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Chapter 14
Passive Optical Network(PON)
Introduction and brief history
PON Architecture and Elements
Difference b\w Ethernet PON and ATM PON
Advantages and Disadvantages
Applications of PON
• Passive optical networks (PONs) are an optical
broadband access technology that provide an
optical last-mile solution.
• A PON is a point-to multipoint optical network
that uses passive optical components such as
splitter, coupler, and splicer.
• An optical component is said to be passive if it
does not require active power to function.
• In 1995, a group of vendors and telecom service providers, in an
attempt to standardize PON access networks, formed the Full
Service Access Network (FSAN) coalition.
• One goal of the FSAN coalition is to develop and standardize a costeffective yet fast solution to create a “full service access network”
that would extend emerging high-speed services, such as IP data,
video, and 10/100 Ethernet, over fiber optics networks to
residential and business customers worldwide (Spears 1999). The
FSAN coalition decided to adopt ATM over a passive optical
network, known as ATM PON. In 1999, the ITU-T’s Study Group 15
adopted the FSAN coalition’s ATM PON specifications as standards
G.983.1 (ITU-T, 1999).
• An alternative, Ethernet PON technology, emerged
while the ATM PON specifications were being finalized.
The Ethernet PON efforts have been undertaken mainly
by a group of startup companies and research
institutes. Ethernet PON is gaining momentum as
optical Ethernet (see Chap. 6) such as Gigabit Ethernet
and 10 Gigabit Ethernet start taking hold in the metro
network marketplace. This chapter discusses both ATM
and Ethernet PON.
PON Basics
PON technology has two essential
characteristics that make it a good choice for a
broadband access network
1) It supports point-to-multipoint architecture and allows
multiple customers to share a single fiber facility. This is an
essential requirement of an access network.
2) A PON system does not require much maintenance because
of the passive nature of outside plant components of a PON.
PON Architecture
• A PON network consists of three major components:
1) an optical line terminator (OLT),
2) an optical splitter and a combiner or a cascade of them,
3) set of optical network units (ONUs) at the customer
• This is a passive optical network because there are no
active components between the OLT and ONUs.
• This figure for diagram of passive optical
PON Architecture
1) Optical Line Terminal (OLT)
• OLT is the headend of an optical cable network
• Optical Line Terminal An OLT is a special-purpose
switch located either at a service provider’s
central office (CO), a service provider’s point of
presence, or An OLT connects to one optical
splitter and combiner or a cascade of them
Main functions of an OLT
1. It broadcasts the downstream data to the connected
ONUs over a single fibber and sends traffic to a splitter
2. It aggregates upstream traffic from multiple customer
sites. It can use one of several multiplexing techniques
such as TDM, CDM, or WDM.
3. It is responsible for interfacing metro backbone
networks and performing network protocol conversions
such as Ethernet to ATM or IP to ATM, as necessary
Passive Optical Splitter and Coupler
• The passive splitter and coupler, the only
passive components of a PON, are normally
placed inside vaults in manholes.
Main functions of Passive Optical Splitter and
• To split optical signals going from an OLT to
ONUs and combine them in the other direction.
• In the downstream direction, as the light
broadcast from an OLT hits the splitter, it is
deflected onto multiple fiber connections,
depending on the splitter used. A splitter may
branch from 2 to 32 or 64 branches.
Optical Network Unit
Optical Network Unit PON systems terminates at so-called ONUs,
also known as optical network terminals (ONTs).
• An ONU takes in light that is sent from a passive splitter, converts it
to specific types of bandwidth (such as 10/100-Mbit/s Ethernet,
ATM, and T1 voice and data), and passes it on to enterprise routers,
PBXs, switches, or residential homes. ONUs have an active optical
component such as a laser or LED to send optical signals back to the
central office at the command of the OLT. Given that the bandwidth
allocated to an ONU is merely a branch of that of the OLT, an
inexpensive LED can be a good choice.
General functions an ONU
• It converts optical signals to electrical signals and
then to an application bandwidth for a user end
terminal such as a PC, a TV, a home hub,
enterprise routers, etc.
• It generates optical signals for upstream traffic.
• It interfaces last-yard access devices like a
wireless LAN card or asynchronous digital
subscriber loop (ADSL) line at customer premises.
ATM PON and Ethernet PON
• ATM PON: An ATM PON carries all services in ATM
cells, in both upstream and downstream directions.
• One main consideration for adopting ATM PON is the
guaranteed bandwidth and well-defined QoS provided
by ATM technology.
• Ethernet PONs: carry all services in variable-length
Ethernet frames, each of which has a maximum length
of 1518 bytes, in both upstream and downstream
ATM PON architecture
Hint: the maximum optical signals from a transmitter are passively split into up
to 64 ONT. VPI(virtual path identifier b/w ONTs)
Ethernet PON architecture
Comparison ATM PON and Ethernet PON
Ethernet PON
Technology complexity
more complexity
compared Ethernet PON
Simple plug and play
No built-in QoS
Data rate
Maximum upstream 155
Mpbs ,Downstream
No standard bandwidth
defined yet
distinguishing one ONU
from another
Uses VPI
Uses Mac Addressing
Multiple access control
TDMA (proposal only)
WAN interface
Support service
Data,Voice and Video
Data, Voice and Video
Initial field trial stage
Very initial trial stage
Advantages of PON
• Point-to-multipoint fiber-lean architecture
instead of running a separate stand of fibber
from CO to every customer. Uses a single
stand of fiber to serve up to 32 subscribers
• it uses optical fibres so that the band with is
high, can reach a longer distances
• Low cost equipment's per subscriber
Advantages of PON
• Passive components require a little components,
and have a high MTBF (Mean time between
• Additional buildings can be add to the network
easily and inexpensively.
• Supports a broad range of application icluding
Triple play(voice, Video and Data) of a single fibber
Advantages of PON
• Offers a large amount of high speed
bandwidth providing greater flexibility for
adding future services.
• Flexible and scalable bandwidth assignment
• Central office (instead of multiple ports) there
is only one optical port of the network.
Disadvantages of PON
1) Requiring more protection around the fiber
cable compared with copper cable
2) Cost
Application Of PON
• Fiber to the curb (FTTC), where an ONU resides at a roadside wire
• Fiber to the building (FTTB), where an ONU resides inside a
telecommunications closet of a multitenant business or residential
• Fiber to the floor (FTTF), where an ONU is located at a wire cabinet
of a building floor
• Fiber to the home (FTTH), where an ONU is located inside a
residential customer’s home
• Passive optical networks (PONs) are an optical
broadband access technology that provide an
optical last-mile solution.
• A PON is a point-to multipoint optical.
Main challenges
• How the splitter knows the path or which User
of this data belongs to, as we know splitter is
not intelligent device like router and switch?
• How voice video and Data propagate inside a
single fiber?