From my experience (in tinyos 1.x):
  Yes.. the CC2420RadioM has a built in backoff before trying to
transmit a message, as well it polls the CCA pin to ensure the channel
is free.  Also, the command sent to the controller tells it to wait
for a clear channel before sending.  No RTS/CTS that I know of...

GenericComm doesn't provide any MAC services.  It acts as a router
sending messages to the appropriate module depending on the message
type.

You can try to ensure there was no collision at the basestation by
enabling ACK's and checking the ack field when sendDone is signaled.




On 6/7/07, Gary Pan <[EMAIL PROTECTED]> wrote:
I have been used GenericComm interface a lot. I use it to send and receive
radio message. I wonder that if GenericComm does RTS-CTS-ASK scheme as well
as backoff? I found that CC2420RadioM module in the lib folder also provides
send and receive interface. Does it has the RTS-CTS scheme?

Here is an application I want to achieve. I broadcast a message to query
motes to return data. When two motes receive the command at the same time
and start transfer data back. How can I ensure that there is no collision at
the base station? How do I know the base station get all the readings from
both motes. On the other hand, does GenericComm or CC2420RadioM has some
kind of MAC protocol built in? Thanks

Gary


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