<s>
Packets	B-Protocol
that	O
hold	O
Internet	B-Protocol
Protocol	I-Protocol
data	O
carry	O
a	O
4-bit	O
IP	O
version	O
number	O
as	O
the	O
first	O
field	O
of	O
its	O
header	B-General_Concept
.	O
</s>
<s>
Currently	O
,	O
only	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
packets	I-Protocol
are	O
seen	O
on	O
the	O
Internet	O
,	O
having	O
IP	O
version	O
numbers	O
4	O
and	O
6	O
,	O
respectively	O
.	O
</s>
<s>
IP	O
versionDescriptionStatus0Internet	O
Protocol	O
,	O
pre-v4Reserved.1-3Unassigned.4Internet	O
Protocol	O
version	O
4	O
(	O
IPv4	B-Protocol
)	O
Active.5Internet	O
Stream	O
Protocol	O
or	O
STObsolete	O
;	O
superseded	O
by	O
ST-II.5Internet	O
Stream	O
Protocol	O
or	O
ST-IIObsolete.6Simple	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
SIP	O
)	O
Obsolete	O
;	O
merged	O
into	O
IPv6	B-Protocol
in	O
1995.6Internet	O
Protocol	O
version	O
6	O
(	O
IPv6	B-Protocol
)	O
Active.7TP/IX	O
The	O
Next	O
Internet	O
(	O
IPv7	O
)	O
Obsolete.8P	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
PIP	O
)	O
Obsolete	O
;	O
merged	O
into	O
SIP	O
in	O
1993.9TCP	O
and	O
UDP	O
over	O
Bigger	O
Addresses	O
(	O
TUBA	O
)	O
Obsolete.9IPv9April	O
fools	O
 '	O
day	O
joke.9Chinese	O
IPv9Abandoned.10-14Unassigned.15Version	O
field	O
sentinel	O
valueReserved	O
.	O
</s>
<s>
During	O
the	O
development	O
of	O
the	O
first	O
version	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
in	O
the	O
1970s	O
,	O
the	O
initial	O
experimental	O
versions	O
1	O
to	O
3	O
were	O
not	O
standardized	O
.	O
</s>
<s>
However	O
,	O
ST-II	O
had	O
reused	O
version	O
5	O
of	O
the	O
original	O
ST	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
when	O
it	O
became	O
apparent	O
that	O
IPv4	B-Protocol
could	O
not	O
sustain	O
routing	O
in	O
a	O
growing	O
Internet	O
,	O
several	O
new	O
Internet	B-Protocol
Protocols	I-Protocol
were	O
proposed	O
.	O
</s>
<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
that	O
finally	O
emerged	O
was	O
assigned	O
version	O
number	O
6	O
,	O
being	O
the	O
lowest	O
free	O
number	O
greater	O
than	O
4	O
.	O
</s>
