Some more thoughts on this...
On Mar 28, 2009, at 8:44 PM, Tony Li wrote:
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.
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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