public static void main(String[] args)
    {        
        try
        {
            //////////////////////////////////////////
            // Step 1: Initialize the GridSim package. It should be called
            // before creating any entities. We can't run this example without
            // initializing GridSim first. We will get run-time exception
            // error.
            
            // number of grid user entities + any Workload entities.
            int num_user = 5;
            Calendar calendar = Calendar.getInstance();

            // a flag that denotes whether to trace GridSim events or not.
            boolean trace_flag = false;

            // Initialize the GridSim package
            System.out.println("Initializing GridSim package");
            GridSim.init(num_user, calendar, trace_flag);

            //////////////////////////////////////////
            // Step 2: Creates one or more GridResource entities

            // baud rate and MTU must be big otherwise the simulation
            // runs for a very long period.
            double baud_rate = 1000000;     // 1 Gbits/sec
            double propDelay = 10;   // propagation delay in millisecond
            int mtu = 100000;        // max. transmission unit in byte
            int rating = 400;        // rating of each PE in MIPS
            int i = 0;
            
            // more resources can be created by
            // setting totalResource to an appropriate value
            int totalResource = 3;
            ArrayList resList = new ArrayList(totalResource);
            String[] resArray = new String[totalResource];
            
            for (i = 0; i < totalResource; i++)
            {
                String resName = "Res_" + i;
                GridResource res = createGridResource(resName, baud_rate,
                                                      propDelay, mtu, rating);

                // add a resource into a list
                resList.add(res);
                resArray[i] = resName;
            }

            //////////////////////////////////////////
            // Step 3: Get the list of trace files. The format should be:
            // ASCII text, gzip or zip.

            // In this example, I use the trace files from:
            // http://www.cs.huji.ac.il/labs/parallel/workload/index.html
            String[] fileName = {
                "l_lanl_o2k.swf.zip",     // LANL Origin 2000 Cluster (Nirvana)
                "l_sdsc_blue.swf.txt.gz", // SDSC Blue Horizon
            };

            String dir = "../";     // location of these files
            String customFile = "custom_trace.txt"; // custom trace file format
            
            // total number of Workload entities
            int numWorkload = fileName.length + 1;  // including custom trace

            //////////////////////////////////////////
            // Step 4: Creates one or more Workload trace entities.
            // Each Workload entity can only read one trace file and
            // submit its Gridlets to one grid resource entity.

            int resID = 0;
            Random r = new Random();
            ArrayList load = new ArrayList();     
            
            for (i = 0; i < fileName.length; i++)
            {
                resID = r.nextInt(totalResource);
                Workload w = new Workload("Load_"+i, baud_rate, propDelay, mtu, 
                                    dir + fileName[i], resArray[resID], rating);

                // add into a list
                load.add(w);
            }

            // for the custom trace file format
            Workload custom = new Workload("Custom", baud_rate, propDelay, mtu,
                                           dir + customFile, resArray[resID], rating);

            // add into a list
            load.add(custom);

            // tells the Workload entity what to look for.
            // parameters: maxField, jobNum, submitTime, runTime, numPE
            custom.setField(4, 1, 2, 3, 4);
            custom.setComment("#");     // set "#" as a comment

            //////////////////////////////////////////
            // Step 5: Creates one or more grid user entities.

            // number of grid user entities
            int numUserLeft = num_user - numWorkload;
            
            // number of Gridlets that will be sent to the resource
            int totalGridlet = 5;

            // create users
            ArrayList userList = new ArrayList(numUserLeft);
            for (i = 0; i < numUserLeft; i++)
            {
                // if trace_flag is set to "true", then this experiment will
                // create User_i.csv where i = 0 ... (num_user-1)
                NetUser user = new NetUser("User_"+i, totalGridlet, baud_rate,
                                           propDelay, mtu, trace_flag);

                // add a user into a list
                userList.add(user);
            }

            //////////////////////////////////////////
            // Step 6: Builds the network topology among entities.

            // In this example, the topology is:
            // user(s)     --1Gb/s-- r1 --10Gb/s-- r2 --1Gb/s-- GridResource(s)
            //                       |
            // workload(s) --1Gb/s-- |

            // create the routers.
            // If trace_flag is set to "true", then this experiment will create
            // the following files (apart from sim_trace and sim_report):
            // - router1_report.csv
            // - router2_report.csv
            Router r1 = new RIPRouter("router1", trace_flag);   // router 1
            Router r2 = new RIPRouter("router2", trace_flag);   // router 2

            // connect all user entities with r1 with 1Mb/s connection
            // For each host, specify which PacketScheduler entity to use.
            NetUser obj = null;
            for (i = 0; i < userList.size(); i++)
            {
                // A First In First Out Scheduler is being used here.
                // SCFQScheduler can be used for more fairness
                FIFOScheduler userSched = new FIFOScheduler("NetUserSched_"+i);
                obj = (NetUser) userList.get(i);
                r1.attachHost(obj, userSched);
            }
                        
            // connect all Workload entities with r1 with 1Mb/s connection
            // For each host, specify which PacketScheduler entity to use.
            Workload w = null;
            for (i = 0; i < load.size(); i++)
            {
                // A First In First Out Scheduler is being used here.
                // SCFQScheduler can be used for more fairness
                FIFOScheduler loadSched = new FIFOScheduler("LoadSched_"+i);
                w = (Workload) load.get(i);
                r1.attachHost(w, loadSched);
            }

            // connect all resource entities with r2 with 1Mb/s connection
            // For each host, specify which PacketScheduler entity to use.
            GridResource resObj = null;
            for (i = 0; i < resList.size(); i++)
            {
                FIFOScheduler resSched = new FIFOScheduler("GridResSched_"+i);
                resObj = (GridResource) resList.get(i);
                r2.attachHost(resObj, resSched);
            }

            // then connect r1 to r2 with 10 Gbits/s connection
            // For each host, specify which PacketScheduler entity to use.
            baud_rate = 10000000;            
            
            Link link = new SimpleLink("r1_r2_link", baud_rate, propDelay, mtu);
            FIFOScheduler r1Sched = new FIFOScheduler("r1_Sched");
            FIFOScheduler r2Sched = new FIFOScheduler("r2_Sched");

            // attach r2 to r1
            r1.attachRouter(r2, link, r1Sched, r2Sched);

            //////////////////////////////////////////
            // Step 7: Starts the simulation
            GridSim.startGridSimulation();

            //////////////////////////////////////////
            // Final step: Prints the Gridlets when simulation is over

            // also prints the routing table
            r1.printRoutingTable();
            r2.printRoutingTable();

            GridletList glList = null;
            for (i = 0; i < userList.size(); i++)
            {
                obj = (NetUser) userList.get(i);
                glList = obj.getGridletList();
                printGridletList(glList, obj.get_name(), trace_flag);
            }
            
            // prints the Gridlets inside a Workload entity
            for (i = 0; i < load.size(); i++)
            {
                w = (Workload) load.get(i);
                w.printGridletList(trace_flag);
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
            System.out.println("Unwanted errors happen");
        }
    }