<s>
In	O
MPLS	B-Protocol
,	O
a	O
label	O
with	O
the	O
value	O
of	O
1	O
represents	O
the	O
router	B-Protocol
alert	I-Protocol
label	I-Protocol
.	O
</s>
<s>
However	O
,	O
if	O
the	O
packet	O
is	O
forwarded	O
further	O
,	O
the	O
Router	B-Protocol
Alert	I-Protocol
Label	I-Protocol
should	O
be	O
pushed	O
back	O
onto	O
the	O
label	O
stack	O
before	O
forwarding	O
.	O
</s>
<s>
The	O
use	O
of	O
this	O
label	O
is	O
analogous	O
to	O
the	O
use	O
of	O
the	O
"	O
Router	O
Alert	O
"	O
option	B-Protocol
in	O
IPv4	B-Protocol
packets	O
.	O
</s>
<s>
Since	O
this	O
label	O
cannot	O
occur	O
at	O
the	O
bottom	O
of	O
the	O
stack	O
,	O
it	O
is	O
not	O
associated	O
with	O
a	O
particular	O
network	B-Application
layer	I-Application
protocol	O
.	O
</s>
