A Scenario Editor for Mobile Ad-hoc Networks. Oliver Wellnitz. Sven Lahde. Emanuel Eden. Lars Wolf. IBR, Technische Universität Braunschweig.
A Scenario Editor for Mobile Ad-hoc Networks Oliver Wellnitz
Sven Lahde
Emanuel Eden
Lars Wolf
IBR, Technische Universit¨at Braunschweig M¨ uhlenpfordtstrasse 23, 38106 Braunschweig, Germany {wellnitz|lahde|eeden|wolf}@ibr.cs.tu-bs.de
1
Introduction
Evaluating ideas and algorithms in real world mobile ad-hoc networks is difficult because it is hard to achieve repeatable and reliable results. The most important problem with these evaluations is the wireless channel due to interference, diffraction and changing atmospheric conditions. Another problem is the total number of nodes involved in creating larger ad-hoc networks. Hence, simulators like NS-2, OPNET or others are used to analyse ad-hoc networks in a sealed environment. But even here problems with realistic radio propagation and user mobility models remain. For the simulation of mobile ad-hoc networks, a rectangular area is often used. Inside this rectangle mobile nodes are positioned randomly and the random waypoint model is employed to describe their mobility. The usability of this approach has been discussed for some time[3]. Our research work focuses on creating realistic scenarios for mobile ad-hoc networks. One reason why the simple random waypoint mobility model is so widely in use may be that the creation of realistic scenarios is a complex and time-consuming task. For this purpose, we have created the NS-Mapper scenario editor which can help users creating more realistic mobile ad-hoc scenarios. The user can manually define mobile nodes and movement patterns as well as let the computer create nodes and movements randomly. All nodes are restricted to certain areas of the scenarios which prevents nodes from passing through walls or other obstacles. In related work, one can find existing mobility or scenario editors. However, they often focus on special scenarios such as vehicular networks[2] and can usually not be applied to mobile ad-hoc networks in general.
2
NS-Mapper
Our scenario editor consists of two layers: The default GUI-based version in which scenarios can be modelled by the user and a command line version for creating simulation files from scenario descriptions automati-
cally. An NS-Mapper scenario consists of manually modelled nodes and node mobility as well as randomly created nodes and their movement. A user can manually define the number, the position and the mobility of nodes he is especially interested in as well as their traffic pattern. After that, he can let the editor randomly create a given number of additional nodes to form a larger ad-hoc network. NS-Mapper scenarios can then be used to create a number of NS-2 simulation files where all random elements are recalculated with different seed settings. This allows for the creation of scenarios with a group of fixed nodes which behave in a predetermined way and some random nodes which create background traffic and provide connectivity in the ad-hoc network according to some general settings.
Figure 1: The NS-Mapper GUI Figure 1 shows a screenshot of the NS-Mapper GUI with a train station scenario. The user interface is divided into two main areas with the menu on top. The left area shows all elements and properties of a scenario. On the right side there is a graphical representation of the scenario which displays the position of all mobile nodes. To help users recreating existing real world areas, maps in GIF, JPEG or PNG format can be loaded as background. Furthermore, NS-Mapper supports additional functions which are not shown in this figure. Firstly, the paths and waypoints of all mobile elements
can also be shown in the editor. And secondly, a time slide bar lets the user analyse the position of every node in the simulation at any given time. Another feature of our editor are the so called movement fields. A movement field is a rectangle or polygon in which mobile nodes can be created and roam. Mobile nodes are not allowed to exist outside a movement field. This property can be used to model walls or other areas where nodes cannot move through. A node can move from its own to an adjacent movement field iff these movement fields are interconnected or overlap. There are two kinds of movement fields: static and dynamic fields. Static movement fields remain at their position throughout the simulation. For dynamic fields, the user can create one or more time-based movement vectors which contain start time, stop time, speed and/or destination. All mobile nodes move with their associated movement field which means that a field’s movement vector is added to the movement vector of its nodes. Basically, dynamic movement fields move around with the mobile nodes sitting or moving on top of them. Examples of a static movement field are paths were nodes can move along, pavements, streets, or rooms in buildings. Dynamic movement fields can be used to create moving objects such as busses, trains or other vehicles or transportation mechanisms. The movement of dynamic fields is always created by the user as our implementation currently does not allow for random mobility for movement fields. While static nodes are directly created by the user, NS-Mapper can also create an arbitrary number of random nodes. Random nodes are placed according to a given random node placement strategy. Another strategy concerns random node movement. Any node, independently whether it was placed by the user or created randomly, can be chosen to move according to a random node movement strategy. For static nodes, this allows random movement with a fixed starting point in all simulations of a scenario. Besides the setup and movement of mobile nodes, data traffic has also to be modelled for a scenario. A user can create arbitrary CBR and/or several different TCP traffic patterns between static and/or random nodes. Furthermore, additional traffic can also be generated automatically by NS-Mapper and is controlled by two user-defined parameters. The first parameter limits the total number of connections for a mobile node. The second parameter represents the possibility of a connection to another node. With NS-Mapper all random strategies are implemented as plugins. The plugin interface can be used to easily implement new or modify existing strategies for
random node placement, movement or data traffic. For now, mobility scenarios can be exported for the NS-2 simulator only, although exports for other simulators are imaginable. NS-Mapper can create an arbitrary number of different simulations for one scenario by recalculating all random components in the simulation.
3
Scenarios
In order to demonstrate the capabilities of NS-Mapper, we present two different scenarios in this section. Figure 2 shows a snapshot of a park scenario created from a map of a real park. In this scenario there are three fixed nodes that want to communicate with each other. These three nodes (one server and two clients) are positioned on small static movement fields and are supposed to be sitting in the meadows. Roads and other ways are also modelled as static movement fields. Additional random nodes move on these movement fields along the roads through the park and create connectivity between the fixed nodes.
Figure 2: A park scenario consisting of polygon movement fields with fixed nodes Depending on the position of the random nodes and sources and sinks of background traffic at any given time, traffic between the fixed nodes may flow smoothly, compete with background traffic for available bandwidth or is interrupted because of node movement. All of these situations can be created from this single park scenario. Furthermore, increased or reduced background traffic or other parameters can be changed easily to evaluate a scenario under different conditions. In another scenario, we created a train and a train station where people wait for the next train, get on, ride along and get off at the next station. This scenario resembles the one seen in Figure 1, however this time our interest was focused on the train itself. Hence, we
modelled the train as a fixed movement field and moved the train station around. In order to prevent people to get on the train while it is approaching the station, the movement fields of the train station and train are not connected. When the train has stopped, we positioned additional small movement fields between train station and train to simulate the train doors.
4
Future Work
Currently, we have implemented only basic random strategies for node placement, movement and commu-
nication. However, more complex strategies are needed for realistic behaviour of mobile nodes. Group behaviour and group mobility models have been discussed in the ad-hoc research community for some time[1]. Other ideas for mobility strategies concern entry and exit points where mobile nodes can enter and exit the simulated area at any time during the simulation as well as special points of interest to which mobile nodes head and where they remain for some time. A destination- or goal-oriented behaviour would also improve realistic node behaviour in mobile ad-hoc scenarios.
References [1] T. Camp, J. Boleng, and V. Davies. A Survey of Mobility Models for Ad Hoc Network Research. Wireless Communications & Mobile Computing (WCMC): Special issue on Mobile Ad Hoc Networking: Research, Trends and Applications, 2(5):483–502, 2002. [2] F. K. Karnadi, Z. H. Mo, and K. Lan. An Implementation of Realistic Mobility Models for VANET. In Proceedings of the Eleventh Annual International Conference on Mobile Computing and Networking (ACM Mobicom), Cologne, Germany, Aug. 2005. [3] J. Yoon, M. Liu, and B. Noble. Random waypoint considered harmful. In Proceedings of the 22nd annual joint conference of the IEEE Computer and Communcations Societies (IEEE INFOCOM), San Francisco, USA, Apr. 2003.
