ol and service layers E2e security is of particular interest to what are called e-workers, equipped with a laptop and a mobile. The e-worker workplace varies a lot: central office, local offices, the home, customer locations, airports and other hot spots. However, let us start with reference points and SLAs. 15.4 DEFINITION OF AN ACTOR INTERFACE REFERENCE POINT A reference point is a set of conformance specifications for end-to-end important properties for the service. It comprises a) the set of interfaces that describe the interactions that take place between the various entities responsible for performing a particular task, b) service level specifications (SLSs) between the entities and c) behavioural specifications between entities. Thus, reference points are a prescriptive part of the specifications which can be used to test an implementation's conformance. A reference point is needed to enable the conforming entities to evolve independently of each other. Figure 15.7 shows a reference point and an interface example. It also contains SLS and behavioural specifications. This example covers QoS, security, signalling, mobility management, and network management. Interconnection l3 Network management interface Service level specification and l3 Policy management interface behavioural specifications Reference point 13 Mobility management interface l1 Call control signalling interface 12 Authentication, authorization and accounting interface Figure 15.7 Example of properties in a reference point 15.5 SERVICE LEVEL AGREEMENTS In this paragraph the expressions SLA and (Service) interconnection agreement are used. SLA has a wider interpretation. Let us start with the interconnection agreement, which is more of a peer-to-peer agreement. See Figure 15.8. An interconnection agreement should contain at least the following: Commercial criteria: Make sure you know how interconnection impacts your business. Service criteria: Make sure that the interconnection agreement includes agreement on service provision and QoS in order