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286 Glossary

lightpath and that provide the following functionality at a
minimum: performance monitoring and management, restora-
tion and rerouting, wavelength translation, and delivery of
customer services. OADMs and DWDM terminals are included
in this category.

OSI seven-layer model A standard architecture for data
communications. Layers define the hardware and software
required for multi-vendor information processing equipment
to be mutually compatible.
Path A logical connection between a point where an STS or VT is
multiplexed to the point where it is demultiplexed.
Path Terminating Equipment (PTE) Network elements, such
as fiber-optic terminating systems, which can access, generate,
TEAMFLY
and process Path Overhead.

Payload The portion of the SONET signal available to carry
service signals such as DS1 and DS3. The contents of an STS
SPE or VT SPE.
Photon The basic unit of light transmission used to define the
lowest (physical) layer in the OSI seven-layer model.
Photonic A term coined for devices that work using photons,
analogous to “electronic” for devices working with electrons

Plastic fiber An optical fiber having a plastic core and plastic
cladding.
Plesiochronous A network with nodes timed by separate clock
sources with almost the same timing.
Point-to-point transmission A transmission between two des-
ignated stations.

POP (Point-of-Presence) A point in the network where inter-
exchange carrier facilities like DS3 or OC-N meet with access
facilities managed by telephone companies or other service
providers.
Polarization The direction of the electric field in the lightwave.
Port Hardware entity at each end of the link.

POTS Plain old telephone service.

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Team-Fly