Hmm. You could probably make the claim that there aren't any wired link
layers that don't have losses, too. I guess that it's all relative.
What are the loss rates in wired systems?
Certainly it is possible to find path/channel combinations in 802.15.4
networks that have zero loss at the link layer over periods of many
weeks and millions of packets, which I think gets called "carrier class"
reliability.
If we're smart, we'll be able to build networks that use such
path/channel combos almost exclusively. As you point out, this is a
DLL/MAC issue, so its solution doesn't belong in this forum (that's what
the 15.4E task group was created to address). But the abstraction does
belong here, and it's important to understand what's really going on in
15.4 (and other RF) channels to make intelligent routing decisions on
them.
To date most of the published WSN channel models have interpreted abrupt
multi-path interference as a lossy path, and that will lead to bad
decisions at the routing layer.
ksjp
Philip Levis wrote:
On Oct 29, 2007, at 10:38 AM, Kris Pister wrote:
JP - the RL2N charter looks good. My only concern is over the second
L in L2 - are these networks intrinsically lossy, or is that just due
to the current protocols?
The "lossy" means at the link layer. There aren't any wireless link
layers that don't have losses. They might mask them to higher layers
through retransmissions, but losses occur. Of course, a network layer
may select links that have a very low loss rate, but, well, that's
part of what all of this effort is about.
Phil
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