3.6: 7-Layer OSI Model
Eduqas / WJEC
What are networking standards?
Networking standards are rules that allow computer systems to communicate across networks. Standards have been created to ensure devices can exchange data and work together.
What is the 7-layer OSI Model?
The OSI (Open Systems Interconnection) model is split into 7 layers. The model is used to visualise the different parts of a network as each of the seven layers has a specific role.
Splitting a network design into layers is beneficial to programmers as it simplifies design, making it easier to modify and use.
Each layer has a certain purpose and is associated with different protocols.
The seven layers are explained below:
Allows humans and software applications to use the network e.g. browsers (HTTP/HTTPS) and email (SMTP) and file transfer (FTP).
The purpose of the presentation layer is to display data in a standard format that other devices can accept and understand.
The session layer establishes a connection between computers allowing data to be sent between them. Data can be synchronised in each session to allow for efficient data transfer.
TCP breaks the data down into data packets. This layer makes sure the data is sent and received in the correct order and reassembled at the destination without errors.
IP is responsible for addressing and routing data packets. The optimal route for the data to take is calculated in this layer.
Also known as the 'Internet Layer'.
Ethernet sets out the format of data packets. This layer handles transmission errors and passes data to the physical layer.
This layer converts the data packets into bits so they can be transferred across a physical connection using routers and switches.
3.6 - 7-Layer OSI Model:
1a. What are networking standards? 
1b. Describe why network designs are split into layers. 
2. Create a diagram similar to the one above and describe each layer of the OSI Model. 
3. Look at the statements below and name the layer that is being described:
a. This layer ensures data packets are sent and received correctly.
b. This layer checks for errors in transmission and sets out the data packet format.
c. This layer displays data in a format that can be understood.
d. This layer allows software like web browsers to interact with the network.
e. This layer transfers bits across a connection using routers.
f. This layer establishes a connection between computer systems.
g. This layer uses addresses to ensure data packets take the correct route.