2. BRIDGING THE GAP BETWEEN CYBER AND PHYSICAL SYSTEMS
Tartarus platforms are shown hosting mobile agents Mi (M1 and M2) and static agents Si (S1, S2 and S3). The mobile agents under migration are depicted as M uMi. In Figure2.2,S1 and S2 are hosted at Node 1 whileS3 at Node 3. Further, M1 and M2 are under execution at Nodes 2 and 3 respectively while M uM3 is a mobile agent 3 migrating from Node 2 to Node 1 on a wireless link. The intra-node communication between a static agentS3 and a mobile agentM2 is shown on Node 3.
2.4. TARTARUS: REAL-WORLD APPLICATION
Figure 2.3: The top-view of the implementation setup of the Cyber-Physical System comprising computer nodes (not shown physically) and Pi board with Webcam all configured as Tartarushosts. (The robots are linked to the computer based hosts via Bluetooth)
a Pi controller board, configured as aTartarus platform. Thus, each of these nodes has theTartarussoftware installed to make them act asTAH. The figure also shows three robots - one commuter and two others which are stationed at a docking station and are specially designed for specific purposes which include rescue and salvage operations. The commuter, robot nicknamed Santa, is the one that travels along the black-lines path and is analogous to a vehicle on a conventional road. All robots maintain a wireless link (Bluetooth) with a node in the network. Heterogeneity in hardware and software environments is emphasized by the use of the PC based nodes running on Windows and the Pi on Linux, all of which act as TAH. A Webcam, interfaced to the Pi board placed near the path, serves as aMonitoring nodein the CPS network. More of such monitoring nodes could be envisioned to be populated along the length of the path with motors to control their pan and tilt. The 12 PCs used were the maximum available at the time of experiment. However, more number of nodes can be added to increase the scale of the network.
2. BRIDGING THE GAP BETWEEN CYBER AND PHYSICAL SYSTEMS
Figure 2.4: The Pi basedTartarus host interfaced to the Webcam
Figure 2.5: The snapshot captured by the Webcam mounted on the Pi based Tartarus host
As the commuterSantatravels along the black path from Source A to Destina- tion B, it encounters a roadblock, a green object symbolizing the tree. As soon as, this robot detects the obstacle using its ultrasonic sensor, it communicates to the nearest Monitoring node, which in this case is the Pi. The static agent within the monitoring Pi basedTAH host, in turn, initiates an action to assess the problem by activating its webcam and taking a snapshot of the current situation. The snapshot is then forwarded to the human administrator available at another remoteTAH in the network. Figure2.5shows the image captured by the webcam in our implemen- tation. Based on the snapshot, the human administrator ascertains the gravity of
2.4. TARTARUS: REAL-WORLD APPLICATION
the situation and spawns a Tartarus mobile agent into the CPS network with the instruction to find the appropriate kind of rescue robot that is able to remove the obstruction from the location of the problem. The program to be executed by the rescuerobot to overcome the problem at hand is also bundled in as its payload. The mobile agent migrates into the CPS network and forages for the specified Rescue robot. Since there are two different types ofRescue robots, namedRudolph with a capability of pushing objects and Claus which has claws to pick and place objects, stationed at the docking station, the mobile agent compares their respective con- figurations against its requirements and chooses theClaus. It then initializesClaus to start following the black path towards the location of the roadblock. On reach- ing the specified locationClaus, using the program in the agent’s payload performs the grabbing of the obstacle using its claws and removes it from the path. The commuter robot Santa, now finds the path free and continues its sojourn along its path to eventually reach its destination. Having accomplished its task, theTartarus mobile agent guides Clausback to its docking stationœ.
2.4.1 Discussions
While the scenario of the CPS with robots implemented seems naïve, it throws more light on the feasibility of using Tartarus as a platform for realizing a full-fledged CPS. With a proper (wired or wireless) network of Tartarusplatform in place, it is possible to make mobile agents move to sense and actuate the connected physical devices including robots and sensors across the network. This potentially opens up a plethora of applications in the real world where robots, sensors, gadgets, and mobile devices need to communicate to perform tasks in a distributed, decentralized and asynchronous manner. In the above implementation, it could happen that Claus, while at work on the problem, needs the assistance of Rudolph for pushing an object. Claus (or the human administrator) can thus request its nearest TAH to spawn mobile agents to usher in Rudolph to the site of action. Further, if the tasks involved need to be performed in a collaborative and synchronized manner the same could be achieved using a set of mobile agents [87]. The human administrator
œA video of the implementation can be accessed at the following link: https://www.youtube.
com/watch?v=qcLgqFjAtik
2. BRIDGING THE GAP BETWEEN CYBER AND PHYSICAL SYSTEMS
could pitch in to change the course of actions of the robots and other devices that populate the net by spawning new mobile agents carrying the new programs as their payloadson-the-fly. Such agents would seek and search the targeted robots in the CPS network and replace the older programs within the robot/devices, thereby changing their respective behaviors when the overall system is still in operation (on-the-fly).