<s>
Within	O
communication	O
protocols	O
,	O
TLV	O
(	O
type-length-value	B-Protocol
or	O
tag-length-value	B-Protocol
)	O
is	O
an	O
encoding	O
scheme	O
used	O
for	O
optional	O
informational	O
elements	O
in	O
a	O
certain	O
protocol	O
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
way	O
that	O
unknown	O
XML	B-Protocol
tags	O
can	O
be	O
safely	O
skipped	O
;	O
</s>
<s>
Core	O
TCP/IP	B-Protocol
protocols	I-Protocol
(	O
particularly	O
IP	B-Protocol
,	O
TCP	B-Protocol
,	O
and	O
UDP	B-Protocol
)	O
use	O
predefined	O
,	O
static	O
fields	O
.	O
</s>
<s>
Some	O
application	B-Application
layer	I-Application
protocols	O
,	O
including	O
HTTP/1.1	B-Protocol
(	O
and	O
its	O
non-standardized	O
predecessors	O
)	O
,	O
FTP	B-Protocol
,	O
SMTP	B-Protocol
,	O
POP3	B-Protocol
,	O
and	O
SIP	B-Application
,	O
use	O
text-based	O
"	O
Field	O
:	O
Value	O
"	O
pairs	O
formatted	O
according	O
to	O
.	O
</s>
<s>
(	O
HTTP	B-Protocol
represents	O
length	O
of	O
payload	O
with	O
a	O
Content-Length	O
header	O
and	O
separates	O
headers	O
from	O
the	O
payload	O
with	O
an	O
empty	O
line	O
and	O
headers	O
from	O
each	O
other	O
with	O
a	O
new	O
line	O
.	O
)	O
</s>
<s>
ASN.1	B-Protocol
specifies	O
several	O
TLV-based	O
encoding	O
rules	O
(	O
BER	O
,	O
DER	O
)	O
,	O
as	O
well	O
as	O
non-TLV	O
based	O
ones	O
(	O
PER	O
,	O
XER	B-Protocol
)	O
.	O
</s>
<s>
More	O
recently	O
,	O
XML	B-Protocol
has	O
been	O
used	O
to	O
implement	O
messaging	O
between	O
different	O
nodes	O
in	O
a	O
network	O
.	O
</s>
<s>
These	O
messages	O
are	O
typically	O
prefixed	O
with	O
line-based	O
text	O
commands	O
,	O
such	O
as	O
with	O
BEEP	B-Protocol
.	O
</s>
