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CBNT practice questions

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Question 1Broadband network fundamentals and architecture

In a DOCSIS access network, which device is responsible for scheduling upstream transmission grants to cable modems?

  1. The headend combiner
  2. The optical node
  3. The CMTS Correct answer.
  4. The set-top box

Explanation

The Cable Modem Termination System acts as the controller on the shared upstream channel, allocating minislots and grants so that cable modems transmit in assigned windows. Without this scheduling, upstream collisions would prevent reliable shared-channel operation.

Question 2Broadband network fundamentals and architecture

Which PON technology uses fixed-length downstream frames of 125 microseconds and supports both ATM and Ethernet encapsulation?

  1. ADSL2+
  2. GPON Correct answer.
  3. G.fast
  4. DOCSIS 3.1

Explanation

GPON (ITU-T G.984) is built around a 125 microsecond frame structure and can carry both ATM cells and Ethernet frames through its encapsulation modes. The fixed framing is what allows GPON to provide deterministic bandwidth allocation to ONUs.

Question 3Broadband network fundamentals and architecture

The main architectural reason an HFC network places fiber between the headend and neighborhood optical nodes is to:

  1. Allow each subscriber to receive a dedicated wavelength
  2. Eliminate the need for upstream scheduling on the shared medium
  3. Reduce the number of active amplifiers in the subscriber drop
  4. Shorten the coaxial span and thereby reduce noise accumulation and maintenance Correct answer.

Explanation

Pushing fiber deeper reduces the length of the coaxial plant, which limits the cascaded amplifier count and the associated noise and distortion buildup. It also shrinks the size of each serving area, improving reliability and maintenance economics.

Question 4Broadband network fundamentals and architecture

In an EPON based on IEEE 802.3ah, how is downstream traffic delivered to ONUs?

  1. ONUs contend for downstream timeslots using CSMA/CD
  2. Each ONU receives only the frames addressed to its own LLID by filtering
  3. The OLT broadcasts frames and each ONU filters by LLID Correct answer.
  4. A dedicated point-to-point fiber runs from the OLT to every ONU

Explanation

EPON downstream is a broadcast channel: the OLT transmits frames carrying a Logical Link Identifier, and each ONU discards frames not matching its assigned LLID. Upstream, by contrast, is arbitrated with grants to avoid collisions.

Question 5Broadband network fundamentals and architecture

Which layer of the OSI model is primarily responsible for establishing, managing, and terminating sessions between broadband subscriber applications?

  1. Transport layer
  2. Data link layer
  3. Network layer
  4. Session layer Correct answer.

Explanation

The session layer handles dialogue control, including setup, maintenance, and teardown of sessions between communicating endpoints. Transport handles end-to-end delivery, and the network and data link layers handle addressing and framing respectively.

Question 6Broadband network fundamentals and architecture

A technician needs to verify the optical power arriving at an ONU is within the receiver's specified range. Which instrument is appropriate?

  1. Time-domain reflectometer
  2. Optical power meter Correct answer.
  3. Protocol analyzer
  4. Spectrum analyzer

Explanation

An optical power meter calibrated for the relevant wavelength directly measures received optical power so it can be compared with the ONU's sensitivity specification. A TDR or OTDR locates faults, while spectrum and protocol analyzers serve other purposes.

Question 7Broadband network fundamentals and architecture

In a DOCSIS network, what is the purpose of the downstream MAP message?

  1. To encrypt the downstream video stream
  2. To assign upstream bandwidth grants to cable modems Correct answer.
  3. To provision the cable modem configuration file
  4. To measure the downstream signal-to-noise ratio

Explanation

The MAP message is transmitted downstream by the CMTS to announce which cable modems may transmit in specific upstream minislots. It is the mechanism that coordinates contention-free upstream access.

Question 8Broadband network fundamentals and architecture

Which statement best describes the role of a splitter in a passive optical network?

  1. It amplifies the optical signal before it reaches each ONU
  2. It assigns upstream grants to each ONU
  3. It divides one optical signal among multiple fibers without electrical power Correct answer.
  4. It converts optical signals into electrical signals for the ONU

Explanation

A PON splitter is a passive device that divides optical power from a single feeder fiber among several distribution fibers. Being passive, it requires no electrical power and introduces splitting loss proportional to the split ratio.

Question 9Broadband network fundamentals and architecture

A provider deploys a 1:32 PON splitter and later wants to add subscribers on the same feeder. Which consequence should the designer expect?

  1. Removal of the need for OLT ranging
  2. Higher per-subscriber optical power at each ONU
  3. Automatic doubling of upstream bandwidth
  4. Increased splitting loss and reduced power budget margin Correct answer.

Explanation

Increasing the split ratio divides the same optical power among more outputs, so each ONU receives less power and the link budget margin shrinks. Designers must check that the remaining margin still satisfies the ONU sensitivity and OLT receive requirements.

Question 10Broadband network fundamentals and architecture

Which protocol allows a broadband access node to authenticate subscribers against a central server and return an address assignment in one exchange?

  1. TFTP
  2. RADIUS Correct answer.
  3. NTP
  4. SNMP

Explanation

RADIUS carries authentication, authorization, and accounting requests between a network access server and a central policy server, and can return attributes including address assignment details. SNMP, NTP, and TFTP serve management, time, and file transfer functions respectively.

Question 11Broadband network fundamentals and architecture

In a GPON network, why must the OLT perform ranging of each ONU?

  1. To set the downstream wavelength assigned to each ONU
  2. To negotiate the encryption keys used on the PON
  3. To determine the splitter ratio in use
  4. To align upstream burst arrival times so transmissions do not overlap at the OLT Correct answer.

Explanation

ONUs sit at different distances, so their propagation delays differ. Ranging measures each delay and assigns an equalization delay so all upstream bursts arrive in their allotted timeslots without colliding.

Question 12Broadband network fundamentals and architecture

Which technique allows a DOCSIS 3.1 cable modem to transmit on multiple upstream channels simultaneously to increase throughput?

  1. Orthogonal frequency-division multiplexing only
  2. Channel bonding Correct answer.
  3. Time-division duplexing
  4. Ethernet passive optical networking

Explanation

Channel bonding aggregates several upstream channels into a single logical channel, multiplying the capacity available to a cable modem. DOCSIS 3.1 uses OFDM and OFDMA as its modulation schemes, but bonding is what combines channels into a wider pipe.

Question 13Broadband network fundamentals and architecture

Which broadband access architecture terminates subscriber lines at a remote node close to the customer and connects back to the core over fiber?

  1. Fixed wireless point-to-point from the core
  2. FTTN with VDSL2 Correct answer.
  3. ADSL over a long local loop from the central office
  4. Satellite broadband

Explanation

Fiber to the node places a remote DSLAM near the subscriber, shortening the copper loop and enabling higher-speed VDSL2 service. The fiber backhaul carries aggregated traffic to the core network.

Question 14Broadband network fundamentals and architecture

What does the term 'last mile' refer to in broadband network architecture?

  1. The fiber link between two core routers
  2. The connection between the subscriber premises and the first aggregation point Correct answer.
  3. The undersea cable segment between continents
  4. The peering link at an internet exchange

Explanation

The last mile is the access segment that connects the subscriber premises to the nearest access or aggregation node in the provider network. It is typically the most costly and bandwidth-constrained part of the end-to-end path.

Question 15Broadband network fundamentals and architecture

A network designer observes that upstream utilization on a shared HFC segment spikes when many subscribers upload simultaneously. Which architectural factor best explains this behavior?

  1. Upstream traffic bypasses the CMTS entirely
  2. Each subscriber has a dedicated upstream fiber to the CMTS
  3. The upstream channel is shared and arbitrated, so contention rises with active users Correct answer.
  4. Upstream capacity scales linearly with the number of subscribers

Explanation

HFC upstream is a shared medium in which the CMTS grants transmission opportunities, so the aggregate capacity is divided among active subscribers. As more users transmit at once, contention and scheduling delay increase.

Question 16Broadband network fundamentals and architecture

Which IEEE standard defines Ethernet in the First Mile, including EPON?

  1. IEEE 802.1Q
  2. IEEE 802.3af
  3. IEEE 802.3ah Correct answer.
  4. IEEE 802.11ac

Explanation

IEEE 802.3ah is the Ethernet in the First Mile amendment, which added EPON and other subscriber access provisions to Ethernet. The other standards cover wireless LAN, VLAN tagging, and power over Ethernet.

Question 17Broadband network fundamentals and architecture

In a DOCSIS network, a cable modem must obtain an IP address before downloading its configuration file. Which pair of protocols typically supports this initial step?

  1. RTP and RTCP
  2. SMTP and IMAP
  3. BGP and OSPF
  4. DHCP and TFTP Correct answer.

Explanation

After ranging and registration, the cable modem uses DHCP to obtain an address and the address of the configuration server, then retrieves the file via TFTP. Routing, mail, and real-time media protocols play no role in modem provisioning.

Question 18Broadband network fundamentals and architecture

Which characteristic distinguishes a passive optical network from an active star Ethernet access network?

  1. The PON requires a dedicated fiber pair per subscriber
  2. The PON cannot support upstream traffic
  3. The PON distribution network contains no powered intermediate devices Correct answer.
  4. The PON uses coaxial cable for the feeder segment

Explanation

A PON relies on unpowered splitters in the distribution network, whereas an active star uses powered switches or repeaters in the field. This passivity reduces field maintenance and power costs.

Question 19Broadband network fundamentals and architecture

What is the primary function of a DSLAM in a broadband access network?

  1. To terminate undersea optical cables
  2. To aggregate subscriber DSL lines and forward their traffic toward the core Correct answer.
  3. To provide power over Ethernet to access points
  4. To assign wavelengths on a DWDM ring

Explanation

A DSLAM concentrates many subscriber DSL lines onto a high-capacity uplink toward the aggregation or core network. It also handles per-line modulation and subscriber traffic separation.

Question 20Broadband network fundamentals and architecture

Which factor most directly limits the achievable data rate on a copper local loop in a VDSL2 deployment?

  1. The size of the DHCP address pool
  2. Loop length and the resulting attenuation and crosstalk Correct answer.
  3. The version of SNMP used for monitoring
  4. The number of VLANs configured at the DSLAM

Explanation

Copper loop attenuation rises with distance, and crosstalk among binder pairs degrades the signal, so both shorten the usable reach at high bit rates. VLAN counts, address pools, and management protocol versions do not set the physical line rate.

Question 21Broadband network fundamentals and architecture

In a broadband network, which device function separates subscriber traffic into distinct broadcast domains at Layer 2?

  1. A passive splitter
  2. A hub
  3. A media converter
  4. A VLAN-capable switch Correct answer.

Explanation

A VLAN-capable switch tags frames and confines each VLAN to its own broadcast domain, which improves security and reduces broadcast traffic. Hubs, media converters, and splitters do not perform this separation.

Question 22Broadband network fundamentals and architecture

An engineer must choose between GPON and EPON for a new deployment where the operator's equipment is Ethernet-centric and the standard must align with IEEE specifications. Which choice fits best?

  1. GPON, because it is defined by IEEE 802.3ah
  2. GPON, because it does not require any upstream scheduling
  3. EPON, because it uses ATM cell encapsulation exclusively
  4. EPON, because it is defined by IEEE 802.3ah and carries Ethernet natively Correct answer.

Explanation

EPON is standardized in IEEE 802.3ah and transports Ethernet frames natively, which suits an Ethernet-centric operator. GPON is an ITU-T standard and both PON types require upstream scheduling.

Question 23Broadband network fundamentals and architecture

What role does the optical line terminal play in a PON?

  1. It splits the optical signal passively among subscribers
  2. It terminates the PON at the provider side and manages ONU scheduling and control Correct answer.
  3. It converts the PON to coaxial cable for the drop
  4. It terminates the PON at the subscriber premises

Explanation

The OLT sits at the provider end of the PON, aggregates traffic from many ONUs, and controls upstream scheduling through grants and ranging. The subscriber end is terminated by the ONU.

Question 24Broadband network fundamentals and architecture

A provider wants to reduce the size of each HFC serving area to improve per-subscriber capacity. Which change best accomplishes this?

  1. Increasing the number of amplifiers in cascade
  2. Adding more set-top boxes to the plant
  3. Raising the downstream modulation order only
  4. Splitting the node so each node serves fewer homes passed Correct answer.

Explanation

Node splitting reduces the number of homes passed per node, so the shared capacity of each segment is divided among fewer subscribers. Adding amplifiers increases cascade and noise rather than reducing serving area size.

Question 25Broadband network fundamentals and architecture

Which statement correctly describes upstream transmission in a PON?

  1. The OLT transmits grants downstream and ONUs never transmit upstream
  2. ONUs transmit in assigned timeslots so bursts arrive at the OLT without overlap Correct answer.
  3. Upstream uses CSMA/CD among ONUs to resolve collisions
  4. All ONUs transmit continuously on separate wavelengths

Explanation

PON upstream is time-division multiplexed: the OLT grants timeslots and each ONU transmits its burst only in its assigned slot, with ranging ensuring correct arrival timing. This avoids collisions on the shared feeder.

Question 26Broadband network fundamentals and architecture

Which term describes the physical path between a subscriber premises and the first point of aggregation in a broadband access network?

  1. The content delivery network
  2. The core network
  3. The operations support system
  4. The access network Correct answer.

Explanation

The access network is the segment that connects individual subscriber premises to the operator's first aggregation point, often called the access node. The core network interconnects aggregation points at a regional or national scale, and CDNs and OSS are service and management layers rather than transport paths.

Question 27Broadband network fundamentals and architecture

In a hybrid fiber-coaxial access network, which node converts between the optical transport signal and the coaxial distribution plant?

  1. The set-top box
  2. The tap
  3. The cable modem termination system
  4. The optical node Correct answer.

Explanation

The optical node is the boundary device in HFC that receives optical signals from the headend or hub and converts them to RF for the coaxial plant, and performs the reverse for upstream. The CMTS sits at the hub and terminates modem traffic, while taps and set-top boxes are subscriber-side elements.

Question 28Broadband network fundamentals and architecture

Which broadband access technology delivers service over the existing twisted-pair telephone loop using a modem at the customer premises and an aggregation device in the exchange?

  1. GPON
  2. VDSL2 Correct answer.
  3. DOCSIS
  4. Metro Ethernet

Explanation

VDSL2 is a digital subscriber line technology that operates over copper twisted pair, with a CPE modem and a DSLAM aggregating lines in the exchange or a remote cabinet. DOCSIS runs over coaxial cable plant, GPON over optical fiber, and Metro Ethernet typically over fiber or dedicated copper Ethernet links.

Question 29Broadband network fundamentals and architecture

What is the main purpose of the distribution network between an access node and subscriber premises in a broadband architecture?

  1. To host centralized billing records
  2. To provide the physical fan-out from the aggregation point to individual subscribers Correct answer.
  3. To cache popular video content for the whole region
  4. To terminate the operator's core routing protocols

Explanation

The distribution network provides the physical fan-out, including splitters, cabinets, taps, and feeder and drop cables, that carries signals from the aggregation point toward individual subscribers. Routing termination, billing, and content caching belong to other layers of the architecture.

Question 30Broadband network fundamentals and architecture

Which layer of a broadband access network typically aggregates traffic from many access nodes and hands it to the core?

  1. The drop cable layer
  2. The aggregation or edge layer Correct answer.
  3. The customer premises layer
  4. The in-home wiring layer

Explanation

The aggregation or edge layer collects traffic from multiple access nodes, applies policy and routing, and connects upward to the core. Drop cables, customer premises equipment, and in-home wiring are all at the subscriber end of the architecture.

Question 31Broadband network fundamentals and architecture

In a passive optical network, which element distributes a single fiber feeder among multiple subscriber fibers without electrical power?

  1. The media converter
  2. The optical amplifier
  3. The passive optical splitter Correct answer.
  4. The optical add-drop multiplexer

Explanation

A passive optical splitter divides the feeder fiber's optical power among several distribution fibers and requires no electrical power, which is central to PON economics. Amplifiers, media converters, and add-drop multiplexers are either active or intended for other optical transport roles.

Question 32Broadband network fundamentals and architecture

Which function does a broadband remote access server perform in a service provider access network?

  1. It assigns wavelengths to PON branches
  2. It converts coaxial RF to optical signals
  3. It terminates subscriber sessions and enforces per-subscriber policy and accounting Correct answer.
  4. It provides Layer 2 switching inside the subscriber home

Explanation

The BRAS terminates subscriber sessions, typically using PPP or IP session control, and applies authentication, address assignment, policy, and accounting functions. Wavelength assignment, HFC conversion, and in-home switching are handled by entirely different devices.

Question 33Broadband network fundamentals and architecture

What does the term 'broadband' fundamentally describe in an access network context?

  1. A transmission medium that carries only a single narrowband channel
  2. A protocol for billing subscribers
  3. A network that uses only wireless links
  4. A medium or system capable of carrying a wide band of frequencies or high data rates Correct answer.

Explanation

Broadband refers to a transmission capability that supports a wide frequency band or high data rate, allowing many services to share the access medium. It is not tied to a particular medium such as wireless, and it is not a billing concept.

Question 34Broadband network fundamentals and architecture

A provider is designing an access network and wants a single fiber feeder to serve 64 subscribers while keeping outside-plant electronics to a minimum. Which architecture best fits this requirement?

  1. A passive optical network with a 1:64 splitter Correct answer.
  2. An active star Ethernet network with a powered switch per subscriber
  3. A DOCSIS network with one coaxial drop per subscriber
  4. A point-to-point fiber link per subscriber

Explanation

A PON with a 1:64 splitter shares one feeder fiber among 64 subscribers using only passive components in the outside plant. Point-to-point fiber uses one feeder per subscriber, active star places powered electronics in the field, and DOCSIS relies on coaxial distribution rather than a fiber feeder to each subscriber.

Question 35Broadband network fundamentals and architecture

An engineer must explain why a PON downstream signal can be received by every ONU on the same splitter branch. Which property explains this behavior?

  1. The splitter broadcasts the downstream optical signal to all connected ONUs Correct answer.
  2. Each ONU is assigned a dedicated downstream wavelength by the splitter
  3. The OLT encrypts each frame with a per-ONU key before transmission
  4. The ONUs coordinate downstream reception using time slots

Explanation

In a PON the downstream signal from the OLT is split passively and reaches every ONU on the branch, so logical separation relies on addressing and encryption rather than physical separation. Upstream, by contrast, is coordinated in time to avoid collisions.

Question 36Broadband network fundamentals and architecture

A technician is troubleshooting a VDSL2 subscriber whose attainable rate drops sharply as line length increases. Which underlying effect best explains this?

  1. Longer loops receive a lower-priority queue in the aggregation network
  2. Signal attenuation and crosstalk increase with copper loop length Correct answer.
  3. The CPE reduces its transmit power automatically on long loops
  4. The DSLAM assigns shorter time slots to longer loops

Explanation

On copper loops, longer distances increase attenuation and expose the signal to more crosstalk, both of which reduce the achievable signal-to-noise ratio and therefore the data rate. Queueing priority and time-slot assignment do not cause the distance-dependent rate decline.

Question 37Broadband network fundamentals and architecture

In a DOCSIS network, which device provides the timing reference that cable modems use to align their upstream transmissions?

  1. The provisioning server
  2. The trivial file transfer server
  3. The CMTS through downstream synchronization messages Correct answer.
  4. The DHCP relay agent

Explanation

The CMTS sends downstream synchronization information that lets cable modems establish a common time reference and align upstream bursts into their assigned minislots. Provisioning and configuration servers handle addressing and configuration files, not physical-layer timing.

Question 38Broadband network fundamentals and architecture

Which statement best describes the difference between a fiber-to-the-home and a fiber-to-the-cabinet deployment?

  1. FTTH serves only business customers, while FTTC serves only residential customers
  2. FTTH terminates fiber at the subscriber premises, while FTTC terminates fiber at a street cabinet and uses copper for the final drop Correct answer.
  3. FTTH requires active electronics in the home, while FTTC requires none in the field
  4. FTTH uses coaxial cable for the final drop, while FTTC uses fiber throughout

Explanation

FTTH carries fiber all the way to the subscriber premises, whereas FTTC stops the fiber at a cabinet or distribution point and relies on copper, such as VDSL2, for the remaining short drop. The other options misstate the media or the customer segments involved.

Question 39Broadband network fundamentals and architecture

A network planner wants to reduce contention on a shared upstream segment serving many subscribers. Which design change most directly addresses contention?

  1. Reducing the number of subscribers per upstream segment Correct answer.
  2. Adding more content caches at the headend
  3. Shortening the DHCP lease time
  4. Increasing the downstream modulation order

Explanation

Upstream contention arises because subscribers share a common upstream channel, so reducing the number of subscribers per segment lowers the competition for upstream capacity. Modulation order, caching, and lease timers affect other aspects and do not directly reduce upstream sharing.

Question 40Broadband network fundamentals and architecture

Which protocol is commonly used to authenticate a broadband subscriber session at a BRAS and to carry per-session policy attributes?

  1. NTP
  2. SNMP
  3. LLDP
  4. RADIUS Correct answer.

Explanation

RADIUS carries authentication, authorization, and accounting information between the access device and a central server, and can return per-session policy attributes. SNMP is for management, NTP for time synchronization, and LLDP for neighbor discovery.

Question 41Broadband network fundamentals and architecture

An operator is comparing GPON and point-to-point Ethernet for a new residential build and wants to minimize fiber count in the feeder. Which advantage of GPON is most relevant?

  1. GPON shares one feeder fiber among many subscribers through passive splitting Correct answer.
  2. GPON guarantees a fixed data rate to each subscriber regardless of load
  3. GPON eliminates the need for any customer premises equipment
  4. GPON provides a dedicated fiber pair to every subscriber

Explanation

GPON's passive splitting lets a single feeder fiber serve many subscribers, greatly reducing feeder fiber count compared with point-to-point Ethernet. It does not provide dedicated fibers, remove CPE, or guarantee fixed per-subscriber rates independent of load.

Question 42Broadband network fundamentals and architecture

Which element in an HFC network combines multiple downstream RF channels into a single optical transmitter input at the hub?

  1. The cable modem
  2. The tap
  3. The line extender
  4. The combiner Correct answer.

Explanation

A combiner merges several downstream RF channels so they can be carried together over the fiber and coaxial plant. Taps and line extenders distribute and amplify RF in the field, and cable modems are subscriber devices.

Question 43Broadband network fundamentals and architecture

A provider wants to offer symmetric multi-gigabit service where the fiber reaches the subscriber and the access plant contains no powered field electronics. Which architecture satisfies both conditions?

  1. ADSL2+ from the central office
  2. XGS-PON with passive splitters Correct answer.
  3. VDSL2 from a street cabinet
  4. DOCSIS 3.1 over a deep-fiber HFC plant

Explanation

XGS-PON delivers fiber to the subscriber and uses only passive splitters in the field, supporting symmetric multi-gigabit rates. DOCSIS and DSL variants rely on coaxial or copper segments, and cabinet-based VDSL2 requires powered field equipment.

Question 44Broadband network fundamentals and architecture

Why does a broadband access network often place a Layer 2 aggregation switch between access nodes and the BRAS?

  1. To provide power to passive optical splitters
  2. To convert RF signals into Ethernet frames
  3. To terminate optical wavelengths from the core
  4. To concentrate many access node uplinks into a smaller number of higher-capacity paths and apply VLAN separation Correct answer.

Explanation

A Layer 2 aggregation switch concentrates uplinks from many access nodes and uses VLANs to keep subscriber traffic separated before it reaches the BRAS. Wavelength termination, RF conversion, and powering passive splitters are functions of other devices.

Question 45Broadband network fundamentals and architecture

In a PON, which mechanism prevents upstream bursts from different ONUs on the same branch from colliding at the splitter?

  1. The OLT grants upstream transmission opportunities in scheduled time slots Correct answer.
  2. The splitter filters out overlapping bursts
  3. The ONUs negotiate directly with each other over a control channel
  4. Each ONU transmits continuously on its own wavelength

Explanation

Upstream PON transmission is time-division multiplexed: the OLT schedules grants so that each ONU transmits only in its assigned window, preventing collisions at the combiner. Continuous per-ONU wavelengths, splitter filtering, and direct ONU negotiation are not how PON upstream coordination works.

Question 46Broadband network fundamentals and architecture

A provider observes that a single subscriber's misconfigured device is flooding broadcast traffic across many access nodes. Which architectural control most directly limits the scope of that flooding?

  1. Shortening the DHCP lease duration
  2. Assigning each access node uplink to a separate VLAN or broadcast domain Correct answer.
  3. Increasing the downstream modulation order
  4. Enabling jumbo frames on the aggregation switch

Explanation

Placing each access node uplink in its own VLAN or broadcast domain confines broadcast traffic to that segment and prevents it from spreading across the aggregation network. Modulation, lease timers, and frame size do not bound broadcast propagation.

Question 47Broadband network fundamentals and architecture

An operator plans to migrate from GPON to XGS-PON while reusing the existing optical distribution network. Which consideration is most critical for coexistence during the transition?

  1. Ensuring the existing splitter and fiber plant support the additional downstream and upstream wavelengths used for coexistence Correct answer.
  2. Disabling VLAN separation on the aggregation switch
  3. Replacing all ONUs with DOCSIS cable modems
  4. Increasing the DHCP lease time on the BRAS

Explanation

Coexistence of GPON and XGS-PON on the same ODN depends on wavelength planning, with separate downstream and upstream bands combined and filtered at the OLT and supported by the splitter and fiber plant. Replacing ONUs with cable modems, changing lease timers, or removing VLAN separation would not enable coexistence and would break the architecture.

Question 48Broadband network fundamentals and architecture

A design team must choose between a centralized BRAS and a distributed edge BRAS model for a large access network. Which trade-off most accurately describes the distributed model?

  1. It reduces core transport of subscriber sessions but increases the number of policy points to manage Correct answer.
  2. It guarantees lower latency for every service regardless of placement
  3. It removes the need for aggregation switching in all cases
  4. It eliminates the need for subscriber authentication entirely

Explanation

Distributed edge BRAS placement keeps subscriber session termination closer to the access edge, reducing session traffic hauled to a central site, but it multiplies the policy and management points that must be kept consistent. It does not remove authentication, eliminate aggregation, or guarantee lower latency for all services.

Question 49Broadband network fundamentals and architecture

In an HFC plant, why does the upstream spectrum generally occupy a narrower band than the downstream spectrum?

  1. Upstream signals originate at many subscribers and must pass through amplifiers and the node, where noise funneling and limited amplifier return-path bandwidth constrain usable spectrum Correct answer.
  2. Downstream traffic is always smaller in volume than upstream traffic
  3. Coaxial cable cannot carry frequencies below 50 MHz
  4. Upstream lasers are incapable of carrying any modulated signal

Explanation

The upstream path combines noise from many subscriber branches at the node, an effect known as noise funneling, and return-path amplifiers have historically offered less usable bandwidth, so the upstream occupies a narrower spectrum. Upstream lasers do carry modulated signals, downstream traffic is typically larger, and coax can carry low frequencies but the lowest band is often reserved or impaired.

Question 50Broadband network fundamentals and architecture

A provider wants to raise per-subscriber capacity on an HFC network without replacing the coaxial plant. Which combination of changes is most consistent with that goal?

  1. Node splitting to shrink serving areas and wider channel bonding in DOCSIS 3.1 Correct answer.
  2. Increasing DHCP lease times and reducing the number of taps
  3. Converting the plant to ADSL2+ and shortening the drop cables
  4. Replacing the CMTS with a BRAS and disabling upstream channels

Explanation

Node splitting reduces the number of subscribers sharing each segment, and DOCSIS 3.1 channel bonding plus higher-order modulation increases capacity per segment, together raising per-subscriber throughput without rebuilding the coax. The other options either degrade capacity or address unrelated functions.