nokia 4a0-205 practice test

Nokia Optical Networking Fundamentals

Last exam update: Nov 18 ,2025
Page 1 out of 3. Viewing questions 1-15 out of 40

Question 1

What is the definition of OSNR?

  • A. The OSNR is defined as the ratio between the transmitted optical power and the received optical power over 1 km of fiber including both signal and optical noise.
  • B. The OSNR is the ratio between the optical output signal power and the optical input signal power of the device being analyzed.
  • C. The OSNR is defined as the ratio between the average optical signal power and the average optical noise power over a specific spectral bandwidth.
  • D. The OSNR is defined as the ratio between the optical signal power (including noise) and the optical noise power over a specific spectral bandwidth.
Mark Question:
Answer:

C


Explanation:
The OSNR is defined as the ratio between the average optical signal power and the average optical
noise power over a specific spectral bandwidth. This is also known as the signal-to-noise ratio (SNR),
and it is a measure of how much signal is present in the optical signal compared to the noise, usually
expressed in decibels (dB).

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Question 2

Which of the following are the main reasons for fiber attenuation?

  • A. Refraction and reflection
  • B. Scattering and absorption
  • C. Chromatic dispersion (CD) and polarization mode dispersion
  • D. Small channel spacing
Mark Question:
Answer:

B


Explanation:
Scattering and absorption are the main reasons for fiber attenuation. Scattering occurs when light
bounces off the sides of the fiber, while absorption happens when light is absorbed by the glass or
other materials that make up the fiber. Chromatic dispersion (CD) and polarization mode dispersion
(PMD) are also factors that can cause attenuation, but they are not the main causes. Small channel
spacing can also cause attenuation, but it is a secondary factor and is only significant in certain cases.

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Question 3

What is the meaning of first, second, and third window in the optical fiber propagation context?

  • A. These windows correspond to three different minimum and maximum optical power levels used for optical transmission.
  • B. These windows are three different wavelength intervals where the WDM optical transmission occurs.
  • C. These three windows are three different angles of incidence of the light injected by the laser into the fiber.
  • D. Different optical transmission windows correspond to different safety requirements and rules for the related lasers operating with these windows.
Mark Question:
Answer:

B


Explanation:
In optical fiber propagation context, the first, second, and third window refer to different wavelength
intervals where the WDM (Wavelength Division Multiplexing) optical transmission occurs.
The first window is the lowest loss window and is typically in the range of 1300-1324nm. This is the
most commonly used window for long-haul communications.
The second window is the 1550 nm window and is the most widely used window for long-haul and
ultra-long-haul communications. This window has a lower attenuation than the first window, but it
also has more dispersion, which can limit the maximum transmission distance.
The third window is the range of 1625-1675 nm, it is also called the L-band window. This window has
lower attenuation than the first and second window but its usage is limited due to the high cost of
equipment and lack of commercial devices.
These windows are used in WDM systems to increase the capacity of the fiber by transmitting
multiple channels of data at different wavelengths on the same fiber.
A,C,D are not correct as they are not related to the meaning of first, second, and third window in the
optical fiber propagation context.
Reference:
Nokia Optical Networking Fundamentals, Nokia Press (ISBN:978-1-4822-8109-4)
https://www.nokia.com/networks/solutions/optical-networking/
https://en.wikipedia.org/wiki/Wavelength-division_multiplexing

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Question 4

In which window(s) does the attenuation reach its minimum peak?

  • A. First window (850 nm)
  • B. Second window (1300 nm)
  • C. Third window (1550 nm)
  • D. Both first and second windows
Mark Question:
Answer:

C


Explanation:
The third window (1550 nm) is where the attenuation reaches its minimum peak. This is because the
materials used in fiber optic cables have minimal absorption in this wavelength range. The first and
second windows (850 nm and 1300 nm respectively) have higher attenuation due to the materials
used in the fiber optic cables.

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Question 5

Which of the following statements is true about chromatic dispersion (CD)?

  • A. Different channels have different bandwidth and this causes different CD performances.
  • B. The fiber attenuation changes along the fiber, and when the light crosses these differences the CD takes place.
  • C. Different wavelengths propagate at different speeds within the same media and therefore different colors travel in the fiber with different speed.
  • D. The fiber attenuation introduces inter-channel interference.
Mark Question:
Answer:

C


Explanation:
Different wavelengths propagate at different speeds within the same media and therefore different
colors travel in the fiber with different speed. This phenomenon is known as chromatic dispersion
and causes light to spread out as it travels through the fiber over distance, leading to signal
attenuation and distortion. The fiber attenuation does not introduce inter-channel interference, but
it can cause attenuation of the signal. Different channels have different bandwidths, but this does not
affect CD performance.

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Question 6

How does a Raman pump work in the 1830 specific implementation?

  • A. The amplification is done simultaneously for all channels as they enter the board.
  • B. As the incoming signal power increase, the gain of the amplifier is reduced.
  • C. The pump light travels in the same direction of the signal, amplifying it while it flows in the fiber towards the following node.
  • D. The pump light travels in the opposite direction of the signal to be amplified, amplifying it while it arrives from the adjacent node.
Mark Question:
Answer:

D


Explanation:
In Raman amplification, a pump laser is used to excite the Raman-active molecules in the fiber, which
then amplifies the signal light as it travels in the opposite direction. In the 1830 specific
implementation, the pump laser is typically a high-power laser that is launched into the fiber in the
opposite direction to the signal. The pump light interacts with the Raman-active molecules in the
fiber, which then amplifies the signal light as it travels in the opposite direction. This allows the
Raman pump to provide a gain that increases with distance, which can be used to compensate for
the loss of signal power as it travels through the fiber.

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Question 7

WDM allows transmission systems to:

  • A. Transport multiple signals transparently, onto several wavelengths, all together over one single fiber
  • B. Increase the bit rate of each client signal by spreading it over multiple wavelengths
  • C. Share a single signal among multiple fibers doing load balancing, and thus increasing the reliability of the optical transmission
  • D. Allocate different signals to different time slots
Mark Question:
Answer:

A


Explanation:
WDM (Wavelength Division Multiplexing) allows transmission systems to transport multiple signals
transparently, onto several wavelengths, all together over one single fiber. This allows for increased
capacity, as many different signals can be transmitted at the same time and along the same fiber.
Other advantages include improved signal integrity and reduced signal attenuation.

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Question 8

When monitoring the quality of the received signal in WDM, an open eye indicates:

  • A. Low noise
  • B. High distortion
  • C. High jitter
  • D. Presence of high inter-symbolic interference
Mark Question:
Answer:

A


Explanation:
An open eye pattern indicates that the signal is not affected by noise, and the received signal is of
high quality. This is because an open eye pattern is the result of a signal that is aligned in time, and is
not affected by noise or other distortions.
Reference:
"Optical Fiber Communications" by Gerd Keiser
"Fiber-Optic Communications Technology" by Djafar K. Mynbaev
"Optical Communications" by Gerd Keiser

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Question 9

Which of the following sentences about FlexGrid is false?

  • A. FlexGrid allows a more efficient channel spacing.
  • B. Channels in FlexGrid systems are allocated with a granularity of 27.5GHz.
  • C. FlexGrid systems use specific sets of boards. Old generation WDM systems need to be upgraded to support FlexGrid.
  • D. The FlexGrid is currently standardized by ITU-T.
Mark Question:
Answer:

C


Explanation:
FlexGrid is a flexible grid technology that allows for variable channel spacing and bandwidth
allocation. It uses the same sets of boards as the traditional fixed grid systems and it does not require
upgrading the old generation WDM systems.
Reference:
"Flexible Grid Optical Networks: From Concepts to Realizations" by Diomidis S. Michalopoulos and
George K. Karagiannidis
"Flexible Grid and Flexible Spectrum Optical Networks" by Diomidis S. Michalopoulos and George K.
Karagiannidis
"Flexible Grid Optical Networks" by Diomidis S. Michalopoulos and George K. Karagiannidis

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Question 10

What is the function of a pre-amplifier in an optical network?

  • A. Through the pre-amplifier, the optical signal is amplified at the receiver side after it travels along the fiber from another node.
  • B. Through the pre-amplifier, the optical signal is amplified at the transmitter side before it is sent to the line span.
  • C. Through the pre-amplifier, the optical signal is amplified both the receiver side and at the transmitter side.
  • D. Through the pre-amplifier, the optical signal is amplified within the node internally to recover internal losses due, for instance, to cascaded filters.
Mark Question:
Answer:

B


Explanation:
A pre-amplifier is an optical amplifier that is used to boost the power of the received optical signal
before it is detected by the receiver in an optical communication system. This is done to overcome
the loss of power that occurs as the signal travels through the optical fiber and to ensure that the
receiver can detect the signal. The pre-amplification stage is typically located close to the receiver in
order to minimize the distance that the signal has to travel between the amplifier and the receiver,
which helps to reduce the noise and distortion in the signal.

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Question 11

What is a degree-1 node?

  • A. A node with only one direction and therefore a terminal node
  • B. A node with only one express channel and therefore made of two sides
  • C. A node with only east and west sides without directions towards north and south
  • D. A node with one direction only and therefore used as In-Line-Amplifier (ILA)
Mark Question:
Answer:

A


Explanation:
A degree-1 node is a node that only has one direction, and it is therefore a terminal node. This
means that the node only has one input and one output port. It does not have any other ports to
connect to other nodes or fibers. This is a common feature of some optical transport networks, such
as ring networks, where a degree-1 node serves as the endpoint of the ring.

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Question 12

With reference to trails and services, which of the following sentences is correct?

  • A. Trails are transported over services; that is, trails are clients with respect to services.
  • B. A trail can interconnect three ports, while a service always two.
  • C. Services are transported over trails; that is, services are clients with respect to trails.
  • D. A service is always associated to a single wavelength, while a trail can involve multiple wavelengths.
Mark Question:
Answer:

C


Explanation:
Services are transported over trails; that is, services are clients with respect to trails. A service is a
logical connection that is used to transport data from one point to another. It is created over a trail,
which is a physical connection that is established by using multiple wavelengths. As such, services are
clients with respect to trails, as they are transported over them.

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Question 13

What is a trail?

  • A. An entity to encapsulate a low order signal into a high order container
  • B. A transparent transport of a client signal
  • C. A link between end points to increase the power budget of the optical link
  • D. A physical link between two optical amplifiers
Mark Question:
Answer:

B


Explanation:
A trail is a transparent transport of a client signal. A trail is a physical link between two points in an
optical network, allowing for the transport of a client signal from one point to the other. It is a low-
order signal, such as a 10G Ethernet or a Fibre Channel signal, encapsulated into a high-order
container, such as a 40G or 100G signal. This allows for the transport of the client signal over longer
distances, increasing the power budget of the optical link.

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Question 14

Which use case is most suitable for the deployment of a star topology?

  • A. Access networks, for collecting traffic towards the main central node
  • B. ASON networks, to protect traffic via GMPL5 protocols
  • C. Backbone networks, for supporting protection routes
  • D. SNCP-protected links
Mark Question:
Answer:

A


Explanation:
A star topology is a network design where all devices are connected to a central hub, which acts as a
central point of control and management for the network. This type of topology is commonly used in
access networks, where a central node is used to aggregate traffic from multiple users or devices,
and then forward it to the core network. This design allows for efficient use of resources and easy
management of the network.
Reference:
"Computer Networking: A Top-Down Approach" by James Kurose and Keith Ross (Chapter 3)
"Data Communications and Networking" by Behrouz A. Forouzan (Chapter 2)

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Question 15

What is the metro area network?

  • A. The metro area network is that portion of network that passes through a city to provide connections to several customers.
  • B. The metro area network is located between access and core domains.
  • C. The metro area network is made of OCS/SWDM nodes only, as no pure photonic nodes are used here.
  • D. The metro area network is located in between two access area networks and made of photonic nodes only (no OCS/SWDM nodes are used there).
Mark Question:
Answer:

A


Explanation:
The Metro Area Network (MAN) is a telecommunications network that spans a metropolitan area
and connects multiple local area networks (LANs) or business networks together. It typically covers
an area that is larger than a LAN but smaller than a wide area network (WAN). The purpose of a MAN
is to provide a high-bandwidth, low-latency communication infrastructure for businesses and other
organizations in a metropolitan area.
Reference:
Cisco, "Metro Ethernet Services,"
https://www.cisco.com/c/en/us/solutions/service-provider/metro-ethernet-services/index.html
Techopedia, "Metro Area Network (MAN),"
https://www.techopedia.com/definition/26896/metro-
area-network-man

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