Bharat Sanchar Nigam Limitedrttctvm.bsnl.co.in/ftth_basics.pdf · 2018-02-26 · FTTH Basics, Maintenance & Wiring at Subscribers’ Premises 3 Chapter 1 Fiber To The Home Today,

FTTH Basics, Maintenance & Wiring at Subscribers’ Premises 1

Bharat Sanchar Nigam Limited

*******************************************

FTTH Basics, Maintenance & Wiring at

Subscribers’ Premises *******************************************

Printed by

REGIONAL TELECOM TRAINING CENTRE Thiruvananthapuram – 695 040


INDEX

SL No. TOPIC Page No.

1 Fiber To The Home 1

2 FTTH Optical Link Design 17

3 Maintenance & Wiring at Subscribers’ Premises

22

4 Optical Measuring Instruments and Tools 40

5 ONU specification and configuration 47


Chapter 1

Fiber To The Home

Today, majority of broadband connectivity is offered through Digital Subscriber Line

(DSL), Cable Modem and to the limited extent with Wireless technology. FTTH provides

enormous bandwidth and long reach offering multi-play services (Data, Voice, Video etc.) on

a single fiber. FTTH is future proof solution for providing add-on services such as Video on

demand, Online Gaming, HDTV etc.

Growing demand for high speed internet is the primary driver for the new access

technologies which enable experiencing true broadband. Today’s, there is an increasing

demand for high bandwidth services in market around the world. However, traditional

technologies, like Digital Subscriber Line (DSL) and cable modem technologies, commonly

used for “broadband access,” which have access speeds to the order of a megabit per second,

with actual rates strongly dependent on distance from the exchange (central office) and

quality of the copper infrastructure, can not fulfill today’s customer demand for bandwidth

hungry applications such as high-definition TV, high-speed Internet access, video on demand,

IPTV, online gaming, distance learning etc. Amongst various technologies, the access

methods based on the optical fiber has been given extra .emphasis keeping into long term

perspective of the country. It has many advantages over other competing access technologies

of which ‘Being Future Proof’ and providing ‘True Converged Network’ for high quality

multi-play are the salient ones. The stable and long term growth of Broadband is, therefore,

going to be dependent on robust growth of fiber in the last mile.

However, for providing multi-play services (voice, video, data etc.) and other

futuristic services fiber in the local loop is must. The subscriber market for multi-play is large

and growing and includes both residences and businesses. Businesses need more bandwidth

and many of the advanced services that only fiber can deliver. All view Multi- Play as a

strong competitive service offering now and into the future and are looking at fiber as the

way to deliver. Optical fiber cables have conventionally been used for longdistance

communications. However, with the growing use of the Internet by businesses and general

households in recent years, coupled with demands for increased capacity, the need for optical


fiber cable for the last mile has increased. A primary consideration for providers is to decide

whether to deploy an active (point-to-point) or passive (point-tomultipoint) fiber network.

Fiber To The x (FTTx)

Today, fiber networks come in many varieties, depending on the termination point: building

(FTTB), home (FTTH), curb (FTTC) etc. For simplicity, most people have begun to refer to

the fiber network as FTTx, in which x stands for the termination point. As

telecommunications providers consider the best method for delivering fiber to their

subscribers, they have a variety of FTTx architectures to consider. FTTH, FTTB,and FTTC

each have different configurations and characteristics.

FTTH (Fiber To The Home):

FTTH is now a cost-effective alternative to the traditional copper loop. “Fiber to the Home”

is defined as a telecommunications architecture in which a communications path is provided

over optical fiber cables extending from an Optical Line Terminal (OLT) unit located in

central office (CO) connects to an Optical Network Terminal (ONT) at each premise. Both

OLTs and ONTs are active devices. This communications path is provided for the purpose of

carrying telecommunications traffic to one or more subscribers and for one or more services

(for example Internet Access, Telephony and/or Video-Television). FTTH consists of a single

optical fiber cable from the base station to the home. The optical/electrical signals are

converted and connection to the user’s PC via an Ethernet card. FTTH is the final

configuration of access networks using optical fiber cable.

Fig. 1 FTTH Configuration

FTTB (Fiber To The Building):


“Fiber to the Building” is defined as a telecommunications architecture in which a

communications path is provided over optical fiber cables extending from an Optical Line

Terminal (OLT) unit located in central office (CO) connects to an Optical Network Unit

(ONU at the boundary of the apartment or office or building enclosing the home or business

of the subscriber or set of subscribers, but where the optical fiber terminates before reaching

the home living space or business office space and where the access path continues to the

subscriber over a physical medium other than optical fiber (for example copper loops).

Fig. 2 FTTB Configuration

FTTB regarded as a transitional stage to FTTH. By introducing fiber cables from the fiber

termination point to the home living space or business office space FTTB can be converted to

full FTTH. Such a conversion is desirable as FTTH provides better capacity and longevity

than FTTB. Optical fiber cable is installed up to the metallic cable installed within the

building. A LAN or existing telephone metallic cable is then used to connect to the user.

FTTC (Fiber To The Curb):

A method of installing optical fiber cable by the curb near the user’s home. An optical

communications system is then used between the ONU installed outside (such as near the

curb or on Street Cabinet) from the installation center. Finally, copper cable is used between

the ONU and user.


Fig.3 FTTC Configuration

Why FTTH?

FTTH is a true multi-service communications access which simultaneously handles several

phone calls, TV/video streams, and Internet users in the home/office. There are several

advantages of deploying FTTH over other traditional access technologies as given below:

• FTTH provides end-users with a broad range of communications and entertainment

services, and faster activation of new services.

• Competition is beginning to offer a “multi-play” (i.e., voice, video, data etc) bundle.

• FTTH provides Service Provider’s with the ability to provide “cutting edge” technology and

“best-in-class” services.

• Deploying a fiber optic cable to each premise will provide an extraordinary amount of

bandwidth for future services.

• FTTH provides carriers with an opportunity to increase the average revenues per user

(ARPU), to reduce the capital investment required to deliver multiple services, and to lower

the costs of operating networks

• FTTH provides the community in which it’s located with superior communications which

enhance the efficiency of local business and thus deliver economic advantage for the

community.

• Around the world FTTH is viewed as strategic national infrastructure similar to roads,

railways, and telephone networks.


Technology Options for FTTH Architecture:

When deciding which architecture to select a provider has many things to consider including

the existing outside plant, network location, the cost of deploying the network, subscriber

density and the return on investment (ROI). At present different technology options are

available for FTTH architecture .The network can be installed as an active optical network, or

a passive optical network (PON).

Active Optical Network

The active optical network implementation is known as the “Active Node” and is simply

described as a “point-to-point” solution. Subscribers are provided a dedicated optical fibre

cable and the distribution points are handled by active optical equipment. These active

architectures have been setup as either “Home Run Fiber” or “Active Star Ethernet”.

Home Run Fiber (Point-to-Point) Architecture

A Home Run Fiber architecture is one in which a dedicated fiber line is connected at the

central office (CO) to a piece of equipment called an Optical Line Terminator (OLT). At the

end user location, the other side of the dedicated fiber connects to an Optical Network

Terminal (ONT). Both OLTs and ONTs are active, or powered, devices, and each is equipped

with an optical laser The Home Run fiber solution offers the most bandwidth for an end user

and, therefore, also offers the greatest potential for growth. Over the long term Home Run

Fiber is the most flexible architecture; however, it may be less attractive when the physical

layer costs are considered. Because a dedicated fiber is deployed to each premise, Home Run

Fiber requires the installation of much more fiber than other options, with each fiber running

the entire distance between the subscriber and the CO.

Point To Point

CO

User’s Premise

Point To Point

CO

User’s Premise

Fig. 4 Home Run Fiber (Point-to-Point) architecture


Active Star Ethernet (Point-to-Multi Point) Architecture

Active Star Ethernet (ASE) architecture is a point-to-Multi-point architecture in which

multiple premises share one feeder fiber through a Ethernet switch located between the CO

and the served premises.

P2M Switched

Ethernet

CO

User’s Premise

P2M Switched

Ethernet

CO

User’s Premise

Fig. 5 Active Star Ethernet (ASE) architecture

With Active Star Ethernet (ASE) architecture, end users still get a dedicated fiber to their

location; however, the fiber runs between their location and Ethernet switch. Like Home Run

Fiber, subscribers can be located as far away from the Ethernet switch and each subscriber is

provided a dedicated “pipe” that provides full bidirectional bandwidth. Active Star Ethernet

reduces the amount of fiber deployed; lowering costs through the sharing of fiber.

Passive Optical Network (Point-to-Multipoint) Architecture

A Passive Optical Networks (PON) is based on the premise of a point-to-multipoint

architecture. Passive Optical Network is essentially a cost effective optical fiber based access

system for providing multi-play (voice, video, data etc) services, being rolled out by BSNL

shortly, to both business and residential customers. A Passive Optical networks (PON) use

optical fiber and optical power splitters to connect the Optical Line Terminal (OLT) at the

local exchange (CO) to the subscriber’s Optical Network Unit (ONU) on his premises.

Passive splitters are located downstream from the CO and can split the fiber signal up to 32

or more times over a maximum distance of 10-20 km. This means that the bandwidth is split,

or shared, between users as well. The architecture is called passive because all splitters and

intermediate equipment located between the CO and the ONT is passive; that is, it has no

active electronics and therefore does not need separate power. This approach greatly

simplifies network operation & maintenance, and reduces the cost. Another advantage is that

much less fiber is required than in point-to point topologies.


Active FTTx Passive FTTx

Optoelectronics No electronics Only a glass splitter

Lasers No lasers

Receivers No receivers

Power supply No power supply

Batteries No batteries

Equipment racks No equipment racks

Environmental control No environmental control

Active FTTX Passive FTTx

There are two common splitter configurations are being used for PON architecture i.e.

centralized and the cascaded approaches

A. Centralized Splitter Approach

In Centralized Splitter Approach typically uses a 1x32 splitter in an outside plant

enclosure, such as a fiber distribution terminal. In the case of a 1x32 splitter, each device is

connected to an OLT in the central office. In this approach, optical splitters are concentrated

in a single location from which all customer’s optical network terminals (ONTs) at 32 homes

are connected.


1X321X32

Central Office

Splitter Splitter

1X321X32

Central Office

Splitter Splitter

Fig. 7 Centralized Splitter Approach

Cascaded Splitter Approach

A cascaded split configuration results in pushing splitters deeper into the network as shown in

fig.6. Passive Optical Networks (PONs) utilise splitter assemblies to increase the number of

homes fed from a single fibre. In a Cascaded PON, there will be more than one splitter

location in the pathway from central office to customer. Currently, standard splitter formats

range from 1 x 2, 1 x 4, 1 x 8, 1 x 16 and 1 x 32 so a network might use a 1 x 4 splitter

leading to a 1 x 8 splitter further downstream in four separate locations. Optimally, there

would eventually be 32 fibers reaching the ONTs of 32 homes.

1X2

1X16

1X16

1X2

Central Office

SplittersSplitters

1X41X4

1X8

1X2

1X16

1X16

1X2

Central Office

SplittersSplitters

1X41X4

1X81X8

Fig.8 Cascaded Splitter Approach

There are several “flavors” of PON technology, i.e. new access technology named APON

(ATM Passive Optical Network), BPON (Broadband Passive Optical Networking), EPON


(Ethernet Passive Optical Networking) and GPON (Gigabit Passive Optical Networking)

which delivers gigabit-per-second bandwidths while offering the low cost and reliability.

APON

ATM PON (APON) was standardized by the ITU in 1998 and was the first PON standard

developed. It uses ATM principles as the transport method and supports 622 Mbps

downstream services and 155 Mbps upstream service shared between 32-64 splits over a

maximum distance of 20 km.

BPON

Shortly after APON, Broadband PON (BPON) followed and is very similar to APON. BPON

also uses ATM, but it also boasts superior features for enhanced broadband services like

video. BPON has the higher performance numbers then APON pre-splitting maximum of 1.2

Gbps downstream and 622 Mbps upstream.

EPON

The IEEE standardized Ethernet PON (EPON) in the middle of 2004. It uses Ethernet

encapsulation to transport data over the network. EPON operates at rates of 1.25Gbps both

downstream and upstream (symmetrical) over a maximum reach of 20 Kms

GPON

Gigabit PON (GPON) is the next generation of PON’s from the line of APON and BPON.

The ITU has approved standard G.984x for it. GPON will support both ATM and Ethernet

for Layer 2 data encapsulation so is clearly an attractive proposition. It supports 2.5 Gbps

downstream and 1.25 Gbps upstream.

GE-PON A-PON/B-

PON

G-PON

LineRate(Downstream) 1.25G 155M,

622M

1.2G 1.2G,

2.4G,

Basic protocol MPCP ATM GFP

Line code 8B/10B Scrambled

NRZ

Scrambled

NRZ

Protocol Standard 802.3ah ITU-T

G.983.1

ITU-T

G.984.1


OLT/ONU OAM standard 802.3ah ITU-T

G.983.2

ITU-T

G.984.2

Security standard Vendor

agreement or

802.1

ITU-T

G.983.1

ITU-T

G.984.1

DBA Standard N/A ITU-T

G.983.4

ITU-T

G.983.4

Redundant protection standard N/A ITU-T

G.983.5

ITU-T

G.983.5

System management support

standard

N/A ITU-T

G.983.6

ITU-T

G.983.7

ITU-T

G.983.8

ITU-T

G.984.4

Analog Video service WDM overlay WDM

overlay

WDM

overlay

Ethernet Native Ethernet Ethernet

over ATM

GFP

E1/T1/E3/T3 service TDMoE CBR CBR

POTS service VoIP VoATM DS0

FOR

GEPON Optical Feature GPON Optical Feature

Optical fiber: Single mode (SMF) Optical fiber: Single mode (SMF)

Connector: SC connector Connector: SC connector

Optical loss budget: up to 29dB Optical loss budget: up to 29dB

Max split/OLT port: up to 32/64 (reach

up to 20/10km)

Max split/OLT port: up to 64 (reach up

to 15km)

PON link data rate: 1.25Gbps

symmetrical

PON link data rate: Up stream

2.5Gbps, down stream 1.25Gbps

Wavelength: Tx: 1490nm, Rx: 1310nm Wavelength: Tx: 1490nm, Rx: 1310nm,

RF overlay wavelength: 1550nm RF overlay wavelength: 1550nm


GEM Mode only

Downstream/Upstream Forward Error

Correction (FEC)

PON Architecture:

The key interface points of PON are in the central office equipment, called the OLT for

optical line terminal, and the CPE, called ONU for optical network unit (for EPON) and ONT

for optical network terminal (for GPON). Regardless of nomenclature, the important

difference between OLT and ONT devices is their purpose. OLT devices support

management functions and manage maximum up to 128 downstream links. In practice, it is

common for only 8 to 32 ports to be linked to a single OLT in the central office. On the other

hand the ONT (or ONU) devices in the CPE support only their own link to the central office.

Consequently, the ONT/ONU devices are much less expensive while the OLTs tend to be

more capable and therefore more expensive.

1. OLT: The OLT resides in the Central Office (CO). The OLT system provides

aggregation and switching functionality between the core network (various network

interfaces) and PON interfaces. The network interface of the OLT is typically connected to

the IP network and backbone of the network operator. Multiple services are provided to the

access network through this interface,.

2. ONU/ONT: This provides access to the users i.e. an External Plant / Customer

Premises equipment providing user interface for many/single customer. The access node

installed within user premises for network termination is termed as ONT. Whereas access

node installed at other locations i.e. curb/cabinet/building, are known as ONU. The

ONU/ONT provide, user interfaces (UNI) towards the customers and uplink interfaces to

uplink local traffic towards OLT.

3. PON: Distributed or single staged passive optical splitters/combiners provides

connectivity between OLT & multiple ONU/ONTs through one or two optical fibers. Optical

splitters are capable of providing up to 1:64 optical split, on end to end basis. These are

available in various options like 1:4, 1:8, 1:16, 1:32 and 1:64.

4. NMS: Management of the complete PON system from OLT.

One OLT serves multiple ONU/ONTs through PON

TDM/TDMA protocol between OLT & ONT


Single Fiber/ Dual Fiber to be used for upstream & downstream

Provision to support protection for taking care of fiber cuts, card failure etc.

Maximum Split Ratio of 1:64

Typical distance between OLT & ONT can be greater than 15Km (with unequal

splitting - up-to 35Km)

· Downstream transmission I.e. from OLT to ONU/ONT is usually TDM

· Upstream traffic I.e. from ONU/ONT to OLT is usually TDMA

PON system may be symmetrical or asymmetrical

PON and fiber infrastructure can also be used for supporting any one way distributive

services e.g. video at a different wavelength PON is configured in full duplex mode in a

single fiber point to multipoint (P2MP) topology. Subscribers see traffic only from the head

end, and not from each other. The OLT (head end) allows only one subscriber at a time to

transmit using the Time Division Multiplex Access (TDMA) protocol. PON systems use

optical splitter architecture, multiplexing signals with different wavelengths for downstream

and upstream.

EPON & GPON Applications:

Residential or Business Services

High Speed Internet


Transparent LAN Service

Broadcast Video

Multi-Play (Voice, Video, Data etc.)

TDM Telephony

Video on Demand

On –line Gaming

IPTV etc

User Categories

FTTH / FTTB Networks may deliver services to the following categories of users:

Residential refers to private users in their homes. Residential users may live in “MDU”

(multi-dwelling units such as apartments/condominiums) or “SFU” (single family dwelling

units such as stand-alone houses/villas/landed property).

Business refers to large (corporate), medium, and small (Small Business, Small Office Home

Office) business users. Businesses may occupy “MTU” (multi-tenanted units such as office

blocks/towers) or “STU” (single-tenanted units such as a stand-alone office building or

warehouse).

Active Network Elements in EPON

Active Electronic components of EPON consists of CO chassis and ONUs that are

located at both ends of the PON. The CO chassis is located at the service provider’s CO,

head end or POP and houses OLTs, network interface modules(NIM) and the switch Card

Module(SCM). The PON connects an OLT card to 64 ONUs, each located at a home,

business or MTU. The ONU provides customer interfaces for data, video and voice

services as well as network interfaces for transmitting traffic back to the OLT.

CO Chassis

The CO chassis provides the interface between the EPON system and the sevice

provider,s core data, video and telephony networks. The chassis also links to the service

provider’s core operations network through an element management system. (EMS).

WAN interfaces on the CO chassis will typically interface with the following types of

equipment.

DCSs, which transport non switched and non locally switched TDM traffic to the

telephony network. Common DCS interfaces include digital signal(DS-1, E-1, STM-1 etc.

Voice gateways, which transport locally switched TDM/voice traffic to the public

switched telephone network (PSTN)

IP routers or ATM edge switches, which direct data traffic to the core data network.


Video network devices, which transport video traffic to the core video network.

Key functions and features of the CO chassis include the following

Multiservice interface to the core WAN

Gigabit Ethernet interface to the PON

Layer 2 and 3 switching and routing

QoS issues service level agreements

Traffic aggregation

Houses OLT’s and SCM

Optical Network Unit

The ONU provides the interface between the customer’s data, video and telephony networks

and the PON. The primary function of the ONU is to receive traffic in an optical format and

convert it to the customer’s desired format (Ethernet, IP multicast, POTS, E1 etc.) A unique

feature of EPON’s is that, in addition to terminating and converting the optical signal, the

ONU’s provide Layer 2 and 3 switching functionality which allows internal routing of

enterprise traffic at the ONU. EPON are also well suited to delivering video services in either

CATV format using a third wavelength or IP video.

Key features and functions of the ONU include the following.

Customer interfaces for POTS, E1, 100Base-T, IP multicast and dedicated wavelength

services.

Layer 2 and 3 switching and routing capabilities.

Provisioning of data in 64kbps increments upto 1Gbps

Low start up costs and plug and play expansion

Standard Ethernet interfaces eliminate the need for additional DSL or cable modems.

EMS

The EMS manages the different elements of the PON and provides the interface into the

service provider’s core operations network. Its management responsibilities include the

full range of fault, configuration, accounting, performance and security (FCAPS)

functions.

Key features and functions of the EMS include the following

Full FCAPS functionality via a modern graphical user interface (GUI)

Capable of managing dozens of fully equipped PON systems.

Supports hundreds of simultaneous GUI users.


How Ethernet PON’s work

The key difference between EPONs and APONs is that in EPONs, data is transmitted in

variable-length packets packets of upto 1518 bytes according to the IEEE 802.3 protocol for

Ethernet, whereas in APONs, data is transmitted in fixed length 53 byte cells ( with 48 byte

payload and five byte overhead), as specified by the ATM protocol. So traffic using ATM

protocol is time consuming and creates onerous overhead that is commonly referred to as the

“ATM Cell tax”. Ethernet was tailor ,made for carrying IP traffic and dramatically reduces

the overhead relative to ATM.

GEPON uses Wavelength Division Multiplexing (WDM)

Technology.

– Downstream Wavelength: 1490nm.

– 1550nm is optional downstream for Video broadcast.

– Upstream Wavelength: 1310nm.

OLT broadcasts packets to ONUs. ONU processes only on the packets labeled with its

Logical Link ID (LLID).

Note: OLT assigns the LLID to ONU upon successful registration.Upstream traffic is based

upon TDM technology. Each ONU is allowed to send packets only in its pre-assigned time

slots. The time slot is synchronized so that the upstream packets from one ONU will not be

interfered by other packets from other ONUs. In upstream direction, ONUs aggregate frames

and transmit them in a burst during a timeslot assigned by the OLT. In downstream direction,

ONUs selectively forward frames based on unique tag (Logical Link ID) Bandwidth

Assignment is done using request/grant mechanism. All grant and request messages are

Ethernet MAC Control frames All OAM messages are Ethernet frames.



Chapter 2

FTTH Optical Link Design

Specifications should be taken either from the manufacture specifications Here we will

discuss the link design of FTTH -GEPON of UTSTAR system as an example.

Component and Loss


1. Calculate the reach of the network diagram shown below

Can the system reach 10 Km

What is the maximum reach?


Down stream power budget =

Maximum Reach =


Up stream power budget =

Maximum Reach =

2. Calculate the reach of the network diagram shown below

Can the system reach 10 Km

What is the maximum reach?

Down stream power budget =

Maximum Reach =


Up stream power budget =

Maximum Reach =


Chapter 3

Maintenance & Wiring at Subscribers’ Premises

BLOCK WIRING OF MULTI-STOREY BUILDING FOR FIBRE

1.0 SCOPE

There is growing need and demand to deliver end- to-end services in the wake of

similar offers from other telecom Service Providers and the need for quick delivery of

services. This is also beneficial as it enables timely delivery of services as residents move in.

In this scenario, it is pertinent to get standard wiring done up to the end point to deliver voice,

data and broadband services.

These specifications also include Fibre to the Home (FTTH) wiring, which may be

used where applicable based on GPON specs available as on date.

It is necessary to emphasize that it is not possible to spell a rigid methodology for

block wiring. Method of block wiring and the various arrangements necessary for the same in

a multistorey building may vary depending upon the size and the purpose for which the

building is being constructed and the various types of telecommunication services required.

Therefore this document may be used as general guideline since actual implementation may

vary depending upon type of building, requirement and many unforeseen situations e.g. at

which stage block wiring is undertaken (during construction or after construction), the

permission being given by builder/society/resident about the particular way/material to be

used etc. Even then, it is always preferable to have some broad guidelines whereas specifics

may be decided at site only with mutually agreed and feasible methodology.

2.0 DESCRIPTION

2.1. GENERAL

2.1.1. Smaller Buildings

While the question of providing internal conduit wiring for smaller buildings is

essentially one of laying conduits and junction boxes properly at suitable places, providing


block wiring in multi-storey buildings is more complicated. It requires the following

arrangements to be made:-

a. Leading in underground cable from the main road into the building.

b. Provision of sufficient space and arrangement for terminating the

underground cables and feeder cables to different floors.

c. Identification of vertical risers to take the feeder cables to different floors.

d. Arrangement for distribution of the cables in each floor through the conduits.

e. Making arrangement for wiring within the flat/shop, if required.

f. Shall have up to 32 connections

2.1.2. Big Multi storey Buildings

In a big multi-storey building with up to two risers sufficient attention should be paid

to the above points so as to draw the telephone cables smoothly. It is tentatively proposed

that we may insist on the following facilities to be provided:

a) Ducts with necessary inspection holes for leading in cable into the building.

b) Safe and conveniently accessible space for termination. If cables already laid

for each floor/flat etc then this place for termination of outside cable should be

just adjacent to the cables termination coming from different floors/flats so

that jumpering is possible neatly.

c) Identification of vertical cable riser if the number of floors in the building

exceeds 3, which in all likelihood be available in multi-storey buildings as it is

a mandatory requirement to get the sanction of building plan from concerned

local authority in most States.

d) Number of connection ranges from 32 to 48/96.

2.1.3. Large Multi storey Buildings

In case of large multi-storey buildings with multiple risers or for that matter

even in upcoming new houses wiring for telephone connections is generally done in a

concealed manner through conduits and proper entry points for Risers as Multi-storey

buildings are primarily intended for Commercial, Business and Office use as well as for

residential purposes and it is natural that Telecommunication facilities should be required to

be provided in such multi-storey building complex. These requirements are to be planned


well in advance so that suitable provisions are made in the building plan in such a way that

the demands for telecommunication services in any part of the building at any floor are met at

any time during the life of this building. If there is no pre-planned wiring, if wiring is

insufficient then wiring done afterwards will be a surface, unconcealed wiring. This can be

avoided if telephone wiring is planned and demand of telecom facility is forecasted liberally

and carried out as part of building construction, just like electrical wiring. Number of

connections expected more than 100, 19 inch racks FDF is preferable in this case.

2.2.

In the unlikely situation of risers not being provided, the cable may be brought to each

floor via Conduit/PVC pipe of suitable dimension. The ISI mark PVC pipe of required size /

diameter shall be fixed along the duct / shaft of the building or suitable The PVC pipe shall

be fixed on the wall / runway with proper clamps / saddles with a maximum spacing of 50

cms. The PVC pipe shall be drawn from the cellar / ground floor to the respective floors of

the building.

There may be situation, where no duct for cable lead-in has been provided

in the building. In such situation possibility should be explored for making any

feasible arrangement to bring the cable underground inside the building. Option of laying

overhead should be used only as the last alternative and as a temporary solution only till

underground arrangement is feasible.

2.3. If no concealed dedicated conduits with access on each bend are provided, then

rectangle channels may be used, so that there is no undue pressure on fibre and it can be

accessible easily for the distribution of fibres on each floor/ inside the flat/ shop, It is again

reiterated that in case of external wiring, exact type of conduit/ channel can be decided only

after keeping the look of the building and how well it can be integrated with it, the consent of

the owner/society. The surface shall be painted and brought to original finish. Now day’s

flexible conduits are also available in the market.

The standards can be made rigid, only after practically implementing the various

methods and there by pros and cons as the situation demands.

2.4. Cable Lead In:

Conduits of iron solid-drawn of lap weld with galvanized or stove enamel surface, in

the size ranges from 19mm to 64mm (19, 25, 31, 38, 51 and 64) may be used. Use of PVC

conduits of suitable sizes (ISI make) is desirable in view of their smooth inner surface. All

these conduits must have easily accessible inspection bends. One or two steel wires must be


drawn in these conduits to facilitate later pulling of optical fibre cables. Also, the TEC

specifications are available for 40mm &32 mm outer dia. The 96F/48F cables have outer

diameter of 18 mm. The pulling force does not exceed 2.5 Kg X Weight of the cable of 1 KM.

The OF Cable to the Multi Storey Building for FTTH may drawn as per the Planning

Guidelines of BSNL vide letter No.214-117/2000 TPL (CX) dated 31.01.01. Annexure V.

Before terminating the OF cable, the number of fibres to be dropped is planned and equal

number of many pigtails are spliced. The OF Cable termination is done either in basement or

ground floor as permitted by the Building authorities on TJB (OFTB) or Customer Premises

FDMS. The TJB dimensions are 50x29.5x9.5 Cms. Refer to Figure.7

3.0 METHOD OF INTERNAL BLOCK WIRING.

A. OPTICAL FIBRE TERMINATION

3.1. Laying Practice underground in customer premises as per the standard practice /

Norms as shown in Figure 1.


FIGURE 1


FIGURE 2

3.2. For Optical Fibre Cable of Sizes 24F/48F/96F, Optical Cable leads into the

building / multistoried building using PLB ducts up to the entry point of the Premises /

Building and suction pipe (25 mm) from the entry point to the MDUB for termination /

distribution in Multi Dwelling Unit Box-Type-II (MDUB) as per TEC GR No. GR/FTB02/01

Sep 2005 at Ground floor / the space provided by the building authority for external cable

entrance. The MDUB should be mounted at a height of 2.5 meters. The


optical fibre cable shall be routed at every bend with a minimum bending diameter of

20D (where D is the Cable diameter). The mounting of MDUB should have sufficient space

near its exit and entry holes. In case of 2F / 4F / 6F taken out from the MDUB, Patch cords /

Optical fibre cable shall be used for different floors as shown in figure 2. For more than 6

Fibres arrangement another MDUB shall be used to cater the requisite connections. Further

for higher fibre counts, Building Premises Box, as per GR for Fibre Distribution and

Management System (FDMS) for Ribbon type optical fibre cables (GR No. GR/FDM-02/01.

Jan 2001) may be used. The FDMS for Building Premises can be installed in the basement of

a building to act as distribution box as shown in figure 3.

FIGURE 3

The fibres of incoming cable shall be distributed into outgoing cables either by

directly splicing fibres of incoming cable to fibres of outgoing cables or patching the

incoming fibres to outgoing fibres as shown in Figure 3. The Optical fibre termination and

distribution box shall be mounted at a standard height of 2.5 meters to manage the fibre

management effectively. It should be properly covered with gasket sealing and should have

lock and key arrangement. The minimum bending diameter allowed for the fibre coils inside

the splice trays shall be at least 70 mm. The output cables i.e. Optical fibre cables (4F/6F)

laying through the riser of the multi storied building, lead distribution to each floor should be

routed using PVC Conduit with a minimum bending diameter.


3.3. There are two basic types of bends in fiber—micro bends and macro bends. As

the names indicate, micro bends are very small bends or deformities in the

fiber, while macro bends are larger bends (see the figure 4 below).

FIGURE 4

The fiber’s radius around bends impacts the fiber network’s long-term reliability and

performance. Simply put, fibers bent beyond the specified minimum bend diameters can

break, causing service failures and increasing network operations costs.

3.4. Optical fibre termination at each floor of the multi storey building using

Subscriber premises Box Type-I as per TEC GR No. GR/FTB-02/01 Sep

2005. The Subscriber premises Box should be type approved by Quality

assurance Circle, BSNL, Bangalore. The wall mounted Patch panel 6F Cable

is a typical arrangement of Optical fibre and Patch Cords as shown in Figure

5 & 6.

Wall Mounted Patch panel 6 F

FIGURE 5


Patch cords laying leading to individual flats using splitter adjacent to Subscriber

premises Box depends upon the number of proposed connections.

3.5. Splitter: The splitter is a passive device which accepts one or two fibres and

gives out 2/4/8/16/32/64 optical outputs. The output of splitter is provided with SC-UPC

(Blue) type connectors.

This patch cord can be crimped in the field and the patch cord conforms to G-657

standards. This cable is available in coils of more than 100 meters. Hence, depending on the

floor length, the patch cord can be prepared at site.

If the number of flats in the building is 32 or less, the splitter can be installed

adjacent to TJB. This will not necessitate installation of multiple splitters in each floor. Care

should be taken to protect the splitter from moisture and dust. The typical losses of various

splitters are shown in Table –I.

TABLE -I

Sl.No Type of splitter Loss

1 2 4.0 dB

2 4 7.5 dB

3 8 11.0 dB

4 16 14.0 dB

5 32 18.0 dB

6 64 21.5 dB

Generally, the splitters are represented as (1,2x4), (1,2x8).

FIGURE 6


1- indicates one input fibre

2- indicates two input fibres (Second fibre in protection

path) 3- indicates the number of outputs.

3.6. ONE FIBRE CAN BE GIVEN A MAXIMUM OF 32 SPLITS: If the number

of flats in the building is more than 32 in each floor, one fibre can be terminated in each floor,

and depending on the number of flats in each floor, suitable splitter can be provided in

each floor. As shown in Figure. 8, 9, 10. Link Budget shall be taken into

consideration as per existing norms.

GPON Optical Fibre Specification

■ Fibre Type: ITU G.652 from GLC to premise and ITU G.652 or G.657 in

premise

■ Single-mode fibre with zero-dispersion wavelength around 1310 nm

■ Minimum optical return loss: -40 dB

■ Maximum PON length: 20 km standard

3.7. In case of Fibre to the Home (FTTH) in the multi storey buildings, fibres

will be required to be laid to individual homes. The Fibre cable will be

brought to the basement/ ground floor or to the middle height of the

multistoried building (as per the requirement / demand / place value) / any

other suitable location of the building and from there OF cables of suitable

sizes will be drawn to each floor and terminated in the Fibre Distribution

Frame (FDF) (wall mounted and covered) in each floor. The splitters may be

used for utilizing the same fibre for multiple customers. The location of

splitter will depend on the total no. of fibre (i.e. no. of flats in the building

and of course on the characteristics of the splitter. There may be requirement

of only one splitter for the whole building if the building is small. If the no.

of flats in a multi-story are more, even we may have to plan more splitters

may be floor wise.


For the purpose of drawing of fibres, separate conduits should be insisted. If

conduits are concealed, then those parts of it should be accessible wherever

there is a bend, so that fibre cable can be drawn without damaging the fibre.

3.8.

a. Equipment Specification-Annexure-I

b. Permanently lubricated duct (PLB duct) specification-Annexure-II

c. Bending / Junction Specification-Annexure-III

d. Pigtail / Patch cord conduit / electrical shielding specification- Annexure-IV

3.9. CONCLUSION: The FTTH an access technology network through which

high speed data services are provided to the customer through Optical Fibre

up to his premises.

Also, it is deployment of triple play services through Optic fibre cable from

Central Office to Individual Home. This is the most reliable next generation

triple play network design in which each home is provided with separate fibre

optic.

Passive Optical Splitter (Wall Mounting)

Figure 7


Dimensions 39 cmsx26.5cmsx7.5cms.

Port Count ■ M x N where M representing the input ports can be 1 or 2, and N

representing the output ports can be 4, 8, 16, 32, or 64.

Environmental

■ The 1xN and 2xN passive optical splitters conform to the

environmental requirements specified for ‘B2’ category for QM-333 (issue

2-1998) BSNL QA document.

FTTH ARRANGEMENT FOR LESS THAN 32 FLATS (TJB &

SPLITTER IN G.FLOOR OR BASEMENT)

Figure 8


1: 32 SPLITTER FIBRE ARRANGEMENTS DONE IN FIELD

Figure 9


(FTTH ARRANGEMENT WITH TJB IN G.FLOOR & SPLITTER IN EACH FLOOR)

Figure 10


Annexure I

Equipment Specification

Type I Type-II

Material of Box Polycarbonate/Polypropylene Polycarbonate/Polypropylene

Typical installation Location Indoor Only Indoor / Semi Covered

Length (mm) (without entry ports,

glands etc) (+/- 2 mm)

150 240

Width mm (+/- 2 mm) 200 160

Depth (mm) (+/- 2 mm) 40 80

Incoming Cables 1X4F or 1X6F 1X 24F

Outgoing Cables None Up to 6 Cable (total no. fibres

not exceeding 24)

No. of Organizer trays 1 12

Maximum Patching Capacity 6 24

Cable entry Ports (Cable diameter6mm

to 14mm)

1 7

Pig tail / Patch cord exit Ports

Required No. X 3.0 mm diameter

1 None


Annexure II

Permanently lubricated duct (PLB duct) specification

PLB duct 32 mm /

26 mm PLB duct 40 mm /

33 mm PLB duct 50 mm /

42 mm

Outside diameter 32 mm / 26 mm 40 mm / 33 mm 50 mm / 42 mm

Standard length 1000+/-100 meters 1000+/-100 meters 1000+/-100

meters

Maximum outer diameter of OF Cable

can be installed by blowing technique

12 mm 16 mm 21 mm

Note: Selection of duct size depend on the outside diameter of the O.F. Cable to be installed

Indoor Protection Size

Suction Pipe 25 mm

PVC Conduit / Casing Capping As per the requirement ( Normally 25 mm)

Annexure III

Bending / Junction Specification

Precautions to be taken Standard followed

Bending Diameter of OF Cable 20D where D is the Diameter of the OF Cable

Bending Diameter of Fibre 70 mm

Loss of an adapter taken into account = or < 0.10 dB

Type 2 Splitter 4.0 dB Loss







Annexure IV

Pigtail / Patch cord conduit / electrical shielding specification

Subscribers fitting Standard followed

PVC Conduit As per the requirement (Normally 25 mm)

Casing Capping As per the requirement (Normally 25 mm)

Earthing To be checked at the Subscriber end

Annexure V

Planning guidelines of BSNL vide Letter No. 214-117/2000 TPL (CX) Dated

31/01/2001 Annexure VI

Bend Insensitive Optical Fibre Cable

G.657A fibre cable is for application in FTTH networks, and is compatible with

G.652 Fibre

Fiber Properties

Fibre Style Unit Single Mode

Condition Nm 1310/1550

Attenuation dB/Km 0.40/0.30

Dispersion 1550 nm Ps (nm * Km) </= 18

1625 nm Ps (nm * Km) </= 22

850 nm MHZ*Km

1330 nm MHZ*Km

Optical fibre Cable Structure

Fibre Count 1

Fibre Property Colour Original

OD 242 +/- 7um

Tight Buffered property White Environmental Protection PVC

OD 0.87 +/- 0.05 mm

Thickness 0.31 +/- 0.02mm

Outer Jacket Thickness 0.46 +/- 0.05 mm

Material Environmental Protection LSZH

OD 2.80-2.95 mm


Applications Units Notes

Temp Range Deg Centigrade -20Deg Cent to + 70

Deg Cent

Nominal weight g/m 7.3

Min. Bending radius (mm) Dynamic mm 20H

Min. Bending radius (mm) Static mm 10H

Max. Tension (N) Short-term N 150

Max. Tension (N) Long-term N 80

Max. Crushing Resistance (N/100 Sq mm) N/100 Sq mm 500

LIST OF ABBREVIATIONS

ABS Acrylonitrile Butadiene Styrene

BIS Bureau of Indian Standards

BSNL Bharat Sanchar Nigam Limited

IS Indian Standards

ISO International Standard Organizations

ITU International Telecommunication Union

FTTH Fibre to the Home

GPON Gigabit Passive Optical Network

EI engineering Instructions

PVC Poly Vinyl Chloride

FDMS Fibre Distribution and Management System

MDUB Multi Dwelling Unit Box

SPB Subscriber Premises Box

PLB Duct Permanently Lubricated duct

FDF Fibre distribution Frame

OFTDB Optical fibre termination and distribution Box

BP building Premises

OF Optical Fibre

TQA Telecom Quality Assurance

QM Quality Manual

TEC Telecommunications Engineering Centre

TJB Termination Joint Box

GR Generic requirements

Kg Kilogram

Sq cm Square Centimeter


Chapter 4

Optical Time Domain Reflectometer

Object :

Principle of operation of Optical Time Domain Reflectometer. Fault location, Fibre,

connector and splice loss measurement by OTDR.

Principle of operation of OTDR

OTDR is based on the principle of back scattering of light. Back scattering results from

Rayleigh scattering and Fresnel reflections. Rayleigh scattering is caused by refractive

displacement due to density and compositional variations in the fibre. In a quality fibre, the

scattered light can be assumed to be evenly distributed with length. Fresnel reflections occur

because of changes in refractive index at connections, splices and fibre ends. A portion of the

Rayleigh scattered light and Fresnel reflected light reaches the input and as back scattered

light.

The OTDR technique consists of sending impulses to the fiber and measuring the time delay

and intensity of the backscattered signal. The backscatter effect occurs because of the same

reasons that we have attenuation on optical fiber, scattering. What happens is that some of the

light gets reflected back due to changes in the molecular density of the glass. Measuring this

light is equivalent to measuring fiber attenuation.

The structure of an OTDR is basically a light source to emit signal pulses and an optical

receiver connected to a data processing unit. The emitted signal is sent directly into the fiber

and the incoming reflection directed to the receiver by a beamsplitter. The light source is

synchronized with the receiver so that time delay between outgoing and incoming signals can

be measured.

Much like the radar principle, the intensity of the reflected signal depends on the fiber

attenuation and occasional bends, twists or splices. The time delay of the reflected signal is

related to the position of the fault in the fiber.

The result of an OTDR measure is a curve of reflected signal intensity versus time delay

whereas the curve slope corresponds to the attenuation coefficient. Discontinuities in the

curve indicate additional attenuation due to splices and peaks indicate large reflections,

possibly due to reflections on connectors.


Fig. 1 : OTDR BLOCK DIAGRAM Figure shows the schematic diagram of an OTDR. A short, high powered Pulse is injected

through the beam splitter into the fibre. The light is then back-scattered as it travels through

the fibre. The beam splitter directs the back scattered light to the photodetector. The

amplified output of the detector serves as the vertical input to the oscilloscope. Because the

power to the detector is extremely small, repeated measurements are made by the Electronics

of the OTDR, the SNR is improved by averaging the readings, after which the results are

displayed.

The OTDR screen displays time horizontally and power vertically. Fibre attenuation appears

as a line decreasing from the Input End of the fibre to the output end.

GENERAL WAVEFORM ANALYSIS BY OTDR:

The CRT waveform display, when measuring the splice and transmission losses of a fibre is

shown in figure. The horizontal axis is the distance equivalent to the transmission time that

actually corresponds to the fibre length.

The vertical axis represents reflected light power detected by the OTDR.

The first spike to the extreme left is caused by Fresnel reflection at the near-end connector.

The backscattered light indicates the fibre characteristics. For example, if the fibre is low loss

and the characteristics are homogenous along the entire fibre, the trace will be a straight line

falling along the horizontal axis.


The gradient corresponds to the optical fibre loss. If there is a break or a connection along the

fibre, a Fresnel reflection will also appear as shown in Figure.

When a fibre with a spliced connection is measured, a spike similar to the type caused by a

break does not appear, although a step does appear. The step indicates the splice loss. If the

fibre is broken or the end of the fibre cable is detected, a large Fresnel reflection will appear.

Fig.2 : General Waveform Analysis

Both the input and the back scattered light attenuate over distance, so that detected signal

becomes smaller over time. A connector, splice fibre end or abnormality in the fibre appears

as an increase in power on the screen, since backscattering from Fresnel reflections will be

greater than back-scattering from Rayleigh scattering.

The quality of a splice can be evaluated by the amount of back scattering. Greater back

scattering means a higher loss splice.

Improvement in received power is possible by increasing pulse width at the expense of length

resolution. Back scattered signals are normally buried in noise because of their tiny

amplitudes. Special techniques are used to improve S/N of received signal in OTDR.

Whenever the optical pulse launched into the fibre encounters a transition in media, for

example, at a fibre ‘break’, connectors, splicing points and free fibre ends, reflection occurs

in addition to refraction. Depending upon the reflection coefficient at that point, the reflected

light is received back at the sending end of the fibre. This reflected light is typically 4 % of

incident light. Thus, the reflected light received at the sending has a much higher power level


as compared to back-scattered light, which is typically 50 dB lower than the incident optical

power. Resolution is determined by optical pulse width and the response time of the receiver.

Sharp lasers mey be used for very short pulse width but resolution is limited by response time

of high speed photodiode. It is possible to make resolution to be as small as few mm.

Sampling rate of 50 Mhz corresponds to resolution of 2 meters.

CONCEPT OF DEADZONE Dead zones are related to the presence of reflections. Dead zone occurs when

reflected signal saturates the OTDR receiver. The dead-zone is the distance corresponding to

the initial length of fiber under test. whose trace is missed in OTDR, due to the saturation of

the receiver circuit of OTDR by strong signal like Fresnel reflection and due to imperative

property of this circuit that a certain time is lost in transforming the time into distance. The

back scattered signals received from the initial distance (dead zone) take too less a time to be

transformed into corresponding trace by the receiver circuit. The dead zone is the sum of

pulse-width and the distance corresponding to recovery time of the receiver circuit. The

smaller the pulse- width the smaller the dead zone.

Most OTDRs use a cursor to mark a horizontal point on the trace and display the

distance in terms of time and physical distance.

OTDR dynamic range is the difference between the initial backscatter level and the noise

level after 3 minutes of measurement time, expressed in db. Dynamic range and power losses

within the fibre system set the length possible before the back scattered light becomes too

weak to be detected. With typical low-loss fibre used in long distance telecommunication, the

OTDR can be used on lengths of 20 to 140 KM.

GHOST SPIKES

These spikes are caused by (1) large fresenal reflection, (2) wrong “Distance range “

selection. Ghost spikes can be eliminated by :

1. cleaning connectors and filling matching fluid.

2. selecting “distance range” twice the length of fiber under test.

3. set markers to avoid ghost spike or use 2PA method instead of LSA.

Uses of OTDR

Loss per unit length, splice and connector evaluation and fault location, are three field

uses of OTDR. These measurements are very important during installation and for system

maintenance.


OTDR measurements are used to evaluate the attenuation characteristics of a fiber.

These measures concern the attenuation coefficient, splice loss or plug connections allowing

the installer to determine with considerable precision what are the problems in a fiber and

where they are located.

1. Length of O.F.C Section

2. Distance up to the O.F.C. break point.

3. Loss in db/km. & Total Loss of O.F.C. Section

4. Nos. of splices in OFC Section & individual Splice Loss.

5. Connector Loss.

CORRECTION FACTOR The correction factor is best determined by comparing a known cable length to the

corresponding fibre length as measured with the OTDR. This factor compensates for fibre

over length and OTDR variance. Below is the equation for calculating the correction factor.

CABLE LENGTH

CORRECTION FACTOR = -------------------------- FIBER LENGTH

CABLE LENGTH = FIBER LENGTH X CORRECTION FACTOR Fault location using the correction factor (example)

1. From the route/cable plan, the distance between splice points # 2 and # 3 is

4782 m.

2. On the OTDR, the fiber distance to splice point # 2 is 11.612m. the fiber

distance to splice point 03 is 16.467m.

3. By subtracting, the fiber distance between splice points # 2 and # 3 is

calculated to be 4855m.

4. Correction factor = 4782/4855 = 0.985.

5. On the OTDR, the fiber distance from splice point # 3 to the fault is 2230m.


6. Cable length = (2230) (0.985) = 2196m.

7. From the route/cable plan, the meter mark at splice point # 3 or the cable

section containing the fault is 0019m.

8. Fault location is calculated at meter mark: 0019 meter mark + 2196 meters =

2215 meter mark.

The MW9070A Optical Time Domain Reflectometer (OTDR) has been developed for

finding faults in optical fibres when installing and maintaining optical fiber system. It can be

used to measure total loss, interval loss, splice loss and cable length (distance).

The automatic measurement procedure and the small lightweight portable design

make it very easy to use at field installation and maintenance of optical fibers. In addition, the

internal memory can save measured waveforms for subsequent analysis and print-out. The

MW9070A also has an interface for connecting a computer to process measurement results.

Faults are located and losses are measured automatically by just pressing the [Start]

key after setting the setting the measurement conditions at the Setup screens.

Trace Waveform

The trace waveform is displayed with the attenuation on the y-axis and the distance on

the x-axis. The left end of the trace display is the OTDR optical output and the right end is

the far end of the fibre cable. The symbol is displayed at faults in the cable.

Measurement Conditions


Light Wavelength (), Distance Range (DR), Pulse width (PW), Index of Refraction

(IOR), Number of Averagings (Average)

Search Results

Total number of Faults (Total), Total Fiber Length (Fiber Length), Total Loss of

Entire Fibre (Total Loss)

Event Table

Number of Fault counted from Left (no.), Distance from OTDR(Position), Splice

Loss, Return (R.loss), Total Loss to the Fault (T.Loss).

Trace Waveform

The trace waveform is displayed with the attenuation on the y-axis and the distance on

the x-axis.

Measurement Conditions

Light Wavelength (), Distance Range (DR). Pulse Width (PW).

Index of Refraction (IOR). Number of Averagings (Average). Measurement Results


CHAPTER-5

FTTH ONU Configuration

Alphion Make

Specifications Link Budget 28 dB

Wavelength Upstream:1310 nm | Downstream: 1490 nm

Line rate Upstream: 1.244 Gb/s | Downstream: 2.488 Gb/s

Output power +0.5 to +5.0 dBm

Sensitivity , overload -28 dBm,

-8dBm

Connector SC/APC

Configuration steps

BSNL Optical Fiber cable is directly connected to FTTH Modem and an Ethernet

cable from ONT is connected to PC or laptop.

In ONT there are three LEDs Power, Fiber & Data which show the connection

status. Power and Fiber LEDs must be green and stable, and Data LED is in a

blinking state.

IP address of your PC or Laptop should be selected as obtain IP address

automatically.

Open Internet Explorer/ Chrome or any other browser

Type 192.168.1.251 in address bar

A pop-up window which will ask for FTTH modem username and password

Username = root

Password = admin

Click on Network

Click on WAN

Put your connection’s FTTH username and password on this page

User name = [email protected]

Password = XXXXXXXX

Remember that Username & password is provided by BSNL.

Click on Apply

After few seconds Data LED on ONT will be stable. If it’s not getting stable recheck

the whole process or contact to BSNL.

mailto:[email protected]

Documents

Bharat Sanchar Nigam Limitedrttctvm.bsnl.co.in/ftth_basics.pdf · 2018-02-26 · FTTH Basics, Maintenance & Wiring at Subscribers’ Premises 3 Chapter 1 Fiber To The Home Today,