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VoIP Standards For Real-Time Performance Management

By Kaynam Hedayat, Brix Networks


After many years of hype and promises, VoIP is finally here. For providers and enterprises alike the question of should we consider VoIP? has been replaced by how quickly and reliably can we deploy VoIP? Because we are still in the evolutionary stages of VoIP technology, this inevitable move has created new challenges in VoIP network operation and management.

Many initial VoIP deployments are often part of hybrid VoIP-legacy networks. However, VoIP networks are becoming the cornerstone of todays telephony networks, and the overall infrastructure relies more than before on the performance and availability of IP-based networks and VoIP services.

This reliance, along with the uncertainty about VoIP network availability and performance, is behind the appearance of new performance and monitoring standards. These emerging standards range from new ways to collect and report performance-related information, to methods that extend this information to network management applications.

The building-block standard that addresses VoIP performance management is RTP Control Protocol Extended Reports (RTCP-XR). RTCP-XR provides extensions to the RTCP protocol for reporting detailed RTP and VoIP-related metrics. RTCP-XR is a mechanism for reporting detailed RTP and VoIP metrics.

There are new standards that take advantage of RTCP-XR to enable operations and management applications. These range from methods for reporting RTP and VoIP metrics in the context of a user call by the endpoints involved in the call, to methods for proactively measuring network performance to the user edge of VoIP networks. In both methods, RTCP-XR collects and reports the metrics.

Reporting performance metrics in the context of user calls provides network operators with visibility into the user experience. This is a common method for gaining visibility into end-to-end network performance, and complements monitoring agents that provide visibility at different segments of the network. However, this approach is reactive, not proactive. The user knows about the problem before the network operator. Reactive monitoring has partially worked in more mature TDM networks. However, VoIP is still a young technology. IP networks are multi-vendor and complex, and the network is no longer isolated. Proactively addressing performance and availability problems is mandatory to ensure successful VoIP networks and services deployment.

Media Loopback
One method of meeting the challenges mentioned above is monitoring the media delivery performance through test and monitoring calls where media is looped back from the receiver to the caller. Media loopback is especially popular in ensuring transport quality to the networks edge. Today, in networks that deliver real-time media, and short of running ping and traceroute to the edge, service providers are left without the necessary tools to actively monitor, manage, and diagnose service quality issues.

This monitoring method has been used in TDM and analog networks. Special intelligent endpoints, deployed at strategic locations, loop back media and cooperate with the caller to measure call performance. This method, however, can be costly and does not scale to support large networks. Furthermore, it does not offer the granularity of testing to a specific endpoint or location that may be exhibiting problems.

VoIP offers an interesting opportunity for deploying this capability. What if the intelligence of looping back media and cooperating for performance management was embedded in endpoints, such as SIP-based phones and IMS-based mobile handsets? This is the goal of the An Extension to the Session Description Protocol (SDP) for Media Loopback draft within the MMUSIC group of the IETF.

The concept of media loopback is very simple: the caller asks the receiver to loop back every packet it receives. The two endpoints exchange performance metrics via RTCP-XR and provide the data to higher-level applications, such as performance management and monitoring systems. Typically, policies such as not ringing the user for loopback sessions and rejecting loopback calls if the user is busy are put in place to enable non-intrusive monitoring.

The An Extension to the Session Description Protocol (SDP) for Media Loopback takes the concept further by introducing different loopback types for measuring service performance and availability services at different end point layers. The extensions are limited and based on the current standards for lightweight implementations.

IP telephony promises more than just having another type of phone on your desktop. The potential is for more advanced and better performing services. As VoIP evolves, its success relies on proactive operation and management strategies that scale to large networks. Multiple emerging standards are attempting to address large-scale network monitoring, and they have RTCP-XR as their foundation. The An Extension to the Session Description Protocol (SDP) for Media Loopback draft from the MMUSIC group of IETF is one of a series of standards that brings the value of RTCP-XR to operation and management applications. IT

Kaynam Hedayat is the chief technology officer of Brix Networks. For more information, please visit


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