<s>
Provider-aggregatable	B-Protocol
address	I-Protocol
space	I-Protocol
(	O
PA	O
)	O
is	O
a	O
block	O
of	O
IP	B-Protocol
addresses	I-Protocol
assigned	O
by	O
a	O
regional	O
Internet	O
registry	O
to	O
an	O
Internet	O
service	O
provider	O
which	O
can	O
be	O
aggregated	B-Protocol
into	O
a	O
single	O
route	O
advertisement	O
for	O
improved	O
Internet	O
routing	O
efficiency	O
.	O
</s>
<s>
Unlike	O
provider-independent	B-Protocol
address	I-Protocol
space	I-Protocol
,	O
the	O
end-user	O
of	O
address	O
blocks	O
within	O
a	O
provider-supplied	O
space	O
cannot	O
reuse	O
the	O
addresses	O
if	O
they	O
change	O
up-stream	O
connectivity	O
providers	O
.	O
</s>
