[Tinyos-devel] PacketLink interface, CC2420 impl, problems with Broadcast packets TinyOS 2.0.2.2

[J. Ryan Stinnett]

Avinash -

Broadcast packets are not ACKed at all.  If I understand correctly, you 
are checking in the sendDone event whether or not the packet was ACKed, 
and retrying if it was not, correct?  This check should not be performed 
on broadcast packets since ACKs are never sent for them.

- Ryan

Avinash Sridharan wrote:
> Hi All,
>  I am not sure if this is the right forum to send this mail, or should I 
> be sending it to the TinyOS-help mailing list.
> 
> I was using the the PacketLink interface on the Tmote Sky's with the 
> CC2420 stack. In my code I have broadcast beacons that are send out at 
> periodic intervals. When I started using the PacketLink interface I 
> started seeing a considerable drop in my throughput (this is observed 
> using logs from the mote).
> 
> I added some code to see the number of retransmission attempts for each 
> packet being sent out. In my test case I had a fully connected network 
> (with all links having a PRR of ~ 1). Ideally I should be seeing all 
> packets being ACKED and the number the sent attempts on packets being 1. 
> This was the case for the packets that were being unicasted however for 
> the broadcast packets the transmission attempts were always the maximum 
> number of retries and they were never ACKED (this was true for all 
> broadcast packets).
> 
> On digging a bit deeper I realised that the CC2420PacketC (which 
> provides the PacketAcknowledgement interface) does not check for the 
> destination address and simply returns the ACK field in the metadata. 
> Once I added a condition for the checking the broadcast address (and 
> always returning true for BROADCAST), performance returned to normal.
> 
> Is this a valid bug ? Is the fix correct, or should this condition be 
> handled at some other point ?
> 
> regards,
> Avinash
> 
> 
> -- 
> Phd Dept. of Electrical Engineering
> University of Southern California
> http://www-scf.usc.edu/~asridhar
> 
> 
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