Wireless Data Networks, TLEN 5520/ECEN 5032Lab. #2Varun Vora, Martin HeusseDue in class: Apr. 15thYou can use your own laptops or the provided ones (please contact Varun1). In this case,use the Dell laptop that can have 2 wireless interfaces as the middle node, so that it can be setup as an AP and monitor the traffic at the same time.Put all interfaces in 11b mode, so that things do not go too fast…1 Throughput measurements1.1 Infrastructure modeSet up three laptops in an infrastructure mode with 1 laptop as AP and the other two as clients.• Make sure all three laptops can ping each other.• Measure the throughput from one client to the other using udpmt and tcpmt.1.2 Ad hoc modePut all three laptops in ad hoc (IBSS) mode.• Which laptops are sending beacons? Why?• Measure the throughput among the previous two laptops using udpmt and tcpmt.• Which setup performs better? Infrastructure or ad hoc? Why? Comment on the resultsyou [email protected] Hidden nodesAPFigure 1: Hidden nodesKeep the laptops in adhoc mode. We are going to see the impact of the presence of nodesthat are hidden to each other (see Fig. 1).Come up with a setup where the middle laptop can exchange data with the two otherlaptops, but the extreme (far-end) laptops cannot talk to each other.• Now put the middle laptop in AP mode and the other two laptops as clients (managedmode). Here the clients do not hear each other, so they may consider that the channelis free and start a transmission even though the other one is currently transmitting.• To analyse the hidden node problem, run throughput tests (UDP) from both clients tothe AP simultaneously. Run wireshark on the AP to see the collisions. (how do youassess there are numerous collisions?)• Note the throughput readings. Can you comment on the stability? Do you think thereare asymmetrical collisions?2.1 Hidden node with RTS/CTSEnable the RTS/CTS options on the laptops.• Again run the throughput tests and capture the frames on the AP using wireshark.Remember to use two different interfaces on the AP. One will act as the hostap andother will be put in monitor mode to capture the frames.• Observe the RTS/CTS frame exchanges. Also note the throughput readings.• Is RTS/CTS helpful?23 Inter-arrival histogramsUse the -H option of udptarget (and the options -m and -M) to compute histograms of theinter-arrival intervals between packets. (You can also extract this information from tcpdumpor wireshark). Use only one UDP traffic. What can you see on the histograms?Hints:• Try the histogram with and without the burst option: ifconfig ath<X> [-]burst• Even in 11b mode, the slot time stays at 9µs! You have to change it to 20µs by runningthe command:sysctl dev.ath.<X>.slottime=20(To observe the current slot time, simply run: sysctl dev.ath.<X>.slottime)4 Useful Commands• ifconfig <interface> mediaopt [hostap adhoc monitor] —to put it in therespective mode;ifconfig <interface> -mediaopt [hostap adhoc monitor] —to put it back inmanaged mode;ifconfig <interface> media [DS/<X>Mbps OFDM/<X>Mbps]ifconfig <interface> mode [11b 11g]ifconfig <interface> channel <channelno>ifconfig <interface> ssid <name>ifconfig <interface> <ipaddress> up• ifconfig <interface> rtsthreshold - —to disable RTS/CTSifconfig <interface> rtsthreshold <size> —to enable RTS/CTS for all packetsof up to size bytes in length;• udptarget -p [portno]udpmt -p <portno of target> <ipaddress of