<s>
An	O
H.323	B-Application
Gatekeeper	I-Application
serves	O
the	O
purpose	O
of	O
Call	B-Protocol
Admission	I-Protocol
Control	I-Protocol
and	O
translation	O
services	O
from	O
E.164	O
IDs	O
(	O
commonly	O
a	O
phone	O
number	O
)	O
to	O
IP	O
addresses	O
in	O
an	O
H.323	B-Protocol
telephony	O
network	O
.	O
</s>
<s>
Gatekeepers	O
can	O
be	O
combined	O
with	O
a	O
gateway	O
function	O
to	O
proxy	O
H.323	B-Protocol
calls	O
and	O
are	O
sometimes	O
referred	O
to	O
as	O
Session	O
Border	O
Controllers	O
.	O
</s>
<s>
A	O
gatekeeper	O
can	O
also	O
deny	O
access	O
or	O
limit	O
the	O
number	O
of	O
simultaneous	O
connections	O
to	O
prevent	O
network	B-Protocol
congestion	I-Protocol
.	O
</s>
<s>
H.323	B-Protocol
endpoints	O
are	O
not	O
required	O
to	O
register	O
with	O
a	O
gatekeeper	O
to	O
be	O
able	O
to	O
place	O
point	O
to	O
point	O
calls	O
,	O
but	O
they	O
are	O
essential	O
for	O
any	O
serious	O
H.323	B-Protocol
network	O
to	O
control	O
call	O
prefix	O
routing	O
and	O
link	O
capacities	O
among	O
other	O
functions	O
.	O
</s>
