NCTUns network simulation and emulation for wireless
Contents
1. CHCELA vaP localhost NC Tuns 2 0 03725 2005 mocro Tun T T Fig 2 The node editor invoked for editing the protocol stack and protocol module parameters of a wireless LAN access point access point has been invoked In this editor the modules used in the access point s protocol stack are shown and the parameters of the more advanced wireless physical module are being set More GUI operation illustrations are available in Reference 21 6 Emulation Supports The NCTUns network simulator can be easily turned into an emulator With emulation we can test the functions and performance of a real world host and see how it would perform under various network conditions without getting knowing or modifying its internal protocol stack When NCTUns is operating as an emulator a real world host e g a WLAN ad hoc mode mobile host a WLAN infrastructure mode mobile host or a router can exchange packets with any node in a simulated network In the emulator mode all nodes and links specified in the simulated network are still simulated by NCTUns i e the simulation machine where the simulation speed is purposely slowed down to match the speed of the wall clock Copyright 2005 John Wiley amp Sons Ltd In NCTUns a real world device is referred to as an external node and is represented by a different node icon in the topology editor The NCTUns external nodes can interact with the simulated net work in two2. puting Systems 2004 19 Ciarletta L Emulating the future with of pervasive computing research and development In Proceedings of the Third Inter national Conference on Pervasive Computing May 2005 Munich Germany 20 Tsarmpopoulos N Kalavros I Lalis S A low cost and simple to deploy peer to peer wireless network based on open source Linux routers In Proceedings of the First IEEE International Conference on Testbeds and Research Infrastructure for the Development of Networks and Communities February 2005 Trento Italy 21 NCTUns 2 0 GUI User Manual available at http NSL csie nctu edu tw nctuns html 22 VISSIM 3 70 User Manual PTV Planung Transport Verkehr AG company 23 Lin Y B Chlamtac I Wireless and Mobile Network Architec tures John Wiley New York USA 2000 Authors Biographies Shie Yuan Wang is an associate pro fessor in the Department of Computer Science and Information Engineering at National Chiao Tung University Taiwan He received his Master degree and Ph D in Computer Science from Harvard University in 1997 and 1999 respectively His research interests include wireless networks Internet technologies network simulations and operating systems Yi Bing Lin M 96 SM 96 F 04 is chair professor and vice president of Research and Development National Chiao Tung University His current research interests include wireless communications and mobile comput ing Dr Lin has published ove
3. TCP IP network protocol stack used in the simulation is the real world implementation Note that in this simulation methodology the kernel of the simulation machine is shared by all simulated nodes Therefore although two TCP IP protocol stacks are depicted in Figure 1 actually they are the same one the protocol stack of the simulation machine In addition to bandwidth and signal propagation delay characteristics we can simulate more interface Copyright 2005 John Wiley amp Sons Ltd details by adding more protocol modules to the simulation engine In this figure we see that there is one routing protocol module ARP protocol module packet scheduling or buffer management module PSBM IEEE 802 11 b MAC module WMAC and IEEE 802 11 b wireless physical module WPHY associated with each interface 4 High Level Architecture NCTUns uses a distributed architecture to support remote and concurrent simulations This feature uses an open system architecture to enable protocol mod ules to be added to the simulator This task can be easily done in just a few mouse clicks via its GUI operating environment Functionally NCTUns can be divided into eight components described in the fol lowing subsections 4 1 GUI Operating Environment The fully integrated GUI environment enables a user to edit a network topology configure the protocol modules of a network node set the parameter values of a protocol module specify mobile
4. configurations In the first configuration see Figure 3 a the application programs running on an external node can exchange packets with the application programs running on a node in the simulated network For example a TCP connection can be set up between two application programs with one running in the real network while the other running in the simulated network These two real world application programs can then exchange their packets via the TCP connection to complete a spe cific job e g a web server and client completing a web page retrieval With this feature network de vice developers can test whether their applications and protocols conform to standards specifications or inter operability requirements before releasing them to the market For example a newly developed VoIP phone device can interact with a fully tested VoIP program running in the simulated network to see whether it can pass the interoperability and conformance tests This feature is enabled by the Wirel Commun Mob Comput 2005 5 899 916 906 S Y WANG AND Y B LIN a I a l Fa l l External Node Real world Device I H2 N l I i l External Node l I ij TCP connection 1 i l l i Real world Device l I External Node Real world Device b Simulated Network Simulation Machine Fig 3 The two differe
5. imple mentation on hosts the IP protocol stack implementa tion on routers and links are all compiled together to form a single user level program A simulator con structed using this approach cannot easily provide UNIX POSIX API for real world application pro grams to run normally to generate network traffic Although some simulators may provide their own non standard API to let real world application pro grams to interact with them via IPC library calls real world application programs still need to be re written so that they can use the internal API be compiled and linked with the simulator and be Copyright 2005 John Wiley amp Sons Ltd concurrently executed with the simulator during simulation 3 Simulation Methodology The kernel re entering simulation methodology was proposed in References 2 3 5 where tunnel network interface is the key facility in the kernel re entering methodology A tunnel network interface available on most UNIX machines is a pseudo network inter face that does not have a physical network attached to it The functions of a tunnel network interface from the kernel s point of view are the same as those of an Ethernet network interface A network application program can send or receive packets through a tunnel network interface just as if these packets were sent to or received from a normal Ethernet interface Each tunnel interface has a corresponding device special file in the dev dire
6. of a single machine We have used the conservative synchroniza tion algorithm 14 to turn NCTUns into a parallel and distributed network simulator that generates the same simulation results as the sequential version 5 Radio Resource Management and QoS Supports NCTUns supports radio resource management QoS and mobility researches It has been used in several research work e g 15 20 to study these research areas At the physical layer the wireless channel models supported include 1 a simplified model like that used in ns 2 where only a transmission range and an interference range are specified for a wireless inter face 2 a two ray ground reflection model that considers large scale path loss and computes the received power at a distance The computed power is then compared against BER bit error rate versus power versus modulation scheme versus encoding decoding scheme curves to derive a BER for the received packet 3 a Rayleigh fading model that further considers the effect of small scale fading and multipath propagation Depending on the focus of the research one can choose an appropriate physical layer channel model to balance simulation result accuracy and simulation speed At the MAC layer the wireless MAC protocols supported include 1 CSMA CA with RTS CTS used for IEEE 802 11 b networks 2 multiple frequency time division multiplexed access MF TDMA for GPRS cellular networks and 3 multichannel a
7. simulation job to the job dispatcher the dispatcher will select an available simulation machine to execute this job If no machine is available the submitted job can be queued and managed by the dispatcher as a background job Various scheduling policies can be used to schedule their service order 13 4 4 Coordinator The NCTUns coordinator is a user level program executed on every machine where a simulation server resides The coordinator informs the job dispatcher whether this machine is currently busy in running a simulation or not When executed it first registers itself with the dispatcher to join in the dispatcher s simulation machine farm When its status idle or Copyright 2005 John Wiley amp Sons Ltd busy changes the dispatcher is notified of this new status Based on the machine status information the dispatcher chooses an available machine from its machine farm to service a job When the coordinator receives a job from the dispatcher it forks executes a simulation server to simulate the specified network and protocols The forked simulation server process will kill itself when its simulation is finished During simulation the coordinator may also fork start or kill end some real world application programs as specified in the job Because the coordinator has the process IDs of the forked traffic generators it can register these traffic generators with the kernel and all time related system calls issu
8. the right via another simulated mobile host in the middle Initially the application running on the external mobile host can exchange packets with the application running on the mobile host on the right via the middle mobile host As time proceeds the external mobile host begins to move away from the middle mobile host not in the real world but in the simulated network the mobile host move ment path can be easily set up as described in Section 7 and it eventually moves out of the trans mission range of the middle mobile host During this period the application running on the external node can no longer communicate with the applica tion running on the mobile host on the right Later on when the external node moves back to the mobile node in the middle the communication between the two applications will be able to continue Infrastructure mode mobile network The usage of external infrastructure mode mobile node is Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 909 v XA to Luss enkt s HIE sjo ajas EE PARBRAID ER P aj a External Mobile Node Simulated Mobile Node Simulated Mobile Node 3e 1e 2 4 T f poi s P X A 8 4 st y a N a Se d Be pe e oS if i E 0 000 000 000 000 5 ao ono ooo ooo omma A A i D Il m Difor anos J Select Node ID 2 7120 339 9 Fig 4 Mobile ad hoc network emulation similar to those of external hosts and external ad hoc mode mobil
9. time mismatch between the simulation clock and the wall clock may increase up to 3 ms However we found that when NCTUns is used in the multiple machine mode where the above mentioned components are run on separate machines the precision is quite high and seldom degrades 6 2 Adding an External Node to the Network Topology An emulation is set up as follows First a user clicks on the external node icon in the tool bar and add it to the network topology This is to indicate how the external node is connected to the simulated network Second the user enters the IP address used by that external node in the real network through the GUI This information must be known by the emulation daemon so that it can forward packets originated from the simulated network to the external node Like any node in the simulated network the GUI will assign an IP address to each external node s inter face This IP address is not a public IP address used in the real world Instead it is a private IP address used in the simulated network so that a user can specify the destination IP address of a packet if he she intends to send the packet to that node To send packets to the external node a simulated node uses this assigned private IP address as these packets destination IP address These packets will traverse the simulated network as in the simulation mode and then reach the external node represented in the simulated network The emulation daemon s
10. to get know or modify its protocol stack The NCTUns network simulator can be easily turned into an emulator by just selecting an option During emulation a real world network device can exchange packets with a simulated device in NCTUns One can use this capability to test the protocol conformance and interoperability of a network device 8 This paper is organized as follows Section 2 surveys related work Section 3 briefly presents the kernel re entering sim ulation methodology Section 4 presents the NCTUns high level architecture In Section 5 we present the wireless radio resource management support provided by NCTUns In Sec tion 6 we describe the emulation support provided by NCTUns and how emulation can be applied to wireless LAN mobile devices in the real world Section 7 illustrates how NCTUns is used to study mobile ad hoc sensor inter vehicle communication IVC networks wireless mesh networks and gen eral packet radio service GPRS networks Section 8 discusses a performance optimization technique that NCTUns employs to significantly speed up Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 901 wireless simulations Finally Section 9 concludes this paper 2 Related Work In the following we discuss related work and the differences between NCTUns and them Dummynet 9 when it was originally proposed also used tunnel interfaces to use the real world TCP IP protocol s
11. WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Wirel Commun Mob Comput 2005 5 899 916 Published online in Wiley InterScience www interscience wiley com DOI 10 1002 wem 354 NCTUns network simulation and emulation for wireless resource management Shie Yuan Wang and Yi Bing Lin Department of Computer Science and Information Engineering National Chiao Tung University Hsinchu Taiwan Summary This paper describes NCTUns an innovative network simulator and emulator for wireless and mobile networks Effects of various radio resource management and quality of service QoS schemes on higher layer protocols and real world applications can be easily studied using NCTUns In this paper we elaborate on NCTUns simulation methodology architecture design functionalities performance and applications NCTUns simulation for wireless ad hoc sensor inter vehicle communication networks GPRS cellular networks and wireless mesh networks are also illustrated More details about this tool can be found in http NSL csie nctu edu tw nctuns html Copyright 2005 John Wiley amp Sons Ltd KEY WORDS network simulation network emulation wireless network radio resource management QoS 1 Introduction Radio resource management and quality of service QoS schemes are important for next generation wireless and mobile networks With them scarce wireless bandwidth can be more efficiently utilized and applications demanding a certain level
12. aces i and j in dev It then executes a while loop In each step of this loop it simulates a packet s transmission in the direction from node i to node j by reading a packet from the special file of tunnel Wirel Commun Mob Comput 2005 5 899 916 902 S Y WANG AND Y B LIN TCP_sender O Mobile Node 1 TCP_receiver CO Mobile Node 2 Simulation Engine Route Route ARP ARP PSBM PSBM WMAC WMAC WPHY m gt WPHY TCP_sender TCP_receiver User level Kernel TCP IP Stacki Tunne nnel interface 1 erface 2 J NW Fig 1 The top single hop TCP IP wireless network can be simulated by the bottom design interface i waiting for the packet s transmission on the channel to finish in virtual time and then writing this packet to the special file of tunnel interface j The bottom of Figure 1 depicts this simulation scheme Since replacing a real channel with a simu lated channel happens outside the kernel the kernels on both nodes do not know that their packets actually are exchanged in a simulated network The TCP sender and receiver programs which run on top of the kernels do not know the fact either As a result all existing real world application programs can run on the simulated network all existing real world net work utility programs can be executed in the simula tion and the
13. cation programs and are being used in real world sensor networks e g there are several commercial companies selling sensor network products in the market Since real world application programs can directly run on simulated nodes in NCTUns all developed data fusion agent programs can readily run with NCTUns Third since applica tion programs developed for simulations can directly run on real machines in NCTUns it is advantageous to develop data and information fusion agents as appli cation programs on NCTUns Later on they can be immediately deployed in the real world or be sold as commercial products For a large network with thousands of mobile nodes individually opening the GUI dialog box of each node to configure its application programs and moving path require significant effort To simplify this task NCTUns provides a command to read a traffic configuration file Typically such file is generated by a script or a program written by the user After the GUI reads this file each traffic generator i e appli cation program command string will be put into the application tab of the specified node in the GUI Also Copyright 2005 John Wiley amp Sons Ltd each moving path description in this file will be set as the moving path of the specified node in the GUI This facility saves significant effort because the user need not invoke each node s GUI dialog box individually to enter its application commands and set its movin
14. ctory If an application program opens a tunnel interface s special file and writes a packet into it the packet will enter the kernel From the kernel s viewpoint the packet appears to come from a real network and will pass through the kernel s TCP IP protocol stack as an Ethernet packet would do On the other hand if the application program reads a packet from a tunnel interface s special file the first packet in the tunnel interface s output queue will be dequeued and copied to the application program To the kernel the packet appears to have been transmitted onto a real link and this pseudo transmission is not different from an Ethernet packet transmission Using tunnel network interfaces we can easily simulate the wireless network depicted in Figure 1 where a TCP sender application program running on node 1 sends TCP packets to a TCP receiver applica tion program running on node 2 We set up the virtual simulated network with two operations First we configure the kernel routing table of the simulation machine so that tunnel network interface 1 is chosen as the outgoing interface for the TCP packets sent from node 1 to node 2 and tunnel network interface 2 is chosen for the TCP packets sent from node 2 to node 1 Second the wireless channel is simulated by a simulation engine process For the direction from node i to node j i 1 or 2 and j 3 i the simula tion engine opens the special files of tunnel network interf
15. e arrive at the simulation machine we use the IP fire wall facility provided by FreeBSD or Linux to inter cept these packets and divert them to one emulation daemon responsible for this external node The re quired IP firewall rules are automatically generated by the GUI program They are automatically installed into the operating system by NCTUns when an emulation run is executed Therefore a user need not install these firewall rules When the emulation daemon responsible for this external node receives these packets it will function like an NAT to translate their source IP addresses which is the public IP address of this external node into the private IP address assigned to this external node in the simulated network After this translation the emulation daemon will re inject them into the kernel of the simulation machine and these packets will traverse the simulated network based on the routing tables stored in the simulated network 6 3 Mobile Network Emulation We give two examples of mobile network emulations mobile ad hoc network and mobile infrastructure network 1 Mobile ad hoc network NCTUns supports emu lations with external mobile nodes which can be wireless LAN ad hoc mode or infrastructure mode devices An external mobile node is repre Copyright 2005 John Wiley amp Sons Ltd 2 sented by a node in the simulated network and the mobility of this node in the simulated network is specified in the
16. e nodes The only difference is that in the GUI dialog box of the external infra structure mode mobile node the user needs to provide the IP address of the gateway in the simulated network for this mobile node Figure 5 shows an emulation example in which one external infrastructure mode mobile node in the real world communicates with a simulated host at the top via a simulated wireless access point Like the ad hoc mobile node emulation case the external infrastructure mode mobile node in the real world may communicate with the simu lated host at the top initially As time proceeds it will leave the coverage represented by the inner circle of the simulated wireless access point and no longer can communicate with that simulated host Later on when it enters the coverage area of the simulated wireless access point again the communication continues 7 Various Wireless Network Supports This section describes the NCTUns supports on various wireless networks Copyright 2005 John Wiley amp Sons Ltd 7 1 Military Sensor IVC Mobile Ad Hoc Networks In mobile ad hoc network studies one usually wants to change the protocol stack or the parameter values used by mobile nodes to see how the changes would affect the overall performance of the mobile network In NCTUns this task can be easily done for thousands of mobile nodes without requiring the user to config ure individual mobile nodes A user before executing a GUI comma
17. ed by these registered traffic generators will be performed based on the virtual time of the simu lated network rather than the real time When the simulation server is running the coordi nator communicates with the job dispatcher and the GUI program on behalf of the simulation server For example the simulation server periodically sends the current virtual time of the simulated network to the coordinator The coordinator then forwards this in formation to inform the GUI user of the simulation progress During simulation the user can also on line set or retrieve an object s value e g to query or set a switch s switch table Message exchanges between the simulation server and the GUI program are per formed via the coordinator 4 5 Kernel Modification NCTUns modifies the kernel of the simulation ma chine so that a simulation server can correctly run on it During a simulation the timers of TCP connections in a simulated network should be triggered in the simulation time rather than in the real time The same processing should also be applied to the time related services requested by the application programs that are run on simulated nodes For example when the kernel receives the sleep 5 system call issued by an application program process it should suspend the execution of the process for 5s in simulation time rather than in real time Also the kernel needs to automatically perform UDP TCP port mapping between a port nu
18. eive command mes sages sent over the simulated network to complete the above tasks This feature is useful for military tactics mobile ad hoc network research and intelligent trans portation systems ITS IVC network research as elaborated below In a military tactics mobile ad hoc network a mobile node can be viewed as a military vehicle e g a tank on which an intelligent agent program acts as a commander controlling the movement of the vehicle The commanders on these mobile nodes use ad hoc wireless links to communicate with each other Based on the information acquired from other com manders a commander can make decisions to move the vehicle In a battlefield a vehicle may be des troyed by the enemy force It is also possible that a vehicle suddenly appears in the battlefield e g car ried and dropped by an airplane To support these military scenarios NCTUns provides control API functions e g setNextTurningPoint to allow an application program e g the commander running on a simulated mobile node to control the movement of the node In an IVC information network in ITS a mobile node can be viewed as a vehicle on which an intelli gent agent program acts as a control unit that controls the movement of the vehicle Recent studies have proposed to use an ad hoc IVC network approach to quickly distribute an emergent message among vehi cles without infrastructure support i e via the uses of GSM or GPRS cellular
19. ess and mobile networks Wirel Commun Mob Comput 2005 5 899 916 916 S Y WANG AND Y B LIN Acknowledgments The NCTUns project was supported in part by MOE program for promoting Academic Excellence of Uni versities under the grant number 91 E FA06 4 4 and the NSC Excellence Project under the grant number NSC93 2752 E 0090005 PAE We also thank the edi tor and reviewers for their valuable suggestions which greatly help us improve the quality of this paper References 1 McCanne S Floyd S ns LBNL network simulator http www nrg ee lbl gov ns 2 Wang SY Kung HT A simple methodology for constructing extensible and high fidelity TCP IP network simulators IEEE INFOCOM 99 March 21 25 1999 New York USA 3 Wang SY Kung HT A new methodology for easily construct ing extensible and high fidelity TCP IP network simulators Computer Networks 2002 40 2 257 278 4 Wang SY Harvard TCP IP network simulator 1 0 available at http www eecs harvard edu networking simulator html 5 Wang SY Chou CL Huang CH et al The design and implementation of the NCTUns 1 0 Network Simulator Computer Networks 2003 42 2 175 197 6 Wang SY NCTUns in the column software tools for network ing IEEE Networks 2003 17 4 4 7 Wang SY Chou CL Lin CC et al The design and implemen tation of the NCTUns 2 0 network simulation engine Sub mitted for publication 8 Wang SY Liao KC Innovative network emulation
20. g path The above facility is also useful for creating a mobility pattern not provided by NCTUns In the current version NCTUns can only automatically generate random waypoint paths for mobile nodes or allow a user to manually specify the moving paths of mobile nodes However a user may want to study a mobile network with a different mobility pattern For example to acquire a realistic vehicle moving sce nario not provided by NCTUns one can first use a microscopic vehicle traffic simulator to generate rea listic moving paths of vehicles moving on a highway or in a city Such traffic simulators consider the car following and lane changing driver s behavior and the characteristics of various vehicles The user then imports this moving path file into the GUI and studies how these vehicles mobile nodes in the simulation wirelessly exchange their packets based on the im ported moving patterns With this import facility any mobility pattern can be studied with NCTUns Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 911 Besides the above capabilities NCTUns can dyna mically create destroy and disable enable a mobile node during a simulation Each mobile node can also dynamically change its moving path including the moving direction and moving speed used protocol stack and used parameter values e g a radio s transmit power during a simulation In addition each mobile node can also rec
21. g system Through a defined API it provides basic simulation services to protocol modules to be described later Such services include virtual clock maintenance timer management event scheduling variable regis trations etc The simulation engine needs to be compiled with various protocol modules to form a single user level program called simulation server A simulation server takes a simulation job description file suite as input runs the simulation and generates data and packet transfer log files When a simulation server is running it utilizes a lot of kernel resources Therefore we do not allow other simulation servers to run at the same time on the same machine 4 3 Protocol Module and Job Dispatcher NCTUns supports various protocol modules A pro tocol module implements a layer of a protocol stack e g the ARP protocol or a FIFO queue A protocol module is composed of a set of functions It needs to be compiled with the simulation engine to create a simulation server Inside the simulation server multi ple protocol modules can be chained to form a proto col stack The NCTUns simulation job dispatcher is a user level program that supports concurrent simulations on multiple simulation machines The job dispatcher should be executed and remain alive to manage multi ple simulation machines The job dispatcher coordinates a large number of GUI users and a large number of simulation machines When a user submits a
22. ing the simulation Figure 11 compares the number of events generated per simulated second between the original and the optimization implementations under different network sizes The settings are the same as those used in the previous comparison This figure indicates that the optimized implementation signifi cantly outperforms the original one Copyright 2005 John Wiley amp Sons Ltd 9 Conclusions In this paper we present the NCTUns network simulator and emulator for conducting wireless communication and network researches NCTUns has several unique features that cannot be easily achieved by existing simulators For example real world TCP IP protocol stack is directly used to generate simulation results and real world applica tion programs can readily run on simulated nodes to generate realistic traffic These two properties en able researchers to use NCTUns to study the perfor mance of various radio resource management and QoS schemes and their effect on higher layer pro tocols and real world applications In addition NCTUns also supports emulation in which simu lated traffic and real world traffic can interact with each other This capability is useful for testing the function and performance of real world networking devices Currently we are developing simulation modules for supporting IEEE 802 16 WiMax networks Ka band satellite networks and IPv6 networks All of these networks are important next generation wirel
23. mber specified by a simulation user and the port number that is actually used inside the kernel This mapping allows multiple real world application programs to bind to the same port number on different nodes in a simulated network Consider an example where two web server processes are running on two different Wirel Commun Mob Comput 2005 5 899 916 904 S Y WANG AND Y B LIN nodes in a simulated network and they both want to bind to the well known port number 80 Without converting these two 80 port numbers to two different port numbers inside the kernel the above setup cannot be simulated due to port number collision 4 6 User Level Daemon and Real World Application Program The NCTUns protocol daemons run at the user level to perform specific jobs For example the real world routed using the RIP routing protocol or gated using the OSPF routing protocol daemons run with NCTUns to set up the routing tables in a simulated network The NCTUns real world application programs run at the user level to either generate network traffic configure network or monitor network traffic etc For example the tcpdump program can run on a simulated network to capture packets flowing over a link and the traceroute program can run on a simulated network to find out the routing path traversed by a packet 4 7 Remote Concurrent and Parallel Simulations NCTUns uses a distributed architecture by which simulation machine
24. mproved the methodology in the NCTUns 1 0 network simulator referred to as NCTUns 5 Due to the kernel re entering simula tion methodology NCTUns directly uses the real world TCP IP protocol stack in either FreeBSD or Linux operating system to generate more accurate simulation results than those generated by a simulator that abstracts away a lot of protocol details In addi tion all existing or to be developed application pro grams that run on these operating systems can directly run with NCTUnhs to generate realistic traffic for a simulated network These two properties enable re searchers to evaluate the effect of a new radio resource management or QoS scheme on real world applica tions and their end to end performance 6 Regarding network devices and protocols supports for wireless LAN networks wireless mesh networks GPRS networks QoS DiffServ networks RTP RTCP SIP VoIP protocols and several other wireless stan dards such as IEEE 802 11 e QoS protocol have been added to NCTUns Regarding simulation speed we have designed and implemented a new simulation eng ine that combines the advantages of the discrete event simulation methodology and the kernel re entering simulation methodology for fast simulation execution 7 Regarding operating system platform NCTUns can be run on both FreeBSD and Linux Regarding functionalities NCTUns supports emulation which can evaluate a real world network device without the need
25. n engine Since the packets delivered from an external node to a simulated node need to enter the simulation machine the external node must be physically con nected to the simulation machine via some physical network can be as simple as a physical link Ideally such a network should have infinite bandwidth and zero latency For example a 100 Mbps Fast Ethernet network may be used for this purpose For NCTUns an external node must reside on the same subnet as the simulation machine otherwise the emulation func tion will not work properly To receive the packets from an external node and further inject them into the simulated network a user level emulation daemon is run up on the simulation machine for each external node These daemons play a similar role as a user level network address transla tor NAT daemon They intercept packets translate IP and port numbers and then further inject packets into their destinations the simulated network or the external hosts Commands for running up these daemons are automatically generated by the GUI program and are automatically executed by the simu lation engine These user level daemons may incur extra latency during context switching According to our test results a machine with 1 GHz CPU or above can limit the packet latency caused by the emulation daemon to within 100 Ms To direct an external node s packets to the simula tion machine some routing entries must be set up on the e
26. nd multiradio MAC protocols for reducing the bad effect of signal interference in wireless mesh networks QoS support provided for IEEE 802 11 b wireless LAN networks is IEEE 802 1le protocol NCTUns includes a full implementation of enhanced distribu tion coordination function EDCF to differentiate eight different priority traffic classes and hybrid co ordination function HCF to support contention free medium accesses Replacing an existing protocol module with a new one developed by a researcher can be easily done with a few mouse clicks in the node editor of NCTUns Figure 2 shows that the node editor for a wireless LAN Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION Applications Actions 905 Thu Ape 21 1021Pm v Node Editor v Module Eai s MACS MACROS MN DE PHYO i Ele Edt Tools Sening i n iw S BA lt phy axptar Link Bandaith o Ops E EE Frequency Channel 3 Rayleigth Fading Variance t100 s Additional Naise da 0 0 J Switch Transmit Power 15 Wbm Antenna Gam 1 0 ot a Wireless Signal Transmission Range r Wisch way to set Receive Sensitivity amp By Distance By Receive Power Threshold ap M023 Receive Sensitivity Range 550 0 ten i 1 we Power T add cm ESAR ny O Log Link Uriizaion as me tnt 100K J phy _ O inanes t C Osgoi j Fi anpty_Nt_PO_ot i Oin 4 Ag Ta KB s weap lty NPr gi J gi J IIX
27. nd to automatically insert thousands of mobile nodes into the topology editor can first invoke the node editor of the GUI to specify the protocol stack and parameter values used for these mobile nodes With this setting all inserted mobile nodes will use the same protocol stack and parameter values In addition to protocol stack and parameter settings data and information fusion operation also useful in mobile sensor networks to reduce traffic volume and make intelligent decisions In NCTUns data and information fusion agents running on each mobile node can be conveniently implemented as user level application programs This implementation provides several advantages First since such agents contain intelligence and are usually complicated it is better to implement them separately rather than implement them as protocol Wirel Commun Mob Comput 2005 5 899 916 910 S Y WANG AND Y B LIN Elle Ede Toots Setting Simulation View Help kKAweoceUigeoenkiv ss ige select isjssnn PABABRSBIDER P ke amp Access Point oe gt al 3 a a a fl 42 p so f A i Simulated Mobile Node os f pn 7 j Extemal Mobile Noda At g j g as w a el e cli mumm AAN biim Delete a node Node ID 2 Fig 5 Wireless LAN infrastructure mode network emulation modules and mix their codes with the simulation engine code Second such agents may have been implemented as appli
28. networks One application is to quickly distribute such a message from a scene where a vehicle accident occurs to all following vehicles and the control units on the following vehicles will then automatically slow down the cars to avoid subsequent collisions Another application is to automatically maintain the safety distance between a vehicle and its lead or following vehicle through these control units without driver involvement In these two applications a mobile node also needs to actively control its moving speed and direction Figure 6 shows an example of IVC network studied in NCTUns The tiny vehicle icons in the figure represent real world vehicles moving on the highway The appearance of a small and large circles centered at a vehicle icon represent that the vehicle is transmitting a wireless packet and they represent the transmission and interference ranges of the wireless interface respectively The moving paths of these vehicles are eS lg of XNcTUss 2 0 Beta Version mi Komde l6 a CTUns2 0 Bem Version A Gp Fig 6 An example of IVC network Copyright 2005 John Wiley amp Sons Ltd Wirel Commun Mob Comput 2005 5 899 916 912 S Y WANG AND Y B LIN imported from the log file generated by the VISSIM vehicle microscopic traffic simulator 22 7 2 Wireless Mesh Networks In a wireless mesh network e g IEEE 802 11s access points function like routers to forward packets among themsel
29. nodes moving paths plot performance curves playback animations of logged packet transfers etc From a network topology the GUI program can generate a simulation job description file suite Since the GUI program uses Internet TCP IP sockets to communicate with other components it can submit a job to a remote simulation machine for execution When the simulation is finished the simulation results and generated log files are transferred back to the GUL The user then either examines logged data plots performance curves or plays back packet transfer animations During a simulation the user can query or set an object s value e g the routing table of a router or the switch table of a switch at any time If the user does not want to do any query or set operation during a simulation the user can choose to disconnect but not terminate the currently running simulation so that he she can use the GUI to handle other simulation jobs The user can later re connect to a disconnected simulation regardless whether it is still running or has finished A user thus can submit many simulation jobs simultaneously This can increase simulation throughput if multiple simulation machines are avail able to service these jobs concurrently Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 903 4 2 Simulation Engine The NCTUns simulation engine is a user level pro gram that functions like a small operatin
30. ns 2 because there is no concept of IP addresses in an ns 2 simu lated network In ns 2 a traffic generator agent needs to be bound to a traffic sink agent at the beginning of a simulation During simulation it cannot dynamically change its destination node at run time like a normal real world application program does Second existing and to be developed real world application programs may not be directly run with traditional network simulators Instead applications in these simulators need to be simplified and re implemented as functions and compiled with the simulation engine program Such over simplified functions usually are not realistic e g a generated packet stream whose packet transmission time inter vals are drawn from a statistic distribution As such when the simulator runs as a user level process on top of the operating system s kernel a real world applica tion program cannot deliver packets to the simulator via the standard UNIX POSIX system call API e g socket sendto recvfrom etc because they run at the same level For this reason the application programs supported by a traditional network simula tor are only those that have been simplified modified and re implemented in the simulator To overcome these problems Wang invented a kernel re entering simulation methodology 2 3 and Copyright 2005 John Wiley amp Sons Ltd implemented it in the Harvard network simulator 4 Later on Wang i
31. nt emulation configurations supported by NCTUns kernel re entering simulation methodology and is very unique Alternatively two external hosts can exchange their packets via the simulated network In Figure 3 b a TCP connection is set up between two application programs with one running on one external host the other running on another external host and the TCP connection traversing through several nodes in the simulated network Since the TCP packets exchanged by these two real world application programs need to pass through the simulated network and experience various simulated network characteristics network device developers can test how their applications and protocols would perform under various network conditions For example we can easily test the sound quality generated by two VoIP phone devices when the phone call needs to go through a simulated net work with about 300ms network delay and 10 packet loss rate Although existing emulators can support this configuration the simulated network supported by them mostly is only a link abstraction which may delay drop and reorder real world packets based on a certain statistics distribution In the Copyright 2005 John Wiley amp Sons Ltd NCTUns network emulator on the other hand the simulated network where real world packets go through can be a complicated network with many nodes The size of the simulated network can be very large as long as the speed of the simula
32. of QoS e g voice over IP can be adequately supported Several radio resource management and QoS schemes are being proposed for next generation wireless and mobile networks such as IEEE 802 16 WiMax net works and IEEE 802 11 WiFi networks with IEEE 802 1 1e QoS supports Evaluating the performance of these schemes in various conditions can help research ers discover their design flaws and performance limitation In a network providing QoS guarantees for an application e g VoIP should be end to end and up to the application layer The effect of a radio resource management or a QoS scheme on network layer routing protocols e g IP transport layer protocols e g TCP UDP and application layer protocols e g HTTP should all be considered Performance analysis of these schemes at a lower layer such as the MAC layer cannot reflect the real performance of these applications To obtain more realistic end to end application layer performance the processing and the interactions among these layers and real world appli cations need to be investigated Network simulators are valuable tools for research ers to design test diagnose and evaluate network pro tocols under various network conditions Conducting Correspondence to Shie Yuan Wang Department of Computer Science and Information Engineering National Chiao Tung University Hsinchu Taiwan iB mail shieyuan csie nctu edu tw Contract grant sponsor MOE contract gran
33. r 190 journal articles and more than 200 conference papers Lin is the co author of the book Wireless and Mobile Net work Architecture with Imrich Chlamtac published by John Wiley Sons Lin is an IEEE fellow an ACM fellow an AAAS fellow and an IEE fellow Wirel Commun Mob Comput 2005 5 899 916
34. s can be far away from the ma chines where the GUI programs are run For example the simulation service machines may reside at NCTU in Taiwan while the GUI users come from many different places of the world Multiple simulation jobs can be concurrently simulated on different ma chines one machine serves one job to increase the total simulation throughput When the NCTUns simulation jobs are run on multiple machines we say that NCTUns is operating in the multiple machine mode 13 This mode supports remote and concurrent simulations In the single machine mode the simulation jobs run on the same machine With the inter process communi cation IPC design NCTUns can be used for either mode without changing its program code Only the mode parameter in its configuration file needs to be changed NCTUns can also be turned into a parallel and distributed network simulator This is particularly suitable for simulating a very large wireless network with thousands of mobile nodes In this mode differ ent nodes of a network are simulated by the NCTUns simulation engines running on different machines The real world application programs run on these Copyright 2005 John Wiley amp Sons Ltd mobile nodes are forked and executed on different machines This approach can effectively spread the total memory space demand imposed by these appli cation programs over multiple machines hence over coming the memory space limitation
35. s using the NCTUns Tool to be published as a book chapter in the Progress in Computer Network Research book which will be published by Nova Science Publisher Inc at the end of 2005 9 Rizzo L Dummynet a simple approach to the evaluation of network protocols ACM Computer Communication Review 1997 27 1 31 41 10 VMware Exterprise class virtualization software http www vmware com 11 OPNET Inc http www opnet com 12 SSF network module SSFnet available at http www ssfnet org 13 Lin Y B Parallel independent replicated simulations on a network of workstations Simulation 1995 64 2 102 110 14 Fujimoto RM Parallel and Distributed Simulation Systems Wiley Inter Science John Wiley and Sons Inc New York USA 2000 15 Wang SY Hwang CC Chou CL On striping traffic over multiple IEEE 802 11 b wireless channels ACM Wireless Networks accepted and to appear 16 Wang SY Optimizing the packet forwarding performance of wireless chain networks Computer Communication 2003 26 14 1515 1532 Copyright 2005 John Wiley amp Sons Ltd 17 Tsai TC Tu CM An adaptive IEEE 802 11 MAC in multi hop wireless ad hoc networks considering large interference range Lecture Notes in Computer Science 2003 2928 87 100 18 Liu YH Chen YC A distributed buffer management approach supporting IPv6 mobility In Proceedings of the 10th IEEE International Workshop on Future Trends of Distributed Com
36. simulations In the future with some protocol module modifications NCTUns can also support more recent cellular network proposals such as W CDMA Figure 8 shows an example of GPRS network studied in NCTUns From this figure we see the GPRS phones base stations SGSNs GGSNs and GPRS switches that connect multiple SGSNs with multiple GGSNs In NCTUns each GPRS phone is lv Eile Ede Toots Setting Simulation View Help Ls XA cies f plae wN 4 000 OD acs amann A A gt I m Coo O85 Be OMG see Pee one Fig 7 An example 4 x 3 wireless mesh network Copyright 2005 John Wiley amp Sons Ltd Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 913 Ele Edt Tools Setting Simudation View tiep ait Ik XAeocedisweakvs s ge sajoi i oa nuE I7ARBRAID ER P ae i 5 m Base Staton E i E he JA Hki p Base Station nd Sei Base Station 1 d a 0 000 00 00 O80 pannon F 5 J m GPRS Swiich 3 S a 1e b Tt h A i af com om wn A A lD AL m ifa Stoo x Fig 8 An example of GPRS network given an IP address to exchange IP packets with any host on the fixed network Internally a GPRS phone behaves like a host It uses the real world TCP UDP IP protocol stack to communicate with the outside world and any real world application program can run on it This means that in NCTUns a real world web browser program e g
37. t numbers 91 E FA06 4 4 NSC93 2752 E 0090005 PAE Copyright 2005 John Wiley amp Sons Ltd 900 S Y WANG AND Y B LIN simulations is more economical flexible and safer than performing real experiments For example in large wireless and mobile networks where thousands of nodes need to move significant performance eva luation cost will be saved via simulations because one need not to purchase many equipments to do the real experiments In addition simulation results are easier to analyze than experimental data because simulation results are repeatable while experimental results usually are unrepeatable due to many uncontrollable factors in the real world However traditional network simulators usually have the following drawbacks First results of traditional simulations are not as convincing as those produced by real hardware and software equipment In order to reduce development complexity and cost most network simulators only simulate real world network protocols and application implementations with limited details This abstraction may lead to inaccurate results For example in ns 2 package 1 it is documented that there is no dy namic receiver s advertised window for TCP As another example in a real network a UDP based application program can change its destination host i e change the used destination IP address for an outgoing UDP packet at run time on a per packet basis However this cannot be done in
38. tack in the simulation machine However since its release in 1997 Dummynet has changed substantially and now is used as a real time traffic shaper or a bandwidth and delay manager in the FreeBSD kernel It is no longer used as a network simulator VMware 10 can implement virtual machines It can provide virtual x86 like hardware environments within which a number of different operating systems can be executed With this capability a number of virtual machines can be implemented on a single real machine to act as hosts or routers They can be configured to form an emulated network and packets generated by real world application programs run on these virtual machines can be exchanged through the emulated network Although VMware can be used as an emulator it is not a network simulator As such its result is not repeatable and a simulation case cannot be finished more quickly than the simulated time in the real world In addition it is very heavy weight A virtual machine consumes much resource and runs substantially slower than the real machine some times by an order of magnitude OPNET modeler 11 ns 2 and SSFnet 12 re present the traditional network simulation approach In this approach the thread supporting event schedu ler application code not real world application pro grams that generates network traffic utility programs that configure monitor or gather statistics about a simulated network the TCP IP protocol stack
39. the Mozilla on Linux can run on a GPRS phone to fetch web pages from a real world web server e g the Apache via the simulated GPRS channels NCTUnss support for GPRS cellular network si mulations provides more freedom for researchers to study such networks NCTUns implements detailed GPRS protocol modules e g RadioPhy MAC RLC LLC SNDCP BSSGP NS and GTP 23 and allows their parameter values and designs to be easily chan ged For example the channel time slot allocation and scheduling algorithm can be varied to study its effects on contending GSM and GPRS traffic 8 Performance Optimization NCTUns uses a performance optimization technique to speed up large scale wireless network simulations Copyright 2005 John Wiley amp Sons Ltd In a real world wireless network when a node trans mits a packet through its wireless interface the wi reless interface of every surrounding node in the network may receive this packet To simulate this phenomenon a traditional approach makes many copies of the packet and delivers each copy to every surrounding wireless interface for further processing Although this implementation is correct the simula tion speed may significantly degrade due to excessive packet processing and duplications When the wireless nodes are scattered in a large field many of them will not sense the signal of a wireless packet transmitted by a node that is far from them In this situation even
40. though NCTUns makes a copy of the transmitted packet and delivers a copy to each of them they will simply discard the delivered packets because the signal strength of the received packets is below their carrier sense power threshold Therefore CPU cycles and memory space are wasted for duplicating delivering storing and processing these unnecessary packets To optimize the performance of wireless network simulations NCTUns moves the above power level comparison tests from receiving nodes to the sending node A copy of a packet is created and delivered to Wirel Commun Mob Comput 2005 5 899 916 914 S Y WANG AND Y B LIN re i Fig 9 A 10 x 10 mobile ad hoc network configuration another node only when the comparison test is passed In this optimization implementation a significant amount of packet processing cost can be saved To illustrate this optimization technique Figure 9 shows an example 10 x 10 mobile ad hoc network in which the node spacing between two neighboring nodes is set to 200m In this network the receive and carrier sense power thresholds of all wireless interfaces are set to certain values that correspond to 250 and 550m respectively which are graphically indicated by the inner and outer circles centered at the 5th row 5th column node In this figure many nodes Time Required for the Simulation sec 0 50 100 150 Number of Mobile Nodes T T Optimization OFF Optimiza
41. tion ON 200 250 300 350 Fig 10 The time required for a simulation with respect to the number of mobile nodes Copyright 2005 John Wiley amp Sons Ltd Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 915 6e 06 5e 06 4e 06 3e 06 2e 06 No of Events Generated per Simulated Second 1e 06 50 100 150 Optimization OFF Optimization ON 200 250 300 350 Number of Mobile Nodes Fig 11 The number of events generated per simulated second with respect to the number of mobile nodes are outside the scope of the outer circle and the new implementation can save a lot of overhead by not duplicating and delivering packets to them Figure 10 compares the simulation execution times between the original and the optimization implemen tations with different numbers of nodes The simula tion period is 60s in simulation time During the simulation each node round robinly transmits a 1500 byte UDP packet to other nodes in the network at the rate of 10 packet sec The sizes of the networks are 64 8 x 8 100 10x 10 144 12 x 12 255 15 x 15 384 18 x 18 respectively This figure indicates that without using the performance optimi zation technique the execution time will grow ex ponentially Since each packet is treated and processed as a simulation event the optimization technique also reduces the number of events and the memory storage dur
42. tion machine s CPU can simulate the network at real time In addition in NCTUns real world packets can interact and compete with the packet traffic dynamically generated by application programs running on simu lated nodes This capability is illustrated in Figure 3 b by showing that TCP connection 1 is competing with TCP connection 2 for the bandwidth of the link connecting R1 to R2 To our knowledge no existing emulators support this type of traffic mix between simulated and real world packets To describe the connectivity between an external node and a simulated node each external node is represented by an external node icon in the simulated network A GUI user can easily specify the connec tivity by drawing a link between an external node and a simulated node Lik e other links in the simulated network such a link has its own delay and bandwidth properties simulated by NCTUns Wirel Commun Mob Comput 2005 5 899 916 NCTUns NETWORK SIMULATION AND EMULATION 907 We note that the physical link connecting the simulation machine and the external node need not apply any MAC protocol processing to the real world packets when they are transmitted over the link Instead it only needs to transfer the real world pack ets from one end of the link to the other end of the link as fast as possible Simulations of properties e g bandwidth delay BER etc for the link connecting the external node is done by the simulatio
43. topology editor During emulation the packets generated by the external mobile node will be transferred to the simulation machine and then enter the simulated wireless network For the simulated network these packets seem to be generated by the corre sponding mobile node in the simulated network Since the corresponding mobile node uses a wireless interface to connect to the simulated wireless network in either the ad hoc mode or the infrastructure mode these real world packets will be transferred wirelessly in the simulated net work and may contend with other wireless pack ets that are generated in the simulated network Note that real world packets will experience the wireless MAC protocols e g IEEE 802 11 b MAC in the simulated network rather than the wireless MAC protocols that are implemented in the wireless interface of the external mobile node This situation is similar to a fixed network emula tion where the link connecting the simulation machine and an external node needs to deliver real world packets between two ends of the link as fast as possible and need not apply any MAC protocol processing to them In addition because the moving path of an external node is specified in the simulated network rather than in the real world an external mobile node in the real world need not move Figure 4 shows an emulation example in which one external ad hoc mobile host on the left communicates with a simulated mobile host on
44. upporting this external node will intercept these packets change their destination IP addresses from the one used in the simulated network to the one used in the real network and then forward them to the external node in the real network Wirel Commun Mob Comput 2005 5 899 916 908 S Y WANG AND Y B LIN Now we describe how to direct traffic generated by an external node to the simulated network i e to the simulation machine Suppose that the simulation machine s IP address in the real world is 10 0 0 1 and the external machine s IP address is 10 0 0 2 and they are physically connected via an Ethernet cable Suppose that the external node makes a TCP connec tion to a simulated node whose assigned private IP address is 1 0 3 1 Then on the external node the user should first execute the route add 1 0 16 10 0 0 1 command to add the required routing entry to the system routing table In the above command 1 0 16 means that the destination network address is 1 0 X X 16 means that the netmask is 255 255 0 0 Note that every node in the simulated network is assigned a private IP address of the form of 1 0 X X As such the above command indicates that all outgoing IP destination address 1 0 X X should be first sent to the gateway whose IP address is 10 0 0 1 Since 10 0 0 1 is the simulation machine s IP address these packets will be delivered to the simulation machine When the packets generated by an external nod
45. ves A mobile station associates itself with an access point and transmits receives packets to from the associated access point The access point upon receiving a packet from the mobile station wirelessly sends it to a neighboring access point for further forwarding The forwarding process continues until the packet reaches an access point that connects to the Internet Through this approach a major part of wiring cost can be saved because only a few access points need to connect to the Internet to provide Internet access for all mobile stations NCTUns provides 802 11 b AP module for wire less mesh network study Several routing approaches suitable for wireless mesh networks have been im plemented and are being tested in NCTUns We have implemented AODV DSR and DSDV routing proto col modules for the MANET approach the RIP and OSPF routing protocol daemons for the fixed network approach and the spanning tree protocol for the cellular approach to build a spanning routing tree among access points and the user location tracking database Figure 7 shows an example 4 x 3 wireless mesh network We can see that packets generated by mobile stations are wirelessly forwarded among access points until they reach the access points at the top left and top right corners where an Internet con nection is available 7 3 GPRS Cellular Networks In addition to simulating IEEE wireless LAN NCTUns also supports wide area GPRS cellular net work
46. xternal node To direct packets originated from the simulated network to the external node the emulation daemon also needs some information A GUI user thus needs to do some settings on both the external node and the simulation machine to ensure that an emulation case works correctly 6 1 Adjusting Simulation Speed Once a user adds an external node into the network topology the speed of the simulation engine will be automatically set to the speed of the wall clock This means that during an emulation the simulated net work will be simulated at the speed of the wall clock Copyright 2005 John Wiley amp Sons Ltd During an NCTUns emulation the clock of the simulated network is synchronized with the wall clock every I ms and therefore the emulation function s latency precision is about ms For example suppose that a user uses the real world ping program to measure the round trip time of the path between an external node and a simulated node and the round trip time RTT of this path is 100 ms in the simulated network then the reported RTT on the external node may be some value between 99 and 101 ms From experimental results we found that the pre cision may get worse if NCTUns is used in the single machine mode During emulation the GUI program simulation engine traffic generator application pro grams and some daemon programs compete for the machine s CPU cycles which results in degraded emulation precision The
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