Julian,
Yes (with correction): "guess if there is an DATA frame based on the UDP
packet size of an ACK frame".
If you want further confirmation, verify that the 10th byte (just beyond
the ACK frame) in the packet is DATA(128).
--Michael
jc wrote:
Michael,
So your saying we should guess if there is an ack frame based on packet size?
Julian
On Apr 19, 2010, at 12:55 PM, Michael Chen wrote:
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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