<s>
In	O
intelligent	O
networks	O
(	O
IN	O
)	O
and	O
cellular	O
networks	O
,	O
service	B-Protocol
layer	I-Protocol
is	O
a	O
conceptual	O
layer	O
within	O
a	O
network	O
service	O
provider	O
architecture	O
.	O
</s>
<s>
It	O
aims	O
at	O
providing	O
middleware	B-General_Concept
that	O
serves	O
third-party	O
value-added	O
services	O
and	O
applications	O
at	O
a	O
higher	O
application	B-Application
layer	I-Application
.	O
</s>
<s>
The	O
service	B-Protocol
layer	I-Protocol
provides	O
capability	O
servers	O
owned	O
by	O
a	O
telecommunication	O
network	O
service	O
provider	O
,	O
accessed	O
through	O
open	O
and	O
secure	O
Application	B-Application
Programming	I-Application
Interfaces	I-Application
(	O
APIs	B-Application
)	O
by	O
application	B-Application
layer	I-Application
servers	O
owned	O
by	O
third-party	O
content	O
providers	O
.	O
</s>
<s>
The	O
service	B-Protocol
layer	I-Protocol
also	O
provides	O
an	O
interface	O
to	O
core	O
networks	O
at	O
a	O
lower	O
resource	O
layer	O
.	O
</s>
<s>
The	O
lower	O
layers	O
may	O
also	O
be	O
named	O
control	O
layer	O
and	O
transport	B-Architecture
layer	I-Architecture
(	O
the	O
transport	B-Architecture
layer	I-Architecture
is	O
also	O
referred	O
to	O
as	O
the	O
access	O
layer	O
in	O
some	O
architectures	O
)	O
.	O
</s>
<s>
The	O
concept	O
of	O
service	B-Protocol
layer	I-Protocol
is	O
used	O
in	O
contexts	O
such	O
as	O
Intelligent	O
networks	O
(	O
IN	O
)	O
,	O
WAP	B-Protocol
,	O
3G	B-Architecture
and	O
IP	B-Protocol
Multimedia	I-Protocol
Subsystem	I-Protocol
(	O
IMS	B-Protocol
)	O
.	O
</s>
<s>
It	O
is	O
defined	O
in	O
the	O
3GPP	O
Open	O
Services	O
Architecture	O
(	O
OSA	O
)	O
model	O
,	O
which	O
reused	O
the	O
idea	O
of	O
the	O
Parlay	O
API	B-Application
for	O
third-party	O
servers	O
.	O
</s>
<s>
In	O
software	O
design	O
,	O
for	O
example	O
Service-oriented	O
architecture	O
,	O
the	O
concept	O
of	O
service	B-Protocol
layer	I-Protocol
has	O
a	O
different	O
meaning	O
.	O
</s>
<s>
The	O
service	B-Protocol
layer	I-Protocol
of	O
an	O
IMS	B-Protocol
architecture	O
provides	O
multimedia	O
services	O
to	O
the	O
overall	O
IMS	B-Protocol
network	O
.	O
</s>
<s>
This	O
layer	O
contains	O
network	O
elements	O
which	O
connect	O
to	O
the	O
Serving-CSCF	O
(	O
Call	O
Session	O
Control	O
Function	O
)	O
using	O
the	O
IP	B-Protocol
multimedia	I-Protocol
Subsystem	I-Protocol
Service	O
Control	O
Interface	O
(	O
ISC	O
)	O
.	O
</s>
<s>
The	O
ISC	O
interface	O
uses	O
the	O
SIP	B-Application
signalling	O
protocol	O
.	O
</s>
<s>
The	O
network	O
elements	O
contained	O
within	O
the	O
service	B-Protocol
layer	I-Protocol
are	O
generically	O
referred	O
to	O
as	O
'	O
service	O
platforms	O
 '	O
however	O
the	O
3GPP	O
specification	O
(	O
3GPP	O
TS	O
23.228	O
V8.7.0	O
)	O
defines	O
several	O
types	O
of	O
service	O
platforms	O
:	O
</s>
<s>
The	O
SIP	B-Protocol
Application	I-Protocol
Server	I-Protocol
(	O
AS	O
)	O
performs	O
the	O
same	O
function	O
as	O
a	O
Telephony	O
Application	O
Server	O
in	O
a	O
pre-IMS	O
network	O
,	O
however	O
it	O
is	O
specifically	O
tailored	O
to	O
support	O
the	O
SIP	B-Application
signalling	O
protocol	O
for	O
use	O
in	O
an	O
IMS	B-Protocol
network	O
.	O
</s>
<s>
The	O
IM-SSF	O
(	O
IP	O
Multimedia	O
Service	O
Switching	O
Function	O
)	O
acts	O
as	O
a	O
gateway	O
between	O
the	O
IMS	B-Protocol
network	O
and	O
application	O
servers	O
using	O
other	O
telecommunication	O
signalling	O
standards	O
such	O
as	O
INAP	B-Protocol
and	O
CAMEL	O
.	O
</s>
<s>
In	O
service-oriented	O
architecture	O
(	O
SOA	O
)	O
,	O
the	O
service	B-Protocol
layer	I-Protocol
is	O
the	O
third	O
layer	O
in	O
a	O
five-abstraction-layer	O
model	O
.	O
</s>
<s>
The	O
model	O
consists	O
of	O
Object	O
layer	O
,	O
Component	O
layer	O
,	O
Service	B-Protocol
layer	I-Protocol
,	O
Process	O
layer	O
and	O
Enterprise	O
layer	O
.	O
</s>
<s>
The	O
service	B-Protocol
layer	I-Protocol
can	O
be	O
considered	O
as	O
a	O
bridge	O
between	O
the	O
higher	O
and	O
lower	O
layers	O
,	O
and	O
is	O
characterized	O
by	O
a	O
number	O
of	O
services	O
that	O
are	O
carrying	O
out	O
individual	O
business	O
functions	O
.	O
</s>
