|
URL:
http://www.iec.org/online/tutorials/hfc_tele/
HFC architecture uses fiber to carry voice, video and data from the headend or central office to the
optical node serving a neighborhood. At the optical node, downstream optical
signal is converted to an electrical signal and carried via coax to drops at
customer locations where a service unit separates video, data and telephony
signals for direct connection to customer devices (televisions, computers,
telephones, etc.). A single optical node will typically support a number of
coaxial distribution feeds. Noise on the uplink direction within an HFC network
is an issue. HFC networks mainly provide asymmetrical services - i.e. broadcast
services from the cable operator to the subscriber - with a limited return
path. Due to the popularity of bi-directional services such as Video-on-Demand,
high-speed Internet and Voice over IP, cable operators
have begun plant upgrades that provide these services. Many CATV networks use
HFC.
Main Features of Technology
|
Technology
|
A
combination of fiber cable and coaxial cable for distributing signal
|
|
Bandwidth
|
Broadband
|
|
Operation
|
A local
CATV company usually provides fiber cable, say, to the curbside (FTTC) of a
residence. The fiber then connects with a coaxial cable inside the residence.
This is how cable TV is delivered to the home from the CATV headend. The same
concept applies to delivering data to a commercial or industrial customer’s
facility if it already has CATV connection. At the CATV headend, current technology
calls for using a cable modem to feed data traffic into the PSTN network or
other public network
|
|
Capacity
|
Depends
upon the design of the system; fiber capacity is limited by end equipment;
coaxial by need to support both TV and data downloads
|
|
Coverage
|
Same as
cable TV
|
|
Data rate
|
The
theoretical size of the cable link is very large-a total of some 735 MHz
usable bandwidth. HFC divides the total bandwidth into a downstream (to the
home) band and an upstream (to the hub) band. The downstream band typically
occupies 50-750 MHz, while the upstream band typically occupies from 5-40 MHz
|
|
No. of
channels
|
Slow speed
devices can be groomed into higher speed channels by using CATV multiplex
equipment at the fiber node
|
|
Multiplexing
|
Data can
be multiplexed with video via the CATV network
|
|
Power
|
CATV
provides the necessary powering of the local equipment
|
|
Regulatory
|
No
licensing required
|
Key Advantages
|
Coverage
|
Takes
advantage of existing cable TV network and eliminates the need for any new
infrastructure
|
|
Interference
|
None
|
|
Security
|
Very
difficult to be tapped into by others
|
|
Reliability
|
Very high
because it is a cabled system. Question is how well will the provider support
the network
|
|
Cost
|
Radio
frequency components required for cable modem operation are inexpensive
|
Key Disadvantages
|
Data rate
|
The medium
is designed primarily for downstream communication (TV)
|
|
Upstream
channel
|
5-50MHz
bandwidth and is usually noisy, needs filtering and cannot support higher
speed data
Service
providers do not make upstream channel robust due to lack of use
Will be
shared in the future and may become overloaded due to heavy traffic
|
|
Cost
|
If remote
device is not located near a TV connection point, may need extensive premise
re-wiring
|
Keywords:
physical layer, high speed, Fiber optic, Coax, Access, CATV
|
