Subject: Re: [rrg] Terminology, 2nd pass

From: [email-masked] (Noel Chiappa)
Date: Mon, 30 Mar 2009 17:43:02 -0400 (EDT)

> From: Scott Brim <[email-masked]>

    > Is "the place you're trying to end up at" a point in the topology where
    > something is attached, or is it the something itself?

The former, although presumably one only wants to get to the former in order
to get to the latter.

    > If it's the second, you might call the name of it an identifier.

Normally, yes.

However, if the name of the latter (for whatever reason) had information
about the location built into it (think of them as 'locators for endpoints'),
then it would not be an identifier. Now, I happen to think that's a bad
approach, in engineering terms (q.v. IPvN address), but it is logically
consistent (in terms of the terminology).

    > a name used as a locator can have any amount of structure in it, more
    > or less, and that doesn't change whether it's a locator or not. 

That's kind of like being 'a little bit pregnant'. A name either has _no_
location information _built into it_, or is has some - and all the latter
such names are 'locators'. (And notice that IEEE numbers have _no_ location
information built into them.)

    > I'm saying that the degree of structure in the name does not decide
    > whether it can be called a locator or not.

Under the above definition, I concur.

    >> To most of us, "locator" means 'a _structured_ name for a place in the
    >> topology'.

    > Does it matter to you how much structure is in the name?

Not as long as the structure is related to the location. For a
counter-example, even though an IEEE number does have stucture, that
structure is not about the location.

    >> the _original_ definition of "locator" did _not_ include use "by [the]
    >> forwarding": the term 'locator' was defined _precisely_ to have a term
    >> that meant 'structured name for a place in the topology that is _not_
    >> used by the forwarding'.

    > How was it used then?

To name map nodes.

    > What did forwarding use?

Flow identifiers (think MPLS tags).

     Noel

---

From: Scott Brim <[email-masked]>
Date: Mon, 30 Mar 2009 18:15:57 -0400

Excerpts from Noel Chiappa on Mon, Mar 30, 2009 05:43:02PM -0400:
>     > Is "the place you're trying to end up at" a point in the
>     > topology where something is attached, or is it the something
>     > itself?
> 
> The former, although presumably one only wants to get to the former
> in order to get to the latter.

OK.  It was a layering question.  "you" are apparently the network
trying to deliver a packet to an attachmen point, as opposed to an
endpoint trying to deliver a packet to a peer endpoint.  I would have
gone the other way but now I know what you mean.

> However, if the name of the latter (for whatever reason) had
> information about the location built into it (think of them as
> 'locators for endpoints'), then it would not be an identifier. Now,
> I happen to think that's a bad approach, in engineering terms (q.v.
> IPvN address), but it is logically consistent (in terms of the
> terminology).

OK

> information built into them.)

OK

> structure is not about the location.

OK.  Those two almost go hand-in-hand, but not quite.  I want to
assert that that attribute:

  - A locator has structure in it related to topological position

is a subset of the current working definition:

  - A locator is associated with topological position such that if a
    node moves its locator may have to change.

The reason is that the second includes the first but can be true even
if a name does not have any structure in it.  Test case: suppose I am
an evil network administrator and I decide that all odd-numbered IP
addresses need to be on that Ethernet over there, and all
even-numbered IP addresses on this Ethernet over here.  At least for
the final steps, there is no structure related to location, and yet it
may have to change if a node moves between those two Ethernets.
Thoughts?

>     >> the _original_ definition of "locator" did _not_ include use
>     >> "by [the] forwarding": the term 'locator' was defined
>     >> _precisely_ to have a term that meant 'structured name for a
>     >> place in the topology that is _not_ used by the forwarding'.
> 
>     > How was it used then?
> 
> To name map nodes.
> 
>     > What did forwarding use?
> 

OK

Scott