Jonathan Hui wrote:
Timothy J. Salo wrote:
o They don't interoperate. Again, is system-level
interoperability one of our objectives? If it isn't, I
suggest we simply say so.
Hasn't the IETF traditionally concerned itself with
interoperability at L3 and above?
I think there is no question that 6lowpan is breaking new
ground within the IETF. As far as I know, this is the first
IETF Working Group that intends to specify a layer-two
routing solution. (Yes, yes, I know. We could claim that
it is actually "mesh under routing" or layer 2.5 routing, or
layer 2.3457 routing. But nonetheless, 6lowpan intends to
specify a routing solution that operates on link-layer
addresses. And, I think this is unique within the IETF.)
Given that 6lowpan is already working on a layer-two routing
solution (no matter what you call it) it seems to me that
we have created a strong argument that, at least in some
environments, it is important to think about how things
should be done below layer three. This should permit us
to think about layer-two issues that we think may be important.
I don't think this WG
should be worried about interoperability between arbitrary link layers
simply because they utilize a radio with 'IEEE 802.15.4' in its
datasheet. Note that just because a radio may be IEEE 802.15.4
compliant, doesn't mean it can communicate with any arbitrary IEEE
802.15.4 radio. There may be differences in frequency (2.4 GHz, 916 MHz,
868 MHz), modulation (BPSK, ASK, O-QPSK), baudrate (20, 100, 250 kbps).
Then there's IEEE 802.15.4-2006 vs. 802.15.4a vs. the
currently-in-progress 802.15.4e. I'd be surprised if the
energy-management mechanisms in 802.15.4-2006 are at all compatible with
802.15.4e. Note that there are commonalities in all of this (addressing,
frame format, etc). I don't think it is in the best interest of this WG
to pick a single slice and say we will develop solutions that address
only that one slice.
Well, dramatic as you try to make it sound, these parameters can't
be selected independently. Customers in ITU Region 2 have about
two choices:
o 2.450 GHz / 250 kbps / O-QPSK
o 915 MHz / 40 kbps / DSSS with BKSK
I think 868 MHz operation is only permitted in Europe (but I think
915 MHz ISM operation is restricted to ITU Region 2, which doesn't
include Europe). Interestingly, I believe that devices operating in
the 868 MHz ISM band [in Europe] are permitted to operate at only a
1% duty cycle.
So yes, customers may, depending where they are, have as many as
_two_ (not the 36 you seemed to be trying to lead us to believe)
incompatible physical layer choices. (Although which two choices
customers have varies by geographic, or more precisely ITU, region).
Correct me if I am wrong, but you appear to be arguing that because
the 802.15.4 spec offers customers two choices, then the IETF should
make no effort to ensure system-level interoperability. I am not
convinced that this is the right answer (or the right reasoning).
By the way, I am glad to see your support for the notion that
6lowpan is targeting 802.14.4 _networks_, rather than 802.15.4
_radios_. This permits us to at least consider making use
of 802.15.4 functionality that might not be implemented in
802.15.4-compatible chips.
-tjs
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