University of Michigan - Ann Arbor

Networking is broken down into distinct layers to manage complexity. In a layered model, each layer handles a specific task and relies on the layer immediately below it. This separation of concerns allows individual layers to be designed, updated, and changed independently without disrupting the rest of the system.

The classic educational framework is the Open Systems Interconnection (OSI) model, which organizes network communication into seven layers ranging from physical hardware signals to end-user software:

* **Layer 1 (Physical):** Handles the physical transmission medium, such as actual cables, radio waves, and electrical voltages.
* **Layer 2 (Data Link):** Moves data between two directly connected devices on a local segment using MAC addresses.
* **Layer 3 (Network):** Moves packets across multiple interconnected networks using logical IP addresses.
* **Layer 4 (Transport):** Manages end-to-end delivery of data between software programs using protocols such as TCP and UDP.
* **Layer 5 (Session):** Manages and coordinates ongoing conversations between applications.
* **Layer 6 (Presentation):** Formats and encrypts data to ensure it is usable across systems.
* **Layer 7 (Application):** Encompasses the software interfaces that users directly interact with, such as web browsers and email clients.

Layered Architecture and the OSI Model

Match each OSI model layer to its correct responsibility.

In a layered networking model, each layer handles a specific task and relies on the layer immediately ___ it.

Order these OSI model layers from the lowest layer (Layer 1) to the highest layer (Layer 5).

Identify the two specific OSI model layers responsible for resolving these issues: one for data formatting and encryption, and one for moving packets across interconnected networks using IP addresses.

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