Hi all,
Thank you all for the highly spirited debate and my apologies for being
unable to contribute. Other high priority matters have been in the
foreground.
I've read the entire debate so far and am struck by the fact that we
made a change in the 2nd pass and early in the thread and I don't think
everyone picked up on the importance of the distinction. Specifically,
it's vital to understand that a locator and identifier have semantics
that are only relevant at a particular layer. Furthermore, talking
about identifiers and locators in absolute terms is not constructive;
they are necessarily relative terms.
Remember that both identifiers and locators start off as simply tokens.
Names that we assign to things. We assign them semantic values that
happen to matter at a particular layer. When regarded outside of that
layer, those names then are simply opaque.
For a better example, let's stop arguing about Ethernet. We have to
operate with many link layers and our terminology must reasonably apply
to all of them. Let's look at what happens with IP over X.25. An X.25
address is a long string of bits and within the X.25 network, if
administered in a sane fashion, the address is hierarchically assigned
and nicely structured. However, from the perspective of layer 3, it is
wholly opaque. Just a token, nothing more. It has no semantics _at
layer 3_. Similarly, from the perspective of layer 2, the IP address is
neither locator nor identifier. It's just payload bits.
The key point here is that the semantics of a namespace is only relative
to the layer where it is applicable. The rest of the time, it's just
opaque bits.
As another example, let's look at the FQDN. At the application layer,
it's clear that it's a practical identifier. We map it through DNS to
get an IP address that gives us a network layer identifier and locator.
However, at the network layer, the FQDN itself is nothing but a string.
So, it's all relative.
Putting this all together, here's pass 3. Again, if I missed something
or have misunderstood, please feel free to bring it up. The goal here
is to reach rough consensus on these definitions and we're definitely close.
Regards,
Tony
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locator A locator is a name that has topological sensitivity at a
given layer and changes if the point of attachment at that
layer changes. By default, a locator refers to layer 3.
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 at a given layer;
identifiers have no topological sensitivity, and do not
have to 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 used as both an interface
locator and an endpoint identifier.
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