Subject: [rrg] Terminology, 2nd pass

From: Tony Li <[email-masked]>
Date: Sat, 28 Mar 2009 20:44:11 -0700

Hi all,

Here's where we are after one round of comments.

Tony

locator	   A locator is a name that has topological sensitivity and must
	   change if the point of attachment changes.  By convention,
	   a locator refers to layer 3 by default.  It is also
	   possible to have locators at other layers.  Locators may
	   have other properties, such as their scope (local or global
	   (default)) and their lifetime (ephemeral or permanent
	   (default)).

identifier An identifier is the name of an object; identifiers have no
	   topological sensitivity, and do not change, even if the
	   object changes its point(s) of attachment within the
	   network topology.  Identifiers may have other properties,
	   such as the scope of their uniqueness (local or global
	   (default)), the probability of their uniqueness
	   (statistical or absolute (default)), and their lifetime
	   (ephemeral or permanent (default)).

address    An address is a name that is both an interface locator and an
	   endpoint identifier.

---

From: Klaas Wierenga <[email-masked]>
Date: Sun, 29 Mar 2009 17:40:00 +0200

On Mar 29, 2009, at 5:44 AM, Tony Li wrote:

Hi Tony,

> locator	   A locator is a name that has topological sensitivity and  

MUST? In for example mobile networks the layer 3 locator often doesn't  
change if the point of attachment changes. So does "point of  
attachment" refer to attachment at the layer the locator refers to?

> 	   topological sensitivity, and do not change, even if the

"do not change" -> "do not have to change"?

> address    An address is a name that is both an interface locator  

Klaas

---

From: Tony Li <[email-masked]>
Date: Sun, 29 Mar 2009 11:04:26 -0700

Hi Klaas,

Klaas Wierenga wrote:
> change if the point of attachment changes. So does "point of attachment" 
> refer to attachment at the layer the locator refers to?
> 
>>        a locator refers to layer 3 by default.  

Ok, but in a mobile network, it's usually the L2 point of attachment 
that's changing, not the L3 point of attachment.  When you do change 
that (i.e., roaming), then your locator is indeed changing and all sorts 
of registration mechanisms are in place to update your locator.

> "do not change" -> "do not have to change"?

Sure.  Someone might want to change their identifier at the time that 
they roam for privacy reasons.  That's certainly reasonable.

Thanks,
Tony

---

From: Klaas Wierenga <[email-masked]>
Date: Sun, 29 Mar 2009 22:16:22 +0200

Hi Tony,

> of registration mechanisms are in place to update your locator.

agreed, does it get too complicated if you write:

"A locator is a name that has topological sensitivity and that must
change if the point of attachment (at the layer the locator refers to)
changes"

?

not sure myself, the definition gets a bit complicated, but I think it
is important to note that changing points of attachment on one layer
don't necessarily mean changing locators at another....

> they roam for privacy reasons.  That's certainly reasonable.

Right, that was my reasoning too, without the "do not have to" readers
may presuppose persistence.

Klaas

---

From: Tony Li <[email-masked]>
Date: Sun, 29 Mar 2009 13:22:37 -0700

Hi Klass,

> don't necessarily mean changing locators at another....

How about:

	   A locator is a name that has topological sensitivity at a
	   given layer and must change if the point of attachment at
	   that layer changes.  By default, a locator refers to layer
	   3.

Tony

---

From: Klaas Wierenga <[email-masked]>
Date: Sun, 29 Mar 2009 22:25:47 +0200

Tony,

>        that layer changes.  By default, a locator refers to layer

works for me!

Klaas

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From: "Joel M. Halpern" <[email-masked]>
Date: Sun, 29 Mar 2009 16:27:08 -0400

Note that some mobile (cellular) networks use cascaded, proxied, MIP 
tunnels such that the the local L3 (network oriented) point of 
attachment changes, even though the host does nto see that.

In general, different routing systems may require that the host visible 
IP address changes at different granularities of motion.  However, the 
point with any locator is that there is some granularity of topological 
change beyond which the locator must change.  (If I understood Dow 
properly Friday, this is the converse of the point he was making. 
Routing systems may use identifiers with no topological significance in 
all cases, in which case there is no need for locators.  Or the routing 
system may require that the locators not only exist, but change to 
reflect every minute change of topological placement.  Or they may 
operate between those two extremes.  What we know is that a locator, if 
it exists in the solution, is something that changes when the 
topological location of the located thing changes sufficiently.)

Yours,
Joel

Klaas Wierenga wrote:
> _______________________________________________
> rrg mailing list
> [email-masked]
> http://www.irtf.org/mailman/listinfo/rrg
>

---

From: Dow Street <[email-masked]>
Date: Sun, 29 Mar 2009 13:38:18 -0700

Some more thoughts on this...

> address    An address is a name that is both an interface locator  

As a starting point, I think we can say that a system has objects and  
names for those objects.  A name belongs to a namespace, which may set  
bounds on the valid values for names within that namespace (e.g. max  
number of bits).  A particular instance of a namespace may also have a  
set of semantics associated with it, where the semantics are oriented  
toward the "expected" use of the name.

A given name could be a locator, an identifier, or both.  Whether it  
is considered to be a locator or identifier depends on *how the name  
is used*.  A name alone is just a name - it is the binding of name to  
use (i.e. role) that makes it a locator or identifier.  As such, it is  
quite possible that a name can serve various roles, or be used in  
different ways, by different components of the system at the same  
time.  Furthermore, the scope and/or nature of the named object can  
differ between different users of the name.  (Is this the name of an  
IP interface, a stack, a host, etc?)

So, what makes a name into a locator?

"A name is defined to be a "locator" when it is used in the context  
of, or perhaps by, a system that has a notion of geography, topology,  
or distance, and the value of the name, combined with a location in  
the system, produces a vector of relevance to that system's geography  
or topology."

Looking at Tony's definitions above, there is something about the  
phrase "must change if the point of attachment changes" that does not  
seem quite right.  (Still trying to figure out why, though...)

R,
Dow

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From: Scott Brim <[email-masked]>
Date: Mon, 30 Mar 2009 07:25:35 -0400

> of registration mechanisms are in place to update your locator.

First, assuming your implied claim that "some locator must change when
your point of attachment changes" is true, that still doesn't mean that
a particular locator must change when your point of attachment changes.
 We still don't want "must" in the definition of a locator.  See my
previous mail for proposed words (at the top).

Second, in reality there is no L2 locator involved.  MAC addresses need
not change even if forwarding is using them.  And in the real world it's
all done with tunnels anyway.

> they roam for privacy reasons.  That's certainly reasonable.

Right.  See my previous message for proposed text.

---

From: Scott Brim <[email-masked]>
Date: Mon, 30 Mar 2009 07:40:39 -0400

Dow Street allegedly wrote on 03 29 2009 4:38 PM:
> names for those objects.  

and functions that act on those objects and names for the functions.

> A given name could be a locator, an identifier, or both.  Whether it is
> considered to be a locator or identifier depends on *how the name is
> used*.  

I'm so pleased to meet a fellow believer in the wilderness.  Usage is
the primary issue.  However, _intended_ usage can also apply (for
example, if I pass you a message which has a field in it that contains
something I want you to use as a locator, it's a locator).  And some
names can only be usefully used a particular way due to the way they are
constructed or administered.

> A name alone is just a name - it is the binding of name to use
> (i.e. role) that makes it a locator or identifier.  As such, it is quite
> possible that a name can serve various roles, or be used in different
> ways, by different components of the system at the same time. 
> Furthermore, the scope and/or nature of the named object can differ
> between different users of the name.  (Is this the name of an IP
> interface, a stack, a host, etc?)
> 
> "A name is defined to be a "locator" when it is used in the context of,
> or perhaps by, a system that has a notion of geography, topology, or
> distance, and the value of the name, combined with a location in the
> system, produces a vector of relevance to that system's geography or
> topology."
> 
> Looking at Tony's definitions above, there is something about the phrase
> "must change if the point of attachment changes" that does not seem
> quite right.  (Still trying to figure out why, though...)

Noel Chiappa allegedly wrote on 03 29 2009 5:13 PM:
>     > From: Dow Street <[email-masked]>
> 
> When it has _structure_ which relates to _where_ the named thing is.
> 
> I.e. MAC is not a locator, even when used in a bridging system, because
> there's no structure in it - MACs are just identifiers for the interface.

Right, it is administered in such a way that it cannot be used
effectively as a locator.  That limits its use ... but if tomorrow I
enforced assignment of my MACs hierarchically and dynamically, suddenly
<Ta Da> they could be locators.  It's not a property of the thing
itself, just how it is used.

>     > "A name is defined to be a "locator" when it is used in the context of,
>     > nor perhaps by, a system that has a notion of geography, topology, or
>     > distance, and the value of the name, combined with a location in the
>     > system, produces a vector of relevance to that system's geography or
>     > topology."
> 
> I _think_ this says the same thing as the above , but in a mathematical way,
> but I'm not sure.
> 
>     > there is something about the phrase "must change if the point of
>     > attachment changes" that does not seem quite right. 
> 
> Well, one thing is that a locator may change, even if the physical location
> the entity is plugged in hasn't changed, if the structure of the network has
> been rearranged (e.g. a chunk of topology has been re-homed, e.g. to a
> different ISP).

I think that falls under "change in topological location".  The topology
changes so the topological location changes, even if the attachment
point hasn't.