OCR A-level Computer Science: Networking, Protocols, and Security

A-Level Computer Science: Networking, Protocols, and Security

1. Network Fundamentals

a. Introduction:

• Networks allow computers to communicate and share resources.
• A network is a collection of interconnected devices, including computers, servers, printers, etc.

b. Types of Networks:

• Local Area Network (LAN): Covers a small geographical area, like a home or office.
• Wide Area Network (WAN): Connects geographically dispersed locations, often using public networks like the internet.

c. Network Topologies:

• Bus Topology: All devices are connected to a single shared cable.
• Star Topology: Devices connect to a central hub or switch.
• Ring Topology: Devices connect in a closed loop, with data flowing in one direction.

d. Network Devices:

• Routers: Direct traffic between networks, selecting the best path for data.
• Switches: Connect devices within a network, forwarding data only to the intended recipient.
• Modems: Convert digital signals to analog signals (and vice-versa) for transmission over telephone lines.

2. The TCP/IP Model

a. Introduction:

• The Transmission Control Protocol/Internet Protocol (TCP/IP) is a suite of protocols that define how data is transmitted over the internet.
• It's a layered model, with each layer responsible for a specific function.

b. Layers of the TCP/IP Model:

1. Application Layer: This layer deals with user applications and provides services like email, file transfer, and web browsing. Examples: HTTP, FTP, SMTP. 2. Transport Layer: Ensures reliable delivery of data between applications, managing connections and error handling. Examples: TCP, UDP. 3. Network Layer: Responsible for routing data across the network, choosing the best path. Example: IP. 4. Data Link Layer: Deals with physical transmission of data on the network, handling error detection and correction. 5. Physical Layer: Defines the physical characteristics of the network, including cables, connectors, and signal types.

c. Packet Switching:

• Data is broken down into small units called packets.
• Each packet is independently routed and may take different paths.
• At the destination, packets are reassembled into the original data.

3. Network Security

a. Threats:

• Malicious Software (Malware): Viruses, worms, trojans, etc.
• Denial of Service (DoS) Attacks: Overloading a network to prevent legitimate users from accessing resources.
• Unauthorized Access: Gaining access to sensitive data without permission.

b. Security Measures:

• Firewalls: Act as a barrier between a network and the external world, blocking unauthorized access.
• Encryption: Transforms data into an unreadable format, making it secure during transmission.
• Antivirus Software: Detects and removes malicious software.
• Intrusion Detection Systems (IDS): Monitor network traffic for suspicious activity.

c. DNS and Security:

• Domain Name System (DNS): Converts domain names (like "google.com") into IP addresses.
• Security is essential to prevent attackers from redirecting traffic to malicious websites.

d. Protocols and Security:

• Secure Sockets Layer (SSL) and Transport Layer Security (TLS) are protocols that provide encryption for communication over the internet.
• Secure Shell (SSH): A secure protocol for remote access to servers.
• Virtual Private Networks (VPNs): Create an encrypted tunnel over a public network, providing secure communication.

4. Conclusion

Understanding networking principles, protocols, and security measures is crucial for anyone working with computers and the internet. By implementing appropriate security measures, we can protect our data and ensure smooth, secure communication.