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mod_event_socket is a TCP based interface to control FreeSWITCH. The default values are to bind to port 8021 and the default password is ClueCon. See the Configuration section below for a note on when to use instead of

The module operates in two modes, inbound and outbound. Those terms are relative to FreeSWITCH.


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Inbound mode means you run your applications (in whatever languages) as clients and connect to the FreeSWITCH server to invoke commands and control FreeSWITCH.


In inbound mode, your application (Client A, Client B: Python, Perl, etc) connects to the FreeSWITCH™ server on the given port and sends commands, as shown in the above diagram. The rest of this document is biased toward this inbound mode, though there is a lot of overlap with outbound mode. Using inbound socket connections you can check status, make outbound calls, etc.

If you would like to handle incoming calls using inbound mode, you should add the park command to your dialplan. Otherwise the dialplan might complete executing before your client can send commands to the event socket.


Outbound mode means you make a daemon (with whatever language) and then have FS connect to it. You add an extension to the dialplan and put <action application="socket" data="ip:port sync full"/> and create a script that runs on that ip:port and answer, playback and everything else you need on the script. Since revision git-8c794ac on 14/03/2012 you can connect to IPv6 addresses. When using IPv6 addresses the port parameter is required: <action application="socket" data="::1:8021"/> connects to ::1 on port 8021. Since this revision hostnames resolving to IPv6 addresses can be used.

In outbound mode, also known as the "socket application" (or socket client), FreeSWITCH™ makes outbound connections to another process (similar to Asterisk's FAGI model). Using outbound connections you can have FreeSWITCH™ call your own application(s) when particular events occur. See Event Socket Outbound for more details regarding things specific to outbound mode.


First enable the mod_event_socket module in modules.conf.xml (in a system compiled from source this is located in /usr/local/freeswitch/conf/autoload_configs/modules.conf.xml)

By default the module is enabled but restricted to localhost by the settings specified below.

The module settings can be changed in the event_socket.conf.xml file (in a system compiled from source this is located in /usr/local/freeswitch/conf/autoload_configs/event_socket.conf.xml):

<configuration name="event_socket.conf" description="Socket Client">
    <param name="listen-ip" value=""/>
    <param name="listen-port" value="8021"/>
    <param name="password" value="ClueCon"/>

The default settings allow socket connections only from the local host. To allow connections from any host on the network, use instead of the default

<configuration name="event_socket.conf" description="Socket Client">
    <!-- Allow socket connections from any host -->
    <param name="listen-ip" value=""/>
    <param name="listen-port" value="8021"/>
    <param name="password" value="ClueCon"/>


Since revision git-8c794ac on 14/03/2012 you can listen on IPv6 addresses. On dual stack hosts you can listen on both IPv4 and IPv6 addresses using:

<configuration name="event_socket.conf" description="Socket Client">
    <!-- Allow socket connections from any host -->
    <param name="listen-ip" value="::"/>
    <param name="listen-port" value="8021"/>
    <param name="password" value="ClueCon"/>


Access lists can be named in acl.conf.xml and enabled in event_socket.conf.xml or allow ip ranges directly in event_socket.conf.xml

This is recommended for enhanced security if you allow ESL connections from another machine.

<param name="apply-inbound-acl" value="<acl_list|cidr>"/>


<param name="apply-inbound-acl" value=""/>


Multiple apply-inbound-acl params will not work.

As of 1.6 you must supply an ACL. In order to allow all IPs you can use to event_socket.conf.xml

Example Clients

The idea is that you would write your own client, but here are some examples.


Liverpie (language independent IVR proxy) is a free little piece of software, written in Ruby, that talks to FreeSWITCH on one side, and to any web application on the other, regardless of language, platform etc. It translates FreeSWITCH mod_socket dialogue into HTTP talk (embedding various parameters in HTTP headers), so you can write your own http-speaking finite state machine and hook it to FreeSWITCH via Liverpie. Note also that Liverpie expects the response in YAML so you can save yourself the pain of providing XML if you are comfortable with Liverpie doing the translation.

Find Liverpie here:

Telnet Client

telnet to port 8021 and enter "auth ClueCon" as password to authenticate. From here you can send any of the commands listed in this document. Note that you need to provide a double empty line after the command so it processed.

Ruby Libraries

Python Libraries

  • Twisted based client and example can be found in the the scripts/python/freepy directory of the FreeSWITCH source code
  • eventsocket: an alternative twisted protocol which supports inbound and outbound methods + examples
  • PySWITCH: one more library for Python and Twisted programmers. It has extensive support for FreeSWITCH API, bgapi and Dialplan Tools.
  • greenswitch: This is an implementation of Event Socket Protocol using gevent greenlets. It is already in production and processing hundreds of calls per day.
  • switchio: asyncio powered cluster control which leverages modern Python's new native coroutines. Comes with a full-blown auto-dialer originally built for stress testing.

PHP Client

Website based PHP example PHP Event Socket

Another example in PHP : freeswitcheventsocketlistener

Java Client Libraries

Java_ESL describes several options for using Java to communicate with the ESL.

Javascript / Node.js library

  • Node-esl module available on GitHub and on npm. Provides support for both Inbound and Outbound connections, a Server helper for multiple Outbound connections, and implements the Event Socket Library interface. Examples can be found in the examples directory of the source.

.NET Client library

Support is included in tree for building under Windows. See libs/esl/managed managed_esl.201x.

There is a sample application included named ManagedEslTest. This will demonstrate how the start a simple inbound example as provided but also shows the other modes as well.

The managed portions are platform neutral but the esl swig wrapper (the ESL project in the managed solution) is platform dependent and must be built for the intended platform. You must also have previously built the main FreeSWITCH project as the native esl library is included from there otherwise you will receive a esl.lib not found error.

[1] AgbaraVOIP .NET Client


Go Client library (golang)

These Go libraries support both inbound and outbound event socket connections.


Command Documentation

The following section aims at documenting all commands that can be sent. This section is a work in progress.


Send an api command (blocking mode)

Api commands are documented in the mod_commands [old_wiki] section.


api originate sofia/ 1000   # connect to extension 1000
api sleep 5000


Send an api command (non-blocking mode) this will let you execute a job in the background and the result will be sent as an event with an indicated uuid to match the reply to the command)

The same API commands available as with the api command, however the server returns immediately and is available for processing more commands.

Example return value:

Content-Type: command/reply
Reply-Text: +OK Job-UUID: c7709e9c-1517-11dc-842a-d3a3942d3d63

When the command is done executing, FreeSWITCH fires an event with the result and you can compare that to the Job-UUID to see what the result was. In order to receive this event, you will need to subscribe to BACKGROUND_JOB events.

If you want to set your own custom Job-UUID over plain socket:

bgapi status
Job-UUID: d8c7f660-37a6-4e73-9170-1a731c442148


Content-Type: command/reply
Reply-Text: +OK Job-UUID: d8c7f660-37a6-4e73-9170-1a731c442148
Job-UUID: d8c7f660-37a6-4e73-9170-1a731c442148


Tells FreeSWITCH not to close the socket connection when a channel hangs up. Instead, it keeps the socket connection open until the last event related to the channel has been received by the socket client.



Disable socket lingering. See linger above.



Enable or disable events by class or all (plain or xml or json output format)

The event command are used to subscribe on events from FreeSWITCH. You may specify any number events on the same line, they should be separated with space.

The events are listed in the Event List page.



Subsequent calls to 'event' won't override the previous event sets. Supposing, you've first registered for DTMF

  event plain DTMF 

then you may want to register for CHANNEL_ANSWER also, it is enough to give

  event plain CHANNEL_ANSWER

and you will continue to receive DTMF along with CHANNEL_ANSWER, later one doesn't override the previous.

Special Case - 'myevents'

The 'myevents' subscription allows your inbound socket connection to behave like an outbound socket connect. It will "lock on" to the events for a particular uuid and will ignore all other events, closing the socket when the channel goes away or closing the channel when the socket disconnects and all applications have finished executing.


  myevents <uuid>

Once the socket connection has locked on to the events for this particular uuid it will NEVER see any events that are not related to the channel, even if subsequent event commands are sent. If you need to monitor a specific channel/uuid and you need watch for other events as well then it is best to use a filter.

You can also set the event format (plain, xml or json):


  myevents plain <uuid>
  myevents json <uuid>
  myevents xml <uuid>

The default format is plain.


The divert_events switch is available to allow events that an embedded script would expect to get in the inputcallback to be diverted to the event socket.


  divert_events on
  divert_events off

An inputcallback can be registered in an embedded script using setInputCallback(). Setting divert_events to "on" can be used for chat messages like gtalk channel, ASR events and others.

Read more


Specify event types to listen for. Note, this is not a filter out but rather a "filter in," that is, when a filter is applied only the filtered values are received. Multiple filters on a socket connection are allowed.


  filter <EventHeader> <ValueToFilter>


The following example will subscribe to all events and then create two filters, one to listen for HEARTBEATS and one to listen for CHANNEL_EXECUTE events.

Now only HEARTBEAT and CHANNEL_EXECUTE events will be received. You can filter on any of the event headers. To filter for a specific channel you will need to use the uuid:

  filter Unique-ID d29a070f-40ff-43d8-8b9d-d369b2389dfe 

This method is an alternative to the myevents event type. If you need only the events for a specific channel then use myevents, otherwise use a combination of filters to narrow down the events you wish to receive on the socket.

To filter multiple unique IDs, you can just add another filter for events for each UUID. This can be useful for example if you want to receive start/stop-talking events for multiple users on a particular conference.

  filter plain all
  filter plain CUSTOM conference::maintenance
  filter Unique-ID $participantB
  filter Unique-ID $participantA
  filter Unique-ID $participantC


This will give you events for Participant A,B and C on any conference. To receive events for all users on a conference you can use something like:

filter Conference-Unique-ID $ConfUUID

You can filter on any of the parameters you get in a freeSWITCH event:

  filter plain all
  filter call-direction Inbound
  filter Event-Calling-File mod_conference.c
  filter Conference-Unique-ID $ConfUUID


You can use them individually or compound them depending on whatever end result you desire for the type of events you want to receive

filter delete

Specify the events which you want to revoke the filter. filter delete can be used when some filters are applied wrongly or when there is no use of the filter.


  filter delete <EventHeader> <ValueToFilter>


  filter delete Event-Name HEARTBEAT

Now, you will no longer receive HEARTBEAT events. You can delete any filter that is applied by this way.

  filter delete Unique-ID d29a070f-40ff-43d8-8b9d-d369b2389dfe

This is to delete the filter which is applied for the given unique-id. After this, you won't receive any events for this unique-id.

  filter delete Unique-ID

This deletes all the filters which are applied based on the unique-id.


Send an event into the event system (multi line input for headers)

sendevent <event-name>  


For MWI you make the FreeSWITCH event SWITCH_EVENT_MESSAGE_WAITING with headers:

MWI-Messages-Waiting (yes/no)
MWI-Message-Account <any sip url you want>
MWI-Voice-Message x/y (a/b)
read/unread (urgent read/urgent unread)

Example of sendevent to switch phone MWI led (tested on yealink)

No Message:

MWI No Message


Some Message:

MWI With Message


To have Snom phones reread their settings from the settings server you can use:




Example of sendevent with a message body, the length of the body is specified by content-length:



SIP Proxy Example

To send through a proxy, use the event headers: contact-uri, to-uri, and from-uri
In this example, the SIP proxy is and the UA can be reached at 1002@


Another example with a notify:

NOTIFY Example


Results in a packet like this:




Example for Sipura/Linksys/Cisco phone or ATA to resync config with a specified profile URL:

Cisco Resync



Results in a packet like this:

Cisco Resync result



  • If 'Auth Resync-Reboot' is set to yes (default) in the phone than you have to specify the reverse-auth-user and reverse-auth-pass fields
  • If you only put 'event-string: resync' in the body then the unit will use its stored profile URI

Example usage for CSTA event:

CSTA Event



Example of send event with a MESSAGE and a message body, the length of the body is specified by content-length:

Send Message


Results in a packet like this:

Send Message result



To display a text message on a Snom 370 or Snom 820 the message must be of type "text/plain".


Some phones require authentication for NOTIFY requests. FS can respond to a digest challenge if reverse authentication credentials are supplied for the user. See: XML User Directory

I've not found any documentation of any additional event headers, hopefully someone else with add that information. The events themselves can be found here: Event List


Something that was undocumented but is supported; SIP INFO messages can be sent to every IP you need.





Send a message to the call of given uuid (call-command execute or hangup), see examples below.

Send message are used to send messages that controls the behavior of FreeSWITCH. You need to provide a uid (the unique id for each call/session).

originate a call directly to park by making an ext the ext part of the originate command &park()

IMPORTANT! All sendmsg commands must be followed by 2 returns.

Since messaging format is similar to RFC2882 if you are using any libraries that follow the line wrapping recommendation of RFC 2822 make sure that you disable line wrapping as FreeSWITCH will ignore wrapped lines.





The first command is Call-Command, it can do one of the following subcommands:


Execute is used to execute applications. Check the Dialplan XML section for more information about all commands.

The format should be:

Execute format



This alternate format can be used for app args that are truncated by the module's 2048 octet limit:


If you would like to correlate the CHANNEL_EXECUTE and CHANNEL_EXECUTE_COMPLETE events that are generated when the command you send using sendmsg is executed you can add an Event-UUID header with a UUID you specify. In the corresponding events, the UUID will be in the Application-UUID header. If you do not specify an Event-UUID, Freeswitch will generate a UUID for the Application-UUID.


Event-UUID: 22075ce5-b67b-4f04-a6dd-1726ec14c8bf


Hangup the call.


sendmsg <uuid>
call-command: hangup
hangup-cause: <one of the causes listed below>

Additional information


Unicast is used to hook up spandsp for faxing over a socket.

Additional information from Brian:

Brian's note

"That is a nice way for a script or app that uses the socket interface to get at the media. It's good because then spandsp isn't living inside of FreeSWITCH and it can run on a box sitting next to it. It scales better."

unicast example



No description.

sendmsg <uuid>
call-command: nomedia
nomedia-uuid: <noinfo>



Close the socket connection.


auth <password>


log <level>

Enable log output. Levels same as the console.conf values



Disable log output previously enabled by the log command


nixevent <event types | ALL  | CUSTOM custom event sub-class>

Suppress the specified type of event. Useful when you want to allow 'event all' followed by 'nixevent <some_event>' to see all but 1 type of event.



Disable all events that were previously enabled with event.

See Also

Authentication: Some phones require authentication for NOTIFY requests. FS can respond to a digest challenge if reverse authentication credentials are supplied for the user. See: XML_User_Directory_Guide#reverse_authentication