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

[Razvan Musaloiu-E.]

Hi!

On Thu, 6 Sep 2007, J. Ryan Stinnett wrote:

> Avinash -
>
> Broadcast packets are not ACKed at all.

If a broadcast packet has the 'Acknowledge request' set then it will be 
acked by the CC2420 chip.

--
Razvan ME

> 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
>> 
>> 
>