Network Layers (Edexcel GCSE Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
The Concept of Layers
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
What is a layer?
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'
What are the advantages of layers?
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
TCP/IP Model
What is the TCP/IP model?
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 |
Packet length | ||
Sequence number | ||
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 |
Worked Example
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
Each packet has a sequence number (added at the sending end) [1]
The packets are put back into (sequence) order (at the destination) [1]
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