<s>
A	O
terminal	B-Device
server	I-Device
connects	O
devices	O
with	O
a	O
serial	B-Protocol
port	I-Protocol
to	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
.	O
</s>
<s>
Products	O
marketed	O
as	O
terminal	B-Device
servers	I-Device
can	O
be	O
very	O
simple	O
devices	O
that	O
do	O
not	O
offer	O
any	O
security	O
functionality	O
,	O
such	O
as	O
data	O
encryption	O
and	O
user	O
authentication	O
.	O
</s>
<s>
The	O
primary	O
application	O
scenario	O
is	O
to	O
enable	O
serial	O
devices	O
to	O
access	O
network	O
server	O
applications	O
,	O
or	O
vice	O
versa	O
,	O
where	O
security	O
of	O
the	O
data	O
on	O
the	O
LAN	B-General_Concept
is	O
not	O
generally	O
an	O
issue	O
.	O
</s>
<s>
There	O
are	O
also	O
many	O
terminal	B-Device
servers	I-Device
on	O
the	O
market	O
that	O
have	O
highly	O
advanced	O
security	O
functionality	O
to	O
ensure	O
that	O
only	O
qualified	O
personnel	O
can	O
access	O
various	O
servers	O
and	O
that	O
any	O
data	O
that	O
is	O
transmitted	O
across	O
the	O
LAN	B-General_Concept
,	O
or	O
over	O
the	O
Internet	O
,	O
is	O
encrypted	O
.	O
</s>
<s>
Usually	O
,	O
companies	O
that	O
need	O
a	O
terminal	B-Device
server	I-Device
with	O
these	O
advanced	O
functions	O
want	O
to	O
remotely	O
control	O
,	O
monitor	O
,	O
diagnose	O
and	O
troubleshoot	O
equipment	O
over	O
a	O
telecommunications	O
network	O
.	O
</s>
<s>
A	O
console	B-Device
server	I-Device
(	O
also	O
referred	O
to	O
as	O
console	B-Device
access	I-Device
server	I-Device
,	O
console	O
management	O
server	O
,	O
serial	O
concentrator	O
,	O
or	O
serial	B-Device
console	I-Device
server	I-Device
)	O
is	O
a	O
device	O
or	O
service	O
that	O
provides	O
access	O
to	O
the	O
system	B-Device
console	I-Device
of	O
a	O
computing	O
device	O
via	O
networking	O
technologies	O
.	O
</s>
<s>
Although	O
primarily	O
used	O
as	O
an	O
Interface	B-Protocol
Message	I-Protocol
Processor	I-Protocol
starting	O
in	O
1971	O
,	O
the	O
Honeywell	B-Device
316	I-Device
could	O
also	O
be	O
configured	O
as	O
a	O
Terminal	B-Device
Interface	I-Device
Processor	I-Device
(	O
TIP	O
)	O
AND	O
PROVIDE	O
terminal	B-Device
server	I-Device
support	O
for	O
up	O
to	O
63	O
ASCII	B-Protocol
serial	O
terminals	O
through	O
a	O
multi-line	O
controller	O
in	O
place	O
of	O
one	O
of	O
the	O
hosts	O
.	O
</s>
<s>
Historically	O
,	O
a	O
terminal	B-Device
server	I-Device
was	O
a	O
device	O
that	O
attached	O
to	O
serial	O
RS-232	O
devices	O
,	O
such	O
as	O
"	O
green	O
screen	O
"	O
text	O
terminals	O
or	O
serial	O
printers	O
,	O
and	O
transported	O
traffic	O
via	O
TCP/IP	B-Protocol
,	O
Telnet	B-Protocol
,	O
SSH	B-Protocol
or	O
other	O
vendor-specific	O
network	O
protocols	O
(	O
e.g.	O
,	O
LAT	B-General_Concept
)	O
via	O
an	O
Ethernet	O
connection	O
.	O
</s>
<s>
Digital	O
Equipment	O
Corporation	O
's	O
DECserver	B-Device
100	O
(	O
1985	O
)	O
,	O
200	O
(	O
1986	O
)	O
and	O
300	O
(	O
1991	O
)	O
are	O
early	O
examples	O
of	O
this	O
technology	O
.	O
</s>
<s>
(	O
An	O
earlier	O
version	O
of	O
this	O
product	O
,	O
known	O
as	O
the	O
DECSA	B-Device
Terminal	B-Device
Server	I-Device
was	O
actually	O
a	O
test-bed	O
or	O
proof-of-concept	O
for	O
using	O
the	O
proprietary	O
LAT	B-General_Concept
protocol	I-General_Concept
in	O
commercial	O
production	O
networks	O
.	O
)	O
</s>
<s>
With	O
the	O
introduction	O
of	O
inexpensive	O
flash	B-Device
memory	I-Device
components	O
,	O
Digital	O
's	O
later	O
DECserver	B-Device
700	O
(	O
1991	O
)	O
and	O
900	O
(	O
1995	O
)	O
no	O
longer	O
shared	O
with	O
their	O
earlier	O
units	O
the	O
need	O
to	O
download	O
their	O
software	O
from	O
a	O
"	O
load	O
host	O
"	O
(	O
usually	O
a	O
Digital	O
VAX	B-Device
or	O
Alpha	O
)	O
using	O
Digital	O
's	O
proprietary	O
Maintenance	B-Operating_System
Operations	I-Operating_System
Protocol	I-Operating_System
(	O
MOP	O
)	O
.	O
</s>
<s>
In	O
fact	O
,	O
these	O
later	O
terminal	B-Device
server	I-Device
products	O
also	O
included	O
much	O
larger	O
flash	B-Device
memory	I-Device
and	O
full	O
support	O
for	O
the	O
Telnet	B-Protocol
part	O
of	O
the	O
TCP/IP	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
Many	O
other	O
companies	O
entered	O
the	O
terminal-server	O
market	O
with	O
devices	O
pre-loaded	O
with	O
software	O
fully	O
compatible	O
with	O
LAT	B-General_Concept
and	O
Telnet	B-Protocol
.	O
</s>
<s>
A	O
"	O
terminal	B-Device
server	I-Device
"	O
is	O
used	O
many	O
ways	O
but	O
from	O
a	O
basic	O
sense	O
if	O
a	O
user	O
has	O
a	O
serial	O
device	O
and	O
they	O
need	O
to	O
move	O
data	O
over	O
the	O
LAN	B-General_Concept
,	O
this	O
is	O
the	O
product	O
they	O
need	O
.	O
</s>
<s>
Raw	O
TCP	O
socket	O
connection	O
:	O
A	O
raw	O
TCP	O
socket	O
connection	O
which	O
can	O
be	O
initiated	O
from	O
the	O
terminal	B-Device
server	I-Device
or	O
from	O
the	O
remote	O
host/server	O
.	O
</s>
<s>
TCP	O
sessions	O
can	O
be	O
initiated	O
from	O
the	O
TCP	O
server	O
application	O
or	O
from	O
the	O
terminal	B-Device
server	I-Device
.	O
</s>
<s>
Raw	O
UDP	O
socket	O
connection	O
:	O
For	O
use	O
with	O
UDP	O
based	O
applications	O
,	O
terminal	B-Device
servers	I-Device
can	O
convert	O
serial	O
equipment	O
data	O
for	O
transport	O
across	O
UDP	O
packets	O
on	O
a	O
point-to-point	O
basis	O
or	O
shared	O
across	O
multiple	O
devices	O
.	O
</s>
<s>
Console	O
management	O
-	O
reverse	B-Protocol
Telnet	I-Protocol
,	O
reverse	O
SSH	B-Protocol
:	O
In	O
console	O
management	O
terminology	O
,	O
users	O
can	O
use	O
reverse	B-Protocol
Telnet	I-Protocol
or	O
SSH	B-Protocol
to	O
connect	O
to	O
a	O
serial	O
device	O
.	O
</s>
<s>
They	O
run	O
Telnet	B-Protocol
or	O
SSH	B-Protocol
on	O
their	O
client	O
(	O
PC	O
)	O
and	O
attach	O
to	O
the	O
terminal	B-Device
server	I-Device
,	O
then	O
connect	O
to	O
the	O
serial	O
device	O
.	O
</s>
<s>
In	O
this	O
application	O
,	O
terminal	B-Device
servers	I-Device
are	O
also	O
called	O
console	B-Device
servers	I-Device
because	O
they	O
are	O
used	O
to	O
connect	O
to	O
console	B-Protocol
ports	I-Protocol
which	O
are	O
found	O
on	O
products	O
like	O
routers	O
,	O
PBXes	O
,	O
switches	O
and	O
servers	O
(	O
Linux	B-Application
or	O
Sun	O
)	O
.	O
</s>
<s>
The	O
idea	O
is	O
to	O
gain	O
access	O
to	O
those	O
devices	O
via	O
their	O
console	B-Protocol
port	I-Protocol
.	O
</s>
<s>
Connect	O
serial-based	O
applications	O
with	O
a	O
COM/TTY	O
port	O
driver	O
:	O
Many	O
software	O
applications	O
have	O
been	O
written	O
to	O
communicate	O
with	O
devices	O
that	O
are	O
directly	O
connected	O
to	O
a	O
server	O
's	O
serial	O
COM	B-Protocol
ports	I-Protocol
(	O
robotic	O
assembly	O
machines	O
,	O
scanners	O
,	O
card	O
readers	O
,	O
sensors	O
,	O
blood	O
analyzers	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
Companies	O
may	O
want	O
to	O
network	O
these	O
applications	O
because	O
the	O
devices	O
that	O
were	O
directly	O
connected	O
to	O
the	O
server	O
's	O
COM	B-Protocol
ports	I-Protocol
need	O
to	O
be	O
moved	O
to	O
a	O
location	O
some	O
distance	O
away	O
from	O
the	O
application	O
server	O
.	O
</s>
<s>
Since	O
the	O
original	O
application	O
was	O
designed	O
to	O
talk	O
directly	O
to	O
a	O
specific	O
COM	B-Protocol
port	I-Protocol
,	O
a	O
solution	O
seamless	O
to	O
both	O
the	O
application	O
and	O
device	O
must	O
be	O
implemented	O
to	O
enable	O
communication	O
across	O
an	O
IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
(	O
i.e.	O
,	O
a	O
solution	O
that	O
makes	O
the	O
application	O
think	O
it	O
is	O
talking	O
directly	O
to	O
a	O
COM	B-Protocol
port	I-Protocol
.	O
)	O
</s>
<s>
In	O
this	O
application	O
,	O
serial	B-Protocol
ports	I-Protocol
can	O
be	O
connected	O
to	O
network	O
servers	O
or	O
workstations	O
running	O
COM	B-Protocol
port	I-Protocol
redirector	O
software	O
operating	O
as	O
a	O
virtual	O
COM	B-Protocol
port	I-Protocol
.	O
</s>
<s>
Many	O
terminal	B-Device
server	I-Device
vendors	O
include	O
COM	B-Protocol
port	I-Protocol
redirector	O
software	O
with	O
their	O
terminal	B-Device
servers	I-Device
.	O
</s>
<s>
This	O
application	O
need	O
is	O
most	O
common	O
in	O
Windows	O
environments	O
,	O
but	O
also	O
exists	O
in	O
Linux	B-Application
and	O
Unix	O
environments	O
.	O
</s>
<s>
Serial	O
tunneling	O
between	O
two	O
serial	O
devices	O
:	O
Serial	O
tunneling	O
enables	O
users	O
to	O
establish	O
a	O
link	O
across	O
Ethernet	O
to	O
a	O
serial	B-Protocol
port	I-Protocol
on	O
another	O
terminal	B-Device
server	I-Device
.	O
</s>
<s>
For	O
example	O
,	O
a	O
user	O
needs	O
to	O
replace	O
RS-232	O
,	O
RS-422	O
or	O
RS-485	O
wire	O
and	O
run	O
their	O
data	O
over	O
Ethernet	O
without	O
making	O
any	O
changes	O
to	O
the	O
server	O
or	O
the	O
ultimate	O
serial	O
device	O
,	O
a	O
user	O
wants	O
to	O
replace	O
a	O
parallel	O
leased	O
line	O
modem	B-Application
network	O
with	O
their	O
parallel	O
Ethernet	O
network	O
,	O
or	O
someone	O
has	O
a	O
pick	O
and	O
place	O
machine	O
that	O
puts	O
ICs	O
on	O
boards	O
,	O
and	O
they	O
want	O
to	O
move	O
the	O
server	O
into	O
a	O
back	O
room	O
where	O
the	O
equipment	O
will	O
be	O
safe	O
from	O
damage	O
.	O
</s>
<s>
Virtual	O
modem	B-Application
:	O
Virtual	O
modem	B-Application
is	O
another	O
example	O
of	O
a	O
back-to-back	O
application	O
.	O
</s>
<s>
It	O
may	O
be	O
used	O
to	O
replace	O
modems	B-Application
but	O
still	O
use	O
an	O
AT	O
command	O
set	O
.	O
</s>
<s>
A	O
console	B-Device
server	I-Device
(	O
console	B-Device
access	I-Device
server	I-Device
,	O
console	O
management	O
server	O
,	O
serial	O
concentrator	O
,	O
or	O
serial	B-Device
console	I-Device
server	I-Device
)	O
is	O
a	O
device	O
or	O
service	O
that	O
provides	O
access	O
to	O
the	O
system	B-Device
console	I-Device
of	O
a	O
computing	O
device	O
via	O
networking	O
technologies	O
.	O
</s>
<s>
Most	O
commonly	O
,	O
a	O
console	B-Device
server	I-Device
provides	O
a	O
number	O
of	O
serial	B-Protocol
ports	I-Protocol
,	O
which	O
are	O
then	O
connected	O
to	O
the	O
serial	B-Protocol
ports	I-Protocol
of	O
other	O
equipment	O
,	O
such	O
as	O
servers	O
,	O
routers	O
or	O
switches	O
.	O
</s>
<s>
The	O
consoles	O
of	O
the	O
connected	O
devices	O
can	O
then	O
be	O
accessed	O
by	O
connecting	O
to	O
the	O
console	B-Device
server	I-Device
over	O
a	O
serial	O
link	O
such	O
as	O
a	O
modem	B-Application
,	O
or	O
over	O
a	O
network	O
with	O
terminal	B-Application
emulator	I-Application
software	O
such	O
as	O
telnet	B-Protocol
or	O
ssh	B-Protocol
,	O
maintaining	O
survivable	O
connectivity	O
that	O
allows	O
remote	O
users	O
to	O
log	O
in	O
the	O
various	O
consoles	O
without	O
being	O
physically	O
nearby	O
.	O
</s>
<s>
Dedicated	O
console	B-Device
server	I-Device
appliances	O
are	O
available	O
from	O
a	O
number	O
of	O
manufacturers	O
in	O
many	O
configurations	O
,	O
with	O
the	O
number	O
of	O
serial	B-Protocol
ports	I-Protocol
ranging	O
from	O
one	O
to	O
96	O
.	O
</s>
<s>
These	O
Console	B-Device
Servers	I-Device
are	O
primarily	O
used	O
for	O
secure	O
remote	O
access	O
to	O
Unix	O
Servers	O
,	O
Linux	B-Application
Servers	O
,	O
switches	O
,	O
routers	O
,	O
firewalls	O
,	O
and	O
any	O
other	O
device	O
on	O
the	O
network	O
with	O
a	O
console	B-Protocol
port	I-Protocol
.	O
</s>
<s>
The	O
purpose	O
is	O
to	O
allow	O
network	O
operations	O
center	O
(	O
NOC	O
)	O
personnel	O
to	O
perform	O
secure	O
remote	O
data	O
center	O
management	O
and	O
out-of-band	B-Application
management	I-Application
of	O
IT	O
assets	O
from	O
anywhere	O
in	O
the	O
world	O
.	O
</s>
<s>
Products	O
marketed	O
as	O
Console	B-Device
Servers	I-Device
usually	O
have	O
highly	O
advanced	O
security	O
functionality	O
to	O
ensure	O
that	O
only	O
qualified	O
personnel	O
can	O
access	O
various	O
servers	O
and	O
that	O
any	O
data	O
that	O
is	O
transmitted	O
across	O
the	O
LAN	B-General_Concept
,	O
or	O
over	O
the	O
Internet	O
,	O
is	O
encrypted	O
.	O
</s>
<s>
Marketing	O
a	O
product	O
as	O
a	O
console	B-Device
server	I-Device
is	O
very	O
application	O
specific	O
because	O
it	O
really	O
refers	O
to	O
what	O
the	O
user	O
wants	O
to	O
do	O
—	O
remotely	O
control	O
,	O
monitor	O
,	O
diagnose	O
and	O
troubleshoot	O
equipment	O
over	O
a	O
network	O
or	O
the	O
Internet	O
.	O
</s>
<s>
Some	O
users	O
have	O
created	O
their	O
own	O
console	B-Device
servers	I-Device
using	O
off-the-shelf	O
commodity	B-Device
computer	I-Device
hardware	O
,	O
usually	O
with	O
multiport	O
serial	B-Protocol
cards	I-Protocol
typically	O
running	O
a	O
slimmed-down	O
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
such	O
as	O
Linux	B-Application
.	O
</s>
<s>
Such	O
"	O
home-grown	O
"	O
console	B-Device
servers	I-Device
can	O
be	O
less	O
expensive	O
,	O
especially	O
if	O
built	O
from	O
components	O
that	O
have	O
been	O
retired	O
in	O
upgrades	O
and	O
allow	O
greater	O
flexibility	O
by	O
putting	O
full	O
control	O
of	O
the	O
software	O
driving	O
the	O
device	O
in	O
the	O
hands	O
of	O
the	O
administrator	O
.	O
</s>
<s>
This	O
includes	O
full	O
access	O
to	O
and	O
configurability	O
of	O
a	O
wide	O
array	O
of	O
security	O
protocols	O
and	O
encryption	O
standards	O
,	O
making	O
it	O
possible	O
to	O
create	O
a	O
console	B-Device
server	I-Device
that	O
is	O
more	O
secure	O
.	O
</s>
<s>
However	O
,	O
this	O
solution	O
may	O
have	O
a	O
higher	O
TCO	O
,	O
less	O
reliability	O
and	O
higher	O
rack-space	O
requirements	O
,	O
since	O
most	O
industrial	O
console	B-Device
servers	I-Device
have	O
the	O
physical	O
dimension	O
of	O
one	O
rack	O
unit	O
(	O
1U	O
)	O
,	O
whereas	O
a	O
desktop	O
computer	O
with	O
full-size	O
PCI	B-Protocol
cards	I-Protocol
requires	O
at	O
least	O
3U	O
,	O
making	O
the	O
home-grown	O
solution	O
more	O
costly	O
in	O
the	O
case	O
of	O
a	O
co-located	B-Application
infrastructure	O
.	O
</s>
<s>
An	O
alternative	O
approach	O
to	O
a	O
console	B-Device
server	I-Device
used	O
in	O
some	O
cluster	B-Architecture
setups	O
is	O
to	O
null-modem	O
wire	O
and	O
daisy-chain	O
consoles	O
to	O
otherwise	O
unused	O
serial	B-Protocol
ports	I-Protocol
on	O
nodes	O
with	O
some	O
other	O
primary	O
function	O
.	O
</s>
