Building Realistic Mobility Models for Mobile Ad Hoc Networks

Adrian Pullin, Colin Pattinson, Ah-Lian Kor
2018 Informatics  
A mobile ad hoc network (MANET) is a self-configuring wireless network in which each node could act as a router, as well as a data source or sink. Its application areas include battlefields and vehicular and disaster areas. Many techniques applied to infrastructure-based networks are less effective in MANETs, with routing being a particular challenge. This paper presents a rigorous study into simulation techniques for evaluating routing solutions for MANETs with the aim of producing more
more » ... oducing more realistic simulation models and thereby, more accurate protocol evaluations. MANET simulations require models that reflect the world in which the MANET is to operate. Much of the published research uses movement models, such as the random waypoint (RWP) model, with arbitrary world sizes and node counts. This paper presents a technique for developing more realistic simulation models to test and evaluate MANET protocols. The technique is animation, which is applied to a realistic scenario to produce a model that accurately reflects the size and shape of the world, node count, movement patterns, and time period over which the MANET may operate. The animation technique has been used to develop a battlefield model based on established military tactics. Trace data has been used to build a model of maritime movements in the Irish Sea. Similar world models have been built using the random waypoint movement model for comparison. All models have been built using the ns-2 simulator. These models have been used to compare the performance of three routing protocols: dynamic source routing (DSR), destination-sequenced distance-vector routing (DSDV), and ad hoc n-demand distance vector routing (AODV). The findings reveal that protocol performance is dependent on the model used. In particular, it is shown that RWP models do not reflect the performance of these protocols under realistic circumstances, and protocol selection is subject to the scenario to which it is applied. To conclude, it is possible to develop a range of techniques for modelling scenarios applicable to MANETs, and these simulation models could be utilised for the evaluation of routing protocols. Informatics 2018, 5, 22 2 of 52 using a cable, in order to access networking facilities; so, again, wireless radio technology is developed, largely in the form of wireless Ethernet (IEEE, 2013, [5]). This allows a computer-which is taken to refer to a broad range of devices, from small handheld smart phones to desktop personal computers (PCs) and increasingly, to consumer devices, such as smart TVs-to connect to a local area network without being tethered by a network cable. The advent of mobile phones and in particular, their development into smart phones has resulted in another networking paradigm, whereby the device connects wirelessly to a telecommunications network, these days through 3G, increasingly 4G (ITU, 2010, [6]), and emerging 5G technologies, which will be deployed between 2020 and 2030 (HuaWei, 2013, [7]). The convergence of mobile phone and computer technology now means that there is a blurring of devices, such that clear distinctions between phones, tablet devices, netbooks, laptop computers, games consoles, televisions (TVs), etc. are no longer possible. All these devices are computers and can communicate via networks, predominantly using one of the previously mentioned wireless technologies. These wireless technologies allow a significant amount of device mobility and portability. Movement within the range of a wireless access point or a specific mobile telephone mast is trivial, and roving between access points or masts is straightforward, at least from a user's point of view. Thus, the concept of mobile computing emerges. One thing that links all of these devices and networks, both in terms of data communications and operational paradigm, is the reliance on an existing wireless infrastructure to which they can connect. This last hop link is known as the "last segment of end to end performance from a server to an end user device, which includes any Wi-Fi network at home, business, or public Wi-Fi hotspot, etc." (Badu Networks, 2016, [8]). It provides a significant degree of flexibility over a cable, but it is dependent on there being a pre-installed local area network (for wireless Ethernet) or telecommunications network (for 3G, 4G, and 5G). This reliance on pre-configured networks is satisfactory in many cases and has resulted in existing network infrastructures. However, the deployment and management of network infrastructures could be complex, costly, and time consuming (Computerworld, 2011, [9]). Such solutions could be vulnerable to failure caused by natural disasters, accidental, or deliberate interference. Therefore, there do arise circumstances where traditional pre-installed networking systems are not available. Examples are disaster zones, where the networking infrastructure has been destroyed, and battlefields, where there is insufficient time to deploy an infrastructure. In such cases, a networking solution is required that does not rely on anything pre-installed at all, and this leads to the concept of mobile ad hoc networks (Johnson and Maltz, 1996, [10]). A mobile ad hoc network (MANET) is an emerging type of wireless networking where mobile nodes associate on an extemporaneous or ad hoc basis (Cisco, nd, [11] ). It comprises a collection of mobile computers that communicate with each other via a self-organising, self-forming, self-healing communication network, without reliance on fixed infrastructures or centralised control or resources (Johnson and Maltz, 1996, [10]). Within a MANET, each computer or node has the potential to act as a data source, a data sink, and/or a router. The nature of each computer is not generally important as long as it can support the stated aspects of the MANET. MANET research predates modern developments in mobile devices and in particular, Wireless Local Area Network (LAN) (IEEE 802.11/Wi-Fi). Details of IEEE 802.11™ (Wireless LANs) are found here (IEEE, 2016, [12]). Wireless networking technologies now allow a heterogeneous collection of devices, which have compatible communications technology, such as 802.11, to be formed into a MANET. Much research that has been conducted on IEEE 802.11-based MANET address the following issues: power management protocols (Tseng et al., 2003, [13]); development of multicast aware MAC protocol (Gossain et al., 2004, [14]) followed by improvement of the MAC protocol (Dureja et al., 2010, [15]) and adaptive MAC 802.11 protocol (Patheja et al., 2013, [16]); development of a scalable and adaptive clock synchronization protocol. However, the development of MANET technology presents a range of challenges that are the subject of extensive research. Informatics 2018, 5, 22 3 of 52 Problem Statement The development of simulations plays a vital role in Mobile Ad Hoc Network (MANET)-related research. All aspects of the simulation need to be as realistic as possible for it to provide valid and meaningful data. Any aspect of the simulation model will lead to significant research questions. This research does not consider the following: radio propagation models, the implementation of protocols, power consumption, or security issues. There are significant differences in the performance results of simulations due to variations in the world models used. Many MANET protocol studies still employ basic simulation models with little or no relevance to the common, real-world applications cited for mobile ad hoc networks. In order to facilitate transferability to the real world, it is necessary to employ robust and realistic simulations of real-world scenarios for the evaluation of protocols. Realistic MANET simulations add soundness and credibility to evaluations of MANET routing protocols (Cavilla et al., 2004, [17]; Munjal et al., 2010, [18]); they produce vastly different results compared to commonly used simplistic models (Sommer et al., 2007, [19]) and will lead to real deployments (Lan and Chou, 2008, [20]). This research article addresses three important aspects for the development of a world model: simulation time, node count, and movement aspects of realistic models. They form the bases for the measures used for the evaluation of the model. The techniques and models presented here could be applied to research areas where mobility models are necessary, though issues addressed in this research are closely related to MANET. The main contribution of this work is to provide researchers access to models that facilitate easy construction of rigorous MANET simulation scenarios. The input to our models consists of desired values for the three previously mentioned measures. Subsequently, our models output parameters for a simulation scenario that approximately meets the benchmarks. Our first MANET model is designed based on a human movement mobility model (e.g., Musolesi and Muscolo, 2006, [21]; Papargeorgiou et al., 2012, [22]). The second model is a shipping model based on maritime movements in the Irish Sea. To reiterate, our models enable researchers to test MANET routing protocols in a more realistic manner, thereby improving the credibility of their MANET simulation studies. Research Aim The main aim of this research is to develop new techniques for producing realistic mobility and world models that could be used to evaluate MANET protocols in two different contexts: modelled battlefield and shipping movement. Its other goal is to show that different MANET application scenarios require different routing protocols. This is demonstrated by the fact that these realistic models yield significantly different results from commonly used simulation models, such as the random waypoint model (RWP). Their performance also varies when applied to common protocols. Thus, there is no single solution to the MANET routing problem, and different application areas will have different suitable protocols. Literature Review The literature reviewed in this paper encompasses the following: MANET, its operations, applications, performance evaluation, and nS-2 to simulate MANET routing algorithms. Mobile Ad Hoc Network (MANET) The development of mobile ad hoc networks can be traced back to projects run by the American Defence Advanced Research Projects Agency (DARPA) in the 1970s, when packet radio systems (PRNET) are developed to carry Advanced Research Projects Agency Network (ARPANET) between fixed and mobile nodes (Jubin and Tornow, 1987, [23]). A key focus in MANET has been the routing problem, and a large number of routing protocols have been proposed: destination-sequenced distance-vector routing (DSDV, Perkins and Bhagwat, 1994, [24]); dynamic source routing (DSR, Johnson and Maltz, 1996, [10]); ad hoc on-demand distance vector routing (AODV, Perkins and Royer, Informatics 2018, 5, 22 4 of 52 1999, [25]) and its variations: ad hoc on-demand multipath distance vector (AOMDV, Singh et al., 2017, [26]) and NACK-based AODV (N-AODV, Bianchi et al., 2014b, [27]; Bianchi et al., 2015b, [28]) to provide quicker access to a network topology compared to typical AODVs. Most of these protocols only exist in design or simulated forms used for initial evaluation. Some MANETs are modelled using formal models (e.g., Petri Nets (Bianchi and Pizzutilo, 2010, [29]), abstract state machines (ASMs, Bianchi, et al., 2014a, [30]), tools with formal descriptions to evaluate MANET protocols (e.g., Datamonitor in Lalanne and Maag, 2013, [31]), and use of a formal passive testing approach to detect flaws in MANET protocols (ibid; Cavalli et al., 2009, [32]). ASMs provide a means to facilitate high-level analysis of a system (Borger and Stark, 2003, [33]), including properties of the system under study (Vessio, nd [34]), while Bianchi and colleagues (2015a) [35] have provided predicate abstractions to verify formal models of abstract state machines). The Internet Engineering Task Force (IETF) mobile ad hoc networks working group has a small number of protocols documented via requests for comments (RFCs) (13 as of September 2013) (IEFT, nd, [36] ). Currently, there is no commercial nor publicly available MANET implementation. A literature search reveals frequently asked questions (FAQs) posted to the IEFT MANET mailing list requesting concrete examples of actual MANET deployment. Some of the vague responses to these requests are "the military are using them ", etc. (Antonakkais, 2007, [37]; Buraiky, 2008, [38]; Buddenberg, 2011, [39]). Caballero-Gil and colleagues (2014) [40] state that "The practical deployment of vehicular networks is still a pending issue". The reasons for this are beyond the scope of this research, but MANET research still remains in the experimental stage due to the technological challenges discussed by Hoebeke and colleagues (nd) [41] . Conti and Giordano (2007) [42] stress that though pure, general-purpose MANET is yet to exist in the real world, technologies based on the multi-hop ad hoc networking paradigm (e.g., VANET, Mesh, and Opportunistic networks) have been successfully deployed and are penetrating the mass market. Basic Operations of MANET The underlying principle of a mobile ad hoc network is that each device can contribute to the formation of the network by acting as a router, passing messages (data packets) to its neighbors, as well as being either a data source, data sink, or both. With such cooperation, nodes that are outside direct communication range from each other can exchange data using intermediate nodes as routers (Johnson and Maltz, 1996, [10]). This cooperative communication allows a network to be connected without relying on any existing infrastructure. The presence of any particular node in the network is not guaranteed, because any node can join or leave at any time. Due to the mobile nature of the nodes and the absence of a fixed infrastructure, a MANET requires wireless communication. This is because wired links would prevent movement, and a wired link would constitute a fixed infrastructure. The development of low-cost wireless data communications in the form of IEEE 802.11 wireless Ethernet (Wi-Fi)-based systems has significantly helped in the research and development of MANETs by providing a usable, lower protocol layer of technology for building MANETs. This is evidenced by the almost universal adoption of IEEE 802.11 as the MAC layer in papers published after the release of the IEEE 802.11 standard in 1997 (IEEE, 2013, [5]) and its inclusion in the ns-2 extensions provided by the Monarch Project (Monarch Project, 2004, [43]). During an MANET operation, node A may wish to send data to node B. Note that the MANET itself does not have any knowledge of the data contents, the reason of its transmission, or the relationship between the nodes. Just like the more common, fixed infrastructure-based network model, MANETs operate on a layer model, and the network is only concerned with data delivery. The generation and processing of the data is the responsibility of the source or sink nodes. If nodes A and B are within each other's communication range, then A can send directly to B in a single hop. However, in most cases, there will be no direct link, so a mobile ad hoc network is necessary. Node A will send the data to an intermediate node, which will pass the data on to another node, and so on, until the destination, node B, is reached. However, this example has several assumptions. They are as follows: node A knows how to reach node B; node A either knows the logical location of B or at least
doi:10.3390/informatics5020022 fatcat:nc7fzyxhkzazhaykpbiyp45rty