Re: [Roll] RPL Metric ID

[Adam Dunkels <adam at sics.se>]

Anders Brandt wrote:
> Can battery-powered 802.15.4. nodes quickly return to sleep if they are
> not the intended recipient?

Some can, but the biggest energy savings is in mechanisms that keep the 
radio off for most of the time, and switch it on to listen for traffic 
from neighbors. These mechanisms are typically layered on top of 
802.15.4, although I believe there is ongoing work in the 802.15.4 wg to 
put such mechanisms into the standard. There are several techniques to 
do this, and the most common is called low-power listening (LPL) in 
which nodes turn on their radio at regular intervals to listen for a 
packet in the air. If there is a packet in the air (and it is addressed 
to the node), it switches on the radio for a longer time to receive the 
packet. Before sending a packet, a sender sends a preamble (typically a 
string of packets) to wake up the receiver.

Thus with such mechanisms there is an energy penalty for packet 
transmissions, but the energy is spent both by the sender and the receiver.

/adamn
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Adam Dunkels <adam at sics.se>, +46707731614
http://twitter.com/adunk | http://www.sics.se/~adam/