Julian,
There is no different in deserializing this and the Reload message
itself, both are full of variable length and nested structures. It's
actually a lot simpler,
1. Receive a UDP packet (after DTLS decryption) that starts with ACK
(129) but the packet is size greater than 9 (size of ACK frame).
2. Consume the first 9 bytes and handles the ACK frame.
3. Discard the first 9 bytes, and handles the remaining PDU as a normal
DATA frame (deserialize).
--Michael
jc wrote:
Yes but that's darn ugly and would be a deserialization nightmare. :-)
Sent from my iPhone
On Apr 16, 2010, at 8:23 PM, Michael Chen <[email protected]>
wrote:
Julian,
UDP transport requires the reload fragment to fit in a single MTU
size packet after DTLS encryption. In this case, after DTLS
decryption, you get a PDU with known size. Each element in this PDU
has their own account of their size. Therefore,
sizeof(ACK_frame) == 5;
sizeof(DATA_frame) ==
sizeof(RELOAD_header) +
sizeof(RELOAD_message) +
sizeof(Security_block);
sizeof(PDU) == sizeof(ACK_frame) + sizeof(DATA_frame)
If the message is fragmented, then this only applies to the first
fragment, which is also inside the boundary of DATA_frame (the 24-bit
frame size).
Am I right?
--Michael
jc wrote:
On Apr 15, 2010, at 7:06 PM, Michael Chen wrote:
-------- Original Message --------
Subject: Re: Reload bcast and mcast discovery
From: jc <[email protected] <mailto:[email protected]>>
Date: Thu, April 15, 2010 2:02 pm
To: Michael Chen <[email protected]
<mailto:[email protected]>>
Right, sorry I keep thinking in the context of ALL messages. Pings
will work ok using this method but currently no other PDU's because
of possible need to fragment. In order to support this changes to
the base draft would need to occur allowing messages without a
framing header unless you have a way around this?
I guess it is unlikely the group will accept frameless message at
this point, which is why I am hesitated to do it. However, I do
have an alternative.
What if the base draft allows sending the ACK frame with the
response message in the same UDP packet? The response PDU would
look like this:
[ACK_frame]
[DATA_frame]
[RELO_header]
[RELO_message]
[Security block]
This keeps the compatibility of framing header and Simple
Reliability for UDP (it's the same logical order of PDUs in TCP).
This usage can be extended to include regular link layer responses
when the response is single hopped like bootstrap node discovery.
What do you think?
I think that "piggybacking" ack frames to response's is much needed
and I welcome this change. This would solve any ack related
headaches that I know currently exist and as you mention will reduce
traffic by 50% under certain conditions.
--Michael
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