[e2e] Port numbers, SRV records or...?
davide+e2e at cs.cmu.edu
Wed Aug 9 23:55:23 PDT 2006
>>> 25 years ago we figured out how much naming and
>>> addressing we need but we choose to ignore the
>> Care to supply a pointer?
> RFC 1498
I've meant to give that a careful read, and this time I
did--with the result that I'm really unsure what an
"attachment point" is.
Saltzer himself points out that this is a troublesome
concept for DIX Ethernet (the old broadcast-along-coax
kind), with MAC addresses serving roughly but not exactly
It's possible to describe an attachment point in a switched
Ethernet network: port X on switch aa:bb:cc:dd:ee:ff--but
the only people who worry about such an attachment point
are your network operations staff, and only when the machine
turns into a monster. A remote endpoint does not need to
resolve a service onto a node and then the node onto such
an attachment point for communication to work.
There's more trouble when one considers wireless networks.
I don't think an "attachment point" can be a (latitude,
longitude, altitude) tuple, but I don't think it can be
anything else either. My "attachment point" could be the
base station I'm registered with, and the architecture of
cellular phone systems (where phones are seriously not the
same things as base stations) somewhat argues that way.
There are complexities here, though: in a soft-handoff
CDMA system, a handset routinely communicates with multiple
base stations simultaneously--is it x% attached to one
tower and (1-x)% attached to another? Here a remote peer
is firmly not involved in knowing my attachment point--it
doesn't figure out where I'm attached and then consider
paths to me.
Things get odder in ad-hoc networks or sensor networks,
where power control and variable coding mean that each
node is connected to every other node at some cost (really
a space of (power,delay) values), which may be varying and
may be hard to measure.
If "attachment point" is challenged by shared-medium
Ethernet, switched Ethernet, "wireless Ethernet", CDMA
cellular phone systems, ad-hoc networks, and sensor
networks, I'm having trouble seeing the crispness of the
concept--which was apparently clear to Saltzer. If I've
missed something obvious, please clue me in...
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