[Tinyos-devel] 2.0.2 CC2420

[Jun]

Razvan ME,

Many many thanks! That's what we are looking for.

Jun

On Feb 12, 2008 5:08 PM, Razvan Musaloiu-E. <razvanm at cs.jhu.edu> wrote:

> Hi!
>
> The format of an ack frame is depicted in Figure 23 on page 42 in the
> CC2420 datasheet:
>        http://focus.ti.com/lit/ds/symlink/cc2420.pdf
>
> All the best!
> Razvan ME
>
> On Tue, 12 Feb 2008, Jun wrote:
>
> > Phil,
> >
> > Thank you very much for your clarification. I remember 802_11 is taking
> the
> > same approach by only including destination address in an ACK frame,
> > which suffers from the same problem you described.
> >
> > We are trying to develop a "pure" software ACK now, but we don't know
> > how to "format" an ACK. The only information we have on the format is
> > from CC2420ReceiveP.nc as follows
> >      if (((( header->fcf >> IEEE154_FCF_ACK_REQ ) & 0x01) == 1)
> >          && (header->dest == call amAddress())
> >          && ((( header->fcf >> IEEE154_FCF_FRAME_TYPE ) & 7) ==
> IEEE154_TYPE_DATA)) {
> >          ...
> >      }
> >
> > In order to generate a legitimate ACK in software, is it enough to just
> fill in
> > the header->fcf,  header->dest fields in cc2420_header_t structure as
> > indicated by the above code. Any advice or suggestion will be greatly
> > appreciated.
> >
> > Thank you,
> >
> > Jun
> >
> > On Feb 12, 2008 3:20 PM, Philip Levis <pal at cs.stanford.edu> wrote:
> >
> >>
> >> On Feb 12, 2008, at 12:58 PM, Jun wrote:
> >>
> >>> Hi David,
> >>>
> >>> Thank you very much for your prompt response.
> >>> Could you explain more on "the current ACK frame is inherently
> >>> broken"?
> >>
> >> The ACK does not contain the source address, only the sequence
> >> number. So you don't know who is acking. This means that you can get
> >> false positives. Some other node happened to receive a packet with
> >> the same sequence number and ACKs it; you think your destination
> >> received the packet when it didn't.
> >>
> >> Phil
> >>
> >
> >
> >
> > --
> > --
> > Mailto: yanjunrockets at gmail.com
> >
>



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