3.5- Fundamentals of Computer Networks

computer science

What is a network?

A series of computers and other devices that are connected together and can share data resources.

What are the advantages of networking

Sharing resources

• Files can be stored on centralised servers and be accessed by anyone authorised

• peripheral devices like printers can be shared

• internet connection can be shared

Centralised management

• User profiles and security can be managed centrally

• Software can be distributed across the network rather than onto to each computer individually

• All files can be backed up onto a central server

What is the internet?

An international collection of networks.

What is the World Wide Web?

A collection of websites and other resources.

What is Packet Switching?

When messages are broken down into small data packets and sent individually across a network and reassembled at the receiving end.

What is a Domain Name System (DNS)?

A system where a web address is translated into an IP address.

What are DNS servers?

A collection of web addresses and their associated IP addresses. There are 13 Root DNS Servers worldwide.

What is an IP Address?

The identifier of a network connected device that allows the device to communicate across the Internet. 2 Types: IPv4 (192.168.0.1) and IPv6.

What is a MAC Address

A unique identifier of a Network Interface Card. It is used to assist with packet switching.

What is a Network Interface Card (NIC)?

Allows you to connect to a network. Can be used to connect to a wired or wireless network.

What is a Router?

A device that sends data packets on their way in the best direction.

What is a switch?

A device that sends packets to its intended recipient using the recipient's MAC Address.

What is Wi-Fi?

A way of connecting to a network wirelessly using radio waves. This is normally susceptible to interference from objects and other nearby devices. Wifi is a trademark name for a family of related protocols for a WLAN

What is a Wireless Access Point?

A device that allows wireless devices to connect to a wired network using Wi-Fi. These are normally integrated into the Router but can be a standalone device.

What is a WAN (Wide Area Network)?

• Cover a wide geographical area

• Often under collective or distributed ownership.

• The biggest example of a WAN is the internet

What is a LAN network (Local Area Network)?

• Cover a relatively small geographical area

• These are often owned and controlled/managed by a single person or organisation.

• Have less users than WANs

What is a Personal Area Network (PAN)?

• Centred around a single user or device

• Limited area- around 10m

What is Bandwidth?

The amount of data that can be carried at any one time.

What is Latency?

The time delay of transmitted data travelling from the sender to the recipient.

What is a Star Topology?

• Each device has its own connection to the central switch

• Switch routes transmission to devices using their MAC address

What is a Bus Topology?

• All signals transmitted through the central backbone

• Terminators on either end to prevent stray signals bouncing back down the cable

Advantages of Bus over Star

• Cheaper as there is significantly less cabling

• Simpler to install

Advantages of Star over Bus

• If the main cables breaks on a bus, the whole network goes down, while this will not happen in star

• As more users are added to bus, performance of the network depletes, as there will be more data collisions, as data will travel in both directions on the network, meaning data will have to be retransmitted; this does not happen on star as each device has its own connection and packets will be routed by the switch

• Greater security risk as all devices on a bus network can see all the data being transmitted across it, while this doesn’t happen on star

What is a Fiber Optic Cable?

Uses light waves transmitted in a glass tube to transmit data.

What are Copper cables?

• Uses electrical signals transmitted in a wire to transmit data

• Used in ethernet cables

• Vulnerable to electromagnetic interference

What is needed to connect to a wireless network

NIC (Network Interface Card)

Advantages of Wired over Wireless

• Faster and more consistent transmission

• While copper cables can be susceptible to electromagnetic interference, fibre optic cables can avoid this, and prevent interference for higher quality transmission- wireless can have signal reduced by walls and other wireless devices

• Maintains a good strength for longer (especially if fibre optic is used)- wireless have a limited area and require repeater devices to expand the range

• Cannot be easily intercepted- without encryption wireless can be easily intercepted

Advantages of wireless over wired

• Cheaper to add a new device, as no new additional cabling required

• Easier to add new devices as no new cabling required

What is a Network Protocol?

A set of rules that allows devices to communicate on a network

What is Ethernet?

A family of standard local network protocols.

What is Tethering?

Linking devices using Bluetooth by creating a PAN.

What is Authentication?

Verifying that a user is allowed to access content on a device.

What is Encryption?

Encoding of data so it can no longer be easily read (Plaintext to Ciphertext)

What is Plaintext?

The message that the user wants to encrypt.

What is Ciphertext?

The encrypted data.

What is a Key?

A sequence of numbers used to encrypt and decrypt data.

What is an Encryption Algorithm?

The formula used to encrypt the plaintext.

What is Symmetric Encryption?

A single key is used to encrypt and decrypt data.

What is an Asymmetric Encryption?

Two keys are used to encrypt and decrypt the data.

What is a Public Key?

The key used to encrypt the data. This is normally made publicly available.

What is a Private Key?

The key used to decrypt the data. This is normally kept with the recipient.

What is a Caesar Cipher Shift?

A method of encryption involving moving positions left and right.

What is Cryptanalysis?

The objective of trying to decode the ciphertext. This is normally found by finding out the key.

What is a Brute Force Attack?

A method of cryptanalysis where every possible key is tried until the correct key is found and the message can be decrypted

What is the Key Strength?

2^no of bits

What is frequency analysis?

Using how common letters are to decrypt messages.

What are Wireless Encryption Standards?

A method of encrypting wireless broadcasts while data is being transmitted. There is 2 common types: WEP and WPA

What is a Firewall?

A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.

What is MAC Address Filtering?

MAC address filtering allows devices to access, or be blocked from accessing a network based on their physical address embedded within the device’s network adapter- blocks based on the NIC

What is HTTP?

• HyperText Transfer Protocol

• Provides a way for users to interact with web resources. Transmits messages between client and server using hypertext

What is HTTPS?

• HyperText Transfer Protocol Secure

• A secure protocol that encrypts information transmitted when on the internet so it can't be hacked.

• HTTPS is an extension of HTTP and allows secure transfer of data between a browser and a website by encrypting data. The web browser will check the website server’s security certificate and ensure it is legitimate. This means it’s not possible to see or eavesdrop on what you’re browsing or for your data to be stolen

What is FTP?

• File Transfer Protocol

• Allows secure transfer of files between client and server.

• Files are uploaded to and downloaded from the server using FTP.

What is a Simple Mail Transfer Protocol (SMTP)

• Enables users to send (and receive) email messages. Initiates sessions between user and mail server.

• Server then forwards messages.

• Uses a process called ‘store and forward’ to store messages and forward as necessary.

• The server decides which server to send the message to and the inbox provider then downloads the message and places it in the recipient’s inbox.

• Often used in conjunction with IMAP

What is IMAP

• Internet Mail Access Protocol

• Stores email messages on an ISP server but allows user to manipulate messages as though on a local device.

• Local devices access the ISP server to access the messages.

• IMAP works with desktop clients and webmail clients.

• Allows simultaneous logins from different devices to one account

What is POP3?

• Post Office Protocol

• A protocol used to receive emails. It downloads the entire message to the device and removes the email from the server.

What is a User Datagram Protocol?

• Communications protocol that establishes low latency and loss- tolerating connections between applications.

• Enables the transfer of data before an agreement is provided by the receiving party.

• This speeds up transfers.

• Continuous flow of data without checking for lost packets

What is transmission control protocol

• Connects network devices to the Internet. It defines how applications can create channels of communication across a network.

• It manages how a message is assembled into smaller packets before transmission and reassembles packets in the correct order at destination.

• It checks to make sure all the packets have arrived and if not sends a message to resend the lost packets

What is internet protocol (IP)?

• Relays data across network boundaries.

• It defines how to address and route each packet to make sure it reaches the right destination.

What is a TCP/IP Stack

Defines how different protocols operate to pass data packets across a network.

What is the application layer?

• The layer that selects the correct protocol to use depending on the application in use and what you are trying to do.

• This is where the network applications, such as web browsers or email programs, operate.

• HTTP, HTTPS SMTP, IMAP and FTP protocols operate in this layer.

What is the transport layer?

• The layer that creates the connection between the 2 hosts,

• Agrees the communication settings such as the size of the packets.

• TCP and UDP operate in this layer.

What is the internet layer?

• Addresses and packages data for transmission.

• Routes the packets across the network.

• IP operates in this layer.

What is the Link layer?

• The layer that is the physical hardware that connects the 2 hosts together.

• This is where the network hardware such as the NIC (network interface card) is located. OS device drivers also sit here.