On Jun 26, 2009, at 10:24 AM, Christian Vogt wrote:
Dear all -
I am catching up on folks' previous discussion on identifier
properties.
I'm doing the same, albert 10 days after Christian, in preparation for
next IETF. Just finished all the msgs on this thread.
This discussion is really useful; I wish I had participated earlier.
same here!!!
I'll save the detailed comments for a face-face chat as next IETF is
really coming soon.
For a quick comment here: I'd just say that I would like to second the
view some other people have expressed earlier, that is whether a good
architecture should have nothing more than necessary --- this is
quoted from one of Joel's msgs but I removed the adjective "absolutely".
I view a good architecture as a good engineering design, the necessity
should be measured by whether it is the best engineering tradeoff;
pushing a design to the extreme point may or may not represent the
best tradeoff.
Lixia
One thought that has been brought up is the inevitable coexistence of
multiple types of identifiers. This makes sense given the variety of
things to be identified. In fact, the multitudinousness of
identifiers
is not new: Many applications have their own identifiers already
today.
But are all these identifier types essential elements of an Internet
architecture? I would argue most of them are not -- they are useful
within the scope of a particular Internet application, but they are
not
essential for the Internet per se to function. In fact, I see only
two
purposes for which the Internet architecture must have identifiers:
(1) service identification, identifying a piece of communication
software that responds to incoming contact establishment attempts
(2) session identification, identifying the protocol state
corresponding
to a particular session after contact establishment
Individual Internet architecture solutions may use combinations of
more
than one identifier for either of these two purposes. For example,
service identification in the existing Internet is achieved by
combining
a host identifier (DNS name, or IP address in its role as a host
identifier) and a host-local service identifier (well-known port
number). So an Internet architecture may have more than two types of
identifiers. But again, it seems that all of those identifiers would
serve only the above two purposes, after all.
Given the distinct identifier purposes, the properties of identifiers
may naturally be specific to a particular purpose. For example, the
property of enabling session referrals clearly applies to only session
identification, but not to service identification. On the other hand,
stability is a property that is more important for service
identification than for session identification, since two hosts
engaged
in a session may be able to handle changes of session identifiers.
Thoughts?
- Christian
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