# Networking for Cloud Robotics: The DewROS Platform and Its Application
## 4 Our Use Case: The SHERPA Project  
The goal ofthe SHERPA project is to perform S&R operations in hazardous environments with the assistance of a team of robots. In this context, different aerial and ground robotic platforms assist human operators in accomplishing the rescue mission. The SHERPA team is mainly composed of a set of small- and large-scale aerial robots with different abilities and a ground rover which is able to transport weighted objects and endowed with higher computation capabilities. The introduction of cloud computing in the SHERPA projects allow the robots to delegate the majority of their tasks to cloud resources, improving the overall performance of the mission, and helping the robot in the elaboration of the huge amount of data generated by onboard sensors (image elaboration, object detection, scene interpretation, etc.). Each robot in the team is able to generate various types of multimedia data, which are exploited to accomplish the rescue mission. In particular, the video and images gathered by the robots' camera sensor must be analyzed to detect the presence of avalanche victims or potential risks to human operators, while the GPS and localization information of each robot is used to plan and execute the rescue mission. Considering the critical issues related to SHERPA project domain, it is crucial to choose the best network configuration in terms of performance and accessibility to allow robots to use cloud services. In this context, network performance is typically evaluated by considering three main parameters: _bitrate_ (the transmission speed), _latency_ (the time elapsed from when the packet is sent to when it arrives at destination), and _loss_ (which defines how many packets do not reach their destination) [33, 34]. Additional parameters must be considered to properly choose the network configuration, related to the operating conditions of the networks, e.g., if it has to work outdoors or indoors, and its coverage in both cases. The most appealing network technologies for the SHERPA domain are the _IEEE 802.11 wireless LAN_, the _Mobile Cellular_, the _WiMAX_, and the _Satellite Network_. Among these, considering the results presented in the literature [5], the most efficient and effective solution seems to be represented by the satellite technology. This could provide the SHERPA team with sure coverage in the whole alpine area (as well as everywhere else, in case the SHERPA team has to be employed in other scenarios). Figure 2: General three-tier architecture of our Dew Robotics Platform based on ROS. In this context, communication with the cloud can be managed by a single central element called _sherpa box_, with fewer requirements in terms of mobility, while each actor of the SHERPA team would send the data that require Cloud computation, analysis, or storage in the _sherpa box_, which will act as a relay to the Cloud. The box will then act as a gateway to the Internet for the SHERPA team, moving slowly, to follow possible major shifts in the team, remaining in a central position with respect to the team's operating zone. The proposed network architecture is depicted in Figure 3. The figure shows how the robots interact among themselves through a local network, and how such network of robots can then interact with applications located in a Cloud using the _sherpa box_ as a relay. The next section describes the customization and usage of DewROS in the SHERPA domain. The remaining two ROS nodes of our platform, the _Encoder_ and the _Annotator_ are part of the Fog tier and are deployed on the ground rover so that they can use its onboard resources to execute medium-weight tasks. The ROS master, which is another process-consuming resource, has been allocated on the rover, the leader of the robotic platform. The _Encoder_, previously subscribed to the _Frame Topic_, will obtain and compress the retrieved images with a chosen codec, writing them in a sequence of video segments, called video chunks.