Copyright © 2004 FhG FOKUS
Copyright © 2005 Voice Sistem
Copyright © 2010 Daniel-Constantin Mierla (asipto.com)
Table of Contents
list_file (string)
db_url (string)
table_name (string)
setid_col (string)
destination_col (string)
flags_col (string)
priority_col (string)
force_dst (int)
flags (int)
use_default (int)
dst_avp (str)
grp_avp (str)
cnt_avp (str)
dstid_avp (str)
attrs_avp (str)
hash_pvar (str)
setid_pvar (str)
ds_ping_method (string)
ds_ping_from (string)
ds_ping_interval (int)
ds_probing_threshhold (int)
ds_ping_reply_codes (string)
ds_probing_mode (int)
ds_hash_size (int)
ds_hash_expire (int)
ds_hash_initexpire (int)
ds_hash_check_interval (int)
List of Examples
ds_select_dst usageds_mark_dst usageds_mark_dst usageds_load_unset usageTable of Contents
list_file (string)
db_url (string)
table_name (string)
setid_col (string)
destination_col (string)
flags_col (string)
priority_col (string)
force_dst (int)
flags (int)
use_default (int)
dst_avp (str)
grp_avp (str)
cnt_avp (str)
dstid_avp (str)
attrs_avp (str)
hash_pvar (str)
setid_pvar (str)
ds_ping_method (string)
ds_ping_from (string)
ds_ping_interval (int)
ds_probing_threshhold (int)
ds_ping_reply_codes (string)
ds_probing_mode (int)
ds_hash_size (int)
ds_hash_expire (int)
ds_hash_initexpire (int)
ds_hash_check_interval (int)
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, like: round-robin, weight based load balancing, call load distribution, hashing over SIP message attributes.
The module can be used as a stateless load balancer, it does not depend on any call state tracing module. It requires TM module if you enable auto-discovery of active/inactive gateways.
It is very lightweight, therefore suitable for handling heavy SIP traffic. Its small footprint and ability to load balancing rules from a text plain file makes it suitable for embedded systems.
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. .
Path to the file with destination sets.
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")
...
If you want to load the sets 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")
...
If you want to load the sets 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")
...
The column's name in the database storing the gateway's group id.
Default value is “setid”.
The column's name in the database storing the destination's sip uri.
Default value is “destination”.
Example 1.5. Set “destination_col” parameter
...
modparam("dispatcher", "destination_col", "uri")
...
The column's name in the database storing the flags for destination uri.
Default value is “flags”.
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")
...
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”.
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 the failover support is enabled. The functions exported by the module will store the rest of addresses from the destination set in AVP, and use these AVPs to contact next address when the current-tried fails.
Default value is “0”.
If the parameter is set to 1, the last address in destination set is used as last option to send the message. For example, it is good when wanting to send the call to an anouncement server saying: "the gateways are full, try later".
Default value is “0”.
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.
You must set this parameter if you want to do load balancing fail over.
Default value is “null” - don't add AVPs.
The name of the avp storing the group id of the destination set. Good to have it for later usage or checks.
You must set this parameter if you want to do load balancing fail over.
Default value is “null” - don't add AVP.
The name of the avp storing the number of destination addresses kept in dst_avp avps.
You must set this parameter if you want to do load balancing fail over.
Default value is “null” - don't add AVP.
The name of the avp storing the destination unique ID used for call load based dispatching.
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", "$avp(dsdstid)")
...
The name of the avp storing destination's attributes value.
Default value is “null” - don't add AVP.
Example 1.15. Set the “attrs_avp” parameter
...
modparam("dispatcher", "attrs_avp", "$avp(dsattrs)")
...
String with PVs used for the hashing algorithm 7.
You must set this parameter if you want do hashing over custom message parts.
Default value is “null” - disabled.
Example 1.16. Use $avp(i:273) for hashing:
...
modparam("dispatcher", "hash_pvar", "$avp(i:273)")
...
Example 1.17. Use combination of PVs for hashing:
...
modparam("dispatcher", "hash_pvar", "hash the $fU@$ci")
...
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_pvar” parameter
...
modparam("dispatcher", "setid_pvar", "$var(setid)")
...
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 1.19. Set the “ds_ping_method” parameter
...
modparam("dispatcher", "ds_ping_method", "INFO")
...
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 1.20. Set the “ds_ping_from” parameter
...
modparam("dispatcher", "ds_ping_from", "sip:proxy@sip.somehost.com")
...
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 1.21. Set the “ds_ping_interval” parameter
...
modparam("dispatcher", "ds_ping_interval", 30)
...
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 1.22. Set the “ds_probing_threshhold” parameter
...
modparam("dispatcher", "ds_probing_threshhold", 10)
...
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 ser config framework.
Default value is “” (only 200 OK is accepted).
Example 1.23. Set the “ds_ping_reply_codes” parameter
...
modparam("dispatcher", "ds_ping_reply_codes", "class=2;code=403;code=488;class=3")
...
Controls what gateways are tested to see if they are reachable. If set to 0, only the gateways with state PROBING are tested; if set to 1, all gateways are tested; if set to 2, only gateways in inactive state with probing mode set are tested. If set to 1 and there is a failure of keepalive to an active gateway, then it is set to TRYING state.
Default value is “0”.
Example 1.24. Set the “ds_probing_mode” parameter
...
modparam("dispatcher", "ds_probing_mode", 1)
...
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”.
Expiration time in seconds to remove the load on a destination if no BYE was received meanwhile.
Default value is “7200”.
Example 1.26. Set the “ds_hash_expire” parameter
...
modparam("dispatcher", "ds_hash_expire", 3600)
...
The method selects a destination from addresses set.
Meaning of the parameters is as follows:
set - the id of the set from where to pick up destination address. It is the first column in destination list file. The parameter can be an integer or a variable holding an interger.
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 (using rand()).
“7” - hash over the content of PVs string. Note: This works only when the parameter hash_pvar is set.
“8” - use first destination (good for failover).
“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.
“X” - if the algorithm is not implemented, the first entry in set is chosen.
If the bit 2 in 'flags' is set, the rest of the addresses from the destination set is stored in AVP list. You can use 'ds_next_dst()' to use next address to achieve serial forking to all possible destinations.
This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.
Example 1.29. ds_select_dst usage
...
ds_select_dst("1", "0");
...
$var(a) = 4;
ds_select_dst("1", "$var(a)");
...
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. 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.
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.
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.
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 running or down.
This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.
Example 1.30. ds_mark_dst usage
...
failure_route[tryagain] {
...
if(t_check_status("500"))
ds_mark_dst("ip"); # set to inactive and probing
...
}
...
This function returns true, if the current request comes from a host in the given group of the dispatcher-list; otherwise false.
Parameter groupid is optional, when it is missing, then the matching will be done against all addresses in all groups. Upon a match, the 'grp_avp' will be set to groupid of matching address.
This function can be used from ANY_ROUTE.
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.
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 1.32. 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();
}
...
}
...
Sets the status for a destination address (can be use to mark the destination as active or inactive).
Name: ds_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_
MI FIFO Command Format:
:ds_set_state:_reply_fifo_file_ _state_ _group_ _address_ _empty_line_
It lists the groups and included destinations.
Name: ds_list
Parameters: none
MI FIFO Command Format:
:ds_list:_reply_fifo_file_ _empty_line_
It 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: ds_reload
Parameters: none
MI DATAGRAM Command Format:
":ds_reload:\n."
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: sercmd dispatcher.set_state _state_ _group_ _address_ sercmd dispatcher.set_state ip 2 sip:127.0.0.1:5080 ...
It lists the groups and included destinations.
Name: dispatcher.list
Parameters: none
Example:
sercmd dispatcher.list
It 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
sercmd dispatcher.reload
Each destination point must be on one line. First token is the set id (an integer value), followed by destination address (s string value in SIP URI format).
Optionally, these fields can be followed by:
flags: 1 - destination inactive, 2 - destination in probing mode -- you can do bitwise OR to set both flags
priority: sets the priority in destination list (based on it is done the initial ordering inside the set)
attributes: extra filed in form of name1=value1;...;nameN=valueN. There are some predefined names that are used of weight and call load dispatching.
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;my=xyz ...
For database, each element of a line resides in a different column. Next is a dispatcher.list file example:
Example 1.33. dispatcher list file
... # $Id$ # dispatcher destination sets # # line format # setit(int) destination(sip uri) flags(int,opt) priority(int,opt) attributes(str,opt) # proxies 2 sip:127.0.0.1:5080 2 sip:127.0.0.1:5082 # gateways 1 sip:127.0.0.1:7070 1 sip:127.0.0.1:7072 1 sip:127.0.0.1:7074 ...
Next picture displays a sample usage of dispatcher.
Example 1.34. 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 (OpenSER) SIP Server v3.2
# - web: http://www.kamailio.org
# - git: http://sip-router.org
#
# 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
#
####### 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_k/:/usr/local/lib/kamailio/modules/"
loadmodule "db_mysql.so"
loadmodule "mi_fifo.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 "mi_rpc.so"
loadmodule "acc.so"
loadmodule "dispatcher.so"
# ----------------- setting module-specific parameters ---------------
# ----- mi_fifo params -----
modparam("mi_fifo", "fifo_name", "/tmp/kamailio_fifo")
# ----- 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", 1)
modparam("acc", "failed_transaction_flag", 3)
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",
"mysql://openser:openserro@localhost/openser")
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", "$avp(AVP_CNT)")
####### Routing Logic ########
# main request routing logic
route {
# per request initial checks
route(REQINIT);
# handle requests within SIP dialogs
route(WITHINDLG);
### only initial requests (no To tag)
# CANCEL processing
if (is_method("CANCEL"))
{
if (t_check_trans())
t_relay();
exit;
}
t_check_trans();
# record routing for dialog forming requests (in case they are routed)
# - remove preloaded route headers
remove_hf("Route");
if (is_method("INVITE|SUBSCRIBE"))
record_route();
# account only INVITEs
if (is_method("INVITE"))
{
setflag(1); # do accounting
}
# handle presence related requests
route(PRESENCE);
# handle registrations
route(REGISTRAR);
if ($rU==$null)
{
# request with no Username in RURI
sl_send_reply("484","Address Incomplete");
exit;
}
# dispatch destinations
route(DISPATCH);
route(RELAY);
}
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(1); # do accounting ...
setflag(3); # ... 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");
return;
}
# Sample 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;
}
}
}
...
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");
}
...
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");
}
...
|
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 http://www.kamailio.org/. |
|
|
2.4. |
Where can I post a question about this module? |
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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
If you want to keep the mail private, send it to |
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2.5. |
How can I report a bug? |
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Please follow the guidelines provided at: http://sip-router.org/tracker |