Using ns-3 emulation to experiment with Wireless Mesh Network Routing:Lessons learnedJosé Núñez-MartínezResearch EngineerCentre Tecnologic de Telecomunicacions de Catalunya
25/03/2011
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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
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Outline
• Testbed Setup• Ns-3 WMR• Main changes in the routing protocol• Performance Evaluation• Conclusions
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Outline
• Testbed Setup• Ns-3 WMR• Implications in the routing protocol• Performance Evaluation• Conclusions
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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 2.6.32• Madwifi 0.9.4
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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
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Wireless Mesh Tesbed Deployment
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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
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Outline
• Testbed Setup• Ns-3 WMR• Implications in the routing protocol• Performance Evaluation of ns3• Conclusions
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Ns-3 WMR configuration
• EmuNetDevice associated to each interface• associated to ath0
Ptr<EmuNetDevice> device = CreateObject<EmuNetDevice> ();
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 routinglist.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
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Ns-3 WMR configuration
• To disable ARP in the testbed, fix static ARP entries in the node interfaces• Create ARP cache
Ptr<ArpCache> arp = CreateObject<ArpCache> ();
arp->SetAliveTimeout (Seconds(3600*24*365));
• Add ARP cache entry Mac48Address macAddr = Mac48Address("00:0b:6b:81:ce:2a");
Ipv4Address ipAddr = Ipv4Address("10.3.40.193");
ArpCache::Entry * entry = arp->Add(ipAddr);
entry->MarkWaitReply(0);
entry->MarkAlive(macAddr);
• Associate Arp Cache to the IP interfaceipIface->SetAttribute("ArpCache", PointerValue(arp));
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Outline
• Testbed Setup• Ns-3 WMR• Implications in the routing protocol• Ns-3 Emulation Performance Evaluation• Conclusions
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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
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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
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Interaction between ns3 and madwifi driver
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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
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Outline
• Testbed Setup• Ns-3 WMR• Implications in the routing protocol• Ns-3 Emulation Performance Evaluation• Conclusions
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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
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NS-3 performance Processing
• Linux host saturating a WiFi interface in 802.11a 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
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NS-3 performance Sending
• Ns-3 WMR saturating WiFi interface• Performance at the receiver• UDP traffic 4000pkts per second during
30seconds
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Outline
• Testbed Setup• Ns-3 WMR• Implications in the routing protocol• Ns-3 Emulation Performance Evaluation• Conclusions
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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
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Thanks for your kind attention!
• Questions?
José Núñez-MartínezResearch Engineer
Centre Tecnologic de Telecomunicacions de Catalunya
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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
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