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
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
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Testbed Setup
Ns-3 WMR
Main changes in the routing protocol
Performance Evaluation
Conclusions
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Outline
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•
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•
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
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•
•
•
•
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 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
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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 interface
ipIface->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-Martínez
Research Engineer
Centre Tecnologic de Telecomunicacions de Catalunya
jose.nunez@cttc.cat
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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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