<s>
UUCP	B-Protocol
is	O
an	O
acronym	O
of	O
Unix-to-Unix	B-Protocol
Copy	I-Protocol
.	O
</s>
<s>
The	O
term	O
generally	O
refers	O
to	O
a	O
suite	O
of	O
computer	B-Application
programs	I-Application
and	O
protocols	O
allowing	O
remote	O
execution	O
of	O
commands	O
and	O
transfer	O
of	O
files	O
,	O
email	O
and	O
netnews	B-Application
between	O
computers	O
.	O
</s>
<s>
A	O
command	B-Application
named	O
is	O
one	O
of	O
the	O
programs	O
in	O
the	O
suite	O
;	O
it	O
provides	O
a	O
user	O
interface	O
for	O
requesting	O
file	B-Operating_System
copy	O
operations	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
suite	O
also	O
includes	O
(	O
user	O
interface	O
for	O
remote	O
command	B-Application
execution	O
)	O
,	O
(	O
the	O
communication	O
program	O
that	O
performs	O
the	O
file	B-Operating_System
transfers	O
)	O
,	O
(	O
reports	O
statistics	O
on	O
recent	O
activity	O
)	O
,	O
(	O
execute	O
commands	O
sent	O
from	O
remote	O
machines	O
)	O
,	O
and	O
(	O
reports	O
the	O
UUCP	B-Protocol
name	O
of	O
the	O
local	O
system	O
)	O
.	O
</s>
<s>
Although	O
UUCP	B-Protocol
was	O
originally	O
developed	O
on	O
Unix	B-Application
in	O
the	O
1970s	O
and	O
1980s	O
,	O
and	O
is	O
most	O
closely	O
associated	O
with	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
UUCP	B-Protocol
implementations	O
exist	O
for	O
several	O
non-Unix-like	O
operating	O
systems	O
,	O
including	O
DOS	B-Device
,	O
OS/2	B-Application
,	O
OpenVMS	B-Operating_System
(	O
for	O
VAX	O
hardware	O
only	O
)	O
,	O
AmigaOS	B-Application
,	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
and	O
even	O
CP/M	B-Application
.	O
</s>
<s>
UUCP	B-Protocol
was	O
originally	O
written	O
at	O
AT&T	O
Bell	O
Laboratories	O
by	O
Mike	O
Lesk	O
.	O
</s>
<s>
By	O
1978	O
it	O
was	O
in	O
use	O
on	O
82	O
UNIX	B-Application
machines	O
inside	O
the	O
Bell	O
system	O
,	O
primarily	O
for	O
software	O
distribution	O
.	O
</s>
<s>
It	O
was	O
released	O
in	O
1979	O
as	O
part	O
of	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
.	O
</s>
<s>
The	O
first	O
UUCP	B-Protocol
emails	O
from	O
the	O
U.S.	O
arrived	O
in	O
the	O
United	O
Kingdom	O
in	O
1979	O
and	O
email	O
between	O
the	O
UK	O
,	O
the	O
Netherlands	O
and	O
Denmark	O
started	O
in	O
1980	O
,	O
becoming	O
a	O
regular	O
service	O
via	O
EUnet	O
in	O
1982	O
.	O
</s>
<s>
The	O
original	O
UUCP	B-Protocol
was	O
rewritten	O
by	O
AT&T	O
researchers	O
Peter	O
Honeyman	O
,	O
David	O
A	O
.	O
Nowitz	O
,	O
and	O
Brian	O
E	O
.	O
Redman	O
around	O
1983	O
.	O
</s>
<s>
The	O
rewrite	O
is	O
referred	O
to	O
as	O
HDB	O
or	O
HoneyDanBer	O
uucp	B-Protocol
,	O
which	O
was	O
later	O
enhanced	O
,	O
bug	O
fixed	O
,	O
and	O
repackaged	O
as	O
BNU	O
UUCP	B-Protocol
(	O
"	O
Basic	O
Network	O
Utilities	O
"	O
)	O
.	O
</s>
<s>
Each	O
of	O
these	O
versions	O
was	O
distributed	O
as	O
proprietary	O
software	O
,	O
which	O
inspired	O
Ian	O
Lance	O
Taylor	O
to	O
write	O
a	O
new	O
free	B-Application
software	I-Application
version	O
from	O
scratch	O
in	O
1991	O
.	O
</s>
<s>
Taylor	O
UUCP	B-Protocol
was	O
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
Taylor	O
UUCP	B-Protocol
addressed	O
security	O
holes	O
which	O
allowed	O
some	O
of	O
the	O
original	O
network	O
worms	O
to	O
remotely	O
execute	O
unexpected	O
shell	O
commands	O
.	O
</s>
<s>
Taylor	O
UUCP	B-Protocol
also	O
incorporated	O
features	O
of	O
all	O
previous	O
versions	O
of	O
UUCP	B-Protocol
,	O
allowing	O
it	O
to	O
communicate	O
with	O
any	O
other	O
version	O
and	O
even	O
use	O
similar	O
config	O
file	B-Operating_System
formats	O
from	O
other	O
versions	O
.	O
</s>
<s>
UUCP	B-Protocol
was	O
also	O
implemented	O
for	O
non-UNIX	O
operating	O
systems	O
,	O
most-notably	O
DOS	B-Device
systems	O
.	O
</s>
<s>
FSUUCP	O
formed	O
the	O
basis	O
for	O
many	O
bulletin	B-Application
board	I-Application
system	I-Application
(	O
BBS	O
)	O
packages	O
such	O
as	O
Galacticomm	B-Application
's	O
Major	B-Application
BBS	I-Application
and	O
Mustang	O
Software	O
's	O
Wildcat	B-Protocol
!	I-Protocol
</s>
<s>
BBS	O
to	O
connect	O
to	O
the	O
UUCP	B-Protocol
network	O
and	O
exchange	O
email	O
and	O
Usenet	B-Application
traffic	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
UFGATE	O
(	O
John	O
Galvin	O
,	O
Garry	O
Paxinos	O
,	O
Tim	O
Pozar	O
)	O
was	O
a	O
package	O
that	O
provided	O
a	O
gateway	O
between	O
networks	O
running	O
Fidonet	O
and	O
UUCP	B-Protocol
protocols	O
.	O
</s>
<s>
FSUUCP	O
was	O
the	O
only	O
other	O
implementation	O
of	O
Taylor	O
's	O
enhanced	O
'	O
i	O
 '	O
protocol	O
,	O
a	O
significant	O
improvement	O
over	O
the	O
standard	O
'	O
g	O
 '	O
protocol	O
used	O
by	O
most	O
UUCP	B-Protocol
implementations	O
.	O
</s>
<s>
Before	O
the	O
widespread	O
availability	O
of	O
Internet	O
access	O
,	O
computers	O
were	O
only	O
connected	O
by	O
smaller	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
within	O
a	O
company	O
or	O
organization	O
.	O
</s>
<s>
They	O
were	O
also	O
often	O
equipped	O
with	O
modems	B-Application
so	O
they	O
could	O
be	O
used	O
remotely	O
from	O
character-mode	O
terminals	O
via	O
dial-up	O
telephone	O
lines	O
.	O
</s>
<s>
UUCP	B-Protocol
used	O
the	O
computers	O
 '	O
modems	B-Application
to	O
dial	O
out	O
to	O
other	O
computers	O
,	O
establishing	O
temporary	O
,	O
point-to-point	O
links	O
between	O
them	O
.	O
</s>
<s>
Each	O
system	O
in	O
a	O
UUCP	B-Protocol
network	O
has	O
a	O
list	O
of	O
neighbor	O
systems	O
,	O
with	O
phone	O
numbers	O
,	O
login	O
names	O
and	O
passwords	O
,	O
etc	O
.	O
</s>
<s>
When	O
work	O
(	O
file	B-Operating_System
transfer	O
or	O
command	B-Application
execution	O
requests	O
)	O
is	O
queued	O
for	O
a	O
neighbor	O
system	O
,	O
the	O
program	O
typically	O
calls	O
that	O
system	O
to	O
process	O
the	O
work	O
.	O
</s>
<s>
Over	O
time	O
,	O
dial-up	O
links	O
were	O
replaced	O
by	O
Internet	O
connections	O
,	O
and	O
UUCP	B-Protocol
added	O
a	O
number	O
of	O
new	O
link	B-Protocol
layer	I-Protocol
protocols	O
.	O
</s>
<s>
These	O
newer	O
connections	O
also	O
reduced	O
the	O
need	O
for	O
UUCP	B-Protocol
at	O
all	O
,	O
as	O
newer	O
application	O
protocols	O
developed	O
to	O
take	O
advantage	O
of	O
the	O
new	O
networks	O
.	O
</s>
<s>
Today	O
,	O
UUCP	B-Protocol
is	O
rarely	O
used	O
over	O
dial-up	O
links	O
,	O
but	O
is	O
occasionally	O
used	O
over	O
TCP/IP	B-Protocol
.	O
</s>
<s>
UUCP	B-Protocol
's	O
longevity	O
can	O
be	O
attributed	O
to	O
its	O
low	O
cost	O
,	O
extensive	O
logging	O
,	O
native	O
failover	B-General_Concept
to	O
dialup	O
,	O
and	O
persistent	O
queue	O
management	O
.	O
</s>
<s>
UUCP	B-Protocol
is	O
normally	O
started	O
by	O
having	O
a	O
user	O
log	O
into	O
the	O
target	O
system	O
and	O
then	O
running	O
the	O
UUCP	B-Protocol
program	O
.	O
</s>
<s>
Thus	O
,	O
for	O
automated	O
transfers	O
,	O
another	O
machine	O
simply	O
has	O
to	O
open	O
a	O
modem	B-Application
connection	O
to	O
the	O
called	O
machine	O
and	O
log	O
into	O
the	O
known	O
account	O
.	O
</s>
<s>
When	O
uucico	B-Protocol
runs	O
,	O
it	O
will	O
expect	O
to	O
receive	O
commands	O
from	O
another	O
UUCP	B-Protocol
program	O
on	O
the	O
caller	O
's	O
machine	O
and	O
begin	O
a	O
session	O
.	O
</s>
<s>
On	O
starting	O
,	O
uucico	B-Protocol
will	O
respond	O
by	O
sending	O
an	O
identification	O
string	O
,	O
\20Shere=hostname\0,	O
where	O
\20	O
is	O
the	O
control-P	O
character	O
,	O
and	O
\0	O
is	O
a	O
trailing	O
null	O
.	O
</s>
<s>
The	O
caller	O
's	O
UUCP	B-Protocol
responds	O
with	O
\20Scallername	O
options	O
\0,	O
where	O
options	O
is	O
a	O
string	O
containing	O
zero	O
or	O
more	O
Unix-like	B-Operating_System
option	O
switches	O
.	O
</s>
<s>
These	O
can	O
include	O
packet	O
and	O
window	O
sizes	O
,	O
the	O
maximum	O
supported	O
file	B-Operating_System
size	O
,	O
debugging	O
options	O
,	O
and	O
others	O
.	O
</s>
<s>
If	O
the	O
two	O
systems	O
successfully	O
handshake	O
,	O
the	O
caller	O
will	O
now	O
begin	O
to	O
send	O
a	O
series	O
of	O
file	B-Operating_System
requests	O
.	O
</s>
<s>
S	O
causes	O
a	O
file	B-Operating_System
to	O
be	O
Sent	O
from	O
the	O
caller	O
to	O
the	O
called	O
system	O
(	O
upload	O
)	O
.	O
</s>
<s>
When	O
the	O
S	O
command	B-Application
is	O
received	O
on	O
the	O
called	O
system	O
,	O
it	O
responds	O
with	O
SY	O
if	O
it	O
succeeded	O
and	O
it	O
is	O
ready	O
to	O
accept	O
the	O
file	B-Operating_System
,	O
or	O
SNx	O
if	O
it	O
failed	O
,	O
where	O
x	O
is	O
a	O
failure	O
reason	O
.	O
</s>
<s>
If	O
an	O
SY	O
is	O
received	O
by	O
the	O
caller	O
,	O
it	O
begins	O
uploading	O
the	O
file	B-Operating_System
using	O
the	O
protocol	O
selected	O
during	O
the	O
initial	O
handshake	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
When	O
the	O
transfer	O
is	O
complete	O
,	O
the	O
called	O
system	O
responds	O
with	O
CY	O
if	O
it	O
successfully	O
received	O
the	O
file	B-Operating_System
,	O
or	O
CN5	O
if	O
it	O
failed	O
.	O
</s>
<s>
R	O
is	O
a	O
Request	O
for	O
the	O
called	O
system	O
to	O
send	O
a	O
file	B-Operating_System
to	O
the	O
caller	O
(	O
download	O
)	O
.	O
</s>
<s>
It	O
is	O
otherwise	O
similar	O
to	O
S	O
,	O
using	O
RY	O
and	O
RN	O
to	O
indicate	O
the	O
command	B-Application
was	O
accepted	O
and	O
it	O
will	O
begin	O
to	O
send	O
data	O
or	O
had	O
a	O
problem	O
,	O
and	O
expecting	O
a	O
CY	O
and	O
CN5	O
from	O
the	O
caller	O
at	O
the	O
end	O
of	O
the	O
transfer	O
.	O
</s>
<s>
After	O
sending	O
an	O
H	O
command	B-Application
,	O
the	O
calling	O
system	O
sends	O
a	O
final	O
packet	O
(	O
control-P	O
,	O
six	O
ohs	O
,	O
null-terminator	O
)	O
and	O
the	O
called	O
system	O
responds	O
with	O
(	O
control-P	O
,	O
seven	O
ohs	O
,	O
null-terminator	O
)	O
.	O
</s>
<s>
Some	O
systems	O
will	O
simply	O
hang	O
up	O
on	O
the	O
successful	O
reception	O
of	O
the	O
H	O
command	B-Application
and	O
not	O
bother	O
with	O
the	O
final	O
handshake	O
.	O
</s>
<s>
Within	O
the	O
suite	O
of	O
protocols	O
in	O
UUCP	B-Protocol
,	O
the	O
underlying	O
g-protocol	O
is	O
responsible	O
for	O
transferring	O
information	O
in	O
an	O
error-free	O
form	O
.	O
</s>
<s>
The	O
protocol	O
originated	O
as	O
a	O
general-purpose	O
system	O
for	O
packet	O
delivery	O
,	O
and	O
thus	O
offers	O
a	O
number	O
of	O
features	O
that	O
are	O
not	O
used	O
by	O
the	O
UUCP	B-Protocol
package	O
as	O
a	O
whole	O
.	O
</s>
<s>
These	O
include	O
a	O
secondary	O
channel	O
that	O
can	O
send	O
command	B-Application
data	O
interspersed	O
with	O
a	O
file	B-Operating_System
transfer	O
,	O
and	O
the	O
ability	O
to	O
renegotiate	O
the	O
packet	O
and	O
window	O
sizes	O
during	O
transmission	O
.	O
</s>
<s>
These	O
extra	O
features	O
may	O
not	O
be	O
available	O
in	O
some	O
implementations	O
of	O
the	O
UUCP	B-Protocol
stack	O
.	O
</s>
<s>
TT	O
is	O
the	O
packet	O
type	O
,	O
0	O
for	O
control	O
packets	O
(	O
which	O
also	O
requires	O
K	O
=	O
9	O
to	O
be	O
valid	O
)	O
,	O
1	O
for	O
alternate	O
data	O
(	O
not	O
used	O
in	O
UUCP	B-Protocol
)	O
,	O
2	O
for	O
data	O
,	O
and	O
3	O
indicates	O
a	O
short	O
packet	O
that	O
re-defines	O
the	O
meaning	O
of	O
K	O
.	O
In	O
a	O
data	O
packet	O
,	O
XXX	O
is	O
the	O
packet	O
number	O
for	O
this	O
packet	O
from	O
0	O
to	O
7	O
,	O
and	O
YYY	O
is	O
the	O
last	O
that	O
was	O
received	O
correctly	O
.	O
</s>
<s>
In	O
a	O
control	O
packet	O
,	O
XXX	O
indicates	O
the	O
command	B-Application
and	O
YYY	O
is	O
used	O
for	O
various	O
parameters	O
.	O
</s>
<s>
In	O
theory	O
,	O
a	O
system	O
using	O
4k	O
packets	O
and	O
7	O
packet	O
windows	O
(	O
4096x7	O
)	O
would	O
offer	O
performance	O
matching	O
or	O
beating	O
the	O
best	O
file-transfer	O
protocols	O
like	O
ZMODEM	B-Device
.	O
</s>
<s>
Taylor	O
UUCP	B-Protocol
did	O
not	O
support	O
G	O
,	O
but	O
did	O
support	O
any	O
valid	O
requested	O
window	O
or	O
packet	O
size	O
,	O
so	O
remote	B-Protocol
systems	I-Protocol
starting	O
G	O
would	O
work	O
fine	O
with	O
Taylor	O
's	O
g	O
,	O
while	O
two	O
Taylor	O
systems	O
could	O
negotiate	O
even	O
faster	O
connections	O
.	O
</s>
<s>
Telebit	O
modems	B-Application
used	O
protocol	B-Protocol
spoofing	I-Protocol
to	O
improve	O
the	O
performance	O
of	O
g-protocol	O
transfers	O
by	O
noticing	O
end-of-packet	O
markers	O
being	O
sent	O
to	O
the	O
remote	B-Protocol
system	I-Protocol
and	O
immediately	O
sending	O
an	O
back	O
to	O
the	O
local	O
host	O
,	O
pretending	O
that	O
the	O
remote	B-Protocol
system	I-Protocol
had	O
already	O
received	O
the	O
packet	O
and	O
decoded	O
it	O
correctly	O
.	O
</s>
<s>
The	O
data	O
between	O
the	O
two	O
modems	B-Application
was	O
error-corrected	O
using	O
a	O
proprietary	O
protocol	O
based	O
on	O
MNP	B-Device
that	O
ran	O
over	O
Telebit	O
's	O
half-duplex	O
connections	O
much	O
better	O
than	O
g-protocol	O
would	O
normally	O
,	O
because	O
in	O
the	O
common	O
64x3	O
case	O
the	O
remote	B-Protocol
system	I-Protocol
would	O
be	O
sending	O
a	O
constant	O
stream	O
of	O
s	O
that	O
would	O
overflow	O
the	O
low-speed	O
return	O
channel	O
.	O
</s>
<s>
Combined	O
with	O
the	O
modem	B-Application
's	O
naturally	O
higher	O
data	O
rates	O
,	O
they	O
greatly	O
improved	O
overall	O
throughput	O
and	O
generally	O
performed	O
about	O
seven	O
times	O
the	O
speed	O
of	O
a	O
2400	O
bit/s	O
modem	B-Application
.	O
</s>
<s>
They	O
were	O
widely	O
used	O
on	O
UUCP	B-Protocol
hosts	O
as	O
they	O
could	O
quickly	O
pay	O
for	O
themselves	O
in	O
reduced	O
long-distance	O
charges	O
.	O
</s>
<s>
UUCP	B-Protocol
implementations	O
also	O
include	O
other	O
transfer	O
protocols	O
for	O
use	O
over	O
certain	O
links	O
.	O
</s>
<s>
This	O
was	O
originally	O
intended	O
for	O
use	O
on	O
X.25	B-Protocol
links	O
,	O
which	O
were	O
popular	O
for	O
a	O
time	O
in	O
the	O
1980s	O
.	O
</s>
<s>
It	O
does	O
not	O
packetize	O
data	O
,	O
instead	O
,	O
the	O
entire	O
file	B-Operating_System
is	O
sent	O
as	O
a	O
single	O
long	O
string	O
followed	O
by	O
a	O
whole-file	O
checksum	O
.	O
</s>
<s>
d-protocol	O
was	O
similar	O
to	O
x	O
,	O
but	O
intended	O
for	O
use	O
on	O
Datakit	B-General_Concept
networks	O
that	O
connected	O
many	O
of	O
Bell	O
Labs	O
offices	O
.	O
</s>
<s>
t-protocol	O
originated	O
in	O
the	O
BSD	O
versions	O
of	O
UUCP	B-Protocol
and	O
is	O
designed	O
to	O
run	O
over	O
8-bit	O
error-free	O
TCP/IP	B-Protocol
links	O
.	O
</s>
<s>
It	O
has	O
no	O
error	O
correction	O
at	O
all	O
,	O
and	O
the	O
protocol	O
consists	O
simply	O
of	O
breaking	O
up	O
command	B-Application
and	O
file	B-Operating_System
data	O
into	O
512	O
or	O
1024-byte	O
packets	O
to	O
easily	O
fit	O
within	O
typical	O
TCP	O
frames	O
.	O
</s>
<s>
A	O
simple	O
UUCP	B-Protocol
mail	O
address	O
was	O
formed	O
from	O
the	O
adjacent	O
machine	O
name	O
,	O
an	O
exclamation	O
mark	O
(	O
often	O
pronounced	O
bang	O
)	O
,	O
followed	O
by	O
the	O
user	O
name	O
on	O
the	O
adjacent	O
machine	O
.	O
</s>
<s>
Mail	O
could	O
furthermore	O
be	O
routed	B-Protocol
through	O
the	O
network	O
,	O
traversing	O
any	O
number	O
of	O
intermediate	O
nodes	O
before	O
arriving	O
at	O
its	O
destination	O
.	O
</s>
<s>
Initially	O
,	O
this	O
had	O
to	O
be	O
done	O
by	O
specifying	O
the	O
complete	O
path	O
,	O
with	O
a	O
list	O
of	O
intermediate	O
host	B-Protocol
names	I-Protocol
separated	O
by	O
bangs	O
.	O
</s>
<s>
User	O
barbox	O
!	O
user	O
would	O
generally	O
publish	O
their	O
UUCP	B-Protocol
email	O
address	O
in	O
a	O
form	O
such	O
as	O
…!	O
bigsite	O
!	O
foovax	O
!	O
barbox	O
!	O
user	O
.	O
</s>
<s>
Bang	O
paths	O
of	O
eight	O
to	O
ten	O
machines	O
(	O
or	O
hops	O
)	O
were	O
not	O
uncommon	O
in	O
1981	O
,	O
and	O
late-night	O
dial-up	O
UUCP	B-Protocol
links	O
could	O
cause	O
week-long	O
transmission	O
times	O
.	O
</s>
<s>
The	O
"	O
pseudo-domain	O
"	O
ending	O
.uucp	B-Protocol
was	O
sometimes	O
used	O
to	O
designate	O
a	O
hostname	B-Protocol
as	O
being	O
reachable	O
by	O
UUCP	B-Protocol
networking	O
,	O
although	O
this	O
was	O
never	O
formally	O
registered	O
in	O
the	O
domain	B-Protocol
name	I-Protocol
system	I-Protocol
(	O
DNS	B-Protocol
)	O
as	O
a	O
top-level	O
domain	O
.	O
</s>
<s>
The	O
uucp	B-Protocol
community	O
administered	O
itself	O
and	O
did	O
not	O
mesh	O
well	O
with	O
the	O
administration	O
methods	O
and	O
regulations	O
governing	O
the	O
DNS	B-Protocol
;	O
.uucp	B-Protocol
works	O
where	O
it	O
needs	O
to	O
;	O
some	O
hosts	O
punt	O
mail	O
out	O
of	O
SMTP	B-Protocol
queue	O
into	O
uucp	B-Protocol
queues	O
on	O
gateway	O
machines	O
if	O
a	O
.uucp	B-Protocol
address	O
is	O
recognized	O
on	O
an	O
incoming	O
SMTP	B-Protocol
connection	O
.	O
</s>
<s>
Usenet	B-Application
traffic	O
was	O
originally	O
transmitted	O
over	O
the	O
UUCP	B-Protocol
protocol	O
using	O
bang	O
paths	O
.	O
</s>
<s>
These	O
are	O
still	O
in	O
use	O
within	O
Usenet	B-Application
message	O
format	O
Path	O
header	O
lines	O
.	O
</s>
<s>
They	O
now	O
have	O
only	O
an	O
informational	O
purpose	O
,	O
and	O
are	O
not	O
used	O
for	O
routing	B-Protocol
,	O
although	O
they	O
can	O
be	O
used	O
to	O
ensure	O
that	O
loops	O
do	O
not	O
occur	O
.	O
</s>
<s>
In	O
general	O
,	O
like	O
other	O
older	O
e-mail	O
address	O
formats	O
,	O
bang	O
paths	O
have	O
now	O
been	O
superseded	O
by	O
the	O
"	O
@	O
notation	O
"	O
,	O
even	O
by	O
sites	O
still	O
using	O
UUCP	B-Protocol
.	O
</s>
<s>
A	O
UUCP-only	O
site	O
can	O
register	O
a	O
DNS	B-Protocol
domain	O
name	O
,	O
and	O
have	O
the	O
DNS	B-Protocol
server	O
that	O
handles	O
that	O
domain	O
provide	O
MX	B-Protocol
records	I-Protocol
that	O
cause	O
Internet	O
mail	O
to	O
that	O
site	O
to	O
be	O
delivered	O
to	O
a	O
UUCP	B-Protocol
host	O
on	O
the	O
Internet	O
that	O
can	O
then	O
deliver	O
the	O
mail	O
to	O
the	O
UUCP	B-Protocol
site	O
.	O
</s>
<s>
UUCPNET	O
was	O
the	O
name	O
for	O
the	O
totality	O
of	O
the	O
network	O
of	O
computers	O
connected	O
through	O
UUCP	B-Protocol
.	O
</s>
<s>
Often	O
,	O
particularly	O
in	O
the	O
private	O
sector	O
,	O
UUCP	B-Protocol
links	O
were	O
established	O
without	O
official	O
approval	O
from	O
the	O
companies	O
 '	O
upper	O
management	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
network	O
was	O
constantly	O
changing	O
as	O
new	O
systems	O
and	O
dial-up	O
links	O
were	O
added	O
,	O
others	O
were	O
removed	O
,	O
etc	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
Mapping	O
Project	O
was	O
a	O
volunteer	O
,	O
largely	O
successful	O
effort	O
to	O
build	O
a	O
map	O
of	O
the	O
connections	O
between	O
machines	O
that	O
were	O
open	O
mail	B-Protocol
relays	I-Protocol
and	O
establish	O
a	O
managed	O
namespace	O
.	O
</s>
<s>
These	O
files	O
were	O
then	O
published	O
monthly	O
in	O
a	O
newsgroup	B-Application
dedicated	O
to	O
this	O
purpose	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
map	O
files	O
could	O
then	O
be	O
used	O
by	O
software	O
such	O
as	O
"	O
pathalias	O
"	O
to	O
compute	O
the	O
best	O
route	O
path	O
from	O
one	O
machine	O
to	O
another	O
for	O
mail	O
,	O
and	O
to	O
supply	O
this	O
route	O
automatically	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
maps	O
also	O
listed	O
contact	O
information	O
for	O
the	O
sites	O
,	O
and	O
so	O
gave	O
sites	O
seeking	O
to	O
join	O
UUCPNET	O
an	O
easy	O
way	O
to	O
find	O
prospective	O
neighbors	O
.	O
</s>
<s>
Many	O
UUCP	B-Protocol
hosts	O
,	O
particularly	O
those	O
at	O
universities	O
,	O
were	O
also	O
connected	O
to	O
the	O
Internet	O
in	O
its	O
early	O
years	O
,	O
and	O
e-mail	B-Protocol
gateways	I-Protocol
between	O
Internet	O
SMTP-based	O
mail	O
and	O
UUCP	B-Protocol
mail	O
were	O
developed	O
.	O
</s>
<s>
A	O
user	O
at	O
a	O
system	O
with	O
UUCP	B-Protocol
connections	O
could	O
thereby	O
exchange	O
mail	O
with	O
Internet	O
users	O
,	O
and	O
the	O
Internet	O
links	O
could	O
be	O
used	O
to	O
bypass	O
large	O
portions	O
of	O
the	O
slow	O
UUCP	B-Protocol
network	O
.	O
</s>
<s>
A	O
"	O
UUCP	B-Protocol
zone	O
"	O
was	O
defined	O
within	O
the	O
Internet	O
domain	B-Protocol
namespace	I-Protocol
to	O
facilitate	O
these	O
interfaces	O
.	O
</s>
<s>
With	O
this	O
infrastructure	O
in	O
place	O
,	O
UUCP	B-Protocol
's	O
strength	O
was	O
that	O
it	O
permitted	O
a	O
site	O
to	O
gain	O
Internet	O
e-mail	O
and	O
Usenet	B-Application
connectivity	O
with	O
only	O
a	O
dial-up	B-Application
modem	I-Application
link	O
to	O
another	O
cooperating	O
computer	O
.	O
</s>
<s>
This	O
was	O
at	O
a	O
time	O
when	O
true	O
Internet	O
access	O
required	O
a	O
leased	B-Architecture
data	I-Architecture
line	I-Architecture
providing	O
a	O
connection	O
to	O
an	O
Internet	O
Point	O
of	O
Presence	O
,	O
both	O
of	O
which	O
were	O
expensive	O
and	O
difficult	O
to	O
arrange	O
.	O
</s>
<s>
By	O
contrast	O
,	O
a	O
link	O
to	O
the	O
UUCP	B-Protocol
network	O
could	O
usually	O
be	O
established	O
with	O
a	O
few	O
phone	O
calls	O
to	O
the	O
administrators	O
of	O
prospective	O
neighbor	O
systems	O
.	O
</s>
<s>
uux	B-Protocol
is	O
remote	O
command	B-Application
execution	O
over	O
UUCP	B-Protocol
.	O
</s>
<s>
The	O
uux	B-Protocol
command	B-Application
is	O
used	O
to	O
execute	O
a	O
command	B-Application
on	O
a	O
remote	B-Protocol
system	I-Protocol
,	O
or	O
to	O
execute	O
a	O
command	B-Application
on	O
the	O
local	O
system	O
using	O
files	O
from	O
remote	B-Protocol
systems	I-Protocol
.	O
</s>
<s>
The	O
command	B-Application
is	O
run	O
by	O
the	O
daemon	O
,	O
which	O
handles	O
remote	O
execution	O
requests	O
as	O
simply	O
another	O
kind	O
of	O
file	B-Operating_System
to	O
batch-send	O
to	O
the	O
remote	B-Protocol
system	I-Protocol
whenever	O
a	O
next-hop	O
node	O
is	O
available	O
.	O
</s>
<s>
The	O
remote	B-Protocol
system	I-Protocol
will	O
then	O
execute	O
the	O
requested	O
command	B-Application
and	O
return	O
the	O
result	O
,	O
when	O
the	O
original	O
system	O
is	O
available	O
.	O
</s>
<s>
Even	O
when	O
executing	O
a	O
command	B-Application
on	O
an	O
always-available	O
neighbor	O
,	O
uux	B-Protocol
is	O
not	O
instant	O
.	O
</s>
<s>
UUCP	B-Protocol
usage	O
began	O
to	O
die	O
out	O
with	O
the	O
rise	O
of	O
Internet	O
service	O
providers	O
offering	O
inexpensive	O
SLIP	B-Protocol
and	O
PPP	B-Protocol
services	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
Mapping	O
Project	O
was	O
formally	O
shut	O
down	O
in	O
late	O
2000	O
.	O
</s>
<s>
The	O
UUCP	B-Protocol
protocol	O
has	O
now	O
mostly	O
been	O
replaced	O
by	O
the	O
Internet	O
TCP/IP	B-Protocol
based	O
protocols	O
SMTP	B-Protocol
for	O
mail	O
and	O
NNTP	B-Protocol
for	O
Usenet	B-Application
news	I-Application
.	O
</s>
<s>
In	O
July	O
2012	O
,	O
Dutch	O
Internet	O
provider	O
XS4ALL	O
closed	O
down	O
its	O
UUCP	B-Protocol
service	O
,	O
claiming	O
it	O
was	O
"	O
probably	O
one	O
of	O
the	O
last	O
providers	O
in	O
the	O
world	O
that	O
still	O
offered	O
it	O
"	O
;	O
it	O
had	O
only	O
13	O
users	O
at	O
that	O
time	O
(	O
however	O
prior	O
to	O
its	O
shut-down	O
it	O
had	O
refused	O
requests	O
from	O
new	O
users	O
for	O
several	O
years	O
)	O
.	O
</s>
<s>
One	O
surviving	O
feature	O
of	O
UUCP	B-Protocol
is	O
the	O
chat	O
file	B-Operating_System
format	O
,	O
largely	O
inherited	O
by	O
the	O
Expect	O
software	O
package	O
.	O
</s>
<s>
UUCP	B-Protocol
was	O
in	O
use	O
over	O
special-purpose	O
high	O
cost	O
links	O
(	O
e.g.	O
</s>
<s>
In	O
addition	O
to	O
legacy	O
use	O
,	O
in	O
2021	O
new	O
and	O
innovative	O
UUCP	B-Protocol
uses	O
are	O
growing	O
,	O
especially	O
for	O
telecommunications	O
in	O
the	O
HF	B-Algorithm
band	O
,	O
for	O
example	O
,	O
for	O
communities	O
in	O
the	O
Amazon	O
rainforest	O
for	O
email	O
exchange	O
and	O
other	O
uses	O
.	O
</s>
<s>
A	O
patch	O
to	O
Ian	O
's	O
UUCP	B-Protocol
was	O
contributed	O
to	O
UUCP	B-Protocol
Debian	O
Linux	O
package	O
to	O
adapt	O
for	O
the	O
HERMES	O
(	O
High-Frequency	B-Algorithm
Emergency	O
and	O
Rural	O
Multimedia	O
Exchange	O
System	O
)	O
project	O
,	O
which	O
provides	O
UUCP	B-Protocol
HF	B-Algorithm
connectivity	O
.	O
</s>
<s>
In	O
the	O
mid	O
2000s	O
,	O
UUCP	B-Protocol
over	O
TCP/IP	B-Protocol
(	O
often	O
encrypted	O
,	O
using	O
the	O
SSH	B-Protocol
protocol	O
)	O
was	O
proposed	O
for	O
use	O
when	O
a	O
computer	O
does	O
not	O
have	O
any	O
fixed	O
IP	B-Protocol
addresses	I-Protocol
but	O
is	O
still	O
willing	O
to	O
run	O
a	O
standard	O
mail	B-Protocol
transfer	I-Protocol
agent	I-Protocol
(	O
MTA	O
)	O
like	O
Sendmail	B-Application
or	O
Postfix	B-Application
.	O
</s>
<s>
Bang-like	O
paths	O
are	O
still	O
in	O
use	O
within	O
the	O
Usenet	B-Application
network	O
,	O
though	O
not	O
for	O
routing	B-Protocol
;	O
they	O
are	O
used	O
to	O
record	O
,	O
in	O
the	O
header	O
of	O
a	O
message	O
,	O
the	O
nodes	O
through	O
which	O
that	O
message	O
has	O
passed	O
,	O
rather	O
than	O
to	O
direct	O
where	O
it	O
will	O
go	O
next	O
.	O
</s>
<s>
"	O
Bang	O
path	O
"	O
is	O
also	O
used	O
as	O
an	O
expression	O
for	O
any	O
explicitly	O
specified	O
routing	B-Protocol
path	O
between	O
network	O
hosts	O
.	O
</s>
<s>
That	O
usage	O
is	O
not	O
necessarily	O
limited	O
to	O
UUCP	B-Protocol
,	O
IP	O
routing	B-Protocol
,	O
email	O
messaging	O
,	O
or	O
Usenet	B-Application
.	O
</s>
<s>
The	O
concept	O
of	O
delay-tolerant	B-Protocol
networking	I-Protocol
protocols	O
was	O
revisited	O
in	O
the	O
early	O
2000s	O
.	O
</s>
<s>
Similar	O
techniques	O
as	O
those	O
used	O
by	O
UUCP	B-Protocol
can	O
apply	O
to	O
other	O
networks	O
that	O
experience	O
delay	O
or	O
significant	O
disruption	O
.	O
</s>
