On Tue, Jul 24, 2012 at 10:35 PM, 최익성 <[email protected]> wrote:
> Dear Eric Decker. > > Thank you very much for your kind explanation. > > I know that the collision detection is not required in CSMA/CA. > > Is there any way to detect the collision at transmitter? > Not that I am aware of. The issue is whether the h/w can can hear itself when transmitting. I don't think the cc2420 has the capabililtiy and with out hearself then doing collision detection becomes problematic. > In case of slotted aloha in ISO 18000-7, do we need detect the collision > only at receiver? > No idea. I'm not familar with slotted aloha. A collision seen at a receiver can show up in various ways. I don't know if that means that the receiver can reliably determine that a collision has taken place. Regardless, I don't see how the receiver detecting a collision can in any reasonable fashion impact the operation of the transmitter. The transmitter needs to detect the collision. If you must do a protocol that requires reliable collision detection, you must select your radio h/w such that CD is supported. > > Thank you very much. > > Sincerely Yours, > > Ick-Sung Choi. > > > > -----Original Message----- > *From:* "Eric Decker"<[email protected]> > *To:* "최익성"<[email protected]>; > *Cc:* <[email protected]>; > *Sent:* 2012-07-25 (수) 13:25:52 > *Subject:* Re: [Tinyos-help] Collision detection at transmitter. > > > > On Tue, Jul 24, 2012 at 6:56 PM, 최익성 <[email protected]> wrote: > > Dear tinyos developers. > > I have a basic question about collision detection at transmitter. > > > Its CSMA/CA not CSMA/CD so it is collision avoidance. > > > In CSMA/CA, transmitter transmits the frame. If there is a collision, > the transmitter tries to transmit the frame after random backoff time. > > How can the transmitter detects the collision? > > Typically this kind of thing is implemented in h/w. You don't specify > what h/w you are using... (Yes, it would have been helpful if you told us > the specifics of what h/w you are using). So I'm assuming the telosb with > the cc2420 radio. > > the cc2420 hardware does Clear Channel Assessment and provides status bits > that tell the driver what is happening. I believe if the channel is busy > it is up to the driver to handle the back off. > > I would suggest you take a look at the cc2420 manual (pg 50) and look at > the cc2420 driver where it deals with CCA and possibly the STXONCCA command > strobe. > > > Thank you very much. > > Sincerely Yours, > > Ick-Sung Choi. > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > > > > -- > Eric B. Decker > Senior (over 50 :-) Researcher > > > -- Eric B. Decker Senior (over 50 :-) Researcher
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