\subsection*{Practice Week 3: Introduction to the OSI Model Layers}

\begin{objetivopractica}
The student will examine network communication through Wireshark to identify different protocol layers and understand how the OSI model organizes network functions. This practice will demonstrate how data gets processed through multiple layers during transmission and reception between network devices.
\end{objetivopractica}

The practice begins with the student opening Wireshark and starting packet capture on their active network interface. They generate network traffic by visiting a simple website, creating observable communication that can be analyzed according to OSI model principles.

\definicion{OSI model}{A seven-layer reference model that standardizes how network communication functions are organized}

The student examines captured packets in Wireshark and selects one HTTP packet for detailed analysis. By clicking on the packet in the list, they access the detailed packet information that shows how data is organized in layers, each with specific functions.

% \includegraphics[width=\textwidth]{figuras/captura03_packet_layers.png}

In the packet details panel, the student identifies the physical layer characteristics by examining the frame information. Although the actual electrical signals are not visible, Wireshark shows frame timing and size information that represents the physical transmission properties.

\definicion{physical layer}{The OSI layer responsible for transmitting raw electrical signals over physical media}

The student locates the data link layer information by examining the Ethernet frame headers. This section shows \sigla{MAC}{Media Access Control} addresses that identify the network interfaces involved in local communication. The student observes source and destination MAC addresses.

\definicion{MAC address}{A unique hardware identifier assigned to each network interface controller}

The network layer analysis involves examining the \sigla{IP}{Internet Protocol} header information. The student identifies source and destination IP addresses that enable communication across different networks. This layer provides logical addressing that works across various physical networks.

% \href{https://www.youtube.com/watch?v=XXXXXXX}{OSI layers in Wireshark analysis}

\definicion{IP address}{A logical address that identifies devices on networks and enables routing across the internet}

For the transport layer, the student examines \sigla{TCP}{Transmission Control Protocol} header information in the packet details. They observe port numbers that identify specific applications or services on the communicating devices. Common ports include 80 for web traffic and 443 for secure web communication.

\definicion{port number}{A numerical identifier that specifies which application or service handles network communication}

The session layer functionality is less visible in individual packets but the student can observe session establishment through TCP connection setup. They examine how multiple packets work together to establish, maintain, and terminate communication sessions between applications.

% \includegraphics[width=\textwidth]{figuras/captura03_tcp_session.png}

The presentation layer involves data formatting and encryption. The student examines HTTPS traffic to observe how encryption transforms readable data into protected formats. They notice that encrypted packets contain unreadable content, demonstrating presentation layer security functions.

\definicion{encryption}{The process of converting data into a coded format to protect it from unauthorized access}

At the application layer, the student analyzes protocols such as HTTP, FTP, and SMTP that directly serve user applications. The examination shows how these protocols implement specific communication rules and data formats that applications understand and process.

The practice includes comparing encrypted and unencrypted traffic to understand presentation layer functions. The student observes how HTTPS traffic appears scrambled while HTTP traffic shows readable content, demonstrating how encryption protects data during transmission.

The student documents their observations by creating a simple table that matches each OSI layer with examples found in their packet captures. This documentation reinforces the relationship between theoretical models and practical network operation.

The practice concludes with the student reflecting on how the OSI model helps organize complex network operations into manageable functional categories. They understand that real networks implement these functions even when they don't explicitly follow the seven-layer structure.

\begin{rubrica}
The student must submit a report containing clear evidence of completing the practice. The document should include screenshots, explanations of observations, and reflection on the learning achieved. The submission must demonstrate that the student understood the concept and was able to apply it with the indicated software.
\end{rubrica}

\subsection*{Suggested Report Format}

\textbf{Title:} Practice Week 3 - Introduction to the OSI Model Layers \\
\textbf{Objective:} Written by the student according to what they understood. \\
\textbf{Development:} Clear narration of actions performed. \\
\textbf{Evidence:} Screenshots or other data obtained. \\
\textbf{Conclusions:} Technical reflection on what was learned. \\
\textbf{Personal Opinion:} Student's free opinion about the usefulness or difficulty of the practice.