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Revision as of 11:42, 23 May 2011 by Ashwin (Talk | contribs) (Approach)

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Click-MAC Extensions for ns-3-click

  • Student: Ashwin Narayan
  • Mentors: Ruben Merz and Lalith Suresh
  • Abstract: This project deals with the MAC extensions for ns-3 click. The current integration of the Click Modular Router with ns-3 is confined to only ns-3’s network device types and doesn’t yet permit the use of Click’s Wifi MAC specific elements. This project aims to enable the same by implementing Radiotap support, and a Monitor Wifi Mac High interface.


GSoC 2010 saw the integration of the Click Modular Router with ns-3. The implementation, however, is limited only to layer 3 or in other words, Click's use is confined only to all of ns-3's network device types. This project deals with making Click's Wifi MAC specific elements compatible with ns-3-click.

A major step in the project would be the implementation of full radiotap headers support. The radiotap header cannot simply be added in YansWifiPhy as this would create issues with the current implementations of MacLow and MacRxMiddle. The current NS-3 Click integration is limited to L3 and leaves ns-3 to handle L2. The radiotap header would probably best be added on the receiver path as close to NetDevice as possible. The implementation would require a redesign in the method of packet forwarding with the radiotap pertinent data. The radiotap header could be created in MacLow and the necessary modifications must be made for sending the header upwards.

Creation of Radiotap Header
The Radiotap Header can be created in MacLow::ReceiveOk(Ptr<Packet> packet, double rxSnr, WifiMode txMode, WifiPreamble preamble).

       RadiotapHeader radiotaphdr;
       uint8_t frameFlags = RadiotapHeader::FRAME_FLAG_NONE;
       bool isShortPreamble = (WIFI_PREAMBLE_SHORT == preamble);
       radiotaphdr.SetTsft (Simulator::Now ().GetMicroSeconds ());
       if (isShortPreamble)
           frameFlags |= RadiotapHeader::FRAME_FLAG_SHORT_PREAMBLE;
       radiotaphdr.SetFrameFlags (frameFlags);
       radiotaphdr.SetRate (rate);
       if (channelFreqMhz < 2500)
           radiotaphdr.SetChannelFrequencyAndFlags (channelFreqMhz,
             RadiotapHeader::CHANNEL_FLAG_SPECTRUM_2GHZ | RadiotapHeader::CHANNEL_FLAG_CCK);
           radiotaphdr.SetChannelFrequencyAndFlags (channelFreqMhz,
             RadiotapHeader::CHANNEL_FLAG_SPECTRUM_5GHZ | RadiotapHeader::CHANNEL_FLAG_OFDM);
       double signalDbm = RatioToDb (m_sendAckEvent->GetRxPowerW ()) + 30;
       double noiseDbm = RatioToDb(m_sendAckEvent->GetRxPowerW() / rxSnr) - GetRxNoiseFigure() + 30 ;
       radiotaphdr.SetAntennaSignalPower (signalDbm);
       radiotaphdr.SetAntennaNoisePower (noiseDbm);

channelFreqMhz can be determined using YansWifiPhy::GetChannelFrequencyMhz() while rate can be obtained from tx.GetDataRate().

In MacLow::Receive(), the rxpacket segment of the code should be modified so that m_rxCallback (packet, &hdr) includes the Radiotap Header. The signature as well as the invocations of the callback must also be modified.

       void MacLow::SetRxCallback (Callback<void,Ptr<Packet>,const WifiMacHeader *,RadiotapHeader> callback) {

m_rxCallback = callback; }

PCAP refactoring
The PromiscSniffTx/Rx traces can be modified to pass the Raditap Header as an argument and thereafter, using PcapFileWriter.

Modifications for sending up the stack
While the Radiotap Header is created in MacLow, it must be sent up the stack till MacHigh where it can be added to the packet for Click use.

RegularWifiMac::Receive (Ptr<Packet> packet, const WifiMacHeader *hdr, RadiotapHeader radiotaphdr)

MonitorMacHigh can inherit directly from WifiMac and we could copy only the non-QoS part from RegularMacWifi. Thus, the MonitorMacHigh implementation doesn't need to know the type of station being implemented in the Click graph.

       packet->AddHeader (radiotaphdr);

There would be changes required in IPv4L3ClickRouting would be stripping off headers (the radiotap headers must be stripped as high in the stack as possible) to extract required information and pushing them using SendDown() where we can pass the required click information through netdev->Send(). I might need to strip off a WifiMacHeader at Ipv4L3ClickProtocol::SendDown() to extract Mac address information before sending out the packet through the NetDevice.

       RadiotapHeader radiotaphdr;
       netdev->Send(p, radiotaphdr.GetInfo(), protocol);