## 5 UAN11 Field Test  
This section report results from the application of the above mentioned algorithms to the UAN project experimental activities held in Trondheim, Norway, in May 2011. The network (see Figure 11) was composed by up to four fixed nodes including the base station, two AUVs of Folaga class and one additional mobile node set-up on the Research Vessel Gunnerus using a transducer located at about 20 m depth. The command and control was located on shore at about 800 m from the base station. To give an idea of the tested network characteristics a brief description of the UAN architecture is now provided. Each node was equipped with an acoustic modem developed by UAN partner Kongsberg and capable of transmitting up to a rate of 500 bps. The network architecture used a CSMA protocol and the FLOOD routing algorithm [26] both directly implemented in the modems, an IP tunneling mechanism to establish the IP connection and UDP as transport protocol. Finally, the communication among the vehicles was achieved through the publish/subscribe system MOOS [27]. The most recent development of the Folaga class vehicle [28, 29], was used during the experiment with a dedicated payload section which included the Kongsberg acoustic modem (electronics and transducer), and the system architecture previously described was implemented over a PC104 SECO104-CX700M board, based on a 1 GHz processor, 1 GB of RAM, a 4 GB flash disk (see Figure 12), running Linux Ubuntu 9.10. This board represents the high-level control element of each vehicle, and it is hardwired (RS232) to the acoustic modem for the communication with the other agents. Finally, the board controls the behaviour of the vehicle by communicating, through an Ethernet link, with a low-level controller which acts on the vehicle motors. The presence of such a mobile agent allowed for change in the network geometry to tackle changes in the environment. During the test, which involved several different communication objectives not covered in this work as they would go beyond the scope of the paper, the vehicles were used as data-relays to improve and to re-establish broken communication links between fixed nodes (network adaptivity to changing environmental conditions) and they were integrated into the UAN wide-area protection system for the protection of a high value asset co-located with the UAN base-station. Figure 13 shows a zoomed view of the network and the Folaga path in the afternoon of May 27. In the first part of the day the vehicle was acoustically controlled by the UAN command and control center with the objective of patrolling inside an area where an intrusion was suspected. However, the C2 set up a waypoint for the vehicle (WP2) which was too far away from the remainder nodes of the network and the vehicle lost the connectivity. According to the behavior described in Section 3 the vehicle autonomously planned a new mission to move towards the high value asset (the base station) to be protected where it could in fact re-enter the network. At this point the command and control took over the control of the vehicle again sending a new mission (manually aborted on the spot to proceed with other communication tests and hence not shown in the picture). During the experiment, the network was tested at first without the security features activated and then with the cryptography, integrity and authentication services enabled. Figure 14 shows a comparison in terms of Average Delivery Ratio (ADR). The ADR is defined as the average ratio between the number of received messages by a node and the number of sent messages to that node. It is clear from the picture that when the security was activated there was a decrease of 8% in the ADR. This decrease is due to two concurrent effects:  
* The message expansion caused by the authenticator which in turn increases the probability of packet loss. * A decrease in the acoustic communication conditions.