## 3 M2M Information and Services
### ETSI M2M Service Capability Layer  
ETSI provides an M2M network architecture specification with a generic set of service capabilities. The idea of the architecture is to provide horizontal service capability layer that can be applied to several vertical M2M application domains with standardized reference points. The ETSI M2M Network is composed of two domains: (1) The Device and Gateway domain with M2M devices and Gateways and (2) the Network domain with core network access, M2M service capabilities, M2M applications and management functions, see Figures 5 and 6. Three different Service Capability Layers are specified: a Device Service Capability Layer, a Gateway Service Capability Layer and a Network Service Capability Layer. Each SCL exposes the services required by the M2M applications residing in the underlying M2M Network. The ETSI adopted a RESTful [72] architecture style for the M2M Applications and/or M2M SCL information exchange [18]. Each SCL is comprised of several services groups: Application Enablement Capability (AEC) for providing M2M point of contact for using the M2M applications of the corresponding SCL, Generic Communication Capability (GCC) for interfacing between the different SCL available on a given M2M Network, Reachability, Addressing and Repository Capability (RARC) for managing events relative subscriptions and notifications as well as for handling applications registration data and information storage, Communication Selection Capability (CSC) for network selection and alternativecommunication service selection after a communication failure, Remote Entity Management Capability (REM) for remote provisioning, Security Capability (SECC), History and Data Retention for archiving data (HDR), and Interworking Proxy (IP) for integrating non ETSI compliant systems. The presented service capabilities are logical groups of functions identified by ETSI, but all of them are not mandatory [18]. Only the external reference points, dIa, mId and mIa, between the M2M applications and SCLs are mandatory. Where the dIa interfaces devices applications and Gateway or Device Service Capability Layer, the mId interfaces the M2M Gateway or Device Service Capability Layer and the M2M Network Service Capability Layer and the mIa interfaces backend M2M Applications and the M2M Network Service Capability Layer. These interfaces aim to be applicable to a wide range of network technology and application and access independent [35]. Figure 5: M2M system with ETSI M2M standard reference points. Figure 6: Interfaces of ETSI M2M system. The ETSI M2M architecture indicates that it does not explicitly specify means for integrating legacy devices or other already existing non-ETSI compliant systems, but it presents integration points (Interworking Proxy) on the Gateway and Network Service Capability Layers [15]. Figure 7 presents the different M2M Service Capability Layers that comprise the ETSI M2M Network as well as the related reference points. According to the ETSI M2M architecture, an M2M Gateway can act as a proxy for M2M devices available in the same local area network. Once M2M devices applications are registered on a given GSCL, they become available to the registered SCLs and M2M applications if they acquire the appropriate access rights. Ex: Network applications can subscribe to information produced by a sensor (Device application) registered on a reachable GSCL. Figure 8 explains how this can be done. We presume that the GSCL is registered to the NSCL and that the Device Application is registered to the GSCL. First the Network application registers to the NSCL (001). Then Network Application Enablement capability checks if the issuer is authorized to be registered and treats the request (002). The registration information is then stored by the Network Reachability, Addressing and Repository Capability. After it Network Application receives a positive answer (003). The Network Application subscribes to the data produced by the desired sensor (Device application) (004).