Topic 3 - Networks

3.1 Networks

Network fundamentals

3.1.1 Identify different types of networks

LAN: Local Area Network. A small group of computers connected, usually over a very small area - a single room or a building. Usually done with copper cables.

MAN: Metropolitan Area Network. Network over a larger are, usually city-size, connecting computers and LANs. Sometimes done with fiber optics as high speeds are required.

WAN: Wide Area Network. Network over large geographical areas, often across and beyond entire continents. Most known WAN is the internet. Various transmission media, like phone cables, fiber optics and satellite transmission. Connects many computers, LANs or WANs.

VLAN: Virtual Local Area Network. A type of network where computers behave like they were in the same LAN, but in reality they are far apart in different networks, from where they tunnel in into the virtual LAN. An example is Hamachi, often used by gamers to play multiplayer games that only support LAN parties, over the internet.

WLAN: Same as a LAN, just with radio wave connections instead of wires. In general slower than a LAN.

3.1.2 Outline the importance of standards in the construction of networks

Computer need standards to be able to communicate with each other, just as we need clear defined grammatical rules to be able to talk with each other.

3.1.3 Describe how communication over networks is broken down into different layers

The computer communications networks we use today are based on the OSI reference model. Aim of the OSI model is to allow communications across many different technical plattforms and to allow easy development. To reach this, the model defines seven consecutive layers with individual roles. It is easy to switch between the protocols in the same layer, even if they have a central function like the Internet Protocol (IP).

Sketch of the OSI model:

OSI Layer		Category	Protocol example	Units transferred
7	Application	Application oriented	HTTP, FTP, HTTPS	Data
6	Presentation
5	Session
4	Transport	Transport oriented	TCP, UDP SCTP, SPX	TCP = segments UDP = datagrams
3	Network		ICMP, IGMP, IP, IPsec, IPX	packets
2	Data Link		Ethernet, Token Ring FDDI, ARCNET	Frames
1	Physical (bit transmitting)			Bits

Following is a summary of the functions of each layer, but the IB does not require students to understand the functioning of the layers.

Layer 7 - Application layer: Services, applications and network management. This layer provides functions for the applications running on a computer. Data input and output happens over this layer.

Layer 6 - Presentations layer: This layer is the system specific presentations of the data (i. e. ASCII). It enables the correct exchange of data between different systems. Also, data compression and encryption belong to this layer. In general, it ensures that data sent by the application layer can be read by the presentation layer of the receiving system. If necessary, it works as a translation layer between the different data formats used by the two systems.

Layer 5 - Session layer: This layer takes care of the communication between two systems. It provides services to repair broken down sessions and creates the sessions for an organized and synchronised data transfer.

Layer 4 - Transport layer: Functions of this layer include segmenting the data stream and avoiding congestion. It provides a standardised interface for the above layers so that they don't need to be concerned with the features of the communication networks.

Layer 3 - Network Layer: In packet oriented networks, this layer is responsible for the forwarding of data packets. Data forwarding happens over the entire network and includes the routing of packets between the network nodes. The most importand functions of this layer include the provision of addresses across the network, routing and the processes of actualising and creating routing tables and the fragmenting of data packets.

Layer 2 - Data Link layer: Task of this layer is to ensure a faultless transmission of data and to regulate access to the transmission medium, by breaking up the bit stream in frames and providing those with checksums to be able to detect a corrupted data packet.

Layer 1 - Physical layer: This is the lowest layer. It provides mechanic, electric and functional help to activate and deactivate physical connections, keep them active and transmit bits through them. These can be electric, optical, electromagnetic waves or sound signals. This layer involves how a bit is transmitted across a medium.

3.1.4 Identify the technologies required to provide a VPN

One LAN that is connected to the internet.
One computer outside of the LAN that is also connected to the internet.
Some configuration.
VPN client and server.
A gateway.

3.1.5 Evaluate the use of a VPN

Through a VPN, it is possible to connect to a LAN that is protected from outside access through the internet. So, now it is possible for workers to connect to a company's internal network from almost anywhere on the world. This gave rise to home offices, as many office jobs do not require consultation and hence can be completed from home. For example, a mother workin half time as an accountant can bring her children to school in the morning, can then download necessary papers form the company's network through a VPN and complete her work, and by the time she finishes, she can pick her kids up from school. This has saved a significant amount of time in her daily schedule that would otherwise have been spent on travelling to and from work.

Data transmission

3.1.6 Define the terms: protocol, data packet

Protocol: a set of rules that communicating parties use when using a communication network.

Data packet: the compartmentalized pieces of information into which a message is broken down in a packet switching network system.

3.1.7 Explain why protocols are necessary

Protocols are the set of rules computers follow when communicaating across a network. Without them, no information can be transmitted as computers don't know how to interpret the signals coming through the network. Similarly, if you don't know a foreign language, you cannot talk with people who only speak that language.

3.1.8 Explain why the speed of data transmission across a network can vary

• Many users may want to transmit data through the network at the same time
• Interference to the network from the outside can corrupt many data packages, causing them to have been retransmitted

3.1.9 Explain why compression of data is often necessary when transmitting across a network

Earlier, data transmission often happened through the slow phone network, so compressing data for faster transmission was essential. Today, the transmission speeds have greatly increased, but we are transmitting far more data over the networks than earlier (movies, social media, news), so compression is needed to be able to transmit the enormous amounts of data without using up all the bandwidth.

3.1.10 Outline the characteristics of different transmission media

Metal conductor:

• Cheap
• Average to high speed
• High reliability
• Relatively secure

Fibre optics:

• Expensive
• Very high speed
• High reliability
• Relatively secure

Wireless:

• Price varying by size of network (WLAN is usually cheap)
• Middle speed
• Average reliability
• Insecure

3.1.11 Explain how data is transmitted by packet switching

Packet switching is a method of transmitting information over a computer network. The information is broken down into smaller pieces, the packets that are then transmitted across the network.

Every packet contains:

• The source of the packet
• The destination of the packet
• Length of the information part
• A running number of the packet
• Classification of the packet

The packets are transported as individual and independent units through the network, so they can travel on many different ways.

Advantages:

• Because the single packets are small, waiting times are low and because packets can travel through multiple channels independently, the network will be utilized better.
• Resources will be given fairly to participants in the network.
• Because of small packet size transmitting errors can be detected fast.
• High resistance against fallouts. If part of the network falls out packets can route around the broken down transmission lines.

Disadvantages:

• Because transport routes are not fixed, overloadings can occur at transmitting stations.
• Packets don't arrive in order (because they can take separate ways).
• All participants have to use the same network protocols.
• No constant bandwidth can be guaranteed and big fluctuations in bandwidth can happen.

Wireless networking

3.1.12 outline the advantages and disadvantages of wireless networks

Advantages:

• Easy to set up (no cablilng required)
• Can be installed almost anywhere (no need to drill holes etc.)
• Allows mobility (computers don't have to stay in same place)
• Easy to add new participants to network

Disadvantages:

• Traffic through network can be intercepted by unauthorized people
• Slow transmission speeds
• Interference from other wireless stations, cables etc. can happen, reducing speed
• Signal range depends on participating devices' antenna
• Many different standards may not compatible with each other (There are 5 differnt WLAN standards). Making wireless access points compatible with each standard is complicated (differnt antenna) and resource consuming, and can influence transmission speeds for individual participants.

3.1.13 Describe the hardware and software components of a wireless network

Hardware components:

• Antenna
• Networking interface card

Software components:

• Drivers providing the abstraction required by the operating system and inmplenting functions
• Firmware of the network card implementing transport oriented protocols

3.1.14 Describe the characteristics of wireless networks

WiFi:

• Also called Wireless LAN (WLAN)
• Used in laptops to connect wirelessly to home network
• Most preferred netwrok type to implement a home network
• Allows relatively slow to fast data transmissions (depending on the version)
• Backwards compatible with most older WiFi standards
• Small transmitting radius makes it suited for homes

WiMAX:

• Worldwide Interoperability for Microwave Access
• Designed for large distance high speed internet access
• Relatiely cheap method of providing internet over a large area - suited for poorer countries
• Rivaled by Long Term Evolution (LTE) standard
• Can be used as a form of wireless variant of DSL phone transmission lines

3G:

• The primary way mobile phones access the internet today
• Allows the tunneling of phone lines (mibiles don't have to switch back to phone network when receiving a call
• Relatively fast
• Network is heavily overloaded in germany

3.1.15 Describe the different methods of network security

Data encryption: information is scrambled using a set of mathematical rules and passwords so that it is only readable by the communicating parties. Examples are AES and RSA.

userID: a userID and password are used to identify the user. Usually, traffic after identification is handled using some type on encryption method.

3.1.16 Evaluate the advantages and disadvantages of each method of network security

Encryption types:

Advantages:

• A strong encryption is very hard to break
• Computer are fast enough to encrypt data on-the-fly

Disadvantages:

• Often, users are lazy and take a password that is easy to guess
• The password needs to be transmitted over the network to receiver to allow them to read the message
• Some encryptions are designed to haave backdoors built in

userID:

Advantages:

• Access rights to the network can be set for each user
• User groups can be created to manage user rights in batches

Disadvantages:

• A userID can be stolen
• system can be bypassed
• Does not protect against intercepting messages in the network

Topic 2 - Computer organization

2.1 Computer organization

Computer architecture

2.1.1 Outline the architecture of the CPU and the functions of the ALU and the CU and the registers within the CPU

CPU: the Central Processing Unit, is the brain of the computer. This highly compact and powerful chip controls all the peripheries and processes inside the computer and does the calculations on the data the system handles.

ALU: the Arithmetic Logic Unit, is a circuit that is part of the CPU and does all the arithmetic calculations.

CU: the Control Unit, is the control circuit of the CPU. It handles the loading of new commands into the CPU and the decoding of these commands. Also, it directs the data flow and the operation of the ALU.

Registers: they are small, very fast circuits that store intermediate values from calculations or instructions inside the CPU. They are often referred to as cache memory inside the CPU. There are two types of these memory we need to know: The Memory Address Register (MAR) and theMemory Data Register (MDR). The MAR register holds the address of the next memory cell that data will need to be read from or written to, while the MDR holds data that will be written to the RAM or that was read from RAM. The MAR gives the address the data of the MDR will be read from or written to.

We are expected to be able to draw a diagram with the CPU, ALU, CU, MAR and MDR!

2.1.2 Describe primary memory

Random Access Memory (RAM): memory unit that can be read to and written from at any location. Therefore it is used as primary memory in computers to hold data and instructions. It is volatile, so it loses its contents when power is turned off.

Read-Only Memory (ROM): memory unit that can only be read from. It is non-volatile, so it keeps its contents when power is turned off. Used to store the BIOS (today UEFI) of the computer, the small control program that directs turning on the computer.

2.1.3 Explain the use of cache memory

A type of small, high-speed memory inside the CPU used to hold frequently used data, so that the CPU needs to access the much slower RAM less frequently.

2.1.4 Explain the machine instruction cycle

The machine instructions cycle is is also called the fetch-execute cycle. It consists of the steps: fetching the next instruction, decoding the instruciton, executing the instruction. Often, a fourth step is added between the decoding and executing steps, called getting data, but because computers ultimately deal with data all the time, this step is often left out. This process is repeated all over again until the computer is turned off.

The role of data bus: data is transferred from or to the RAM using this bus.
The role of address bus: this bus tells the RAM from which location data will be needed to be read or written to.

A really good video explaining the fetch-execute cycle is on YouTube.

Secondary memory

2.1.5 Identify the need for persistent storage

Persistent storage is needed to store data and programs after the computer is turned off. Otherwise, all the programs and data would be need reinstalled every time the computer is restarted. Also, RAM is limited in a computer while large amounts of secondary storage are relatively cheap, so storing unused data and programs in secondary storage is useful to make space for running ones.

Operating systems and application systems

2.1.6 Describe the main functions of an operating system

Memory management: managing the usage of RAM by the single programs using the computer. To allow programs to be less concerned with computer architecture. Each program gets a space - a page - in RAM to run in. In this space the program believes it has all the computer for itself (it uses logical memory addresses that are then translated into physical memory addresses by the OS). Also, memory management manages the swapping of memory pages. When RAM gets full.

Control and monitoring of system functions: The OS controls the working of the peripherals and creates an abstraction of them for the programs to use. This way, the programs only need to be concerned with the tasks they are supposed to carry out and not with the different architectures of different computers and peripherals.

2.1.7 Outline the use of a range of application software

Word processor: A program to create and edit continuous texts

Spreadsheet: A program to manage calculations on complex amounts of data

Desktop Publishing: A program to edit media in a way to be published, like magazines, books or posters

Computer Aided Design (CAD): Software to digitally design and edit parts to be manufactured. Often includes a Computer Aided Manufacturing (CAM) module to be able to use the model to directly produce a prototype.

Web browser: Its clear, isn't it?

2.1.8 Identify common features of applications

• Possibility to terminate the application
• Possibility to save current working
• Toolbars
• Dialogue boxes
• Menus
• User interface (GUI) components

Binary representation

2.1.9 Define the terms: bit, byte, binary, decimal, hexadecimal

Bit: smallest unit in computers, either a 1 or a 0

Byte: a group of 8 bits

Binary: computers use the binary (base 2) number system

Decimal: This is the number system we use (base 10)

Hexadecimal: Base 16 number system. It has a base that is a power of 2, so we can use it to make reading binary codes shorter and thus easier to read. 4 binary characters grouped together give a hexadecimal character.

2.1.10 Outline the way in which data is represented in the computer

Computer work with the binary number system, so everything in them is represented in 1s and 0s. So, the data that we want to store in the computer needs to be encoded in 1s and 0s. For different media types, different encodings exist.

Text needs to be also transformed into 0s and 1s. To do this, a character set is used. A character set is a collection of characters and the binary codes that represent them. Today, the most used character sets areASCII and UTF.

ASCII: stands for American Standard Code for Information Interchange. It uses 7 (later 8) bits to encode the characters, so in total 2⁸=256 different characters can be represented.

UTF: is a superset of ASCII. It was developed because people realized that the 256 characters of ASCII are not enough to satisfy our need for a suitable number of characters. The goal of the maker of UTF is nothing less than to represent every character humans have ever used.

Strings: representation of characters in a continous bit chain

Integers: representation of numbers in computers. Whole numbers. Negatives can be represented by the 'two's complement' method.

Floats: representation of fractions within the computer. It is a special version of the scientific notation. It consists of a sign bit, the mantissa, the number itself, and the exponent which states how many characters left or right of the number the radix point 'floats'. The radix point is the version of the decimal point that can be applied in any number system. In the 64 bit float, 1 bit is used for the sign, 52 are used for the mantissa and 11 are used for the exponent.

Simple logic gates

2.1.11 Define the Boolean operators: AND, OR, NOT, NAND, NOR and XOR

AND: true only if both of the inputs are true

OR: true if at least one of the inputs are true

NOT: inverts a value, makes a false from a true and vice versa

NAND: NOT + AND gates together. False if both the inputs are true, otherwise true

NOR: NOT + OR gates together. Only true of both of the inputs are false, otherwise true

XOR: exclusive OR. Only true if only one of the inputs is true, otherwise false

2.1.12 Construct truth tables using the above operators

A truth table is a table listing all the connections in a logic circuit and can thus be used to trace output to different inputs.

a	b	c	d	e	f	g	h	i
false	false	false	false	true	true	false	true	true
false	true	false	true	true	false	false	false	false
true	false	true	false	false	true	false	false	false
true	true	true	true	false	false	true	false	true

2.1.13 Construct a logic diagram using AND, OR, NOT, NAND, NOR and XOR gates

There is nothing much to say to this…… Just get the logic right.

The IB do not require us to draw the specific symbols for the gates, we should just draw a circle and write the name of the gate into it.

However, we are expected to draw straight lines and 90° angles