Dear Eric Decker. Thank you very much for your kind advice and explanation. Sincerely Yours, Ick-Sung Choi.
-----Original Message----- From: "Eric Decker"<[email protected]> To: "최익성"<[email protected]>; Cc: <[email protected]>; Sent: 2012-07-25 (수) 15:08:23 Subject: Re: [Tinyos-help] Collision detection at transmitter. 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
_______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
