The term hybrid
fiber coax (HFC) was derived from the structure of the cable architecture,
which uses optical transmitters and fiber nodes
interspersed with long cascades of radio frequency (RF) coax amplifiers.
In this network, the fiber provides the high-speed
backbone, and the coax is used to connect end users to the backbone
(CableLabs
or 3Com
diagram). The coaxial portion of the HFC
networks uses a tree-and-branch topology (CableLabs
diagram) with a shared LAN-like structure. Usually,
each optical node serves 500 to 2,000 homes.
Within
this structure, the downstream direction broadcasts RF signals over
the 54-860 MHz spectrum. To maintain acceptable signal-to-noise ratios
to every subscriber on the cable plant, bandwidth beyond 860 MHz cannot
be effectively utilized in the current design.
Current
HFC networks are designed to provide asymmetrical services - i.e.
broadcast services from the cable operator to the subscriber - with
a limited return path. Due to the anticipated popularity of bi-directional
services such as VOD (Video-on-Demand), high-speed Internet and VoIP
(Voice over IP), cable operators have begun massive plant upgrades
that will eventually provide these services nationally.
Narad's Virtual
Fiber solution is initially targeted at cable operators who want to
expand subscriber opportunities to serve SMEs (small to medium-sized
businesses). The solution will enable services including business-grade
telephony, virtual private networking, content distribution, storage
area networking and open Internet access. The company hopes to eventually
market the solution to residential consumers, as well as sell their
chip sets to manufacturers of consumer premise equipment.
The Virtual Fiber
Solution uses bandwidth above the normal cable TV and modem frequencies,
to enable fiber optic capacity within the coaxial portions of the network.
Specifically, it divides the tree-and-branch coaxial network into multiple
point-to-point segments interlinked by Ethernet switching elements.
These new links can then be used to transmit and receive additional
high data-rate signals.
The solution uses
two channels for the 100Mbit/s service (between the standard 860MHz
range and the 1GHz limit) to make up for the fact that existing cable
plant does not have the bandwidth required to handle the 2GHz needed
for the full 1Gbit/s service. The chipset includes both 1Gbit/s and
100Mbit/s, to enable service upgrades using firmware, once legacy equipment
is replaced.
The system consists
of several components, one of which is the Narad Broadband Access Network
(NBAN) discussed in the original WAVE article (and expanded on below).
Other components include the Narad Service Delivery Platform (NSDP),
a bundle of software programs that simplify broadband IP service delivery,
and the Narad Content Management System (NCMS), which helps to manage
and deliver advanced content-based broadband IP services.
The focus of our
tutorial, the NBAN, is a platform that promises to deliver 100 Mbps/1
Gbps symmetrical switched Ethernet over existing HFC networks by placing
Ethernet switches at strategic points in the network. The four hardware
components of the platform include:
Narad Broadband Interface Unit (BIU) - this is the customer premise
device. It functions as the entry point for subscriber services and
serves as an intelligent Integrated Access Device (IAD) to consolidate
diverse traffic flows onto the network. The BIU has a single physical
coax interface that connects it to the HFC network, and two customer
interface ports. One of these ports delivers existing services such
as broadcast television and DOCSIS traffic flows over coax. The other
is a 10/100Base-T interface to connect Ethernet-attached switches,
routers, gateways, or computers.
Narad Subscriber Access Switch (SAS) - this switch resides on
the cable network and combines the operation of a conventional tap
for existing services below 860 MHz and HFC Ethernet switching functions
for the high-speed data channels.
Narad Network Distribution Switch (NDS) - this switch provides the
functions of a distribution amplifier for signals below 860 MHz, as
well as trunk-to-trunk switching function between the 1 Gbps trunk
channels.
Narad Optical Network Distribution Switch (ONDS) - this switch
sits in front of an optical node and combines the signals below
860 MHz from the headend with the Gigabit Ethernet signals from
the headend router. As a result it provides optical-to-electrical
conversion of NBAN traffic and includes redundant optical transceivers.
The system also includes a Broadband Management System (BMS),
a topology server, which enables remote management of the network
from a local or regional Network Operations Center (NOC) and automates
the functions of fault, configuration, and performance management,
as well as a Service Mediation Manager (SMM), which ensures that
service provisioning and service instance requests can be supported
by the network within defined QoS parameters.
