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

[Avinash Sridharan]

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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