Using ns-3 emulation to experiment with Wireless Mesh Network Routing: Lessons learned José Núñez-Martínez Research Engineer Centre Tecnologic de Telecomunicacions de Catalunya 25/03/2011

2 Goal of this talk Give the implementation details of porting the implementation of a routing protocol to a real WMN testbed by means of ns-3 emulation framework Initial results on the the performance evaluation of the ns-3 emulation framework in a real testbed

3 Outline Testbed Setup Ns-3 WMR Main changes in the routing protocol Performance Evaluation Conclusions

4 Outline Testbed Setup Ns-3 WMR Implications in the routing protocol Performance Evaluation Conclusions

5 Wireless Mesh Node Motherboard: Portwell Mini-ITX 1.6Ghz processor Storage: 80Gb PATA hard disk. Wireless Interfaces up to four mini-PCI CM9 atheros wireless 54Mbps 5Ghz band pseudo ad-hoc mode, one antenna 3G Femtocell connected through Ethernet iface via Switch OS Linux Fedora Core Madwifi 0.9.4

6 Wireless Mesh Testbed Deployed in the first floor of the CTTC building An approximate area of 1200 square meters 12 WiFi nodes acting as Wireless Mesh Routers Static and non-power constrained Backbone wireless mesh network Using 1 WiFi interface and 1 Ethernet to connect Femtocells Wifi Mesh initially set up to single radio single channel Network control via Ethernet LAN Controller for remote management purposes

7 Wireless Mesh Tesbed Deployment

8 Testbed Routing Configuration Flows directed to a Femtocell Add static routes to packets directed to the Femtocell connected by Ethernet Interface Backpressure to route packets to another Femtocell not directly connected by Ethernet Interface Flows coming from a Femtocell Static Default route added to reach the WMR directly connected via Ethernet Interface Static Default route of the GW in the mesh to reach Core Network Flows originated at the WMR Generate them within ns-3

9 Outline Testbed Setup Ns-3 WMR Implications in the routing protocol Performance Evaluation of ns3 Conclusions

10 Ns-3 WMR configuration EmuNetDevice associated to each interface associated to ath0 Ptr device = CreateObject (); device->SetAttribute ("Address", Mac48AddressValue ("00:0b:6b:81:ce:2a"); device->SetAttribute ("DeviceName", StringValue (deviceName)); Static Routing and Backpressure Routing Static routing more priority than backpressure routing and removed routes associated in static routing to use backpressure routing list.Add (staticRouting, 10); // static routing list.Add (backpressure, 0); //dynamic backpressure routing staticRouting->RemoveRoute (1); //so that backpressure would be used to route within the WMN

11 Ns-3 WMR configuration To disable ARP in the testbed, fix static ARP entries in the node interfaces Create ARP cache Ptr arp = CreateObject (); arp->SetAliveTimeout (Seconds(3600*24*365)); Add ARP cache entry Mac48Address macAddr = Mac48Address("00:0b:6b:81:ce:2a"); Ipv4Address ipAddr = Ipv4Address(" "); ArpCache::Entry * entry = arp->Add(ipAddr); entry->MarkWaitReply(0); entry->MarkAlive(macAddr); Associate Arp Cache to the IP interface ipIface->SetAttribute("ArpCache", PointerValue(arp));

12 Outline Testbed Setup Ns-3 WMR Implications in the routing protocol Ns-3 Emulation Performance Evaluation Conclusions

13 Dynamic Backpressure Routing protocol Implementation EMU_MODE/SIMU_MODE depending on the mode there are some changes in the routing protocol module backpressure.Set("Mode", EnumValue(EMU_MODE)); Due to the particularities of dynamic backpressure routing there are some coding differences Interaction with WiFi MAC Queues Routing Protocol require some adjustments in emulation mode

14 Transmission Opportunities in EMU_MODE Recall that packets coming from upper//lower layers are not necessarily immediately forwarded Instead of this they are stored waiting for transmission opportunities In SIMU_MODE a callback from WiFi MAC layer is launched whenever there are free data slots in the WiFi MAC Layer In this case the real host has to tell somehow to ns-3 whether there is a new transmission opportunity or not

15 Interaction between ns3 and madwifi driver

16 Interacion between NS-3 and Madwifi driver Madwifi patched to trigger interruption Create a file in /proc/sys/ Patch madwifi driver to Write in /proc/sys/ file when the HW buffer is full Another write event when HW buffer is not full In the ns-3 dynamic backpressure routing module create a thread waiting for some write event on a file in /proc/sys/ Use select() system call waiting for a write event Continuous transmission opportunity in the routing module by default When the thread is unblocked and previously was idle transmission opportunities are locked

17 Outline Testbed Setup Ns-3 WMR Implications in the routing protocol Ns-3 Emulation Performance Evaluation Conclusions

18 NS-3 Mac Spoofing Be careful with the selected MAC address to spoof BSSID_MASK: mask to set up potential mac addresses of the VAPS associated to a WiFi card Not every random mac address is appropriate at least for WiFi cards In madWiFi higher bits of the mac address identify the VAP With MAC addresses which do not satisfy BSSID_MASK the WiFi card discard data packets though some of them are able to be processed

19 NS-3 performance Processing Linux host saturating a WiFi interface in a mode 4000pkts per second payload 1024bytes Ns-3 WMR processing packets EmuNetDevice RxQueueSize Performance degradation due to queue drops in EmuNetDevice Appropiate EmuNetDevice queue size

20 NS-3 performance Sending Ns-3 WMR saturating WiFi interface Performance at the receiver UDP traffic 4000pkts per second during 30seconds

21 Outline Testbed Setup Ns-3 WMR Implications in the routing protocol Ns-3 Emulation Performance Evaluation Conclusions

22 Conclusions Implementation particularities of the routing protocol and ns3 WMR router configuration Main issues with respect to ns-3 simulation are given by the interaction with the testbed But essentials of the routing protocol do not change HELLO messages, routing algorithm Initial ns-3 Emulation Performance Evaluation is satisfactory but more tests are needed Delays

23 Thanks for your kind attention! Questions? José Núñez-Martínez Research Engineer Centre Tecnologic de Telecomunicacions de Catalunya

24 Receiving and Transmitting Ns-3 WMR receiving and transmitting 2000 packets second Wifi card prioritizes packet reception (i.e., red flow) Ns-3 WMR receiving and transmitting at a rate of 1000 packets per second