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AirNet Interview Questions with Answers

Posted on :26-04-2016

Q1. What is broadband?

ANS:

- Broadband is an internet access with high speed.
- Unlike dial-up connection, broadband connection is permanently connected.
- It allows internet and telephone calls to take place simultaneously. No new land line is required.
- Modulation is done in broadband on signals to transform data better.


Q2. What are the classifications of Wireless technologies and systems?

ANS:

• Cellular mobile radio systems 
• Cordless telephones 
• Wide-area wireless data systems 
• High-speed WLANs 
• Paging/messaging systems 
• Satellite-based mobile systems


Q3. Mention the function of the base station. 

ANS:

The base station serves as a bridge between all mobile users in the cell and connects the simultaneous mobile calls via telephone lines or microwave links to the mobile switching center (MSC).


Q4. State certain access technologies used in mobile satellite communication systems. 

ANS:

FDMA, TDMA and CDMA.


Q5. Distinguish between 1G and 2G cellular networks. 

ANS:

First generation cellular systems introduced in early 1980s were based on analog FM technology and designed to carry narrow band circuit switched voice services. Second generation cellular systems introduced in early 1990s use digital modulation and offers more spectral efficiency and voice quality.


Q6. Distinguish between 3G and 4G cellular networks. 

ANS:

The main difference between 3G and 4G technologies is the data speed (2-3 Mbps for 3G vs. 5-30 Mbps actual current 4G speeds). 

Also, 4G LTE uses a completely different radio technology (OFDM vs CDMA) and MOMO (multiple input and output transmitter-receiver antennas).


Q7. What is difference between baseband and broadband transmission?

ANS:

In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.


Q8. What is line attenuation?

ANS:

Attenuation is the loss of signal over distance.
* 20bB. and below = Outstanding
* 20dB-30dB. = Excellent
* 30dB-40dB. = Very Good
* 40dB-50dB. = Good
* 50dB-60dB. = Poor and may experience connectivity issues
* 60dB. and above = Bad and will experience connectivity issues

Line attenuation also affects your speed.

* 75 dB+: Out of range for broadband
* 60-75 dB: max speed up to 512 kbps
* 43-60 dB: max speed up to 1 Mbps
* 0-42 dB: speed up to 2 Mbps+


Q9. What is SNR?

ANS:  

Signal-to-noise  means  the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power, often expressed in (dB).
  1. 6dB or below noise margin is bad, it will experience no synch or intermittent synch problems
  2. 7dB-10dB is fair but does not leave much room for variances in conditions
  3. 11dB-20dB is good with little or no synch problems (if no large variation)
  4. 20dB-28dB is excellent
  5. 29dB or above is outstanding


Q10. Explain Broadband Call Flow?

ANS: 
  1. When the PPPoE client is dialed, the PPPoE client broadcasts a PPPoE Active Discovery Initiation (PADI) message to BNG.
  2. The BNG that receive the PADI message respond with a PPPoE Active Discovery Offer (PADO) message advertising the domains and contexts they support if configured to advertise.
  3. The PPPoE Client sends a PPPoE Active Discovery Request (PADR) message to the BNG.
  4. The BNG receives the PADR message and prepares to bring up the PPP session.  Then responds with PPPoE Active Discovery Session-Confirmation (PADS) message advertising PPPoE session ID.
  5. The PPPoE Client sends PPP LCP Configuration Request message advertising to BNG.
  6. The BNG responds with PPP LCP Configuration Ack if PPP parameters are acceptable.
  7. The BNG then sends PPP CHAP Challenge to PPPoE Client.
  8. The PPPoE Client responds with PPP CHAP Response.
  9. The BNG sends  Access-Request packet to AAA Server with the sessions PPP username and CHAP password.
  10. AAA sever reply Access-Accept to BNG and BNG will release public ip to the subscriber.


Q11. What is CDMA?

ANS:

CDMA (Code Division Multiple Access) and GSM (Global System for Mobiles) are shorthand for the two major radio systems used in cell phones. Both acronyms tend to group together a bunch of technologies run by the same entities.


Q12. What is a Broadband modem?

ANS:

A Broadband modem is a small piece of hardware which allows you to connect to the Internet. This is essential in order to receive Broadband. 


Q13. What are the channels used in mobile communication systems?
 
ANS:

1. Forward voice channels (FVC) 
2. Reverse voice channels (RVC) 
3. Forward control channels (FCC) 
4. Reverse Control channels (RCC)


Q14. What are the limitations of conventional mobile telephone system? 

ANS:

• Limited service capability 
• Poor service performance 
• Inefficient frequency spectrum utilization


Q15. Why 800 MHz frequency is selected for mobiles?

ANS:

Fixed Station Services - 30 MHz to 100 MHz Television Broadcasting - 41 MHz to 960 MHz FM Broadcasting - 100 MHz Air to Ground system - 118 MHz to 136 MHz Maritime mobile services - 160 MHz Military Aircraft use - 225 MHz to 400 MHz Frequency bands between 30 MHz to 400 MHz is crowded with large number of services and above 10 GHz is not used due to propagation path loss, multipath fading and improper medium due to rain activity. So 800 MHz is chosen for mobile communication.


Q16. State the types of modulation schemes used in mobile communication. 

ANS:

Gaussian minimum shift keying,
Differential Quadrature Phase Shift Keying.


Q17. Mention the different types of random access protocols. 

ANS:

ALOHA, Slotted ALOHA, Carrier Sense Multiple Access, Carrier Sense Multiple Access /Collision Detection.


Q18. What is TDMA?

ANS:

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot.


Q19. What is CSMA?

ANS:

Carrier sense multiple access (CSMA) is a probabilistic media access control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum.


Q20. What is ALOHA?
  
ANS:

Aloha, also called the Aloha method, refers to a simple communications scheme in which each source (transmitter) in a network sends data whenever there is a frame to send. If the frame successfully reaches the destination (receiver), the next frame is sent. If the frame fails to be received at the destination, it is sent again.


  
   






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