<s>
Hybrid	B-Architecture
fiber-coaxial	I-Architecture
(	O
HFC	O
)	O
is	O
a	O
telecommunications	O
industry	O
term	O
for	O
a	O
broadband	B-General_Concept
network	O
that	O
combines	O
optical	B-Architecture
fiber	I-Architecture
and	O
coaxial	O
cable	O
.	O
</s>
<s>
In	O
a	O
hybrid	B-Architecture
fiber-coaxial	I-Architecture
cable	I-Architecture
system	O
,	O
the	O
television	O
channels	O
are	O
sent	O
from	O
the	O
cable	O
system	O
's	O
distribution	O
facility	O
,	O
the	O
headend	O
,	O
to	O
local	O
communities	O
through	O
optical	B-Architecture
fiber	I-Architecture
subscriber	B-Architecture
lines	I-Architecture
.	O
</s>
<s>
The	O
fiberoptic	B-Architecture
trunk	O
lines	O
provide	O
adequate	O
bandwidth	O
to	O
allow	O
future	O
expansion	O
and	O
new	O
bandwidth-intensive	O
services	O
such	O
as	O
cable	B-Device
internet	I-Device
access	I-Device
through	O
DOCSIS	B-Protocol
.	O
</s>
<s>
The	O
fiber	B-Architecture
optic	I-Architecture
network	O
extends	O
from	O
the	O
cable	O
operators	O
 '	O
master	O
headend	O
,	O
sometimes	O
to	O
regional	O
headends	O
,	O
and	O
out	O
to	O
a	O
neighborhood	O
's	O
hubsite	O
,	O
and	O
finally	O
to	O
an	O
optical	O
to	O
coaxial	O
cable	O
node	O
which	O
serves	O
anywhere	O
from	O
25	O
to	O
2000	O
homes	O
.	O
</s>
<s>
A	O
master	O
headend	O
will	O
usually	O
have	O
satellite	O
dishes	O
for	O
reception	O
of	O
distant	O
video	O
signals	O
as	O
well	O
as	O
IP	B-Protocol
aggregation	O
routers	B-Protocol
.	O
</s>
<s>
The	O
various	O
services	O
are	O
encoded	O
,	O
modulated	B-Application
and	O
upconverted	O
onto	O
RF	O
carriers	O
,	O
combined	O
onto	O
a	O
single	O
electrical	O
signal	O
and	O
inserted	O
into	O
a	O
broadband	B-General_Concept
optical	O
transmitter	O
which	O
in	O
practice	O
is	O
a	O
transmitter	O
module	O
in	O
an	O
"	O
optics	O
platform	O
"	O
or	O
headend	O
platform	O
such	O
as	O
an	O
Arris	O
CH3000	O
.	O
</s>
<s>
This	O
optical	O
transmitter	O
converts	O
the	O
electrical	O
signal	O
to	O
a	O
downstream	O
optically	O
modulated	B-Application
signal	O
that	O
is	O
sent	O
to	O
the	O
nodes	O
.	O
</s>
<s>
Fiber	B-Architecture
optic	I-Architecture
cables	O
connect	O
the	O
headend	O
or	O
hub	O
to	O
the	O
optical	O
nodes	O
in	O
a	O
point-to-point	O
or	O
star	B-Architecture
topology	I-Architecture
,	O
or	O
in	O
some	O
cases	O
,	O
in	O
a	O
protected	O
ring	B-Architecture
topology	I-Architecture
.	O
</s>
<s>
A	O
fiber	B-Architecture
optic	I-Architecture
node	O
has	O
a	O
broadband	B-General_Concept
optical	O
receiver	O
,	O
which	O
converts	O
the	O
downstream	O
optically	O
modulated	B-Application
signal	O
coming	O
from	O
the	O
headend	O
or	O
hub	O
to	O
an	O
electrical	O
signal	O
going	O
to	O
the	O
customers	O
.	O
</s>
<s>
the	O
downstream	O
signal	O
is	O
a	O
RF	O
modulated	B-Application
signal	O
that	O
typically	O
begins	O
at	O
50MHz	O
and	O
ranges	O
from	O
550	O
to	O
1000MHz	O
on	O
the	O
upper	O
end	O
.	O
</s>
<s>
The	O
fiber	B-Architecture
optic	I-Architecture
node	O
also	O
contains	O
a	O
reverse	O
-	O
or	O
return-path	O
transmitter	O
that	O
sends	O
communication	O
from	O
customers	O
back	O
to	O
the	O
headend	O
.	O
</s>
<s>
In	O
North	O
America	O
,	O
this	O
reverse	O
signal	O
is	O
a	O
modulated	B-Application
RF	O
ranging	O
from	O
5	O
–	O
42MHz	O
while	O
in	O
other	O
parts	O
of	O
the	O
world	O
,	O
the	O
range	O
is	O
5	O
–	O
65MHz	O
.	O
</s>
<s>
If	O
there	O
are	O
not	O
many	O
fiber-optic	B-Architecture
cables	I-Architecture
to	O
the	O
node	O
,	O
wavelength	B-Architecture
division	I-Architecture
multiplexing	I-Architecture
can	O
be	O
used	O
to	O
combine	O
multiple	O
optical	O
signals	O
onto	O
the	O
same	O
fiber	O
.	O
</s>
<s>
The	O
tap	O
terminates	O
into	O
a	O
small	O
coaxial	O
drop	O
using	O
a	O
standard	O
screw	O
type	O
connector	O
known	O
as	O
an	O
F	B-Protocol
connector	I-Protocol
.	O
</s>
<s>
By	O
using	O
frequency-division	B-Protocol
multiplexing	I-Protocol
,	O
a	O
HFC	B-Architecture
network	I-Architecture
may	O
carry	O
a	O
variety	O
of	O
services	O
,	O
including	O
analog	O
TV	O
,	O
digital	O
TV	O
(	O
SDTV	B-Device
or	O
HDTV	B-Device
)	O
,	O
video	B-Application
on	I-Application
demand	I-Application
,	O
telephony	O
,	O
and	O
internet	O
traffic	O
.	O
</s>
<s>
The	O
HFC	B-Architecture
network	I-Architecture
is	O
typically	O
operated	O
bi-directionally	O
,	O
meaning	O
that	O
signals	O
are	O
carried	O
in	O
both	O
directions	O
on	O
the	O
same	O
network	O
from	O
the	O
headend/hub	O
office	O
to	O
the	O
home	O
,	O
and	O
from	O
the	O
home	O
to	O
the	O
headend/hub	O
office	O
.	O
</s>
<s>
The	O
very	O
first	O
HFC	B-Architecture
networks	I-Architecture
,	O
and	O
very	O
old	O
unupgraded	O
HFC	B-Architecture
networks	I-Architecture
,	O
are	O
only	O
one-way	O
systems	O
.	O
</s>
<s>
Traditionally	O
,	O
since	O
video	O
content	O
was	O
sent	O
only	O
to	O
the	O
home	O
,	O
the	O
HFC	B-Architecture
network	I-Architecture
was	O
structured	O
to	O
be	O
asymmetrical	O
:	O
one	O
direction	O
has	O
much	O
more	O
data-carrying	O
capacity	O
than	O
the	O
other	O
direction	O
.	O
</s>
<s>
As	O
additional	O
services	O
have	O
been	O
added	O
to	O
the	O
HFC	B-Architecture
network	I-Architecture
,	O
such	O
as	O
Internet	O
access	O
and	O
telephony	O
,	O
the	O
return	O
path	O
is	O
being	O
utilised	O
more	O
.	O
</s>
<s>
Multi-system	O
operators	O
(	O
MSOs	O
)	O
developed	O
methods	O
of	O
sending	O
the	O
various	O
services	O
over	O
RF	O
signals	O
on	O
the	O
fiber	B-Architecture
optic	I-Architecture
and	O
coaxial	O
copper	O
cables	O
.	O
</s>
<s>
The	O
original	O
method	O
to	O
transport	O
video	O
over	O
the	O
HFC	B-Architecture
network	I-Architecture
and	O
,	O
still	O
the	O
most	O
widely	O
used	O
method	O
,	O
is	O
by	O
modulation	B-Application
of	O
standard	O
analog	O
TV	O
channels	O
which	O
is	O
similar	O
to	O
the	O
method	O
used	O
for	O
transmission	O
of	O
over-the-air	O
broadcast	O
.	O
</s>
<s>
To	O
be	O
able	O
to	O
view	O
a	O
digitally	O
modulated	B-Application
channel	O
,	O
home	O
,	O
or	O
customer-premises	O
equipment	O
(	O
CPE	O
)	O
,	O
e.g.	O
</s>
<s>
By	O
using	O
digital	O
video	O
compression	O
techniques	O
,	O
multiple	O
standard	O
and	O
high-definition	B-Device
TV	I-Device
channels	O
can	O
be	O
carried	O
on	O
one	O
6	O
or	O
8MHz	O
frequency	O
carrier	O
,	O
thus	O
increasing	O
the	O
channel	O
carrying	O
capacity	O
of	O
the	O
HFC	B-Architecture
network	I-Architecture
by	O
10	O
times	O
or	O
more	O
versus	O
an	O
all-analog	O
network	O
.	O
</s>
<s>
Digital	O
subscriber	B-Architecture
line	I-Architecture
(	O
DSL	O
)	O
is	O
a	O
technology	O
used	O
by	O
traditional	O
telephone	O
companies	O
to	O
deliver	O
advanced	O
services	O
(	O
high-speed	O
data	O
and	O
sometimes	O
video	O
)	O
over	O
twisted	O
pair	O
copper	O
telephone	O
wires	O
.	O
</s>
<s>
It	O
typically	O
has	O
lower	O
data	O
carrying	O
capacity	O
than	O
HFC	B-Architecture
networks	I-Architecture
and	O
data	O
speeds	O
can	O
be	O
range-limited	O
by	O
line	O
lengths	O
and	O
quality	O
.	O
</s>
<s>
Satellite	O
television	O
competes	O
very	O
well	O
with	O
HFC	B-Architecture
networks	I-Architecture
in	O
delivering	O
broadcast	O
video	O
services	O
.	O
</s>
<s>
Analogous	O
to	O
HFC	O
,	O
fiber	B-Architecture
in	I-Architecture
the	I-Architecture
loop	I-Architecture
(	O
FITL	B-Architecture
)	O
technology	O
is	O
used	O
by	O
telephone	O
local	O
exchange	O
carriers	O
to	O
provide	O
advanced	O
services	O
to	O
telephone	O
customers	O
over	O
the	O
plain	O
old	O
telephone	O
service	O
(	O
POTS	O
)	O
local	B-Architecture
loop	I-Architecture
.	O
</s>
<s>
In	O
the	O
2000s	O
,	O
telecom	O
companies	O
started	O
significant	O
deployments	O
of	O
fiber	B-Architecture
to	I-Architecture
the	I-Architecture
x	I-Architecture
(	O
FTTX	B-Architecture
)	O
such	O
as	O
passive	B-Architecture
optical	I-Architecture
network	I-Architecture
solutions	O
to	O
deliver	O
video	O
,	O
data	O
and	O
voice	O
to	O
compete	O
with	O
cable	O
operators	O
.	O
</s>
