Subject: [manet] hot to determine whether collision occurs at receiver

From: "zhui_dream" <[email-masked]>
Date: Fri, 10 Nov 2006 08:41:47 +0800

Hi, all
  
  Recently i am working in the analysis of MAC level collision of 802.11 network. one problem I face is that at receiver, are there any method to determine wthether a collision occurs during the packet reception.
  In NS-2 simulation, the collision/capture functions is used to handle the collision. but in realistic network, how does the wireless card do for this? Does it just regard the signal from other packets as noise ?
   Thanks, any materials or suggestions is welcomed 
                                     Shahe Lv 

zhui_dream
2006-11-10
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From: "bill josephson" <[email-masked]>
Date: Fri, 10 Nov 2006 16:53:01 -0800

The 802.11 Distributed Coordination Function basic access requires that
the intended receiver transmit an explicit acknowledgement onto the
medium upon receipt of a valid 802.11 frame intended for that receiver.
The receiver performs the acknowledgement after validation of the
headers, trailers, and the Cyclic Redundancy Checksum.  The
acknowledgement occurs very soon after successful reception, prior to
any station sensing the channel idle.  Detection of collision is not
supported by 802.11.

-----Original Message-----
From: zhui_dream [mailto:[email-masked]] 
Sent: Thursday, November 09, 2006 4:42 PM
To: manet
Subject: [manet] hot to determine whether collision occurs at receiver

  Hi, all
  
  Recently i am working in the analysis of MAC level collision of 802.11
network. one problem I face is that at receiver, are there any method to
determine wthether a collision occurs during the packet reception.
  In NS-2 simulation, the collision/capture functions is used to handle
the collision. but in realistic network, how does the wireless card do
for this? Does it just regard the signal from other packets as noise ?
   Thanks, any materials or suggestions is welcomed 
                                     Shahe Lv 

  _____  

zhui_dream
2006-11-10

---

From: David Young <[email-masked]>
Date: Mon, 13 Nov 2006 10:32:49 -0600

On Fri, Nov 10, 2006 at 08:41:47AM +0800, zhui_dream wrote:
> network. one problem I face is that at receiver, are there any method
> to determine wthether a collision occurs during the packet reception.

Some WLAN cards let you capture "damaged" frames (i.e., those whose
payload does not match the frame checksum).  If the transmitter sends
frames whose content the receiver knows ahead of time, or else if the
receiver copies the same frame in a subsequent retransmission, then
perhaps the receiver can infer that a collision occurred by looking at
the character of the frame damage.

Dave

-- 
David Young             OJC Technologies
[email-masked]      Urbana, IL * (217) 278-3933