Voice over IP (VoIP) services are seen as a significant opportunity for Service Providers to offer value for money services to Enterprises, through the ability to make cost savings and to provide value added services within the network. However, take-up is potentially limited by the perceived risk of poor quality of the services. By providing best practices for monitoring of quality, this Application Note will enable Service Providers to offer high quality VoIP services and to use customer oriented metrics to enable SLA agreements between Service Providers and Customers to be managed.

For end-users, quality can be measured in terms of a number of factors, including the Speech Quality of the call, the Connectivity Quality of the call connection process, as well as traditional factors such as Availability of the service, Security, etc. This Application Note presents Best practice for the Speech Quality and Call Connectivity factors.

For Speech Quality, this best practice presents the case for real time monitoring of live calls, and for the use of well known speech quality metrics based on International Standards, rather than the simplistic but potentially misleading packet based measures of jitter and packet loss. The advantages and disadvantages of active monitoring techniques (using test calls) are also considered.
For Call Connectivity Quality, this best practice presents a series of suitable metrics that address traditional aspects of connection quality, plus those that are considered a concern for VoIP services. Examples of each are Call Setup Delay, and Media Path Setup Failure.

Four types of VoIP services or ‘scenario’ are considered, including various levels of hosted or managed services, plus network VoIP. Hosted and managed services can be defined as those where the service provider provides and/or manages equipment at the customer premises, where this could be network access equipment (edge routers, etc.), VoIP access equipment (e.g. Media Gateways) or desktop terminals (IP telephones, Softphones, etc.). Network VoIP is defined as any service where the Service Provider provides and manages no equipment at the customer premises.

Examples of Key Quality Indicators that are appropriate for use in SLAs between Service Providers and Customers are included, and also how these can be derived from suitable Key performance Indicators as reported by the Network. Methods of measuring and reporting these KPIs and metrics are also discussed. There is a significant amount of commonality in these measurements and metrics for each type of VoIP service.

The best practice presented draws on approved documents and some work in progress in the ITU-T, ETSI and the IETF.
The principal recommendation for metrics of speech quality is that they are derived from analysis of speech signals or estimated from analysis of packet behaviour in real time should be used. KQIs and KPIs should therefore be based on speech quality metrics expressed as a MOS or R factor , rather than e.g. simple measurements of jitter and packet loss. Furthermore, if MOS or R factor is estimated from analysis of packet behaviour, then it should be based on an analysis of the real time distribution of jitter and packet loss.
The principal recommendation for metrics of call connectivity quality is that they include metrics that indicate service level problems such as failure to build a media path and network initiated call completions as well as more traditional metrics such as Call Setup Delay, Call Release Delay, etc.
Finally, this Application Note adds a series of KQIs suitable for management of SLAs between Service Providers and Organisations representing Emergency Telecommunications Services Users. 


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