Network Layers (Edexcel GCSE Computer Science)

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Networks rely on many complex parts all working together at the same time, from different types of network, the different operating models, the internet, wired and wireless to encryption, addressing and protocols
Managing the complexity of networks is helped with the use of layers

A layer is a sub part of a more complex task
Dividing network tasks into layers reduces the complexity and makes each layer more manageable
An example of layers can be seen in the TCP/IP protocol which uses a 4-layer model known as a 'stack'

Layers are self-contained which makes managing, repairing and upgrading easier as each layer can be worked on independent of other layers
Layers allow for focus on specific parts of a protocol without affecting other layers
Promotes data exchange (interoperability) between hardware and software

The TCP/IP model is made up of two protocols (TCP & IP), containing 4 layers, that work together to package, address, transmit and receive data on a wide area network (Internet)
There are four layers that make up the TCP/IP protocol stack:
- Application
- Transport
- Internet
- Link
Different protocols operate on different layers
Data is split up into packets for transmission across the internet
A packet consists of:

Header	Payload	Footer
Sender & receiver IP address	Actual data being transported	Additional security information (less common)
Packet length
Sequence number (1 of 5 etc.)
Error checking (checksums)

Data passes down through layers of the stack when it is being sent and up through the layers when it is received

Layer	Function	Protocols
Application	Application software such as web browsers and email clients operate here	HTTP, HTTPS, FTP, SMTP, POP3, IMAP
Transport	Enables communication between two hosts to agree settings such as size of packets. Splits data in to packets	TCP/IP
Internet	Addresses and packages data for transmission. Routes the packets across the network
Link	Physical network hardware such as NIC is located, OS device drivers also sit here	Ethernet/Wi-Fi

The transport layer of network protocols splits data into packets before sending it. All the packets are received correctly.

Describe the process that ensures the data received matches the original [2]

Answer

to absolutely everything:

the (exam) results speak for themselves:

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