PART A
1. Characteristics of networks.
The effectiveness of a network depends on three characteristics.
1. Delivery: The system must deliver data to the correct destination.
2. Accuracy: The system must deliver data accurately.
3. Timeliness: The system must deliver data in a timely manner.
2. Half duplex mode
In a Half-duplex channel, direction can be reversed, i.e., the station can transmit and
receive the data as well. Messages flow in both the directions, but not at the same time. The
entire bandwidth of the communication channel is utilized in one direction at a time. In half-
duplex mode, it is possible to perform the error detection, and if any error occurs, then the
receiver requests the sender to retransmit the data.
• A Walkie-talkie is an example of the Half-duplex mode.
• In Walkie-talkie, one party speaks, and another party listens. After a pause,
the other speaks and first party listens. Speaking simultaneously will create
the distorted sound which cannot be understood.
3. Advantages and disadvantages of hybrid topology.
Advantages of Hybrid Topology
1. Reliable as Error detecting and trouble shooting is easy.
2. Effective.
3. Scalable as size can be increased easily.
4. Flexible.
Disadvantages of Hybrid Topology
1. Complex in design.
2. Costly
4. What are the responsibilities of Data Link Layer(DLL)
It is responsible for transmitting frames from one node to the next node. The other
responsibilities of this layer are,
• Framing
• Physical addressing
• Flow control
• Error control
• Medium Access control
5. Draw ARP packet format (page no :6)
6. Purpose of flow control
If the rate at which the data are absorbed by the receiver is less than the rate
produced in the sender, the Data link layer imposes a flow control mechanism.
7. Parity check
One bit, called parity bit is added to every data unit so that the total number of 1’s in the
data unit becomes even (or) odd.
• The source then transmits this data via a link, and bits are checked and verified at the
destination.
• Data is considered accurate if the number of bits (even or odd) matches the number
transmitted from the source.
• This techniques is the most common and least complex method.
1. Even parity – Maintain even number of 1s E.g., 1011 → 1011 1
2. Odd parity – Maintain odd number of 1s E.g., 1011 → 1011 0
(OR)
The parity bit is added to the data before sending to ensure error detection during
transmission. Once the data reaches the receiver, the parity bit is checked to verify whether
the data was transmitted correctly. After checking, the parity bit is typically removed before
the data is processed or used by the receiver.
1. Even parity – Maintain even number of 1s E.g., 1011 → 1011 1
2. Odd parity – Maintain odd number of 1s E.g., 1011 → 1011 0
8. Difference between transmission delay and propagation delay.
Transmission Time: It is the amount of time required to push all the packet’s bits into the
wire.
Propagation Time: It measures the time required for a bit to travel from the source to the
destination
9. Two types of congestion control mechanism
10. Major five components involved in Computer networks
• nodes
• links
• protocols
• network interfaces
• network services
11. Full duplex mode
In Full duplex mode, the communication is bi-directional, i.e., the data flow in both the
directions.
• Both the stations can send and receive the message simultaneously.
• Full-duplex mode has two simplex channels. One channel has traffic moving in one
direction, and another channel has traffic flowing in the opposite direction.
• The Full-duplex mode is the fastest mode of communication between devices.
• The most common example of the full-duplex mode is a Telephone network. When
two people are communicating with each other by a telephone line, both can talk
and listen at the same time.
12. Advantages and disadvantages of mesh topology
13. Three types of addresses of Link layer protocol.
• Unicast Address
• Multicast Address
• Broadcast Address
14. Functions of Arp.
• ARP maintains a cache table in which MAC addresses are mapped to IP addresses.
• If a host wants to send an IP datagram to a host,it first checks for a mapping in the
cache table.
• If no mapping is found, it needs to invoke the Address Resolution Protocol over the
network.
• It does this by broadcasting an ARP query onto the network.
• This query contains the target IP address.
• Each host receives the query and checks to see if it matches its IP address.
• If it does match, the host sends a response message that contains its linklayer
address (MAC Address) back to the originator of the query.
• The originator adds the information contained in this response to its ARP table
15. Advantages and disadvantages of stop and wait protocol.
Advantages
• Simplicity
• Reliable Transmission
• Low Overhead
• Error Detection
• No Complex Buffering
Disadvantages
• Inefficient Use of Bandwidth
• Increased Latency
• Limited Throughput
• Not Suitable for Large Data Transfers
• Retransmission Overhead
16. Categories of error control.
17. Queuing delay and transmission delay.
Queuing Delay:
The queuing delay for a packet in a router is measured as the time a packet waits in
the input queue and output queue of a router.
Delay = The time a packet waits in input and output queues in a router
Transmission Delay:
A source host or a router cannot send a packet instantaneously. A sender needs to
put the bits in a packet on the line one by one. The transmission delay is longer for a longer
packet and shorter if the sender can transmit faster. The Transmission delay is calculated
using the formula
Delay = (Packet length) / (Transmission rate)
18. How will you measure the performance of a network.
The performance of a network can be measured in terms of Delay, Throughput and Packet
loss.
19. What is congestion control?
Congestion in the network layer is a situation in which too many datagrams are present in an
area of the Internet. Congestion may occur if the number of datagrams sent by source
computers is beyond the capacity of the network or routers.
20. Define collision.
A collision in computer networks occurs when two or more devices attempt to send data
over the same communication channel simultaneously, resulting in the interference of their
signals. This can lead to data corruption or loss, as the transmitted frames or packets become
garbled or unreadable.
