[Smac-users] transmit SYNC or not at the listen time

[John Heidemann]

On Fri, 18 Feb 2011 16:39:36 +0800, "zhp apple." wrote: 
>Dear all,
> 
>Could you help me answer a question whether each node need to transmit SYNC
>packet at the listen time, or just the nodes who want to send data should
>trasmit the SYNC packets to its neighbour?

SYNCs are independent of transmissions, and can be rare.

"Medium Access Control With Coordinated Adaptive Sleeping for Wireless
Sensor Networks" (Ye et al, IEEE/ACM ToN, 2004) talks about this
question in IV.B Maintaining Synchronization, but only says "The
synchronization period can be quite long."  In our implementation, this
typically means many minutes.

Although that paper talks about the constraints that govern exactly how
often one must SYNC, it doesn't actually solve it.

However, we did solve for optimal SYNC times for *SCP-MAC* in "Ultra-Low
Duty Cycle MAC with Scheduled Channel Polling" (Ye et al, ACM Sensys,
2006).  See Figure 5 and section 3.3, showing optimal times run from ~4
to ~25 minutes.  The SYNC requirements of S-MAC should be similar.

   -John Heidemann