Tag Archives: ESL

Originating calls in FreeSWITCH

Through fs_cli you can orignate calls from FreeSWITCH.

At the CLI you can use the originate command to start a call, this can be used for everything from scheduled wake up calls, outbound call centers, to war dialing.

For example, what I’m using:

originate sofia/external/[email protected]:5061 61399999995 XML default
  • originate is the command on the FS_CLI
  • sofia/external/[email protected]:5061 is the call URL, with the application (I’m using mod_sofia, so sofia), the Sofia Profile (in my case external) and the SIP URI, or, if you have gateways configured, the to URI and the gateway to use.
  • 6139999995 is the Application
  • XML is the Dialplan to reference
  • default is the Context to use

But running this on the CLI is only so useful, we can use an ESL socket to use software to connect to FreeSWITCH’s API (Through the same mechanism fs_cli uses) in order to programmatically start calls.

But to do that first we need to expose the ESL API for inbound connections (Clients connecting to FreeSWITCH’s ESL API, which is different to FreeSWITCH connecting to an external ESL Server where FreeSWITCH is the client).

We’ll need to edit the event_socket.conf.xml file to define how this can be accessed:

<configuration name="event_socket.conf" description="Socket Client">
    <param name="nat-map" value="false"/>
    <param name="listen-ip" value=""/>
    <param name="listen-port" value="8021"/>
    <param name="password" value="yoursecretpassword"/>
    <param name="apply-inbound-acl" value="lan"/>
    <param name="stop-on-bind-error" value="true"/>

Obviously you’ll need to secure this appropriately, good long password, and tight ACLs.

You may notice after applying these changes in the config, you’re no longer able to run fs_cli and access FreeSWITCH, this is because FreeSWITCH’s fs_cli tool connects to FreeSWITCH over ESL, and we’ve just changed tha parameters. You should still be able to connect by specifying the IP Address, port and the secret password we set:

fs_cli --host= --password=yoursecretpassword --port=8021

This also means we can run fs_cli from other hosts if permitted through the ACLs (kinda handy for managing larger clusters of FreeSWITCH instances).

But now we can also connect a remote ESL client to it to run commands like our Originate command to setup calls, I’m using GreenSwitch with ESL in Python:

import gevent
import greenswitch
import sys
#import Fonedex_TelephonyAPI
import uuid

import logging

esl_server_host = ""
logging.debug("Originating call to " + str(destination) + " from " + str(source))
logging.debug("Routing the call to " + str(dialplan_entry))
fs = greenswitch.InboundESL(host=str(esl_server_host), port=8021, password='yoursecretpassword')
      logging.debug("Connected to ESL server at " + str(esl_server_host))
      raise SystemError("Failed to connect to ESL Server at " + str(esl_server_host))

r = fs.send('bgapi originate {origination_caller_id_number=' + str(source) + '}sofia/external/' + str(destination) + '@ default XML')

And presto, a call is originated!

FreeSWITCH + ESL = Programmable Voice

No great secret, I’m a big Python fan.

Recently I’ve been working on a few projects with FreeSWITCH, and looking at options for programmatically generating dialplans, instead of static XML files.

Why not Static XML?

So let’s say I define a static XML dialplan.

It works great, but if I want to change the way a call routes I need to do it from the dialplan,

That’s not ideal if you’re using a distributed cluster of FreeSWITCH instances, or if you want to update on the fly.

Static XML means we have to define our dialplan when setting up the server, and would have to reconfigure the server to change it.

So what about mod_xml_curl?

When I’ve done this in the past I’ve relied on the mod_xml_curl module.

mod_xml_curl gets the XML dialplan using Curl from a web server, and so you setup a web server using Flask/PHP/etc, and dynamically generate the dialplan when the call comes in.

This sounds good, except you can’t update it on the fly.

mod_xml_curl means call routing decisions are made at the start of the call, and can’t be changed midway through the call.

So what’s ESL?

ESL is the Event Socket Library, essentially a call comes in, an ESL request is made to an external server.

For each step in the dialplan, an ESL request will be sent to the external server which tells it to do,

ESL allows us to use all FreeSWITCH’s fantastic modules, without being limited as to having to perform the call routing logic in FreeSWITCH.

So how do I use ESL?

You’ll need two create an ESL server,

Luckily there’s premade examples for popular languages;

Once you’ve got a basic server defined we’ll need to put some config in our XML Dialplan to say “transfer all your thinking to ESL!”;

<!-- Send everything that's numbers to ESL for Processing --> 
    <extension name="esl_route">
      <condition field="destination_number" expression="^\d*$">
        <action application="socket" data=""/>
        <action application="log" data="ERR Made it past ESL - Play error."/>
        <action application="playback" data="ivr/ivr-call_cannot_be_completed_as_dialed"/>

In the above example my ESL server is on / port 5000.

Now any calls coming in will be transfered to ESL and where it goes from there, is something you define in your prefered programming language.

In the next post I’ll cover how I’ve been addressing this using Python and Greenswitch.