Introduction
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61287802F1-34B
Revision B
2 Introduction
The 452/454 ADTRAN Optical Network Terminal (ONT) is a Gigabit Passive Optical Network
(GPON) ONT that provides the services detailed below.
Figure 1
illustrates the ONT Housing.
2.1 Description
GPON technology provides a consistent and common approach to advancing the public
communications network using:
■ Traditional telephone services (Plain Old Telephone Service (POTS))
■ High speed data services
■ Video services
The GPON network consists of an Optical Line Terminal (OLT) located at the central office,
and an Optical Network Terminal (ONT) located at the customer premises. Between them lies
the Optical Distribution Network (ODN) consisting of fibers and passive splitters or couplers. A
splitter is a device that divides an optical signal into two or more signals. It can also
reassemble signals from multiple signal sources into one signal. The GPON technology is
based on Passive Optical Network (PON) technology.
Traditionally, telecommunication networks use devices that require power to transmit data
from one point to another including processors, memory chips, repeaters, and relays. With
passive optical networks, components that need power to transmit data between the central
office and the customer premises are replaced by passive components that guide traffic based
on splitting optical wavelengths to end points along the way. These passive components, such
as splitters and coupler devices, work by passing or restricting light and do not require power
to transmit data.
In a PON, a single piece of fiber can be run from the serving exchange out to a subdivision or
office park. Then, individual fiber strands can be run to each building. Also, serving equipment
can be split from the main fiber using passive splitters/couplers. This allows one piece of fiber
cable from the exchange to the customer to be shared by many customers. This dramatically
lowers the overall costs of deployment for Fiber To The Premises (FTTP) applications.
In this type of network, subscriber voice, video, and data devices are connected to the GPON
via the ONT. The ONT translates IP data and analog voice into GPON Encapsulated Method
(GEM) frames and combines/splits the signal with analog and/or digital video to and from the
OLT. The signal is split/combined at the OLT similar to the ONT.
Signal transmission from an ONT to the OLT uses a type of Time Division Multiple Access
(TDMA). TDMA is a technique used to frame channels of data. In this technique, data commu
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nication sessions originating from multiple points are transmitted in turn. Each data communi
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cation session is assigned a time slot in the TDMA frame and transmits (or accesses that time
slot) only at that time.
To allow for the transmission of downstream and upstream traffic on a single fiber, different
wavelengths are used for both directions. Downstream traffic uses 1490 nm while upstream
traffic uses 1310 nm. The ONT employs diplexers (or triplexers, in the case of TV overlay) to
separate wavelengths.
Downstream data is broadcast from the OLT to all ONTs. Each ONT processes the data
destined to it by matching the address at the protocol transmission unit header. The
downstream PON signal is broadcast to up to 32 ONTs with a data rate of 2.5 Gbps for voice
and data, plus the additional video overlay wavelength division multiplexing (WDM) signal.
