<s>
In	O
telecommunications	O
,	O
packet	B-Protocol
switching	I-Protocol
is	O
a	O
method	O
of	O
grouping	O
data	B-General_Concept
into	O
packets	B-Protocol
that	O
are	O
transmitted	O
over	O
a	O
digital	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Packets	B-Protocol
are	O
made	O
of	O
a	O
header	B-General_Concept
and	O
a	O
payload	O
.	O
</s>
<s>
Data	B-General_Concept
in	O
the	O
header	B-General_Concept
is	O
used	O
by	O
networking	B-Device
hardware	I-Device
to	O
direct	O
the	O
packet	B-Protocol
to	O
its	O
destination	O
,	O
where	O
the	O
payload	O
is	O
extracted	O
and	O
used	O
by	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
application	B-Application
software	I-Application
,	O
or	O
higher	B-Protocol
layer	I-Protocol
protocols	I-Protocol
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
is	O
the	O
primary	O
basis	O
for	O
data	B-General_Concept
communications	O
in	O
computer	B-Architecture
networks	I-Architecture
worldwide	O
.	O
</s>
<s>
During	O
the	O
early	O
1960s	O
,	O
Polish-American	O
engineer	O
Paul	O
Baran	O
developed	O
a	O
concept	O
he	O
called	O
"	O
distributed	O
adaptive	O
message	O
block	O
switching	O
"	O
,	O
with	O
the	O
goal	O
of	O
providing	O
a	O
fault-tolerant	B-General_Concept
,	O
efficient	O
routing	B-Protocol
method	O
for	O
telecommunication	O
messages	O
as	O
part	O
of	O
a	O
research	O
program	O
at	O
the	O
RAND	O
Corporation	O
,	O
funded	O
by	O
the	O
United	O
States	O
Department	O
of	O
Defense	O
.	O
</s>
<s>
His	O
ideas	O
contradicted	O
then-established	O
principles	O
of	O
pre-allocation	O
of	O
network	O
bandwidth	O
,	O
exemplified	O
by	O
the	O
development	O
of	O
telecommunications	O
in	O
the	O
Bell	O
System	O
.	O
</s>
<s>
Davies	O
is	O
credited	O
with	O
coining	O
the	O
modern	O
term	O
packet	B-Protocol
switching	I-Protocol
and	O
inspiring	O
numerous	O
packet	B-Protocol
switching	I-Protocol
networks	O
in	O
the	O
decade	O
following	O
,	O
including	O
the	O
incorporation	O
of	O
the	O
concept	O
into	O
the	O
design	O
of	O
the	O
ARPANET	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
A	O
simple	O
definition	O
of	O
packet	B-Protocol
switching	I-Protocol
is	O
:	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
allows	O
delivery	O
of	O
variable	B-General_Concept
bit	I-General_Concept
rate	I-General_Concept
data	B-General_Concept
streams	O
,	O
realized	O
as	O
sequences	O
of	O
packets	B-Protocol
,	O
over	O
a	O
computer	B-Architecture
network	I-Architecture
which	O
allocates	O
transmission	O
resources	O
as	O
needed	O
using	O
statistical	B-Algorithm
multiplexing	I-Algorithm
or	O
dynamic	B-Protocol
bandwidth	I-Protocol
allocation	I-Protocol
techniques	O
.	O
</s>
<s>
As	O
they	O
traverse	O
networking	B-Device
hardware	I-Device
,	O
such	O
as	O
switches	O
and	O
routers	B-Protocol
,	O
packets	B-Protocol
are	O
received	O
,	O
buffered	O
,	O
queued	O
,	O
and	O
retransmitted	O
(	O
stored	B-Protocol
and	I-Protocol
forwarded	I-Protocol
)	O
,	O
resulting	O
in	O
variable	O
latency	B-Protocol
and	O
throughput	O
depending	O
on	O
the	O
link	O
capacity	O
and	O
the	O
traffic	O
load	O
on	O
the	O
network	O
.	O
</s>
<s>
Packets	B-Protocol
are	O
normally	O
forwarded	O
by	O
intermediate	O
network	O
nodes	O
asynchronously	O
using	O
first-in	B-Operating_System
,	I-Operating_System
first-out	I-Operating_System
buffering	O
,	O
but	O
may	O
be	O
forwarded	O
according	O
to	O
some	O
scheduling	O
discipline	O
for	O
fair	B-Algorithm
queuing	I-Algorithm
,	O
traffic	O
shaping	O
,	O
or	O
for	O
differentiated	O
or	O
guaranteed	O
quality	O
of	O
service	O
,	O
such	O
as	O
weighted	B-Algorithm
fair	I-Algorithm
queuing	I-Algorithm
or	O
leaky	B-Algorithm
bucket	I-Algorithm
.	O
</s>
<s>
Packet-based	O
communication	O
may	O
be	O
implemented	O
with	O
or	O
without	O
intermediate	O
forwarding	O
nodes	O
(	O
switches	O
and	O
routers	B-Protocol
)	O
.	O
</s>
<s>
In	O
case	O
of	O
a	O
shared	O
physical	O
medium	O
(	O
such	O
as	O
radio	O
or	O
10BASE5	O
)	O
,	O
the	O
packets	B-Protocol
may	O
be	O
delivered	O
according	O
to	O
a	O
multiple	O
access	O
scheme	O
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
contrasts	O
with	O
another	O
principal	O
networking	O
paradigm	O
,	O
circuit	B-Protocol
switching	I-Protocol
,	O
a	O
method	O
which	O
pre-allocates	O
dedicated	O
network	O
bandwidth	O
specifically	O
for	O
each	O
communication	O
session	O
,	O
each	O
having	O
a	O
constant	O
bit	O
rate	O
and	O
latency	B-Protocol
between	O
nodes	O
.	O
</s>
<s>
In	O
cases	O
of	O
billable	O
services	O
,	O
such	O
as	O
cellular	O
communication	O
services	O
,	O
circuit	B-Protocol
switching	I-Protocol
is	O
characterized	O
by	O
a	O
fee	O
per	O
unit	O
of	O
connection	O
time	O
,	O
even	O
when	O
no	O
data	B-General_Concept
is	O
transferred	O
,	O
while	O
packet	B-Protocol
switching	I-Protocol
may	O
be	O
characterized	O
by	O
a	O
fee	O
per	O
unit	O
of	O
information	O
transmitted	O
,	O
such	O
as	O
characters	O
,	O
packets	B-Protocol
,	O
or	O
messages	O
.	O
</s>
<s>
A	O
packet	B-Protocol
switch	I-Protocol
has	O
four	O
components	O
:	O
input	O
ports	O
,	O
output	O
ports	O
,	O
routing	B-Protocol
processor	O
,	O
and	O
switching	O
fabric	O
.	O
</s>
<s>
The	O
concept	O
of	O
switching	O
small	O
blocks	O
of	O
data	B-General_Concept
was	O
first	O
explored	O
independently	O
by	O
Paul	O
Baran	O
at	O
the	O
RAND	O
Corporation	O
during	O
the	O
early	O
1960s	O
in	O
the	O
US	O
and	O
Donald	O
Davies	O
at	O
the	O
National	O
Physical	O
Laboratory	O
(	O
NPL	O
)	O
in	O
the	O
UK	O
in	O
1965	O
.	O
</s>
<s>
During	O
the	O
late	O
1950s	O
,	O
the	O
US	O
Air	O
Force	O
established	O
a	O
wide	O
area	O
network	O
for	O
the	O
Semi-Automatic	B-Device
Ground	I-Device
Environment	I-Device
(	O
SAGE	O
)	O
radar	O
defense	O
system	O
.	O
</s>
<s>
The	O
work	O
focuses	O
on	O
three	O
key	O
ideas	O
:	O
use	O
of	O
a	O
decentralized	O
network	O
with	O
multiple	O
paths	O
between	O
any	O
two	O
points	O
,	O
dividing	O
user	O
messages	O
into	O
message	O
blocks	O
,	O
and	O
delivery	O
of	O
these	O
messages	O
by	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
switching	O
.	O
</s>
<s>
Davies	O
independently	O
developed	O
a	O
similar	O
message	O
routing	B-Protocol
concept	O
and	O
more	O
detailed	O
network	O
design	O
in	O
1965	O
.	O
</s>
<s>
He	O
invented	O
the	O
term	O
packet	B-Protocol
switching	I-Protocol
,	O
and	O
proposed	O
building	O
a	O
commercial	O
nationwide	O
data	B-Architecture
network	I-Architecture
in	O
the	O
UK	O
.	O
</s>
<s>
Roger	O
Scantlebury	O
,	O
a	O
member	O
of	O
Davies	O
 '	O
team	O
,	O
presented	O
their	O
work	O
at	O
the	O
1967	O
Symposium	O
on	O
Operating	B-General_Concept
Systems	I-General_Concept
Principles	O
and	O
suggested	O
it	O
to	O
Larry	O
Roberts	O
for	O
use	O
in	O
the	O
ARPANET	O
.	O
</s>
<s>
Davies	O
had	O
chosen	O
some	O
of	O
the	O
same	O
parameters	O
for	O
his	O
original	O
network	O
design	O
as	O
did	O
Baran	O
,	O
such	O
as	O
a	O
packet	B-Protocol
size	O
of	O
1024	O
bits	O
.	O
</s>
<s>
In	O
1966	O
,	O
Davies	O
proposed	O
that	O
a	O
network	O
should	O
be	O
built	O
at	O
the	O
laboratory	O
to	O
serve	O
the	O
needs	O
of	O
NPL	O
and	O
prove	O
the	O
feasibility	O
of	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
To	O
deal	O
with	O
packet	B-Protocol
permutations	O
(	O
due	O
to	O
dynamically	O
updated	O
route	O
preferences	O
)	O
and	O
to	O
datagram	B-Protocol
losses	O
(	O
unavoidable	O
when	O
fast	O
sources	O
send	O
to	O
a	O
slow	O
destinations	O
)	O
,	O
he	O
assumed	O
that	O
"	O
all	O
users	O
of	O
the	O
network	O
will	O
provide	O
themselves	O
with	O
some	O
kind	O
of	O
error	O
control	O
"	O
,	O
thus	O
inventing	O
what	O
came	O
to	O
be	O
known	O
as	O
the	O
end-to-end	B-Application
principle	I-Application
.	O
</s>
<s>
After	O
a	O
pilot	O
experiment	O
in	O
1969	O
,	O
the	O
NPL	B-Protocol
Data	I-Protocol
Communications	I-Protocol
Network	I-Protocol
began	O
service	O
in	O
1970	O
.	O
</s>
<s>
Leonard	O
Kleinrock	O
researched	O
the	O
application	O
of	O
queueing	O
theory	O
in	O
the	O
field	O
of	O
message	B-Protocol
switching	I-Protocol
for	O
his	O
doctoral	O
dissertation	O
at	O
MIT	O
in	O
1961-2	O
and	O
published	O
it	O
as	O
a	O
book	O
in	O
1964	O
.	O
</s>
<s>
In	O
1968	O
,	O
Lawrence	O
Roberts	O
contracted	O
with	O
Kleinrock	O
to	O
carry	O
out	O
theoretical	O
work	O
at	O
UCLA	O
to	O
measure	O
and	O
model	O
the	O
performance	O
of	O
packet	B-Protocol
switching	I-Protocol
in	O
the	O
ARPANET	O
,	O
which	O
underpinned	O
the	O
development	O
of	O
the	O
network	O
in	O
the	O
early	O
1970s	O
.	O
</s>
<s>
The	O
NPL	O
team	O
also	O
carried	O
out	O
simulation	O
work	O
on	O
packet	B-Protocol
networks	I-Protocol
,	O
including	O
datagram	B-Protocol
networks	O
.	O
</s>
<s>
The	O
French	O
CYCLADES	O
network	O
was	O
designed	O
by	O
Louis	O
Pouzin	O
in	O
the	O
early	O
1970s	O
to	O
study	O
internetworking	B-Architecture
.	O
</s>
<s>
It	O
was	O
the	O
first	O
to	O
implement	O
the	O
end-to-end	B-Application
principle	I-Application
of	O
Davies	O
,	O
and	O
make	O
the	O
hosts	B-Device
responsible	O
for	O
the	O
reliable	O
delivery	O
of	O
data	B-General_Concept
on	O
a	O
packet-switched	B-Protocol
network	I-Protocol
,	O
rather	O
than	O
this	O
being	O
a	O
service	O
of	O
the	O
network	O
itself	O
.	O
</s>
<s>
His	O
team	O
was	O
thus	O
first	O
to	O
tackle	O
the	O
highly	O
complex	O
problem	O
of	O
providing	O
user	O
applications	O
with	O
a	O
reliable	O
virtual	B-Protocol
circuit	I-Protocol
service	O
while	O
using	O
a	O
best-effort	O
service	O
,	O
an	O
early	O
contribution	O
to	O
what	O
will	O
be	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
.	O
</s>
<s>
In	O
May	O
1974	O
,	O
Vint	O
Cerf	O
and	O
Bob	O
Kahn	O
described	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Program	I-Protocol
,	O
an	O
internetworking	B-Architecture
protocol	O
for	O
sharing	O
resources	O
using	O
packet-switching	B-Protocol
among	O
the	O
nodes	O
.	O
</s>
<s>
The	O
specifications	O
of	O
the	O
TCP	O
were	O
then	O
published	O
in	O
(	O
Specification	O
of	O
Internet	O
Transmission	B-Protocol
Control	I-Protocol
Program	I-Protocol
)	O
,	O
written	O
by	O
Vint	O
Cerf	O
,	O
Yogen	O
Dalal	O
and	O
Carl	O
Sunshine	O
in	O
December	O
1974	O
.	O
</s>
<s>
This	O
monolithic	O
protocol	O
was	O
later	O
layered	O
as	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
,	O
TCP	O
,	O
atop	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
IP	O
.	O
</s>
<s>
In	O
the	O
late	O
1970s	O
and	O
early	O
1980s	O
,	O
national	O
and	O
international	O
public	O
data	B-Architecture
networks	I-Architecture
emerged	O
based	O
on	O
the	O
X.25	B-Protocol
protocol	O
.	O
</s>
<s>
X.25	B-Protocol
is	O
built	O
on	O
the	O
concept	O
of	O
virtual	B-Protocol
circuits	I-Protocol
emulating	O
traditional	O
telephone	O
connections	O
.	O
</s>
<s>
For	O
a	O
period	O
in	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
,	O
the	O
network	O
engineering	O
community	O
was	O
polarized	O
over	O
the	O
implementation	O
of	O
competing	O
protocol	B-Protocol
suites	I-Protocol
,	O
commonly	O
known	O
as	O
the	O
Protocol	B-Protocol
Wars	I-Protocol
.	O
</s>
<s>
It	O
was	O
unclear	O
which	O
of	O
the	O
OSI	O
model	O
and	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
would	O
result	O
in	O
the	O
best	O
and	O
most	O
robust	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
Complementary	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
CMOS	B-Device
)	O
VLSI	O
(	O
very-large-scale	O
integration	O
)	O
technology	O
led	O
to	O
the	O
development	O
of	O
high-speed	O
broadband	B-General_Concept
packet	B-Protocol
switching	I-Protocol
during	O
the	O
1980s1990s	O
.	O
</s>
<s>
Beginning	O
in	O
the	O
mid-1990s	O
,	O
Leonard	O
Kleinrock	O
sought	O
to	O
be	O
recognized	O
as	O
the	O
"	O
father	O
of	O
modern	O
data	B-Architecture
networking	I-Architecture
"	O
.	O
</s>
<s>
However	O
,	O
Kleinrock	O
's	O
claims	O
that	O
his	O
work	O
in	O
the	O
early	O
1960s	O
originated	O
the	O
concept	O
of	O
packet	B-Protocol
switching	I-Protocol
and	O
that	O
this	O
work	O
was	O
the	O
source	O
of	O
the	O
packet	B-Protocol
switching	I-Protocol
concepts	O
used	O
in	O
the	O
ARPANET	O
are	O
disputed	O
by	O
other	O
Internet	O
pioneers	O
,	O
including	O
by	O
Robert	O
Taylor	O
,	O
Paul	O
Baran	O
,	O
and	O
Donald	O
Davies	O
.	O
</s>
<s>
Baran	O
and	O
Davies	O
are	O
recognized	O
by	O
historians	O
and	O
the	O
U.S.	O
National	O
Inventors	O
Hall	O
of	O
Fame	O
for	O
independently	O
inventing	O
the	O
concept	O
of	O
digital	O
packet	B-Protocol
switching	I-Protocol
used	O
in	O
modern	O
computer	B-Architecture
networking	I-Architecture
including	O
the	O
Internet	O
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
may	O
be	O
classified	O
into	O
connectionless	B-Protocol
packet	B-Protocol
switching	I-Protocol
,	O
also	O
known	O
as	O
datagram	B-Protocol
switching	O
,	O
and	O
connection-oriented	B-Protocol
packet	B-Protocol
switching	I-Protocol
,	O
also	O
known	O
as	O
virtual	B-Protocol
circuit	I-Protocol
switching	I-Protocol
.	O
</s>
<s>
Examples	O
of	O
connectionless	B-Protocol
systems	O
are	O
Ethernet	O
,	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
,	O
and	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
Connection-oriented	B-Protocol
systems	O
include	O
X.25	B-Protocol
,	O
Frame	B-Protocol
Relay	I-Protocol
,	O
Multiprotocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
,	O
and	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
.	O
</s>
<s>
In	O
connectionless	B-Protocol
mode	O
each	O
packet	B-Protocol
is	O
labeled	O
with	O
a	O
destination	O
address	O
,	O
source	O
address	O
,	O
and	O
port	O
numbers	O
.	O
</s>
<s>
It	O
may	O
also	O
be	O
labeled	O
with	O
the	O
sequence	B-Protocol
number	I-Protocol
of	O
the	O
packet	B-Protocol
.	O
</s>
<s>
This	O
information	O
eliminates	O
the	O
need	O
for	O
a	O
pre-established	O
path	O
to	O
help	O
the	O
packet	B-Protocol
find	O
its	O
way	O
to	O
its	O
destination	O
,	O
but	O
means	O
that	O
more	O
information	O
is	O
needed	O
in	O
the	O
packet	B-General_Concept
header	I-General_Concept
,	O
which	O
is	O
therefore	O
larger	O
.	O
</s>
<s>
The	O
packets	B-Protocol
are	O
routed	B-Protocol
individually	O
,	O
sometimes	O
taking	O
different	O
paths	O
resulting	O
in	O
out-of-order	B-Protocol
delivery	I-Protocol
.	O
</s>
<s>
At	O
the	O
destination	O
,	O
the	O
original	O
message	O
may	O
be	O
reassembled	O
in	O
the	O
correct	O
order	O
,	O
based	O
on	O
the	O
packet	B-Protocol
sequence	B-Protocol
numbers	I-Protocol
.	O
</s>
<s>
Thus	O
a	O
virtual	B-Protocol
circuit	I-Protocol
carrying	O
a	O
byte	O
stream	O
is	O
provided	O
to	O
the	O
application	O
by	O
a	O
transport	B-Architecture
layer	I-Architecture
protocol	O
,	O
although	O
the	O
network	O
only	O
provides	O
a	O
connectionless	B-Protocol
network	B-Application
layer	I-Application
service	O
.	O
</s>
<s>
Connection-oriented	B-Protocol
transmission	O
requires	O
a	O
setup	O
phase	O
to	O
establish	O
the	O
parameters	O
of	O
communication	O
before	O
any	O
packet	B-Protocol
is	O
transferred	O
.	O
</s>
<s>
The	O
packets	B-Protocol
transferred	O
may	O
include	O
a	O
connection	O
identifier	O
rather	O
than	O
address	O
information	O
and	O
the	O
packet	B-General_Concept
header	I-General_Concept
can	O
be	O
smaller	O
,	O
as	O
it	O
only	O
needs	O
to	O
contain	O
this	O
code	O
and	O
any	O
information	O
,	O
such	O
as	O
length	O
,	O
timestamp	O
,	O
or	O
sequence	B-Protocol
number	I-Protocol
,	O
which	O
is	O
different	O
for	O
different	O
packets	B-Protocol
.	O
</s>
<s>
When	O
a	O
connection	O
identifier	O
is	O
used	O
,	O
routing	B-Protocol
a	O
packet	B-Protocol
requires	O
the	O
node	O
to	O
look	O
up	O
the	O
connection	O
identifier	O
in	O
a	O
table	O
.	O
</s>
<s>
Connection-oriented	B-Protocol
transport	B-Architecture
layer	I-Architecture
protocols	O
such	O
as	O
TCP	O
provide	O
a	O
connection-oriented	B-Protocol
service	I-Protocol
by	O
using	O
an	O
underlying	O
connectionless	B-Protocol
network	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
end-to-end	B-Application
principle	I-Application
dictates	O
that	O
the	O
end	O
nodes	O
,	O
not	O
the	O
network	O
itself	O
,	O
are	O
responsible	O
for	O
the	O
connection-oriented	B-Protocol
behavior	O
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
is	O
used	O
to	O
optimize	O
the	O
use	O
of	O
the	O
channel	O
capacity	O
available	O
in	O
digital	O
telecommunication	O
networks	O
,	O
such	O
as	O
computer	B-Architecture
networks	I-Architecture
,	O
and	O
minimize	O
the	O
transmission	O
latency	B-Protocol
(	O
the	O
time	O
it	O
takes	O
for	O
data	B-General_Concept
to	O
pass	O
across	O
the	O
network	O
)	O
,	O
and	O
to	O
increase	O
robustness	B-Application
of	O
communication	O
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
is	O
used	O
in	O
the	O
Internet	O
and	O
most	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
.	O
</s>
<s>
The	O
Internet	O
is	O
implemented	O
by	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
using	O
a	O
variety	O
of	O
link	B-Protocol
layer	I-Protocol
technologies	O
.	O
</s>
<s>
For	O
example	O
,	O
Ethernet	O
and	O
Frame	B-Protocol
Relay	I-Protocol
are	O
common	O
.	O
</s>
<s>
Newer	O
mobile	O
phone	O
technologies	O
(	O
e.g.	O
,	O
GSM	O
,	O
LTE	O
)	O
also	O
use	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
is	O
associated	O
with	O
connectionless	B-Protocol
networking	O
because	O
,	O
in	O
these	O
systems	O
,	O
no	O
connection	O
agreement	O
needs	O
to	O
be	O
established	O
between	O
communicating	O
parties	O
prior	O
to	O
exchanging	O
data	B-General_Concept
.	O
</s>
<s>
X.25	B-Protocol
is	O
a	O
notable	O
use	O
of	O
packet	B-Protocol
switching	I-Protocol
in	O
that	O
,	O
despite	O
being	O
based	O
on	O
packet	B-Protocol
switching	I-Protocol
methods	O
,	O
it	O
provides	O
virtual	B-Protocol
circuits	I-Protocol
to	O
the	O
user	O
.	O
</s>
<s>
These	O
virtual	B-Protocol
circuits	I-Protocol
carry	O
variable-length	O
packets	B-Protocol
.	O
</s>
<s>
In	O
1978	O
,	O
X.25	B-Protocol
provided	O
the	O
first	O
international	O
and	O
commercial	O
packet	B-Protocol
switching	I-Protocol
network	O
,	O
the	O
International	B-Protocol
Packet	I-Protocol
Switched	I-Protocol
Service	I-Protocol
(	O
IPSS	O
)	O
.	O
</s>
<s>
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
also	O
is	O
a	O
virtual	B-Protocol
circuit	I-Protocol
technology	O
,	O
which	O
uses	O
fixed-length	O
cell	B-Protocol
relay	I-Protocol
connection	B-Protocol
oriented	I-Protocol
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
Technologies	O
such	O
as	O
Multiprotocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
and	O
the	O
Resource	B-Protocol
Reservation	I-Protocol
Protocol	I-Protocol
(	O
RSVP	B-Protocol
)	O
create	O
virtual	B-Protocol
circuits	I-Protocol
on	O
top	O
of	O
datagram	B-Protocol
networks	O
.	O
</s>
<s>
MPLS	B-Protocol
and	O
its	O
predecessors	O
,	O
as	O
well	O
as	O
ATM	O
,	O
have	O
been	O
called	O
"	O
fast	O
packet	B-Protocol
"	O
technologies	O
.	O
</s>
<s>
MPLS	B-Protocol
,	O
indeed	O
,	O
has	O
been	O
called	O
"	O
ATM	O
without	O
cells	O
"	O
.	O
</s>
<s>
Virtual	B-Protocol
circuits	I-Protocol
are	O
especially	O
useful	O
in	O
building	O
robust	O
failover	O
mechanisms	O
and	O
allocating	O
bandwidth	O
for	O
delay-sensitive	O
applications	O
.	O
</s>
<s>
The	O
history	O
of	O
packet-switched	B-Protocol
networks	I-Protocol
can	O
be	O
divided	O
into	O
three	O
overlapping	O
eras	O
:	O
early	O
networks	O
before	O
the	O
introduction	O
of	O
X.25	B-Protocol
;	O
the	O
X.25	B-Protocol
era	O
when	O
many	O
postal	O
,	O
telephone	O
,	O
and	O
telegraph	O
(	O
PTT	O
)	O
companies	O
provided	O
public	O
data	B-Architecture
networks	I-Architecture
with	O
X.25	B-Protocol
interfaces	O
;	O
and	O
the	O
Internet	O
era	O
which	O
initially	O
competed	B-Protocol
with	I-Protocol
the	O
OSI	O
model	O
.	O
</s>
<s>
Research	O
into	O
packet	B-Protocol
switching	I-Protocol
at	O
the	O
National	O
Physical	O
Laboratory	O
(	O
NPL	O
)	O
began	O
with	O
a	O
proposal	O
for	O
a	O
wide-area	O
network	O
in	O
1965	O
,	O
and	O
a	O
local-area	B-General_Concept
network	I-General_Concept
in	O
1966	O
.	O
</s>
<s>
The	O
NPL	B-Protocol
network	I-Protocol
,	O
ARPANET	O
,	O
and	O
SITA	O
HLN	O
became	O
operational	O
in	O
1969	O
.	O
</s>
<s>
Before	O
the	O
introduction	O
of	O
X.25	B-Protocol
in	O
1976	O
,	O
about	O
twenty	O
different	O
network	O
technologies	O
had	O
been	O
developed	O
.	O
</s>
<s>
Two	O
fundamental	O
differences	O
involved	O
the	O
division	O
of	O
functions	O
and	O
tasks	O
between	O
the	O
hosts	B-Device
at	O
the	O
edge	O
of	O
the	O
network	O
and	O
the	O
network	O
core	O
.	O
</s>
<s>
In	O
the	O
datagram	B-Protocol
system	O
,	O
operating	O
according	O
to	O
the	O
end-to-end	B-Application
principle	I-Application
,	O
the	O
hosts	B-Device
have	O
the	O
responsibility	O
to	O
ensure	O
orderly	O
delivery	O
of	O
packets	B-Protocol
.	O
</s>
<s>
In	O
the	O
virtual	O
call	O
system	O
,	O
the	O
network	O
guarantees	O
sequenced	O
delivery	O
of	O
data	B-General_Concept
to	O
the	O
host	O
.	O
</s>
<s>
The	O
X.25	B-Protocol
protocol	I-Protocol
suite	I-Protocol
uses	O
this	O
network	O
type	O
.	O
</s>
<s>
AppleTalk	B-Application
is	O
a	O
proprietary	O
suite	O
of	O
networking	O
protocols	O
developed	O
by	O
Apple	O
in	O
1985	O
for	O
Apple	B-Device
Macintosh	I-Device
computers	I-Device
.	O
</s>
<s>
AppleTalk	B-Application
included	O
features	O
that	O
allowed	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
to	O
be	O
established	O
ad	O
hoc	O
without	O
the	O
requirement	O
for	O
a	O
centralized	O
router	B-Protocol
or	O
server	O
.	O
</s>
<s>
The	O
AppleTalk	B-Application
system	O
automatically	O
assigned	O
addresses	O
,	O
updated	O
the	O
distributed	O
namespace	O
,	O
and	O
configured	O
any	O
required	O
inter-network	B-Architecture
routing	I-Architecture
.	O
</s>
<s>
It	O
was	O
a	O
plug-n-play	B-Device
system	O
.	O
</s>
<s>
AppleTalk	B-Application
implementations	O
were	O
also	O
released	O
for	O
the	O
IBM	B-Device
PC	I-Device
and	O
compatibles	O
,	O
and	O
the	O
Apple	B-Device
IIGS	I-Device
.	O
</s>
<s>
AppleTalk	B-Application
support	O
was	O
available	O
in	O
most	O
networked	O
printers	O
,	O
especially	O
laser	O
printers	O
,	O
some	O
file	B-Application
servers	I-Application
and	O
routers	B-Protocol
.	O
</s>
<s>
AppleTalk	B-Application
support	O
was	O
terminated	O
in	O
2009	O
,	O
replaced	O
by	O
TCP/IP	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
The	O
ARPANET	O
was	O
a	O
progenitor	O
network	O
of	O
the	O
Internet	O
and	O
one	O
of	O
the	O
first	O
networks	O
,	O
along	O
with	O
ARPA	O
's	O
SATNET	O
,	O
to	O
run	O
the	O
TCP/IP	B-Protocol
suite	I-Protocol
using	O
packet	B-Protocol
switching	I-Protocol
technologies	O
.	O
</s>
<s>
It	O
initially	O
had	O
only	O
one	O
host	O
but	O
was	O
designed	O
to	O
support	O
many	O
hosts	B-Device
.	O
</s>
<s>
BNR	O
later	O
made	O
major	O
contributions	O
to	O
the	O
CCITT	O
X.25	B-Protocol
project	O
.	O
</s>
<s>
The	O
Cambridge	B-General_Concept
Ring	I-General_Concept
was	O
an	O
experimental	O
ring	B-Architecture
network	I-Architecture
developed	O
at	O
the	O
Computer	O
Laboratory	O
,	O
University	O
of	O
Cambridge	O
.	O
</s>
<s>
CompuServe	O
developed	O
its	O
own	O
packet	B-Protocol
switching	I-Protocol
network	O
,	O
implemented	O
on	O
DEC	B-Device
PDP-11	I-Device
minicomputers	B-Architecture
acting	O
as	O
network	O
nodes	O
that	O
were	O
installed	O
throughout	O
the	O
US	O
(	O
and	O
later	O
,	O
in	O
other	O
countries	O
)	O
and	O
interconnected	O
.	O
</s>
<s>
Over	O
time	O
,	O
the	O
CompuServe	O
network	O
evolved	O
into	O
a	O
complicated	O
multi-tiered	O
network	O
incorporating	O
ATM	O
,	O
Frame	B-Protocol
Relay	I-Protocol
,	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
and	O
X.25	B-Protocol
technologies	O
.	O
</s>
<s>
The	O
CYCLADES	O
packet	B-Protocol
switching	I-Protocol
network	O
was	O
a	O
French	O
research	O
network	O
designed	O
and	O
directed	O
by	O
Louis	O
Pouzin	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
network	O
to	O
use	O
the	O
end-to-end	B-Application
principle	I-Application
and	O
make	O
the	O
hosts	B-Device
responsible	O
for	O
reliable	O
delivery	O
of	O
data	B-General_Concept
,	O
rather	O
than	O
the	O
network	O
itself	O
.	O
</s>
<s>
DECnet	B-Protocol
is	O
a	O
suite	O
of	O
network	O
protocols	O
created	O
by	O
Digital	O
Equipment	O
Corporation	O
,	O
originally	O
released	O
in	O
1975	O
in	O
order	O
to	O
connect	O
two	O
PDP-11	B-Device
minicomputers	B-Architecture
.	O
</s>
<s>
Initially	O
built	O
with	O
three	O
layers	B-Architecture
,	O
it	O
later	O
(	O
1982	O
)	O
evolved	O
into	O
a	O
seven-layer	O
OSI-compliant	O
networking	O
protocol	O
.	O
</s>
<s>
The	O
DECnet	B-Protocol
protocols	O
were	O
designed	O
entirely	O
by	O
Digital	O
Equipment	O
Corporation	O
.	O
</s>
<s>
However	O
,	O
DECnet	B-Protocol
Phase	O
II	O
(	O
and	O
later	O
)	O
were	O
open	O
standards	O
with	O
published	O
specifications	O
,	O
and	O
several	O
implementations	O
were	O
developed	O
outside	O
DEC	O
,	O
including	O
one	O
for	O
Linux	B-Application
.	O
</s>
<s>
It	O
mixed	O
circuit	B-Protocol
switching	I-Protocol
and	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
The	O
contract	O
for	O
its	O
implementation	O
was	O
awarded	O
to	O
an	O
Anglo	O
French	O
consortium	B-Application
led	O
by	O
the	O
UK	O
systems	O
house	O
Logica	O
and	O
Sesa	O
and	O
managed	O
by	O
Andrew	O
Karney	O
.	O
</s>
<s>
Work	O
began	O
in	O
1973	O
and	O
it	O
became	O
operational	O
in	O
1976	O
including	O
nodes	O
linking	O
the	O
NPL	B-Protocol
network	I-Protocol
and	O
CYCLADES	O
.	O
</s>
<s>
The	O
transport	B-Architecture
protocol	I-Architecture
of	O
the	O
EIN	O
was	O
the	O
basis	O
of	O
the	O
one	O
adopted	O
by	O
the	O
International	B-Protocol
Networking	I-Protocol
Working	I-Protocol
Group	I-Protocol
.	O
</s>
<s>
The	O
Experimental	O
Packet	B-Protocol
Switched	I-Protocol
Service	O
(	O
EPSS	O
)	O
was	O
an	O
experiment	O
of	O
the	O
UK	O
Post	O
Office	O
Telecommunications	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
public	O
data	B-Architecture
network	I-Architecture
in	O
the	O
UK	O
when	O
it	O
began	O
operating	O
in	O
1977	O
.	O
</s>
<s>
In	O
1965	O
,	O
at	O
the	O
instigation	O
of	O
Warner	O
Sinback	O
,	O
a	O
data	B-Architecture
network	I-Architecture
based	O
on	O
this	O
voice-phone	O
network	O
was	O
designed	O
to	O
connect	O
GE	O
's	O
four	O
computer	O
sales	O
and	O
service	O
centers	O
(	O
Schenectady	O
,	O
New	O
York	O
,	O
Chicago	O
,	O
and	O
Phoenix	O
)	O
to	O
facilitate	O
a	O
computer	O
time-sharing	O
service	O
.	O
</s>
<s>
After	O
going	O
international	O
some	O
years	O
later	O
,	O
GEIS	O
created	O
a	O
network	O
data	B-General_Concept
center	O
near	O
Cleveland	O
,	O
Ohio	O
.	O
</s>
<s>
IPSANET	B-Protocol
was	O
a	O
semi-private	O
network	O
constructed	O
by	O
I	O
.	O
P	O
.	O
Sharp	O
Associates	O
to	O
serve	O
their	O
time-sharing	O
customers	O
.	O
</s>
<s>
The	O
Internetwork	B-Protocol
Packet	I-Protocol
Exchange	I-Protocol
(	O
IPX	O
)	O
and	O
Sequenced	O
Packet	B-Protocol
Exchange	O
(	O
SPX	O
)	O
are	O
Novell	O
networking	O
protocols	O
from	O
the	O
1980s	O
derived	O
from	O
Xerox	B-Protocol
Network	I-Protocol
Systems	I-Protocol
 '	O
IDP	O
and	O
SPP	O
protocols	O
,	O
respectively	O
which	O
date	O
back	O
to	O
the	O
1970s	O
.	O
</s>
<s>
IPX/SPX	B-Protocol
was	O
used	O
primarily	O
on	O
networks	O
using	O
the	O
Novell	B-Operating_System
NetWare	I-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Merit	O
Network	O
,	O
an	O
independent	O
nonprofit	O
organization	O
governed	O
by	O
Michigan	O
's	O
public	O
universities	O
,	O
was	O
formed	O
in	O
1966	O
as	O
the	O
Michigan	O
Educational	O
Research	O
Information	O
Triad	O
to	O
explore	O
computer	B-Architecture
networking	I-Architecture
between	O
three	O
of	O
Michigan	O
's	O
public	O
universities	O
as	O
a	O
means	O
to	O
help	O
the	O
state	O
's	O
educational	O
and	O
economic	O
development	O
.	O
</s>
<s>
With	O
initial	O
support	O
from	O
the	O
State	O
of	O
Michigan	O
and	O
the	O
National	O
Science	O
Foundation	O
(	O
NSF	O
)	O
,	O
the	O
packet-switched	B-Protocol
network	I-Protocol
was	O
first	O
demonstrated	O
in	O
December	O
1971	O
when	O
an	O
interactive	O
host-to-host	O
connection	O
was	O
made	O
between	O
the	O
IBM	B-Device
mainframe	I-Device
systems	O
at	O
the	O
University	O
of	O
Michigan	O
in	O
Ann	O
Arbor	O
and	O
Wayne	O
State	O
University	O
in	O
Detroit	B-Application
.	O
</s>
<s>
Over	O
the	O
next	O
several	O
years	O
,	O
in	O
addition	O
to	O
host-to-host	O
interactive	O
connections	O
,	O
the	O
network	O
was	O
enhanced	O
to	O
support	O
terminal-to-host	O
connections	O
,	O
host-to-host	O
batch	O
connections	O
(	O
remote	O
job	O
submission	O
,	O
remote	O
printing	O
,	O
batch	O
file	O
transfer	O
)	O
,	O
interactive	O
file	O
transfer	O
,	O
gateways	O
to	O
the	O
Tymnet	B-Application
and	O
Telenet	O
public	O
data	B-Architecture
networks	I-Architecture
,	O
X.25	B-Protocol
host	O
attachments	O
,	O
gateways	O
to	O
X.25	B-Protocol
data	B-Architecture
networks	I-Architecture
,	O
Ethernet	O
attached	O
hosts	B-Device
,	O
and	O
eventually	O
TCP/IP	B-Protocol
;	O
additionally	O
,	O
public	O
universities	O
in	O
Michigan	O
joined	O
the	O
network	O
.	O
</s>
<s>
In	O
1965	O
,	O
Donald	O
Davies	O
of	O
the	O
National	O
Physical	O
Laboratory	O
(	O
United	O
Kingdom	O
)	O
designed	O
and	O
proposed	O
a	O
national	O
commercial	O
data	B-Architecture
network	I-Architecture
based	O
on	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
The	O
proposal	O
was	O
not	O
taken	O
up	O
nationally	O
but	O
,	O
in	O
1966	O
,	O
he	O
designed	O
a	O
local	B-General_Concept
network	I-General_Concept
using	O
"	O
interface	O
computers	O
"	O
,	O
today	O
known	O
as	O
routers	B-Protocol
,	O
to	O
serve	O
the	O
needs	O
of	O
NPL	O
and	O
prove	O
the	O
feasibility	O
of	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
By	O
1968	O
Davies	O
had	O
begun	O
building	O
the	O
NPL	B-Protocol
network	I-Protocol
to	O
meet	O
the	O
needs	O
of	O
the	O
multidisciplinary	O
laboratory	O
and	O
prove	O
the	O
technology	O
under	O
operational	O
conditions	O
.	O
</s>
<s>
NPL	O
and	O
the	O
ARPANET	O
were	O
the	O
first	O
two	O
networks	O
to	O
use	O
packet	B-Protocol
switching	I-Protocol
,	O
and	O
were	O
interconnected	O
in	O
the	O
early	O
1970s	O
.	O
</s>
<s>
Octopus	O
was	O
a	O
local	B-General_Concept
network	I-General_Concept
at	O
Lawrence	O
Livermore	O
National	O
Laboratory	O
.	O
</s>
<s>
It	O
connected	O
sundry	O
hosts	B-Device
at	O
the	O
lab	O
to	O
interactive	O
terminals	O
and	O
various	O
computer	O
peripherals	O
including	O
a	O
bulk	O
storage	O
system	O
.	O
</s>
<s>
Philips	O
Research	O
Laboratories	O
in	O
Redhill	O
,	O
Surrey	O
developed	O
a	O
packet	B-Protocol
switching	I-Protocol
network	O
for	O
internal	O
use	O
.	O
</s>
<s>
It	O
was	O
a	O
datagram	B-Protocol
network	O
with	O
a	O
single	O
switching	O
node	O
.	O
</s>
<s>
PARC	B-Protocol
Universal	I-Protocol
Packet	I-Protocol
(	O
PUP	O
or	O
Pup	O
)	O
was	O
one	O
of	O
the	O
two	O
earliest	O
internetworking	B-Architecture
protocol	B-Protocol
suites	I-Protocol
;	O
it	O
was	O
created	O
by	O
researchers	O
at	O
Xerox	O
PARC	O
in	O
the	O
mid-1970s	O
.	O
</s>
<s>
The	O
entire	O
suite	O
provided	O
routing	B-Protocol
and	O
packet	B-Protocol
delivery	O
,	O
as	O
well	O
as	O
higher	O
level	O
functions	O
such	O
as	O
a	O
reliable	O
byte	O
stream	O
,	O
along	O
with	O
numerous	O
applications	O
.	O
</s>
<s>
Further	O
developments	O
led	O
to	O
Xerox	B-Protocol
Network	I-Protocol
Systems	I-Protocol
(	O
XNS	O
)	O
.	O
</s>
<s>
It	O
was	O
used	O
to	O
gain	O
experience	O
with	O
packet	B-Protocol
switching	I-Protocol
technology	O
before	O
the	O
specification	O
of	O
TRANSPAC	O
was	O
frozen	O
.	O
</s>
<s>
RCP	O
was	O
a	O
virtual-circuit	B-Protocol
network	O
in	O
contrast	O
to	O
CYCLADES	O
which	O
was	O
based	O
on	O
datagrams	B-Protocol
.	O
</s>
<s>
RCP	O
influenced	O
the	O
X.25	B-Protocol
specification	O
,	O
which	O
was	O
deployed	O
on	O
TRANSPAC	O
and	O
other	O
public	O
data	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
"	O
The	O
experimental	O
packet-switched	B-Protocol
Nordic	O
telecommunication	O
network	O
SCANNET	O
was	O
implemented	O
in	O
Nordic	O
technical	O
libraries	O
in	O
the	O
1970s	O
,	O
and	O
it	O
included	O
first	O
Nordic	O
electronic	O
journal	O
Extemplo	O
.	O
</s>
<s>
SITA	O
is	O
a	O
consortium	B-Application
of	O
airlines	O
.	O
</s>
<s>
These	O
groups	O
of	O
institutions	O
shared	B-General_Concept
resources	I-General_Concept
to	O
provide	O
better	O
computing	O
facilities	O
than	O
could	O
be	O
afforded	O
individually	O
.	O
</s>
<s>
In	O
the	O
early	O
1980s	O
a	O
standardisation	O
and	O
interconnection	O
effort	O
started	O
,	O
hosted	O
on	O
an	O
expansion	O
of	O
the	O
SERCnet	O
research	O
network	O
and	O
based	O
on	O
the	O
Coloured	B-Protocol
Book	I-Protocol
protocols	I-Protocol
,	O
later	O
evolving	O
into	O
JANET	O
.	O
</s>
<s>
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
SNA	O
)	O
is	O
IBM	O
's	O
proprietary	O
networking	O
architecture	O
created	O
in	O
1974	O
.	O
</s>
<s>
Telenet	O
was	O
the	O
first	O
FCC-licensed	O
public	O
data	B-Architecture
network	I-Architecture
in	O
the	O
United	O
States	O
.	O
</s>
<s>
It	O
was	O
founded	O
by	O
Bolt	O
Beranek	O
&	O
Newman	O
with	O
Larry	O
Roberts	O
as	O
CEO	O
as	O
a	O
means	O
of	O
making	O
packet	B-Protocol
switching	I-Protocol
technology	O
public	O
.	O
</s>
<s>
Telenet	O
initially	O
used	O
a	O
proprietary	O
virtual	B-Protocol
connection	I-Protocol
host	O
interface	O
,	O
but	O
changed	O
the	O
host	O
interface	O
to	O
X.25	B-Protocol
and	O
the	O
terminal	O
interface	O
to	O
X.29	O
.	O
</s>
<s>
Tymnet	B-Application
was	O
an	O
international	O
data	B-General_Concept
communications	O
network	O
headquartered	O
in	O
San	O
Jose	O
,	O
CA	O
that	O
utilized	O
virtual	O
call	O
packet	B-Protocol
switched	I-Protocol
technology	O
and	O
used	O
X.25	B-Protocol
,	O
SNA/SDLC	O
,	O
BSC	O
and	O
ASCII	O
interfaces	O
to	O
connect	O
host	B-Device
computers	I-Device
(	O
servers	O
)	O
at	O
thousands	O
of	O
large	O
companies	O
,	O
educational	O
institutions	O
,	O
and	O
government	O
agencies	O
.	O
</s>
<s>
Tymnet	B-Application
was	O
also	O
connected	O
to	O
dozens	O
of	O
other	O
public	O
networks	O
in	O
the	O
U.S.	O
and	O
internationally	O
via	O
X.25/X.75	O
gateways	O
.	O
</s>
<s>
Xerox	B-Protocol
Network	I-Protocol
Systems	I-Protocol
(	O
XNS	O
)	O
was	O
a	O
protocol	B-Protocol
suite	I-Protocol
promulgated	O
by	O
Xerox	O
,	O
which	O
provided	O
routing	B-Protocol
and	O
packet	B-Protocol
delivery	O
,	O
as	O
well	O
as	O
higher	O
level	O
functions	O
such	O
as	O
a	O
reliable	O
stream	O
,	O
and	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
It	O
was	O
developed	O
from	O
PARC	B-Protocol
Universal	I-Protocol
Packet	I-Protocol
(	O
PUP	O
)	O
.	O
</s>
<s>
There	O
were	O
two	O
kinds	O
of	O
X.25	B-Protocol
networks	O
.	O
</s>
<s>
Some	O
such	O
as	O
DATAPAC	B-Protocol
and	O
TRANSPAC	O
were	O
initially	O
implemented	O
with	O
an	O
X.25	B-Protocol
external	O
interface	O
.	O
</s>
<s>
Some	O
older	O
networks	O
such	O
as	O
TELENET	O
and	O
TYMNET	B-Application
were	O
modified	O
to	O
provide	O
a	O
X.25	B-Protocol
host	O
interface	O
in	O
addition	O
to	O
older	O
host	O
connection	O
schemes	O
.	O
</s>
<s>
DATAPAC	B-Protocol
was	O
developed	O
by	O
Bell-Northern	O
Research	O
which	O
was	O
a	O
joint	O
venture	O
of	O
Bell	O
Canada	O
(	O
a	O
common	O
carrier	O
)	O
and	O
Northern	O
Telecom	O
(	O
a	O
telecommunications	O
equipment	O
supplier	O
)	O
.	O
</s>
<s>
Northern	O
Telecom	O
sold	O
several	O
DATAPAC	B-Protocol
clones	O
to	O
foreign	O
PTTs	O
including	O
the	O
Deutsche	O
Bundespost	O
.	O
</s>
<s>
X.75	B-Protocol
and	O
X.121	B-Protocol
allowed	O
the	O
interconnection	O
of	O
national	O
X.25	B-Protocol
networks	O
.	O
</s>
<s>
A	O
user	O
or	O
host	O
could	O
call	O
a	O
host	O
on	O
a	O
foreign	O
network	O
by	O
including	O
the	O
DNIC	B-Protocol
of	O
the	O
remote	O
network	O
as	O
part	O
of	O
the	O
destination	O
address	O
.	O
</s>
<s>
AUSTPAC	B-Protocol
was	O
an	O
Australian	O
public	O
X.25	B-Protocol
network	O
operated	O
by	O
Telstra	O
.	O
</s>
<s>
Started	O
by	O
Telecom	O
Australia	O
in	O
the	O
early	O
1980s	O
,	O
AUSTPAC	B-Protocol
was	O
Australia	O
's	O
first	O
public	O
packet-switched	B-Protocol
data	I-Protocol
network	I-Protocol
and	O
supported	O
applications	O
such	O
as	O
on-line	O
betting	O
,	O
financial	O
applications	O
—	O
the	O
Australian	O
Tax	O
Office	O
made	O
use	O
of	O
AUSTPAC	B-Protocol
—	O
and	O
remote	O
terminal	O
access	O
to	O
academic	O
institutions	O
,	O
who	O
maintained	O
their	O
connections	O
to	O
AUSTPAC	B-Protocol
up	O
until	O
the	O
mid-late	O
1990s	O
in	O
some	O
cases	O
.	O
</s>
<s>
Access	O
was	O
via	O
a	O
dial-up	O
terminal	O
to	O
a	O
PAD	B-Protocol
,	O
or	O
,	O
by	O
linking	O
a	O
permanent	O
X.25	B-Protocol
node	O
to	O
the	O
network	O
.	O
</s>
<s>
Launched	O
on	O
March	O
11	O
,	O
1985	O
,	O
it	O
was	O
the	O
first	O
local	O
public	O
packet-switched	B-Protocol
network	I-Protocol
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Datanet	O
1	O
was	O
the	O
public	O
switched	O
data	B-Architecture
network	I-Architecture
operated	O
by	O
the	O
Dutch	O
PTT	O
Telecom	O
(	O
now	O
known	O
as	O
KPN	O
)	O
.	O
</s>
<s>
Strictly	O
speaking	O
Datanet	O
1	O
only	O
referred	O
to	O
the	O
network	O
and	O
the	O
connected	O
users	O
via	O
leased	B-Architecture
lines	I-Architecture
(	O
using	O
the	O
X.121	B-Protocol
DNIC	B-Protocol
2041	O
)	O
,	O
the	O
name	O
also	O
referred	O
to	O
the	O
public	O
PAD	B-Protocol
service	O
Telepad	O
(	O
using	O
the	O
DNIC	B-Protocol
2049	O
)	O
.	O
</s>
<s>
And	O
because	O
the	O
main	O
Videotex	B-Operating_System
service	O
used	O
the	O
network	O
and	O
modified	O
PAD	B-Protocol
devices	O
as	O
infrastructure	O
the	O
name	O
Datanet	O
1	O
was	O
used	O
for	O
these	O
services	O
as	O
well	O
.	O
</s>
<s>
DATAPAC	B-Protocol
was	O
the	O
first	O
operational	O
X.25	B-Protocol
network	O
(	O
1976	O
)	O
.	O
</s>
<s>
Eirpac	B-Protocol
is	O
the	O
Irish	O
public	O
switched	O
data	B-Architecture
network	I-Architecture
supporting	O
X.25	B-Protocol
and	O
X.28	O
.	O
</s>
<s>
Eirpac	B-Protocol
is	O
run	O
by	O
Eircom	O
.	O
</s>
<s>
Nine	O
member	O
states	O
of	O
the	O
European	O
Economic	O
Community	O
contracted	O
with	O
Logica	O
and	O
the	O
French	O
company	O
SESA	O
to	O
set	O
up	O
a	O
joint	O
venture	O
in	O
1975	O
to	O
undertake	O
the	O
Euronet	O
development	O
,	O
using	O
X.25	B-Protocol
protocols	O
to	O
form	O
virtual	B-Protocol
circuits	I-Protocol
.	O
</s>
<s>
In	O
addition	O
to	O
providing	O
X.25	B-Protocol
packet	B-Protocol
switching	I-Protocol
,	O
message	B-Protocol
switching	I-Protocol
software	O
was	O
also	O
included	O
.	O
</s>
<s>
Iberpac	B-Protocol
is	O
the	O
Spanish	O
public	O
packet-switched	B-Protocol
network	I-Protocol
,	O
providing	O
X.25	B-Protocol
services	O
.	O
</s>
<s>
Iberpac	B-Protocol
was	O
run	O
by	O
Telefonica	O
.	O
</s>
<s>
In	O
1978	O
,	O
X.25	B-Protocol
provided	O
the	O
first	O
international	O
and	O
commercial	O
packet-switching	B-Protocol
network	O
,	O
the	O
International	B-Protocol
Packet	I-Protocol
Switched	I-Protocol
Service	I-Protocol
(	O
IPSS	O
)	O
.	O
</s>
<s>
The	O
X.25	B-Protocol
network	O
,	O
which	O
used	O
the	O
Coloured	B-Protocol
Book	I-Protocol
protocols	I-Protocol
,	O
was	O
based	O
mainly	O
on	O
GEC	B-Device
4000	I-Device
series	I-Device
switches	O
,	O
and	O
ran	O
X.25	B-Protocol
links	O
at	O
up	O
to	O
8Mbit/s	O
in	O
its	O
final	O
phase	O
before	O
being	O
converted	O
to	O
an	O
IP-based	B-Protocol
network	I-Protocol
in	O
1991	O
.	O
</s>
<s>
Packet	B-Protocol
Switch	I-Protocol
Stream	I-Protocol
(	O
PSS	O
)	O
was	O
the	O
Post	O
Office	O
Telecommunications	O
(	O
later	O
to	O
become	O
British	O
Telecom	O
)	O
national	O
X.25	B-Protocol
network	O
with	O
a	O
DNIC	B-Protocol
of	O
2342	O
.	O
</s>
<s>
PSS	O
also	O
included	O
public	O
dial-up	O
PAD	B-Protocol
access	O
,	O
and	O
various	O
InterStream	O
gateways	O
to	O
other	O
services	O
such	O
as	O
Telex	O
.	O
</s>
<s>
REXPAC	O
was	O
the	O
nationwide	O
experimental	O
packet	B-Protocol
switching	I-Protocol
data	B-Architecture
network	I-Architecture
in	O
Brazil	O
,	O
developed	O
by	O
the	O
research	O
and	O
development	O
center	O
of	O
Telebrás	O
,	O
the	O
state-owned	O
public	O
telecommunications	O
provider	O
.	O
</s>
<s>
TRANSPAC	O
was	O
the	O
national	O
X.25	B-Protocol
network	O
in	O
France	O
.	O
</s>
<s>
It	O
was	O
developed	O
locally	O
at	O
about	O
the	O
same	O
time	O
as	O
DATAPAC	B-Protocol
in	O
Canada	O
.	O
</s>
<s>
It	O
began	O
operation	O
in	O
1978	O
,	O
and	O
served	O
commercial	O
users	O
and	O
,	O
after	O
Minitel	B-Application
began	O
,	O
consumers	O
.	O
</s>
<s>
UNINETT	O
was	O
a	O
wide-area	O
Norwegian	O
packet-switched	B-Protocol
network	I-Protocol
established	O
through	O
a	O
joint	O
effort	O
between	O
Norwegian	O
universities	O
,	O
research	O
institutions	O
and	O
the	O
Norwegian	O
Telecommunication	O
administration	O
.	O
</s>
<s>
The	O
original	O
network	O
was	O
based	O
on	O
X.25	B-Protocol
;	O
Internet	B-Protocol
protocols	I-Protocol
were	O
adopted	O
later	O
.	O
</s>
<s>
VENUS-P	O
was	O
an	O
international	O
X.25	B-Protocol
network	O
that	O
operated	O
from	O
April	O
1982	O
through	O
March	O
2006	O
.	O
</s>
<s>
Venepaq	O
is	O
the	O
national	O
X.25	B-Protocol
public	O
network	O
in	O
Venezuela	O
.	O
</s>
<s>
When	O
Internet	O
connectivity	O
was	O
made	O
available	O
to	O
anyone	O
who	O
could	O
pay	O
for	O
an	B-Architecture
Internet	I-Architecture
service	O
provider	O
subscription	O
,	O
the	O
distinctions	O
between	O
national	O
networks	O
blurred	O
.	O
</s>
<s>
The	O
user	O
no	O
longer	O
saw	O
network	O
identifiers	O
such	O
as	O
the	O
DNIC	B-Protocol
.	O
</s>
<s>
Some	O
older	O
technologies	O
such	O
as	O
circuit	B-Protocol
switching	I-Protocol
have	O
resurfaced	O
with	O
new	O
names	O
such	O
as	O
fast	B-Protocol
packet	I-Protocol
switching	I-Protocol
.	O
</s>
<s>
The	O
Computer	B-General_Concept
Science	I-General_Concept
Network	O
(	O
CSNET	O
)	O
was	O
a	O
computer	B-Architecture
network	I-Architecture
funded	O
by	O
the	O
NSF	O
that	O
began	O
operation	O
in	O
1981	O
.	O
</s>
<s>
Its	O
purpose	O
was	O
to	O
extend	O
networking	O
benefits	O
for	O
computer	B-General_Concept
science	I-General_Concept
departments	O
at	O
academic	O
and	O
research	O
institutions	O
that	O
could	O
not	O
be	O
directly	O
connected	O
to	O
ARPANET	O
due	O
to	O
funding	O
or	O
authorization	O
limitations	O
.	O
</s>
<s>
Internet2	O
is	O
a	O
not-for-profit	O
United	O
States	O
computer	B-Architecture
networking	I-Architecture
consortium	B-Application
led	O
by	O
members	O
from	O
the	O
research	O
and	O
education	O
communities	O
,	O
industry	O
,	O
and	O
government	O
.	O
</s>
<s>
NSFNET	O
was	O
also	O
the	O
name	O
given	O
to	O
several	O
nationwide	O
backbone	B-General_Concept
networks	O
operating	O
at	O
speeds	O
of	O
56	O
kbit/s	O
,	O
1.5	O
Mbit/s	O
(	O
T1	O
)	O
,	O
and	O
45	O
Mbit/s	O
(	O
T3	O
)	O
that	O
were	O
constructed	O
to	O
support	O
NSF	O
's	O
networking	O
initiatives	O
from	O
1985-1995	O
.	O
</s>
<s>
Initially	O
created	O
to	O
link	O
researchers	O
to	O
the	O
nation	O
's	O
NSF-funded	O
supercomputing	B-Architecture
centers	O
,	O
through	O
further	O
public	O
funding	O
and	O
private	O
industry	O
partnerships	O
it	O
developed	O
into	O
a	O
major	O
part	O
of	O
the	O
Internet	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
five	O
NSF	O
supercomputer	B-Architecture
centers	O
,	O
NSFNET	O
provided	O
connectivity	O
to	O
eleven	O
regional	O
networks	O
and	O
through	O
these	O
networks	O
to	O
many	O
smaller	O
regional	O
and	O
campus	O
networks	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
JVNCNet	O
,	O
the	O
John	O
von	O
Neumann	O
National	O
Supercomputer	B-Architecture
Center	O
Network	O
in	O
Princeton	O
,	O
New	O
Jersey	O
,	O
serving	O
Delaware	O
and	O
New	O
Jersey	O
;	O
</s>
<s>
It	O
is	O
a	O
12,000	O
-mile	O
high-speed	O
national	O
computer	B-Architecture
network	I-Architecture
owned	O
and	O
operated	O
by	O
the	O
U.S.	O
research	O
and	O
education	O
community	O
that	O
runs	O
over	O
fiber-optic	O
lines	O
.	O
</s>
<s>
The	O
Very	O
high-speed	O
Backbone	B-General_Concept
Network	O
Service	O
(	O
vBNS	O
)	O
came	O
on	O
line	O
in	O
April	O
1995	O
as	O
part	O
of	O
a	O
National	O
Science	O
Foundation	O
(	O
NSF	O
)	O
sponsored	O
project	O
to	O
provide	O
high-speed	O
interconnection	O
between	O
NSF-sponsored	O
supercomputing	B-Architecture
centers	O
and	O
select	O
access	O
points	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
The	O
network	O
was	O
engineered	O
and	O
operated	O
by	O
MCI	B-Application
Telecommunications	I-Application
under	O
a	O
cooperative	O
agreement	O
with	O
the	O
NSF	O
.	O
</s>
<s>
By	O
1998	O
,	O
the	O
vBNS	O
had	O
grown	O
to	O
connect	O
more	O
than	O
100	O
universities	O
and	O
research	O
and	O
engineering	O
institutions	O
via	O
12	O
national	O
points	O
of	O
presence	O
with	O
DS-3	O
(	O
45	O
Mbit/s	O
)	O
,	O
OC-3c	O
(	O
155	O
Mbit/s	O
)	O
,	O
and	O
OC-12c	O
(	O
622	O
Mbit/s	O
)	O
links	O
on	O
an	O
all	O
OC-12c	O
backbone	B-General_Concept
,	O
a	O
substantial	O
engineering	O
feat	O
for	O
that	O
time	O
.	O
</s>
<s>
The	O
vBNS	O
installed	O
one	O
of	O
the	O
first	O
ever	O
production	O
OC-48c	O
(	O
2.5	O
Gbit/s	O
)	O
IP	B-Protocol
links	I-Protocol
in	O
February	O
1999	O
and	O
went	O
on	O
to	O
upgrade	O
the	O
entire	O
backbone	B-General_Concept
to	O
OC-48c	O
.	O
</s>
<s>
Most	O
universities	O
and	O
research	O
centers	O
migrated	O
to	O
the	O
Internet2	O
educational	O
backbone	B-General_Concept
.	O
</s>
<s>
In	O
January	O
2006	O
,	O
when	O
MCI	O
and	O
Verizon	B-Application
merged	O
,	O
vBNS+	O
became	O
a	O
service	O
of	O
Verizon	B-Application
Business	I-Application
.	O
</s>
