Wired & Wireless Networks, Protocols & Layers (OCR GCSE Computer Science): Revision Notes

The Concept of Layers

The Concept of Layers in Network Protocols

Layers are groups of protocols that handle different parts of the communication process in a network. Each layer has its own specific function, but all layers work together to ensure data is transmitted correctly between devices. Layers simplify the complex process of communication by breaking it into smaller, manageable tasks.

How Layers Are Used in Protocols

• Layers are self-contained, meaning each one performs its task independently of the others. This separation makes it easier to troubleshoot, update, or modify one layer without affecting the rest.
• Data is passed between adjacent layers. For example, data from Layer 2 can be sent to Layer 1 or Layer 3, but Layer 1 can only communicate directly with Layer 2.
• Layers allow different protocols to work together within a structured framework, ensuring smooth communication between devices.

Layer Name	Protocols in Layer	Examples
1. Data Link	Physical hardware that connects two hosts such as the NIC and cabling	Ethernet
2. Network	Making connections and controlling the packet switching, directing the data packets	IP
3. Transport	Controls the data flow and splits data into packets	TCP
4. Application	Selects the correct protocol depending on the application. E.g., sending an email or viewing a website	HTTP, FTP, SMTP

Benefits of Using Layers

• Modularity: Each layer can be updated or improved independently without affecting other layers, making it easier to maintain and upgrade systems.
• Interoperability: Standards within each layer ensure that hardware and software from different manufacturers can work together. For example, devices using different brands of hardware can still communicate if they follow the same protocol at each layer.
• Simplification: Breaking down network communication into layers makes it easier to understand, design, and manage. Each layer has a specific task, reducing complexity.

• Troubleshooting: Problems can be isolated to a specific layer, making it easier to find and fix issues in network communication.

The 4-Layer TCP/IP Model

The TCP/IP model is an example of how layers are used in network communication. It has four main layers that each perform a different role:

1. Application Layer: Deals with the protocols that depend on the application being used, such as HTTP for websites or SMTP for sending emails.
2. Transport Layer: Manages the splitting of data into packets and ensures reliable delivery. TCP (Transmission Control Protocol) works here.
3. Network Layer: Handles how data is routed between devices across different networks, using protocols like IP.
4. Data Link Layer: Controls the physical hardware, such as network cables and the network interface card (NIC), that connects devices.