Computer Networks: Circuit Switching, Packet Switching, TCP, UDP, and Wireless Networks, Exams of Computer Networks

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CS 372

Intro to Computer

Networks

COMPLETED EXAM

1. What is the difference between circuit switching and packet switching? Explain the advantages and disadvantages of each method.

• Circuit switching is a method of establishing a dedicated connection between two nodes in a network, such as a telephone call. The connection is reserved for the duration of the communication and no other nodes can use the same link. Packet switching is a method of dividing data into smaller units called packets and sending them over a shared network, where each packet can take different paths to reach the destination. The packets are reassembled at the receiver's end. The advantages of circuit switching are that it provides a guaranteed quality of service, low latency and no packet loss. The disadvantages are that it is inefficient in terms of bandwidth utilization, as the link may be idle during periods of silence or low activity. Packet switching, on the other hand, has the advantages of being more efficient in terms of bandwidth utilization, as multiple nodes can share the same link, and more flexible, as packets can adapt to network congestion or failures. The disadvantages are that it may introduce variable latency, packet loss and jitter, which can affect the quality of service for some applications.

2. What are the functions of the data link layer and the network layer in the OSI model? Give an example of a protocol for each layer.

• The data link layer is responsible for providing reliable and error-free transmission of data frames between adjacent nodes in a network. It also handles framing, addressing, flow control and error detection and correction. An example of a protocol for this layer is Ethernet, which defines the format and structure of data frames, as well as the MAC address scheme for identifying nodes. The network layer is responsible for providing logical addressing and routing of packets across different networks. It also handles fragmentation, reassembly and congestion control. An example of a protocol for this layer is IP, which defines the format and structure of packets, as well as the IP address scheme for identifying networks and hosts.

3. What are the differences between TCP and UDP? Explain the features and applications of each protocol.

• TCP and UDP are two transport layer protocols that provide end-to-end communication between applications. TCP is a connection-oriented protocol that establishes a reliable and ordered delivery of data between two endpoints. It uses a three-way handshake to establish a connection, acknowledgments to confirm receipt of data, sequence numbers to reorder data segments, windowing to control the flow of data, and retransmission to recover from data loss. TCP is suitable for applications that require reliability and consistency, such as web browsing, email and file transfer. UDP is a connectionless protocol that provides an unreliable and unordered delivery of data between two endpoints. It does not use any mechanism to establish a connection, confirm receipt of data, reorder data segments, control the flow of data or recover from data loss. UDP is suitable for applications that require speed and efficiency, such as streaming media, online gaming and voice over IP.

4. What are the differences between unicast, multicast and broadcast communication? Give an example of each type.

• Unicast communication is a one-to-one communication between a sender and a receiver. The sender sends data to a specific destination address that identifies the receiver. An example of unicast communication is an email message sent from one user to another user. Multicast communication is a one-to-many communication between a sender and multiple receivers. The sender sends data to a group address that identifies a set of receivers that belong to the same group. An example of multicast communication is a video conference session where one user broadcasts their video stream to multiple users who join the same session. Broadcast communication is a one-to-all communication between a sender and all receivers in a network. The sender sends data to a special address that indicates all nodes in the network. An example of broadcast communication is an ARP request where one node queries the MAC address of another node by sending a message to all nodes in the network.

5. What are the differences between symmetric encryption and asymmetric encryption? Explain how each method works and give an example of an algorithm for each method.

• Symmetric encryption and asymmetric encryption are two methods of encrypting data to ensure confidentiality and integrity. Symmetric encryption uses the same key to encrypt and decrypt data between two parties. The key must be shared securely before communication can take place. Symmetric encryption is fast and efficient but vulnerable to key compromise or interception. An example of an algorithm for symmetric encryption is AES, which uses a fixed-length key to perform multiple rounds of substitution and permutation on blocks of data. Asymmetric encryption uses different keys to encrypt and decrypt data between two parties. The sender uses the public key of the receiver to encrypt data, while the receiver uses their private key to decrypt data. The public key can be distributed openly while the private key must be kept secret by its owner. Asymmetric encryption is secure but slow and complex due to mathematical operations involved. An example of an algorithm for asymmetric encryption is RSA, which uses large prime numbers to generate public and private keys and perform modular arithmetic on data. What is the difference between TCP and UDP protocols? Explain with an example of an application that uses each protocol.
  • TCP stands for Transmission Control Protocol, which is a reliable, connection-oriented and stream-based protocol that ensures the delivery of data in the same order as it was sent. TCP uses a three-way handshake to establish a connection, and uses acknowledgments and retransmissions to handle packet loss. An example of an application that uses TCP is HTTP, which is used for web browsing.
  • UDP stands for User Datagram Protocol, which is an unreliable, connectionless and datagram-based protocol that does not guarantee the delivery or order of data. UDP does not use any handshaking or acknowledgment mechanisms, and does not retransmit lost packets. An example of an application that uses UDP is DNS, which is used for domain name resolution.

What are the functions of the network layer and the data link layer in the OSI model? Give an example of a protocol or device that operates at each layer.

• The network layer is responsible for routing packets across different networks, and providing logical addressing and internetworking. An example of a protocol that operates at the network layer is IP, which defines the format and structure of packets and their addresses. An example of a device that operates at the network layer is a router, which forwards packets based on their destination addresses.
• The data link layer is responsible for transferring frames between adjacent nodes on the same network, and providing physical addressing and error detection. An example of a protocol that operates at the data link layer is Ethernet, which defines the format and structure of frames and their addresses. An example of a device that operates at the data link layer is a switch, which forwards frames based on their MAC addresses. What are the advantages and disadvantages of using circuit switching and packet switching techniques for data transmission? Give an example of a network that uses each technique.
• Circuit switching is a technique that establishes a dedicated physical path between two endpoints for the duration of a communication session, and allocates a fixed amount of bandwidth for each connection. An advantage of circuit switching is that it provides guaranteed quality of service and low latency, as there is no contention or congestion on the path. A disadvantage of circuit switching is that it wastes bandwidth when there is no data to transmit, as the path cannot be shared by other connections. An example of a network that uses circuit switching is the Public Switched Telephone Network (PSTN), which is used for voice calls.
• Packet switching is a technique that divides data into small units called packets, and sends them over a shared network without establishing a dedicated path. Each packet has a header that contains information such as source and destination addresses, sequence number and checksum. An advantage of packet switching is that it utilizes bandwidth efficiently, as multiple connections can share the same network resources. A disadvantage of packet switching is that it may cause variable delay, jitter and packet loss, as packets may take different routes and encounter congestion on the network. An example of a network that uses packet switching is the Internet, which is used for various applications such as email, web browsing and video streaming. What are the differences between unicast, multicast and broadcast communication modes? Explain with an example of an application or scenario that uses each mode.
• Unicast communication mode is when one sender transmits data to one receiver using a unique address. This mode provides point-to-point communication, and ensures privacy and reliability. An example of an application that uses unicast communication mode is FTP, which is used for file transfer between two hosts.
• Multicast communication mode is when one sender transmits data to multiple receivers using a group address. This mode provides one-to-many or many-to-many communication, and reduces bandwidth consumption by sending only one copy of data to multiple destinations. An example of an application that uses multicast communication mode is IPTV, which is used for streaming live TV channels to multiple subscribers.
• Broadcast communication mode is when one sender transmits data to all receivers on the same network using a special address. This mode provides one-to-all communication, and allows discovery and announcement services. An example of an application that uses broadcast communication mode is DHCP, which is used for dynamic IP address allocation to hosts on a network.

What are the benefits and challenges of using wireless networks compared to wired networks? Give an example of a wireless network standard or technology that addresses some of these challenges.

• Wireless networks are networks that use electromagnetic waves such as radio waves or infrared waves to transmit data without using physical cables or wires. Some benefits of using wireless networks are:
• Mobility: Wireless networks allow users to access network resources from anywhere within the coverage area, without being restricted by physical locations or boundaries.
• Scalability: Wireless networks can accommodate more users and devices easily, without requiring additional wiring or infrastructure.
• Cost: Wireless networks can reduce the cost of installation and maintenance, as they do not require expensive cables or equipment.
• Some challenges of using wireless networks are:
• Security: Wireless networks are more vulnerable to unauthorized access and attacks, as the signals can be intercepted or jammed by malicious users or devices.
• Interference: Wireless networks are susceptible to interference from other wireless devices or sources, such as microwave ovens or cordless phones, which can degrade the signal quality and performance.
• Reliability: Wireless networks are dependent on environmental factors such as weather, terrain or obstacles, which can affect the signal strength and availability.
• An example of a wireless network standard or technology that addresses some of these challenges is Wi- Fi, which is a family of standards that define the protocols and specifications for wireless local area networks (WLANs). Wi-Fi provides features such as encryption, authentication and channel selection to enhance the security, reliability and performance of wireless networks. What is the main difference between packet-switching and circuit switching in terms of resource allocation? Answer: Packet-switching is a technique that divides data into smaller units called packets and sends them over a shared network, where each packet may take a different route to reach its destination. Circuit switching is a technique that establishes a dedicated connection between two endpoints for the duration of the communication, where the resources are reserved exclusively for that connection. Rationale: This question tests the basic understanding of the two techniques and their implications for network efficiency and reliability. What are some advantages and disadvantages of packet-switching compared to circuit switching? Answer: Some advantages of packet-switching are:
• It can utilize the network resources more efficiently by allowing multiple packets to share the same link.
• It can adapt to changing network conditions by routing packets through different paths if some links are congested or broken.
• It can support different types of data with different quality of service requirements by using different

protocols and priorities. Some disadvantages of packet-switching are:

• It may introduce delays, jitter, and packet loss due to variable network conditions and queuing at intermediate nodes.
• It may require more overhead for packet headers, error detection, and retransmission.
• It may not guarantee a certain level of performance or reliability for real-time or sensitive applications. Rationale: This question tests the ability to compare and contrast the two techniques in terms of their benefits and drawbacks for different scenarios and applications. . What are some examples of networks that use packet-switching and circuit switching? Answer: Some examples of networks that use packet-switching are:
• The Internet, which is a global network of interconnected networks that use the Internet Protocol (IP) to exchange packets of data.
• Local area networks (LANs), which are networks that connect devices within a limited geographic area, such as a building or a campus, using protocols such as Ethernet or Wi-Fi.
• Cellular networks, which are networks that provide wireless communication services to mobile devices using protocols such as GSM or LTE. Some examples of networks that use circuit switching are:
• Public switched telephone network (PSTN), which is a network that provides voice communication services using analog or digital signals over dedicated circuits.
• Integrated services digital network (ISDN), which is a network that provides digital communication services over existing telephone lines using multiple channels for voice, data, and video.
• Optical transport network (OTN), which is a network that provides high-speed optical communication services over fiber-optic cables using wavelength division multiplexing (WDM). Rationale: This question tests the ability to apply the knowledge of the two techniques to real-world examples and recognize their characteristics and applications. What are some factors that affect the performance of packet-switched networks? Answer: Some factors that affect the performance of packet-switched networks are:
• Bandwidth, which is the amount of data that can be transmitted over a link per unit time, measured in bits per second (bps).
• Latency, which is the time it takes for a packet to travel from its source to its destination, measured in milliseconds (ms).
• Jitter, which is the variation in latency over time, measured in ms.
• Packet loss, which is the percentage of packets that are lost or discarded during transmission due to errors, congestion, or timeouts. Rationale: This question tests the ability to identify and explain the key metrics and factors that influence

the quality of service (QoS) and user experience (UX) of packet-switched networks. What are some techniques or protocols that can improve the performance of packet-switched networks? Answer: Some techniques or protocols that can improve the performance of packet-switched networks are:

• Routing algorithms, which are methods that determine the best path for each packet to reach its destination based on criteria such as distance, cost, load, or reliability.
• Congestion control algorithms, which are methods that regulate the rate or volume of packets entering the network to avoid overload and ensure fair allocation of resources.
• Error control algorithms, which are methods that detect and correct errors in packets using techniques such as checksums, acknowledgments, retransmission, or forward error correction (FEC).
• Quality of service (QoS) mechanisms, which are methods that prioritize or reserve resources for different types of packets based on their requirements such as delay, bandwidth, jitter, or loss. Rationale: This question tests the ability to recognize and describe some common solutions or standards that enhance the functionality and efficiency of packet-switched networks. What is the main difference between packet-switching and circuit switching in terms of security? Answer: Packet-switching is more vulnerable to security threats than circuit switching because packets can be intercepted, modified, or spoofed by malicious actors at any point along their route. Circuit switching is more secure than packet-switching because it establishes a direct and exclusive connection between the endpoints, which makes it harder for attackers to access or tamper with the data. Rationale: This question tests the basic understanding of the two techniques and their implications for network security and privacy. What are some security challenges or risks associated with packet-switching? Answer: Some security challenges or risks associated with packet-switching are:
• Eavesdropping, which is the unauthorized interception and reading of packets by third parties.
• Modification, which is the unauthorized alteration or deletion of packets by third parties.
• Spoofing, which is the impersonation of a legitimate sender or receiver by using forged packets or addresses.
• Replay, which is the retransmission of old or duplicate packets by third parties to cause confusion or damage.
• Denial of service (DoS), which is the intentional flooding of the network with excessive or malicious packets to disrupt its normal operation or availability.

Rationale: This question tests the ability to identify and explain some common types of attacks or threats that target packet-switched networks. What are some security solutions or protocols that can protect packet-switched networks? Answer: Some security solutions or protocols that can protect packet-switched networks are:

• Encryption, which is the process of transforming data into an unreadable form using a secret key, so that only authorized parties can decrypt and access it.
• Authentication, which is the process of verifying the identity and legitimacy of a sender or receiver using methods such as passwords, certificates, or tokens.
• Integrity, which is the process of ensuring that data has not been modified or corrupted during transmission using methods such as hashes, signatures, or message authentication codes (MACs).
• Non-repudiation, which is the process of proving that data has been sent or received by a specific party using methods such as timestamps, receipts, or digital signatures.
• Firewall, which is a device or software that filters and blocks unwanted or harmful packets from entering or leaving the network based on predefined rules or policies. Rationale: This question tests the ability to recognize and describe some common solutions or standards that enhance the security and trustworthiness of packet-switched networks. What are some advantages and disadvantages of circuit switching compared to packet switching? Answer: Some advantages of circuit switching are:
• It can provide a consistent and predictable level of performance and reliability for real-time or sensitive applications such as voice or video calls.
• It can reduce delays, jitter, and packet loss by avoiding variable network conditions and queuing at intermediate nodes.
• It can simplify error control by relying on the physical quality of the connection rather than on software mechanisms. Some disadvantages of circuit switching are:
• It can waste network resources by allocating them even when there is no data to transmit or when there is low demand.
• It can limit scalability and flexibility by requiring prior reservation and configuration of resources for each connection.
• It can increase costs and complexity by requiring dedicated hardware and infrastructure for each connection. Rationale: This question tests the ability to compare and contrast the two techniques in terms of their benefits and drawbacks for different scenarios and applications.

10. What are some factors that affect the performance of circuit-switched networks? Answer: Some factors that affect the performance of circuit-switched networks are:

• Bandwidth, which is the amount of data that can be transmitted over a connection per unit time, measured in bits per second (bps).
• Delay, which is the time it takes to establish, maintain, and terminate a connection, measured in seconds (s).
• Availability, which is the probability that a connection can be successfully established and maintained between two endpoints, measured in percentage (%).
• Quality, which is the degree of distortion or degradation of signals due to noise, interference, attenuation, or distortion. Rationale: This question tests the ability to identify and explain the key metrics and factors that influence the quality of service (QoS) and user experience (UX) of circuit-switched networks. What are the four layers of the TCP/IP model and what are their functions? Answer: The four layers of the TCP/IP model are:
• Application layer: This layer provides the interface between the user applications and the network. It defines protocols for data exchange, such as HTTP, FTP, SMTP, etc.
• Transport layer: This layer provides reliable and/or unreliable data delivery services between hosts. It defines protocols for end-to-end communication, such as TCP and UDP.
• Internet layer: This layer provides logical addressing and routing of packets across networks. It defines protocols for packet forwarding, such as IP, ICMP, ARP, etc.
• Network access layer: This layer provides physical access to the network media. It defines protocols for data transmission and reception, such as Ethernet, Wi-Fi, etc. What is the difference between TCP and UDP in terms of reliability, connection, and overhead? Answer: TCP is a reliable, connection-oriented, and stream-based transport protocol. It ensures that the data is delivered in order and without errors by using sequence numbers, acknowledgments, retransmissions, and flow control. TCP also establishes a connection between the sender and receiver before data transfer. However, TCP has more overhead than UDP due to its additional features. UDP is an unreliable, connectionless, and datagram-based transport protocol. It does not guarantee that the data is delivered in order or without errors. UDP also does not establish a connection between the sender and receiver before data transfer. However, UDP has less overhead than TCP due to its simplicity. What is the purpose of ICMP in the internet layer? Answer: ICMP stands for Internet Control Message Protocol. It is a protocol that is used to send error and control messages between hosts and routers in the internet layer. ICMP messages are encapsulated in IP datagrams and have a specific format that includes a type, a code, a checksum, and optional data fields. Some examples of ICMP messages are echo request/reply (used for ping), destination unreachable (used to indicate that a packet cannot be delivered), time exceeded (used to indicate that a packet has expired), etc.

What are the advantages and disadvantages of using NAT (Network Address Translation) in the network access layer? Answer: NAT stands for Network Address Translation. It is a technique that allows multiple devices to share a single public IP address when accessing the internet. NAT works by translating the private IP addresses of the devices to the public IP address of the router and vice versa. Some advantages of using NAT are:

• It conserves the limited IPv4 address space by reducing the number of public IP addresses needed.
• It enhances security by hiding the private IP addresses of the devices from external networks.
• It allows flexibility in changing the network topology or ISP without affecting the devices. Some disadvantages of using NAT are:
• It breaks the end-to-end principle of the internet by modifying the IP headers of the packets.
• It causes problems for some applications that rely on the original IP addresses or port numbers of the packets, such as peer-to-peer or VoIP applications.
• It increases the processing load on the router that performs NAT. What are some examples of application layer protocols and what are their functions? Answer: Some examples of application layer protocols are:
• HTTP (Hypertext Transfer Protocol): It is a protocol that defines how web browsers and web servers communicate over the internet. It uses a request-response model where the browser sends an HTTP request to the server and receives an HTTP response with the requested content or an error message.
• FTP (File Transfer Protocol): It is a protocol that defines how files are transferred between hosts over the internet. It uses two connections: a control connection for exchanging commands and responses, and a data connection for transferring files.
• SMTP (Simple Mail Transfer Protocol): It is a protocol that defines how email messages are sent from one host to another over the internet. It uses a client-server model where the client sends an SMTP request to the server with the email message and receives an SMTP response with an acknowledgment or an error message.