<s>
The	O
PARC	B-Protocol
Universal	I-Protocol
Packet	I-Protocol
(	O
commonly	O
abbreviated	O
to	O
PUP	O
or	O
PuP	O
,	O
although	O
the	O
original	O
documents	O
usually	O
use	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>
(	O
Technically	O
,	O
the	O
name	O
"	O
PUP	O
"	O
only	O
refers	O
to	O
the	O
internetwork-level	O
protocol	O
,	O
but	O
it	O
is	O
also	O
applied	O
to	O
the	O
whole	O
protocol	B-Protocol
suite	I-Protocol
.	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>
The	O
PUP	O
protocol	O
was	O
created	O
in	O
roughly	O
the	O
same	O
time	O
frame	O
as	O
the	O
earliest	O
parts	O
of	O
the	O
development	O
of	O
TCP/IP	B-Protocol
for	O
the	O
Internet	O
and	O
also	O
the	O
same	O
time	O
period	O
as	O
the	O
early	O
Ethernet	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
at	O
PARC	O
.	O
</s>
<s>
In	O
the	O
1980s	O
Xerox	O
used	O
PUP	O
as	O
the	O
base	O
for	O
the	O
Xerox	B-Protocol
Network	I-Protocol
Systems	I-Protocol
(	O
XNS	B-Protocol
)	O
protocol	B-Protocol
suite	I-Protocol
;	O
some	O
of	O
the	O
protocols	O
in	O
the	O
XNS	B-Protocol
suite	O
(	O
such	O
as	O
the	O
Internetwork	B-Architecture
Datagram	O
Protocol	O
)	O
were	O
lightly	O
modified	O
versions	O
of	O
the	O
ones	O
in	O
the	O
PUP	O
suite	O
,	O
but	O
others	O
are	O
quite	O
different	O
,	O
reflecting	O
the	O
experience	O
gained	O
with	O
PUP	O
and	O
IP	O
.	O
</s>
<s>
The	O
main	O
internetwork	B-Protocol
layer	I-Protocol
protocol	O
is	O
PUP	O
,	O
which	O
roughly	O
corresponds	O
to	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
layer	O
in	O
TCP/IP	B-Protocol
.	O
</s>
<s>
A	O
full	O
PUP	O
network	B-Protocol
address	I-Protocol
consists	O
of	O
an	O
8-bit	O
network	O
number	O
,	O
an	O
8-bit	O
host	O
number	O
,	O
and	O
a	O
16-bit	O
socket	O
number	O
.	O
</s>
<s>
Unlike	O
TCP/IP	B-Protocol
,	O
socket	O
fields	O
are	O
part	O
of	O
the	O
full	O
network	B-Protocol
address	I-Protocol
in	O
the	O
PUP	O
header	B-General_Concept
,	O
so	O
that	O
upper-layer	O
protocols	O
did	O
not	O
need	O
to	O
implement	O
their	O
own	O
demultiplexing	O
;	O
PUP	O
also	O
supplies	O
packet	B-Protocol
types	O
(	O
again	O
,	O
unlike	O
IP	O
)	O
.	O
</s>
<s>
Also	O
,	O
an	O
optional	O
2-byte	O
checksum	O
covers	O
the	O
entire	O
packet	B-Protocol
.	O
</s>
<s>
PUP	O
packets	B-Protocol
are	O
up	O
to	O
554	O
bytes	O
long	O
(	O
including	O
the	O
20	O
byte	O
PUP	O
header	B-General_Concept
)	O
,	O
and	O
the	O
checksum	O
.	O
</s>
<s>
This	O
is	O
a	O
smaller	O
packet	B-Protocol
size	O
than	O
IP	O
,	O
which	O
requires	O
all	O
hosts	O
to	O
support	O
a	O
minimum	O
of	O
576	O
bytes	O
(	O
but	O
allows	O
packets	B-Protocol
of	O
up	O
to	O
65K	O
bytes	O
,	O
if	O
the	O
hosts	O
support	O
them	O
)	O
;	O
individual	O
PUP	O
host	O
pairs	O
on	O
a	O
particular	O
network	O
might	O
use	O
larger	O
packets	B-Protocol
,	O
but	O
no	O
PUP	O
router	O
is	O
required	O
to	O
handle	O
them	O
.	O
</s>
<s>
Larger	O
packets	B-Protocol
can	O
be	O
fragmented	O
.	O
</s>
<s>
A	O
protocol	O
named	O
the	O
Gateway	O
Information	O
Protocol	O
(	O
an	O
ancestor	O
of	O
RIP	B-Protocol
)	O
is	O
used	O
as	O
both	O
the	O
routing	B-Protocol
protocol	I-Protocol
,	O
and	O
for	O
hosts	O
to	O
discover	O
routers	O
.	O
</s>
<s>
PUP	O
also	O
includes	O
a	O
simple	O
echo	O
protocol	O
at	O
the	O
internetwork	B-Protocol
layer	I-Protocol
,	O
similar	O
to	O
IP	O
's	O
ping	B-Protocol
,	O
but	O
operating	O
at	O
a	O
lower	O
level	O
.	O
</s>
<s>
The	O
second	O
was	O
the	O
primary	O
transport	O
layer	O
protocol	O
,	O
Byte	O
Stream	O
Protocol	O
(	O
BSP	O
)	O
,	O
which	O
was	O
analogous	O
to	O
TCP	B-Protocol
.	O
</s>
<s>
Like	O
TCP	B-Protocol
,	O
BSP	O
's	O
semantics	O
and	O
operation	O
were	O
in	O
terms	O
of	O
bytes	O
;	O
this	O
was	O
discarded	O
in	O
favour	O
of	O
packets	B-Protocol
for	O
the	O
equivalent	O
protocol	O
in	O
XNS	B-Protocol
,	O
Sequenced	O
Packet	B-Protocol
Protocol	O
.	O
</s>
<s>
Some	O
of	O
them	O
,	O
such	O
as	O
Telnet	B-Protocol
and	O
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
,	O
were	O
basically	O
the	O
same	O
protocols	O
as	O
used	O
on	O
the	O
ARPANET	O
(	O
much	O
as	O
occurred	O
with	O
the	O
TCP/IP	B-Protocol
suite	I-Protocol
)	O
.	O
</s>
<s>
the	O
ARPANET	O
already	O
made	O
heavy	O
use	O
of	O
remote	O
management	O
for	O
controlling	O
the	O
Interface	B-Protocol
Message	I-Protocol
Processors	I-Protocol
which	O
made	O
it	O
up	O
)	O
.	O
</s>
<s>
PuP	O
showed	O
that	O
internetworking	B-Architecture
ideas	O
were	O
feasible	O
,	O
influenced	O
the	O
design	O
work	O
on	O
TCP/IP	B-Protocol
,	O
and	O
laid	O
a	O
foundation	O
for	O
the	O
later	O
XNS	B-Protocol
protocols	O
.	O
</s>
<s>
The	O
biggest	O
impact	O
of	O
PuP	O
was	O
probably	O
as	O
a	O
key	O
component	O
of	O
the	O
office	O
of	O
the	O
future	O
model	O
first	O
demonstrated	O
at	O
Xerox	O
PARC	O
;	O
that	O
demonstration	O
would	O
not	O
have	O
been	O
anything	O
like	O
as	O
powerful	O
as	O
it	O
was	O
without	O
all	O
the	O
capabilities	O
that	O
a	O
working	O
internetwork	B-Architecture
provided	O
.	O
</s>
<s>
The	O
Gateway	O
Information	O
Protocol	O
's	O
descendant	O
,	O
RIP	B-Protocol
(	O
with	O
minor	O
modifications	O
to	O
carry	O
the	O
addresses	O
of	O
any	O
protocol	B-Protocol
family	I-Protocol
)	O
,	O
remains	O
in	O
use	O
today	O
in	O
other	O
protocol	B-Protocol
suites	I-Protocol
,	O
including	O
TCP/IP	B-Protocol
.	O
</s>
<s>
One	O
version	O
of	O
RIP	B-Protocol
served	O
as	O
one	O
of	O
the	O
initial	O
so-called	O
interior	B-Protocol
gateway	I-Protocol
protocols	I-Protocol
for	O
the	O
growing	O
Internet	O
,	O
before	O
the	O
arrival	O
of	O
the	O
more	O
modern	O
OSPF	B-Protocol
and	O
IS-IS	B-Protocol
.	O
</s>
<s>
It	O
is	O
still	O
in	O
use	O
as	O
an	O
interior	B-Protocol
routing	I-Protocol
protocol	I-Protocol
,	O
in	O
small	O
sites	O
with	O
simple	O
requirements	O
.	O
</s>
<s>
In	O
terms	O
of	O
flaws	O
,	O
the	O
PUP	O
protocol	B-Protocol
family	I-Protocol
was	O
not	O
device	O
independent	O
,	O
in	O
modern	O
terminology	O
the	O
IP	O
and	O
MAC	O
layers	O
were	O
combined	O
into	O
a	O
single	O
layer	O
,	O
which	O
made	O
wide	O
scale	O
adoption	O
difficult	O
.	O
</s>
<s>
For	O
this	O
reason	O
a	O
successor	O
,	O
the	O
XNS	B-Protocol
(	O
Xerox	O
Networking	O
System	O
)	O
was	O
developed	O
by	O
the	O
Xerox	O
Office	O
Systems	O
Division	O
using	O
many	O
of	O
the	O
ideas	O
of	O
PUP	O
,	O
but	O
also	O
including	O
a	O
globally	O
unique	O
48-bit	O
host	O
identifier	O
(	O
which	O
became	O
MAC	O
address	O
in	O
DIX	O
v2	O
and	O
later	O
IEEE	O
802.3	O
)	O
which	O
solved	O
these	O
problems	O
:	O
</s>
