LAB 3 Switched LANs A Set of Local Area Networks Interconnected by Switches 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 finite 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 regardless 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 configuration 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 21 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 Office 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 The prefix ethernet16 indicates that the device supports up to 16 Ethernet connections 1 Select Topology Rapid Configuration From the drop down menu choose Star and click OK 2 Click the Select Models button in the Rapid Configuration dialog box From the Model List drop down menu choose ethernet and click OK 3 In the Rapid Configuration dialog box set the following five values Center Node Model ethernet16 hub Periphery Node Model ethernet station Link Model 10BaseT Number 16 Y 50 and Radius 42 Click OK 22 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 attribute 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 LAB 3 Switched LANs 23 Configure the Network Nodes Here you will configure the traffic generated 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 reconfiguring each node individually 3 Expand the hierarchies of the Traffic Generation Parameters attribute and the Packet Generation Arguments attribute Set the four values indicated by the arrows in the figure to the right 4 Click OK to close the attribute editing window s 5 Save your project Network Simulation Experiments Manual Choose Statistics The Ethernet Delay represents the endend delay of all packets received by all the stations Traffic Received in packets sec by the traffic sinks across all nodes 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 Traffic Sent in packets sec by the traffic sources across all nodes Collision Count is the total number of collisions encountered by the hub during packet transmissions 24 Configure the Simulation Here we need to configure the duration of the simulation 1 Click on the Configure 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 create 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 LAB 3 Switched LANs 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 deploying 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 click OK 7 Right click on the switch Edit Attributes Name it Switch and click OK 8 Reconfigure the network to look like the following one a To remove a link select it and choose Cut from the Edit menu or simply press the Delete key You can select multiple links and delete all of them at once b To add a new link use the 10BaseT link available in the Object Palette 25 Network Simulation Experiments Manual Run the Simulation To run the simulation for both scenarios simultaneously 1 Select Manage Scenarios from the Scenarios menu 2 Change the values under the Results column to collect or recollect for both scenarios Compare with the following figure