13.1 Concepts of Optical Networks
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Wide Area Network (WAN) A WAN spans a large geographical area. The transmission distances can range from links between switching facilities in neighboring
cities to cross-country terrestrial or intercontinental undersea lines. The large collection of WAN resources are owned and operated by either private organizations or
telecommunication service providers.
Enterprise and Public Networks When a private organization (for example, a
company, a government entity, a medical facility, a university, or a commercial enterprise) owns and operates a network, it is called an enterprise network. These networks
only provide services to the members of the organization. On the other hand, networks
that are owned by the telecom carriers provide services such as leased lines or realtime telephone connections to the general public. These networks are referred to as
public networks, because the services are available to any users or organizations that
wish to subscribe to them.
Central Office A centralized switching facility in a public network is called a central
office (CO) or a point of presence (POP). The CO houses a series of large telecom
switches that establish temporary connections for the duration of a requested service
time between subscriber lines or between users and network resources.
Backbone The term backbone means a link that connects multiple network
segments. For example, a backbone handles internetwork traffic; that is, traffic that
originates in one network segment and is transmitted to another segment. Backbones
can be short or long links.
Long-Haul Network A long-haul network interconnects distant cities or geographical regions and spans hundreds to thousands of kilometers between central offices.
For example, this could be a high-capacity link carrying terabits of information
between New York and San Francisco, between countries in Africa, or between
Australia, China, and Singapore.
Data Center Network (DCN) The exponential rise of Internet traffic resulting
from applications such as streaming video, social networking, search engines, cloud
storage, and cloud computing has created the establishment of powerful data centers.
Such a center can be a building, dedicated space within a building, or a group of buildings used to house telecom associated components such as storage systems. These
applications are data-intensive and require high interaction between the servers in
the data center. A specialized optical network called a data center network (DCN)
is used to transmit large amounts of highly dynamic data traffic between data center
servers. Section 13.7 gives more details on configurations and operations of a DCN.
Passive Optical Network Many different transmission media can be used in an
access network, including twisted-pair copper wires, coaxial cable, optical fibers, and
radio links. Optical distribution networks that do not require any active optoelectronic
components in the access region offer a number of operating advantages over other
media. This implementation is called a passive optical network (PON) and is the
basis for the fiber-to-the-premises (FTTP) networks described in Sect. 13.8.
511
Wide Area Network (WAN) A WAN spans a large geographical area. The transmission distances can range from links between switching facilities in neighboring
cities to cross-country terrestrial or intercontinental undersea lines. The large collection of WAN resources are owned and operated by either private organizations or
telecommunication service providers.
Enterprise and Public Networks When a private organization (for example, a
company, a government entity, a medical facility, a university, or a commercial enterprise) owns and operates a network, it is called an enterprise network. These networks
only provide services to the members of the organization. On the other hand, networks
that are owned by the telecom carriers provide services such as leased lines or realtime telephone connections to the general public. These networks are referred to as
public networks, because the services are available to any users or organizations that
wish to subscribe to them.
Central Office A centralized switching facility in a public network is called a central
office (CO) or a point of presence (POP). The CO houses a series of large telecom
switches that establish temporary connections for the duration of a requested service
time between subscriber lines or between users and network resources.
Backbone The term backbone means a link that connects multiple network
segments. For example, a backbone handles internetwork traffic; that is, traffic that
originates in one network segment and is transmitted to another segment. Backbones
can be short or long links.
Long-Haul Network A long-haul network interconnects distant cities or geographical regions and spans hundreds to thousands of kilometers between central offices.
For example, this could be a high-capacity link carrying terabits of information
between New York and San Francisco, between countries in Africa, or between
Australia, China, and Singapore.
Data Center Network (DCN) The exponential rise of Internet traffic resulting
from applications such as streaming video, social networking, search engines, cloud
storage, and cloud computing has created the establishment of powerful data centers.
Such a center can be a building, dedicated space within a building, or a group of buildings used to house telecom associated components such as storage systems. These
applications are data-intensive and require high interaction between the servers in
the data center. A specialized optical network called a data center network (DCN)
is used to transmit large amounts of highly dynamic data traffic between data center
servers. Section 13.7 gives more details on configurations and operations of a DCN.
Passive Optical Network Many different transmission media can be used in an
access network, including twisted-pair copper wires, coaxial cable, optical fibers, and
radio links. Optical distribution networks that do not require any active optoelectronic
components in the access region offer a number of operating advantages over other
media. This implementation is called a passive optical network (PON) and is the
basis for the fiber-to-the-premises (FTTP) networks described in Sect. 13.8.