01

Internet

This network is the most widely known. It provides users with access to many services like online shopping, video and audio streaming and much more. It works worldwide through different kind of media.

Bluetooth

Bluetooth is a short range computer network for interconnecting peripheral devices to some master node. Today it is often used to connect wearables, small sensors, headphones, and cars to your mobile phone.

LTE

Long-Term Evolution (LTE) is a standard for computer networks interconnecting mobile phones. It will be replaced by 5G in the future.

CAN

The Controller Area Network is a robust network for interconnecting controllers in machines and cars. LoRaWAN

The Long Range Wide Area Network is a long range, low power network interconnecting small sensor nodes deployed in the countryside. It is very slow but covers a large area with just one base station

• transmission of single bytes through some medium

• modulation of the physical medium

• A/D conversion • error detection

• error correction

• combining bytes into blocks or frames to form messages

• creating a virtual view on the physical interconnection

• addressing of participants

• path finding from one participant to another (routing)

• encryption/ decryption

A model is an abstract description of reality. It describes important entities and their interaction with themselves and the environment. According to the goal, information about reality is reduced, combined, or disassembled. In some cases a model just consists out of mathematical formulas.

The problem is, that developers of computer networks will use different model structures. These models are then not comparable or partly interchangeable.

A reference model is a model to create other models. It is the base of these models and is linked to a certain context. Reference models can be seen as design patterns for models.

The ISO/ OSI model (Open System Interconnection model)

Physical Layer

Data-Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

The physical layer is responsible for handling the raw communication of bits through a medium. At this stage there is no full interpretation of the bits available. Some bits are interpreted as control words to identify the link status between one or more participants. The physical layer also describes which physical medium, the kind of modulation, and the encoding of the data.

The Data-Link Layer watches the communication through the physical layer and gives the transferred bits a meaning by combining them into frames a very early type of message. Using these frames the data-link layer implements protocols to detect or even correct data after transmission through the physical layer. It can also prevent overloading of the physical channel by flow control.

Nodes or participants of computer networks can be interconnected in many ways. Often participants are not directly linked and messages have to travel through intermediate nodes to reach their destination. To present a consistent view on this physical interconnection scheme, called virtual or logical view, the network layer abstracts from it, provides an addresses scheme and routing algorithms to find paths within the network. If the size of the transferred data like files and video streams exceed the maximum message the network layer splits this data into multiple messages.

Depending on the used physical network interconnection messages of the network layer may travel on different path to its destination. But messages may also been lost during travel or could be duplicated. To mitigate these problems the transport layer provides services to ensure the correct ordering of the messages and error handling for missing or damaged messages. It can also provide a service without any of this, but this service is than marked as unreliable.

The session layer is responsible for session management. A session combines task belonging together, for example started by an authentication task and finished by a logout task. The session layers service also provides tasks to pause and resume a session.

The participants of a network are often using different hardware like Central Processing Units (CPUs). These CPUs sometimes have different data en coding in memory, called endianess. One task of the presentation layer is the conversion between a network endianess and the individual endianesses of the nodes. But it could also be used for decryption and encryption or language translation.

The application layer provides services to applications run by users. These services are unique to each application like web-browsers and web-servers. Therefore, every application can specify its own application layer for communication

A service within the ISO/ OSI model defines the calling interface between two layers. This interface is used by two neighboring layers to pass information between them.

An example service between two layers is given by two C functions:

• int recv(int fd, int *src, char *buffer, int maxlength); • int send(int fd, int dst, char *buffer, int length)

A protocol is an operation sequence of messages or frames transmitted according to rules between network participants. They use the available service description of their lower or upper layer to pass information.

Two simple example protocols:

The use of a reference model for computer networks has many advantages like:

• Structure/ Functions very similar when designing computer network devices

• Standardization of subcomponents compatibility

• interchangeability of components, layers, protocols

• Hardware/Software Co-design

• easy maintainability

• upgradeability

The TCP/IP Reference Model has been developed during the early days of the Internet.

The top three layers of the ISO/ OSI model are merged into one layer. The transport layer is named host-to-host layer and the network layer is called Internet because of its specific focus. The bottom two layers are again merged into one.

But the functions the layers have to perform are the same. The TCP/IP model is a more practical approach.

ISO 27032:

The Cyberspace can be described as a virtual environment, which does not exist in any physical form, but rather, a complex environment or space resulting from the emergence of the Internet, plus the people, organizations, and activities on all sort of technology devices and networks that are connected to it.

Better definition for class:

Cyberspace is a mixed virtual and physical domain build on top of IT-Systems and the Internet. Within the Cyberspace participants conduct activities. These activities may influence the physical world directly or indirectly and may be performed in the three layers ClearNet, DeepNet, and DarkNet.

Information Technology (IT) is the use of electronic devices to process any kind of electronic information or data. The processing includes creating, changing, storing, transmitting, receiving, and deleting of data.

An Information Technology System (IT-System) is a dynamic technical system with the ability to process and store data. In this context dynamic means, that the internal state of the system changes over time according to computations and external inputs. A static system can not process any data and, therefore, can not be an IT-System. IT-Systems can be built up out of smaller IT-Systems.

A very simple IT-System:

A basic IT-System consits out of hardware providing the computing power, the data storage, and the input and output capacity of the system.

The next layer of the IT-System is the operating system or, in case of virtualization, the hypervisor. Both are pure software and provide hardware abstraction for the development of software.

Another layer within IT-Systems are system-libraries. They use operating-system programming interfaces to support developers with simple functions and simpler interfaces to develop applications.

The top of an IT-System are the applications. Typical applications are but are not limited to:

• webservers

• webbrowsers

• email applications

• text processing programs

• control programs for pump stations

• electrical smart meter progra

• individual persons

• groups of persons

• organizations

• companies

• states

Activities can be performed between all these classes. Typical activities within Cy berspace include but are not limited to sending and receiving messages, buying and selling goods, building websites or virtual rooms, developing software, streaming audio or video content, and tweeting or liking content from other participants.

1. ClearNet everything is public accessible

2. DeepNet everything is private

3. DarkNet everything is private and participants are anonymous for outside observers

Cybersecurity is the security within Cyberspace. It focuses on the defense against negative activities like Cybercrime, Cybervandalism, Cyberterrorism, and Cyberwar. It can be partitioned into defensive and offensive security. A large part of Cybersecurity is IT-Security. It is important to notice that Cybersecurity is not a state but a continuous process,

IT-Security is a subset of Cybersecurity. It focuses on the defense of Information Tech nology against negative activities like Cybercrime, Cybervandalism, Cyberterrorism, and Cyberwar. In most cases the most important assets to defend are IT-Systems connected by the Internet