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. As explained in other parts of EG 202 009 [7] and [8]@ the monitoring of a QoS commitment should refer to contractual values set either by governmental rules or in a mutual agreement between the provider and its customer. This is why achieving a SLA is more often perceived as the best means to meet specific QoS requirements while ensuring the optimal cost/quality ratio to the customer and the provider in a win-win perspective. Nowadays@ there are several standards describing QoS measurements but the questions of which indicators are to be monitored and which values they should meet are still open. This part of the document defines a framework for a Service Level Agreement between a customer and a supplier of Telecommunications Services. Such framework uses the service specific QoS parameters proposed in EG 202 009-2 [8] to evaluate the Quality of Service@ while EG 202 009-1 [7] gives guidance to identify the parameters relevant to the users. The following concepts are defined: a) The services covered by the SLA. b) The performance or quality criteria pertinent from the user point of view with reference to indicator values. c) The methods to achieve the indicator values needed to measure the performance or the quality of service. d) The service level that the supplier is agreeing to ensure. In addition@ a Service Level Agreement aims to define a common quality management process used by the supplier and the customer@ including: a) Outage management. b) Statistics for prevention. c) Usage statistics. d) Etc. Such framework is intended to avoid the multiple misunderstandings that@ by experience@ are appearing between the customer and the supplier or between different departments within the supplier company. The main principles for the definition of this quality management process are: ? To define the services according to the applications performed by the user and transparent to 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 may be different. ? To define the quality criteria with respect to 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 the quality@ depending on those that are relevant for the technology used. In any case the criteria should take into account the effects perceived by the user and not their causes in the network. Therefore@ the present document does not intend to describe measurement techniques since specific ETSI TCs are dealing with such techniques and have the appropriate technical knowledge to develop standards in this area. The purpose of the document is rather to give guidance in using such standards in a SLA and defining indicator values.