1LAB 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 . CSMA A Direct Link Network with Media Access Control 1Network Simulation Experiments Manual2 3. In the Startup Wizard: Initial Topology dialog box, make sure that Create Empty Scenario is selected · Click Next · Choose Offi ce 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 confi guration, select Topology · Rapid Confi guration . From the drop-down menu choose Bus and click OK . 2. Click the Select Models button in the Rapid Confi guration dialog box. From the Model List drop-down menu choose ethcoax and click OK . Local area networks (LANs) are designed to span distances of up to a few thousand meters. The eth_tap is an Ether-net bus tap that connects a node with the bus. The eth_coax is an Ethernet bus that can connect nodes with bus receivers and transmit-ters through taps. A higher delay is used here as an alternative to generating higher traffi c, which would require much longer simulation time. Thickness specifi es the thickness of the line used to “draw” the bus link. 3. In the Rapid Confi guration dialog box, set the following eight values, and click OK . 4. To confi gure 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 .3 5. Now you have created the network. It should look like the following illustration. Confi gure the Network Nodes To confi gure the traffi c generated by the nodes: 1. Right-click on any of the 30 nodes · Select Similar Nodes to select all 30 nodes in the network. LAB 1 CSMANetwork Simulation Experiments Manual4 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 attri-bute and hence to test the network performance under different loads. 6. Click OK to return to the Project Editor , and Save your project. Confi gure 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 Confi gure/Run Simulation button: · Make sure that the Common tab is chosen · Assign 15 s to the Duration . 2. Right-click on any of the 30 nodes · Edit Attributes . 3. Check the Apply Changes to Selected Objects check box to avoid reconfi guring each node individually. 4. Expand the Traffi c 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 argument of the exponential distribu-tion is the mean of the interval between successive events. In the exponential distribution, the probability of occur-rence 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. The interarrival time is the time between suc-cessive packet genera-tions in the “ON” state.5 2. Click on the Object Attributes tab. 3. Click the Add button. The Add Attribute dialog box should appear fi lled with the pro-moted 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 ( Offi ce Network.node_0.Traffi c Generation …. ) · Click the Wildcard button · Click on node_0 and choose (*) from the drop-down menu · Click OK . 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 . LAB 1 CSMANetwork Simulation Experiments Manual6 4.