Fiber to the home is broadband option
By Derek Johnson and Donna Keegan
Network World, 08/05/02
As the result of lowered network costs, fiber to the home is becoming a feasible alternative to current broadband offerings, such as DSL and cable modem.
Fiber to the home offers data rates of 10/100 Ethernet, scalable to Gigabit Ethernet or higher. It uses the Data Over Cable Service Interface Specification (DOCSIS) standard for security. And it's optimized for voice, data and video.
Currently, there are two preferred ways to deploy fiber to the home - passive optical network (PON), which uses a point-to-multipoint architecture, and point-to-point solutions. ATM-based PON is described in ITU-T Recommendations G.983.1 and 983.3. Major carriers, such as BellSouth, helped write the specifications for PON and are advocating for its standardization and use.
Carry on with PON
With PON, the data rate is shared among a maximum of 32 subscribers in a neighborhood by passively splitting the signal among them. Several hundred homes are connected into optical line termination devices at the central office or head end.
Privacy is ensured by adding personal encryption for each subscriber. DOCSIS ensures cable modem security. Fixed network and exchange costs are shared among all subscribers, thus reducing the key cost/subscriber metric. This solution has no outside plant electronics, reducing network complexity and life-cycle costs, and improving reliability. As a result, the economics are becoming attractive to service providers.
Point-to-point
Another common architecture is a point-to-point network. Enterprise LAN electronics can deliver services to single-family homes and multidwelling units. Standards bodies and equipment vendors are improving this technology to carry the multiplicity of services subscribers want, with the advantage of using existing components and technology. Connecting subscribers directly to a centralized switch offers very high bandwidth capacity. In either deployment, fiber provides the ultimate upgrade path. Data solutions can scale from 1M to 10G bit/sec per home without changing the fiber or outside plant equipment, only the electronics (and resulting software changes). Fiber technology also provides the highest bandwidth, has a longer life expectancy than copper or coaxial cable, and is resistant to electromagnetic interference.
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Once fiber reaches the home, it terminates at an optical network termination (ONT) or an optical network unit (ONU) located at or near the customer premises. ONUs are mounted indoors or outdoors in a hardened, weatherproof box on the side of a home or building. ONTs service Ethernet networks inside homes. They convert the light signal from the fiber strand into an electrical signal.
The data ports use basic wave division multiplexing (WDM) to send and receive on a single strand of fiber at 1550nm and 1310nm to transmit and receive the data. Using WDM on a single strand means less fiber is used, which makes the architecture more cost-effective.
A typical unit would have four 10/100 ports that would be used for Internet access, video on demand (VOD), and four plain-old-telephone-service ports, offering single party, voice grade and services such as caller ID. The VOD port would be sent using an MPEG format where it would be decompressed and sent to a set-top box. |
