Samenvatting voor het vak Computer Networks & Security van de lecture notes van de docenten.
Summary of the course Computer Networks & Security of the lecture notes from the teachers.
Chapter 1 – Introduction
1.1 Networks and computer networks
1.1.1 Networks
A network is an interconnected set of components.
1.1.2 Computer networks
We can define a computer network from two perspectives:
1. Physically (hardware): a computer network is a hardware infrastructure interconnecting end-
devices.
2. Logically (software): a computer network is a system for facilitating information exchange
between applications that do not share a physical memory component or memory space.
The end-devices are systems connected to the edge of a network, typically made up of hardware with
a Network Interface Card (NIC) and operating systems.
1.2 Push behind networks
1.2.1 Technological development
Moore found that the total processing power of a computer doubles every two years. This is known as
Moore’s law. It suggests that all devices that are not capable enough to connect to the Internet due to
lack of computational power will be powerful enough soon.
1.2.2 Industrial development
Metcalfe’s law: the value, usefulness or utility of a network equals the square of the number of users.
1.2.3 Economic and social aspects
E-commerce and societal demands play an important role in the development of the Internet and
Internet-based services.
1.3 Standards and regulations on networks
Standardization of hardware and protocols is crucial for device interoperability between different
sellers. The Internet is an important means of communication and broadcasting. You want to regulate
the use and utilization of the Internet.
1.4 Network physical infrastructure
A computer network infrastructure consists of leaf nodes that are connected to the network core
through access networks.
1.4.1 End devices and access networks
At the edge of a network are the network end devices, also called hosts. Examples are clients and
servers, where a client is a party that initiates a connection while a server is the one that continuously
awaits incoming connections. Embedded systems are a special purpose computer hardware dedicated
to that purpose.
An access network connects the network edge to a router in the network core. Most
households are connected to television and telephone with DSL and Cable Internet. However, FTTH
has now become affordable. Below is the table for comparing the three.
1.4.2 Network core
The network core consists of interconnected routers that can transfer data between hosts. This is done
in two ways:
1. Circuit switching: provides a dedicated circuit per call. The resources on the links on the path
are reserved for a call. This gives an upper limit to the number of calls that can be supported,
guaranteeing quality. Dividing the network resources can be done by FDM (based on
frequency) or TDM (based on time) or a combination of the two.
2. Packet switching: divides the data into packets and when another is processed, packets are
stored until they can be processed. It works with a store and forward behavior, which means
that the entire packet must arrive at router before it can be transmitted. The duration is NL/R .
1.5 The Internet: Today
We can define the Internet in two ways:
1. Physically (structure): a global public network of computer networks that uses globally
accepted communication protocols that govern sending and receiving messages between
billions of end-devices and networks.
2. Logically (functionality): a global facility that provides communication services to network
applications.
1.6 Internet of Things (IoT): Tomorrow
The Internet can be embedded in the “things” (constrained devices connected to constrained
networks). In IoT, machine-to-machine communications will be responsible for the majority of
Internet packet traffic. IoT aims to connect networked embedded systems of all types to the Internet
and it scales to many networked devices per human. Physically, the IoT is the Internet plus an
extension into the physical world surrounding us. Logically, the IoT stands for the vision of the
Internet of tomorrow, which extends the reach of distributed applications to resource-poor devices.
1.7 Network security
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, COMPUTER NETWORKS AND SECURITY LAURA DE LAAT
1.7.1 Security and network security goals
Security requirements are expressed in terms of security attributes. The most common are (CIA triad):
1. Confidentiality: information stays secret.
2. Integrity: information stays correct.
3. Availability: I can get at my information.
Another attribute is privacy: information about me is not misused. The security requirements together
with the security policies of a system tell you what attributes should be achieved when. A security
model is a framework to express and interpret policies.
1.7.2 Threats
The security attributes of the system may be at risk from several types of threats. To decide what the
right mechanisms are to achieve the security requirements of the system, we need an attacker model
that captures the capabilities and intentions of an attacker.
1.7.3 Security engineering
A chain is as strong as its weakest list. The following aspects of a system have the following issues:
1. Design: the system design does not address security goals or has inherent features/goals that
imply security problem.
2. Software quality: software bugs with buffer overflow vulnerabilities.
3. Security tool selection: no proper crypto.
4. System usage: the system is not used correctly.
There is often a clear trade-off between security and usability, performance and costs. Besides that,
there is also a trade-off between different security attributes. It is very hard to measure security, but
CCWAPSS came up with criteria for web application security.
Throughout the design, implementation, deployment, and use of a system, we should consider
the requirements that the users will have for the system and how attackers will try to exploit the
system. This forms the security requirement engineering, which combines several solutions to achieve
the best possible trade-offs.
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