Passive Optical Network (3)
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Transcript of Passive Optical Network (3)
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7/30/2019 Passive Optical Network (3)
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The PON is an access network based on Optical Fiber. It is designed to provide virtually
unlimited bandwidth to the subscriber. A passive Optical network is a single, shared optical fiber
that uses a passive optical splitter to divide the signal towards individual subscribers. PON ispoint to multipoint network architecture. PON is called passive because other than at the central
office there are no active element within the access network. A PON enables an service provider
to deliver a true triple play offering of voice, video and data
PON Architecture: The elements of a PON are (i) Optical Line Terminal(OLT) (ii) Passive
Optical Splitter and (iii) Optical Network Unit(ONU).The Optical Line Terminal is the main element of the network and is usually placed in the Local
Exchange. It is a network element with PON line card, basically a aggregation switch. It works
as an interface between core network and PON network.
Optical Splitter is a passive device with single input and multiple output. Optical power at input
is split evenly between outputs. Not only signal travels from input to the outputs, signal can also
travel from the output to the input. Splitters can be placed anywhere in between CO and
Subscriber premises. It is used to connect an optical port of OLT with multiple subscribers.
Optical Network units(ONUs) serve as an interface to the network and are deployed at customerpremises. It provides several interfaces for accessing triple play services and in the upper side it
connects with the OLT via optical splitter.
OAC: Optical Access Network
An access network is a network that connects a service provider with its home or business
subscribers. The architecture of an access network (Figure 1) is composed of three majorcomponents :
The first component is a hub, which is usually referred to asCentral Office (CO)
. The secondcomponent is referred to as Remote Node (RN). The third component is referred to as Network
Interface Unit (NIU).
An access network can be seen to consist of two different networks:1).Distribution network is the network that connects the RNs with the NIUs. 2).Feeder network
is the network that connects the CO with the RNs.
There mainly two different access network architectures utilizing optical fiber are commercially
deployed in the field. These are Hybrid Fiber Coax (HFC) and Fiber-To-The-x (FTTx).
1 Hybrid Fiber Coax(HFC):
HFC is an access network utilizing optical fiber is commercially deployed in field.
The structure of HFC is such that the feeder network takes advantage of the optical fiberas transmission medium and the distribution network employs coaxial cable infrastructure
that has already existed in many places for many years.
2 Fiber access system(FTTx):
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In FTTx, optical fiber is used in both feeder and distribution networks. The x letter in the
FTTx usually stands for Cabinet (Cab), Curb (C), Building (B), Home (H) or Premises (P)
depending on how close the optical fiber is drawn with respect to the subscribers location.The rest of the transmission path between the x and the subscriber is electrical. Fiber to the
x (FTTX) is a generic term for any broadband network architecture using optical fiber to
replace all or part of the usual metal local loop used for last-mile telecommunications.
PON Standard: There are three standards with respect to PONs: (i) BPON (ii) EPON (iii)
GPON.
(i) APON/BPON: The ATM passive optical network(APON) was the first attempt
towards a PON standard. It is governed by the ITU-T and is designated as ITU-T
G.983. It established the general requirements for PON protocols. APON useAsynchronous Transfer Mode(ATM) as the underlying transport mechanism to
carry used data. BPON did not gain much popularity due to lack of bandwidth and
widespread use of Ethernet protocol.
(ii) EPON: The Ethernet Passive Optical Network (EPON/GE-PON)is governed by
IEEE and is designated as IEEE 802.3ah. EPON is based on Ethernet , unlikeother PON technologies which are based on ATM. It provides simple, easy-to-
manage connectivity to Ethernet-based IP equipment both at the customer
premises and at the central office. It is well suited to carry packetized traffic aswell as time-sensitive voice and video traffic. It offers 1.25Gbps data rate for both
upstream and downstream. EPON supports 1:16 split ratio i.e. 16 ONUs at a
range of 20 km can be connected with a single port of OLT.
(iii) GPON: The most recent PON standard is the ITU-T G.984 GPON(Gigabit PON)
standard, which offers 2.488 Gbps bandwidth and direct support of both
TDM(POTs & E1) and Ethernet traffic at the edge of the network with possibletriple play voice, data and video services on the same PON. GPON can support
ONUs that are located as far as 30 Km from the OLT. GPON offer higher split
ratio of 1: 32/64/128 which results in an OLT reduction by more than a factor of 2over EPON.