Nokia 4A0-205 Practice

What is the definition of OSNR?

• 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.

• The OSNR is the ratio between the optical output signal power and the optical input signal power of the device being analyzed.

• The OSNR is defined as the ratio between the average optical signal power and the average optical noise power over a specific spectral bandwidth.

• The OSNR is defined as the ratio between the optical signal power (including noise) and the optical noise power over a specific spectral bandwidth.

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

• Refraction and reflection

• Scattering and absorption

• Chromatic dispersion (CD) and polarization mode dispersion (PMD)

• Small channel spacing

Answer explanation

page 16 Attenuation measures the amount of light loss between input and output. Two main intrinsic factors are absorption and scattering. Extrinsic attenuation is caused by physical bending, stress from manufacturing, and other external factors.

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

• These windows correspond to three different minimum and maximum optical power levels used for optical transmission.

• These windows are three different wavelength intervals where the WDM optical transmission occurs.

• These three windows are three different angles of incidence of the light injected by the laser into the fiber.

• Different optical transmission windows correspond to different safety requirements and rules for the related lasers operating with these windows.

Answer explanation

page 18 Three transmission ranges have been identified for optical transmission. The first window is around 850 nm. the second window is 1310 nm, and the third window is 1550 nm.

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

• First window (850 nm)

• Second window (1300 nm)

• Third window (1550nm)

• Both first and second windows

Answer explanation

page 18 The absorbtion peak is between the second and third windows (1440 nm) due to OH (hydroxyl) elements introduced in the manufacturing process.

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

• 
  

• Different channels have different bandwidth and this causes different CD performances.

• The fiber attenuation changes along the fiber, and when the light crosses these differences the CD takes place.

• Different wavelengths propagate at different speeds within the same media and therefore different colors travel in the fiber with different speed.

• The fiber attenuation introduces inter-channel interference.

Answer explanation

page 20 Different wavelengths (sometimes called "colors") injected into the same fiber will arrive at slightly different times.

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

• The amplification is done simultaneously for all channels as they enter the board.

• As the incoming signal power increase, the gain of the amplifier is reduced.

• The pump light travels in the same direction of the signal, amplifying it while it flows in the fiber towards the following node.

• The pump light travels in the opposite direction of the signal to be amplified, amplifying it while it arrives from the adjacent node.

Answer explanation

page 39 Raman amplifiers operate based on a different physical principle than EDFAs. It is typically placed at the receiver, and the pump travles in the opposite direction with respect to the incoming signal.

WDM allows transmission systems to:

• Transport multiple signals transparently, onto several wavelengths, all together over one single fiber

• Increase the bit rate of each client signal by spreading it over multiple wavelengths

• Share a single signal among multiple fibers doing load balancing, and thus increasing the reliability of the optical transmission

• Allocate different signals to different time slots

Answer explanation

page 59 The idea that different wavelengths can be sent over one single fiber without interfering with each other.

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

• Low noise

• High distortion

• High jitter

• Presence of high inter-symbolic interference

Answer explanation

page 45 An open eye pattern corresponds to minimal signal distortion.

Which of the following sentence about FlexGrid is false?

• FlexGrid allows a more efficient channel spacing.

• Channels in FlexGrid systems are allocated with a granularity of 27.5 GHz.

• FlexGrid systems use specific sets of boards. Old generation WDM systems need to be upgraded to support FlexGrid.

• The FlexGrid is currently standardized by ITU-T.

Answer explanation

page 82 Flexgrid minimum slot is 12.5 GHZ, FlexGrid is the IT G.694.1 standard. FlexGrid allows more efficient spacing. FlexGrid requires newer boards.

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

• . Through the pre-amplifier, the optical signal is amplified at the receiver side after it travels along the fiber from another node.

• Through the pre-amplifier, the optical signal is amplified at the transmitter side before it is sent to the line span.

• Through the pre-amplifier, the optical signal is amplified both the receiver side and at me transmitter side.

• Through the pre-amplifier, the optical signal is amplified within the node internally to recover internal losses due, for instance, to cascaded filters.

Answer explanation

page 31 Pre-amplifiers (ingress amplifier) boost the signal at the receiving side after the light traverses the fiber.