Typical Fiber Optic Networks and Block Diagrams
| RFoG - Stands for Radio Frequency over Glass.
RFoG is a type of passive optical networking that proposes to transport
RF signals that are now transported over copper (principally over hybrid
fiber and coax cable), over a Passive Optical Network.
In the forward direction RFoG is either a stand alone Point to Multi-Point system or an optical overlay for existing Passive Optical Network (PON) such as Gigabyte Passive Optical Network (GPON). Reverse RF support is provided by transporting the upstream or return path into on a separate return path or wavelength. RFoG offers backwards compatibility with existing RF modulation technology, as a result the existing equipment located at the headend and customer premise can still be utilized. RFoG offers a means to support RF technologies in locations where only fiber is available, or where copper is not permitted or feasible. This technology is targeted towards Cable TV operators and their existing HFC networks. Below is a typical RFoG Network. Click on the products in the network to learn more about them: |
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GPON - Stands for Gigabyte
Passive Optical Network. There are three main
components in a GPON network (other than the
fiber itself). The GPON Optical Line Terminal
(OLT) is the network concentrator, usually
installed in a Central Office (CO). The
splitter (or splitters) allows a single
fiber from the headend to be shared among a
number of subscribers. The Optical Network
Terminal (ONT) serves a single residence,
converting optical signals to electrical signals
that can be used within the home. Note that the
ITU standards call the subscriber device an
Optical Network Unit (ONU), and many use ONU to
mean an ONT serving several subscribers, which
would be common in an installation serving a
number of apartments in the same building.
GPON is specified to be a single or dual fiber system, but almost all GPON systems are single fiber like virtually all popular FTTH technologies. There is little reason to use dual fibers, although this option is indeed allowed in the standard. Below is a typical GPON Network. Click on the products in the network to learn more about them: |
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HFC - Stands for Hybrid Fiber-Coaxial. It
is a telecommunications industry term for a broadband network
which combines optical fiber and coaxial cable. It has been
commonly employed globally by cable TV operators since the early
1990s.
The fiber optic network extends from the cable operator's headend out to a neighborhood's hubsite, and finally to a fiber optic node which serves anywhere from 25 to 2000 homes. A headend will usually have satellite dishes for reception of distant video signals as well as IP aggregation routers. Some headends also house telephony equipment for providing telecommunications services to the community. The headend will receive the video signal and add to it the Public, Educational and/or Governmental channels and encode, modulate and upconvert onto RF carriers, combined onto a single electrical signal and inserted into a broadband optical transmitter. This optical transmitter converts the electrical signal to a downstream optically modulated signal that is sent to the nodes. Fiber optic cables connect the headend to optical nodes in a point-to-point or star topology, or in some cases, in a protected ring topology. A fiber optic node has a broadband optical receiver which converts the downstream optically modulated signal coming from the headend to an electrical signal going to the homes. Today, the downstream signal is a radio frequency modulated signal that typically begins at 50MHz and ranges from 550MHz to 1000MHz on the upper end. The fiber optic node also contains a reverse/return path transmitter that sends communication from the home back to the headend. This reverse signal is a modulated RF frequency ranging from 5 to 42MHz. The optical portion of the network provides a large amount of flexibility. If there are not many fiber optic cables to the node, wavelength division multiplexing can be utilized to combine multiple optical signals onto the same fiber. Optical filters are used to combine and split optical wavelengths onto the single fiber. For example, the downstream signal could be on a wavelength at 1550nm and the return signal could be on a wavelength at 1310nm. Below is a typical HFC Network. Click on the products in the network to learn more about them: |
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