<s>
In	O
the	O
seven-layer	O
OSI	O
model	O
of	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
session	B-Application
layer	I-Application
is	O
layer	B-Application
5	I-Application
.	O
</s>
<s>
The	O
session	B-Application
layer	I-Application
provides	O
the	O
mechanism	O
for	O
opening	O
,	O
closing	O
and	O
managing	O
a	O
session	B-Protocol
between	O
end-user	O
application	O
processes	O
,	O
i.e.	O
,	O
a	O
semi-permanent	O
dialogue	O
.	O
</s>
<s>
Communication	B-Protocol
sessions	I-Protocol
consist	O
of	O
requests	O
and	O
responses	O
that	O
occur	O
between	O
applications	O
.	O
</s>
<s>
Session-layer	B-Application
services	O
are	O
commonly	O
used	O
in	O
application	O
environments	O
that	O
make	O
use	O
of	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
(	O
RPCs	O
)	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
session-layer	B-Application
protocol	O
is	O
the	O
OSI	O
protocol	O
suite	O
session-layer	B-Application
protocol	O
,	O
also	O
known	O
as	O
X.225	O
or	O
ISO	O
8327	O
.	O
</s>
<s>
If	O
a	O
connection	O
is	O
not	O
used	O
for	O
a	O
long	O
period	O
,	O
the	O
session-layer	B-Application
protocol	O
may	O
close	O
it	O
and	O
re-open	O
it	O
.	O
</s>
<s>
Other	O
examples	O
of	O
session	B-Application
layer	I-Application
implementations	O
include	O
Zone	O
Information	O
Protocol	O
(	O
ZIP	O
)	O
–	O
the	O
AppleTalk	B-Application
protocol	O
that	O
coordinates	O
the	O
name	O
binding	O
process	O
,	O
and	O
Session	B-Protocol
Control	O
Protocol	O
(	O
SCP	O
)	O
–	O
the	O
DECnet	B-Protocol
Phase	O
IV	O
session-layer	B-Application
protocol	O
.	O
</s>
<s>
Within	O
the	O
service	O
layering	O
semantics	O
of	O
the	O
OSI	O
network	O
architecture	O
,	O
the	O
session	B-Application
layer	I-Application
responds	O
to	O
service	O
requests	O
from	O
the	O
presentation	B-Application
layer	I-Application
and	O
issues	O
service	O
requests	O
to	O
the	O
transport	B-Architecture
layer	I-Architecture
.	O
</s>
<s>
The	O
session	B-Application
layer	I-Application
of	O
the	O
OSI	O
model	O
is	O
responsible	O
for	O
session	B-Protocol
checkpointing	B-General_Concept
and	O
recovery	O
.	O
</s>
<s>
An	O
example	O
usage	O
of	O
the	O
session	B-Application
layer	I-Application
is	O
session	B-Protocol
beans	O
,	O
which	O
are	O
only	O
active	O
as	O
long	O
as	O
the	O
session	B-Protocol
is	O
active	O
,	O
and	O
are	O
deleted	O
when	O
the	O
session	B-Protocol
is	O
disconnected	O
.	O
</s>
<s>
Java	O
developers	O
can	O
use	O
them	O
to	O
store	O
information	O
about	O
the	O
user	O
during	O
a	O
web	O
session	B-Protocol
.	O
</s>
<s>
An	O
example	O
application	O
is	O
web	B-Protocol
conferencing	I-Protocol
,	O
in	O
which	O
the	O
streams	O
of	O
audio	O
and	O
video	O
must	O
be	O
synchronous	O
to	O
avoid	O
so-called	O
lip	O
sync	O
problems	O
.	O
</s>
<s>
The	O
TCP/IP	B-Protocol
reference	I-Protocol
model	I-Protocol
does	O
not	O
concern	O
itself	O
with	O
the	O
OSI	O
model	O
's	O
details	O
of	O
application	O
or	O
transport	B-Architecture
protocol	I-Architecture
semantics	O
and	O
therefore	O
does	O
not	O
consider	O
a	O
session	B-Application
layer	I-Application
.	O
</s>
<s>
OSI	O
's	O
session	B-Protocol
management	I-Protocol
in	O
connection	O
with	O
the	O
typical	O
transport	B-Architecture
protocols	I-Architecture
(	O
TCP	O
,	O
SCTP	O
)	O
,	O
is	O
contained	O
in	O
the	O
transport-layer	B-Architecture
protocols	I-Architecture
,	O
or	O
otherwise	O
considered	O
the	O
realm	O
of	O
the	O
application	B-Application
layer	I-Application
protocols	O
.	O
</s>
<s>
TCP/IP	B-Protocol
'	O
s	O
layers	O
are	O
descriptions	O
of	O
operating	O
scopes	O
(	O
application	O
,	O
host-to-host	O
,	O
network	O
,	O
link	O
)	O
and	O
not	O
detailed	O
prescriptions	O
of	O
operating	O
procedures	O
or	O
data	O
semantics	O
.	O
</s>
