<s>
Cross-layer	B-Protocol
optimization	I-Protocol
is	O
an	O
escape	O
from	O
the	O
pure	O
waterfall-like	O
concept	O
of	O
the	O
OSI	O
communications	O
model	O
with	O
virtually	O
strict	O
boundaries	O
between	O
layers	O
.	O
</s>
<s>
Its	O
advantages	O
include	O
high	O
adaptivity	O
in	O
a	O
Wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
and	O
a	O
larger	O
optimization	O
space	O
.	O
</s>
<s>
Cross-layer	B-Protocol
optimization	I-Protocol
shall	O
contribute	O
to	O
an	O
improvement	O
of	O
quality	O
of	O
services	O
under	O
various	O
operational	O
conditions	O
.	O
</s>
<s>
The	O
quality	O
aspect	O
is	O
not	O
the	O
only	O
approach	O
to	O
tailor	O
the	O
cross-layer	B-Protocol
optimization	I-Protocol
strategy	O
.	O
</s>
<s>
In	O
scenarios	O
like	O
this	O
,	O
the	O
overall	O
system	O
performance	O
can	O
be	O
improved	O
if	O
the	O
MAC	B-Protocol
can	O
get	O
information	O
from	O
the	O
PHY	B-Application
regarding	O
when	O
and	O
how	O
the	O
noise	O
and	O
interference	O
level	O
is	O
changing	O
,	O
so	O
that	O
the	O
MAC	B-Protocol
can	O
schedule	O
transmission	O
during	O
the	O
periods	O
of	O
time	O
in	O
which	O
noise	O
and	O
interference	O
levels	O
are	O
lower	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
communications	O
system	O
that	O
allows	O
this	O
kind	O
of	O
Cross-layer	B-Protocol
optimization	I-Protocol
is	O
the	O
ITU-T	B-General_Concept
G.hn	I-General_Concept
standard	O
,	O
which	O
provides	O
high-speed	O
local	O
area	O
networking	O
over	O
existing	O
home	O
wiring	O
(	O
power	O
lines	O
,	O
phone	O
lines	O
and	O
coaxial	O
cables	O
)	O
.	O
</s>
