[Tinyos Core WG] Fwd: [Tinyos-devel] message_t

[Philip Levis]

Begin forwarded message:

> From: Jan Hauer <hauer at tkn.tu-berlin.de>
> Date: March 13, 2009 3:49:29 AM PDT
> To: Miklos Maroti <mmaroti at math.u-szeged.hu>
> Cc: tinyos-devel at millennium.berkeley.edu
> Subject: Re: [Tinyos-devel] message_t
>
> Hi Miklos,
>
> I have some questions about your proposal:
>
> 1) I'm not sure if I understood the format() part correctly. Couldn't
> the following happen: The app calls format(). The call propagates
> downwards through all protocol layers. When it reaches the routing
> protocol, the next hop must be chosen which, say, has a short address
> (16-bit): by calling format() on the MAC the routing layer would
> somehow tell the MAC to use/reserve 16-bit for the destination address
> in the MAC header. Some time later the application decides to put some
> data in the payload section and then call send(). Because send() is
> split-phase it might take some more time until the send() call reaches
> the routing layer (packet can be queued in a send-queue on upper
> layers, etc.). By the time send() reaches the routing protocol the
> original next hop has disappeared (was dropped from the forwarding
> table). The next hop now has an extended address (64-bit), which
> wouldn't fit in the MAC header anymore -- so the packet couldn't be
> sent?
>
> 2) When a sendDone() returns FAIL and the application tries to resend
> the same packet, then it might have to clear() the packet content and
> write the same payload again, because this time format() might result
> in a different layout?
>
> 3) To forward a message it has to be copied as soon as the size of any
> headers/footers changes and to be compatible with AM you'd also have
> to copy, right?
>
> Jan
>
> On Thu, Mar 12, 2009 at 10:03 PM, Miklos Maroti
> <mmaroti at math.u-szeged.hu> wrote:
>> Guys,
>>
>> Here is may alternative proposal for the new message_t. Basically, I
>> would require all message_t to be formated (the old Packet.clear with
>> some parameters), then everyone knows where the payload is and where
>> the other header and footer fields are, so we can flexibly set those
>> values (64 bit addresses, security data), finally we send the  
>> message.
>> You need to format a message only if you do not know (first use) or
>> want to change its layout (forward).
>>
>> Comments are welcome.
>>
>> Miklos
>>
> _______________________________________________
> Tinyos-devel mailing list
> Tinyos-devel at millennium.berkeley.edu
> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-devel