Task 1: Multi Play Service Network Architecture and Components

FTTH (Fiber to the Home):

Fiber to the home (FTTH) is the delivery of a communications signal over optical fiber from the operator's switching equipment all the way to a home or business, thereby replacing existing copper infrastructure such as telephone wires and coaxial cables. FTTH is an architecture that uses passive or active network devices to take the signal from central office to customer premises.

FTTH over Passive Optical Network (PON) uses optical splitters to distribute and expand the network to reach the customer. Whereas, FTTH over active optical network uses switches or active equipment (that uses electric power) to provide services to the customer.

Multi Play Service Network

Multi play service is a marketing term for the provisioning, over a single broadband connection, of three bandwidth-intensive service, broadband Internet access and television, and the latency-sensitive telephone.

In general, multi play service network offers:
  1. High Speed Internet.
  2. Voice Call.
  3. IP Television.

FTTH PON Architecture for Multi Play Services: Network Components and Cables

1. Optical Line Terminal (OLT)

A device that serves as the service provider endpoint of a passive optical network. It is the equipment that acts as an interface between PON network user (Customer) and service provider (Like BSNL, Airtel, Jio etc.). It is generally installed at service provider premises and capable of serving thousands of Optical Network Units at a time.

2. Joint Closure

This fiber joint closure is used as a branch out splicing point in fiber access networks. A typical application is to secure spliced fibers in the cabling system. The closure can also be used as a straight joint for traditional cables or micro cables.

3. Splitter (Let’s call it S1)

The fiber optic splitter is one of the most important passive devices in the optical fiber link. It is an optical fiber tandem device with many input and output terminals. Splitter is called a passive device because it does not need electric power to operate.

Passive Optical Splitters are, quite simply, the components that split the optical signal. They are capable of sending incoming optical light from one fiber to many different fibers. It is designed to split an incident light beam into two or more light beams and couple the light beams.

The passive optical splitter can split, or separate, an incident light beam into several light beams at a certain ratio. As a simple example, below figure shows how optical splitter with 1x4 split configurations can separate an incident light beam from a single input fiber cable into four light beams and transmit them through four individual output fiber cables.

For instance, if the input fiber optic cable carries 1000 Mbps bandwidth, each user in the end of output fiber cables can use the network with 250 Mbps bandwidth.

Optical splitter are available in certain splitting ratio viz. 1x2, 1x4, 1x8, 1x16, 1x32, 1x64, 1x128, 2x4, 2x8 etc…. More the split ratio, more the optical loss offered by the splitter.

4. Home termination Box (HTB) (Let’s call it S2)

The FTTH Home Termination Box (HTB) is used to provide connection at user's premises. It is a cost effective solution for protecting passive termination of fibers at single location. Indoor termination box is designed for use in residential, small and large businesses premises.

The unit houses a single splice tray and allows fibers from internal or external cables to be spliced to pigtails for connection to the optical network unit.

The unit can be quickly installed within a home, office or communication room environment. Internal or external cable can enter the unit from the bottom of the box or through the wall.

Outdoor HTBs are installed outside the home and used to split the fibers to be given to different nearby users.

5.Optical Network Unit (ONU)

The optical network unit (ONU) is the user side equipment in the FTTH (PON) network. ONU realizes "Multi Play" applications by providing services such as data, IPTV (interactive network television) and voice.

It communicates with the OLT. Thus, it acts as intermediate service traffic controller between user device and OLT.

Optical fiber is terminated at the ONU. It provides high sensitivity light reception and low input optical power consumption.

ONU offers Plug and Play operations based on auto discovery and configuration. Wifi router is connected to the ONU, if ONU is not designed to transmit wireless signals.

The set top box, laptop, computers, mobile phones or any other network user devices are connected to the ONU and wifi router. ONU has different ports to connect with the different types of user devices.

6.Set Top Box

Set top box is a box-shaped device that connects with ONU or wifi device and television. It works as an intermediate device between optical end user terminal and television set.

It communicates with the OLT. Thus, it acts as intermediate service traffic controller between user device and OLT.

It is preprogrammed device that converts video content to analog or digital TV signals and has intelligence of connecting the internet world with television. The user takes help of set top box for connecting television set to internet and stream desired channels.

ONU offers Plug and Play operations based on auto discovery and configuration. Wifi router is connected to the ONU, if ONU is not designed to transmit wireless signals.

Set top box is generally connected with TV using HDMI or Composite cable.

7. End User Devices

An end user refers to the person who ultimately uses a particular product.

A customer is the person who performs the purchasing transaction.

If a single person purchases and ends up using the product, that person is both an end user and customer.

An end user device can be of any type depending on type of service being used. They may be a Personal computer (Desktop or Laptop), Personal Digital Assistant (PDA), Smart Phone, Television, etc.

8. Cables

Feeder Cable

Cable laid between Central Office or OLT and first splitter or distribution point is called Feeder Cable. This Cable generally has high fiber count to accommodate large numbers of users.

Distribution Cable

The cable connected between two splitters or splitter to HTB is termed as Distribution Cable.

Drop Cable

The cable laid between HTB or Splitter to ONU (customer premises termination point) is called Drop Cable. Sometimes HTB and ONU is connected using Patch Cord. Patch cord is a single fiber cable with connectors on both ends and high flexibility.

HDMI Cable

HDMI Stands for "High-Definition Multimedia Interface."

HDMI is a trademark and brand name for a digital interface used to transmit audio and video data in a single cable.

This cable is able to transfer audio and video signals from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device.

Task 2: Optical Fiber Colour Code Scheme

Colors are used to identify the fibers and tubes in the cable. Below diagram depicts the optical fiber colour code and corresponding fiber number.

Inside the cable or inside each tube in a loose tube cable, individual fibers will be color coded for identification. For splicing, like color fibers are spliced to ensure continuity of color codes throughout a cable run.

There are two situations for multi-fiber cables:

1. For cables that consist of multiple buffer tubes each with 12 or less strands, each tube will be numbered or colored following the same fiber color code, e.g., 1st tube is blue, 2nd is orange, etc.

2. For cables that consist of more than 12 strands, the fiber optic cable color code repeats itself in another tube of different colour.

Task 3: Fiber Splicing and Splice Tray

Splicing is the act of joining two optical fibers end-to-end. During splicing, only glass part of the optical fiber is joined not coatings.

Fusion Splicing

Fusion method fuses the fiber cores together with splice loss less than 0.1dB.

This fusion splice is made by fusing or melting the two ends of fiber together. It uses an electric arc to weld two optical fibers using specialized equipment.

For this process a specialized fusion splicer machine is used to precisely align the two fiber ends then the glass ends are “fused” or “welded” together using electric arc. This produces a transparent, non-reflective and continuous connection between the fibers enabling very low loss light transmission.

The fusion splicer performs optical fiber fusion splicing in two steps.

1. Precisely align the two fibers
2. Generate a small electric arc to melt the fibers and weld them together

In the scenario of multi play services networks, splicing of fiber needs to be performed at:

1. Long outside plant cable runs
2. Splicing of pig tails with the bare fiber of the feeder and distribution cable at splitter point or termination box
3. Cable/fiber cut situations
4. Cable extension scenario

Fusion Splicing Process (Single Fiber)

Fiber splice using Fusion Splicing Machine involves following sequential process.

1. Stripping
2. Cleaning
3. Cleaving
4. Splicing
5. Protection of splice

Process 1 - Stripping

In this process, fiber optic cable and fiber coatings are stripped off.

Fiber cables are stripped to get bare fiber out of the cable whereas bare optical fiber is stripped to remove coatings from the fiber to get only glass material to be spliced.

Tools used in Stripping:

1. Cable Cutter
The cable cutter is used to cut aluminum, copper and communications cables. It can be used to cut the metal covers of the cable.

2. Round Cable Cutter
It is used to make circular cut in the cable at desired location.

3. Cable Sheath Stripper
It is used to cut the jacket of the cable.

4. Fiber Stripper
Stripping tool provides a quick, easy, and reliable way to cut and remove the coatings from an optical fiber

1. The First hole strips the 2-3 mm fiber jacket down to the 900 micron buffer coating.
2. The second hole strips the 900 micron buffer coating down to the 250 micron coating.
3. The third hole strips the 250 micron coating down to the glass fiber without nicks or scratches.

Process 2 - Cleaning

After stripping, the burrs of the fiber coatings remain on the glass fiber. To clean the residual coating, fiber cleaning is performed. Items used for fiber cleaning are:

Fiber cables are stripped to get bare fiber out of the cable whereas bare optical fiber is stripped to remove coatings from the fiber to get only glass material to be spliced.

Tools used in Stripping:

Lint Free Tissue or Wipes
High quality lint free wipes or tissues are used to clean the stripped fiber. They must be soft.

Isopropyl Alcohol
This 99% reagent grade isopropyl is used in cleaning fiber or fiber optic connector endfaces for better transmission performance.
Wet cleaning is more aggressive than dry cleaning, and removes airborne contamination as well as light oil residue from fiber. Tissue is wiped with Isopropyl alcohol for cleaning the fiber.

Process 3 - Cleaving

Cleaving is the process of cutting Optical Fiber perpendicular to the longitudinal axis of the fiber using cleaver.

Tools used in Stripping:

It is intended to create a perfectly flat endface precisely for splicing. Cleaver provides one-Step cleaving and easy fiber loading.

For 40mm sleeve, end of stripped fiber coating should be placed at 15mm marking on cleaver and for 60mm sleeve, end of stripped fiber coating should be placed at 20mm marking on cleaver.

Below is the illustration of fiber cleaving quality:

Process 4 - Splicing

Splice operation is performed using Fusion Splicing Machine, sometimes called Fusion Splicer. This machine aligns the two fiber ends in front of each other and generates arc to melt and joint the fiber.

It is an automated tool in which splicing parameters are preset and factory recommended settings can be selected. However, machine can also be configured manually for different parameters. Below schematic shows the splice machine, its accessories and parts.

Screen or Magnifier Window

The splicer shows the fibers being spliced on the video screen. It also shows the cleave angle of the fiber.

Core and clad can be easily identified on the screen. If everything looks OK, splicer can be instructed further to perform splicing else repeat the previous processes.

Designs and specifications of splice machines differs with the manufacturers. Some of the leading suppliers of the splice machine in India are Fujikura and Sumitomo.

Generally, a machine can produce up to 3000 arc using a pair of electrodes, after which electrodes need to be replaced.

Fiber is placed on the V Groove in the machine that ensures the stability of fiber at a place.

Splice Machine Operation Modes

Splice Mode
In this mode of operation splice machine generates arc to fuse the two ends of fibers in the wind protector of splice machine.

Heater Mode
In this mode, machine is used to heat the protection sleeve containing splice within it.
In splice machine parameters like fiber mode (single mode, multimode) can be configured manually.

Evaluating Splices

Good Splices:
Visually inspect splice after the program has run, using both X and Y views. Some flaws that do not affect optical transmission are acceptable, as shown. Some fibers may cause white or black lines in splice region that are not faults.

Bad Splices:
Some flaws are unacceptable and require re-splicing. These flaws may be black spots or lines, large core offsets, bubbles or bulging splices.

Process 5 - Protection of Splice

This is the process of protecting the splice from external damage, tensile force and environmental effects. Protecting the fiber from bending and tensile forces ensures that the splice does not break during normal handling.

This is done by sliding the fusion splice protection sleeve on the joint and putting it into the heat shrink oven of the splice machine. Protection Sleeve is used to protect the splice.

It is a heat shrinkable tube filled with silica gel. It is composed of an outer and inner sleeve reinforced by an internal member made of stainless steel or ceramics. All these materials altogether ensures joint protection from external elements and breakage.

Protection sleeves of 40mm and 60mm sizes are generally used in field.

Splicing Safety Precautions

Following safety precautions should be taken while performing splicing

1. Try to work in a clean area.
2. Use safety glasses or laser goggles while splicing.
3. Avoid working around heating outlets, as they blow dust all over you.
4. Always use Lint Free Tissues and Isopropyl Alcohol to clean the fiber.
5. Do not touch bare fibers with fingers.
6. Be very careful when disposing of fiber scraps.
7. Perform splicing operation on black safety mat to ensure that the fiber scraps are visible and easy to collect.

Placement of Splice into Splice Tray

Splice tray is used to secure the fiber splice in the closure. Generally, one single fiber splice tray can accommodate 12 splices.

Fiber splice trays are usually placed in the middle of a route where cables are required to be joined or at the termination and patch panel points at the end of the cable runs. Also, splices can be placed in a splice tray which is then placed inside a splice closure for OSP (outside plant) installations or a patch panel box for premises applications. As for indoor application, fiber splice trays are often integrated into patch panels to provide for connections to the fibers.

Installer needs to carefully place the finished splice into the splice tray and loop excess fiber around its guides. It is also ensured that the fiber’s minimum bending radius is not compromised.

This Lab is Developed by @ Virtuality