Pon Topology

1. INTRODUCTION TO PON TOPOLOGY

Early work on efficient fiber to the home architectures was done in the 1990s.

There are two generalizations of PON. The older one ITU-T G.983 standard is based on

asynchronous transfer mode (ATM), and has therefore been referred to as APON (ATM

PON). Gradual falling out of favor of ATM as a protocol led to the full, final version of

ITU-T G.983. It’s referred to more often as broadband PON, or BPON. The IEEE 802.3

Ethernet PON (EPON or GEPON) standard was completed in 2004. EPON uses standard

802.3 Ethernet frames with symmetric 1 gigabit per second upstream and downstream

rates. PON is applicable for data-centric networks, as well as full-service voice, data and

video networks. Recently, starting in early 2006, work began on a very high-speed 10

Gbit/s EPON (XEPON or 10-GEPON) standard.

Fiber-to-the-home (FTTH) gives the value measurement in the ease of network

testing, measuring and monitoring. FTTH technology also offers an attractive solution for

providing high bandwidth from the central office to residences and to small- and

medium-sized businesses. FTTH is cost-effective because it uses a passive optical

network (PON).[1] FTTH is a network infrastructure that is capable of supporting not

only the services the cable operators can offer today, but also the services that will be

offered in the future. We can classify FTTH technologies into two groups. One is AON

(Active Optical Network) which is a cheap solution, but it includes Active devices in the

field causing high maintenance and operation cost [2].

In this study we present a new protocol called Interleaved Polling with Adaptive

Cycle Time (IPACT, pronounced eye-pact). The PON based network under consideration

1

Pon Topology

uses a polling scheme to deliver data encapsulated in Ethernet packets from a collection

of optical network units (ONUs) to a central optical line terminal (OLT) over the PON

access network. The OLT, in turn, is connected to the rest of the Internet.

What is Passive Optical Network (PON)?

PON uses Fiber Optic cables (Optical Fiber).

Passive Optical Network is the leading technology being used in FTTx (like

FTTH) deployments. It has a different topology from other network technologies; It uses

a Point to Multi-Point (P2MP) topology. A single strand of fiber goes out to a passive

optical splitter where its signal is multiplied to 32 different lines. It’s up to the customer’s

system to determine what packets are for that customer, all other packets are discarded. It

has downstream data rates up to 2.5Gbps. A Passive Optical Network (PON) is a network

with no active elements in the signals’ path from source (OLT) to destination (ONU).

2

Pon Topology

2. TYPES OF PON :

There are four types of pon.

2.1 APON:

Also known as ATM PON because it’s based on based on asynchronous transfer

mode (ATM). It’s the first Passive Optical Network It was used primarily for business

applications It has ITU-T G.983 standard. APON is a point-to-multipoint technology.

Compared to point-to-point system, the point-to-multi-point system is comparatively

cheap.

Advantages of APON:

APON, the fiber system is less expensive than copper cable based systems in

providing the same bandwidth. So carriers will be able to increase profit margins, reduce

investment, and increase competitive capability, while users will reduce the service cost

by sharing the resource of the fiber and bandwidth. Longer range for data transfer.

Immune electrical noise.

2.2 BPON:

İts names is Broadband PON.It is a standard based on APON. It adds support for

WDM, dynamic and higher upstream bandwidth allocation, and survivability. It also

3

Pon Topology

created a standard management interface, called OMCI, between the OLT and

ONU/ONT, enabling mixed-vendor networks.

Advantages of BPON:

Since data for content services and VoIP are transmitted with higher priority than

Internet access (Web access), real-time live broadcasting can be viewed with high

quality. Everyone can receive network services equally, without being disturbed by heavy

users. However, it is also possible to give a higher priority to specific users.

2.3 EPON :

Ethernet for subscriber access networks, also referred to as “Ethernet in the First

Mile” (EFM), combines a minimal set of extensions to the IEEE 802.3 Media Access

Control (MAC) and MAC Control sub-layers with a family of Physical (PHY) layers.

EFM also introduces the concept of Ethernet Passive Optical Networks (EPONs), in

which a point to multipoint (P2MP) network topology is implemented with passive

optical splitters, and optical fiber PMDs, that support this topology. In addition, a

mechanism for network Operations, Administration and Maintenance (OAM) is included

to facilitate network operation and troubleshooting. EPON vendors are focusing initially

on developing fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) solutions, with

the long-term objective of realizing a full-service fiber-to-the-home (FTTH) solution for

delivering data, video, and voice over a single platform.

Advantages of EPON:

Higher bandwidth: up to 1.25 Gbps symmetric Ethernet

bandwidth. Lower costs: lower up-front capital equipment and ongoing

operational costs. More revenue: broad range of flexible service offerings

means higher revenues.

2.4 GPON :

4

Pon Topology

In 2001, the FSAN group initiated a effort for standardizing PON networks

operating at bitrates above 1 Gbps. Apart from the need to support higher bit rates, the

overall protocol had to be opened for reconsideration so that the solution would be most

optimal and efficient to support multiple services and operation, administration,

maintenance and provisioning (OAM&P) functionality and scalability. As a result of

FSAN efforts, a new solution emerged in the optical access market place – Gigabit PON

(GPON), offering unprecedented high bit rate support (up to 2.488 Gbps) while enabling

the transport of multiple services, specifically data and TDM, in native formats and with

extremely high efficiency. In January 2003, the GPON standards were ratified by ITU-T

and are known as ITU-T.Recommendations G.984.1, G.984.2 and G.984.3.

Advantages of GPON:

To design a PON that operates at Gigabit and higher data rates . To craft

the physical layer specifications to suit these higher speeds . To define the most

bandwidth efficient protocol that reflects the data-centric trends in customer

traffic.

2.5 PON Variants:

5

Pon Topology

6

Pon Topology

3. STANDARDS FOR PON:

There are two generalizations of PON

The older one ITU-T G.983 standard is based on asynchronous transfer

mod e (ATM), and has therefore been referred to as APON (ATM PON) Gradual

falling out of favor of ATM as a protocol led to the full, final version of ITU-T

G.983 It’s referred to more often as broadband PON, or BPON. A typical

APON/BPON provides 622 megabits per second (Mbit/s) of downstream

bandwidth and 155 Mbit/s of upstream traffic The ITU-T G.984 (GPON)

standard represents a boost in both the total bandwidth and bandwidth

efficiency through the use of larger, variable-length packets GPON

Encapsulation Method (GEM) allows very efficient packaging of user traffic,

with frame segmentation to allow for higher Quality of Service (QoS) for

delay-sensitive traffic such as voice and Communications

The IEEE 802.3 Ethernet PON (EPON or GEPON) standard was completed in

2004

EPON uses standard 802.3 Ethernet frames with symmetric 1 gigabit per

second upstream and downstream rates PON is applicable for data-centric

networks, as well as full-service voice, data and video networks. Recently,

starting in early 2006, work began on a very high-speed 10 Gbit/s EPON

(XEPON or 10-GEPON) standard

● ITU-T G.983 standard

● ITU-T G.984 (GPON) standard

● IEEE 802.3 Ethernet PON (EPON or GEPON) standard

● ITU-T G.652 standard for WDM fibers

7

Pon Topology

3.1 ITU-T G.983 standard

(ATM Passive Optical Network). This was the first Passive optical

network standard. It was used primarily for business applications, and was

based on ATM. (Broadband PON) is a standard based on APON. It adds

support for WDM, dynamic and higher upstream bandwidth allocation, and

survivability. It also created a standard management interface, called OMCI,

between the OLT and ONU/ONT.

3.2 ITU-T G.984 (GPON) standard

(Gigabit PON) is an evolution of the BPON standard. It supports higher

rates, enhanced security, and choice of Layer 2 protocol (ATM, GEM,

Ethernet). By mid-2008, Verizon had installed over 800 thousand lines. British

Telecom, Mobily-SaudiArabia, Etisalat-UAE, and AT&T are in advanced trials.

It is the successor to G.983

3.3 IEEE 802.3 Ethernet PON (EPON or GEPON) standard

EPON or GEPON (Ethernet PON) is an IEEE/EFM standard for using

Ethernet for packet data. 802.3ah is now part of the IEEE 802.3 standard.

There are currently over 25 million installed EPON subscribers. Commercial

upgrade capability to 10G EPON will become available in 2010 (see IEEE

802.3av, 10G-EPON

3.4 ITU-T G.652 standard for WDM fibers

10G-EPON (10 Gigabit Ethernet PON) is an IEEE Task Force for

10Gbit/s, backward compatible with 802.3ah EPON. 10GEPON will use

separate wavelengths for 10G and 1G downstream. 802.3av will continue to

use a single wavelength for both 10G and 1G upstream with TDMA separation.

8

Pon Topology

4. PON ARCHITECTURE :

(a) Tree topology (using 1:N splitter)

OLT

ONU1

ONU2

ONU3

ONU4

ONU5

(b) Bus topology (using 1:2 tap couplers)

OLT

ONU1 ONU2

ONU3 ONU4ONU5

(c) Ring topology (using 2x2 tap couplers)

OLT

ONU1

ONU2

ONU3

ONU4

ONU5

(d) Tree with redundant trunk (using 2:N splitter)

ONU1

OLTONU3

ONU5

ONU2

ONU4

Figure 4.1: PON topology

All transmissions are performed between an optical linterminal (OLT) and optical

network units (ONUs). There are several multipoint topologies suitable for the access

network, including tree, tree-and-branch, ring and bus (Fig ..). A PtMP network with a

CO serving multiple subscribers

9

Pon Topology

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 theoutput 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 customer premises. It provides several interfaces for

accessing triple play services and in the upper side it connects with the OLT

via optical splitter Optical Line Termination (OLT) at the Central Office side

to all Optical Network Terminations (ONTs) on a single wavelength, where the

ONTs filter the data, based on packet/cell identifiers. Note that Time division

multiple access (TDMA) is a technology for shared medium (usually radio)

networks. It allows several users to share the same frequency by dividing it

into different timeslots. The users transmit in rapid succession, one after the

other, each using hisown timeslot. This allows multiple users to share the same

transmission medium (e.g. radio frequency) while using only the part of its

bandwidth they require.

10

Pon Topology

5. FIBER ACCESS NETWORK TOPOLOGIES :

5.1FTTH: Fiber To The Homes

5.2FTTB: Fiber To The Building

5.3FTTC: Fiber To The Curb

5.4FTTCab: Fiber To The Cabinet

5.5FTTM: Fiber To The Node

In so-called point-to-point (P2P) topologies, a separate singlemode fiber runs

from the local exchange to each home (or cabinet at the curbside). While this requires the

installation of much fiber in the field and of many line terminations in the local exchange,

it can deploy simple low-cost (e.g. fast Ethernet) opto-electronic transceivers and it eases

the individual upgrading of services per customer. For wiring relatively small city areas,

such as in the installations made thus far in Europe, this is therefore the most common

topology.

In point-to-multipoint (P2MP) topologies, a single fiber emerging from a single

line termination at the local exchange runs to a splitting point in the field, from where

short separate fibers connect to the homes (or curbside cabinets). This splitting point may

contain an active router to distribute the appropriate traffic destined for each user; such

active functions require however remote powering and maintenance. Hence the use of a

passive optical power splitter is mostly preferred, which yields the well-known Passive

Optical Network (PON) topology. For larger areas to be served with a larger number of

users, the PON topology can be economically more attractive than the point-to-point

topology. Also the repair of breaks in the feeder part of the network is easier in the PON

case, as it involves the repair of one fiber only. Various protection schemes have been

roposed for this topology, providing redundancy of the feeder (and drop) part.

11

Pon Topology

FTTx

Fig 5.1: Fiber access network

12

Pon Topology

6. MULTIPLE ACCESS TECHNIQUES :

The PON feeder line is shared by a number of users, and hence a multiple access

protocol is needed to give everyone his fair share of the available upstream capacity.

Basically,

there are three protocols being considered:

2.6 Time Division Multiple Access (TDMA)

in which each user gets a designated time slot to send his data; this yields

the so-called TDM-PON. The upstream data of the various users have to be carefully

interleaved at the splitter in order to avoid collisions. Hence the data channels are

mutually dependent, and need to be synchronized under command of the local exchange.

The TDMA protocol can be largely implemented in digital low-cost electronics, features

some statistical multiplexing gain, and hence is currently the most popular. It is used in

BPON (ATM-based, up to 622 Mbit/s symmetrically), GPON (Gigabit PON, for speeds

up to 2.5 Gbit/s, and featuring encapsulation of not only ATM cells but also Ethernet

packets and native TDM [ 2 ]), and EPON (Ethernet PON, with variable length Ethernet

packets, also offering dynamic bandwidth allocation [3]).

6.2 Subcarrier Multiple Access (SCMA)

in which each user gets a designated frequency slot. As long as the users deploy

non-overlapping frequency bands to send their data upstream, their data channels are

independent. This solution entails carefully tuned analog RF circuitry per user, may

require very high frequency circuitry when bitrates grow, and hence is

usually considered not economically attractive.

6.3 Wavelength Division Multiple Access (WDMA)

in which each user gets a dedicated wavelength channel by means of a

wavelength-routing splitter (e.g. an arrayed waveguide router, AWGR). This WDM-PON

routes the data in a powerefficient way, and is logically equivalent with a P2P topology.

It thus offers not only the P2P advantages, but also saves on

13

Pon Topology

7. PONS COMPONENTS :

7.1Optical line terminal (OLT)

It is a Central office node. Service provider endpoint of a PON and is placed at

the central office or head end in systems. An optical line terminal which sends and

receives messages or data to/from optical network units (ONUs) connected.

7.2 Optical network units (ONUs)

It is a User nodes. ONUs is provided in the subscriber neighborhood for

terminating the optical fiber transmission line and for providing electrical signals over

metallic lines to the subscribers. So ONUs receives data from OLT by PONS and

converts the optical signal into electrical.

7.3 Optical distribution network (ODN).

fibers and splitters between OLT and ONUs

14

Pon Topology

Fig 7.1: pon components

15

Pon Topology

8. DOWNSTREAM & UPSTREAM :

8.1 Downstream traffic in EPON

In the downstream direction, Ethernet frames transmitted by the OLT pass

through a 1:N (typically 4-64) passive Splitter and reach ONUs. It can broadcast

by nature. Packets are broadcast by the OLT and extracted by their Destination

ONU based on the media-access control (MAC) address. All ONUs are in time

synchronigection.Time slots can carry multiple Ethernet Frames. Permission to

send in a time slot done by the OLT using a Multipoint control protocol (MPCP).

Fig 8.1: Downstream traffic in EPON

16

Pon Topology

8.2 Upstream traffic in EPON

All ONUs are synchronized to a common time reference and each ONU is

allocated a time slot capable of carrying Ethernet frames. An ONU buffers frames

eceived from a subscriber until itstimeslot arrives. Time slots can carry multiple Ethernet

Frames. All ONUs are in time sync. Permission to send in a time slot done by the OLT

using a Multipoint control protocol (MPCP).

Fig 8.2 : Upstream traffic in EPON

17

Pon Topology

9.IPACT(INTERLEAVED POLLING WITH ADAPTIVE

CYCLE TIME) :

In this section we give a high-level overview of the proposed algorithm. For

simplicity of illustration, we will consider a system with three ONUs:

1. Assume that at some time t0 the OLT knows exactly how many bytes are waiting

in each ONU’s buffer and the round-trip time (RTT) to each ONU. OLT keeps

this data in a polling table, shown in Fig. 2a. At time t0 the OLT sends a control

message to ONU1, allowing it to send 6000 bytes (Fig.2a). We call such a

message a Grant. Since, in the downstream direction, the OLT broadcasts data to

all ONUs, a Grant should contain the ID of the destination ONU, as well as the

size of the granted window (in bytes).

2. Upon receiving the Grant from the OLT, ONU1 starts sending its data up to the

size of the granted window (Fig. 2b), in our example up to 6000 bytes. At the

same time the ONU keeps receiving new data packets from users. At the end of its

transmission window, ONU1 will generate its own control message (Request).

The Request sent by ONU1 tells the OLT how many bytes were in ONU1’s buffer

at the moment the Request was generated.In our case there were 550 bytes.

3. Even before the OLT receives a reply from ONU1, it knows when the last bit of

ONU1’s transmission will arrive. This is how OLT knows it:

(a) The first bit will arrive exactly after the RTT time.The RTT in our

calculation includes the actual RTT, Grant processing time, and a preamble

for the OLT to perform bit and byte alignment on received data, that is,

exactly the time interval between sending a Grant to an ONU and receiving

18

Pon Topology

data from the same ONU.

(b) Since the OLT knows how many bytes (bits) it has authorized ONU1 to send,

It knows when the last bit from ONU1 will arrive. Then, knowing RTT for

ONU2, the OLT can schedule a Grant to ONU2 such that the first bit from

ONU2 will arrive soon after the last bit from ONU1, with only a small guard

interval in between (Fig. 2b). The guard intervals provide protection for

luctuations of RTT and control message processing time of various ONUs.

Additionally, the OLT receiver needs some time to readjust its sensitivity due

to the fact that every ONU is located at a different

Distance from the OLT (far-near problem).

4. After some time, the data from ONU1 arrives. At the end of the transmission from

ONU1, there is a new Request that contains information on how many bytes

remained in ONU1’s buffer when the Request transmission began. The OLT will

use this information to update its polling table (Fig. 2c). By keeping track of times

when Grants are sent out and data is received, the OLT constantly updates the

RTT entries for the corresponding ONUs.

5. Similarly to the above step, the OLT can calculate the time when the last bit from

ONU2 will arrive. Hence, it will know when to send the Grant to ONU3 so that its

data is tailed to the end of ONU2’s data. After some more time, the data from

NU2 will arrive. The OLT will again update its table, this time the entry for

ONU2 (Fig. 2d).

19

Pon Topology

Note that if an ONU emptied its buffer completely,it will report 0 bytes back to

the OLT.Correspondingly, in the next cycle, the ONU will be granted 0 bytes, that is, it

will be allowed to send a new Request, but no data.

It should be clear from the above description that there is no need to synchronize

the ONUs, nor is there a need to perform a ranging (making ONUs to appear equidistant

from the OLT by delaying the response from ONUs by a specific amount of time)

traditionally employed in TDMA schemes. Every ONU executes the same procedure

driven by the Grant messages received

from the OLT. The entire scheduling and bandwidth allocation algorithm is located in the

OLT. Thus, it is easy to adaptively change the scheduling at run-time based on some

network conditions; the ONUs don’t need to negotiate or acknowledge new parameters,

nor do they need to switch to new settings synchronously.

In the above algorithm, we started with the OLT already having its table

populated. During system initialization, since round-trip times are unknown, OLT should

poll each ONU one at a time. The reader is referred to [6] for a detailed description of

cold start and ONU initialization

procedures.

20

Pon Topology

Fig 9.1 : Steps of the Polling Algorithm.

21

Pon Topology

10.SMART DROP PROTECTION SCHEMES:

the mechanisms of protection in FTTH-PON access network in breakdown

condition. Purple arrow represents the mechanism of dedicatedprotection in FTTH access

network when there is breakdown occurs at working line. When the failure is detected in

working line, protection mechanism will be activated and convert the optic signal

direction to the protection line. The purple arrow shows the protection mechanism as

dedicated protection. In linear protection

PON-FTTH scheme, each ONU is connected to splitter output terminal by two

fibers; working line and protection line through two optical switches that is controlled by

Access Control System (ACS). So, this research was proposed to implement the

protection scheme by using the 2x1 and 2x2 optical switch which is used to switch the

signal to the protection line when failure occurs in the working line.

The route depends on the restoration mechanism that is activated according to the

types of failure. The two optical switches are allocated in the transmission line in which

both ONU and splitter are located. A first optical switch is used to switch the signal to

protection line at local transmission or switch to protection line at transmission line

nearby. The second optical switches will switch the signal in protection line back to the

original path before sending it to the local ONU. For dedicated path protection, a working

path and an end to- end backup path is established, and resources are assigned to it at

connection set up time.

22

Pon Topology

10.1 Condition 1 :

Figure 10.1 shows the failure is detected in working line, protection mechanism

will be activated and convert the optic signal direction to the protection line. The purple

arrow shows the protection mechanism as dedicated protection.

Figure 10.1: Breakdown at working line and signal diverted to the

protection line.

23

Pon Topology

10.2 Condition 2 :

Figure 10.3 shows the shared protection scheme when breakdown occurs in both

line in working line and protection line. Shared protection scheme will be activated and

optic signal will convert the route to neighbor line protection as depicted in blue arrow.

Figure 10.2: Breakdown at working line and protection line.Signal

diverted to the neighbor protection line.

24

Pon Topology

11. IMPORTANCE OF PON

By the help of PON the bandwith will be much more higher then copper

line connection so we will have access to internet much more faster

PON provides a faster connection to internet because of this large firms

profits more because time is money

PONs rely on light waves for data transfer.

Only passive optical components are used such as optical fiber , splices

and splitters.

PONs minimizes the fiber deployment in both the local exchange office

and the local loop.

PONs provides higher bandwidth due to deeper fiber penetration,

offering gigabit per second solutions.

The PON market in North America is just starting to emerge but in

Japan, the PON market, thanks to government subsidies, is well establish and

growing at a rate of 300% year to year

By comparison DSL is growing 150% year to year in the U.S.

Top companies like Verizon, SBC and Bell South have all announced

some type of PON deployment

Industry analysts expect an equally large take rate by North American

consumes

25

Pon Topology

12. ADVANTAGES OF PON :

point-to-multipoint fiber-lean architecture Instead of running a separate strand of fiber from the CO to every customer. uses a single strand of fiber to serve up to 32 subscribers.

It uses Optical Fibers so that the bandwith is high, can reach longer distances

Low cost of equipment per subscriber

Passive components require little maintenance and have a high MTBF (Mean Time Between Failure)

Additional buildings can be added to the network easily and inexpensively Supports a broad range of applications including triple play (voice, data, video)

over a single fiber and FTTB, FTTC, FTTM, FTTH

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 at the

26

Pon Topology

13. DISADVANTAGES OF PON:

●Installing an Optical Fiber requires special equipment

●If a fiber breaks inside the plastic jacket finding the location of

the problem is difficult

●Repairing a broken Fiber is difficult

●Cost

●Need to deploy new infrastructure replace copper with fiber.

27

Pon Topology

14. CONCLUSION :

Operations and control for EPON as a subscriber access Network. Slotted

transmissions on EPON with OLT and ONUs. Multipoint control protocol - gate and

report messages. Polling algorithm for bandwidth allocation Point-to-point emulation

and shared medium emulation. Evaluate various dynamic bandwidth allocation schemes.

Market for EPON.

We presented the smart drop protection scheme used in passive optical network

for FTTH protection application and the simulation result that was achieved. Employing

the optical switch for 1x2 and 2x2 type will ensure the network to restoration scheme

since it cover for dedicated and shared protection.

We present a simple algorithm for dynamic bandwidth allocation based on an

interleaved polling scheme with an adaptive cycle time. We suggest a novel approach for

an in-band signaling that allows use of a single wavelength for both downstream data and

Grant transmission. Also, we showed this approach to be scalable with the number of

ONUs in the system.

28

Pon Topology

15. REFERENCES :-

[1] “FTTx PON Guide Testing Passive Optical Networks”.

www.exfo.com.

[2] B. Lung, “PON Architecture ‘Futureproofs’ FTTH,” Lightwave,

vol. 16, no. 10, Sept. 1999, pp. 104–7.

[3] Y. Luo et al., IEEE Comm. Mag., 2 (2005), pp. S16-S21

[4] S. Clavenna, “Metro Optical Ethernet,” Lightreading

(www.lightreading.com), Nov. 2000.

[5] K. N. Skalman, H. E. Sandstrom, and M. Gidlund: Techno-economical study for open horizontal IPTV in the access and home networks – from a Swedish perspective, in Proc. NOC, Krems, Austria, July 2008, 218-229.

[6] G.984.2: Gigabit-capable passive optical networks (G-PON): Physical Media Dependent (PMD) layer specification (ITU-T, 2003).

[7] Jani Saheb Shaik. “FTTH Deployment Options for TelecomOperators”.[Available on: http://images.ejeepss.multiply.com/attachment/0/ReZehw CqEAAG9@PIk1/FTTH_India.pdf?nmid=21043306.

[8] S. Clavenna, “Metro Optical Ethernet,” Lightreading (www.lightreading.com), Nov. 2000.

29