Layers

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Layering Concepts

Protocol layer models are often used to help conceptualise the many different network protocols.

Protocol layer models

In a protocol layer model, a protocol layer is simply a group or collection of network protocols that work at a similar level within the networking process.

Layer properties

Layers of a protocol layer model should be independent of each other.
Layers should only interact with each other by considering the inputs and outputs of that layer, not how it works.

Layers everywhere

Layers are not only used within networking.
Layers are one example of a technique called abstraction, which helps to simplify problems.
Layers are commonly used in software development. For example:
- A user interface layer.
- A processing layer.
- A database layer.

TCP and OSI Models

The four-layer Transmission Control Protocol model and the seven-layer Open Systems Interconnection model are two of the best known protocol layer models.

TCP model

Application layer:
- Creates and interprets data (e.g. HTTP, IMAP, FTP).
Transport layer:
- Splitting / joining of data (e.g. TCP).
Internet layer:
- Adding addresses to data (e.g. IP).
Network Access layer:
- Converting data into electrical signal (hardware) (e.g. Ethernet, WiFi).

OSI model

The OSI model is a very similar protocol layer model.
The OSI model has seven layers:
- Application.
- Presentation.
- Session.
- Transport.
- Network.
- Data Link.
- Physical.

Comparing the two models

The two models describe the exact same network system:
- The first three layers of the OSI model are grouped into TCP's 'Application' layer.
- The 'Transport' layers are the same in both models.
- OSI's 'Network' layer is called 'Internet' in the TCP model.
- OSI's bottom two layers are combined into TCP's 'Network Access' layer.

Advantages of Layering

Each layer is self-contained but is able to send and receive data to/from the layers above and below it.

Specialists

Software developers and engineers can be employed to work within one specific layer.
This allows people to specialise in one area.

Layer independence

As long as the inputs and outputs of the layer remain consistent, then the layer can be changed without affecting the other layers.
This allows layers to be improved for efficiency without affecting other parts of the system.

Debugging

Network engineers can diagnose and fix issues within individual layers when problems happen.

Application development

Application developers can create networked applications without knowing the details of how a network physically works.

1Components of a Computer

1.1Structure & Function of the Processor

1.1.1Structure of the CPU

1.1.2Fetch, Decode, Execute Cycle

1.1.3Factors Affecting CPU Performance

1.1.4CPU Architecture

1.2Types of Processors

1.2.1CISC & RISC

1.2.2Multicore & Parallel Cores

1.3Input, Output & Storage

1.3.1Computer Systems

1.3.2Magnetic Storage

1.3.3Optical Storage

1.3.4Types of Optical Storage

1.3.5Types of Memory

1.3.6Flash Memory

1.3.7Virtual Memory

2Software & Software Development

3Exchanging Data

4Data Types, Data Structures & Algorithms

4.1Data Types

4.1.1Data Types

4.1.2Arrays & Strings

4.1.3Representing Numbers

4.1.4Binary Arithmetic

4.1.5Hexadecimal

4.1.6Converting Binary Numbers

4.1.7Floating Points in Binary

4.1.8Floating Point Arithmetic

4.1.9Bitwise Manipulation

4.1.10Character Sets

4.2Data Structures

4.2.1Arrays, Linked Lists & Queues

4.2.2Graphs, Hash Tables & Stacks

4.2.3Trees

4.3Boolean Algebra

4.3.1Computational Logic

4.3.2Boolean Logic

4.3.3Karnaugh Maps

4.3.4Boolean Identities

4.3.5Flip Flops & Adder Circuits

5Legal, Moral, Cultural & Ethical Issues

5.1Computing Related Legislation

5.1.1Data Protection Act (1998)

5.1.2Computer Misuse Act (1990)

5.1.3Copyright Designs and Patents Act (1988)

5.1.4Regulation of Investigatory Powers Act (2000)

5.2Moral & Ethical Issues

5.2.1Online Activity Tracking

5.2.2Censorship

5.2.3Cultural Issues

5.2.4Environmental Issues

5.2.5Layout, Colour Paradigms & Character Sets

6Elements of Computational Thinking

6.1Thinking Abstractly

6.1.1Abstraction

6.2Thinking Procedurally

6.2.1Decomposition

6.3Thinking Logically

6.3.1Pseudocode & Flow Diagrams

7Problem Solving & Programming

7.1Programming Techniques

7.1.1Programming Fundamentals

7.1.2Modularity

7.2Programming Construction

7.2.1Integrated Development Environments

7.2.2Testing

8Algorithms

8.1Algorithms

8.1.1Interpreting, Correcting & Completing Algorithm

8.1.2Sort Algorithms

8.1.3Insertion & Merge Sort

8.1.4Search Algorithms

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