FTTH Interview Questions & Answers

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FTTH Interview Questions & Answers

Searching for FTTH interview questions? Don’t know the sources to prepare for job interviews? Want to crack your interview in first attempt? Here’s a solution for all queries. Get approach our expertise prepared job interview questions page to win in first attempt. FTTH is also known as Fiber to the home (FTTH) and also refer to "fiber to the premises" (FTTP) which uses optical fiber directly from individual buildings like residences, apartment buildings and businesses to offer high-speed Internet access. Search and apply for the various jobs including C, C++ programmer, FTTH Manager, FTTH ODN Network, Front desk, Sr.technical executive, Telecom network executive FTTX engineer, small word data modelling manager etc. Have a look at wisdom jobs FTTH job interview questions and answers page for better results.

FTTH Interview Questions

FTTH Interview Questions
    1. Question 1. What Is Ftth?

      Answer :

      Fiber to the Home (FTTH) is the ultimate fiber access solution where each subscriber is connected to an optical fiber. The deployment options discussed in this tutorial are based on a complete optical fiber path from the OLT right through to the subscriber premises. This choice allows for the provision of high bandwidth services and content to each customer and ensures maximum bandwidth for the future demands of the new services. Therefore, Hybrid options involving ‘part’ fiber and ‘part’ copper infrastructure networks are not included.

    2. Question 2. What Do You Mean By Differential Fiber Distance?

      Answer :

      The differential fiber distance is the difference in the distance between the nearest and furthest ONU/ONT from the OLT.

    3. Question 3. What Is The Maximum Differential Fiber Distance In Gpon?

      Answer :

      In GPON, the maximum differential fiber distance is 20 kms. This affects the size of the ranging window and provides compliance with [ITU-T G.983.1].

    4. Question 4. What Do You Understand By Logical Reach?

      Answer :

      Logical reach is defined as the maximum distance that can be achieved for a particular transmission system, regardless of the optical budget. Logical reach is the maximum distance between ONU/ONT and OLT except for the limitation of the physical layer.

    5. Question 5. What Is The Maximum Logical Reach In Gpon?

      Answer :

      In GPON, the maximum logical reach is defined as 60 kms.

    6. Question 6. What Do You Understand By Mean Signal Transfer Delay?

      Answer :

      The mean signal transfer delay is the average of the upstream and downstream delay values between reference points. This value is determined by measuring round-trip delay and then dividing by 2.

      GPON must accommodate services that require a maximum mean signal transfer delay of 1.5 ms. A GPON system must have a maximum mean Signal Transfer Delay Time of less than1.5 ms between TV reference points.

    7. Question 7. What Do You Understand By Optical Access Network (oan)?

      Answer :

      The OAN is the set of access links sharing the same network-side interfaces and supported by optical access transmission systems. The OAN may include a number of ODNs connected to the same OLT.

    8. Question 8. What Do You Understand By Optical Distribution Network (odn)?

      Answer :

      In the PON context, a tree of optical fibers in the access network, supplemented with power or wavelength splitters, filters or other passive optical devices.

    9. Question 9. What Do You Understand By Optical Line Termination (olt)?

      Answer :

      A device that terminates the common (root) endpoint of an ODN. Then implements a PON protocol such as that defined by [ITU-T G.984]; and then adapts PONPDUs for uplink communications over the provider service interface.

      The OLT provides management and maintenance functions for the subtended ODN and ONUs.

    10. Question 10. What Do You Understand By Optical Network Termination (ont)?

      Answer :

      A single subscriber device that terminates any one of the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDUs to subscriber service interfaces. An ONT is a special case of an ONU.

    11. Question 11. What Do You Understand By Optical Network Unit (onu)?

      Answer :

      A generic term denoting a device that terminates any one of the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDU.

    12. Question 12. What Is The Mean Of Physical Reach In Ftth Technology?

      Answer :

      Physical reach is defined as the maximum physical distance that can be achieved for a particular transmission system. Since, ‘Physical Reach’ is the maximum physical distance between the ONU/ONT and the OLT. However, in GPON, two options are defined for the physical reach: 10 kms, and 20 kms. It is assumed that 10 km is the maximum distance over which FP-LD can be used in the ONU for high bit rates such as 1.25 Gbit/s or above.

    13. Question 13. What You Understand By The Services In Ftth Scenario?

      Answer :

      Services in FTTH are defined as a network service required by operators. Service is described by a name that is clearly recognized by everyone, regardless of whether it is a frame structure name or a general name.

    14. Question 14. What Are The Bit Rates Defined In Gpon?

      Answer :

      GPON aims at transmission speeds greater than or equal to 1.2 Gbit/s. Accordingly, GPON identifies two transmission speed combinations as follows:

      • 1.2 Gbps up, 2.4 Gbps down
      • 2.4 Gbps up, 2.4 Gbps down

      The most important bit rate is 1.2 Gbps up, 2.4 Gbps down, constituting nearly all of the deployed and planned deployment of the GPON systems.

    15. Question 15. What Do You Understand By The Term “split Ratio”? Explain?

      Answer :

      The larger the split ratio is for GPON, the more economical it is from cost perspective. However, a larger split ratio implies greater optical power and bandwidth splitting, which creates the need for an increased power budget to support the physical reach. Split ratios of up to 1:64 are realistic for the physical layer, given current technology. However, anticipating the continued evolution of optical modules, the TC layer must consider split ratios up to 1:128.

    16. Question 16. What Are The Benefits Of Optical Fiber In Ftth?

      Answer :

      Benefits of optical fiber:

      • Very long distances
      • Strong, flexible, and reliable
      • Allows small diameter and light weight cables
      • Safe and secure
      • Immune to electromagnetic interference (EMI)
      • Lower cost

    17. Question 17. What Are The Passive Modules/components In Pon Technology?

      Answer :

      Various modules / components in PON technology are:

      • WDM Coupler
      • 1×N Splitter
      • Optical fiber and cable
      • Connector
      • ODF/Cabinet/Subrack

    18. Question 18. What Are The Active Modules/components In Pon Technology?

      Answer :

      The active modules / components in PON technology are:

      In OLT:

      • Laser transmitter (1490-nm) and
      • Laser receivers (1310-nm)

      For CATV application:

      • Laser amplifier (1550-nm ) and
      • EDFA for amplifying video signal

      In ONU:

      • Power/ Battery for ONU
      • Laser transmitter (1310-nm)
      • Laser receivers (1490-nm)
      • Receivers for CATV signal (1550-nm)

    19. Question 19. What Is The Full Form Of Gpon?

      Answer :

      The full form of GPON is – Gigabit Passive Optical Network

    20. Question 20. What Is Gpon? Explain.

      Answer :

      GPON is an Optical System for the Access Networks, based on ITU-T specifications G.984 series. It can provide a 20 km reach with a 28dB optical budget by using class B+ optics with 1:32 split ratio.

    21. Question 21. Explain The Features Of The Gpon?

      Answer :

      The most commonly known features of GPON are as listed below.

      Downstream transmission:

      • 2.4Gbps
      • BW for one ONT is sufficient to supply multiple HDTV signals
      • QOS allows for delay sensitive traffic (voice)

      Upstream transmission:

      • 1 24Gbps
      • Minimum BW can be guaranteed
      • Unused timeslots can be assigned to heavy users
      • QOS allows for delay sensitive traffic (voice)

    22. Question 22. What Are The Standards That Defines Gpon Technology?

      Answer :

      GPON standards build on the previous BPON specifications. These specifications are all listed below:

      • G.984.1:This document describes the Gigabit-Capable Passive Optical Network general characteristics.
      • G.984.2:This document describes the Gigabit-Capable Passive Optical Network Physical media-Dependent layer specification.
      • G.984.3:This document describes the Gigabit-Capable Passive Optical Network Transmission convergence layer specification.

    23. Question 23. Explain The Gpon Architecture?

      Answer :

      GPON systems have essentially the same physical components that are configured in the same way as in other PON networks. Of course, the products developed for GPON systems are specifically designed for GPON and are not interchangeable with the EPON or BPON gear.

      GPON systems also have many of the same basic capabilities as other PON systems have. The main differences in the architecture are GPON in data throughput. The Gigabit GPON encapsulation methods allow carrying a variety of services including ATM, TDM voice, and Ethernet.

    24. Question 24. What Is The Optical Power Sensitivity For Gpon?

      Answer :

      One of the basic requirements of an optical system is to provide components with sufficient capacity to extend the optical signal to the expected range. There are three categories or classes of components are based on power and sensitivity.

      The classes of components are:

      • Class A optics: 5 to 20dB
      • Class B optics: 10 to 25dB
      • Class C optics: 15 to 30dB

    25. Question 25. What Is The Full Form Of Epon?

      Answer :

      The full form of EPON is – Ethernet Passive Optical Network.

    26. Question 26. Explain The Epon Technology.

      Answer :

      Ethernet Passive Optical Network (EPON) is a PON encapsulate data with Ethernet and can offer 1 Gbps to 10 Gbps capacity. EPON follows the original architecture of a PON. Here, the DTE connected to the trunk of the tree and called as Optical Line Terminal (OLT).

      It is usually located at the service provider, and the connected the DTE branches of the tree are called Optical Network Unit (ONU), located in the premises of the subscriber. The signals from the OLT pass through a passive splitter to achieve the ONU and vice versa.

    27. Question 27. Explain The Qos In Epon?

      Answer :

      Many PON applications require high QoS (e.g. IPTV).

      EPON leaves QoS to higher layers −

      • VLAN tags
      • P bits or DiffServ DSCP
      • In addition, there is a crucial difference between LLID and Port-ID −
      • There is always 1 LLID per ONU
      • There is 1 Port-ID per input port - there may be many per ONU
      • This makes port-based QoS simple to implement at PON layer

    28. Question 28. What Do You Understand By Dba?

      Answer :

      An algorithm implemented in the OLT, using Report and Gate messages to build a transmission program and pass the ONUs is known as a dynamic bandwidth allocation (DBA) algorithm.

    29. Question 29. Explain The Epon Frame Format?

      Answer :

      EPON operation is based on the Ethernet MAC and EPON frames (based on GbE frames), but extensions are needed :

      MultiPoint Control Protocol PDUs :This is the control protocol implementing the required logic.

      Point-to-point emulation (reconciliation):This makes the EPON looks like a point-to-point link and EPON MACs have some special constraints.

      Instead of CSMA/CD, they transmit when granted.

      Time through MAC stack must be constant (± 16 bit durations).

      Accurate local time must be maintained.

    30. Question 30. Explain The Epon Header?

      Answer :

      Standard Ethernet starts with an essentially content-free 8B preamble:

      7B of alternating ones and zeros 10101010

      1B of SFD 10101011

      In order to hide the new PON header, EPON overwrites some of the preamble bytes.

    31. Question 31. Explain The Security Feature In Epon?

      Answer :

      DS traffic is broadcast to all ONUs, so the encryption is essentially easy for a malicious user to reprogram ONU and capture desired frames. US traffic not seen by other ONUs, so the encryption is not needed.

      Do not consider fiber-tappers because EPON does not provide any standard encryption method, but

      • Can supplement with IPsec or MACsec.
      • Many vendors have added proprietary AES-based mechanisms.

      BPON used a mechanism called churning − Churning was a low cost hardware solution (24b key) with several security flaws

      • Engine was linear - simple known-text attack
      • 24b key turned out to be derivable in 512 tries
      • Therefore, G.983.3 added AES support - now used in GPON.

    32. Question 32. What Is Xpon?

      Answer :

      XPON is the next generation PON, which can support data rate up to 10G. XPON can be divided in two categories, i.e., XG-PON1 and XG-PON2. XG-PON1 is backward compatible with GPON, whereas XG-PON2 is completely new development.

    33. Question 33. What Is A Full Form Of Wdm-pon?

      Answer :

      The full form of WDM-PON is – Wavelength Division Multiplex PON.

    34. Question 34. Explain Wdm-pon?

      Answer :

      In WDM-PON, different wavelength is required for different ONT; each ONT gets an exclusive wavelength and enjoys the bandwidth resources of wavelength. In other words, WDM-PON works on a logical Point to Multi Point (P2MP) topology.

    35. Question 35. Explain Odsm-pon?

      Answer :

      The full form of ODSM-PON is – Opportunistic Spectrum and Dynamic PON. In ODSM-PON, the network remains unchanged from CO to user premises except one change, which is active WDM splitter. A WDM splitter will be there between OLT and ONT replacing passive splitter. In ODSM-PON, the downstream adopts WDM, means data towards ONT use different wavelength for different ONT and in upstream and ODSN-PON adopts dynamic TDMA + WDMA technology.

    36. Question 36. What Do You Understand By Optical Signal Splitting? Explain?

      Answer :

      The single fiber starting from OLT is split through passive optical splitters to serve 64 customer premise ONTs. The same fiber carries both the down-stream (OLT towards ONT) and the upstream (ONT towards OLT) bit streams viz., 2.488 Mbps/1490 nm (1480 - 1500nm window) and 1.244 Mbps/1310 nm (1260-1360nm window) through WDM (Wavelength Division Multiplexing) for duplex (bi-directional) operation.

      The same single fiber downstream transmission from the OLT to the ONTs is broadcast with an ONT accepting only the traffic addressed to it. Upstream transmission is Time Division Multiple Access (TDMA) with the each ONT transmitting in turn.

    37. Question 37. What Do You Understand By Rf Overlay For Tv Services? Explain?

      Answer :

      The TV signals (derived from a satellite Head End) are optionally broadcasted on a third optical wavelength of 1550 nm on same (or additional) fiber introduced into the FTTx system through an RF Overlay sub-system. CATV Signal can be coupled with GPON signal after amplification by EDFA.

      The RF CATV signals modulated onto the 1550 nm wavelength. It is extracted through a Demux function built inside ONT and routed to back plane service connection for the STB/TV.

    38. Question 38. Explain The Split Ratios, Maximum Reach & Traffic Management As Per Classes Defined By Itu?

      Answer :

      The maximum permissible optical power attenuation between OLT optical port to ONT input is 28 dB utilizing so called Class B optical network elements. ODN Class A, B, and C are differentiated mainly on the ‘optical transmitter power output’ and ‘bit-rate optical receiver sensitivity. Class A gives the least-optical budget and Class C gives the highest, while cost wise both are in the same order. For maximum 1:64 split ratio, Class B optics are commonly deployed on commercial basis.

    39. Question 39. Explain Ngpon1?

      Answer :

      The following points explain NGPON1:

      • G.987/G.988 XGPON standard have been released in 2011.
      • It standardized the XGPON with 2.5Gbps upstream /10Gbps downstream.
      • GPON and XGPON use different wavelength for coexisting in one network.

    40. Question 40. Explain Ngpon2?

      Answer :

      The following points explain NGPON2:

      • Does not consider being compatible with existing ODN network, a more open standard of PON technology.
      • Focuses to WDM PON and 40G PON.

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