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$1.$ What are the five layers in the Internet protocol stack $?$ What are the principal responsibilities of each of these layers? $(15$ points$).$

ANS $-$ The Internet protocol stack, also known as the TCP$/$IP $($Transmission Control Protocol$/$Internet Protocol$)$ model, consists of five primary layers. Each layer has specific responsibilities and functionalities that contribute to the overall communication and operation of the Internet. The five layers of the Internet protocol stack are:

Physical Layer: The physical layer is responsible for the physical aspects of data transmission, such as the electrical, mechanical, and functional specifications for the physical connection between devices. This layer defines the physical characteristics of the network, including the physical medium $($e$.$g$.,$ cables, wireless signals$),$ signal transmission, and bit$-$level representation.

Data Link Layer: The data link layer is responsible for the reliable and error$-$free transfer of data between directly connected devices. This layer focuses on the framing of data, addressing, and error detection and correction mechanisms. It ensures that the data is delivered without errors or loss, even in the presence of physical layer errors.

Network Layer: The network layer is responsible for logical addressing and routing of data between different networks. This layer determines the path that data should take to reach its destination, using protocols such as the Internet Protocol $($IP$)$ to identify and route packets across network boundaries. The network layer also handles congestion control and quality of service $($QoS$)$ considerations.

Transport Layer: The transport layer is responsible for end$-$to$-$end communication and reliable data transfer between applications. It provides mechanisms for segmentation, flow control, error correction, and sequencing of data. The most well$-$known transport layer protocols are the Transmission Control Protocol $($TCP$)$ and the User Datagram Protocol $($UDP$).$

Application Layer: The application layer is the topmost layer of the Internet protocol stack and is where network applications and services reside. This layer defines the protocols and interfaces that enable specific application$-$level functionalities, such as web browsing, email, file transfer, and streaming media. The application layer provides the user interface and interacts with the underlying layers to facilitate the desired network services.

Each of these layers plays a crucial role in the overall functionality of the Internet, with the lower layers $($physical$,$ data link, and network$)$ focusing on the fundamental aspects of data transmission and the higher layers $($transport and application$)$ providing the necessary services and interfaces for end$-$user applications to communicate effectively over the network.

$2.$ For each of the five layers, what is the name of the packets processed at the layer? $(15$ points$)$

ANS $-$ At the Physical Layer, the data is transmitted as raw bit streams, often referred to as bits or signals, rather than packets.

At the Data Link Layer, the packets are known as frames, which encapsulate the raw data with necessary headers and footers for node$-$to$-$node communication.

At the Network Layer, the packets are referred to as datagrams or packets, with IP $($Internet Protocol$)$ packets being the most common type, containing source and destination IP addresses for routing.

At the Transport Layer, the packets are called segments in the case of TCP $($Transmission Control Protocol$)$ or data grams when using UDP $($User Datagram Protocol$),$ and they include port numbers for process$-$to$-$process communication.

At the Application Layer, the data units do not have a specific name as packets; they are often referred to simply as messages or data, which are specific to each application protocol, such as HTTP requests or responses for web traffic.

$3.$ List two advantages and disadvantages of the layer approach. $(15$ points$)$

ANS $-$ The layered approach in networking organizes the vast range of communication tasks into manageable layers, each responsible for specific functions and services.

Advantages:

Modularity $-$ Facilitates updates and maintenance by allowing changes in one layer without impacting others.

Interoperability $-$ Enables different technologies and systems to work together through standard interfaces.

Disadvantages:

Overhead $-$ Each layer can add its own header to the data packet, increasing the total size and potentially reducing efficiency.

Complexity $-$ Troubleshooting can become more difficult as issues may involve several interdependent layers.

$4.$ What advantage does a circuit$-$switched network have over a packet$-$ switched network? $(15$ points$)$

ANS $-$ A circuit$-$switched network is designed to establish a dedicated communication channel between two endpoints for the duration of a connection. The primary advantage of this approach over a packet$-$switched network, where dat