Modern Cable Television

Module 01 History of Fiber

Optical Carrier level	SONET Frame	SDH Level	Bandwidth (Mbps)	Bandwidth (Gbps)
Optical Carrier level	SONET Frame	SDH Level	Bandwidth (Mbps)	Bandwidth (Gbps)
OC-1	STS-1	STM-0	51.84	N/A
OC-3	STS-3	STM-1	155.52	N/A
OC-12	STS-12	STM-4	622.08	N/A
OC-24	STS-24		1244.16	1.2Gps
OC-48	STS-48	STM-16	2488.32	2.5Gps
OC-192	STS-192	STM-64	9953.28	10Gps
OC-768	STS-768	STM-256	39813.12	40Gps

· LASER: Light Amplification by Stimulated Emission of Radiation

· The Return path of hybrid coax system uses TDMA for RF multiplexing.

· Refraction is the phenomenon that occurs when a ray of light bends from passing from one medium to another medium. * 1 kilometer = 0.62miles

· Impurities in the glass causes most fiber optic attenuation and absorption.

· Optic fiber is normally made from silica glass or plastic.

· *DWDM optical channel spacing goes from 12.5GHz to 200GHz.

· *The forward path of a hybrid coax system uses FDM.

· Total internal reflection is the name of the phenomenon when both refraction and reflection combine and all light is reflected (change direction).

· *Wave Division Multiplexing : describes multiple wavelengths of light on a single fiber optic.

· The greater the density difference between two materials, the more a ray of light will bend. * 32+ channels are supported by DWDM.

· A nanometer is 10 raised to the power -9.

· Stimulated emissions produces the Lasers ray of light.

· Fiber Optic cable : transparent material can transmit light in the access network.

· EDFA (Erbium-doped optical fiber amplifier) typically operates at 1550nm.

· Modal dispersion limits the bandwidth of multi-mode fiber (MMF).

· A Shallow angle light ray travels a more direct path and will arrive sooner.

· Photonics : is the name for a communications network in which information is transmitted entirely in the form of optical signals.

· SONET/ 10gigE networks uses a RING architecture.

· (International Telecommunications Union) defines the wavelengths for WDM.

· Light traveling from a more dense medium to a less dense medium is like traveling from a slow medium to a fast medium; such that a light ray will bend away from the normal.

· 1310 nm = 228.849 THz 1550nm = 193.414 THz.

Module 2 Fiber Basics

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· Optical RX and TX recovers a digital bit stream and the uses the bit stream to re modulate an optical light source

· .An optical Link contributes both noise and distortions to the customer’s premises.

· Amplitude modulation : when the intensity of the optical light matches the strength of the electrical signal level by using these varying intensities.

· p-i-n photodiode, diode, 0-E converter, photodetector : are semiconductors that changes optical light into corresponding electrical signal.

· 1200 to 1250 nm is the wavelength cutoff point from below 1300 nm.

· MFD (mode field diameter) : is a function of source wavelength, fiber core radius, and fiber refractive index profile; the difference in MFD between two fibers being spliced that can create a phenomena known as a “gainer”.

· The density of the material in a fiber optic causes light to travel slower.

· A fiber-based digital transport system such as SONET/SDH allows a primary hub to receive video program transport streams using a video router.

· A peak power LASER wavelength at 1000 nm with a spectral bandwidth of 40 nm will have an output ranging from 980 to 1020 nm.

· Fiber optic systems transmit information is the form of LIGHT.

· A change in mode field diameter (MFD) results in a change in signal velocity.

· Depressed clad / Matched clad are the two basic types of single mode step-index fibers.

· Another term for Lambda is Wavelength.

· Shot noise : this term describes the statistical deviation of the actual number of arriving photons from the average number of photons at the receiver.

· When light ray bounces off glass this is known as reflection.

· Light passing from a Lower IOR to higher is bent towards normal.

· In Fiber optic link: Most of the distortions are generated by the LASER photodiode.

· Dispersion: Compensation is required to deal with different modes of light arriving at the end of a fiber at different rates.

· In single mode fiber, light WILL travel along the axis of the fiber.

· Only ONE mode of light is supported on a typical single mode fiber

· In the return path digital to analog conversion is done at the optical node.

· Random variations in the LASER output amplitude is caused by: relative intensity noise.

· Dark Current is the electrical noise that naturally occurs on an optical circuit.

· To replicate the amplitude variations of electrical signals such as RF, an optical signal must vary the intensity of the LASER.

· Numerical Aperture : is the metric that expresses the light gathering ability of a fiber.

· two advantages of a single mode fiber: lower attenuation & lower modal noise.

· Spectral bandwidth: LASER/LED emits a small range of wavelengths.

· 15dBmV is the RF analog input to an optical transmitter.

· Cone of acceptance: is the name of the angle of light that is allowed in the core of the optical fiber.

· The ray of light is REFRACTED when it passes from air to glass.

· The photodetector’s noise figure is the number one cause of Interfermetric Intensity Noise (IIN).

· Wavelengths above 750nm are not visible (after red light).

· Fiber dehydrators are used to remove water from waveguide or core.

· An optical waveguide carriers the light from point to point.

· The light is supposed to travel in the core.

· MFD (mode field Diameter) the diameter of the fiber optic light at the light at the output end of the fiber is slightly wider than the fiber core.

· Advantages of using Fiber over coax: lighter/smaller, more information can be carried (greater bandwidth), not effected by EMI or RFI, better noise characteristics than RF links.

· When the frequency gets higher the wavelength gets shorter.

· Transmission parameters for single mode fiber: attenuation, chromatic dispersion.

· RIN is expressed as noise power per 1Hz of bandwidth.

· A strand of glass is also known as an optical fiber.

· PIN photodiode is the typical source of post amplifier noise in a LASER transmitter.

· Dispersion: spreading or “smearing” of the light signal.

· mode indicates the path that a ray of light can travel in an optical fiber.

· Optical nodes have a DC test point for testing and measuring a certain DC voltage called the received optical power.

Module 3 Transmission Characteristics of Fiber

http://www.scte.org/mmpres/BTS/BTSM3/

· Dispersion shifted fiber or zero dispersion fiber such as graded index or step index was created to reduce dispersion and attenuation.

· Stimulated Brillouin Scattering : is a generation of a backward propagating stokes waves or acoustic waves affecting high power LASERs and amplifiers.

· Stimulated Brillouin Scattering: occurs when an acoustic waves travel through the glass fiber degrading signal to noise (S/N) ratio and limiting optical power into a fiber.

· Stimulated Brillouin Scattering: limits the maximum optical power which can be sent down a fiber at 1550nm

· The approximate loss per km for 850 multimode fiber 2.0 dB/km

· Double Rayleigh backscatter does NOT improve the optical link’s noise performance

· Double Rayleigh backscatter: backward scattered light is rescattered in the forward direction and combines with normally transmitted light causing interferometric intensity noise (IIN).

· Fiber clad to core offset shall not be greater the 0.05 micrometers (um) as per manufacture specs.

· The longer the length of an optical fiber, the greater the noise contribution from interferometric intensity noise (IIN).

· (IIN) Interferometric intensity Noise is generated in all optical fiber by distributed back reflection mainly due to Rayleigh scattering.

· IIN is caused by double Rayleigh scattering

· Microbends: are irregularities in the interface between the core and cladding

· A microbend is a bend or loop in a fiber with a radius curvature of less than one micron

· Bending of the fiber when pulling into conduits can cause Macrobends.

· Polarization Mode: is the name of the problem that appears only in very high bandwidth (not an issue until 10Gbps) single mode fiber optic systems.

· A narrow ray of light is transmitted through a non-zero dispersion multimode fiber, on the RX end the output pulse will be longer.

· Trapped oxy-hydrogen/hydroxyl ions in the core is the cause of high attenuation at 1310 and 1550 nm.

· Waveguide dispersion: optical energy travels at different velocities in the core and cladding, one polarity of light will encounter a slightly higher index of refraction than the other polarity of light.

· A single-mode fiber supports 2 orthogonal polarizations of light, known as the principal states of polarization.

· Chromatic dispersion: number one cause of dispersion in single mode fiber-optical systems, where different colors of light travel at different speeds through the same material.

· Modal dispersion: number one cause of dispersion in multimode fiber-optical systems, allows light to break up into many different paths and smear.

· Intrinsic factors of fiber optic cable: Concentricity error, mode field diameter, core to clad offset

· Losses due to microbending are included in manufacturer’s performance specs.

· A nickel size bend may leak out 0.5 dB of light @ 1310nm.

· Microbending and Macrobending induced loss is related to MFD.

· Core ovality: is the degree of circularity deviation

· 1310nm losses 0.35 dB per km

Module 4 Optical Cables

http://www.scte.org/mmpres/BTS/BTSM4/

http://www.olcfiber.com/wp-content/uploads/2011/05/fibercolor.jpg

· Main physical components of a fiber cable are: optical fiber, buffer tube, protective covering

· Dark fibers: are fibers that are not used at first and kept as spares for replacing upgrading

· Duplex fiber optic cable is designed for bi-directional communication

· Tensile load installation is expressed in (n) newton.

· Buffer tubes: are extruded cylindrical tubes covering optical fiber(s) that are used for protection and isolation.

· Figure 8: a self-supporting cable used in aerial installations, such as pole to pole or pole to building.

· DWDM ITU grid uses 100 Ghz at 0.8nm

· Typical cable weight for a single mode fiber7.5 kg/km

· Strength members in fiber: aramid yarn, fiberglass epoxy rods, steel

· dBm / mW are measurements for optical fiber

· EDFA: operate at 1550nm

· Patch panel: is used to organize fiber cable connections at the headend, primary hub, or secondary hub

· In a typical cylindrical buffer tube 12 fibers are in a tube

· Cable buffers: loose and tight

· Loose tube: the fiber are allowed to float freely in a buffer tube inside the cable.

· Minimum bending radius: 5x’s the diameter when unstressed/ 10x’s the diameter when stressed

· Optical cable design: Isolate the many strands of optical glass from exterior forces. Prevent moisture from entering the cable and migrating down its length. Perform over a specified temperature range. Possess materials with different coefficients of explansion.

Module 5 Safety

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· Teflon tweezers assure a firm grip on fiber’s glass and provide easy handling for proper disposal.

· Chemicals such as isopropyl alcohol, acetone degreasers and sealing compounds can pose hazards if proper precautions are not taken

· Photosensitive card: are used to test for the presence of light

· Antenna or other registration numbers are available at the base of the tower for safety

· If you are unable to safely change a tower light in 30mins, call operations manager or supervisor immediately.

· (DFB) Distributed feedback LASER operate at 1310nm and 1550nm wavelength

· (FP) LASER has a lower power output than DFB laser and a less coherent output

· Breakaway swivels: provide a safe, effective way to eliminate over pulling of optical fiber cable.

· Floating jig/ overlash jig: allows you to winch more than one cable at a time while preventing the cable from turning

· Class 3B laser: if the direct or reflected beam of typical telecommunications LASERS are viewed it will cause an eye hazard. ( examples of these lasers are YAG: can cause skin burns ANSI class 3B 1310 at 13dBm. EDFA: ANSI class 3B 1550nm 37-40 mW

· DFB LASER: are rated by ANSI as 3A Class LASER. And are the most common lower dispersion 1310 to 1550 nm optical fiber LASER used in the headend

· FP Laser: is the simplest, cost effective, least preforming type of LASER transmitter that exhibits high dispersion

· Test Equip LASER: operate at a very low power output of less than 0.8mW

· Exposure to .005W (5mW) to .500W (500mW) LASER can cause: retinal burns, skin burns, cataracts

· When shipping reels of fiber, ensure the cable arrives ready to use. Verify that: both ends are sealed to ensure no moisture gets into the fiber and no filling compound escapes. * tails secured to the reel to prevent them from coming loose. * during towing, keep the reel in the center of the trailer.

· Safety: is the primary purpose of performing underground service locates prior to installing underground cables in a right-of-way or unground location.

· Glass Splinter: does not fester and get push out/ Minor surgery may be required to remove the glass

Module 6 Optical Cable construction

http://www.scte.org/mmpres/BTS/BTSM6/

· 40 in or 102 cm: is the recommended distance required when cable is lashed along power lines with no danger of inductive interference.

· 30 in or 76 cm: is the recommended bury distance for fiber cables so they are below the frost line

· 5% of additional total cable span is normally stored for excess or slack loops at regular intervals during installation

· During the back pull method, the fiber cable reel should be setup beyond the first pole, at twice the distance of the height of the cable setup chute.

· During the back pull or drive off method, lashing occurs as the fiber optic cable is paid out

· The Fiber’s minimum allowable bend radius during installation is Larger than the bend radius allowed after installation.

· The bend radius of a loaded cable is 20 times the diameter of the cable.

· Drive-off: the moving reel method that is used when the entire route can be traversed by reel-carrying vehicles

· Mid-point: is the type of pulling technique used to reduce pulling tension inside of conduits.

· Strand sag is done to compensate for yearly variations in temperature.

· The rule of thumb for cable sag is 1% of span length.

· Downguys and deadends are installed and tensioned correctly before pulling out a new fiber optic cable onto the strand.

· Post Construction inspection: Check for left behind rollers that were used for fiber cable placement, verify proper storage of excess or slack fiber cable, look for missing pole rise guards that are used to protect fiber cable.

· 15m or 50ft is the coiled slack or excess fiber cable required for the drive-off or moving reel aerial installation method.

· The two general methods of direct burying optical fiber cable are direct plowing and trenching

· Plowing Machine: is used to install fiber in a sodded yard that will likely result in the least visible damage to the property.

· Boring: a construction method used to buried fiber cable under roads, driveways and railroads

· Top feed: method from the cable reel that is always preferred

· Tracer tape: is used above the fiber cable to locate it after it is buried.

· When pulling cable through a series of 90 degree bends, use the figure eight method so the tensile strength is not exceeded.

· Always secure required permits before plowing trenching and boring.

· Unloaded has the cable under no tension at all or up to residual tension of around 25% of maximum pulling tensions.

· Lashing to a high strength steel strand, is the preferred option for supporting aerial fiber cable.

· 60% of strand tensile strength: is the maximum recommended strand tension

· Dynamometer: is a tool to test fiber cable tensile strength

· Tensile strength of (SMF) single mode fiber should be at 600 pounds.

· When cable rollers are spaced too close together it will NOT reduce the pulling tension during installation.

· Before placing fiber in conduit: clearance between the walls of the conduit and other cables that may be present, pulling force needed to get the cable through the conduit or duct.

· When entering a confined space (man hole, underground box) a functioning air monitor (gas meter) should be working.

Module 7 Cable preparation

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· The fiber is prepared and cleaved before it is inserted in a connector

· Optical return loss represent the amount of reflections

· Full-cut splice: you enter the fiber at the end of the fiber

· Mid-sheath splice: you enter the fiber in the middle of the fiber

· Wire cutters are the tool used to remove metal strength members in fiber optic cable.

· Jackets, buffer tubes, and other outer layers can be removed with wire strippers, cutting pliers, utility knives, and other common tools

· Preparing the fiber: 1^st Remove outer protective jacket, 2^nd remove corrugated armor, 3^rd cut the tube

· Evaluate the surface of the fiber cable prior to prepping the fiber

Module 8 Splices and connectors

http://www.scte.org/mmpres/BTS/BTSM8/

· In a Mechanical splice the use of index matching gel is used to fill an air gap that may still exist between the two fibers

· Mechanical splice loss: 0.2 to 0.25dB

· Fusion splice loss: 0.01 to 0.05dB loss

· A splice: Connecting one fiber optic to another permanently and protecting it with a closure

· Connector: a disconnect-able device used to connect a fiber to a source, detector, or another fiber

· Once a fiber is stripped, it is cleaned with 90% isopropyl alcohol.

· Fiber cleaver: to produce a flat, smooth perpendicular fiber end face. The recommended cleave angle or perpendicularity is less than 1 degree.

· The end face should be perfectly square to the fiber (perpendicularity)

· APC (angled polished connector) is used when reflections are a concern (GREEN color 6-10 degree angle)

· Intrinsic losses in mismatched fiber: concentricity error, numerical aperture, mode field diameter

· Extrinsic losses in fiber: Lateral displacement, end separation, Angular/ tilt misalignment, surface roughness

· Lateral displacement: when one fibers axis doesn’t coincide with the other fibers axis. (axis’s are offset) Displacement should be limited to 5% of the total fibers core.

· Angular/tilt misalignment: When the cleaves are not perpendicular, (the axis are not parallel), change in the centers distance

· End separation: Fibers during a splice are not correctly position

· 2 inches: is the recommended length for stripping of the fiber coating

Module 9 Optical testing

http://www.scte.org/mmpres/BTS/BTSM9/

· OTDR: connectors appear as loss and reflections

· OTDR: able to locate damage fiber

· OTDR: detects and analyze part of the optical signal by measuring Fresnel reflections and Rayleigh backscattering

· OTDR: Launch cable is dependent on: pulse width, wavelength used (length is 500m-1000m)

· OTDR: Dynamic range is the determining factor that tells you how much loss you can measure over an entire length of fiber; measured in dB- typical range is 30-55dB. 1310nm has less range than 1550nm.

· OTDR: Dynamic range can be increased by using larger pulse width or by switching from 1310 to 1550nm

· OTDR: variations in backscatter between two spliced fibers look like LOSS.

· OTDR: Measures distance and loss. The negative slope on the OTDR’s display is attenuation

· OTDR: decreasing the noise level of the otdr: longer averaging times in decrease the noise

· Dead zone: determines how close to an OTDR or after a reflection you can detect and measure a splice loss;

· OTDR: Spatial resolution: determines how close together you can detect and measure two OTDR events

· A narrow pulse is used to increase resolution on an OTDR

· Losses displayed on an OTDR are in dB/km

· OTDR: normal horizontal scale is 10m /div

· OTDR: normal vertical scale is 1.0 dB /div

· Spectrum analyzer: Peak hold is used to view a channel’s intermittent noise

· Spectrum analyzer: Dynamic range is the maximum difference in amplitude between two frequencies.

· Increasing a spectrum analyzer’s resolution bandwidth from 30 kHz to 300 kHz, will increase the noise floor by 10 dB

· Optical spectrum analyzer: Dynamic range: the ability to measure weak signals in the presence of strong signals

· Optical spectrum analyzer: resolution bandwidth: the ability to deal with closely spaced optical channels

· OPM (optical power meter), is used to measure the average amount of light coming out of a transmitter or other device, or out of a fiber

· OPM is used to measure the amount of light at a particular wavelength coming from a transmitter or fiber

· In an optical link, signals levels between the headend or hub site to the node are balanced using an optical signal meter (OPM)

· When a cooling circuit in a LASER transmitter fails it increases distortions.

· Overall loss is measured by comparing the light launched into a fiber to the light at the end of the fiber

· HELIX factor: is the term for when the cable distance (sheath length) is shorter than fiber distance.

· Government compliance: all optical and frequency measurements should use National Physical Laboratory, National Institute of Standards and Technology rated equipment

· Band Pass filter: used to prevent the input circuits within spectrum analyzer from overloading and causing intermodulation beats within the analyzer.

· Optical node: have an optical power test point that allows for measuring a DC voltage that closely corresponds to the optical power input level

· Troubleshoot Node: 1^st check node for RF output. 2^nd test for AC/DC power. 3^rd check fuses

· The nominal optical input to a nodes photodetector is 0 dBmV.

Module 10 Fiber Restoration techniques

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· Restoration equipment : generator, camera,

· During connectorization, start by striping back the highest priority fiber optic cable

· Hazards: chemicals, sharp armor edges, LASER light

· Restoration link: the cable’s IOR should match the fiber network’s fiber cable; the links end should be prepared with all fibers in splice trays inside closures

· Troubleshooting: for system go dark 1^st check transmitter, 2^nd check patchcords at the transmitter end, 3^rd check patchcords at the receiver end, 4^th check the cable plant

· Conserve dark fibers: useage of optical couplers, deploying of EDFA’s, digitizing the return path

· Ensure there is sufficient length of the fiber tails (ends) at the fiber splicer

· 3 people on a fiber team that are typically trained response and experienced in using the equipment needed during a fiber outage

· Service locator is used for locations of buried cable when excavation is required

· 3m/10ft to 6m/20ft is the typical length for cut back to ensure there are no stressed fiber breaks at points close to the break location

· Verification: 2 ways by talking with the headend/node or use a clip-on power meter

· Investigation: pictures of locate marking, trucks and license plate, people on site, damage of cable

Module 11 fiber design and application

http://www.scte.org/mmpres/BTS/BTSM11/

· Second order distortion (CSO) ratios generated by a directly modulated (DFB) LASER’s will degrade by roughly 1dB for every 1dB increase in RF drive signal

· Third order distortion (CTB) ratios generated by (DFB) LASER will degrade by roughly 2dB for every 1dB increase in RF drive signal.

· (IDP) integrated detector/preamplifier has a transimpedance amplifier incorporated on the same semiconductor chip as the photodetector that reduces various noise sources.

· Techs will sweep the network to determine the links frequency response using a variable frequency generator

· Optical Couplers are multiport devices used to direct the optical light paths in more than one direction depending on the design of the network

· Detector: a detector stage an optoelectronic transducer is part ot the receiver and converts optical energy into electrical energy

· Detector Characteristics: Spectral response, noise equivalent power (NEP) Responsivity, temperature effects, Quantum efficiency, Photoconductive operation, Maximum reverse voltage, Risetime (tr), Polarity, Linearity, Response time, Dark current, Minimum detectable power.

· SIMPLE STAR: architecture uses separate paths from a common point

· MESH architecture: is a fully redundant topology/architecture

· LASER CHURP: Changes in LASER wavelength as a result of the modulating signal amplitude decreasing and increasing.

· Dynamic range—difference between the minimum and maximum acceptable power levels

· Photodetector characteristics: linearity, risetime, spectral response, Maximum reverse voltage, polarity, dark current, minium detectable power, quantum efficiency, photoconductive operation, temperature effects, Noise equivalent power (NEP)

· PN photodiode: the simplest type of photodiode. Too slow for high speed applications

· PIN photodiode improves efficiency in creating external current and faster speed.

· Avalanche photodiode: Recommended for high bandwidth applications or where internal gain is needed to overcome high pre-amp noise. Data interconnects between hubs or headends

· Avalanche photodiode: are useful in digital optical links but are NOT appropriate for analog HFC Links

· The detector of the photodiode module converts optical energy to electrical energy

· Signals most weakest and distorted: at the photodiode detector, at the first stage amplifier

· Fiber to the Feeder (FTTF) reduces the number of trunk amps to 0.

· Power doubling is two identical amplifiers connected in a SERIES.

· A power doubling integrated circuit (IC) are two identical hybrid amps connected in a series, 2.5 times greater output than the push pull design

· OTN/Secondary hub: are placed deeper into serving area. Typically provide service for 20,000 to 40,000 customers

· Module 12 Optical Power Budgets

http://www.scte.org/mmpres/BTS/BTSM12/

· PATH LOSS: Fiber optic cable, transmitter connector, receiver connector, splices, optical couplers

· Optical couplers: express their loss or combining values in percent loss, are multiport devices used to direct the optical light paths, a four-port directional coupler, also referred to as a 2x2 coupler, is the simplest coupler

Module 13 Advanced Network Applications

http://www.scte.org/mmpres/BTS/BTSM13/

· CWDM: operates at a shorter wavelength than DWDM

· CWDM: support 8 or 16 channels or wavelengths of light

· CWDM: channel spacing is 20nm

· C-Band: spectrum is 1530-1565nm

· FTTN: noise is visible on a customer’s TV screen. The first step would be to troubleshoot the optical link for low light levels, then check for excessively high or low RF network levels

· FTTN: suffer from: Loss of a/c power, splice failure, node module failure, loss of DC power

· Isolation: at the output of an WDM multiplexer, the power difference between an undesired wavelength and the desired wavelength.

· FTTC: Advantages include: Shorter amplifier cascades, lower distortion numbers, Higher RF distribution output levels

· FTTH: delivers fiber to the side of the customers residence

· ePON: requires only a router at the headend or hub which is called: (OLT) Optical line terminal

· ePON: Advantages include: lower cost solution, momentum of Ethernet in LANs may be advantage

· Four-wave mixing: method to minimize the impact is to employ uneven channel spacing

· DWDM: the best indicator of overall performance of individual DWDM channels is Carrier to noise

· DWDM: different channels of information are placed on different wavelengths of light

· DWDM: Cross talk measurement indicates the level of unwanted signal (from other channels + noise) in the passband of the channel under test

· DWDM: issues with DWDM include modulation instability, an interaction between the signal and optical amplifier noise, self and cross phase modulation, where intensity modulation of one optical carrier can modulate the phases of other optical signals in the same fiber.

· PON: Passive optical network, typical optical coupler are 1x32

· Frequency Channel Bonding (stacking) up and down conversion processes may introduce frequency offsets and phase noise to the received return signals

· Frequency Channel Bonding (stacking) is primarily used to increase return bandwidth

· A return sweep transmitter is connected to one of the nodes forward output test point or a reverse sweep injection point

· ONU/ONT: receives data in an optical format and converts it to the customer’s desired format such as Ethernet, IP multicast, POTS, and T1.