LAB 1 CSMA A Direct Link Network with Media Access Control OBJECTIVES This lab is designed to demonstrate the operation of the Ethernet network The simulation in this lab will help you examine the performance of the Ethernet network under different scenarios OVERVIEW The Ethernet is a working example of the more general carrier sense multiple access with collision detect CSMA CD local area network technology The Ethernet is a multiple access network meaning that a set of nodes sends and receives frames over a shared link The carrier sense in CSMA CD means that all the nodes can distinguish between an idle and a busy link The collision detect means that a node listens as it transmits and can therefore detect when a frame it is transmitting has interfered collided with a frame transmitted by another node The Ethernet is said to be a 1 persistent protocol because an adaptor transmits its ready frame with probability 1 whenever a busy line goes idle In this lab you will set up an Ethernet with 30 nodes connected through a coaxial link in a bus topology The coaxial link is operating at a data rate of 10 Mbps You will study how the throughput of the network is affected by the network load as well as the size of the packets PRE LAB ACTIVITIES Read Section 2 6 from Computer Networks A Systems Approach 5th Edition Go to www net seal net and play the following animation Hub PROCEDURE Create a New Project To create a new project for the Ethernet network 1 Start OPNET IT Guru Academic Edition Choose New from the File menu 2 Select Project Click OK Name the project your initials Ethernet and the scenario Coax Click OK 1 Network Simulation Experiments Manual Local area networks LANs are designed to span distances of up to a few thousand meters 3 In the Startup Wizard Initial Topology dialog box make sure that Create Empty Scenario is selected Click Next Choose Office from the Network Scale list Click Next Assign 200 to X Span and keep Y Span as 100 Click Next twice Click OK 4 Close the Object Palette dialog box Create the Network To create our coaxial Ethernet network 1 To create the network configuration select Topology Rapid Configuration From the drop down menu choose Bus and click OK 2 Click the Select Models button in the Rapid Configuration dialog box From the Model List drop down menu choose ethcoax and click OK 2 The eth tap is an Ethernet bus tap that connects a node with the bus 3 In the Rapid Configuration dialog box set the following eight values and click OK The eth coax is an Ethernet bus that can connect nodes with bus receivers and transmitters through taps A higher delay is used here as an alternative to generating higher traffic which would require much longer simulation time Thickness specifies the thickness of the line used to draw the bus link 4 To configure the coaxial bus right click on the horizontal link Select Advanced Edit Attributes from the menu a Click on the value of the model attribute Select Edit from the drop down menu Choose the eth coax adv model b Assign the value 0 05 to the delay attribute propagation delay in seconds per meter c Assign 5 to the thickness attribute d Click OK LAB 1 CSMA 3 5 Now you have created the network It should look like the following illustration Configure the Network Nodes To configure the traffic generated by the nodes 1 Right click on any of the 30 nodes Select Similar Nodes to select all 30 nodes in the network Network Simulation Experiments Manual The argument of the exponential distribution is the mean of the interval between successive events In the exponential distribution the probability of occurrence of the next event by a given time is not at all dependent on the time of occurrence of the last event or the elapsed time since that event 2 Right click on any of the 30 nodes Edit Attributes 3 Check the Apply Changes to Selected Objects check box to avoid reconfiguring each node individually 4 Expand the Traffic Generation Parameters hierarchy a Change the value of the ON State Time to exponential 100 Change the value of the OFF State Time to exponential 0 Note Packets are generated only in the ON state The interarrival time is the time between successive packet generations in the ON state 4 5 Expand the Packet Generation Arguments hierarchy a Change the value of the Packet Size attribute to constant 1024 b Right click on the Interarrival Time attribute and choose Promote Attribute to Higher Level This allows us to assign multiple values to the Interarrival Time attribute and hence to test the network performance under different loads 6 Click OK to return to the Project Editor and Save your project Configure the Simulation To examine the network performance under different loads you need to run the simulation several times by changing the load into the network There is an easy way to do that Recall that we promoted the Interarrival Time attribute for package generation Here we will assign different values to that attribute 1 Click on the Configure Run Simulation button is chosen Assign 15 s to the Duration Make sure that the Common tab LAB 1 CSMA 2 Click on the Object Attributes tab 3 Click the Add button The Add Attribute dialog box should appear filled with the promoted attributes of all nodes in the network if you do not see the attributes in the list close the whole project and reopen it Add the Interarrival Time attribute for all nodes as follows a Click on Office Network node 0 Traffic Generation Click the Wildcard button Click on node 0 and choose from the drop down menu Click OK 5 b A new attribute is now generated containing the asterisk the second one in the list Click on the empty cell to the left of this attribute to add it as shown Click OK Network Simulation Experiments Manual 4 Now you should see the Office Network Traffic Generation Parameter in the list of simulation object attributes Click on that attribute to select it Click the Values button of the dialog box as shown 5 Add the nine shown values Note To add the first value double click on the first cell under the Value column Type exponential 2 into the textbox and press Enter Repeat this process for all nine values 6 6 Click OK Now look at the upper right corner of the Simulation Configuration dialog box and make sure that the Number of runs in set is 9 LAB 1 CSMA 7 For each simulation of the nine runs we need the simulator to save a scalar value that represents the average load in the network and to save another scalar value that represents the average