<s>
Direct	O
Connect	O
clients	B-Protocol
connect	O
to	O
a	O
central	O
hub	B-Protocol
and	O
can	O
download	B-Application
files	B-Operating_System
directly	O
from	O
one	O
another	O
.	O
</s>
<s>
Hubs	B-Protocol
feature	O
a	O
list	O
of	O
clients	B-Protocol
or	O
users	O
connected	O
to	O
them	O
.	O
</s>
<s>
Users	O
can	O
search	O
for	O
files	B-Operating_System
and	O
download	B-Application
them	O
from	O
other	O
clients	B-Protocol
,	O
as	O
well	O
as	O
chat	O
with	O
other	O
users	O
.	O
</s>
<s>
Hess	O
released	O
a	O
new	O
version	O
of	O
Direct	O
Connect	O
,	O
requiring	O
a	O
simple	O
encryption	O
key	O
to	O
initiate	O
a	O
connection	O
,	O
locking	O
out	O
third-party	O
clients	B-Protocol
.	O
</s>
<s>
Some	O
time	O
after	O
,	O
DClite	O
was	O
rewritten	O
as	O
Open	O
Direct	O
Connect	O
with	O
the	O
purpose	O
of	O
having	O
an	O
MDI	O
user	O
interface	O
and	O
using	O
plug-ins	O
for	O
file	O
sharing	O
protocols	O
(	O
similar	O
to	O
MLDonkey	B-Protocol
)	O
.	O
</s>
<s>
Open	O
Direct	O
Connect	O
also	O
did	O
not	O
have	O
complete	O
support	O
for	O
the	O
full	O
file	O
sharing	O
aspects	O
of	O
the	O
protocol	O
,	O
but	O
a	O
port	O
to	O
Java	B-Device
,	O
however	O
,	O
did	O
.	O
</s>
<s>
Later	O
on	O
,	O
other	O
clients	B-Protocol
such	O
as	O
DCTC	O
(	O
Direct	O
Connect	O
Text	O
Client	O
)	O
and	O
DC++	B-Language
became	O
popular	O
.	O
</s>
<s>
As	O
clients	B-Protocol
connect	O
to	O
a	O
central	O
source	O
of	O
distribution	O
(	O
the	O
hub	B-Protocol
)	O
of	O
information	O
,	O
the	O
hub	B-Protocol
requires	O
a	O
substantial	O
amount	O
of	O
upload	O
bandwidth	O
available	O
.	O
</s>
<s>
There	O
is	O
no	O
official	O
specification	O
of	O
the	O
protocol	O
,	O
meaning	O
that	O
every	O
client	O
and	O
hub	B-Protocol
(	O
besides	O
the	O
original	O
NeoModus	O
client	O
and	O
hub	B-Protocol
)	O
has	O
been	O
forced	O
to	O
reverse	O
engineer	O
the	O
information	O
.	O
</s>
<s>
For	O
example	O
,	O
when	O
a	O
client	O
connects	O
to	O
a	O
hub	B-Protocol
's	O
socket	B-Protocol
,	O
the	O
hub	B-Protocol
is	O
first	O
to	O
respond	O
to	O
the	O
client	O
.	O
</s>
<s>
The	O
protocol	O
lacks	O
a	O
specified	O
default	O
character	B-General_Concept
encoding	I-General_Concept
for	O
clients	B-Protocol
or	O
hubs	B-Protocol
.	O
</s>
<s>
The	O
original	O
client	O
and	O
hub	B-Protocol
use	O
ASCII	B-Protocol
encoding	O
instead	O
of	O
that	O
of	O
the	O
Operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Port	O
411	O
is	O
the	O
default	O
port	O
for	O
hubs	B-Protocol
,	O
and	O
412	O
for	O
client-to-client	O
connections	O
.	O
</s>
<s>
Hub	B-Protocol
addresses	O
are	O
in	O
the	O
following	O
form	O
:	O
dchub://example.com[:411],	O
where	O
411	O
is	O
an	O
optional	O
port	O
.	O
</s>
<s>
There	O
is	O
no	O
global	O
identification	O
scheme	O
;	O
instead	O
,	O
users	O
are	O
identified	O
with	O
their	O
nickname	O
on	O
a	O
hub-to-hub	O
basis	O
.	O
</s>
<s>
The	O
ability	O
to	O
kick	O
or	O
move	O
(	O
redirect	O
)	O
a	O
user	O
to	O
another	O
hub	B-Protocol
is	O
supported	O
by	O
the	O
protocol	O
.	O
</s>
<s>
If	O
a	O
user	O
is	O
kicked	O
,	O
the	O
hub	B-Protocol
is	O
not	O
required	O
to	O
give	O
that	O
user	O
a	O
specific	O
reason	O
,	O
and	O
there	O
is	O
no	O
restriction	O
on	O
where	O
a	O
user	O
can	O
be	O
redirected	O
to	O
.	O
</s>
<s>
However	O
,	O
if	O
another	O
client	O
in	O
power	O
instructs	O
the	O
hub	B-Protocol
to	O
kick	O
,	O
that	O
client	O
may	O
send	O
out	O
a	O
notification	O
message	O
before	O
doing	O
so	O
.	O
</s>
<s>
There	O
is	O
no	O
HTTP	B-Protocol
referer	I-Protocol
equivalent	O
.	O
</s>
<s>
Hubs	B-Protocol
may	O
send	O
out	O
user	O
commands	O
to	O
clients	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
the	O
hub	B-Protocol
cannot	O
send	O
a	O
user	O
command	O
that	O
will	O
trigger	O
the	O
default	O
browser	O
to	O
visit	O
a	O
website	O
.	O
</s>
<s>
It	O
can	O
,	O
however	O
,	O
add	O
the	O
command	O
"	O
+rules	O
"	O
(	O
where	O
'	O
+	O
 '	O
indicates	O
to	O
the	O
hub	B-Protocol
that	O
it	O
's	O
a	O
command	O
-	O
this	O
may	O
vary	O
)	O
to	O
display	O
the	O
hub	B-Protocol
's	O
rules	O
.	O
</s>
<s>
These	O
slots	O
denote	O
the	O
number	O
of	O
people	O
that	O
are	O
allowed	O
to	O
download	B-Application
from	O
a	O
user	O
at	O
any	O
given	O
time	O
and	O
are	O
controlled	O
by	O
the	O
client	O
.	O
</s>
<s>
In	O
client-to-client	O
connections	O
,	O
the	O
parties	O
generate	O
a	O
random	O
number	O
to	O
see	O
who	O
should	O
be	O
allowed	O
to	O
download	B-Application
first	O
,	O
and	O
the	O
client	O
with	O
the	O
greater	O
number	O
wins	O
.	O
</s>
<s>
Transporting	O
downloads	B-Application
and	O
connecting	O
to	O
the	O
hub	B-Protocol
requires	O
TCP	B-Protocol
,	O
while	O
active	O
searches	O
use	O
UDP	B-Protocol
.	O
</s>
<s>
Clients	B-Protocol
using	O
active	O
mode	O
can	O
download	B-Application
from	O
anyone	O
else	O
on	O
the	O
network	O
,	O
while	O
clients	B-Protocol
using	O
passive	O
mode	O
users	O
can	O
only	O
download	B-Application
from	O
active	O
users	O
.	O
</s>
<s>
In	O
NeoModus	O
Direct	O
Connect	O
,	O
passive	O
mode	O
users	O
receive	O
other	O
passive	O
mode	O
users	O
 '	O
search	O
results	O
,	O
but	O
the	O
user	O
will	O
not	O
be	O
able	O
to	O
download	B-Application
anything	O
.	O
</s>
<s>
In	O
DC++	B-Language
,	O
users	O
will	O
not	O
receive	O
those	O
search	O
results	O
.	O
</s>
<s>
If	O
a	O
user	O
has	O
searched	O
,	O
DC++	B-Language
will	O
respond	O
with	O
ten	O
search	O
results	O
when	O
the	O
user	O
is	O
in	O
active	O
mode	O
and	O
five	O
when	O
the	O
user	O
is	O
in	O
passive	O
mode	O
.	O
</s>
<s>
Passive	O
clients	B-Protocol
will	O
be	O
sent	O
search	O
results	O
through	O
the	O
hub	B-Protocol
,	O
while	O
active	O
clients	B-Protocol
will	O
receive	O
the	O
results	O
directly	O
.	O
</s>
<s>
Protocol	O
delimiters	B-Algorithm
are	O
"	O
$	O
"	O
,	O
"	O
|	O
"	O
,	O
and	O
.	O
</s>
<s>
For	O
some	O
reason	O
that	O
escape	O
sequence	O
was	O
ignored	O
by	O
DC++	B-Language
developers	O
and	O
they	O
use	O
HTML	B-Language
equivalent	O
if	O
these	O
characters	O
are	O
to	O
be	O
viewed	O
by	O
the	O
user	O
.	O
</s>
<s>
The	O
authors	O
of	O
DC++	B-Language
also	O
proposed	O
a	O
complete	O
replacement	O
of	O
the	O
Direct	O
Connect	O
protocol	O
called	O
ADC	O
,	O
or	O
unofficially	O
,	O
Advanced	O
Direct	O
Connect	O
.	O
</s>
<s>
ADC	O
uses	O
the	O
same	O
network	B-Architecture
topology	I-Architecture
,	O
concepts	O
,	O
and	O
terminology	O
as	O
the	O
original	O
protocol	O
.	O
</s>
<s>
One	O
example	O
of	O
an	O
added	O
feature	O
to	O
the	O
protocol	O
,	O
in	O
comparison	O
with	O
the	O
original	O
protocol	O
,	O
is	O
the	O
broadcasting	O
of	O
Tiger-Tree	B-Algorithm
Hashing	I-Algorithm
of	O
shared	O
files	B-Operating_System
(	O
TTH	O
)	O
.	O
</s>
<s>
The	O
advantages	O
of	O
this	O
include	O
verifying	O
that	O
a	O
file	O
is	O
downloaded	B-Application
correctly	O
,	O
and	O
the	O
ability	O
to	O
find	O
files	B-Operating_System
independently	O
of	O
their	O
names	O
.	O
</s>
<s>
As	O
the	O
protocol	O
allows	O
hubs	B-Protocol
to	O
redirect	O
users	O
to	O
other	O
hubs	B-Protocol
,	O
malicious	O
hubs	B-Protocol
have	O
redirected	O
users	O
to	O
places	O
other	O
than	O
real	O
Direct	O
Connect	O
hubs	B-Protocol
,	O
effectively	O
causing	O
a	O
Distributed	O
Denial	O
of	O
Service	O
attack	O
.	O
</s>
<s>
The	O
hubs	B-Protocol
may	O
alter	O
the	O
IP	B-Protocol
in	O
client	O
to	O
client	O
connections	O
,	O
pointing	O
to	O
a	O
potential	O
victim	O
.	O
</s>
<s>
As	O
of	O
February	O
2009	O
,	O
an	O
extension	O
for	O
clients	B-Protocol
was	O
proposed	O
in	O
order	O
for	O
the	O
attacked	O
party	O
to	O
find	O
out	O
the	O
hub	B-Protocol
sending	O
the	O
connecting	O
users	O
.	O
</s>
