Networks Study Guide

The TCP/IP model organises network communication into four distinct layers: application, transport, internet, and link. When data is sent, it starts at the application layer, where user-facing applications like web browsers or email clients generate the data. This data is then passed down to the transport layer, which is responsible for establishing a connection (TCP) or sending connectionless datagrams (UDP), segmenting the data into smaller packets, and ensuring reliable data transfer, including retransmission of lost packets. The internet layer then handles logical addressing (IP addresses) and routing of these packets across different networks. Finally, the link layer prepares the data for physical transmission over the network medium, such as Ethernet or Wi-Fi, dealing with hardware addresses (MAC addresses) and physical access to the network. As data moves down the layers, each layer adds its own header information (encapsulation). When data is received, the process reverses; each layer strips off its corresponding header as the data moves up the stack (decapsulation), until the original data is reassembled at the application layer for the receiving application.

The Internet is a vast global network of interconnected computer networks. Its structure relies fundamentally on two key components: IP addressing and routers. IP addresses uniquely identify every device connected to the Internet, much like a postal address identifies a building. These addresses allow data packets to be sent to and received from specific destinations. When a device sends data, it's broken down into small packets, each containing the destination IP address. Routers are specialised networking devices that act like traffic controllers. Their primary role is to examine the destination IP address of incoming data packets and determine the most efficient path for these packets to reach their target. They do this by maintaining routing tables, which are databases of known network routes. Routers then forward the packets along these determined paths, hop by hop, until they arrive at the intended recipient. This hierarchical and distributed architecture, combining unique addresses and intelligent forwarding devices, enables seamless communication across the entire global Internet.