SIPREC Module

Răzvan Crainea

OpenSIPS Solutions

Edited by

Răzvan Crainea


Table of Contents

1. Admin Guide
1.1. Overview
1.2. How it works
1.3. Media Handling
1.4. SRS Failover
1.5. Limitations
1.6. Dependencies
1.6.1. OpenSIPS Modules
1.6.2. External Libraries or Applications
1.7. Exported Parameters
1.7.1. media_port_min (integer)
1.7.2. media_port_max (integer)
1.7.3. skip_failover_codes (string)
1.8. Exported Functions
1.8.1. siprec_start_recording([srs [, group [, caller [, callee [, rtpproxy_set] ]]]])

List of Examples

1.1. Set media_port_min parameter
1.2. Set media_port_max parameter
1.3. Set skip_failover_codes parameter
1.4. Use siprec_start_recording() function with a single SRS
1.5. Use siprec_start_recording() function with multiple SRS servers

Chapter 1. Admin Guide

1.1. Overview

This module provides the means to do calls recording using an external recorder - the entity that records the call is not in the media path between the caller and callee, but it is completely separate, thus it can not affect by any means the quality of the conversation. This is done in a standardized manner, using the SIPREC Protocol, thus it can be used by any recorder that implements this protocol.

Since an external server is used to record calls, there are no constraints regarding the location of the recorder, thus it can be placed arbitrary. This offers huge flexibility to your architecture configuration and various means for scaling.

The work for this module has been sponsored by the OrecX Company. This module is fully integrated with the OrecX Call Recording products.

1.2. How it works

The full architecture of a SIP Media Recording platform is documented in RFC 7245. According to this architecture, this OpenSIPS module implements a SRC (Session Recording Client) that instructs a SRS (Session Recording Server) when new calls are started, the participants of the calls and their profiles. Based on this data, the SRS can decide whether the call should be recorded or not.

From SIP signalling perspective, the module does not change the call flow between the caller and callee. The call is established just as any other calls that are not recorded. But for each call that has SIPREC engaged, a completely separate SIP session is started by the SRC (OpenSIPS) towards the SRS, using the OpenSIPS Back-2-Back module. The INVITE message sent to the SRS contains a multi-part body consisting of two parts:

  • Recording SDP - the SDP of the Media Server that will fork the RTP to the recorder.

  • Participants Metadata - an XML-formated document that contains information about the participants. The structure of the document is detailed in RFC 7865.

The SRS can respond with negative reply, indicating that the session does not need to be recorded, or with a positive reply (200 OK), indicating in the SDP body where the media RTP should be sent/forked. When the call ends, the SRC must send a BYE message to the SRS, indicating that the recording should be completed.

Full examples of call flows can be found in RFC 8068.

1.3. Media Handling

Since OpenSIPS is a SIP Proxy, it does not have any Media Capabilities by itself. Thus we need to rely on a different Media Server to capture the RTP traffic and fork it to the SRS. This module currently uses the RTPProxy module in OpenSIPS to instruct the RTPProxy Media Server to fork the RTP media to the SRS.

1.4. SRS Failover

The siprec module supports failover between multiple SRS servers - when calling the siprec_start_recording function, one can provision more SRS URIs, separated by comma. In this case, OpenSIPS will try to use them in the same order specified, one by one, until either one of them responds with a positive reply (200 OK), or the response code is one of the codes matched by the skip_failover_codes regular expression. In the latter case the call is not recorded at all.

1.5. Limitations

This module only implements the SRC specifications of the SIPREC RFC. In order to have a full recording solution, you will also need a SRS solution such as Oreka - an open-source project provided by OrecX.

Although this module provides all the necessary tools to do calls recording, it does not fully implement the entire SIPREC SRC specifications. This list contains some of the module's limitations:

  • There is no Recording Indicator played to the callee - since OpenSIPS continues to act as a proxy, there is no way for us to postpone the media between the caller and callee to play a Recording Indicator message.

  • Cannot handle Recording Sessions initiated by SRS - we do not support the scenario when an SRS suddently decides to record a call in the middle of the dialog.

  • OpenSIPS cannot be queried for ongoing recording sessions - this is scheduled to be implemented in further releases.

1.6. Dependencies

1.6.1. OpenSIPS Modules

The following modules must be loaded before this module:

  • TM - Transaction module.

  • Dialog - Dialog module for keeping track of the call.

  • RTPProxy - RTPProxy module used for controlling the media forked.

  • B2B_ENTITIES - Back-2-Back module used for communicating with the SRS.

1.6.2. External Libraries or Applications

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

  • None.

1.7. Exported Parameters

1.7.1. media_port_min (integer)

The minimum value of the port used in the SDP sent to the SRS. This value should correlate to the port-range configured in the RTPProxy Media Server.

Default value is 35000.

Example 1.1. Set media_port_min parameter

...
modparam("siprec", "media_port_min", 10000)
...
		

1.7.2. media_port_max (integer)

The maximum value of the port used in the SDP sent to the SRS. This value should correlate to the port-range configured in the RTPProxy Media Server.

Default value is 65000.

Example 1.2. Set media_port_max parameter

...
modparam("siprec", "media_port_max", 20000)
...
		

1.7.3. skip_failover_codes (string)

A regular expression used to specify the codes that should prevent the module from failing over to a new SRS server.

By default any negative reply generates a failover.

Example 1.3. Set skip_failover_codes parameter

...
# do not failover on 408 reply codes
modparam("siprec", "skip_failover_codes", "408")

# do not failover on 408 or 487 reply codes
modparam("siprec", "skip_failover_codes", "408|487")

# do not failover on any 3xx or 4xx reply code
modparam("siprec", "skip_failover_codes", "[34][0-9][0-9]")
...
		

1.8. Exported Functions

1.8.1.  siprec_start_recording([srs [, group [, caller [, callee [, rtpproxy_set] ]]]])

Calling this function on an initial INVITE engages call recording to SRSs for that call. Note that it does not necessary mean that the call will be recorded - it just means that OpenSIPS will query instruct the SRS that a new call has sterted, but the SRS might decide that the recording is disabled for those participants.

Note that the call recording is not started right away, but only when the call is actually answered - 200 OK is sent by the callee.

Parameters:

  • srs - a comma-separated list of SRS URIs. These URIs are used in the order specified. See siprec_srs_failover for more information.

  • group (optional) - an opaque values used by the SIPREC protocol to group calls in certain profiles.

  • caller (optional) - a nameaddr header containing information about the caller. If absent, the From header is used.

  • callee (optional) - a nameaddr header containing information about the callee. If absent, the To header is used.

  • rtpproxy_set (optional) - the RTPProxy set used for this call. If absent, the default set provisioned in the rtpproxy module is used.

The function returns false when an internal error is triggered and the call recording setup fails. Otherwise, if all the internal mechanisms are activated, it returns true.

This function can be used from REQUEST_ROUTE.

Example 1.4. Use siprec_start_recording() function with a single SRS

	...
	if (!has_totag() && is_method("INVITE")) {
		$var(srs) = "sip:127.0.0.1";
		xlog("Engage SIPREC call recording to $var(srs) for $ci\n");
		siprec_start_recording("$var(srs)");
	}
	...
	

Example 1.5. Use siprec_start_recording() function with multiple SRS servers

	...
	if (!has_totag() && is_method("INVITE")) {
		$var(srs) = "sip:127.0.0.1, sip:127.0.0.1;transport=TCP";
		xlog("Engage SIPREC call recording to servers $var(srs) for $ci in inbound group\n");
		siprec_start_recording("$var(srs)", "inbound");
	}
	...