Date:	Mon, 26 Oct 2009 07:55:07 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	Ivo Calado <ivocalado@...edded.ufcg.edu.br>
Cc:	dccp <dccp@...r.kernel.org>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/4] Adds random ect generation to tfrc-sp sender side

| >    That is, at the moment both the sender and receiver side of the ECN Nonce
| >    sum verification are placeholders which currently have no effect.
| >
| 
| Okay, then the implementation would be useless now.
I was not suggesting to throw away the patches, we can keep them for
later use.

They are a good starting basis once it makes sense to work with ECN.
Or how can we test ECN if we are not sure that the other parts work
as they are supposed to?

| >  3) Starting an implementation throws up further questions that need to
| >    be addressed, both the basis and the extension need to be verified.
| >
| > I would like to suggest to implement the basis, that is CCID-4 with ECN
| > (using plain ECT(0)), test with that until it works satisfactorily, and
| > then continue adding measures such as the ECN Nonce verification.
| >
| 
| Okay. But, when would be good to at least include random ECT
| generation? When DCCP ECN code will get fixed? Is there any work on
| this?
| 
I asked this on netdev earlier, there was not much enthusiasm.

The issue is that ECN belongs both to the network and the transport layer.
This network layer is in inet_ecn.h, outside of DCCP.

I believe that the changes would not be too hard to do, by changing the
macros. But it requires working with the people on netdev, in particular
to ensure it does not break something in the TCP/SCTP subsystems (both
also use ECN, and then there are also raw sockets).

I also have an interest in resolving this, due to the ugliness at the
moment for enabling ECN on IPv6.

RFC 2884, written by one of the Linux ECN developers, describes early
IPv4 ECN evaluation. It seems that initially it was planned to only 
support ECN over Ipv4, parts of the code may be still from that time.

We can pursue this in parallel to the other issues. Ideally this would be
resolved at the time the other parts of CCID-4 are ready for testing.

| > In summary, I would like to suggest to remove the ECN verification for
| > the moment and focus on the "basic" issues first.
| >
| > Would you be ok with that?
| >
| 
| Yes, we'll keep the ECN verification code here at our git until the
| scenario is ready.
| 
I was going to suggest to put them onto a webpage, such as yours, or on 
www.erg.abdn.ac.uk/users/gerrit/dccp there is also still some space.

Can you please elaborate how to keep your git tree and the one on
eden-feed synchronized? At the moment I have not made any changes other
than the ones I emailed you about. Is there a way of keeping both trees
in synch without running into versioning difficulties?

(The simplest way I can think of is to keep the patches in a separate
 set, or to spawn a subtree which contains the ECN patches on top of the
 CCID-4 tree.)


| > (Also for later) I wonder how to do the sums, with RFC 3168
| > ECT(0) = 0x2 => !0x2 = 0
| > ECT(1) = 0x1 => !0x1 = 0
| >
| 
| I don't understand. Can you try to explain it? Or cite RFC section
| that address it?
 
The values are from figure 1, page 7, the expressions evaluate both as 0:

void main(void)
{
	printf("!0x2 = %d, !0x1 = %d\n", !0x2, !0x1);
}
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