Networks - EdexcelHow the internet is structured

Network layering

In networking, layering means to break up the sending of messages into separate components and activities. Each component handles a different part of the communication. This can be referred to as a protocol stack. The Transmission Control Protocol/Internet Protocol (TCP/IP) is a protocol stack used when connecting a device to the internet.

How the 4-layer TCP/IP model handles data transmission over a network

There are four layers to be considered:

• Application layer - encodes/decodes the message into a form that is understood by the sender and the recipient devices using protocols like HTTP, file transfer protocol (FTP) and SMTP.
• Transport layer - breaks down the message into small pieces called packets. Each packet is given a packet number and the total number of packets. The recipient uses this information to assemble the packets in the correct order. It also allows the recipient to see if there are any missing packets.
• Internet layer - adds the sender’s IP address and that of the recipient. The network then knows where to send the message, and where it came from. This is sometimes called the network layer.
• Link layer - enables the physical transfer of packets between nodes on a network, and between one network and another.

Layering enables standards to be developed, but also to be adapted to new hardware and software over time. For example, different software packages (applications) may use the same transport, internet and link layers but may each use their own application layer. The way the program encodes the message changes - the rest of the communication method remains the same.