Computer Science - Fundamentals of computer network

What is a network

It is a collection of connected computers

Why are networks set up

1. For management of computers

2. To share resources

3. To exchange data between computers without the need for external storage

Examples of resources shared over a network

1. Printers

2. Scanners

3. Internet connections

Factors that affect the performance of a network

1. Choice of hardware

2. Bandwidth

3. Wired vs wireless

4. Topology

What are the different transmission media

1. Fibre-optic cable

2. Twisted-pair copper cable

3. Radio waves

4. Coaxial cable

Features of fibre-optic cables

1. They are made of thin strands of glass that transmits bits as pulses of light

2. They do not suffer interference because they have very high bandwidth

3. Because of lack of interference, it is appropriate for long distance communication

Feature of coaxial cable

An insulated copper wire surrounded by metal wire mesh to prevent interference

Features of a twisted-pair copper cable

1. It is often referred to as ethernet cable

2. The twisted wires in the cable reduce interference from other signals

Features of radio waves

1. They are the transmission media of wireless networking

2. The amplitude (strength) decreases the further it is from its transmitter

3. They are subject to interference form other radio signals

What is a Personal area network (PAN)

It is a network used to connect personal devices and spreads over a small area

What is a local area network (LAN)

It is a network that connects devices over a small geographical area

What is a wide area network (WAN)

It is a network that connects devices over a large geographical area

Features of a WAN

1. A WAN is a collection of computers connected over a large geographical area.

2. WANs are used by multinational organisations that have international offices they need to connect to.

3. A WAN is usually rented from a large telecommunications company because WANs are expensive to set up

Features of a LAN

1. A LAN is a collection of computers connected over a small geographical area.

2. These are typically found in homes, schools, universities, and small companies.

3. The LAN is set up and maintained by the organization that uses it

What is packet switching

It is the process of breaking down data into packets, sending them across the internet to another company and re-assembling them

Describe packet switching in a sender’s local area network

• The sender will generate data in an application on their computer at the application layer.

• The data is split into packets of data at the transport layer.

• Internet Protocol adds IP addresses to each packet at the Internet layer.

• Packets are grouped into frames and sent to the router on the LAN at the network layer

Describe packet switching over the internet

• The sender's router inspects the packet to determine if the destination IP is on the current LAN at the Internet layer.

  • If it is not then it will send the packet onto the Internet (or other wide area network).

• Each packet is sent from the sender's router to the destination router via connected routers.

  • The path of each packet can be different, which maximises efficient use of the network by avoiding bottlenecks.

Describe packet switching in a recipient’s local area network

• Because they have taken different paths, the packets at the destination will be in the wrong order.

  • These packets are unpackaged and reassembled into the correct order using the sequence number of each packet.

What are the 3 common security measures to protect Wi-Fi against hackers

1. Wired Equivalent Privacy (WEP)

2. Wi-Fi Protected Access (WPA)

3. Wi-Fi Protected Access version 2 (WPA2)

What is a star topology

When each device is connected to a central switch or server

Features of a star topology

1. Allows many devices to access the server at the same time

2. If a single client fails then all other clients can continues as usual

3. If the server fails, the whole network is affected

4. It can easily be expanded by adding more devices

5. It can be expensive to run a cable to every single device in a wired star

6. Wireless star networks can sometimes be more cost effective

What is a bus topology

When each computer is connected to a main cable called the bus

Features of a bus topology

1. It does not require many physical cables

2. It is unreliable since if the main cable is broken then the network is shut down completely

3. It is easy to build and new computers can be added very easily

4. Problems with network can be difficult to find since a break in the main cable should have occurred in any place

What is an Internet Protocol (IP) address used for

They are used by routers to identify where data packets need to be sent to and where they come from

Features of IP address

1. They must be unique within the same LAN

2. They do not need to be universally unique

List types of IP addresses

1. Private IP vs public IP

2. IPv4 vs IPv6

3. Static IP vs dynamic IP

Features of a Private vs public IP

1. Devices within a LAN can have private IP addresses

2. Routers which connect a LAN to a WAN also have a public IP address

Features of a IPv4 vs IPv6

1. IPv4 are 32-bit numbers often displayed as 4 numbers separated by dots

2. IPv6 are 128-bit numbers often displayed as 8 groups of 4 hex digits separated by dots

Features of a static vs dynamic IP

1. IP addresses are either static or dynamic

2. A device with a static address will have the same IP address every time it connects to the network

3. A device with a dynamic address will be allocated a new IP address every time it connects to the network

Uses of MAC addressing

1. They can be used to exchange data on the same LAN

2. They are also used by switches and NICs to send data to the intended recipient

What is the format of the MAC addresses

• The first half of the address relates to the manufacturer of the device

• The second half relates to the individual device that has been produced

What is a network protocol

It is a set of rules that define how data is transmitted between connected devices

What are the types of protocols

1. IP

2. Wi-Fi

3. Transmission Control Protocol (TCP)

4. Ethernet

5. User Datagram Protocol (UDP)

6. Hypertext transfer protocol (HTTP)

7. Hypertext transfer protocol secure (HTTPS)

8. File transfer protocol (FTP)

9. Internet message access protocol (IMAP)

10. Simple mail transfer protocol (SMTP)

11. Post office protocol (POT)

What is ethernet

It is a protocol that defines how data should be physically transmitted between network and hardware

What is TCP

It enables communication over the internet

What is a UDP

It is an alternative protocol to TCP but skips the stages which ensures the package has arrived and checks that the package is correct

List the difference between UDP and TCP

1. UDP is faster than TCP

2. UDP is useful when reliability if data is less important than achieving fast transfer e.g. online gaming

What is a Hypertext transfer protocol (HTTP)

It is a protocol that defines how data should be exchanged between web users and servers

What is a Hypertext transfer protocol secure (HTTPS)

It is an encrypted and more secure version of HTTP

What is a File transfer protocol (FTP)

It is a protocol that governs the transmission of files across a network and the internet

What is a IMAP

It is a protocol that governs retrieving emails from email servers

What is SMTP

It is a protocol that governs the sending of emails over a network to a mail server

What is POP

It is a common email protocol that governs retrieving emails from a mail server

What is a protocol layer

It is a group or collection of network protocols that work at a similar level within the networking process

List advantages of layering

1. Specialism

2. Layer independence

3. Debugging

4. Promotes application development

How many layers does a TCP model have

4

Describe the 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, Wi-Fi)

How many layers does an open system interconnection (OSI) model have

7

Describe the OSI model

• The first 3 layers of the OSI model

  • Application

  • Presentation

  • Session

  are grouped into TCP’s application layer
  

• The 4th layer

  • Transport.

  is the same with the TCP transport layer

• The 5th layer

  • Network

  is called the internet in the layer in the TCP model
  

• The bottom two layers

  • Data Link.

  • Physical

  are combined into TCP’s network access layer
  

What are the 3 basic sections of a URL

1. Protocol

2. Domain

3. Path

Examples of protocols in an application layer

HTTP, IMAP, FTP

Examples of protocols in a transport layer

HTTPS, TCP, UDP

Examples of an internet layer

IP

Examples of a network access layer

Ethernet, Wi-Fi