hi all. I'm a student of Information Engeenering at University of Pisa. I'm working on a thesis on data transfer protocol in WSN. I'm using TmoteSky motes an TinyOs 2.x on cygwin. My problem is that i can't be able to exstimate the average transmission time of a packet of 40bytes payload.
When I run Tossim simulations ( with "make micaz sim" ) i found that the average transmission time is about 6,8 milliseconds ( time between AMSend.send() and AMSend.sendDone() ) but when I install my application on motes (with "make telosb install" ) i found that the average transmission time is about 10 milliseconds ( telosb mote send packets back-to-back and is the only mote that send packets ----> NO possible collisions ) It is possible that this time difference is caused by backoff times or other delays? Both Micaz and Telosb platforms uses CC2420 Radio stack, so i think that backoff time should be the same. In my python script i don't change the default values of backoff times: from TOSSIM import * t = Tossim(n.variables.variables()) mac = t.mac() mac.setInitHigh(640) ( should be initial backoff maximum value ) mac.setInitLow(20) ( should be initial backoff minimum value ) mac.setHigh(160) ( should be congestion backoff maximum value ) mac.setLow(20) ( should be congestion backoff minimum value ) Otherwise from 'opt\tinyos-2.x\tos\chips\cc2420\CC2420.h' and 'opt\tinyos-2.x\tos\chips\cc2420\csma\CC2420CsmaP.nc' i think that initial backoff is random and bounded between 10-320 ticks ( 0,3 ---->9,8 milliseconds ) congestion backoff is random and bounded between 10-80 ticks ( 0,3----> 2,4 milliseconds ) Tossim values are double in regard to cc2420 values founded in 'opt\tinyos-2.x\tos\chips\cc2420' directory. I don't understand why in telosb mote ( 250kbit/sec bit-rate) there is this average transmission time of 10 milliseconds: theorically a 40 bytes payload packet should be sent in: about 2 msec ------------>to send 40bytes payload + 18 bytes ( preamble + header + CRC ) at 250kbit/sec-----> (58*8)/ 250 000 + about 5 msec ( average initial backoff ( max backoff time - min backoff time )/2 ) = about 7 milliseconds ( this value is similar to tossim average transmission time) Please anyone can explain to me why there is this difference between tossim simulation and test on motes? or anyone can send to me a datasheet , document, pubblication in which I can found an explanation of backoff time values in cc2420 radio stack on telosb motes? It is very important to me. Best regards Thanks for your answers and your help. Bye salvatore g.
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