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Message from discussion WifiNetDevice::Rx trace: why overheard frames?
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francesco  
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 More options Feb 19 2009, 2:05 am
From: francesco <francesco.malandr...@gmail.com>
Date: Wed, 18 Feb 2009 23:05:01 -0800 (PST)
Local: Thurs, Feb 19 2009 2:05 am
Subject: Re: WifiNetDevice::Rx trace: why overheard frames?
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> Can you be a bit more specific here ?

src/devices/wifi/wifi-net-device.cc, lines 283-314

void
WifiNetDevice::ForwardUp (Ptr<Packet> packet, Mac48Address from,
Mac48Address to)
{
  m_rxLogger (packet, from);
  LlcSnapHeader llc;
  packet->RemoveHeader (llc);
  enum NetDevice::PacketType type;
  if (to.IsBroadcast ())
    {
      type = NetDevice::PACKET_BROADCAST;
    }
  else if (to.IsGroup ())
    {
      type = NetDevice::PACKET_MULTICAST;
    }
  else if (to == m_mac->GetAddress ())
    {
      type = NetDevice::PACKET_HOST;
    }
  else
    {
      type = NetDevice::PACKET_OTHERHOST;
    }
  if (type != NetDevice::PACKET_OTHERHOST)
    {
      m_forwardUp (this, packet, llc.GetType (), from);
    }
  if (!m_promiscRx.IsNull ())
    {
      m_promiscRx (this, packet, llc.GetType (), from, to, type);
    }

}

As far as I could understand, this code checks whether the received L2
payload should be passed to upper layers (i.e. it is either broadcast,
multicast or unicast directed to the current host) or not (case
PACKET_OTHERHOST). In the latter case, it is only passed to upper
layers if the promiscuous mode is activated.
Nevertheless, m_rxLogger is called before the switch statement, i.e.
in _all_ the above cases, including the one in which the frame is
directed to another host.

I think naming this event "Rx" can be misleading. I feel it would be
more correct to move the m_rxLogger call inside the "if (type !=
NetDevice::PACKET_OTHERHOST)" branch, and possibly add a distinct
trace source, say "FrameSeen", where Rx currently is. Anyway, I would
suggest to state more explicitly the exact semantics of Rx in the
documentation.

Francesco


 
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