<s>
Connectionless-mode	B-Protocol
Network	I-Protocol
Service	I-Protocol
(	O
CLNS	B-Protocol
)	O
or	O
simply	O
Connectionless	B-Protocol
Network	I-Protocol
Service	I-Protocol
is	O
an	O
OSI	O
network	O
layer	O
datagram	B-Protocol
service	I-Protocol
that	O
does	O
not	O
require	O
a	O
circuit	O
to	O
be	O
established	O
before	O
data	O
is	O
transmitted	O
,	O
and	O
routes	O
messages	O
to	O
their	O
destinations	B-Protocol
independently	O
of	O
any	O
other	O
messages	O
.	O
</s>
<s>
As	O
such	O
it	O
is	O
a	O
"	O
best-effort	O
"	O
rather	O
than	O
a	O
"	O
reliable	B-Protocol
"	O
delivery	O
service	O
.	O
</s>
<s>
CLNS	B-Protocol
is	O
not	O
an	O
Internet	O
service	O
,	O
but	O
provides	O
capabilities	O
in	O
an	O
OSI	O
network	O
environment	O
similar	O
to	O
those	O
provided	O
by	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
Connectionless-mode	O
Network	O
Protocol	O
(	O
CLNP	B-Protocol
)	O
is	O
an	O
OSI	O
protocol	O
deployment	O
.	O
</s>
<s>
CLNS	B-Protocol
is	O
the	O
service	O
provided	O
by	O
the	O
Connectionless-mode	O
Network	O
Protocol	O
(	O
CLNP	B-Protocol
)	O
.	O
</s>
<s>
CLNP	B-Protocol
is	O
widely	O
used	O
in	O
many	O
telecommunications	O
networks	O
around	O
the	O
world	O
because	O
IS-IS	B-Protocol
(	O
an	O
OSI	O
routing	O
protocol	O
)	O
is	O
mandated	O
by	O
the	O
ITU-T	O
as	O
the	O
protocol	O
for	O
management	O
of	O
Synchronous	B-Protocol
Digital	I-Protocol
Hierarchy	I-Protocol
(	O
SDH	O
)	O
elements	O
.	O
</s>
<s>
From	O
August	O
1990	O
to	O
April	O
1995	O
the	O
NSFNET	O
backbone	O
supported	O
CLNP	B-Protocol
in	O
addition	O
to	O
TCP/IP	B-Protocol
.	O
</s>
<s>
However	O
,	O
CLNP	B-Protocol
usage	O
remained	O
low	O
compared	O
to	O
TCP/IP	B-Protocol
.	O
</s>
<s>
CLNS	B-Protocol
is	O
used	O
by	O
ISO	O
Transport	B-Architecture
Protocol	I-Architecture
Class	O
4	O
(	O
TP4	O
)	O
,	O
one	O
of	O
the	O
five	O
transport	B-Architecture
layer	I-Architecture
protocols	O
in	O
the	O
OSI	O
suite	O
.	O
</s>
<s>
TP4	O
provides	O
reliable	B-Protocol
transport	O
service	O
and	O
functions	O
with	O
either	O
connection-oriented	O
or	O
connectionless	B-Protocol
network	I-Protocol
service	I-Protocol
.	O
</s>
<s>
TP4	O
is	O
the	O
most	O
commonly	O
used	O
of	O
all	O
the	O
OSI	O
transport	B-Architecture
protocols	I-Architecture
and	O
is	O
similar	O
to	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
in	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
Several	O
protocols	O
provide	O
the	O
CLNS	B-Protocol
service	O
:	O
</s>
<s>
Connectionless-mode	O
Network	O
Protocol	O
(	O
CLNP	B-Protocol
)	O
,	O
as	O
specified	O
in	O
ITU-T	O
Recommendation	O
X.233	O
.	O
</s>
<s>
End	O
System-to-Intermediate	O
System	O
(	O
ES-IS	O
)	O
,	O
a	O
routing	O
exchange	O
protocol	O
for	O
use	O
in	O
conjunction	O
with	O
the	O
protocol	O
for	O
providing	O
the	O
CLNS	B-Protocol
(	O
ISO	O
9542	O
)	O
.	O
</s>
<s>
Intermediate	B-Protocol
System-to-Intermediate	I-Protocol
System	I-Protocol
(	O
IS-IS	B-Protocol
)	O
,	O
an	O
intradomain	O
routing	O
exchange	O
protocol	O
used	O
in	O
both	O
the	O
OSI	O
and	O
Internet	O
environments	O
(	O
ISO/IEC	O
10589	O
and	O
RFC	O
1142	O
)	O
.	O
</s>
