scope:

In the current competitive world, Quality of Service (QoS) is becoming, jointly with cost, a key parameter in selling and buying telecommunications services. At the same time, technology and liberalization trends are raising new types of concerns unknown with the Plain Old Telephony Services (POTS) using switched connections provided by a single monopoly supplier.

Nowadays, there are several standards describing QoS measurements but the questions of which indicators are to be monitored from the users point of view and which values they should meet are still open. The present document proposes a reference model to evaluate the Quality of Service from the users point of view, defining the following concepts:

a) the appropriate indicator values from the user point of view;

b) the pertinent performance or quality criteria with reference to the above indicator values;

c) the methods to acquire the indicator values needed to measure the performance or the quality of service;

The main principles for these definitions are:

• To define the services according to the applications performed by the user and not by the technical solution: for example, voice over IP is one of the many technical solutions to communicate between subscribers of the world-wide telephone network; ATM, frame Relay, IP are some of the many technical solutions to ensure a data transmission service between a terminal and a server or between networks. The quality criteria are the same, only the Service Level is different.
• To define the quality criteria with respect of usage and not technique. In speech quality, users are more interested in intelligibility than in bandwidth, distortion, signal to noise ratio or lost packets. Quality criteria should be defined from the functional criteria, then translated into technical criteria. This means that different performance parameters may be used to quantify and monitor the quality, depending on those that are relevant for the technology used.

Therefore, the present document does not intend to describe measurement techniques since several ETSI TCs are dealing with such techniques and have the appropriate technical knowledge to develop standards in this area. EG 202 009-1 [24] gives guidance in using such standards to identify the indicators relevant from the user point of view, in particular to be used in a Service Level Agreements (SLA). The present document intends to define user related service specific QoS parameters while EG 202 009-3 [25] proposes a template for a SLA dealing with all service aspects, including penalties, escalation procedures, areas of responsibility, etc.