Computer Networks 1 : Questions & Answers for Internal

Chapter 1: 

Chapter 2: Lower Layers

*Q. What is bandwidth?

Answer: It refers to maximum amount of data that can be transmitted over a network connection.

It can be :

1. Bandwidth in hertz (Hz): It is a range of frequency. (eg: 4Khz for telephone)

2. Bandwidth in Bits pr second (bps) : It refers to speed of transmission in a channel or link. (eg: 10mbps for Wifi)

*Q. What is throughput?

Answer:It is the rate of successful message delivery over a channel or medium.

*Q. What is latency?

Answer: The latency defines how long it takes for entire message to completely reach destination from time first bit is sent from source.

Latency= propagation time+ transmission time+queueing time+ processsing time

Q. What is propagation time?

Answer: It is the time required for a bit to travel from source to destination.

Propagation time = Distance between two points/ Speed

Q. What is transmission time?

Answer: The time required to transmit entire message over a communication channel is caled transmission time.

Transmission time= message size/ bandwidth

Q. What is queuing time?

Answer: It is the time needed for intermediate or end device to hold a message before it can process. It depends upon load of network.

Q. What is bandwidth-delay product?

Answer: The bandwidth-delay product defines the number a bits that can fill a network link  at a time.

Q. What is jitter?

Answer: Jitter is variation in delay of received packets over a network, which makes packets arrive at destination at irregular intervals.

Q. What is multiple access methods? Give its types.

Answer: Multiple access method are ways to connect multiple stations to same transmission medium to transmit over it and share its capacity.

There are three types:

1. Random Access Methods - Any station can send data at any time

2. Controlled Access Methods- Stations consult other stations before transmission.

3. Channelization Method- The channel is divided into multiple channels.

Q. Explain ALOHA. And its types.

Answer: ALOHA is a random access method for multiple access of same transmission medium. Any station can transmit data at any time.

There are two types of ALOHA:

1. Pure ALOHA : It is the original ALOHA. Since any station can send data at any time , there are chances of collision. So if acknowledgement is not received within a specified time, the station assumes the frame is destroyed and retransmits it. Before retransmission, the station waits for a random amount of time to reduce chances of collision.

After several tries if its not happening then procedure is avoided.

2. Slotted ALOHA : It is improvement to original ALOHA , here the channel is divided into discrete time slots. The stations can only transmit data at beggining of time slots. If it misses the beggining, then it has to wait for next time slot. Here the chances of collision are very low, collision generally happens if both stations transmit at same time.

Q. Explain reservation method.

Answer: In this method, the time is divided into same number of intervals as there are number of stations. Each interval belongs to a station. There is a reservation frame followed by data frame.

Q. Explain polling method.

Answer: In this method, one station is designated as primary and rest are secondary stations. Primary device decides which station is allowed to use the channel. All data transfer must happen through primary device.

It has two functions:

1. Select: When primary device sends the data, it first sends SEL frame, waits for acknowledgement and then sends the data. 

2. Poll:When primary device wants to receive data, the polling is used. It polls each machine if it wants to send data. Then the station either sends NAK if there is nothing to send, or sends the data. Then if primary station receives data, it returns acknowledgement.

Q. Explain Channelization.

Answer: It is a multiple access method in which available bandwidth of a link is shared in time, frequency or through code between different stations.

It is of three types:

FDMA: Frequency division multiple access , where the total channel bandwidth is divided into various frequency bands.

TDMA: Time division multiple access, where total bandwidth is one channel, each station is allocated a time slot in which the data is sent.

CDMA: Code division multiple access, where only one channel occupies entire bandwidth and communication happens through means of codes.

Q. Explain types of switching.

Answer: There are three types of switching:

1. Message switching: In message switching, each switch stores the entire message and forwards its to next switch.

2. Circuit Switching: In circuit switching, a dedicated communication path is established between two devices before they start communicating.

3. Packet Switching: Here the data is broken down into packets, and each packet is routed to its destination without establishing a dedicated path.

Q.  Give the difference between WLAN and Bluetooth.

Answer:

Point	WLAN (Wireless Local Area Network)	Bluetooth
Range	Covers a larger area, typically several hundred feet or more.	Covers a smaller area, typically up to 30 feet.
Speed	High-speed connectivity with data transfer rates of up to 10 Gbps.	Lower data transfer rates, typically up to 1 Mbps.
Interference	Can be subject to interference from other wireless networks or electronic devices.	Uses frequency hopping to avoid interference from other wireless devices.
Power	Requires more power to operate due to the larger range and higher data transfer rates.	Uses less power, making it ideal for low-power devices such as headphones and smartwatches..
Use Case	Typically used to provide wireless connectivity in a larger area, such as a home or office building.	Often used to connect devices that are in close proximity, such as headphones, speakers, and smartwatches.

Q. Explain architecture of bluetooth.

Answer: Bluetooth architecture defines two types of networks: 

1. Piconet: It is a bluetooth device that consists of one primary (master) node and seven active secondary (slave) nodes. All communication happens through master only. It can have upto 255 parked nodes which work only when moved to a state of active node.

2. Scatternet: It is formed by combining various piconets. A slave in one piconet can act as master in another piconet.This way a station can be member of two piconets. But a station cannot be master in two piconets.

Q. What is token passing method

Answer: This is a controlled access method. A station is allowed to send data when it receives a special frame called token. Al the stations are organized in a logical  ring, when the channel is  idle, the token circulates though the ring . When the station wants to send data, it captures the token, sends the data, then releases the token. This way the right to send data is transferred from predecessor to successor.