Sunday, 7 May 2017

Monitoring FreeSWITCH with Homer - adding non-SIP events with hepipe.js

FreeSWITCH (from now on FS) provides a very powerful tool to interact with it: the Event Socket (ESL), made available via the mod_event_socket module (

ESL is a TCP socket where applications can connect to, and perform two types of action:
1. Send commands.
2. Subscribe to events.

The applications subscribing to events will receive the expected notifications through the same TCP connection.
A simple protocol and transport made it possible for various libraries in various languages to be written.

Events from FS can serve multiple purposes. In this article I'm interested in monitoring and event correlation.

Homer ( is a widely used, open source tool to monitor RTC infrastructures. It has a multitude of features, but the core is the ability to collect SIP signalling and other events from RTC applications, and perform a form of correlation. In particular, it's able to correlate the SIP signalling involved in a call with other events like RTCP reports or log lines associated to the same call.

While FS, through the sofia module, has native support for transmitting SIP signalling to Homer, the acquisition of other events can happen by collecting these events from the ESL, filtering them, and sending them to Homer with the proper formatting.

This is what hepipe.js ( does. hepipe.js is a simple nodejs application that is able to:
- connect to FS via ESL
- subscribe to specific event categories
- format the events into HEP messages. HEP is a binary protocol used to transmit data to Homer.

hepipe.js is easy to use:
- Clone it
- Run 'sudo npm install' to install the required dependencies
- Set configuration
- Run it ('sudo node hepipe.js', or 'sudo nodejs hepipe.js')

The configuration is organized in "modules", and for this example you'll have to configure at a minimum the esl module and the hep module.
Edit a config.js file in the same folder as hepipe.js with something like:

var config = {
  hep_config: {
    debug: true,
    HEP_SERVER: '',
    HEP_PORT: 9060
  esl_config: {
    debug: true,
    ESL_SERVER: '',
    ESL_PORT: 8021,
    ESL_PASS: 'ClueCon',
    HEP_PASS: 'multipass',
    HEP_ID: 2222,
    report_call_events: true,
    report_rtcp_events: true,
    report_qos_events: true

module.exports = config;

This will configure the hep module to send data to a Homer instance listening on UDP, IP address, port 9060, and will try to connect to a FS' ESL on localhost, via TCP port 8021 and using the default password. See also other configuration examples in the examples/ folder.

Please note that the ESL requires at least two levels of authorization: a password and an ACL. You can check conf/autoload_config/event_socket.conf.xml in the FS configuration folder to ensure the ACL in use, if any, is compatible to the source IP address of hepipe.js when connecting to FS.

Once config.js will be ready, launch hepipe.js and look at the events being sent to Homer.
Note that you can filter out event types by setting to false some of these:
    report_call_events: true,
    report_rtcp_events: true,
    report_qos_events: true

Assuming FS is configured to send SIP signalling to the same Homer instance, you'll be able to see, associated to its SIP call flows, also the events captured by hepipe.js.

See for example below log lines created by FS, sent to Homer, and then presented together with the SIP signalling in Homer:


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