## 2 M2M Service Networks  
### M2M System  
A M2M system usually consists of a set of M2M asset devices attached in a M2M capillary network, a kind of M2M gateway, M2M communication infrastructure and a set of M2M services and applications as shown on Figure 1. The red line represents a typical scenario related to the remote monitoring and control process in M2M service networks. Such a scenario requires operation of the complete M2M system including the functionalities of M2M information and service, M2M communication and M2M security, which are therefore included in a sensible level into this survey. M2M services and applications can be divided further to multiple levels such as, e.g., information, service platform and applications. The applications are usually domain specific business logic, high level management of the M2M system, devices, and domain specific information. The _information level_ usually contains information management services and exchange transactions between the stakeholders of the system. A standardized common information model can enable smooth information exchange and business interactions between stakeholders of the domain. An example of this kind of common information model is CIM standardized for energy grid [16]. _M2M Service Platform_ includes service solutions and frameworks, which may be applied in multiple domains. The service solutions can contain generic service elements such as e.g., event notification, environment monitoring, service discovery and delivery, generic profiling, access control, generic storage and device management [17]. ETSI M2M has specified a set of service capabilities related to application, communication, reachability, addressing and repository, remote management, security, history and data containers [18]. A standardized M2M service platform could enable smooth application development and interaction between service platforms of different vendors, and services of M2M asset devices to be applied in multiple cases. _M2M communication infrastructure_ contains heterogeneous networks including local M2M asset network (M2M capillary network) such as personal/body area network, vehicular network and wireless sensor network (WSN), and Internet including various overlay networks. The overlay network can logically connect the M2M asset devices, M2M gateways, infrastructure servers and user with each  
Figure 1: A view of a Machine to Machine (M2M) system. other to hide the heterogeneity of physical networks and solve such problems as mobility, device power saving features, security including firewalls and NAT restricted networks. Thus the overlay network is a logical network operating on top of physical networks like, e.g., the Internet. The local asset network can contain M2M gateway(s), which may be needed to connect the local area network to the wide area network. If the local M2M asset devices are able to handle communication themselves such a gateway device is not necessarily needed. Several standardized short range radio technologies such as Bluetooth, ZigBee, RFID, _etc._, can be utilized locally, but also as vendor specific and optimized radio technologies for WSNs. The wide area and Internet connectivity can be provided by, e.g., Telecom operator and/or ISP using, e.g., Ethernet, DSL, GSM, 3 GPP, WiFi, WiMax, _etc._ There are a number of standardization bodies such as IETF, 3 GPP, Bluetooth, _etc._, whose works are related to specific areas of connectivity. _M2M asset devices_ consist of a huge number of heterogeneous embedded devices, which can be general purpose sensors, actuators, tags or M2M gateways in addition to domain, or even business case specific, heterogeneous devices. These devices, ranging from miniaturized sensors to large industrial machinery, operate with different technologies, operational characteristics and environments. It is obvious that all these devices cannot have the same type of interface because the purpose and capabilities can be very different.