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The challenging part of Voice over IP traffic is that it needs to enter in competition with all other network traffic and also be delivered in real-time to achieve a good audio quality level.  The main enemies for a good call quality are packet loss, jitter and delay

Thanks to the built-in Extended Report packet type for RTP Control Protocol (RTPC-XR, RFC3611), Snom phones can address effectively the impact of these VoIP rivals.

How does it work

For illustration purposes, the entities involved in SIP vq-rtcpxr (stands for voice quality RTCP extended report) event reporting will be referred to as follows:

  • REPORTER: an entity involved in the measurement and reporting of media quality, i.e. the Snom IP phone involved in a media session.
  • COLLECTOR: an entity that receives SIP vq-rtcpxr events. A Collector may be a proxy server or another entity that is capable of supporting SIP vq-rtcpxr events.

RTCP-XR must be enabled for computing quality reports to be sent along the SIP call information from a User Agent (known as the Reporter) to a third party device (known as the Collector).

The VoIP Metrics Report Block provides metrics for monitoring VoIP calls. These metrics include packet loss and discard metrics, delay metrics, analog metrics, and voice quality metrics. Voice quality metrics include R factors and Mean Opinion Scores (MOS scores). An R factor is a conversational-quality metric in the range of 0 to 100. MOS-LQ is a listening-quality metric and MOS-CQ a conversational-quality metric, both in the range of 1 to 5.

The data contained in VoIP metrics reports, together with call information from a SIP User Agent (UA) in a session sent to a Collector, give place to a Session Initiation Protocol Event Package for Voice Quality Reporting (RFC6035).

Snom IP phones have the ability to send a voice quality report containing a set of RTCP-XR metrics at the end of a call. These metrics include local measurements of packet loss, jitter and delay, and may also include remote metrics obtained from RTCP-XR reports sent by the other call endpoint. The quality metrics, along with SIP registration information for the call, are encapsulated in a SIP PUBLISH message and are sent to the Collector.

The purpose of the Collector is to correlate, analyze, and display performance metrics sent by Snom IP phones and other devices that are capable of generating RFC6035 SIP session quality reports.

How to enable this feature

Snom phones must be configured as following:

  1. Configure the address of the Collector. In the web user interface, Advanced > SIP(Section)/vq report collector, enter the address into the Voice Quality Report Collector field. Depending on your network configuration, a SIP username may or may not be required. For example:


If using the XML configuration file, enter the address in the following format: 

<vq_report_collector idx="INDEX" perm perm="PERMISSIONFLAG">VALIDVALUE</vq_report_collector>

    • INDEX: since version this setting is a per-identity specific parameter.
    • PERMISSIONFLAG: specifies the read/write permissions for this configuration parameter.
    • VALIDVALUE:  the address (FQDN or IP address) and port number of the Collector.

For example:

<vq_report_collector idx="1" perm="R">sip:account@vqr.voip.intern:5099</vq_report_collector>

2. RTCP-XR metrics calculation must be enabled to be included in the voice quality reports. In the web user interface, go to Advanced > SIP/RTP > RTCP-XR Report Format, type the following:

 voip-metrics stat-summary=loss,dup,jitt

When using XML configuration file, enter the following line: 

<rtcp_xr perm="R">voip-metrics stat-summary=loss,dup,jitt</rtcp_xr>


Collector third parties

Our technological partner Telchemy, elaborated SQmediator® for Snom phones. This enables system administrators to non-intrusively monitor call quality and proactively diagnose the root cause of performance problems. SQmediator collects diagnostic metrics directly from Snom IP phones, providing a real-time view of the performance of every call.