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 the Transmission Control Protocol/Internet Protocol (TCP/IP) model.

There are four layers to be considered:

  • Application layer - encodes/decodes the message in a form that is understood by the sender and the recipient.
  • Transport layer - breaks down the message into small chunks (packets). Each packet is given a packet number and the total number of packets. The recipient uses this information to assemble the packets together in the correct order. It also allows the recipient to see if there are any missing packets.
  • Network 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.
  • Data link layer - enables the transfer of packets between nodes on a network, and between one network and another.

Layering allows 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, network and link layers but have their own application layer. The way the program encodes the message changes - the rest of communication method remains the same.

Layering allows standards to be put in place and simply adapted as new hardware and software is developed.

Similarly, the move from IPv4 addressing to IPv6 affects only the network layer - the other layers remain unaffected. This allows improvements to be made without having to redefine whole communication methods.