. ds_probing_mode (int)

Controls what gateways are tested to see if they are reachable.

  • Value 0: If set to 0, only the gateways with state PROBING are tested. After a gateway is probed, the PROBING state is cleared in this mode.

  • Value 1: If set to 1, all gateways are tested. If set to 1 and there is a failure of keepalive to an active gateway, then it is set to TRYING state.

  • Value 2: if set to 2, only gateways in inactive state with probing mode set are tested.

  • Value 3: If set to 3, any gateway with state PROBING is continually probed without modifying/removing the PROBING state. This allows selected gateways to be probed continually, regardless of state changes.

Default value is 0.

Example 1.27. Set the ds_probing_mode parameter

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

3.27. ds_ping_latency_stats (int)

Enable latency measurement when pinging nodes

  • If set to 0, disable latency measurement.

  • If set to 1, enable latency measurement.

Default value is 0.

Example 1.28. accessing the metrics

# using the command :
kamcmd dispatcher.list
 ...
DEST: {
	URI: sip:1.2.3.4
	FLAGS: AX
	PRIORITY: 9
	LATENCY: {
		AVG: 24.250000 # weigthed moving average for the last few weeks
		STD: 1.035000  # standard deviation of AVG
		EST: 25.000000 # short term estimate, see parameter: ds_latency_estimator_alpha
		MAX: 26        # maximun value seen
		TIMEOUT: 0     # count of ping timeouts
	}
}
 ...

Example 1.29. Set the ds_ping_latency_stats parameter

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

3.28. ds_latency_estimator_alpha (int)

The value to be used to control the memory of the estimator EWMA "exponential weighted moving average" or "the speed at which the older samples are dampened" a goog explanation can be found here : http://www.itl.nist.gov/div898/handbook/pmc/section3/pmc324.htm Because Kamailio doesn't support float parameter types, the value in the parameter is divided by 1000 and stored as float. For example, if you want to set the alpha to be 0.75, use value 750 here.

Default value is 900 => 0.9.

Example 1.30. Set the ds_hash_size parameter

 ...
 modparam("dispatcher", "ds_latency_estimator_alpha", 900)
 ...

3.29. ds_hash_size (int)

The value to be used as power of two to set the number of slots to hash table storing data for call load dispatching (e.g., value 8 will create a hash table with 256 slots). It must be greater than 0 to enable call load dispatching feature (alg 10).

Default value is 0.

Example 1.31. Set the ds_hash_size parameter

 ...
 modparam("dispatcher", "ds_hash_size", 9)
 ...

3.30. ds_hash_expire (int)

Expiration time in seconds to remove the load on a destination if no BYE was received meanwhile.

Default value is 7200.

Example 1.32. Set the ds_hash_expire parameter

 ...
 modparam("dispatcher", "ds_hash_expire", 3600)
 ...

3.31. ds_hash_initexpire (int)

Expiration time in seconds to remove the load on a destination if no 200 for INVITE was received meanwhile and state updated with ds_load_update().

Default value is 7200.

Example 1.33. Set the ds_hash_initexpire parameter

 ...
 modparam("dispatcher", "ds_hash_initexpire", 60)
 ...

3.32. ds_hash_check_interval (int)

Time interval in seconds to scan internal hash table with call load dispatching data for expired items.

Default value is 30.

Example 1.34. Set the ds_hash_check_interval parameter

 ...
 modparam("dispatcher", "ds_hash_check_interval", 60)
 ...

3.33. outbound_proxy (str)

SIP URI of outbound proxy to be used when sending pings.

By default no outbound proxy is defined.

Example 1.35. Set the outbound_proxy parameter

 ...
 modparam("dispatcher", "outbound_proxy", "sip:outbound.example.com")
 ...

3.34. ds_default_socket (str)

Default socket to be used for sending pings and dispatching requests when a gateway has no send socket configured.

By default no default socket is defined, the first configuration script listen directive is used.

Example 1.36. Set the ds_default_socket parameter

 ...
 modparam("dispatcher", "ds_default_socket", "udp:192.168.0.125:5060")
 ...

3.35. ds_timer_mode (int)

Specify the timer process to be used by the module for keepalives and active dialogs tracking.

It can be set to:

  • 0 - use main timer process.

  • 1 - use secondary timer process.

On a server with a lot of traffic, using secondary timer can help with performances, because the main timer can be overloaded by taking care of transactions retransmissions and expirations of items in memory.

Default value is 0.

Example 1.37. Set the ds_timer_mode parameter

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

3.36. event_callback (str)

The name of the function in the kemi configuration file (embedded scripting language such as Lua, Python, ...) to be executed instead of event_route[...] blocks.

The function receives a string parameter with the name of the event, the values are: 'dispatcher:dst-down', 'dispatcher:dst-up'.

Default value is 'empty' (no function is executed for events).

Example 1.38. Set event_callback parameter

...
modparam("dispatcher", "event_callback", "ksr_dispatcher_event")
...
-- event callback function implemented in Lua
function ksr_dispatcher_event(evname)
	KSR.info("===== dispatcher module triggered event: " .. evname .. "\n");
	return 1;
end
...

4. Functions

4.1.  ds_select_dst(set, alg[, limit])

The method selects a destination from addresses set. It returns true if a new destination is set. The selected address is set to dst_uri field (aka the outbound proxy address or the $du variable), not being visible in the SIP request.

If the bit 2 in 'flags' parameter is set, the rest of the addresses from the destination set is stored in AVP list (limited with an optional 'limit' parameter). You can use 'ds_next_dst()' to use next address in order to achieve serial forking to all possible destinations.

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. The parameter can be an integer or a variable holding an integer.

  • alg - the algorithm used to select the destination address. The parameter can be an integer or a variable holding an interger.

    • 0 - hash over callid

    • 1 - hash over from URI.

    • 2 - hash over to URI.

    • 3 - hash over request-URI.

    • 4 - round-robin (next destination).

    • 5 - hash over authorization-username (Proxy-Authorization or "normal" authorization). If no username is found, round robin is used.

    • 6 - random destination (using rand()).

    • 7 - hash over the content of PVs string. Note: This works only when the parameter hash_pvar is set.

    • 8 - select destination sorted by priority attribute value (serial forking ordered by priority).

    • 9 - use weight based load distribution. You have to set the attribute 'weight' per each address in destination set.

    • 10 - use call load distribution. You have to set the attribute 'duid' (as an unique string id) per each address in destination set. Also, you must set parameters 'dstid_avp' and 'ds_hash_size'.

      The algorithm can be used even with stateless proxy mode, there is no SIP dialog tracking depending on other modules, just an internal lightweight call tracking by Call-Id, thus is fast and suitable even for embedded systems.

      The first destination selected by this algorithm is the one that has the least number of calls associated. The rest of the destination list is taken in order of the entries in set - anyhow, until a re-route to next destination happens, the load on each address can change.

      This algorithm can be used only for dispatching INVITE requests as it is the only SIP method creating a SIP call.

    • 11 - use relative weight based load distribution. You have to set the attribute 'rweight' per each address in destination set. Active host usage probability is rweight/(SUM of all active host rweights in destination group).

      The major difference from the weight distribution is the probability recalculation according to rweight value in case of host enabling/disabling

      For example, 100 calls in 3-hosts group with rweight params 1/2/1 will be distributed as 25/50/25. After third host failing distribution will be changed to 33/67/0.

    • 12 - dispatch to all destination in setid at once (parallel forking). Note that the AVPs are no longer set with the values of the destination records, no re-routing making sense in this case.

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

  • limit - the maximum number of items to be stored in AVP list for further failovers (the first selected destination and default destination are the first to be put in the list)

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1.39. ds_select_dst usage

...
ds_select_dst("1", "0");
...
$var(a) = 4;
ds_select_dst("1", "$var(a)");
...
ds_select_dst("1", "4", "3");
...

4.2.  ds_select_domain(set, alg[, limit])

The method selects a destination from addresses set and rewrites the host and port from R-URI. The parameters have same meaning as for ds_select_dst().

If the bit 2 in 'flags' is set, the rest of the addresses from the destination set is stored in AVP list (limited with an optional 'limit' parameter). You can use 'ds_next_domain()' to use next address to achieve serial forking to all possible destinations.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1.40. ds_select_domain usage

...
$var(a) = 4;
if(ds_select_domain("1", "$var(a)")) {
    t_relay();
    exit;
}
...

4.3.  ds_select(set, alg [, limit])

The method selects a destination from addresses set and adds it in the AVPs specified for this module. It is not updating R-URI nor the destination URI. The parameters have same meaning as for ds_select_dst().

If the bit 2 in 'flags' is set, the rest of the addresses from the destination set is stored in AVP list (limited with an optional 'limit' parameter). You can execute 'ds_next_domain()' or 'ds_next_dst()' to use next address to achieve serial forking to all possible destinations.

This function can be used from ANY_ROUTE.

Example 1.41. ds_select usage

...
$var(a) = 4;
if(ds_select("1", "$var(a)")) {
    ds_next_domain();
    t_relay();
    exit;
}
...

4.4.  ds_next_dst()

Takes the next destination address from the AVPs with id 'dst_avp_id' and sets the dst_uri (outbound proxy address).

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.5.  ds_next_domain()

Takes the next destination address from the AVPs with id 'dst_avp_id' and sets the domain part of the request URI.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.6.  ds_mark_dst([state])

Mark the last used address from destination set as inactive ("i"/"I"), active ("a"/"A"), disabled ("d"/"D") or trying ("t"/"T"). Apart of disabled state, a destination can be set in probing mode by adding ("p"/"P") flag. With this function, an automatic detection of failed gateways can be implemented. When an address is marked as inactive or disabled, it will be ignored by 'ds_select_dst' and 'ds_select_domain'.

The parameter state is optional, when it is missing, then the destination will be marked inactive (i.e., same as 'i').

Possible values for state parameter:

  • "a" or "A" - the last destination should be set to active and the error-counter should set to "0".

  • "i" or "I" - the last destination should be set to inactive and will be ignored in future requests.

  • "t" or "T" - the last destination should be set to temporary trying state and failure counter is incremented. When the failure counter reaches the threshold, the destination will be set inactive.

  • "p" and "P" - this has to be used in addition to one of the previous flags - the last destination will be set to probing. This mean the destination will be pinged with SIP OPTIONS requests from time to time to detect if it is up or down.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

Example 1.42. ds_mark_dst usage

...
failure_route[tryagain] {
...
   if(t_check_status("500"))
      ds_mark_dst("ip"); # set to inactive and probing
...
}
...

4.7.  ds_list_exist(groupid)

Check if a specific group is defined in dispatcher list or database.

  • groupid - A group ID to check.

This function can be used from ANY_ROUTE.

Example 1.43. ds_list_exist usage

...
if(ds_list_exist("10")) {
    ...
}
...

4.8.  ds_is_from_list([groupid [, mode [, uri] ] ])

This function returns true, if there is a match of source address or uri with an address in the given group of the dispatcher-list; otherwise false.

Description of parameters:

  • groupid (optional) - if not given or its value is -1, the matching will be done over all addresses in all dispacher groups. Otherwise the matching will be done only against the addresses in the specific group id. The parameter can be an integer or a variable holding an integer value.

  • mode - (optional) - a bitmask to specify how the matching should be done. If is 0, all ip, port and proto are matched. If bit one is set, then port is ignored. If bit two is set, then protocol is ignored. The parameter can be an integer or a variable holding an integer value. It must be provided if the uri parameter is provided.

  • uri (optional) - if is empty or missing, the matching is done against source IP, port and protocol. Otherwise the value has to be a valid SIP URI, used to match against addresses in the dispatcher list. Only IP, port and protocol are matches, any additional parameters are ignored. The parameter can be a static or dynamic (with variables) string. The domain part of the URI can be an IP address or a hostname.

Upon a match, the variable specified by 'setid_pvname' parameter will be set to groupid of matching address and the attributes will be set in variable specified by 'attrs_pvname'.

Note that for backward compatibility mode, when no parameter is given or only groupid is given, the matching is done only for IP address and port (protocol is ignored).

This function can be used from ANY_ROUTE.

Example 1.44. ds_is_from_list usage

...
if(ds_is_from_list()) {
    ...
}
if(ds_is_from_list("10")) {
    ...
}
if(ds_is_from_list("10", "3")) {
    ...
}
if(ds_is_from_list("10", "3", "sip:127.0.0.1:5080")) {
    ...
}
...

4.9.  ds_load_update()

Updates the load state:

  • if it is a BYE or CANCEL - remove the load from destination address used to forward the INVITE

  • if it is a reply to INVITE - set internal state to confirmed for call load structure when reply code is 2xx.

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

4.10.  ds_load_unset()

Remove the call load for the destination that routed the call.

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

Example 1.45. ds_load_unset usage

...
route {
    ...
	if(is_method("BYE|CANCEL"))
        ds_load_update();
    ...
	ds_select_dst("1", "10");
    ...
}

onreply_route {
    ...
    if(is_method("INVITE")
	{
        if(status=~"2[0-9][0-9]")
            ds_load_update();
        else if(status=~"[3-7][0-9][0-9]")
            ds_load_unset();
    }
    ...
}
...

4.11.  ds_reload()

Reloads the groups and included destinations.

Name: ds_reload

Parameters: none

This function can be used from ANY_ROUTE.

5. RPC Commands

5.1.  dispatcher.set_state

Sets the state for a destination address (can be use to mark the destination as active or inactive).

Name: dispatcher.set_state

Parameters:

  • _state_ : state of the destination address

    • a: active

    • i: inactive

    • t: trying

    • d: disabled

    The states a, i or t can be followed by p to set probing mode (e.g. 'ap', 'ip' or 'tp').

  • _group_: destination group id

  • _address_: address of the destination in the _group_

Example:

...
# prototype: kamcmd dispatcher.set_state _state_ _group_ _address_
kamcmd dispatcher.set_state ip 2 sip:127.0.0.1:5080
...

5.2.  dispatcher.list

Lists the groups and included destinations.

Name: dispatcher.list

Parameters: none

Example:

		kamcmd dispatcher.list

5.3.  dispatcher.reload

Reloads the groups and included destinations. The command is disabled for call load based dispatching (algorithm 10) since removal of destinations may leave the list of active calls with broken references.

Name: dispatcher.reload

Parameters: none

Example

		kamcmd dispatcher.reload

5.4.  dispatcher.ping_active

Sets the global state for sending keepalive requests to destinations.

Name: dispatcher.ping_active

Parameters:

  • _state_ : state of sending keepalives

    • 0: inactive (don't send)

    • 1: active (send)

If the state parameter is missing, the current state is returned. When state is changed, new and old values of the state are returned. Default value for state is 1.

Example:

...
# prototype: kamcmd dispatcher.ping_active _state_
kamcmd dispatcher.ping_active 0
...

6. Installation and Running

6.1. Destination List File

Each destination point must be on one line. First token is the set id (an integer value, also referenced by group id), followed by destination address (string value in full SIP URI format).

Optionally, these fields can be followed by:

  • flags (listed by index - can be bitwise mask of values): 0 (value 1) - inactive destination; 1 (value 2) - temporary trying destination (in the way to become inactive if it does not reply to keepalives - there is a module parameter to set the threshold of failures); 2 (value 4) - admin disabled destination; 3 (value 8) - probing destination (sending keep alives);

  • priority: sets the priority in destination list (based on it is done the initial ordering inside the set)

  • attributes: extra fields in form of name1=value1;...;nameN=valueN.

6.1.1. Special Attributes

There are some predefined names:

  • 'duid' - used for call load dispatching. It must be an unique value to identify a destination (gateway address). Practically the load within the group is associated with this value.
  • 'maxload' - used for call load dispatching. It must be a positive integer, defining the upper limit of active calls per destination. When the limit is reached, then the gateway is no longer selected for new calls until an exiting call via that gateway is terminated. If set to 0, then no active call limit is used.
  • 'weight' - used for weight based load distribution. It must be set to a positive integer value beteen 0 and 100. The value represents the percent of calls to be sent to that gateways.
  • 'rweight' - used for relative weight based load distribution. It must be set to a positive integer value between 1 and 100 (otherwise host will be excluded from relative weight distribution type).
  • 'socket' - used to set the sending socket for the gateway. It is used for sending the SIP traffic as well as OPTIONS keepalives.

6.1.2. File Format

Line format is:

...
setid(int) destination(sip uri) flags(int,opt) priority(int,opt) attrs(str,opt)
...

Full line example:

...
1 sip:127.0.0.1:5080 0 0 duid=abc;socket=udp:192.168.0.125:5060;my=xyz
...

For database, each element of a line resides in a different column. Next is a dispatcher.list file example:

Example 1.46. dispatcher list file

...
#
# dispatcher destination sets (groups)
#

# line format
# setid(int) destination(sip uri) flags(int,opt) priority(int,opt) attributes(str,opt)

# proxies
2 sip:127.0.0.1:5080;transport=tcp 0 10 class=4;prefix=448;strip=2
2 sip:127.0.0.1:5082;px=vx 0 5 duid=abc;socket=udp:192.168.0.125:5060;pipe=p10

# gateways
1 sip:127.0.0.1:7070 0 0 duid=xyz;maxload=20
1 sip:127.0.0.1:7072 0 5
1 sip:127.0.0.1:7074

...

6.2. Kamailio config file

Next listing shows a sample config for using the dispatcher module.

Example 1.47. Kamailio config script - sample dispatcher usage

...
#!KAMAILIO
#
# sample config file for dispatcher module
# - load balancing of VoIP calls with round robin
# - no TPC listening
# - don't dispatch REGISTER and presence requests
#
# Kamailio SIP Server
#     - web: http://www.kamailio.org
#     - git: http://github.com/kamailio/
#
# Direct your questions about this file to: sr-users@lists.sip-router.org
#
# Refer to the Core CookBook at http://www.kamailio.org/dokuwiki/doku.php
# for an explanation of possible statements, functions and parameters.
#
# Several features can be enabled using '#!define WITH_FEATURE' directives:
#
# *** To run in debug mode:
#     - define WITH_DEBUG
#

#!ifndef DBURL
#!define DBURL "mysql://kamailio:kamailiorw@localhost/kamailio"
#!endif

# - flags
#   FLT_ - per transaction (message) flags
#	FLB_ - per branch flags
#!define FLT_ACC 1
#!define FLT_ACCMISSED 2
#!define FLT_ACCFAILED 3

####### Global Parameters #########

#!ifdef WITH_DEBUG
debug=4
log_stderror=yes
#!else
debug=2
log_stderror=no
#!endif

memdbg=5
memlog=5

log_facility=LOG_LOCAL0

fork=yes
children=4

/* comment the next line to enable TCP */
disable_tcp=yes

/* uncomment the next line to disable the auto discovery of local aliases
   based on revers DNS on IPs (default on) */
auto_aliases=no

/* add local domain aliases */
# alias="mysipserver.com"

port=5060

/* uncomment and configure the following line if you want Kamailio to
   bind on a specific interface/port/proto (default bind on all available) */
# listen=udp:127.0.0.1:5060

sip_warning=no

####### Modules Section ########

# set module path
mpath="/usr/local/lib/kamailio/modules/"

loadmodule "db_mysql.so"
loadmodule "jsonrpcs.so"
loadmodule "kex.so"
loadmodule "tm.so"
loadmodule "tmx.so"
loadmodule "sl.so"
loadmodule "rr.so"
loadmodule "pv.so"
loadmodule "maxfwd.so"
loadmodule "textops.so"
loadmodule "siputils.so"
loadmodule "xlog.so"
loadmodule "sanity.so"
loadmodule "ctl.so"
loadmodule "acc.so"
loadmodule "dispatcher.so"


# ----------------- setting module-specific parameters ---------------


# ----- jsonrpcs params -----
modparam("jsonrpcs", "pretty_format", 1)


# ----- rr params -----
# add value to ;lr param to cope with most of the UAs
modparam("rr", "enable_full_lr", 1)
# do not append from tag to the RR (no need for this script)
modparam("rr", "append_fromtag", 0)


# ----- acc params -----
modparam("acc", "log_flag", FLT_ACC)
modparam("acc", "failed_transaction_flag", FLT_ACCFAILED)
modparam("acc", "log_extra",
	"src_user=$fU;src_domain=$fd;dst_ouser=$tU;dst_user=$rU;dst_domain=$rd;src_ip=$si")

# ----- tm params -----
modparam("tm", "fr_timer", 2000)
modparam("tm", "fr_inv_timer", 40000)

# ----- dispatcher params -----
modparam("dispatcher", "db_url", DBURL)
modparam("dispatcher", "table_name", "dispatcher")
modparam("dispatcher", "flags", 2)
modparam("dispatcher", "dst_avp", "$avp(AVP_DST)")
modparam("dispatcher", "grp_avp", "$avp(AVP_GRP)")
modparam("dispatcher", "cnt_avp", "$avp(AVP_CNT)")
modparam("dispatcher", "sock_avp", "$avp(AVP_SOCK)")

####### Routing Logic ########


# main request routing logic

request_route {

	# per request initial checks
	route(REQINIT);

	# handle requests within SIP dialogs
	route(WITHINDLG);

	### only initial requests (no To tag)

	# CANCEL processing
	if (is_method("CANCEL"))
	{
		if (t_check_trans())
			t_relay();
		exit;
	}

	# handle retransmissions
	if(t_precheck_trans()) {
		t_check_trans();
		exit;
	}
	t_check_trans();

	# record routing for dialog forming requests (in case they are routed)
	# - remove preloaded route headers
	remove_hf("Route");
	if (is_method("INVITE|SUBSCRIBE"))
		record_route();

	# account only INVITEs
	if (is_method("INVITE")) {
		setflag(FLT_ACC); # do accounting
	}

	# handle presence related requests
	route(PRESENCE);

	# handle registrations
	route(REGISTRAR);

	if ($rU==$null) {
		# request with no Username in RURI
		sl_send_reply("484","Address Incomplete");
		exit;
	}

	# dispatch destinations
	route(DISPATCH);
}


route[RELAY] {
	if (!t_relay()) {
		sl_reply_error();
	}
	exit;
}

# Per SIP request initial checks
route[REQINIT] {
	if (!mf_process_maxfwd_header("10")) {
		sl_send_reply("483","Too Many Hops");
		exit;
	}

	if(!sanity_check("1511", "7")) {
		xlog("Malformed SIP message from $si:$sp\n");
		exit;
	}
}

# Handle requests within SIP dialogs
route[WITHINDLG] {
	if (has_totag()) {
		# sequential request withing a dialog should
		# take the path determined by record-routing
		if (loose_route()) {
			if (is_method("BYE")) {
				setflag(FLT_ACC); # do accounting ...
				setflag(FLT_ACCFAILED); # ... even if the transaction fails
			}
			route(RELAY);
		} else {
			if (is_method("SUBSCRIBE") && uri == myself) {
				# in-dialog subscribe requests
				route(PRESENCE);
				exit;
			}
			if ( is_method("ACK") ) {
				if ( t_check_trans() ) {
					# non loose-route, but stateful ACK;
					# must be ACK after a 487 or e.g. 404 from upstream server
					t_relay();
					exit;
				} else {
					# ACK without matching transaction ... ignore and discard.
					exit;
				}
			}
			sl_send_reply("404","Not here");
		}
		exit;
	}
}

# Handle SIP registrations
route[REGISTRAR] {
	if(!is_method("REGISTER"))
		return;
	sl_send_reply("404", "No registrar");
	exit;
}

# Presence server route
route[PRESENCE] {
	if(!is_method("PUBLISH|SUBSCRIBE"))
		return;

	sl_send_reply("404", "Not here");
	exit;
}

# Dispatch requests
route[DISPATCH] {
	# round robin dispatching on gateways group '1'
	if(!ds_select_dst("1", "4")) {
		send_reply("404", "No destination");
		exit;
	}
	xlog("L_DBG", "--- SCRIPT: going to <$ru> via <$du>\n");
	t_on_failure("RTF_DISPATCH");
	route(RELAY);
	exit;
}

# Try next destionations in failure route
failure_route[RTF_DISPATCH] {
	if (t_is_canceled()) {
		exit;
	}
	# next DST - only for 500 or local timeout
	if (t_check_status("500")
			or (t_branch_timeout() and !t_branch_replied())) {
		if(ds_next_dst()) {
			t_on_failure("RTF_DISPATCH");
			route(RELAY);
			exit;
		}
	}
}

...

7. Event routes

7.1.  dispatcher:dst-down

When defined, the module calls event_route[dispatcher:ds-down] when a destination goes down (becomes probing). A typical use case is to update NMC equipment as to the status of a destination.

...
event_route[dispatcher:dst-down] {
    xlog("L_ERR", "Destination down: $rm $ru ($du)\n");
}
...

7.2.  dispatcher:dst-up

When defined, the module calls event_route[dispatcher:ds-up] when a destination that was previously down (probing) comes up. A typical use case is to update NMC equipment as to the status of a destination.

...
event_route[dispatcher:dst-up] {
    xlog("L_ERR", "Destination up: $rm $ru\n");
}
...

Chapter 2. Frequently Asked Questions

2.1. Does dispatcher provide a fair distribution?
2.2. Is dispatcher dialog stateful?
2.3. Where can I find more about Kamailio?
2.4. Where can I post a question about this module?
2.5. How can I report a bug?

2.1.

Does dispatcher provide a fair distribution?

The algoritms doing hashing over parts of SIP message don't guarantee a fair distribution. You should do some measurements to decide what hashing algorithm fits better in your environment.

Other distribution algorithms such as round robin or call load dispatching do a fair distribution in terms of delivered calls to gateways.

2.2.

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).

2.3.

Where can I find more about Kamailio?

Take a look at https://www.kamailio.org/.

2.4.

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 GIT snapshots should be send to .

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

2.5.

How can I report a bug?

Please follow the guidelines provided at: https://github.com/kamailio/kamailio/issues