DISPATCHER Module

Daniel-Constantin Mierla

   <miconda@gmail.com>

Edited by

Daniel-Constantin Mierla

   <miconda@gmail.com>

Carsten Bock

   ng-voice GmbH

Olle E. Johansson

   Edvina AB

Alessandro Arrichiello

   Hewlett Packard

Luis Martin

Julien Chavanton

   <jchavanton@gmail.com>

Federico Cabiddu

   <federico.cabiddu@gmail.com>

Tyler Moore

   <tmoore@dopensource.com>

   Copyright © 2004 FhG FOKUS

   Copyright © 2005 Voice Sistem

   Copyright © 2010 Daniel-Constantin Mierla (asipto.com)

   Copyright © 2014 Olle E. Johansson, Edvina AB

   Copyright © 2015 Alessandro Arrichiello, Hewlett Packard

   Copyright © 2017, 2018 Julien chavanton, Flowroute

   Copyright © 2020 Federico Cabiddu, Libon

   Copyright © 2025 Tyler Moore, dOpenSource
     __________________________________________________________________

   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. attrs_col (string)
              3.9. force_dst (int)
              3.10. flags (int)
              3.11. use_default (int)
              3.12. xavp_dst (str)
              3.13. xavp_dst_mode (int)
              3.14. xavp_ctx (str)
              3.15. xavp_ctx_mode (int)
              3.16. hash_pvar (str)
              3.17. setid_pvname (str)
              3.18. attrs_pvname (str)
              3.19. ds_ping_method (string)
              3.20. ds_ping_from (string)
              3.21. ds_ping_interval (int)
              3.22. ds_ping_fr_timer (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_retain_latency_stats (int)
              3.29. ds_latency_estimator_alpha (int)
              3.30. ds_hash_size (int)
              3.31. ds_hash_expire (int)
              3.32. ds_hash_initexpire (int)
              3.33. ds_hash_check_interval (int)
              3.34. outbound_proxy (str)
              3.35. ds_default_socket (str)
              3.36. ds_default_sockname (str)
              3.37. ds_ping_socket (str)
              3.38. ds_timer_mode (int)
              3.39. event_callback (str)
              3.40. event_callback_mode (int)
              3.41. ds_attrs_none (int)
              3.42. ds_db_extra_attrs (str)
              3.43. ds_load_mode (int)
              3.44. reload_delta (int)
              3.45. ds_dns_mode (int)
              3.46. ds_dns_interval (int)
              3.47. ds_dns_ttl (int)

        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_select_routes(rules, mode [, limit])
              4.5. ds_next_dst()
              4.6. ds_next_domain()
              4.7. ds_set_dst()
              4.8. ds_set_domain()
              4.9. ds_mark_dst([state])
              4.10. ds_mark_addr(state, setid, uri)
              4.11. ds_list_exists(groupid)
              4.12. ds_is_from_list([groupid [, mode [, uri] ] ])
              4.13. ds_is_active(groupid [, uri])
              4.14. ds_load_update()
              4.15. ds_load_unset()
              4.16. ds_reload()
              4.17. ds_dsg_fetch(setid)
              4.18. ds_dsg_fetch_uri(setid, uri)
              4.19. ds_oc_set_attrs(setid, uri, rval, tval, sval)

        5. RPC Commands

              5.1. dispatcher.set_state
              5.2. dispatcher.set_duid_state
              5.3. dispatcher.list
              5.4. dispatcher.reload
              5.5. dispatcher.ping_active
              5.6. dispatcher.add
              5.7. dispatcher.remove
              5.8. dispatcher.hash
              5.9. dispatcher.oclist

        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 “attrs_col” parameter
   1.9. Set the “force_dst” parameter
   1.10. Set the “flags” parameter
   1.11. Set the “use_default” parameter
   1.12. Set the “xavp_dst” parameter
   1.13. Set the “xavp_dst_mode” parameter
   1.14. Set the “xavp_ctx” parameter
   1.15. Set the “xavp_ctx_mode” parameter
   1.16. Use $avp(hash) for hashing:
   1.17. Use combination of PVs for hashing:
   1.18. Set the “setid_pvname” parameter
   1.19. Set the “attrs_pvname” parameter
   1.20. Set the “ds_ping_method” parameter
   1.21. Set the “ds_ping_from” parameter
   1.22. Set the “ds_ping_interval” parameter
   1.23. Set the “ds_ping_fr_timer” 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_retain_latency_stats” parameter
   1.31. Set the “ds_latency_estimator_alpha” parameter
   1.32. Set the “ds_hash_size” parameter
   1.33. Set the “ds_hash_expire” parameter
   1.34. Set the “ds_hash_initexpire” parameter
   1.35. Set the “ds_hash_check_interval” parameter
   1.36. Set the “outbound_proxy” parameter
   1.37. Set the “ds_default_socket” parameter
   1.38. Set the “ds_default_sockname” parameter
   1.39. Set the “ds_ping_socket” parameter
   1.40. Set the “ds_timer_mode” parameter
   1.41. Set event_callback parameter
   1.42. Set event_callback_mode parameter
   1.43. Set the “ds_attrs_none” parameter
   1.44. Set the “ds_db_extra_attrs” parameter
   1.45. Set the “ds_load_mode” parameter
   1.46. Set reload_delta parameter
   1.47. Set the “ds_dns_mode” parameter
   1.48. Set the “ds_dns_interval” parameter
   1.49. Set the “ds_dns_ttl” parameter
   1.50. latency_optimized_dispatching usage
   1.51. ds_select_dst usage
   1.52. configuring load balancing with congestion detection
   1.53. ds_select_domain usage
   1.54. ds_select usage
   1.55. ds_select_routes usage
   1.56. ds_mark_dst usage
   1.57. ds_mark_addr usage
   1.58. ds_list_exists usage
   1.59. ds_is_from_list usage
   1.60. ds_is_active usage
   1.61. ds_load_unset usage
   1.62. ds_reload usage
   1.63. ds_dsg_fetch() usage
   1.64. ds_dsg_fetch_uri() usage
   1.65. ds_oc_set_attrs() usage
   1.66. dispatcher list file
   1.67. 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. attrs_col (string)
        3.9. force_dst (int)
        3.10. flags (int)
        3.11. use_default (int)
        3.12. xavp_dst (str)
        3.13. xavp_dst_mode (int)
        3.14. xavp_ctx (str)
        3.15. xavp_ctx_mode (int)
        3.16. hash_pvar (str)
        3.17. setid_pvname (str)
        3.18. attrs_pvname (str)
        3.19. ds_ping_method (string)
        3.20. ds_ping_from (string)
        3.21. ds_ping_interval (int)
        3.22. ds_ping_fr_timer (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_retain_latency_stats (int)
        3.29. ds_latency_estimator_alpha (int)
        3.30. ds_hash_size (int)
        3.31. ds_hash_expire (int)
        3.32. ds_hash_initexpire (int)
        3.33. ds_hash_check_interval (int)
        3.34. outbound_proxy (str)
        3.35. ds_default_socket (str)
        3.36. ds_default_sockname (str)
        3.37. ds_ping_socket (str)
        3.38. ds_timer_mode (int)
        3.39. event_callback (str)
        3.40. event_callback_mode (int)
        3.41. ds_attrs_none (int)
        3.42. ds_db_extra_attrs (str)
        3.43. ds_load_mode (int)
        3.44. reload_delta (int)
        3.45. ds_dns_mode (int)
        3.46. ds_dns_interval (int)
        3.47. ds_dns_ttl (int)

   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_select_routes(rules, mode [, limit])
        4.5. ds_next_dst()
        4.6. ds_next_domain()
        4.7. ds_set_dst()
        4.8. ds_set_domain()
        4.9. ds_mark_dst([state])
        4.10. ds_mark_addr(state, setid, uri)
        4.11. ds_list_exists(groupid)
        4.12. ds_is_from_list([groupid [, mode [, uri] ] ])
        4.13. ds_is_active(groupid [, uri])
        4.14. ds_load_update()
        4.15. ds_load_unset()
        4.16. ds_reload()
        4.17. ds_dsg_fetch(setid)
        4.18. ds_dsg_fetch_uri(setid, uri)
        4.19. ds_oc_set_attrs(setid, uri, rval, tval, sval)

   5. RPC Commands

        5.1. dispatcher.set_state
        5.2. dispatcher.set_duid_state
        5.3. dispatcher.list
        5.4. dispatcher.reload
        5.5. dispatcher.ping_active
        5.6. dispatcher.add
        5.7. dispatcher.remove
        5.8. dispatcher.hash
        5.9. dispatcher.oclist

   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
   dispatching 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
   2.2. External libraries or applications

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)
   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. attrs_col (string)
   3.9. force_dst (int)
   3.10. flags (int)
   3.11. use_default (int)
   3.12. xavp_dst (str)
   3.13. xavp_dst_mode (int)
   3.14. xavp_ctx (str)
   3.15. xavp_ctx_mode (int)
   3.16. hash_pvar (str)
   3.17. setid_pvname (str)
   3.18. attrs_pvname (str)
   3.19. ds_ping_method (string)
   3.20. ds_ping_from (string)
   3.21. ds_ping_interval (int)
   3.22. ds_ping_fr_timer (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_retain_latency_stats (int)
   3.29. ds_latency_estimator_alpha (int)
   3.30. ds_hash_size (int)
   3.31. ds_hash_expire (int)
   3.32. ds_hash_initexpire (int)
   3.33. ds_hash_check_interval (int)
   3.34. outbound_proxy (str)
   3.35. ds_default_socket (str)
   3.36. ds_default_sockname (str)
   3.37. ds_ping_socket (str)
   3.38. ds_timer_mode (int)
   3.39. event_callback (str)
   3.40. event_callback_mode (int)
   3.41. ds_attrs_none (int)
   3.42. ds_db_extra_attrs (str)
   3.43. ds_load_mode (int)
   3.44. reload_delta (int)
   3.45. ds_dns_mode (int)
   3.46. ds_dns_interval (int)
   3.47. ds_dns_ttl (int)

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", "/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:passwd@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. attrs_col (string)

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

   Default value is “attrs”.

   Example 1.8. Set “attrs_col” parameter
...
modparam("dispatcher", "attrs_col", "dstattrs")
...

3.9. 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 1.9. Set the “force_dst” parameter
...
modparam("dispatcher", "force_dst", 1)
...

3.10. 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 XAPVs, and use these XAVPs to try next address if
   the current-tried destination fails.

   Default value is “0”.

   Example 1.10. Set the “flags” parameter
...
modparam("dispatcher", "flags", 3)
...

3.11. 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 announcement server saying:
   "the gateways are full, try later".

   Default value is “0”.

   Example 1.11. Set the “use_default” parameter
...
modparam("dispatcher", "use_default", 1)
...

3.12. xavp_dst (str)

   The name of the XAVP which will hold the list with addresses and
   associated properties, in the order they have been selected by the
   chosen algorithm. If use_default is 1, the values of last XAVP
   correspond to the last address in destination set. In case of using
   dispatcher.list file, you have to set the priority field for each
   destination to ensure a particular order there. The first XAVP is the
   current selected destination. All the other addresses from the
   destination set will be added in the XAVP 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 “_dsdst_”.

   Example 1.12. Set the “xavp_dst” parameter
...
modparam("dispatcher", "xavp_dst", "_dsdst_")
...

3.13. xavp_dst_mode (int)

   Control what fields are added to the XAVP specified by xavp_dst
   parameter.

   The addeded fields are:
     * grp - the set id (group id).
     * uri - the URI address.
     * sock - the socket pointer.
     * socket - the socket string - it is added only if xavp_dst_mode has
       bit 2 set (value 2).
     * sockname - the sockname string - it is added only if xavp_dst_mode
       has bit 3 set (value 3).
     * dstid - the destination unique id (in case of call load
       distribution algorithm).
     * attrs - the attributes - they are added if xavp_dst_mode does not
       have the bit 1 set (value 1).

   Default value is “0” (add grp, uri, sock, attr and optionally dstid
   fields).

   Example 1.13. Set the “xavp_dst_mode” parameter
...
    modparam("dispatcher", "xavp_dst_mode", 1)
...
    modparam("dispatcher", "xavp_dst_mode", 2)
...

3.14. xavp_ctx (str)

   The name of the XAVP which will hold some attributes specific to
   dispatcher routing context. The XAVP can hold the next fields: cnt -
   the number of addresses selected for routing.

   Default value is “_dsctx_”.

   Example 1.14. Set the “xavp_ctx” parameter
...
modparam("dispatcher", "xavp_ctx", "_dsctx_")
...

3.15. xavp_ctx_mode (int)

   Control what fields are added to the XAVP specified by xavp_ctx
   parameter. The cnt field is added if xavp_cnt_mode does not have the
   bit 1 set.

   Default value is “0” (add all fields).

   Example 1.15. Set the “xavp_ctx_mode” parameter
...
modparam("dispatcher", "xavp_ctx_mode", 1)
...

3.16. 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 1.16. Use $avp(hash) for hashing:
...
modparam("dispatcher", "hash_pvar", "$avp(hash)")
...

   Example 1.17. Use combination of PVs for hashing:
...
modparam("dispatcher", "hash_pvar", "hash the $fU@$ci")
...

3.17. 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 1.18. Set the “setid_pvname” parameter
...
modparam("dispatcher", "setid_pvname", "$var(setid)")
...

3.18. 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 1.19. Set the “attrs_pvname” parameter
...
modparam("dispatcher", "attrs_pvname", "$var(attrs)")
...

3.19. 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 1.20. Set the “ds_ping_method” parameter
...
modparam("dispatcher", "ds_ping_method", "INFO")
...

3.20. 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 1.21. Set the “ds_ping_from” parameter
...
modparam("dispatcher", "ds_ping_from", "sip:proxy@sip.somehost.com")
...

3.21. 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 1.22. Set the “ds_ping_interval” parameter
...
modparam("dispatcher", "ds_ping_interval", 30)
...

3.22. ds_ping_fr_timer (int)

   If greater than 0, its value is used to set the "fr_timer" value for
   the local transactions created to send out the OPTIONS pings.

   Default value is “0” (not set).

   Example 1.23. Set the “ds_ping_fr_timer” parameter
...
modparam("dispatcher", "ds_ping_fr_timer", 10)
...

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,
   where 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. This means that no probing will be executed at all only
       if flag in config file is set to 8/PROBING (please check
       destination list file syntaxis for more details), it will probe
       only one time at startup or after dispatcher reload.
     * 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. This means that probing will be executed all
       the time, but you can skip some servers with flag 4 in destination
       list file, for example.
     * 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 The estimator can be
   initialized at startup and reload using the attribute latency.
     * 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 :
kamctl rpc dispatcher.list
...
DEST: {
        URI: sip:1.2.3.4
        FLAGS: AX
        PRIORITY: 9
        ATTRS: {
                BODY: latency=24
        }
        LATENCY: {
                AVG: 24.250000 # weighted 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        # maximum 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_retain_latency_stats (int)

   Retain latency stats for existing destinations when reloading from file
   or database.
     * If set to 0, stats for all destinations will be reset on reload.
     * If set to 1, stats for existing destinations will persist across
       reloads.

   Default value is “0”.

   Example 1.30. Set the “ds_retain_latency_stats” parameter
...
modparam("dispatcher", "ds_retain_latency_stats", 1)
...

3.29. ds_latency_estimator_alpha (int)

   The parameter decides how important each latency ping observation is in
   the calculation of the EWMA. The higher the value of alpha, the more
   closely the EWMA tracks the original time series. 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 0.25, use value 250 here.

   Default value is “100 => 0.1”.

   Example 1.31. Set the “ds_latency_estimator_alpha” parameter
...
modparam("dispatcher", "ds_latency_estimator_alpha", 900)
...

3.30. 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 1.32. Set the “ds_hash_size” parameter
...
modparam("dispatcher", "ds_hash_size", 9)
...

3.31. 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 1.33. Set the “ds_hash_expire” parameter
...
modparam("dispatcher", "ds_hash_expire", 3600)
...

3.32. 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 1.34. Set the “ds_hash_initexpire” parameter
...
modparam("dispatcher", "ds_hash_initexpire", 60)
...

3.33. 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 1.35. Set the “ds_hash_check_interval” parameter
...
modparam("dispatcher", "ds_hash_check_interval", 60)
...

3.34. outbound_proxy (str)

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

   By default no outbound proxy is defined.

   Example 1.36. Set the “outbound_proxy” parameter
...
modparam("dispatcher", "outbound_proxy", "sip:outbound.example.com")
...

3.35. 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.

   If parameter "ds_default_sockname" is set, then this parameter is
   ignored.

   Example 1.37. Set the “ds_default_socket” parameter
...
modparam("dispatcher", "ds_default_socket", "udp:192.168.0.125:5060")
...

3.36. ds_default_sockname (str)

   Default socket name 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.

   This parameter is used even if "ds_default_socket" parameter is set
   (this parameter has higher priority).

   Example 1.38. Set the “ds_default_sockname” parameter
...
 listen=udp:1.2.3.4:5060 name "sock1"
...
modparam("dispatcher", "ds_default_sockname", "sock1")
...

3.37. ds_ping_socket (str)

   Default socket to be used for sending ping requests when a gateway has
   no "ping_socket" configured.

   Example 1.39. Set the “ds_ping_socket” parameter
...
modparam("dispatcher", "ds_ping_socket", "udp:192.168.0.125:5060")
...

3.38. 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 1.40. Set the “ds_timer_mode” parameter
...
modparam("dispatcher", "ds_timer_mode", 1)
...

3.39. 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 1.41. 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
...

3.40. event_callback_mode (int)

   Controls when the event_route or the KEMI event callback function are
   executed. If set to 0, they are executed when the destination state
   changes based on OPTIONS keepalives or the use of config functions to
   set the state (e.g., ds_mark_dst(...)). If set to 1, they are executed
   only on state change due to OPTIONS keepalives. If set to 2, the event
   routes will always be executed when a state change occurs, even if no
   previous state exists (for example, on startup or reload).

   Note that event routes are not executed on RPC commands setting the
   destination state.

   Default value is '0'.

   Example 1.42. Set event_callback_mode parameter
...
modparam("dispatcher", "event_callback_mode", 1)
...
-- event callback function implemented in Lua
function ksr_dispatcher_event(evname)
        KSR.info("===== dispatcher module triggered event: " .. evname .. "\n");
        return 1;
end
...

3.41. ds_attrs_none (int)

   If set to 1, "none=yes" is set in the attrs for those records that have
   no attrs value, to ensure that corresponding XAVP fields for records do
   not get mixed up.

   Default value is “0”.

   Example 1.43. Set the “ds_attrs_none” parameter
...
modparam("dispatcher", "ds_attrs_none", 1)
...

3.42. ds_db_extra_attrs (str)

   Set a list of column names to be loaded from database dispatcher table
   and be concatenated to 'attrs' field. The format is:
   'aname1=cname1;aname2=cname2;...;anameN=cnameN'.

   The 'anameX' is the attribute name and 'cnameX' is column name. The
   additional columns must be added to database dispatcher table and their
   type must be a string type (VARCHAR, etc..) or integer type (UNSIGNED
   INT, BIGINT, etc..). These fields can be a convenient way of loading
   IDs, or additional related info into the 'attrs' XAVP when matching a
   dispatcher set.

   Default value is “empty”.

   Example 1.44. Set the “ds_db_extra_attrs” parameter
...
modparam("dispatcher", "ds_db_extra_attrs", "socket=socket;pref=prefix")
...

3.43. ds_load_mode (int)

   If set to 1, the module throws error when failing to add a destination
   address (e.g., invalid URI). If set to 0, it skips the failing address
   and continues with the next ones.

   Default value is “0”.

   Example 1.45. Set the “ds_load_mode” parameter
...
modparam("dispatcher", "ds_load_mode", 1)
...

3.44. reload_delta (int)

   The number of seconds that have to be waited before executing a new
   reload of dispatcher records. By default there is a rate limiting of
   maximum one reload in five seconds.

   If set to 0, no rate limit is configured. Note carefully: use this
   configuration only in tests environments because executing many RPC
   reload commands at the same time can cause unexpected behavior.

   Default value is “5”.

   Example 1.46. Set reload_delta parameter
...
modparam("dispatcher", "reload_delta", 1)
...

3.45. ds_dns_mode (int)

   Specify the how DNS resolving is done for destination addresses.

   It is a bitwise flag and can be set to one or the sum of:
     * 1 - do it at startup and reload (previous behaviour).
     * 2 - do it always when the address is matched with
       ds_is_from_list().
     * 4 - do it startup/reload and refresh on the timer interval
       specified by ds_dns_interval.
     * 8 - do SRV (and NAPTR if enabled in core) query instead of A/AAAA
       lookup. NAPTR is done if protocol and port are not set. SRV is done
       if port is not set.

   Default value is “1”.

   Example 1.47. Set the “ds_dns_mode” parameter
...
modparam("dispatcher", "ds_dns_mode", 2)
...

3.46. ds_dns_interval (int)

   The interval in seconds to periodically refresh the DNS queries for
   destination addresses if ds_dns_mode has value 4 set.

   Default value is “600”.

   Example 1.48. Set the “ds_dns_interval” parameter
...
modparam("dispatcher", "ds_interval_mode", 1800)
...

3.47. ds_dns_ttl (int)

   The interval in seconds to set TTL for DNS results received for queries
   dones inside this module. If 0, this TTL is not set, result and core
   values are used.

   Default value is “0”.

   Example 1.49. Set the “ds_dns_ttl” parameter
...
modparam("dispatcher", "ds_interval_mode", 7200)
...

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_select_routes(rules, mode [, limit])
   4.5. ds_next_dst()
   4.6. ds_next_domain()
   4.7. ds_set_dst()
   4.8. ds_set_domain()
   4.9. ds_mark_dst([state])
   4.10. ds_mark_addr(state, setid, uri)
   4.11. ds_list_exists(groupid)
   4.12. ds_is_from_list([groupid [, mode [, uri] ] ])
   4.13. ds_is_active(groupid [, uri])
   4.14. ds_load_update()
   4.15. ds_load_unset()
   4.16. ds_reload()
   4.17. ds_dsg_fetch(setid)
   4.18. ds_dsg_fetch_uri(setid, uri)
   4.19. ds_oc_set_attrs(setid, uri, rval, tval, sval)

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 are stored in XAVP 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 integer.
          + “0” - hash over callid
          + “1” - hash over from URI.
          + “2” - hash over to URI.
          + “3” - hash over request-URI user.
          + “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' for each address (gateway) in destination
            set. See also the description of the 'weight' attribute in the
            'Special Attributes' section.
          + “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 the parameter
            '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 destinations being active or inactive.
            For example, 100 calls in 3-destinations group with rweight
            params 1/2/1 will be distributed as 25/50/25. If the third
            destination becomes inactive, the distribution is changed to
            33/67/0. If the computation of percentage per destination is
            not an exact integer number, the value is trucated and the
            last destination is used to fill the remaining percentage till
            100.
            Using this algorithm, you can also enable congestion control
            by setting the attribute 'cc=1', when 'cc' is enabled the
            'weight' attribute will also be used to control congestion
            tolerance. When facing congestion the weight of a gateway is
            lowered by 1 for every ms of estimated congestion, a 'rweight'
            value of 50 is recommended. See the example "configuring load
            balancing with congestion detection" below.
            The congestion estimation is done using an Exponentially
            Weighted Moving Average (EWMA). More information about the
            algorithm can be found at
            http://www.itl.nist.gov/div898/handbook/pmc/section3/pmc324.ht
            m. If all the gateways in a set are above their congestion
            threshold(weight), the load distribution is instead done using
            the ratio of estimated congestion ms.
            See also the description of the 'rweight' attribute in the
            'Special Attributes' section.
          + “12” - dispatch to all destinations in setid at once (parallel
            forking). Note that the XAVPs are no longer set with the
            values of the destination records, no re-routing making sense
            in this case. A side effect is that marking the one
            destination as inactive is not possible if the transaction
            fails (which means that all branches failed, or in other
            words, all the destinations were not answering the call).
          + “13” - latency optimized dispatching
            - The algorithm will load balance using round-robin
            prioritizing the gateways with the highest priority.
            - If ds_ping_latency_stats is active the algorithm will adjust
            the priority of the gateway automatically, the priority will
            be lowered by 1 point every time the latency ms is as high as
            the priority.
            - If the attribute 'cc=1' is set, the latency used is
            congestion ms : estimate (current latency ms) - average
            (normal condition latency ms).
            Example 1.50. latency_optimized_dispatching usage
Using this simple formula :
    ADJUSTED_PRIORITY = PRIORITY - (ESTIMATED_LATENCY_MS/PRIORITY)

GATEWAY | PRIORITY | ESTIMATED | ADJUSTED | LOAD
   #    |          |  LATENCY  | PRIORITY | DISTRIBUTION
   1    |    30    |    21     |    30    | 33%
   2    |    30    |    91     |    27    | 0%
   3    |    30    |    61     |    28    | 0%
   4    |    30    |    19     |    30    | 33%
   5    |    30    |    32     |    29    | 0%
   6    |    30    |    0      |    30    | 33%
   7    |    30    |    201    |    24    | 0%


With congestion control the formula becomes :
    CONGESTION_MS = CURRENT_LATENCY_MS - NORMAL_CONDITION_LATENCY_MS
    ADJUSTED_PRIORITY = PRIORITY - (CONGESTION_MS/PRIORITY)
          + “64” - round-robin (next destination) with over load control
            (destination record is skipped based on over load control
            rate).
          + “14” - round-robin (4) if all the destinations in the group
            have the same priority and the priority is greater than 0,
            otherise serial dispatching (8).
          + “X” - if the algorithm is not implemented, the first entry in
            set is chosen.
     * limit - the maximum number of items to be stored in XAVP list for
       further fail-overs (the first selected destination and default
       destination are the first to be put in the list). This can improve
       the performance especially if you are using a large list of
       gateways.

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

   Example 1.51. ds_select_dst usage
...
ds_select_dst("1", "0");
...
$var(a) = 4;
ds_select_dst("1", "$var(a)");
...
ds_select_dst("1", "4", "3");
...

   Example 1.52. configuring load balancing with congestion detection
...
# sample of SQL provisioning statements
INSERT INTO "dispatcher"
VALUES(1,1,'sip:192.168.0.1:5060',0,12,'rweight=50;weight=50;cc=1;','');
INSERT INTO "dispatcher"
VALUES(2,1,'sip:192.168.0.2:5060',0,12,'rweight=50;weight=50;cc=1;','');
...
modparam("dispatcher", "ds_ping_interval", 1) # ping gateways once/second
modparam("dispatcher", "ds_ping_latency_stats", 1) # update congestion metrics
# configure the latency estimator
modparam("dispatcher", "ds_latency_estimator_alpha", 900)
...
if (!ds_select_dst("1", "11")) { # use relative weight based load distribution
...
# sample of output from 'kamctl rpc dispatcher.list'
DEST: {
        URI: sip:192.168.0.1:5060
        FLAGS: AP
        PRIORITY: 12
        ATTRS: {
                BODY: rweight=50;weight=50;cc=1 # configuration values
                DUID:
                MAXLOAD: 0
                WEIGHT: 50
                RWEIGHT: 50
                SOCKET:
                SOCKNAME:
                OBPROXY:
        }
        LATENCY: {
                AVG: 20.104000
                STD: 1.273000
                # estimated congestion is currently 25ms = 45ms(EST) -20ms(AVG)
                EST: 45.005000
                MAX: 132
                TIMEOUT: 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 are stored in XAVP 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 1.53. 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
   XAVP 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 are stored in XAVP 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 1.54. ds_select usage
...
$var(a) = 4;
if(ds_select("1", "$var(a)")) {
    ds_next_domain();
    t_relay();
    exit;
}
...

4.4.  ds_select_routes(rules, mode [, limit])

   The method selects destinations following the rules combining groups
   add algorithms, controlling where the first destination address is
   pushed, and optionally setting a limit of selected addresses.

   Parameters:
     * rules - a string in the format "grp1=alg1;grp2=alg2;...grpN=algN",
       where grpX is an integer number identifying a dispatcher set id and
       algN is a dispatcher algorithm identifier. No white spaces should
       be given in the parameter value. The parameter can contain
       pseudo-variables.
     * mode - control where to push the first selected target address.
       Valid values are: '0', 'd' or 'D' to push the address in
       destination URI; '1', 'r' or 'R' to push the address in R-URI; '2',
       'x' or 'X' to push the address only in the XAVP when failure
       rerouting is enabled. Note that only first character of the
       parameter matters, therefore one can use a more meaningful value
       such as 'ruri' instead of 'r'. The parameter can contain pseudo
       variables.
     * limit - a positive integer value to restrict the number of selected
       target addresses. If it is 0, then no limit is considered. The
       parameter can be a static integer or a variable holding an integer
       value.

   If the bit 2 in 'flags' is set, the rest of the addresses from the
   destination groups are stored in XAVP 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 1.55. ds_select_routes usage
...
$var(alg) = 4;
$var(limit) = 8;
if(ds_select_routes("1=4;2=$var(alg)", "ruri", "$var(limit)")) {
    t_on_failure("REROUTE");
    t_relay();
    exit;
}
failure_route[REROUTE] {
    if(t_check_status("408|5[0-9][0-9]")) {
        if(ds_next_domain()) {
            t_on_failure("REROUTE");
            t_relay();
            exit;
        }
    }
}
...

4.5.  ds_next_dst()

   Takes the next destination address from the corresponding XAVPs and
   sets the dst_uri (outbound proxy address).

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.6.  ds_next_domain()

   Takes the next destination address from the corresponding XAVPs and
   sets the domain part of the request URI.

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.7.  ds_set_dst()

   Takes the current destination address from the corresponding XAVPs and
   sets the dst_uri (outbound proxy address).

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.8.  ds_set_domain()

   Takes the current destination address from the corresponding XAVPs and
   sets the domain part of the request URI.

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

4.9.  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 1.56. ds_mark_dst usage
...
failure_route[tryagain] {
...
   if(t_check_status("500"))
      ds_mark_dst("ip"); # set to inactive and probing
...
}
...

4.10.  ds_mark_addr(state, setid, uri)

   Set the state to the target specified by setid and uri. The parameter
   state can have same value as for ds_mark_dst(). All parameters can
   contain variables.

   This function can be used from ANY_ROUTE.

   Example 1.57. ds_mark_addr usage
...
    ds_mark_addr("ip", "1", "sip:127.0.0.1:5080"); # set to inactive and probing
...

4.11.  ds_list_exists(groupid)

   Function alias: ds_list_exist(groupid)

   Check if a specific group is defined in dispatcher list or database.
     * groupid - A group ID to check.

   It returns true (value 1) if the group exists, or otherwise false (-1
   when the group is not found; -2 when evaluating the parameter fails).

   This function can be used from ANY_ROUTE.

   Example 1.58. ds_list_exists usage
...
if(ds_list_exists("10")) {
    ...
}
...

4.12.  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 dispatcher 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 the parameter is missing, the matching is done with
       ignoring the protocol (value 2). If parameter is 0, all ip, port
       and proto are matched and active status is ignored. If bit one is
       set, then port is ignored. If bit two is set, then protocol is
       ignored. If bit three is set, then state must be active. If bit
       four is set, then socket/sockname be matched. If bit five is set,
       then try to find the most closest target from all dispatcher
       targets with the mandatory ip and combination of local socket,
       protocol, port, the weighted search result is combined from bit
       flags of matched components: ip - 1, port - 2, protocol - 4, local
       socket - 8, the target with the maximum value of flags combination
       will be selected. 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 parameter 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

   Note on default transport (RFC 3263 See 4.1 Selecting a Transport
   Protocol): The dispatcher module normalizes the transport protocol of
   destination URIs according to RFC 3263 default transport rules. When a
   destination in the dispatcher list does not contain an explicit
   ;transport= URI parameter, the module derives and sets the transport
   based on the SIP URI scheme and RFC 3263 resolution procedures (in
   short, UDP for 'sip:' and TCP for 'sips:').

   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 1.59. 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")) {
    ...
}
...

4.13.  ds_is_active(groupid [, uri])

   This function returns true, if there is an active URI in the
   destination group; otherwise false. If the uri parameter is provided,
   then the corresponding destination has to be active.

   Description of parameters:
     * groupid - the group id. The parameter can be an integer or a
       variable holding an integer value.
     * uri (optional) - the URI of the destination. if parameter is empty
       or missing, the any destination is matched.

   This function can be used from ANY_ROUTE.

   Example 1.60. ds_is_active usage
...
if(ds_is_active("10")) {
    ...
}
if(ds_is_active("10", "sip:127.0.0.1:5080")) {
    ...
}
...

4.14.  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.

4.15.  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 1.61. 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();
    }
    ...
}
...

4.16.  ds_reload()

   Reloads the groups and included destinations.

   Name: ds_reload

   Parameters: none

   This function can be used from ANY_ROUTE.

   Example 1.62. ds_reload usage
...
    ds_reload();
...

4.17.  ds_dsg_fetch(setid)

   Sets the destination group id to setid for fetching $dsg(key)
   attributes.

   Parameters: setid - integer or variable holding the set id value

   This function can be used from ANY_ROUTE.

   Example 1.63. ds_dsg_fetch() usage
...
    ds_dsg_fetch("1");
    xinfo("set id: 1 - all: $dsg(count); active: $dsg(active)\n");
...

4.18.  ds_dsg_fetch_uri(setid, uri)

   Sets the destination group id to setid for fetching $dsg(key)
   attributes and the overload-control attributes to the corresponding uri
   record from that group.

   Parameters: setid - integer or variable holding the set id value; uri -
   string or variables holding the SIP URI value.

   This function can be used from ANY_ROUTE.

   Example 1.64. ds_dsg_fetch_uri() usage
...
    ds_dsg_fetch_uri("1", "sip:127.0.0.1:5080");
    xinfo("set id: 1 - all: $dsg(count); active: $dsg(active); $dsg(ocrate)\n");
...

4.19.  ds_oc_set_attrs(setid, uri, rval, tval, sval)

   Sets the overload control rate, time interval limit and sequence number
   for the destination record (setid, uri) following RFC7339
   specifications.

   Description of parameters:
     * setid - the set (group) id. The parameter can be an integer or a
       variable holding an integer value.
     * uri - the URI of the destination.
     * rval - the value of the overload control rate (from 1 to 100) - how
       many times to skip using this destination in 100 selections.
     * tval - time interval limit to apply the overload control rate (in
       milliseconds). If the value is 0 or negative, then the default
       value 500 is used.
     * sval - the sequence number for overload control.

   The parameters can include variables.

   The returns 1 (cfg-true) when the oc attrbutes are udpated for a
   destination record; -1 (cfg-false) when there is an internal error; -2
   (cfg-false) when no destination is updated (e.g., not found or the
   ocseq condition fails).

   This function can be used from ANY_ROUTE.

   Example 1.65. ds_oc_set_attrs() usage
...
    ds_oc_set_attrs("1", "sip:127.0.0.1:5080", "30", "180000", "1");
...

5. RPC Commands

   5.1. dispatcher.set_state
   5.2. dispatcher.set_duid_state
   5.3. dispatcher.list
   5.4. dispatcher.reload
   5.5. dispatcher.ping_active
   5.6. dispatcher.add
   5.7. dispatcher.remove
   5.8. dispatcher.hash
   5.9. dispatcher.oclist

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_ or 'all' to
       update all destinations in the group

   Example:
...
# prototype: kamcmd dispatcher.set_state _state_ _group_ _address_
kamcmd dispatcher.set_state ip 2 sip:127.0.0.1:5080
kamcmd dispatcher.set_state ip 3 all
...

5.2.  dispatcher.set_duid_state

   Sets the state for a destination by matching on 'duid' attribute. The
   first two parameters 'state' and 'group' are the same like for RPC
   command 'dispatcher.set_state'. The third parameter 'duid' is the value
   to be matched against the 'duid' attribute of dispatcher destinations.

   Example:
...
# prototype: kamcmd dispatcher.set_duid_state _state_ _group_ _duid_
kamcmd dispatcher.set_duid_state ip 2 xyz
...

5.3.  dispatcher.list

   Lists the routing groups with destination addresses and corresponding
   attributes.

   Name: dispatcher.list

   Parameters:
     * _rmode_ - (optional) response mode - can be: 'short' to get a
       shorter version of groups and destinations; 'full' to get more
       attributes per destination

   Example:
                kamcmd dispatcher.list
...
DEST: {
        URI: sip:192.168.0.1:5060
        FLAGS: AP
        PRIORITY: 12
}
...

   FLAGS consist out of 2 letters. First letter describe status of
   destination: A-active, I â inactive, T â trying, D â disabled.
   Second letter might be P or X. P is for probing, so AP means
   destination is active and it is tested by SIP options continuously. X
   means that there are no probing or sip pinging. So AX means that
   destination is assumed as active and it is not tested by SIP options.
   DX respectively is disabled destination that is not tested, etc.

5.4.  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

5.5.  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: kamctl rpc dispatcher.ping_active _state_
kamctl rpc dispatcher.ping_active 0
...

5.6.  dispatcher.add

   Add a destination address to the in-memory dispatcher list. Reloading
   the dispatcher will remove any destinations that are only added to the
   in-memory dispatcher list.

   Name: dispatcher.add

   Parameters:
     * _group_: destination group id
     * _address_: address of the destination in the _group_
     * _flags_ (optional): as described in the list file format, default 0
     * _priority_ (optional): as described in the list file format,
       default 0
     * _attrs_ (optional): as described in the list file format, default
       ""

   Example:
...
# prototype: kamcmd dispatcher.add _group_ _address_ _flags_ _priority_ _attrs_
kamcmd dispatcher.add 2 sip:127.0.0.1:5080
kamcmd dispatcher.add 3 sip:127.0.0.1:5075 8
kamcmd dispatcher.add 3 sip:127.0.0.1:5075 0 0 duid=abc;socket=udp:127.0.0.1:506
0
...

5.7.  dispatcher.remove

   Remove a destination address from the in-memory dispatcher list.
   Reloading the dispatcher from file or database will re-add destinations
   that are removed using this command.

   This command will remove all entries that match the group and address.

   Name: dispatcher.remove

   Parameters:
     * _group_: destination group id
     * _address_: address of the destination in the _group_

   Example:
...
# prototype: kamcmd dispatcher.remove _group_ _address_
kamcmd dispatcher.remove 2 sip:127.0.0.1:5080
kamcmd dispatcher.remove 3 sip:127.0.0.1:5075;transport=udp
...

5.8.  dispatcher.hash

   Compute the hash id corresponding to the string parameter values.

   Return the hash id and the corresponding slot, if 'nslots' parameter is
   not 0.

   Name: dispatcher.hash

   Parameters:
     * _nslots_: number of slots
     * _val1_: string value
     * _val2_: (optional) string value

   It can be useful to find what address in a destination group (setid) is
   going to be used when hashing a value or a URI. For a URI, the
   corresponding username and domain have to be provided as _val1_ and
   _val2_. If the URI has a port different than 5060 (or 5061 for TLS),
   then the _val2_ has to be 'domain:port'. The _nslots_ has to be the
   number of addresses in the group (setid). The returned 'slot' value
   represents the index of the address to be used for routing.

   Example:
...
# prototype: kamctl rpc dispatcher.hash _nslots_ _val1_ [_val2_]
kamctl rpc dispatcher.hash 0 alice server.com
kamctl rpc dispatcher.hash 4 bob server.com
...

5.9.  dispatcher.oclist

   List the overload control attributes for the records in a specific
   group.

   Name: dispatcher.oclist

   Parameters:
     * _group_: destination group id

   Example:
...
# prototype: kamcli dispatcher.oclist _group_
kamcli dispatcher.oclist 1
...

6. Installation and Running

   6.1. Destination List File

        6.1.1. Special Attributes
        6.1.2. File Format

   6.2. Kamailio config file

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 - control the mode of using the destination address and
       sending keepalives. The value is a decimal number (inside the text
       file it can be also provided as hexadecimal number). It is a
       bitwise value that can be built using the following flags:
          + 1 (bit at index 0 - 1 <<0) - inactive destination
          + 2 (bit at index 1 - 1 <<1) - 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)
          + 4 (bit at index 2 - 1 <<2) - admin disabled destination
          + 8 (bit at index 3 - 1 <<3) - probing destination (sending keep
            alives);
          + 16 (bit at index 4 - 1 <<4) - skip DNS A/AAAA resolve at
            startup, useful when the hostname of the destination address
            is a NAPTR or SRV record only. Such addresses cannot be
            matched anymore with ds_is_from_list(...).
          + 32 (bit at index 5 - 1 <<5) - no ping to destination
     * 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 between 1 and 100 (inclusive the
       limits), otherwise the destination address is ignored (its weight
       set to 0). The value represents the percent of calls to be sent to
       that gateways. The sum must not exceed 100, otherwise the
       destinations whose weight added to the sum go over 100 are ignored.
       If the sum is less than 100, then the last destination is used to
       fill the missing percentage. See also the description of the
       corresponding algorithm parameter for ds_select_dst().
     * 'rweight' - used for relative weight based load distribution. It
       must be set to a positive integer value between 1 and 100
       (inclusive the limits) otherwise host will be excluded from
       relative weight distribution type - its rweight is set to 0. See
       also the description of the corresponding algorithm parameter for
       ds_select_dst().
     * 'socket' - used to set the sending socket for the gateway. It is
       used for sending the SIP traffic as well as OPTIONS keepalives.
     * 'ping_socket' - used to set the sending socket for ping requests.
       It overwrites the general ds_ping_socket parameter.
     * 'sockname' - used to set by name the sending socket for the
       gateway. It is used for sending the SIP traffic as well as OPTIONS
       keepalives and has priority over 'socket' attribute.
     * 'ping_from' - used to set the From URI in OPTIONS keepalives. It
       overwrites the general ds_ping_from parameter.
     * 'obproxy' - SIP URI of outbound proxy to be used when sending
       pings. It overwrites the general ds_outbound_proxy parameter.
     * 'latency' - latency_stats initialization in ms.
     * 'ocmin' - minimum limit for over load control rate (value between 0
       and 100, default 10).
     * 'ocrate' - over load control rate (value between 0 and 100, default
       100).

6.1.2. File Format

   Line format is:
...
setid(int) destination(sip uri) flags(int,opt) priority(int,opt) attrs(str,opt)
...

   Full line examples:
...
1 sip:127.0.0.1:5080 0 0 duid=abc;socket=udp:127.0.0.1:5060;my=xyz;ping_from=sip
:myproxy.com
1 sip:127.0.0.1:5090 0x8 0 socket=udp:127.0.0.1:5060;prefix=49
...

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

   Example 1.66. dispatcher list file
...
#
# dispatcher destination sets (groups)
#

# line format
# setid(int) destination(sip uri) flags(int,opt) priority(int,opt) attributes(st
r,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 1.67. 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: https://www.kamailio.org
#     - git: http://github.com/kamailio/
#
# Direct your questions about this file to: sr-users@lists.kamailio.org
#
# Refer to the Core CookBook at https://www.kamailio.org/w/documentation/
# 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 "corex.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=$rd;s
rc_ip=$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", "xavp_dst", "_dsdst_")
modparam("dispatcher", "xavp_ctx", "_dsctx_")
modparam("dispatcher", "ds_ping_from", "sip:proxy@kamailio.org")
modparam("dispatcher", "ds_ping_interval", 60)
modparam("dispatcher", "ds_probing_mode", 1)
modparam("dispatcher", "ds_timer_mode", 1)

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


# main request routing logic

request_route {

        # per request initial checks
        route(REQINIT);

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

        # handle retransmissions
        if (!is_method("ACK")) {
                if(t_precheck_trans()) {
                        t_check_trans();
                        exit;
                }
                t_check_trans();
        }

        # handle requests within SIP dialogs
        route(WITHINDLG);

        ### only initial requests (no To tag)

        # 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()) {
                return;
        }

        # sequential request within 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 fa
ils
                }
                route(RELAY);
        }

        if (is_method("SUBSCRIBE") && uri == myself) {
                # in-dialog subscribe requests
                route(PRESENCE);
        }

        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 serv
er
                        t_relay();
                        exit;
                } else {
                        # ACK without matching transaction ... ignore and discar
d.
                        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;
        }
        xdbg("--- SCRIPT: going to <$ru> via <$du> (attrs: $xavp(_dsdst_=>attrs)
)\n");
        t_on_failure("RTF_DISPATCH");
        route(RELAY);
        exit;
}

# Try next destinations 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()) {
                        xdbg("--- SCRIPT: retrying to <$ru> via <$du> (attrs: $x
avp(_dsdst_=>attrs))\n");
                        t_on_failure("RTF_DISPATCH");
                        route(RELAY);
                        exit;
                }
        }
}

...

7. Event routes

   7.1. dispatcher:dst-down
   7.2. dispatcher:dst-up

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.

   Its execution is controlled by event_callback_mode parameter.
...
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.

   Its execution is controlled by event_callback_mode parameter.
...
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 algorithms 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:
     * User Mailing List -
       https://lists.kamailio.org/mailman3/postorius/lists/sr-users.lists.
       kamailio.org/
     * Developer Mailing List -
       https://lists.kamailio.org/mailman3/postorius/lists/sr-dev.lists.ka
       mailio.org/

   E-mails regarding any stable version should be sent to
   <sr-users@lists.kamailio.org> and e-mail regarding development versions
   or GIT snapshots should be sent to <sr-dev@lists.kamailio.org>.

   2.5.

   How can I report a bug?

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