<s>
The	O
Media	B-Protocol
Gateway	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
MGCP	O
)	O
is	O
a	O
telecommunication	O
protocol	O
for	O
signaling	O
and	O
call	O
control	O
in	O
hybrid	O
voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
and	O
traditional	O
telecommunication	O
systems	O
.	O
</s>
<s>
It	O
implements	O
the	O
media	B-Protocol
gateway	I-Protocol
control	I-Protocol
protocol	I-Protocol
architecture	O
for	O
controlling	O
media	O
gateways	O
connected	O
to	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
.	O
</s>
<s>
The	O
media	O
gateways	O
provide	O
conversion	O
of	O
traditional	O
electronic	O
media	O
to	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
network	O
.	O
</s>
<s>
The	O
protocol	O
is	O
a	O
successor	O
to	O
the	O
Simple	B-Protocol
Gateway	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
SGCP	B-Protocol
)	O
,	O
which	O
was	O
developed	O
by	O
Bellcore	O
and	O
Cisco	O
,	O
and	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Device	I-Protocol
Control	I-Protocol
(	O
IPDC	O
)	O
.	O
</s>
<s>
The	O
methodology	O
of	O
MGCP	O
reflects	O
the	O
structure	O
of	O
the	O
PSTN	O
with	O
the	O
control	O
over	O
the	O
network	O
residing	O
in	O
a	O
call	O
control	O
center	O
softswitch	B-Device
,	O
which	O
is	O
analogous	O
to	O
the	O
central	O
office	O
in	O
the	O
telephone	O
network	O
.	O
</s>
<s>
The	O
endpoints	O
are	O
low-intelligence	O
devices	O
,	O
mostly	O
executing	O
control	O
commands	O
from	O
a	O
media	B-Protocol
gateway	I-Protocol
controller	I-Protocol
,	O
also	O
called	O
call	O
agent	O
,	O
in	O
the	O
softswitch	B-Device
and	O
providing	O
result	O
indications	O
in	O
response	O
.	O
</s>
<s>
The	O
protocol	O
represents	O
a	O
decomposition	O
of	O
other	O
VoIP	B-Application
models	O
,	O
such	O
as	O
H.323	B-Protocol
and	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
,	O
in	O
which	O
the	O
endpoint	O
devices	O
of	O
a	O
call	O
have	O
higher	O
levels	O
of	O
signaling	O
intelligence	O
.	O
</s>
<s>
It	O
uses	O
the	O
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
for	O
specifying	O
and	O
negotiating	O
the	O
media	O
streams	O
to	O
be	O
transmitted	O
in	O
a	O
call	O
session	O
and	O
the	O
Real-time	B-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
RTP	O
)	O
for	O
framing	O
the	O
media	O
streams	O
.	O
</s>
<s>
The	O
media	B-Protocol
gateway	I-Protocol
control	I-Protocol
protocol	I-Protocol
architecture	O
and	O
its	O
methodologies	O
and	O
programming	O
interfaces	O
are	O
described	O
in	O
RFC	O
2805	O
.	O
</s>
<s>
MGCP	O
is	O
a	O
master-slave	O
protocol	O
in	O
which	O
media	O
gateways	O
(	O
MGs	O
)	O
are	O
controlled	O
by	O
a	O
call	O
control	O
agent	O
or	O
softswitch	B-Device
.	O
</s>
<s>
This	O
controller	O
is	O
called	O
a	O
media	B-Protocol
gateway	I-Protocol
controller	I-Protocol
(	O
MGC	O
)	O
or	O
call	O
agent	O
(	O
CA	O
)	O
.	O
</s>
<s>
This	O
facilitates	O
centralized	O
gateway	O
administration	O
and	O
provides	O
scalable	O
IP	B-Application
telephony	I-Application
solutions	O
.	O
</s>
<s>
The	O
distributed	O
system	O
is	O
composed	O
of	O
at	O
least	O
one	O
call	O
agent	O
and	O
one	O
or	O
usually	O
,	O
multiple	O
media	O
gateways	O
,	O
which	O
performs	O
the	O
conversion	O
of	O
media	O
signals	O
between	O
circuit-switched	O
and	O
packet-switched	O
networks	O
,	O
and	O
at	O
least	O
one	O
signaling	B-Protocol
gateway	I-Protocol
(	O
SG	O
)	O
when	O
connected	O
to	O
the	O
PSTN	O
.	O
</s>
<s>
A	O
softswitch	B-Device
is	O
typically	O
used	O
in	O
conjunction	O
with	O
signaling	B-Protocol
gateways	I-Protocol
,	O
for	O
access	O
to	O
Signalling	O
System	O
No	O
.	O
</s>
<s>
The	O
call	O
agent	O
does	O
not	O
use	O
MGCP	O
to	O
control	O
a	O
signaling	B-Protocol
gateway	I-Protocol
;	O
rather	O
,	O
SIGTRAN	O
protocols	O
are	O
used	O
to	O
backhaul	B-General_Concept
signaling	O
between	O
a	O
signaling	B-Protocol
gateway	I-Protocol
and	O
the	O
call	O
agents	O
.	O
</s>
<s>
MGCP	O
recognizes	O
three	O
essential	O
elements	O
of	O
communication	O
,	O
the	O
media	B-Protocol
gateway	I-Protocol
controller	I-Protocol
(	O
call	O
agent	O
)	O
,	O
the	O
media	O
gateway	O
endpoint	O
,	O
and	O
connections	O
between	O
these	O
entities	O
.	O
</s>
<s>
Messages	O
are	O
transmitted	O
using	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
Media	O
gateways	O
use	O
the	O
port	B-Protocol
number	I-Protocol
2427	O
,	O
and	O
call	O
agents	O
use	O
2727	O
by	O
default	O
.	O
</s>
<s>
Another	O
implementation	O
of	O
the	O
media	B-Protocol
gateway	I-Protocol
control	I-Protocol
protocol	I-Protocol
architecture	O
is	O
the	O
H.248/Megaco	O
protocol	O
,	O
a	O
collaboration	O
of	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
RFC	O
3525	O
)	O
and	O
the	O
International	O
Telecommunication	O
Union	O
(	O
Recommendation	O
H.248.1	O
)	O
.	O
</s>
<s>
Both	O
protocols	O
follow	O
the	O
guidelines	O
of	O
the	O
overlying	O
media	B-Protocol
gateway	I-Protocol
control	I-Protocol
protocol	I-Protocol
architecture	O
,	O
as	O
described	O
in	O
RFC	O
2805	O
.	O
</s>
