Framework for Simulation of Mobility in OMNeT++ (FraSiMO)
Contents
1. Figure 7 UML model of the DSR example The Entity This class contains the following methods bool connectWith char in char out int idx Returns true if the Entity is successfully connected to the gates named out and in with the Management_Unit with the module id idx This method searchs for free gates at the Management_Unit idx if no gates are free it can create new gates if the maximum number of communication members of this Management_Unit is not reached Then the method creates two connections between Entity and Management_Unit cMessage copyMessage cMessage msg Returns the pointer to a copy of the message msg cMessage deleteMessage cMessage msg Deletes the cMessage msg void disconnect char in char out int idx Disconnect the Entity from the Management_Unit which is connected with the gates named out and in With the methods setFrom and setTo this method redirects the connection pointers to NULL idx is the module id of the managment unit void getCannelID int channelID After calling this method id contains the logical channel on which the Entity receives void getPosition int x int y After calling this method x contains the x value of the position and y the y value cMessage receiveM Waits until a message is received This method should be overridden if one wants to implement new message types e g with a message length or parameters like transmission power void redirect cha2. a FraSiMO simulation since all gates of the gate vector must have consecutive gate IDs The creation of Entities like in our example is not necessarily placed in the management unit Our example management unit receives messages from the gate vector all odd id s are input gates It checks which Entities can receive this message using the method isReachable from the channel model For all receivers it determines the propagation delay and schedules the message with scheduleAt for this time Then the message will be sent to the receivers In some cases the functionality may be nearly identical to ours so one can copy our activity method Only if one has implemented other methods in the channel model like determination of bit error rate BER or signal to noise ration SNR one has to change the method so that the content of the messages will be manipulated corresponding to the packet error rate PER The next task is to implement the communication members First one should derive a class Mobile_Host from the Entity class and override the methods copyMessage and deleteMessage The management unit sends a copy of the message to each receiver but in some cases it is very important to copy not only the message but also the parameters If one wants to send each receiver its own copy of some parameters this copyMessage method is to be specified It is also necessary to implement deleteMessage to destroy these copied parameters The class Entit
3. information about a homogenous network Each Channel_Model is associated with one Management_Unit and is not a separate OMNeT module The World is the global compound module which contains the entire simulation scenario Each simulation has only one World module In the World module global information can be implemented for example information about the Management_Units module ids etc In our example applications we have implemented a method getMaximumLoad which provides the maximum number of communication members for a given Management_Unit Figure 4 the UML diagram of our framework shows how the components of FraSiMO fit into the OMNeT 4 architecture white modules Logical View Figure 4 The UML model Please note that the Channel_Model is not completely red dark gray indicating that the functionality of this module has to be redefined to fit the special needs of a particular medium and or communication structure In the next chapter the FraSiMO modules will be discussed in detail 5 Guide for Creating a Mobile Scenario with FraSiMO In this chapter we will give a guideline for the creation of a mobile simulation scenario Some modules can have different names than in our example all modules which must be necessary explicitly named because other modules of FraSiMO reference these modules are written italic In some cases the explanation will be short so we recommend reading the description of our examp
4. services it may be necessary for one mobile host to enlist the aid of others in forwarding a packet to its destination due to the limited propagation range of each mobile host s wireless transmissions DSR is a routing protocol for such mobile ad hoc networks The sender creates routes on demand A complete description of DSR can be found in reference 3 Our example may be the substructure for own implementations Because of this we have documented all methods of our modules in the second part of this chapter 7 1 Description of the DSR scenario We have implemented the following scenario Table 1 shows a module overview Entity 0 wishes to communicate with Entity 4 It sends a route request routing messages are red in the simulation Every Entity is able to reach his neighbors in a 4 neighborhood cyan light gray These relations are implemented in our channel model ID Module type Name 1 Void 2 World World 3 Management_Unit Management_Unit 4 13 Mobile_Host Ent0 Ent9 Tabelle 2 Module IDs of DSR example A route is built blue route Entity 0 1 2 3 4 but then Entity 2 a part of the route disconnects from the management unit that is it is turned off After a timeout Entity 0 sends another route request After the new route is built magenta route Entity 0 1 6 7 8 3 4 the communication continues over the new route data messages are white in the simulation During the whole time Entity 4 is increasing the distance to
5. the other Entities until it is no longer reachable by any other Entity In this case Entity 0 starts polling for a new route but no new route can be built because the receiver is not reachable Entity 0 s polling will continue indefinitely or until the simulation is aborted Figure 6 Message routes of the DSR example 7 2 The Modules and Methods Figure 7 shows the UML diagram of the DSR example the white modules are a part of OMNeT The Channel_Model This class contains two member functions The method isReachable determines reachability propagationDelay calculates the propagation delay for messages The methods in detail bool isReachable cMessage message Entity sender Entity receiver Returns true if the message from sender can reach receiver The first criteria is the range between sender an receiver which must not be longer than TRESHOLD a macro definition in channel_model h The other criteria is the channel of the receiver set with setChannelID in Entity The method compares channel id of the message with the channel on which the receiver listens double propagationDelay Entity sender Entity receiver Returns the propagation delay between sender and receiver even if the sender cannot reach the receiver The delay is determined by distance over VELOCITY VELOCITY is a macro definition in channel_model h Logical View Module O T Go Ses cSimpleModule
6. with the Tcl Tk environment The Host_1_1 disconnects from the Management_Unit_1 and then connects to Management_Unit_2 The disconnection takes places using the method disconnect of the Entity class This method reinitializes the links to and from the Management Unit to NULL A new connection to a Management Unit is established with the connectWith method class Entity The full description of both methods is available in chapter 7 2 One has to consider that the Tcl Tk environment will not automatically update the display so it must be done manually with setDisplayString The second important aspect is the Connector an Entity which is connected to two different management units It is of course possible to connect with many Management_Units this Connector may be a switch for example ID Module type Name 1 Void 2 World World 3 Management_Unit Management_Unit_1 4 Management Unit Management_Unit_2 5 Mobile_Host Connector 6 Mobile_Host Server_1 domain 1 7 Mobile_Host Host_1_1 domain 1 8 Mobile_Host Host_1_2 domain 1 9 Mobile_Host Server_2 domain 2 10 Mobile_Host Host_2_1 domain 2 11 Mobile_Host Host_2_2 domain 2 Table 1 Module IDs of Nomadicity example 7 The Dynamic Source Routing Example This chapter will explain our example of a Dynamic Source Routing DSR scenario In a mobile ad hoc network 2 with wireless mobile hosts forming a temporary network without the aid of any centralized administration or standard support
7. Framework for Simulation of Mobility in OMNeT FraSiMO Heiko Scheunemann Daniel M Kirsch 1 Abstract This article is an introduction as well as a reference for programmers who want to simulate mobility in communication systems We investigated the possibilities of simulating mobility on the basis of the discrete event simulation system OMNeT To this end we developed the Framework for Simulation of Mobility in OMNeT FraSiMO for OMNeT FraSiMO assists the developer with fundamental classes and methods necessary for the simulation of both nomadic and mobile wireless telecommunication systems On the basis of two examples we explain the main features of FraSiMO a Dynamic Source Routing protocoll and a nomadicity example 2 Introduction Mobility is an aspect in telecommunications which becomes more and more important The use of cellulars PDA s and laptops has increased in the past years and today they are an important part of our society But the simulation of wireless and non wireless mobile communication is still a problem due to difficulties in finding and using the appropriate simulator Most discrete event simulation tools are originally not designed for mobility i e they use only static links between communication members We investigated if it is feasible to handle mobility in OMNeT 1 developed a concept for handling both wireless and nomadic telecommunications and implemented a framework supporting this con
8. cept The framework implementation consists of a C library providing methods and features to support mobility The methods of the Framework for Simulation of Mobility in OMNeT FraSiMO allow an easier link management and simple position handling Our framework is a guideline for design and implementation of various mobile simulation scenarios FraSiMO is completely written in C so it is not necessary to be familiar with the OMNeT specific language NED This paper is organized as follows 3 OMNeT OMNeT is an object oriented modular discrete event simulator based on C The main components we have used are Modules compound and simple Gates Links Messages There are two module types Modules that contain submodules are termed compound modules as opposed simple modules which are the lowest level of the module hierarchy Simple modules contain the algorithms in the model The user implements the simple modules in C using the OMNeT simulation class library 1 Both module types can be connected via links Links originate from an output gate on a module and connect to an input gate on either the same or another module Messages can be send through these links from one module to another The sending and arrivals of messages are considered as discrete events The receiver module becomes the new owner of the message It is also possible to send self messages which are often useful for modeling timers The
9. equest_id gt and lt route_record gt to it and returns it 10 int check_message cMessage message Checks the message type NORMAL ROUTE_REQUEST ROUTE_REPLY ROUTE_ERROR and returns it static cArray copyRoute cArray route Supporting method copies the route and it s members void discard_normal_message cMessage message Removes lt source_route gt parameter from the message and deletes the message void discard_route_reply message cMessage message Removes the parameters lt source_route gt and lt route_record gt from the message and deletes the message void discard_route_request_message cMessage message Removes lt route_record gt parameter from the message and deletes the message int get_next_receiver_id cMessage message Extracts next receiver entry from message s lt source_route gt returns own host id if this is the last entry returns 1 if no source route was found cArray getRoute int source_host_id int destination_host_id long time Returns the route to module id from the routing cache or null if no route exists Additionally this function cleans old entries older than expiration time from the routing cache time should be the simulation time simTime cMessage handle_route_reply message cMessage message long time Takes a route reply message and extracts the route and puts it in the routing cache cMessage handle_route_request_message cMessage message long time Tak
10. es a route request message and the current time as parameters and returns NULL if the original message has to be discarded otherwise it will return a route reply message or a modified route request message If it returns a route reply message a check_message is needed to see if the original message is not NULL If this is so this has become a modified route request message and had to be re broadcast static void killRoute cArray route Supporting method removes all elements from a route and deletes the array Finally there are some debugging methods to print the different routes and the routing cache The World This class contains the method getMaximumLoad which provides the maximum number of communication members for the Management_Units The connectWith method of Entity creates a new connection to a Management_Unit only if this Management_Unit has not reached his maximum number of Entities The method in detail static int getMaximumLoad int id Returns the maximum number of Entities which can be connected to one Management_Unit The id determines the module id of the Management_Unit 11 8 Conclusion With FraSiMO it is now possible to fast and easily build simulation networks intended to be used for simulation of virtually any kind of mobility FraSiMO enhances the basic functionalities of OMNeT significantly without giving up the plain and simple structure provided by OMNeT However it does not relieve the developer
11. iy already provides simple message copying so there is no need to implement these methods if no parameters should be copied In some cases one may also override other methods for example if one wishes to create another kind of connection handling From this Mobile_Host one can now derive many classes with different functionalities These derivations can of course use the methods of Entity to set and get the current position and to create and destroy connections easily to management units When writing your own derivations from Entities remember to change the entries in the macro function Module_Class_Members to fit your derived class name and stack size Then one has to implement the World module After the creation of all communication members one knows which global information all or many subscribers will need In all cases one has to implement the method getMaximumLoad which determines how many Entities can connect to a given management unit This method is necessary for the connectivity of the Entity One can implement other methods for example a method which provides a list of all management units Unlike typical implementations with OMNeT we recommend to create the Entities within the method buildInside of the World or the activity of the management unit It is not necessary to use NED to create a scenario because the module void cc which was originally created with NED contains one World module Last but not least one ha
12. les To create a mobile simulation scenario one first has to determine how many clusters will be needed Each cluster can represent a homogenous network like an Ethernet Yet in some cases it may be useful to represent different parts of a network for example the network of one floor as different clusters and connect them with modules representing switches The second step is to implement the channel model For each cluster one has to implement a channel model although different clusters may use the same channel model if they have the same physical properties The creation of the channel model is in most cases very simple One has to implement methods which decide if a receiver can get the message of a sender method isReachable and how long the propagation delay is method getPropagationDelay This depends in our DSR example on the distance between both Entities and on the logical channel on which the message is send It is also conceivable to implement methods for determination of packet error rate PER or signal to noise ratio SNR If the creation of channel model is finished we recommend implementing the method activity of the management unit while not tested an FSM based implementation of the management unit may also be possible One can use our example management unit as a template Each management unit has to create a gate vector In our framework it is not allowed to use other gates because this will destroy the connectivity of
13. of the duty of implementing the cluster specific characteristics like type of medium air cable or the chosen protocol architecture One of our main objectives was the extensibility of the framework which we have accomplished not only with regard to the simulation developer but also towards anyone who wants to work with the framework itself To improve FraSiMO we suggest implementing an API for visualization of mobility e g display of movement patterns for the Tcl Tk environment of OMNeT We think that FraSiMO will help you much in developing your own simulations and we hope that you will have as much fun working with it as we had developing it 9 References 1 Andras Varga OMNeT Discrete Event Simulation System Version 2 0b4 User Manual http www hit bme hu phd vargaa opp docs usman htm 2 GEDOC Mobile Ad hoc Networks Study Group What Ad hoc Networks are http www siam dcc ufmg br gedoc ad_hoc_eng html 3 David B Johnson David A Maltz Dynamic Source Routing in Ad Hoc Wireless Networks in Mobile Computing Kluwer Academic Publishers 1996 http www ics uci edu atm adhoc paper collection johnson dsr pdf 12
14. r in char out int fromidx int toidx Redirect the Entity from the Management_Unit fromidx which is connected with the gates named out and in to the Managment_Unit toidx That means a disconnect from the Management_Unit fromidx and a connectWith to the Management_Unit toidx void sendM cMessage msg char out Sends a message msg through the gate out protected void setCannelID int channelID Sets the logical channel on which the Entity receives to channellD protected void setPosition int x int y Sets the position to new coordinates x y The Mobile_Host This class is derived from Entity and contains the following methods void activity The functionality of each communication member See the scenario description cMessage copyMessage cMessage msg Returns a copy of the message msg This copied message has also a copied parameter source_route and route_record cMessage deleteMessage cMessage msg Delete the message msg and remove the parameters source_route and route_record The Routing_Package cMessage build_normal_message int destination_host_id cMessage message long time Takes destination_host_id a message and the current time as parameters and adds lt source_route gt parameter to message returns NULL if not possible cMessage build_route_request_message int target_id int request_id Creates a message and adds parameters lt target_id gt lt initiator_id gt lt r
15. ree types of modules described in the following 7 TN h Figure 3 a single cluster i with 4 elements is displayed l i i The elements are linked Handy 2 ae Handy 1 together by the air interface cp channel model 6 l Base Station o 3 These elements will be I b i referenced in the following as Entities Handy 3 1 Figure 3 Cluster The Entity module represents the mobile communication members Each communication member is derived from this class It has to implement methods for message handling sending receiving copying deleting simulation connectivity to allow an Entity module to connect to or disconnect from a Management_Unit module at runtime and position handling set and get the position of the Entity The module Management_Unit is the most important part of our framework It represents a homogenous network a cluster This can be an Ethernet one Token Ring or a GSM cell The Management_Unit has to handle incoming messages from all Entities which are connected on simulation level to this module It decides which modules can receive this message determines aspects like propagation delay bit error rate or signal to noise ratio SNR and sends the message to the connected Entities The information about reachability propagation delay and other network properties is stored and administered in a Channel_Model Additionally there is the Channel_Model a class that holds
16. s to adapt the makefile to the implemented structure or use makemake 6 The Nomadicity Example This chapter will explain our Nomadicity example It is simpler than the DSR scenario and shows no wireless mobility 6 1 Description of the Nomadicity scenario We have implemented the following scenario Table 1 shows a module overview There are two domains which are represented by Management_Unit_1 and Management_Unit_2 eE Server_1 Host_1_1 Host_1_2 VL Management_Unit_1 Connector Management_Unit_2 Gi Server_2 Host_2_1 Host_2_2 Figure 5 The Nomadicity scenario Each host can only communicate with the server of the corresponding domain the connector can communicate with both domain servers Host_1_1 wants to move from domain 1 to domain 2 It sends a switch_domain1_request to it s server Server_1 Server_1 forwards this message to the Connector which sends it to Server_2 Server_2 sends a switch_domainl_ack via Connector to Server_1 and begins to search for new hosts broadcast polling Server_1 forwards the switch_domainl_ack to Host_1_1 This host disconnects travels to domain 2 and connects It receives a seek_new_host from the polling Server_2 extracts the server_id from this message and acknowledges This is the end of this scenario This scenario is very specialized but it shows some interesting aspects First it is a good example for nomadicity and for the problems while displaying nomadicity
17. structure of a scenario modules submodules and links can be specified in a description language called NED However it is possible to create all of these components during runtime of a simulation using the OMNeT specific methods For our own work we did not use NED 4 The Concept of FraSiMO In every communication scenario there are elements that communicate with each other in the following we use the words communication member or subscriber for these elements Some of these elements can be combined to logically separable groups for example because they use the same channel model These groups or clusters play an important role in FraSiMo We distinguished two forms of mobile communication with regard to these clusters First there is movement like a walking subscriber using a cellular Figure 1 The communication participant may be present in the same cluster all the time the channel model is always the same but the quality of transmission changes because of variable distance walls etc The other form is nomadicity Figure 2 which means in our concept switching from one cluster to another Network 1 Gd work 2 Host Networ N etwork 3 Figure 1 Ad Hoc reachability Figure 2 Nomadicity OMNeT allows only bilateral relations between modules and no groups or clusters We had to find a way to represent such a cluster which manages nomadicity and movement inside the cluster So we have designed our framework with th
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