ed terms. The proposed reference model is reflected in Figure 3.2. The above reference model defines a framework that identifies the required logi- cal entities, as well as the relationships existing among them. Two main types of entities are identified in the reference model: adaptation entities and entities for the provision of IMS-online applications. Within the adaptation entities, we also find two further sub-types: entities for the exposure of IMS capabilities and entities for the exchange of multimedia content and events. As a relevant difference, for the interaction with the Web 2.0 world, the entities of the first group use APIs defined by the operator, while the entities of the second group use the APIs defined by the Web 2.0 services to be contacted. In fact, since the entities of the latter group are actually using func- tionalities of Web 2.0 services along with Telco capabilities, they can be consid- ered as platforms for the development and execution of service mash-ups by the operator itself. Service Delivery Platforms flickr Web 2.0 domain facebook http/AJAX Incrusted PSE APIs for publication ast.fm You Tube async towards Web 2.0 sites APIs for access to content channel from Web 2.0 sites Server-to-Server Client-to-Server Media RSS/Atom Operator's open APIs 2.0 Subscription management Access control User- Content and REST VS RPC Client-to-Server IMS thin generated prefs events PSE#1 PSE#N client content distribution IMS 2.0 PSEs platform Interaction through APIs Server-to-Server IMS Exposure layer (APIs) Direct interaction (SIP, XCAP, media) Direct interaction (SIP, XCAP) Enablers layer Presence Others Figure 3.2 The WIMS 2.0 SDP reference model. The entities for the exposure and exploitation of IMS capabilities, and their functionalities, are the following: IMS Exposure Layer: This entity exposes IMS capabilities to the outer world through open Web APIs. On the outer side, it manages HTTP messages associated with the execution of a specific procedure, while, on the inner side, it interacts with 