Guide on OSI Model

The Open Systems Interconnection model, or simply the OSI Model, is a conceptual model used to understand and describe how different network protocols interact and work together to provide network services.

Importance:
Understanding the OSI Model is crucial because it helps to troubleshoot network problems and design robust networks by aligning them with these standardized layers. It promotes interoperability by providing a standard framework for implementing network protocols.

How it Works:
The OSI model is divided into seven different layers, with each layer performing a specific network function:
• Layer 1: Physical Layer - transmission and reception of raw bit streams over a physical medium
• Layer 2: Data Link Layer - reliable transmission of data frames between two nodes connected by a physical layer
• Layer 3: Network Layer - structuring and managing a multi-node network, including addressing, routing and traffic control
• Layer 4: Transport Layer - reliable transmission of data segments between points on a network, including segmentation, acknowledgement and error recovery
• Layer 5: Session Layer - managing communication sessions
• Layer 6: Presentation Layer - translation of data between a networking service and an application; including encryption, compression, and translation services
• Layer 7: Application Layer - provides an interface for applications to access network services

Exam Tips: Answering Questions on OSI Model
1. Remember 'All People Seem To Need Data Processing' as a way to remember the layers in the correct order.
2. Understand the function of each layer thoroughly -- you may get questions focusing on the responsibilities of each layer.
3. Be prepared to identify which layer a certain activity or protocol belongs to, so have an idea of commonly used protocols for each layer.
4. There may be scenario-based questions. Based on the scenario, you may need to point out which layer is at fault. Practicing real world troubleshooting scenarios can help.

Remember, understanding the OSI model isn't just about memorization - it's about comprehension and application in network troubleshooting and design.