<s>
UDP-Lite	B-Protocol
(	O
Lightweight	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
)	O
is	O
a	O
connectionless	B-Protocol
protocol	I-Protocol
that	O
allows	O
a	O
potentially	O
damaged	O
data	O
payload	O
to	O
be	O
delivered	O
to	O
an	O
application	B-Application
rather	O
than	O
being	O
discarded	O
by	O
the	O
receiving	O
station	O
.	O
</s>
<s>
This	O
is	O
useful	O
as	O
it	O
allows	O
decisions	O
about	O
the	O
integrity	O
of	O
the	O
data	O
to	O
be	O
made	O
in	O
the	O
application	B-Application
layer	I-Application
(	O
application	B-Application
or	O
the	O
codec	B-General_Concept
)	O
,	O
where	O
the	O
significance	O
of	O
the	O
bits	O
is	O
understood	O
.	O
</s>
<s>
UDP-Lite	B-Protocol
is	O
described	O
in	O
.	O
</s>
<s>
UDP-Lite	B-Protocol
is	O
based	O
on	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
,	O
but	O
unlike	O
UDP	O
,	O
where	O
either	O
all	O
or	O
none	O
of	O
a	O
packet	O
is	O
protected	O
by	O
a	O
checksum	O
,	O
UDP-Lite	B-Protocol
allows	O
for	O
partial	O
checksums	O
that	O
only	O
covers	O
part	O
of	O
a	O
datagram	O
(	O
an	O
arbitrary	O
count	O
of	O
octets	O
at	O
the	O
beginning	O
of	O
the	O
packet	O
)	O
,	O
and	O
will	O
therefore	O
deliver	O
packets	O
that	O
have	O
been	O
partially	O
corrupted	O
.	O
</s>
<s>
It	O
is	O
designed	O
for	O
multimedia	O
protocols	O
,	O
such	O
as	O
Voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
or	O
streamed	O
video	O
,	O
in	O
which	O
receiving	O
a	O
packet	O
with	O
a	O
damaged	O
payload	O
is	O
better	O
than	O
receiving	O
no	O
packet	O
at	O
all	O
.	O
</s>
<s>
For	O
conventional	O
UDP	O
and	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
,	O
a	O
single	O
bit	O
in	O
error	O
will	O
cause	O
a	O
"	O
bad	O
"	O
checksum	O
,	O
meaning	O
that	O
the	O
whole	O
packet	O
must	O
be	O
discarded	O
:	O
in	O
this	O
way	O
,	O
bit	O
errors	O
are	O
"	O
promoted	O
"	O
to	O
entire	O
packet	O
errors	O
even	O
where	O
the	O
damage	O
to	O
the	O
data	O
is	O
trivial	O
.	O
</s>
<s>
For	O
computing	O
the	O
checksum	O
UDP-Lite	B-Protocol
uses	O
the	O
same	O
checksum	O
algorithm	O
used	O
for	O
UDP	O
(	O
and	O
TCP	O
)	O
.	O
</s>
<s>
Modern	O
multimedia	B-General_Concept
codecs	I-General_Concept
,	O
like	O
G.718	B-Algorithm
and	O
Adaptive	B-Algorithm
Multi-Rate	I-Algorithm
(	O
AMR	O
)	O
for	O
audio	O
and	O
H.264	B-Application
and	O
MPEG-4	B-Algorithm
for	O
video	O
,	O
have	O
resilience	O
features	O
already	O
built	O
into	O
the	O
syntax	O
and	O
structure	O
of	O
the	O
stream	O
.	O
</s>
<s>
This	O
allows	O
the	O
codec	B-General_Concept
to	O
(	O
a	O
)	O
detect	O
errors	O
in	O
the	O
stream	O
and	O
(	O
b	O
)	O
potentially	O
correct	O
,	O
or	O
at	O
least	O
conceal	O
,	O
the	O
error	O
during	O
playback	O
.	O
</s>
<s>
These	O
codecs	B-General_Concept
are	O
ideal	O
partners	O
for	O
UDP-Lite	B-Protocol
,	O
since	O
they	O
are	O
designed	O
to	O
work	O
with	O
a	O
damaged	O
data	O
stream	O
,	O
and	O
it	O
is	O
better	O
for	O
these	O
codecs	B-General_Concept
to	O
receive	O
perhaps	O
200	O
bytes	O
where	O
a	O
few	O
bits	O
are	O
damaged	O
rather	O
than	O
have	O
to	O
conceal	O
the	O
loss	O
of	O
an	O
entire	O
packet	O
that	O
was	O
discarded	O
due	O
to	O
a	O
bad	O
checksum	O
.	O
</s>
<s>
The	O
application	B-Application
layer	I-Application
understands	O
the	O
significance	O
of	O
the	O
data	O
,	O
where	O
the	O
transport	O
only	O
sees	O
UDP	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
This	O
means	O
that	O
error	O
protection	O
can	O
be	O
added	O
if	O
necessary	O
at	O
a	O
higher	O
layer	O
,	O
for	O
example	O
with	O
a	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
scheme	O
.	O
</s>
<s>
The	O
application	B-Application
is	O
the	O
best	O
place	O
to	O
decide	O
which	O
parts	O
of	O
the	O
stream	O
are	O
most	O
sensitive	O
to	O
error	O
and	O
protect	O
them	O
accordingly	O
,	O
rather	O
than	O
have	O
a	O
single	O
"	O
brute	O
force	O
"	O
checksum	O
that	O
covers	O
everything	O
equally	O
.	O
</s>
<s>
where	O
UDP-Lite	B-Protocol
is	O
coupled	O
with	O
the	O
AMR	O
codec	B-General_Concept
to	O
give	O
improved	O
speech	O
quality	O
in	O
lossy	O
network	O
conditions	O
.	O
</s>
<s>
Since	O
most	O
modern	O
link	O
layers	O
protect	O
the	O
carried	O
data	O
with	O
a	O
strong	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
and	O
will	O
discard	O
damaged	O
frames	O
,	O
making	O
effective	O
use	O
of	O
UDP	B-Protocol
Lite	I-Protocol
requires	O
the	O
link	O
layer	O
to	O
be	O
aware	O
of	O
the	O
network	O
layer	O
data	O
being	O
carried	O
.	O
</s>
<s>
Since	O
no	O
current	O
IP	O
stacks	O
implement	O
such	O
cross-layer	O
interactions	O
,	O
making	O
effective	O
use	O
of	O
UDP-Lite	B-Protocol
currently	O
requires	O
specially	O
modified	O
device	O
drivers	O
.	O
</s>
<s>
UDP-Lite	B-Protocol
uses	O
the	O
same	O
set	O
of	O
port	O
numbers	O
assigned	O
by	O
the	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
for	O
use	O
by	O
UDP	O
.	O
</s>
<s>
Support	O
for	O
UDP-Lite	B-Protocol
was	O
added	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
version	O
2.6.20	O
.	O
</s>
<s>
Support	O
for	O
UDP-Lite	B-Protocol
was	O
added	O
in	O
the	O
FreeBSD	B-Operating_System
kernel	B-Operating_System
from	O
r264212	O
.	O
</s>
<s>
The	O
changeset	O
was	O
also	O
MFC'ed	O
back	O
to	O
stable/10	O
and	O
became	O
available	O
in	O
FreeBSD	B-Operating_System
10.1-RELEASE	O
.	O
</s>
<s>
The	O
BSD	O
socket	O
API	O
is	O
extended	O
to	O
support	O
UDP-Lite	B-Protocol
by	O
the	O
third	O
parameter	O
of	O
the	O
system	O
call	O
:	O
Set	O
it	O
to	O
to	O
request	O
a	O
UDP-Lite	B-Protocol
socket	O
:	O
</s>
<s>
If	O
a	O
packet	O
has	O
a	O
coverage	O
length	O
of	O
at	O
least	O
20	O
octets	O
(	O
including	O
header	O
)	O
and	O
its	O
checksum	O
is	O
correct	O
,	O
it	O
will	O
be	O
delivered	O
to	O
application	B-Application
(	O
whole	O
or	O
part	O
of	O
the	O
payload	O
can	O
still	O
be	O
corrupted	O
,	O
because	O
it	O
could	O
be	O
not	O
covered	O
by	O
checksum	O
or	O
because	O
the	O
checksum	O
was	O
correct	O
incidentally	O
,	O
but	O
the	O
latter	O
is	O
very	O
unlikely	O
.	O
)	O
</s>
<s>
If	O
the	O
checksum	O
is	O
incorrect	O
the	O
packet	O
will	O
be	O
dropped	O
,	O
because	O
it	O
is	O
actually	O
impossible	O
to	O
know	O
if	O
the	O
error	O
was	O
inside	O
the	O
payload	O
data	O
or	O
in	O
the	O
UDP-Lite	B-Protocol
header	O
,	O
so	O
the	O
packet	O
could	O
actually	O
be	O
destined	O
for	O
a	O
different	O
program	O
.	O
</s>
<s>
UDP-Lite	B-Protocol
is	O
supported	O
by	O
the	O
following	O
operating	O
systems	O
:	O
</s>
