Security in Mobile Wireless Sensor Networks – A Survey <s> C. Both Sink and Sensor Nodes are Mobile <s> With the increasing sophistication of both manned and unmanned systems for remote ocean exploration, a wealth of knowledge about heretofore-unknown oceanic processes has become available. However, no technologies currently exist to observe organisms and processes without disturbing them, as they move with the natural motion of the oceans. We propose a new class of ocean sensing, whereby free-floating underwater devices operate autonomously and collaborate through an acoustic underwater network between them. This new class of sensing will provide a window into understanding the multifaceted interactions between the ocean's currents, underwater ecosystems and our impact on them. In this paper, we will present the design of our underwater vehicle, which drifts freely with the ocean currents and is equipped with a buoyancy control piston. Results from sea tests illustrate the feasibility of our design, including its depth tracking abilities. <s> BIB001 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> C. Both Sink and Sensor Nodes are Mobile <s> The significant advances of hardware manufacturing technology and the development of efficient software algorithms make technically and economically feasible a network composed of numerous, small, low-cost sensors using wireless communications, that is, a wireless sensor network. WSNs have attracted intensive interest from both academia and industry due to their wide application in civil and military scenarios. In hostile scenarios, it is very important to protect WSNs from malicious attacks. Due to various resource limitations and the salient features of a wireless sensor network, the security design for such networks is significantly challenging. In this article, we present a comprehensive survey of WSN security issues that were investigated by researchers in recent years and that shed light on future directions for WSN security. <s> BIB002 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> C. Both Sink and Sensor Nodes are Mobile <s> As sensor networks are more and more being implemented in real world settings, it is necessary to analyze how the different requirements of these real-world applications can influence the security mechanisms. This paper offers both an overview and an analysis of the relationship between the different security threats, requirements, applications, and security technologies. Besides, it also overviews some of the existing sensor network standards, analyzing their security mechanisms. <s> BIB003 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> C. Both Sink and Sensor Nodes are Mobile <s> A SEA Swarm (Sensor Equipped Aquatic Swarm) is a collection of mobile underwater sensors that moves as a group with water current and enables 4D (space and time) monitoring of local underwater events such as contaminants and intruders. For prompt alert reporting, mobile sensors routes events to mobile sinks (i.e., autonomous underwater vehicles) via geographic routing that is known to be most efficient under mobility and scarce acoustic bandwidth. In order for a packet to be routed to the destination using geographical routing, it requires to know the location of the destination. This is accomplished by having a location service that returns the location of a requested node. Our goal is to design such location service for SEA Swarm. In this paper, we analyze various design choices to realize an efficient location service in SEA Swarm scenarios. We find that conventional ad hoc network location service protocols cannot be directly used, because the entire swarm moves along water current. We prove that maintaining location information in a 2D plane is a better design choice. Given this, we propose a bio-inspired location service called a Phero-Trail location service protocol. In Phero-Trail, location information is stored in a 2D upper hull of a SEA Swarm, and a mobile sink uses its trajectory (a la a pheromone trail of ants) projected to the 2D hull to maintain location information. This enables mobile sensors to efficiently locate a mobile sink. Our results show that Phero- Trail performs better than existing approaches. <s> BIB004
Besides the aforementioned two MWSN topologies, yet another network topology is that both sink and sensor nodes are mobile. For example, a Sensor Equipped Aquatic (SEA) Swarm BIB004 , consisting of a large number of underwater sensor nodes air-dropped to the chosen venue, was deployed to support applications for time critical applications, such as submarine tracking and harbor monitoring. Each node, consisting of various sensors, a fish-like bladder apparatus and a pressure gauge, can dynamically control the depths using the bladders and on-board pressure gauges BIB001 . As shown in Fig. 1 , a SEA Swarm is deployed in a square region, operating and moving as swarm with the water current, searching for invasive submarine or scouting the waters around harbors or underwater mining facilities. A few unmanned submarines may act as mobile sinks to receive alert messages from sensor nodes. Figure 1 . An example of a SEA Swarm: mobile nodes detect events and report them to corresponding mobile sinks. As discussed above, all these three network topologies of MWSNs have the common property that sensors must be able to store sensed data in their memories until meeting with sinks to upload their data. III. THREAT MODEL Due to the fact that sinks (or base stations ) are not always present in MWSNs, new security threats emerge. In this section, we focus on these new challenges which are unique in MWSNs. While we focus more on attacks in MWSNs, interested readers are referred to BIB003 , BIB002 for more in-depth information on common attacks in WSNs.