<s>
Connectionless	B-Protocol
communication	I-Protocol
,	O
often	O
referred	O
to	O
as	O
CL-mode	O
communication	O
,	O
is	O
a	O
data	O
transmission	O
method	O
used	O
in	O
packet	B-Protocol
switching	I-Protocol
networks	O
in	O
which	O
each	O
data	O
unit	O
is	O
individually	O
addressed	O
and	O
routed	O
based	O
on	O
information	O
carried	O
in	O
each	O
unit	O
,	O
rather	O
than	O
in	O
the	O
setup	O
information	O
of	O
a	O
prearranged	O
,	O
fixed	O
data	O
channel	O
as	O
in	O
connection-oriented	B-Protocol
communication	I-Protocol
.	O
</s>
<s>
Under	O
connectionless	B-Protocol
communication	I-Protocol
between	O
two	O
network	O
end	O
points	O
,	O
a	O
message	O
can	O
be	O
sent	O
from	O
one	O
end	O
point	O
to	O
another	O
without	O
prior	O
arrangement	O
.	O
</s>
<s>
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	B-Protocol
)	O
and	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	B-Protocol
)	O
are	O
connectionless	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
A	O
packet	O
transmitted	O
in	O
a	O
connectionless	B-Protocol
mode	O
is	O
frequently	O
called	O
a	O
datagram	B-Protocol
.	O
</s>
<s>
Connectionless	B-Protocol
protocols	I-Protocol
are	O
usually	O
described	O
as	O
stateless	B-Protocol
protocols	I-Protocol
because	O
the	O
end	O
points	O
have	O
no	O
protocol-defined	O
way	O
to	O
remember	O
where	O
they	O
are	O
in	O
a	O
"	O
conversation	O
"	O
of	O
message	O
exchanges	O
.	O
</s>
<s>
Connectionless	B-Protocol
communication	I-Protocol
has	O
lower	O
overhead	O
than	O
connection-oriented	B-Protocol
communication	I-Protocol
because	O
in	O
connection-oriented	B-Protocol
communication	I-Protocol
the	O
communicating	O
peers	O
must	O
first	O
establish	O
a	O
logical	O
or	O
physical	O
data	O
channel	O
or	O
connection	O
in	O
a	O
dialog	O
preceding	O
the	O
exchange	O
of	O
user	O
data	O
.	O
</s>
<s>
Connectionless	B-Protocol
communication	I-Protocol
allows	O
for	O
multicast	O
and	O
broadcast	B-Operating_System
operations	O
in	O
which	O
the	O
same	O
data	O
are	O
transmitted	O
to	O
several	O
recipients	O
in	O
a	O
single	O
transmission	O
.	O
</s>
<s>
In	O
connectionless	B-Protocol
transmissions	O
the	O
service	O
provider	O
usually	O
cannot	O
guarantee	O
that	O
there	O
will	O
be	O
no	O
loss	O
,	O
error	O
insertion	O
,	O
misdelivery	O
,	O
duplication	O
,	O
or	O
out-of-sequence	O
delivery	O
of	O
the	O
packet	O
.	O
</s>
<s>
In	O
connectionless	B-Protocol
mode	O
there	O
is	O
less	O
opportunity	O
for	O
optimization	O
possible	O
when	O
sending	O
several	O
data	O
units	O
between	O
the	O
same	O
two	O
peers	O
.	O
</s>
<s>
By	O
establishing	O
a	O
connection	O
at	O
the	O
beginning	O
of	O
such	O
a	O
data	O
exchange	O
the	O
components	O
(	O
routers	B-Protocol
,	O
bridges	B-Protocol
)	O
along	O
the	O
network	O
path	O
would	O
be	O
able	O
to	O
pre-compute	O
(	O
and	O
hence	O
cache	B-General_Concept
)	O
routing-related	O
information	O
,	O
avoiding	O
re-computation	O
for	O
every	O
packet	O
.	O
</s>
<s>
In	O
connection-oriented	B-Protocol
communication	I-Protocol
,	O
network	O
components	O
can	O
also	O
reserve	O
capacity	O
for	O
the	O
transfer	O
of	O
the	O
subsequent	O
data	O
units	O
of	O
a	O
video	O
download	O
,	O
for	O
example	O
.	O
</s>
<s>
Distinction	O
between	O
connectionless	B-Protocol
and	O
connection-oriented	B-Protocol
transmission	O
may	O
take	O
place	O
at	O
several	O
layers	O
of	O
the	O
OSI	O
Reference	O
Model	O
:	O
</s>
<s>
Transport	B-Architecture
layer	I-Architecture
:	O
TCP	B-Protocol
is	O
a	O
connection-oriented	B-Protocol
transport	B-Architecture
protocol	I-Architecture
.	O
</s>
<s>
UDP	B-Protocol
is	O
connectionless	B-Protocol
.	O
</s>
<s>
Network	B-Application
layer	I-Application
.	O
</s>
<s>
Data	B-Protocol
link	I-Protocol
layer	I-Protocol
:	O
The	O
IEEE	O
802.2	O
protocol	O
at	O
the	O
Logical	O
Link	O
Control	O
sublayer	O
of	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
may	O
provide	O
both	O
connectionless	B-Protocol
and	O
connection-oriented	B-Protocol
services	I-Protocol
.	O
</s>
<s>
In	O
fact	O
,	O
some	O
network	O
protocols	O
(	O
such	O
as	O
SNA	B-Architecture
's	O
Path	O
Control	O
in	O
its	O
early	O
stages	O
)	O
require	O
a	O
connection-oriented	B-Protocol
data	B-Protocol
link	I-Protocol
layer	I-Protocol
.	O
</s>
<s>
Others	O
(	O
like	O
IP	B-Protocol
)	O
do	O
not	O
.	O
</s>
<s>
(	O
After	O
the	O
appearance	O
of	O
APPN	B-Architecture
,	O
SNA	B-Architecture
could	O
operate	O
on	O
a	O
connectionless	B-Protocol
data	O
link	O
service	O
as	O
well	O
.	O
)	O
</s>
<s>
Notable	O
connectionless	B-Protocol
protocols	I-Protocol
are	O
:	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	B-Protocol
)	O
,	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	B-Protocol
)	O
,	O
Internet	B-Protocol
Control	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
(	O
ICMP	O
)	O
,	O
Internetwork	B-Protocol
Packet	I-Protocol
Exchange	I-Protocol
(	O
IPX	B-Protocol
)	O
,	O
Transparent	B-Operating_System
Inter-process	I-Operating_System
Communication	I-Operating_System
,	O
NetBIOS	B-Protocol
,	O
and	O
Fast	B-Protocol
and	I-Protocol
Secure	I-Protocol
Protocol	I-Protocol
(	O
FASP	B-Protocol
)	O
.	O
</s>
