Hi all, Exactly, I know it is implemented according to the standard. I wanted to add interference and I didn't see any other way to add it other than in the MAC (where packets are received and destination address is checked). By saying collision, I mean that two packets arrive at the receiver at the same time. They don't have to belong to the same channel (which am willing to add multi-channel support) in which case it will be interference. If they belong to the same channel and are destined to the same receiver, then it will be a collision. If you have a better idea to tackle interference, please advise me!!! Thank you all for your help! I appreciate it! regards,
On Sun, Nov 16, 2008 at 10:20 AM, Basim Javed <[EMAIL PROTECTED]> wrote: > hello all > > I think Imad wants to infer that a collision has occurred when his receiver > gets two/more packets which overlap in time; hence collision is supposed to > have happened. The point is how to detect the bits which are overlapped in > time...the signals may be less than the threshold value of PHY, or even > strong enough so that info is passed to the MAC. > > regards > basim > > On Sat, Nov 15, 2008 at 10:58 AM, Waleed Tuffaha <[EMAIL PROTECTED]>wrote: > >> >> Hello Imad >> >> The 802.11 Standard uses CSMA/CA ( Carrier Sense Multiple Access with >> Collision Avoidance ). It does not use collision detection. And >> 802.11.ccshould be coded according to the standard, so I guess you >> >> won't be able to >> capture the collided packets inside 802.11.cc. I think you can only >> capture >> the packets that did not pass the CRC check. >> >> >> Best regards, >> -- Waleed Tuffaha >> >> Date: Thu, 13 Nov 2008 10:23:05 -0500 >> > From: "Imad Abdeljaouad" <[EMAIL PROTECTED]> >> > Subject: Re: [ns] collisions in 802.11 or interference >> > To: "Basim Javed" <[EMAIL PROTECTED]> >> > Cc: "ns-users@isi.edu" <ns-users@ISI.EDU> >> > Message-ID: >> > <[EMAIL PROTECTED]> >> > Content-Type: text/plain; charset=ISO-8859-1 >> > >> > Well, my idea was to simulate interference. You are right absolutely >> right, >> > interference happens in the air so the receiver has no idea about it. >> But >> > this is in real life. Since there are no signals in ns2, my idea was to >> > calculate interference at the MAC layer which will know what are the >> > packets >> > (signals) that were sent at the same time on the air. >> > So when the MAC receives more than one packet, I want to record these >> > packets somewhere (and this will give me access to where they are coming >> > from and going to, plus their powers), then I will apply a formula that >> > will >> > calculate interference between all these packets (in real life: >> signals). >> > You are absolutely right, in case of one channel, this will be >> considered >> > as >> > collision IF the received packets are destined to the same receiver/. >> But >> > there are two other cases, if the packet is not destined to that >> receiver, >> > then I think this will be strong interference. Also, if the interfering >> > packet belongs to a different channel (that I am willing to add after I >> > figure out the interference) then this is will be interference depending >> on >> > the correlation between the channels. >> > Do you see my point? >> > The first step I believe would be to capture all packets that come at >> the >> > same time while I am receiving another packet. This way I can process >> them >> > and decide if it is collision or strong or weak interference. I have the >> > formula, all I need are the packets along with their powers and channels >> > they belong to (don't care about the channels now, coz that's coming >> > after). >> > I am still wondering how and where in the 802.11.cc code I can capture >> all >> > colliding/interfering packets and put them somewhere for processing. >> > cheers, >> > >> > On Thu, Nov 13, 2008 at 5:00 AM, Basim Javed <[EMAIL PROTECTED]> >> wrote: >> > >> > > hello Imad >> > > >> > > I can see ur point. >> > > Lets talk on the issues one by one: >> > > >> > > The interference of one packet to an already sent packet creates >> > collision. >> > > right? so interference and collisions happen in the air. I dont see >> why >> > it >> > > is important that the packets should be sent to one receiver and they >> if >> > > they interfere, then collision happens. I think even those nodes who >> are >> > > just listening to the channel, know that collision has happened in the >> > air, >> > > even they were not recipients of the packet. >> > > >> > > Now, how does the node knows that a collision has happened.. through >> the >> > > received signal power, which is lower than a threshold level (i forgot >> > the >> > > name). As far as I remember, the power level can be so low, that a >> node >> > can >> > > not receive a packet, or it is bit high but still not good enough to >> > decrypt >> > > the bits. >> > > >> > > What I am talking above is related to the situation of same channel >> > (single >> > > hop). I think multiple channels are used in neighbouring BSSs. >> > > >> > > About ur formula: how a receiving node can know about the power of the >> > > signal when the packet was sent, in real situation? >> > > >> > > regards >> > > basim >> > > >> > > >> > > >> > > On Wed, Nov 12, 2008 at 4:16 PM, Imad Abdeljaouad < >> [EMAIL PROTECTED] >> > >wrote: >> > > >> > >> Thank you so much, I really need help! >> > >> I would like to add interference support in 802.11. If my >> understanding >> > is >> > >> right, interference happens when signals send on the same channel (or >> > >> adjacent channels, like 1 and 2 or 3 ... to 6) overlap in the medium >> > (the >> > >> air) and cause attenuations to each other. I think this will not be >> > possible >> > >> in ns2 since there are no "real" signals. So I was thinking that what >> I >> > >> should do is collect the signals that arrive at the same time at the >> > >> receiver MAC (and this is where I got collisions) and this means that >> > these >> > >> signals already overlapped in the air since they got to the receiver >> MAC >> > at >> > >> "the same time". >> > >> Do you see my point? >> > >> Once I know which siganls overlapped, I can use a formula to >> calculate >> > >> interference (the fornula uses Power of the signal sent + which >> channel >> > does >> > >> it belong to, to calculate the effect of one sigan on another ). >> > >> >> > >> So the point is, I need to capture the packet*s* that collide while I >> am >> > >> receiving another packet and for how long they collided. >> > >> I don't know if you get my point, but please do not hesitate to ask >> me >> > >> more questions! >> > >> thank you again !!! >> > >> >> > >> On Wed, Nov 12, 2008 at 4:36 AM, Basim Javed <[EMAIL PROTECTED] >> > >wrote: >> > >> >> > >>> hello Imad >> > >>> >> > >>> I want to help you, but I dont understand your definition of >> collision >> > >>> and interference. Can you clarify it plz? >> > >>> basim >> > >>> >> > >>> On Wed, Nov 12, 2008 at 2:55 AM, Imad Abdeljaouad < >> > [EMAIL PROTECTED] >> > >>> > wrote: >> > >>> >> > >>>> >> > >>>> Hi Helber, >> > >>>> Thanks for the prompt response. Actually, I am looking for the code >> in >> > >>>> ns2 >> > >>>> (source code) where we can detect collisions. I want to simulate >> > >>>> interference, so I need to get the packets that were received at >> the >> > >>>> same >> > >>>> time on some node. I know interference happens on the physical >> layer, >> > >>>> but I >> > >>>> think it would be much more easier to implement it on the MAC in >> ns2. >> > So >> > >>>> I >> > >>>> am actually looking the source code part that says here is another >> > >>>> packet >> > >>>> being transmitted while receiving another packet ( which is >> collision >> > if >> > >>>> both packets are meant for the same receiver, and interference if >> both >> > >>>> packets belong to the same (or an adjacent) channel. >> > >>>> Can you help with that ? >> > >>>> cheers, >> > >>>> >> > >>>> On Tue, Nov 11, 2008 at 8:35 PM, Helber Wagner < >> > [EMAIL PROTECTED] >> > >>>> >wrote: >> > >>>> >> > >>>> > Hi, Imad. >> > >>>> > >> > >>>> > As far as I understood your question, you should analyze the >> trace >> > >>>> file >> > >>>> > generated >> > >>>> > by your simulations. >> > >>>> > >> > >>>> > If the MAC trace is enabled in your .tcl file, it will be a row >> > like >> > >>>> "D >> > >>>> > ... COL ..." >> > >>>> > indicating the time, the node, the packet and other information >> > about >> > >>>> a >> > >>>> > collision >> > >>>> > that has been happened. >> > >>>> > >> > >>>> > Finally, a simple perl/awk script can retrieve this information >> > from >> > >>>> the >> > >>>> > trace file. >> > >>>> > >> > >>>> > You can find more about mac trace in NS2 over the Internet. >> > >>>> > >> > >>>> > Good luck. >> > >>>> > >> > >>>> > --- >> > >>>> > Helber Wagner da Silva >> > >>>> > Federal University of Cear? - Brazil >> > >>>> > URL: >> > >>>> > www.great.ufc.br/~helberhws<http://www.great.ufc.br/%7Ehelberhws> >> < >> > http://www.great.ufc.br/%7Ehelberhws>< >> > >>>> http://www.great.ufc.br/%7Ehelberhws> >> > >>>> > >> > >>>> > >> > >>>> > >> > >>>> > ------------------------------ >> > >>>> > *De:* Imad Abdeljaouad <[EMAIL PROTECTED]> >> > >>>> > *Para:* "ns-users@isi.edu" <ns-users@ISI.EDU> >> > >>>> > *Enviadas:* Ter?a-feira, 11 de Novembro de 2008 23:17:46 >> > >>>> > *Assunto:* [ns] collisions in 802.11 or interference >> > >>>> > >> > >>>> > >> > >>>> > Hello there, >> > >>>> > I am looking for the code where collisions in 802.11 occur so >> that I >> > >>>> know >> > >>>> > which packet(s) collided and for how long they collided? this is >> a >> > >>>> step in >> > >>>> > trying to implement interference! >> > >>>> > thank you! >> > >>>> > >> > >>>> > -- >> > >>>> > best regards, >> > >>>> > ________________________ >> > >>>> > Imad Abdeljaouad >> > >>>> > >> > >>>> > ------------------------------ >> > >>>> > Novos endere?os, o Yahoo! que voc? conhece. Crie um email novo< >> > >>>> >> > >> http://br.rd.yahoo.com/mail/taglines/mail/*http://br.new.mail.yahoo.com/addresses >> > >com >> > >>>> a sua cara @ >> > >>>> > ymail.com ou @rocketmail.com. >> > >>>> > >> > >>>> >> > >>>> >> > >>>> >> > >>>> -- >> > >>>> best regards, >> > >>>> ________________________ >> > >>>> Imad Abdeljaouad >> > >>>> >> > >>> >> > >>> >> > >> >> > >> >> > >> -- >> > >> best regards, >> > >> ________________________ >> > >> Imad Abdeljaouad >> > >> >> > > >> > > -- best regards, ________________________ Imad Abdeljaouad
