Communication Layers
In this module 1, you learned about a foundational organizing principle in networking: layers of communication. The OSI model and the TCP/IP model are both commonly used to guide network design, maintenance, and troubleshooting tasks.
This text gave the analogy of a letter being mailed via the post office to illustrate the nature of each layer in the OSI model. Many other analogies can be used to further describe how communications layers function in a system. What examples can you think of? Consider in what ways you notice one person, company, or other entity communicate with another person, company, or other entity indirectly through multiple layers. Then answer the following question:
o What is a real-life example of how layers in a system indirectly connect two entities (such as a person or company) in communication?
A real-life example of how layers in a system indirectly connect two entities in communication can be seen in the process of sending an email. The layers involved can be illustrated as follows:
Application Layer: This layer represents the email client software, such as Microsoft Outlook or Gmail. It allows the user to compose, format, and send the email.
Presentation Layer: In this layer, the email content is encoded into a standardized format, such as Multipurpose Internet Mail Extensions (MIME). This ensures that the email can be properly interpreted by the recipient’s email client.
Session Layer: The session layer establishes and manages the communication session between the sender and the recipient. It handles tasks like authentication and encryption to ensure secure communication.
Transport Layer: This layer is responsible for breaking down the email into smaller packets and ensuring their reliable delivery. It uses protocols like TCP (Transmission Control Protocol) to establish a connection and guarantee that all packets are received in the correct order.
Network Layer: Here, the email packets are transmitted across different networks. The network layer assigns IP addresses to each packet and determines the best route for delivery using protocols like IP (Internet Protocol).
Data Link Layer: This layer handles the physical transmission of data over a network link. It encapsulates the email packets into frames and includes information like MAC addresses to identify the source and destination devices.
Physical Layer: Finally, the physical layer represents the actual physical medium through which the email packets are transmitted, such as Ethernet cables or wireless signals.
In this example, when a person sends an email to another person, the message goes through each layer of the system. The sender’s application layer formats and initiates the email, which is then encoded in the presentation layer, authenticated and encrypted in the session layer, divided into packets in the transport layer, assigned IP addresses in the network layer, encapsulated into frames in the data link layer, and physically transmitted through various physical media in the physical layer.
On the recipient’s end, each layer performs the reverse process, ensuring that the email is delivered correctly to their email client software. Through this layered communication system, two entities are indirectly connected in communication, allowing for seamless and reliable email communication.