## 4 Evaluation
### Car Sharing Experiment
#### 4.2.2 Evaluation Results  
The main evaluation results are shortly overviewed in the following:  
* Parking service system can be applied without making changes into the existing system as the result from applying A2 Nets M2M gateway, which hides the complexity related to local network within a parking lot;
* The complexity related to the on-board system within a car (CANBUS) and related car sensors applying GPS, NFC _etc._ is hidden by the A2 Nets gateway. This is important because usually different types of cars apply different formats with the CANBUS and sensor devices within the car;
* Application of XML based communication in the application level M2M information exchange between Web Server, M2M clients, Gateways and Car-PC Unit offer big advantages such as improvements in scalability, simplicity and interoperability because it is an open standard. In addition, thanks to XML, adding and modifying vehicle data has been easy for the car sharing company. An example of xml message between Car-PC Unit and car sharing Web Server is the following: _<zxml version=\"1.0\" encoding=\"UTF-8\"?> _<car> _<knu>5000 </km> <fuel>45 </fuel> <reserve>NO </reserve> <batter>12 </batter> <lights>ON </lights> <doors>CLOSE </doors> <coolantTemp>90 </coolantTemp><outdoorTemp>20 </outdoorTemp><airbag>OFF </airbag> <handBreak>NO </handBreak>< lat>41.355613</lat> <long>2.070432 </long>/car>  
Figure 22: Car-sharing Communication gateway.  
* The problems encountered when implementing the localization system, have been how to detect as in spaces so small and contiguous (2 meters width), the positioning of a vehicle, without installation of wiring components. If the location is within a closed parking, parking spaces are contiguous, and the receiver is installed in the windshield of the car, has had to adjust directionality IR emitter parking spots, installed on the roof of the plaza to not detect adjacent places. If the parking is open, it must be installed bars or brackets on each parking space to locate the vehicle, because there is no ceiling to install the IR emitter parking spots. The communication with the backend through the services offered by the Gateway has allowed the integration to proceed in a simple and efficient manner;
* The A2 Nets architectural approach proved to be very useful, because it allows development of service interaction and communication within the car and between different sites in smooth way even if each of them belongs to different domains and the needs arises from different requirements;
* The application of virtualization techniques with Layer2 Tunneling has brought a management efficient of IP mobility, which does not affect the upper communication layers, avoiding problems of IP addressing like changes of IP addresses and routing (NAT) that can be found in communication technologies of the different operators;
* The application of a virtual network with Layer2 Tunneling approach proved to be useful in maintaining WAN connection (GPRS, 3G, xDSL, Satellite), and switching it automatically in failure or constrained situation, without changes in upper communication layers. For example, in some cases, when 3G signal is low and connection is not stable, and is better to change to GPRS and communicate with a lower bandwidth but with more stability;
* The system performance needs to depend on the coverage and capacity of telecom networks. Some areas may lack of 3G/GPRS coverage and there are also places where capacity is in full use. For example, it was required to change into the GPRS in the exhibition place in Paris (ITEA2 Co-summit event).