Re: [Roll] [roll] #86: G flag: do we need that text?

Hello Mukul:

>1) For a local instance there can be only one root and one DODAG. G bit cannot and is not used for DODAG selection within an instance. 

The statement above seems to be at odds with following two statements

>2) In a given deployment, a goal can be defined that some P2P DODAGs achieve and others do not. The roots that achieve that goal will set the G bit in their P2P DAGs.
3) the default goal is to create connectivity between origin and target. So by default G should be set to 1.

As per statement 1, the G flag can never be 1 for P2P-RPL DAGs because they use local instance ids.
[Pascal] Statement 1 does not say that at all. Can't fathom how you concluded that... Let me try to reword: There is only what DODAG for a given local instance so there cannot be a selection => G cannot be used for a selection that cannot happen.

---

As per statement 2/3, the G flag could be 1 and is 1 by default.

[Pascal] Yes. I added an item to help the device prioritize when it is asker to participate to many DODAGs (for many P2P flows that it happens to be on the path of). In that case, and if the device cannot particpater to all the P2P DODAGs, then the G bit could be use to decide which are the most important. 

---

I am OK with setting G flag to 1 always (as you, Richard and Phil seem to prefer) but I dont know how to reason this. Do we need to provide a reason at all?

[Pascal] If you define a default goal that the DODAG fills, then you set G to one. For instance, G could mean 'important stuff' like swithing a light on. You'd set it for switching lights but not for reporting the hygrometry of your orchids, which anyway will be retried in a half hour. As a result, if the 2 DAG formations collide, the light on will have precedence...

---------

:) too ...

 Pascal

----- Original Message -----
From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Mukul Goyal" <mukul@uwm.edu>
Cc: roll@ietf.org, "Richard Kelsey" <richard.kelsey@ember.com>, "Philip Levis" <pal@cs.stanford.edu>
Sent: Thursday, April 5, 2012 1:11:42 AM
Subject: RE: [Roll] [roll] #86: G flag: do we need that text?

Hello Mukul:

I suggest a sentence that says that:

1) For a local instance there can be only one root and one DODAG. G bit cannot and is not used for DODAG selection within an instance. 
2) In a given deployment, a goal can be defined that some P2P DODAGs achieve and others do not. The roots that achieve that goal will set the G bit in their P2P DAGs.
3) the default goal is to create connectivity between origin and target. So by default G should be set to 1.
4) if an intermediate router does not have enough resources to participate to all DODAGs then it should favor DODAGs with the G bit on.

The exact wording is yours...

Cheers,

Pascal

-----Original Message-----
From: Mukul Goyal [mailto:mukul@uwm.edu]
Sent: mercredi 4 avril 2012 18:47
To: Pascal Thubert (pthubert)
Cc: roll@ietf.org; Richard Kelsey
Subject: Re: [Roll] [roll] #86: G flag: do we need that text?

Pascal

>In any case, as I suggested earlier and as Richard also suggest now, G SHOULD probably be 1 by default but MAY be set otherwise.

Richard wants the flag to always be either 0 or 1. He prefers it to be always 1 but would settle for it being always zero.

I think this is not a critical point. I am OK with whatever resolution you and Richard arrive at. Kindly provide me the resolution text I should put in the draft.

Thanks
Mukul

----- Original Message -----
From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Mukul Goyal" <mukul@uwm.edu>
Cc: roll@ietf.org, "Richard Kelsey" <richard.kelsey@ember.com>
Sent: Wednesday, April 4, 2012 11:05:50 AM
Subject: RE: [Roll] [roll] #86: G flag: do we need that text?

Mukul:

I think we disagree because of the definition of goal itself. The goal is an abstraction. Same goes for the term Objective in OF. RFC 6550 only gives examples of what G could be used for but that is not limiting. Certainly the abstraction may for instance mean that external nodes are reachable via the root. But it could be something else entirely. For instance it could designate a root that can aggregate data.

In practice, G is used to favor a root that reaches the goal vs. one that does not. But that's senseless for local instances that have by definition a single root.

So whatever you set it to does not make a difference for RFC 6550 operations. I figure it could be used for signaling a "transient goal" information to an OF that could use it for a purpose I can't fathom.

In any case, as I suggested earlier and as Richard also suggest now, G SHOULD probably be 1 by default but MAY be set otherwise.

Pascal

-----Original Message-----
From: Mukul Goyal [mailto:mukul@uwm.edu]
Sent: mercredi 4 avril 2012 16:16
To: Pascal Thubert (pthubert)
Cc: roll@ietf.org; Richard Kelsey
Subject: Re: [Roll] [roll] #86: G flag: do we need that text?

Pascal

>If the goal is to reach the root, then G is 1...

I have told you multiple times that joining a P2P-RPL DAG does not give any sort of connectivity to the node.

Thanks
Mukul

----- Original Message -----
From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Mukul Goyal" <mukul@uwm.edu>, "Richard Kelsey" <richard.kelsey@ember.com>
Cc: roll@ietf.org
Sent: Wednesday, April 4, 2012 9:05:28 AM
Subject: RE: [Roll] [roll] #86: G flag: do we need that text?

Hello Mukul

Floating vs. Grounded depends on the goal of the DODAG. I asked you and will ask again what is your goal?
If the goal is to reach the root, then G is 1... If you want to signal something to the OF using the G bit, leave it  open.

Cheers,
Pascal

-----Original Message-----
From: roll-bounces@ietf.org [mailto:roll-bounces@ietf.org] On Behalf Of Mukul Goyal
Sent: mercredi 4 avril 2012 15:55
To: Richard Kelsey
Cc: roll@ietf.org
Subject: Re: [Roll] [roll] #86: G flag: do we need that text?

>The G flag is 0 if and only if the DODAG is floating.

I think that the G flag is 1 if and only if the DODAG is grounded. The temporary DAGs used in P2P-RPL are not grounded, they are temporary. I think that all transient/temporary DAGs are floating by their very nature.

Thanks
Mukul

----- Original Message -----
From: "Richard Kelsey" <richard.kelsey@ember.com>
To: roll@ietf.org
Cc: mukul@UWM.EDU, jpv@cisco.com, roll@ietf.org
Sent: Wednesday, April 4, 2012 8:36:50 AM
Subject: Re: [Roll] [roll] #86: G flag: do we need that text?

> From: roll issue tracker <trac+roll@trac.tools.ietf.org>
> Date: Wed, 4 Apr 2012 13:08:50 +0000
> 
> #86: G flag: do we need that text?
> 
>  Problem (resolition is proposed)
>  ------------------------------
>  Disagreement on the meaning of 'G' bit and imposed setting to 0;
> 
>  Proposed resolution
>  ---------------------------
>  The origin sets the G flag based on its perception of whether joining

> how the flag's value would affect the rank calculation under the OF 
> being used. By default, the G flag is set to zero given the temporary

> nature of the DAG being created.

I disagree with the proposed resolution.  It adds needless confusion.
The G flag is 0 if and only if the DODAG is floating.
There is no point to allowing floating DODAGs with a P2P-RDO option.  I suggest that the G bit be set to 1 and that routers be explicitly prohibited from creating floating DODAGs with a P2P-RDO option.
                                   -Richard Kelsey _______________________________________________
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