Device Driver-enabled Wireless Network Emulation Elias Weingärtner, Hendrik vom Lehn, and Klaus Wehrle Communication and Distributed Systems RWTH Aachen University {weingaertner, vomlehn, wehrle} @ comsys.rwth-aachen.de ABSTRACT According to the development of new software for wireless Testing and evaluating the performance of actual software networks researchers typically rely on network simulations for wireless networks is difficult. Real-world wireless testbeds or real-world testbed deployments. Network simulations are costly and cumbersome to maintain. Measurement stud- are the primary evaluation technique of choice for to the ies are complicated by many uncontrollable environmental analysis of wireless networks: Contemporary network simu- influences, particularly the wireless channel. Network simu- lators, such as OMNeT++ [30], JiST/SWANS [6], ns-2 [21] lations on the contrary allow the convenient analysis of wire- or ns-3 [24] facilitate the convenient investigation of wire- less networks with a maximum level of controllability; how- less networks. In fact, these simulators provide models for ever they typically do not allow the execution of arbitrary a plethora of wireless network technologies, ranging from and unmodified wireless communication software inside the models of 802.11 [4,16,25] and its different sub-standards to simulation environment. cellular networking technologies like LTE [20] or sensor net- In this paper, we present a new network emulation archi- works operating on IEEE 802.15.4 [9]. While all simulation tecture for the evaluation of wireless communication soft- tools inherit a very high degree of controllabiliy and scal- ware. By bridging the gap between simulation and wire- ability from the underlying concept of discrete event-based less software using a custom device driver, our framework network simulation, one aspect disqualifies them as the one enables arbitrary and unmodified wireless communication and only evaluation technology for wireless networks: With software to be evaluated in a fully simulated network. In rare and specific exceptions [18], network simulators do not accordance to this architecture we present a new 802.11 em- allow the execution of arbitrary wireless networking soft- ulation framework based on ns-3 that allows the investiga- ware in the simulation environment. This issue is critical for tion of arbitrary Wi-Fi software for Linux. It eases both the different reasons: First, this hinders studies of legacy wire- development and the performance analysis of present and less software for which no source code is available. Second, future Wi-Fi software. network simulation frameworks require the wireless software under investigation to be adapted to the simulation environ- ment, which is mostly work intensive and often costly. In Keywords addition, simulation environments strongly differ from oper- Network Simulation, Network Emulation, Wireless Software ating systems forming the original context in which wireless networking software is executed. Hence, it is difficult to uphold the original behavior of networking software if its 1. INTRODUCTION ported to a simulation environment. Both the development process as well as performance eval- Real-world software deployments and testbeds nat- uations of software for wireless networks are often challeng- urally allow the investigation of genuine wireless software ing and sometimes even painful. There are two prominent and hardware. Such testbeds are expensive both in terms of requirements in this regard. First , it is often vital to repeat hardware costs and maintenance. Moreover, measurements an evaluation or an experiment multiple times in a deter- with real-world wireless systems typically also suffer from ministic fashion. Second, a major necessity is the aptitude many uncontrollable environmental conditions. For exam- of investigating real-world software. Ideally, a respective ple the radio propagation on the wireless channel is prone methodology or performance evaluation tool allows for the to unpredictable interferences with other radio devices. In analysis of the wireless software in its genuine context, which addition, node mobility usually originates from vehicle or usually is an entire operating system on a real machine. human movement, which is difficult to reproduce. Hence re- peating real-world measurements under equal conditions is hard if not impossible in most cases. Network emulation [10] enables the analysis of real- Permission to make digital or hard copies of all or part of this work for world network systems and software in a fully controlled 3HUPLVVLRQWRPDNHGLJLWDORUKDUGFRSLHVRIDOORUSDUWRIWKLpersonal or classroom use is granted without fee provided thatVZRUNIRU copies are environment. For this purpose, these real-world communica- SHUVRQDORUFODVVURRPXVHLVJUDQWHGZLWKRXWIHHSURYLGHGWKDWnot made or distributed for profit or commercial advantage and thatFRSLHV copies tions systems pass their traffic through a network simulation DUHQRWPDGHRUGLVWULEXWHGIRUSURILWRUFRPPHUFLDODGYDQWDJHbear this notice and the full citation on the first page. To copy otherwise,DQGWKDW to that reproduces the behavior of an interconnecting network. republish, to post on servers or to redistribute to lists, requires prior specific FRSLHVEHDUWKLVQRWLFHDQGWKHIXOOFLWDWLRQRQWKHILUVWSDJH7RFRS\ Depending on the scenario’s requirements, the form of the permission and/or a fee. RWKHUZLVHWRUHSXEOLVKWRSRVWRQVHUYHUVRUWRUHGLVWULEXWHSIMUTools 2011 March 21–25, Barcelona, Spain. WROLVWV simulation may vary between a mere imitation of packet UHTXLUHVSULRUVSHFLILFSHUPLVVLRQDQGRUDIHHCopyright 2011 ACM ...$5.00. 6,08722/60DUFK%DUFHORQD6SDLQ &RS\ULJKWk,&67 '2,LFVWVLPXWRROV Simulated Nodes Simulation Domain Virtual Node Operating System Mobility Simulated Application Real-World Software Wireless Channel Network Stack Application Simulated Node Wireless Emulation Socket Layer Application Model Gateway Nodes Net. Device Transport Layer Socket Layer Model Network Simulation Operating System Routing Layer Transport Layer Model Figure 1: Conceptual overview of our wireless emu- lation approach: An instance of an entire operating Net. Device Driver Routing Layer Model system is integrated with the network simulation us- ing a custom wireless network device driver. Traffic between the simulation and the device driver is ex- changed at so-called gateway nodes. The network Medium Access Layer (MAC) simulation models the wireless channel, other fully simulated nodes as well as potentially virtual node movement. Physical Layer (PHY) propagation characteristics and a provision of a fully simu- Figure 2: Stack organization in a device-driver en- lated network consisting of simulated hosts, simulated pro- abled emulation scenario. We integrate the OS with tocol stacks and simulated network applications. the network simulation at the MAC layer. The net- In this paper, we revisit the concept of network emulation work simulation models the MAC and the PHY lay- for the evaluation of wireless networking software. Specifi- ers; for fully simulated nodes it provides the entire cally, the contributions of this paper are the following: protocol stack. • We introduce a new architecture for the emulation of wireless networks (Section 2). We integrate the network containing both simulated nodes and so-called gate- wireless software by providing it with a virtual wire- way nodes. The gateway nodes connect the simulation do- less network interface that behaves like a real wire- main with the real-world software prototypes. less networking card, but instead handles the transmis- sion and reception of data using a network simulation. 2.1 Real-world wireless network software This way, any real-world wireless networking software Our architecture integrates entire instances of operating as well as routing and transport protocol implemen- systems executing the wireless software under investigation tations can be investigated inside a fully simulation- into the emulation set-up. The most important cornerstone controlled environment. The simulation models the in our architecture is a special device driver providing the MAC and PHY layers, the wireless channel, potential wireless software with MAC-layer connectivity to the sim- node movement as well as other fully simulated nodes. ulated wireless network. In the following we explain why these design decisions were made. • We present an elaborate discussion of a new 802.11 First, the major design requirement for our emulation ar- emulation framework for ns-3 that we designed corre- chitecture is to enable the incorporation of arbitrary wire- sponding to this architecture (Section 3). Our frame- less software into an emulation scenario. Any software mak- work allows any networking software for Linux making ing use of wireless communication, for instance ad-hoc rout- use of 802.11 wireless networks to be evaluated within ing protocol daemons, VoIP applications or legacy operating ns-3 simulation scenarios of any kind. system applications, should be able to be included into the • The evaluation in Section 4 shows that our framework wireless emulation set-up. For this reason we need to pro- accurately integrates the ns-3 Wi-Fi models with real- vide the wireless software with its genuine environment that world networking software for Linux at the MAC layer, is of course the operating system context for which the soft- both according to latency and network bandwidth. ware was developed for. Second, we generally assume that modifying the software for the inclusion into