Page 312 - Optical Communications Essentials

Optical Networks

302 Chapter Seventeen

■ Fiber to the home (FTTH) is a network technology that deploys fiber optic
cable directly to the home or business to deliver voice, video, and data serv-
ices. Owing to the very high capacity of optical fibers, FTTH can deliver
greater capacity than competing copper-based technologies. This is considered
the deepest penetration of the fiber optics infrastructure and is the most
costly to implement.

17.7. Summary
Networks can be classified broadly as a local-area network (LAN), metropolitan-
area network (MAN) or metro network, and wide-area network (WAN). When a
network is owned and deployed by a private enterprise, it is referred to as an
enterprise network. The networks owned by the telecommunication carriers
provide services such as leased lines or real-time telephone connections to other
users and enterprises. Such networks are referred to as public networks.
To simplify the complexity of modern networks, the International
Organization for Standardization (ISO) developed a model for dividing network
functions into seven layers. Each layer performs specific functions using a
standard set of protocols. A given layer is responsible for providing a service to
the layer above it by using the services of the layer below it. In actual systems
there are many implementation and protocol variations on the classical layering
model. A certain layer may work together with lower or higher layers, or a layer
may be divided into several sublayers.
The words optical layer are used to describe various network functions or
services. The optical layer is a wavelength-based concept and lies just above the
physical layer. Whereas the physical layer provides a physical connection
between two nodes, the optical layer provides lightpath services over that link.
A lightpath is an end-to-end optical connection that may go through one or
more intermediate nodes. For example, in an eight-channel WDM link there are
eight lightpaths, which may go over a single physical line.
The SONET and SDH standards allow network engineers to interconnect
fiber optic transmission equipment from various vendors through multiple-
owner trunk networks. The ANSI Standard T1.105.06 describes SONET, and
ITU-T Recommendation G.957 describes SDH. To ensure interconnection com-
patibility between equipment from different manufacturers, the SONET and
SDH specifications provide details for the optical source characteristics, the
receiver sensitivity, and transmission distances for various types of fibers. Table
17.1 shows commonly used SDH and SONET signal levels and the associated OC
rates. Table 17.2 lists SDH and SONET transmission distances, Table 17.3 gives
wavelength ranges and attenuation for transmission distances up to 80km, and
Table 17.4 lists some representative optical equipment characteristics.
Ethernet is deployed widely in local-area networks with interfaces available
at line rates ranging from 10Mbps to 10Gbps. Ethernet also is being used in
metropolitan-area networks and is extending into wide-area networks. In these
environments Ethernet uses optical fiber transmission links to increase network

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