Computer Networks Sample Paper 1

SECTION A

5*2 = 10 Marks

1. What are the design issues addressed by the Data Link Layer?

1. The Data Link Layer addresses several design issues, including:

• Framing: dividing the stream of bits into manageable units called frames.
• Addressing: providing a way to identify the source and destination of a frame.
• Error detection and correction: detecting and correcting errors that may occur during transmission.
• Flow control: regulating the flow of data between two devices to avoid overwhelming the receiver.
• Access control: determining which device has access to the medium at any given time.

2. What is the purpose of error detection in the Data Link Layer?

The purpose of error detection in the Data Link Layer is to detect errors that may occur during transmission, such as bit errors or noise. By detecting these errors, the Data Link Layer can request retransmission of the affected frames or take other corrective measures to ensure the integrity of the data being transmitted.

3. What is flow control and why is it necessary?

Flow control is the process of regulating the flow of data between two devices to avoid overwhelming the receiver. Flow control is necessary because the receiving device may not be able to process incoming data as fast as it is being transmitted. Without flow control, data packets may be lost or dropped, leading to poor network performance.

4. Name two sliding window protocols used in the Data Link Layer.

Two sliding window protocols used in the Data Link Layer are:

• Selective Repeat: In this protocol, the receiver can selectively request retransmission of only those frames that were received with errors. The sender maintains a window of unacknowledged frames and sends only those frames for which it has received an acknowledgment.
• Go-Back-N: In this protocol, the sender maintains a window of unacknowledged frames and sends them in sequence. If an acknowledgment is not received for a particular frame, the sender retransmits all unacknowledged frames starting from the one that was not acknowledged.

5. Give an example of a controlled access MAC protocol.

An example of a controlled access MAC protocol is Reservation-based protocol, where devices reserve a specific time slot to transmit data. The reservation can be made using a centralized control entity or using a distributed protocol.

6. What is the purpose of the Data Link Layer?

The purpose of the Data Link Layer is to provide reliable, error-free transmission of data over a physical link. The Data Link Layer accomplishes this by providing a number of services, including error detection and correction, flow control, and access control.

7. What is the difference between flow control and error control in the Data Link Layer?

The difference between flow control and error control in the Data Link Layer is that flow control is concerned with regulating the flow of data between two devices to avoid overwhelming the receiver, while error control is concerned with detecting and correcting errors that may occur during transmission.

8. What are the design issues to consider when designing a Data Link Layer protocol?

When designing a Data Link Layer protocol, several design issues must be considered, including:

• The size of the frame and how to divide the stream of bits into manageable units.
• How to provide addressing information to identify the source and destination of a frame.
• How to detect and correct errors that may occur during transmission.
• How to regulate the flow of data between two devices to avoid overwhelming the receiver.
• How to determine which device has access to the medium at any given time.

9. What is the purpose of error detection and correction in the Data Link Layer?

The purpose of error detection and correction in the Data Link Layer is to ensure the integrity of the data being transmitted. By detecting and correcting errors that may occur during transmission, the Data Link Layer can ensure that the data received by the destination device is the same as the data sent by the source device.

10.What is the difference between Stop-and-Wait and Sliding Window flow control techniques?

The main difference between Stop-and-Wait and Sliding Window flow control techniques is that Stop-and-Wait only allows one frame to be transmitted at a time, while Sliding Window allows multiple frames to be transmitted without waiting for an acknowledgment. In Stop-and-Wait, the sender must wait for an acknowledgment before sending the next frame, while in Sliding Window, the sender can send multiple frames before receiving an acknowledgment. Sliding Window is therefore more efficient in terms of network utilization…

Section B

2*5= 10 Marks

1. Compare and contrast the Stop-and-Wait and Sliding Window flow control techniques used in the Data Link Layer.

Stop-and-Wait and Sliding Window are two flow control techniques used in the Data Link Layer. Stop-and-Wait allows only one frame to be transmitted at a time and the sender waits for an acknowledgment before sending the next frame. Sliding Window, on the other hand, allows multiple frames to be transmitted without waiting for an acknowledgment. In Sliding Window, the sender maintains a window of unacknowledged frames and can send up to the window size before receiving an acknowledgment. This makes Sliding Window more efficient in terms of network utilization. However, Stop-and-Wait is simpler and more reliable in environments with high error rates.

2. Explain the purpose of ARQ (Automatic Repeat Request) protocols such as Go Back N and Selective Repeat in the Data Link Layer.

ARQ (Automatic Repeat Request) protocols such as Go-Back-N and Selective Repeat are used in the Data Link Layer to ensure the reliable delivery of data. When a frame is transmitted, the receiver sends an acknowledgment to the sender. If the sender does not receive an acknowledgment, it assumes that the frame was lost and retransmits it. Go-Back-N and Selective Repeat differ in how they handle retransmissions. Go-Back-N retransmits all unacknowledged frames starting from the one that was not acknowledged, while Selective Repeat only retransmits frames that were received with errors.

3. Compare and contrast Go-Back-N and Selective Repeat Automatic Repeat Request (ARQ) protocols used in the Data Link Layer.
Go-Back-N and Selective Repeat are two Automatic Repeat Request (ARQ) protocols used in the Data Link Layer. They both ensure the reliable delivery of data by using acknowledgments and retransmissions. However, they differ in how they handle retransmissions. Go-Back-N retransmits all unacknowledged frames starting from the one that was not acknowledged. This approach is simple but can result in unnecessary retransmissions. Selective Repeat, on the other hand, only retransmits frames that were received with errors. This approach is more efficient but requires more processing power at the receiver.

4. Explain the purpose of High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP) in the Data Link Layer.

High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP) are two protocols used in the Data Link Layer. HDLC is a bit-oriented protocol that provides error detection, flow control, and data transparency. It is widely used in point-to-point and multipoint communication systems. PPP, on the other hand, is a byte-oriented protocol that provides error detection, flow control, and encapsulation of multiple network layer protocols. It is commonly used in dial-up and broadband connections. The purpose of both protocols is to ensure the reliable delivery of data over a physical link.

Computer Networks Sample Paper 2

SECTION A

5*2 = 10 Marks

1. What is the purpose of the Network Layer in the OSI model?

The purpose of the Network Layer in the OSI model is to provide end-to-end delivery of data across multiple networks. This layer is responsible for logical addressing, routing, and fragmentation and reassembly of data packets. It determines the best path for data to travel from the source to the destination based on the network topology and traffic conditions.

2. What are the logical addresses used in IPv4 and IPv6?

In IPv4, the logical address is the IP address, which is a 32-bit binary number divided into four octets and represented in decimal form separated by periods. In IPv6, the logical address is the IPv6 address, which is a 128-bit binary number represented in hexadecimal notation.

3. What are the two types of routing algorithms used in the Network Layer?

The two types of routing algorithms used in the Network Layer are distance vector routing and link state routing.

4. What is the difference between IPv4 and IPv6 addressing schemes?

The main difference between IPv4 and IPv6 addressing schemes is the size of the address space. IPv4 addresses are 32 bits long and can provide approximately 4.3 billion unique addresses, while IPv6 addresses are 128 bits long and can provide approximately 340 undecillion unique addresses. IPv6 also has a more efficient and flexible address allocation system.

5. What are the differences between distance vector and link state routing algorithms?

Distance vector routing is a type of routing algorithm where each router calculates the distance to all other routers in the network and sends updates to its neighbors. These updates are then propagated through the network until all routers have the same information. Link state routing is a type of routing algorithm where each router maintains a database of the network topology and calculates the shortest path to each destination based on that information. Each router floods the network with updates containing information about its local links and the state of its neighbors, allowing all routers to build a complete view of the network topology. Distance vector routing protocols are simple and easy to implement, but they can be slow to converge and can cause routing loops. Link state routing protocols are more complex and require more memory and processing power, but they are more efficient and reliable than distance vector routing.

6. What is the difference between IPv4 and IPv6 packet formats?

The main difference between IPv4 and IPv6 packet formats is the size of the header. IPv4 headers are 20 bytes long, while IPv6 headers are 40 bytes long. IPv6 headers also include support for additional features such as flow labeling and extension headers.

7. What is the purpose of the IP header in a packet?

The purpose of the IP header in a packet is to provide information about the source and destination addresses, the type of protocol being used, the time-to-live (TTL), and any options or flags that may be set. The header allows routers to make forwarding decisions and helps ensure that packets are delivered to the correct destination.

Section B

2*5= 10 Marks

1. Compare and contrast distance vector and link state routing algorithms used in the
Network Layer.

1. Distance vector and link state are two types of routing algorithms used in the Network Layer of the OSI model.

• Distance vector routing algorithms work by having each router send its routing table to its neighboring routers. Each router then updates its own routing table based on the information received from its neighbors. This process continues until all routers have updated their routing tables. Distance vector algorithms use a metric (such as hop count) to determine the best path to a destination. Examples of distance vector routing protocols include RIP and EIGRP.
• Link state routing algorithms, on the other hand, work by having each router send information about its directly connected links to all other routers in the network. Each router then uses this information to construct a map of the entire network, which it uses to determine the best path to a destination. Link state algorithms use more advanced metrics (such as bandwidth and delay) to determine the best path. Examples of link state routing protocols include OSPF and IS-IS.

In summary, the main difference between distance vector and link state routing algorithms is in how they exchange information and determine the best path. Distance vector algorithms exchange information about their routing tables, while link state algorithms exchange information about their directly connected links. Distance vector algorithms use a simple metric, while link state algorithms use more advanced metrics.

2. Explain the differences between IPv4 and IPv6 addressing schemes, including the
advantages and disadvantages of each.

2. IPv4 and IPv6 are two versions of the Internet Protocol used for addressing on the Internet.

• IPv4 addresses are 32 bits long and are typically represented in dotted-decimal notation (such as 192.168.0.1). IPv4 allows for approximately 4.3 billion unique addresses, which is becoming a limiting factor as more and more devices are connected to the Internet. IPv4 has several disadvantages, including a limited address space, the need for NAT (Network Address Translation) to conserve addresses, and a lack of support for some newer technologies.
• IPv6 addresses are 128 bits long and are typically represented in hexadecimal notation (such as 2001:0db8:85a3:0000:0000:8a2e:0370:7334). IPv6 allows for approximately 340 undecillion unique addresses, which should be enough to support the growth of the Internet for many years to come. IPv6 also has several advantages over IPv4, including a larger address space, built-in support for security, and built-in support for new technologies.

In summary, the main differences between IPv4 and IPv6 addressing schemes are the length of the addresses, the way they are represented, the number of unique addresses they allow for, and their support for new technologies.

3. Compare and contrast IPv4 and IPv6 addressing schemes, including the advantages
and disadvantages of each.

3. IPv4 and IPv6 addressing schemes can be compared and contrasted in the following ways:

• Address Space: IPv4 addresses are 32 bits long and can provide approximately 4.3 billion unique addresses, while IPv6 addresses are 128 bits long and can provide approximately 340 undecillion unique addresses.
• Address Representation: IPv4 addresses are represented in dotted-decimal notation, while IPv6 addresses are represented in hexadecimal notation.
• Address Allocation: IPv4 address allocation follows a hierarchical structure, while IPv6 address allocation is more flexible and can be assigned to organizations in a more efficient manner.
• Header Size: IPv4 headers are 20 bytes long, while IPv6 headers are 40 bytes long.
• Security: IPv4 does not have built-in support for security, while IPv6 has support for IPsec.

Advantages of IPv6: It has a much larger address space, which allows for more devices to be connected to the Internet. It also has a more efficient and flexible address allocation system, which can reduce address waste and improve network performance. IPv6 also includes support for security features such as IPsec.

Disadvantages of IPv6: IPv6 is not yet widely supported and adopted, which means that there may be compatibility issues with some devices and software. IPv6 also has a larger header size, which can increase network overhead and reduce performance on some networks.

4. Explain the differences between distance vector and link state routing algorithms,
including their advantages and disadvantages

4. Distance vector and link state routing algorithms are two different types of routing algorithms used in computer networks. Here are the differences between the two:

• Distance Vector Routing: Distance vector routing is a type of routing algorithm where each router calculates the distance to all other routers in the network and sends updates to its neighbors. These updates are then propagated through the network until all routers have the same information. Distance vector routing protocols are simple and easy to implement, but they can be slow to converge and can cause routing loops.
• Link State Routing: Link state routing is a type of routing algorithm where each router maintains a database of the network topology and calculates the shortest path to each destination based on that information. Each router floods the network with updates containing information about its local links and the state of its neighbors, allowing all routers to build a complete view of the network topology. Link state routing protocols are more complex and require more memory and processing power, but they are more efficient and reliable than distance vector routing.

Advantages of Distance Vector Routing: It is simple and easy to implement, and it requires less memory and processing power than link state routing.

Disadvantages of Distance Vector Routing: It can be slow to converge and can cause routing loops, which can lead to network instability and performance issues.

Advantages of Link State Routing: It is more efficient and reliable than distance vector routing, and it can handle larger and more complex networks.

Disadvantages of Link State Routing: It is more complex and requires more memory and processing power than distance vector routing, which can make it more difficult to implement and main