21LAB OBJECTIVES This lab is designed to demonstrate the implementation of switched local area networks. The simulation in this lab will help you examine the performance of different implementations of local area networks connected by switches and hubs. OVERVIEW There is a limit as to how many hosts can be attached to a single network and to the size of a geographic area that a single network can serve. Computer networks use switches to enable the communication between one host and another, even when no direct connection exists between the hosts. A switch is a device with several inputs and outputs leading to and from the hosts that the switch interconnects. The core job of a switch is to take packets that arrive on an input and forward (or switch) them to the right output so that they will reach their appropriate destination. A key problem that a switch must deal with is the fi nite bandwidth of its outputs. If packets destined for a certain output arrive at a switch and their arrival rate exceeds the capacity of that output, then we have a problem of contention. In this case, the switch will queue, or buffer, the packets until the contention subsides. If the contention lasts too long, however, the switch will run out of buffer space and be forced to discard packets. When packets are discarded too frequently, the switch is said to be congested. In this lab, you will set up switched LANs using two different switching devices: hubs and switches. A hub forwards the packet that arrives on any of its inputs to all the outputs regard-less of the destination of the packet. However, a switch forwards incoming packets to one or more outputs, depending on the destination(s) of the packets. You will study how the throughput and collision of packets in a switched network are affected by the confi guration of the network and the types of switching devices that are used. PRE-LAB ACTIVITIES & Read Section 3.1 from Computer Networks: A Systems Approach, 5th Edition . : Go to www.net-seal.net and play the following animations: ❍ Switch ❍ Switched Network With No Server ❍ Switched Network With Server Switched LANs A Set of Local Area Networks Interconnected by Switches 322 Network Simulation Experiments Manual PROCEDURE Create a New Project 1. Start the OPNET IT Guru Academic Edition · Choose New from the File menu. 2. Select Project and click OK · Name the project <your initials>_SwitchedLAN , and the scenario OnlyHub · Click OK . 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 three times · Click OK . 4. Close the Object Palette dialog box. Create the Network To create a switched LAN: 1. Select Topology · Rapid Confi guration . From the drop-down menu choose Star and click OK . 2. Click the Select Models button in the Rapid Confi guration dialog box. From the Model List drop-down menu choose ethernet and click OK . 3. In the Rapid Confi guration dialog box, set the following fi ve values: Center Node Model = ethernet16_hub, Periphery Node Model = ethernet_station, Link Model = 10BaseT, Number = 16, Y = 50 , and Radius = 42 · Click OK . The prefi x ethernet16_ indicates that the device supports up to 16 Ether-net connections. The 10BaseT link represents an Ethernet connection operating at 10 Mbps. 4. Right-click on node_16 , which is the hub · Edit Attributes · Change the name attri-bute to Hub1 and click OK . 5. Now that you have created the network, it should look like the following one. 6. Make sure to save your project.23 Confi gure the Network Nodes Here you will confi gure the traffi c gener-ated by the stations. 1. Right-click on any of the 16 stations (node_0 to node_15) · Select Similar Nodes . Now all stations in the network are selected. 2. Right-click on any of the 16 stations · Edit Attributes. a. Check the Apply Changes to Selected Objects check box. This is important to avoid reconfi guring each node individually. 3. Expand the hierarchies of the Traffi c Generation Parameters attribute and the Packet Generation Arguments attri-bute · Set the four values indicated by the arrows in the fi gure to the right. 4. Click OK to close the attribute editing window(s). 5. Save your project. LAB 3 Switched LANs24 Network Simulation Experiments Manual Choose Statistics To choose the statistics to be collected during the simulation: 1. Right-click anywhere in the project workspace and select Choose Individual Statistics from the pop-up menu. 2. In the Choose Results dialog box, choose the shown four statistics. 3. Click OK . The Ethernet Delay represents the end-end delay of all packets received by all the stations. Traffi c Received (in packets/sec) by the traffi c sinks across all nodes. Traffi c Sent (in packets/sec) by the traffi c sources across all nodes. Collision Count is the total number of collisions encountered by the hub during packet transmissions. Confi gure the Simulation Here we need to confi gure the duration of the simulation: 1. Click on the Confi gure/Run Simulation button: 2. Set the duration to 2.0 minutes . 3. Click OK . Duplicate the Scenario The network we just created utilizes only one hub to connect the 16 stations. We need to cre-ate another network that utilizes a switch and see how this will affect the performance of the network. To do that, we will create a duplicate of the current network: 1. Select Duplicate Scenario from the Scenarios menu and give it the name HubAndSwitch · Click OK . 2. Open the Object Palette by clicking on . Make sure that Ethernet is selected in the pull-down menu on the object palette.25 3. We need to place the hub and switch shown here in the new scenario. 4. To add the Hub , click its icon in the object palette · Move your mouse to the workspace · Click to drop the hub at a location you select. Right-click to indicate you are done deploy-ing hub objects. 5. Similarly, add the Switch , and then close the Object Palette . 6. Right-click on the new hub · Edit Attributes · Name it Hub2 and