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Networks - Coggle Diagram

- - - - Wired transmission media are usually either copper wire or fibre optic cable
      - Unshielded Twisted Pair (UTP)
        
        Most common type of cable used to set up a LAN
        
        Transmits data as electrical pulses
        
        Short range - up to 100 metres
        
        Up to 10 Gbps
        
        High latency because copper is susceptible to interference
        
        Used to connect computers and other devices on a LAN
      - Fibre optic cable
        
        One or more thin strands of glass
        
        Transmits data as pulses of light
        
        Can transmit data over long distances with no loss of signal strength
        
        Up to 100 Gbps
        
        Low latency because it is less susceptible to interference
        
        Used to connect LANs together to form WANs and provide broadband services to private users. Often runs under the ocean
      - Fibre optic broadband networks
        
        Fibre to the cabinet (FTTC)
        
        Fibreoptic cables run from the nearest telephone exchange to a green cabinet in the street, with the final stretch being made using copper wire
        
        Fibre to the premises (FTTP)
        
        The entire connection to the premises is provided by fibre optic cable. Only available in a limited number of locations in the UK - often only used by big businesses
    - - Wireless transmission media do not use a physical conductor, but they use waves to create connections between devices
      - Wi-Fi
        
        Travels up to 100 metres
        
        Up to 10 Gbps
        
        Ideal for a wireless LAN (WLAN)
        
        Every device is fitted with a wireless adapter and antenna, so that it can send and receive radio wave frequencies - 2.4GHz to 5GHz, with a number of channels per frequency range
        
        A router manages communications on the network and can have a built-in Wireless Access Point (WAP) which is a gateway to the internet for all devices
        
        Walls and electrical equipment (microwaves) can reduce the theoretical range
      - Other wireless technologies
        
        Bluetooth - distances up to 10m
        
        Zigbee - low-power radio waves and can connect thousands of IoT devices with transmitters/receivers embedded in them (Barcodes)
        
        Radio-frequency identification (RFID) - electromagnetic fields used to identify and track tags attached to objects. Transmitters/receivers embedded in each tag
        
        Near field communication (NFC) - electromagnetic fields to create high-speed connection between two devices in close proximity. Used in Contactless payment systems, powered by EM Field produced by reader
    - - WIRED
      - WIRELESS
      - Less time-consuming and disruptive to install, only cables are between WAPs - inside ceilings/walls/floors
      - Laying cables is time-consuming and disruptive and creates trip-hazards
      - Flexible. Anyone with a wireless enabled device can access network and move around once connnected
      - Number of access points and locations have to be determined at start. Expanding or changing LAN requires additional cabling
      - Wi-Fi has a theoretical range of 100m, but physical objects and interference can obstruct the signal
      - Can transmit data over long distances and between different buildings on the same site
      - Slow bandwidth - standard Wi-Fi can transmit 3.2Gbps, but available bandwidth is shared by all active devices
      - Fast bandwidth - up to 10Gbps per connection
      - High Latency
      - Low Latency
      - Performance can be inconsistent because Wi-Fi signals are subject to interference
      - Reliable - Constant speed because it is less susceptible to interference
      - Data needs to be encrypted to prevent eavesdropping or interception
      - Data can only be accessed by devices physically attached to the network, so not easy to eavesdrop
  - - - Share files
      - Share hardware devices
      - Share internet connection and services
      - Communicate
      - Work together
      - Make use of IT support services
      - Socialise online
    - - Covers a large area
      - Uses a variety of transmission media to connect LANs together
      - Anyone who uses a WAN must pay the company that owns a part of it
    - - Covers a small area
      - Uses cable or wireless
      - Employ a network manager who is responsible for installing, configuring and maintaining their LAN, supporting users and putting in backup and security measures
  - - - The most widely used topology for wired/wireless networks
      - Every node is connected to a central node, which is likely to be a switch. All data traffic passes through the central node, which is responsible for routing it to its destination
      - Pros and Cons
        
        If one node goes down, the rest can still work
        
        If a cable is damaged, only the device connected to the wire by that line stops working
        
        Data traffic is secure as it only goes straight to one node
        
        It is easy to locate faults
        
        Nodes can be added or removed easily
        
        If the central node fails, the whole network dies
        
        There is a maximum number of nodes, and the capacity of the central node can be low/high
        
        A lot of cabling is needed for a wired network - expensive
        
        Very flexible, so can be used in any situation
    - - Pros and Cons
        
        Very fault tolerant - if one node fails, messages are rerouted
        
        Nodes can be added and removed without having to take the network offline
        
        Any number of additional nodes can be added
        
        High performance because each node is connected to other nodes
        
        Wired mesh network is difficult and expensive to install
      - Every node is connected to multiple other nodes either by cable or wirelessly.
      - Communication is peer-to-peer (P2P), there is no central controlling device. Traffic hops from one node to another to reach its destination in the shortest distance possible
      - Usage in the IoT
        
        Permit machinery to be wirelessly connected to networks and share diagnostic data - wherever they are located
        
        Used for traffic management in smart cities - CCCTV etc and can be used to monitor and control traffic flow to prevent congestion
        
        Ideal to home automation - lights, temperature, security, entertainment
    - - All nodes in the network are connected onto a single cable (backbone)
      - Messages are sent along the cable as electrical signals. A terminator at the end absorbs the signals - to prevent interference
      - Only one message can be sent at a time, so the bus must find a way to prevent collisions
        
        A collision occurs when 2 or more devices send a message at the same time - making them both unreadable
        
        CSMA/CD - Carrier Sense, Method Access with Collision Detection
      - Pros and Cons
        
        Cheap to install - little cabling needed
        
        If one node fails, the rest can still work
        
        Easy to add extra devices to the network
        
        If the cable is damaged, the whole network stops working
        
        The more devices added, the more collisions, the slower it will run
        
        All nodes 'see' traffic - easy to eavesdrop
    - - Each device on a network
  - - - The maximum volume of data that can be transferred per second
    - - The time between the data being transmitted and the moment it reaches its destination (ms)
    - - The speed at which data is transmitted from one device to another (bps)
      - File size (bits) / Transmission speed (bits per second)
  - - - Internet Backbone
        
        Cables, fibre optic links, satellites
        
        Network Access Points (NAPs) connect internet backbones to form a WW mesh network
      - POPs and ISPs
        
        Point of Presence - where a LAN connects to the internet
        
        Internet Service Provider - provides POPs
        
        ISP network connects to a high-level network owned by a telecommunications company - i.e. BT or Verizon
        
        Each has their own internet backbone
    - - Forward data from one network to another across the internet - from source to destination
      - Can keep each other up to date to prevent congested areas
      - IP Addresses
        
        IPv4
        
        32-bits, more than 4bn devices
        
        192.168.182.42
        
        Created in 1970s, so 4bn is no longer sufficient
        
        IPv6
        
        Eight 16-bit hexadecimal numbers, separated by colons
        
        fd2a:1450:4013:c01:0:0:0:5e (leading zeros omitted)
        
        Easier for humans to read
      - IP Address allocations
        
        Router is allocated a unique IP address by its ISP, the router assigns every device on its network a local IP address. It uses these to forward data to the right device. Local IP addresses are not seen outside the network
        
        Devices requiring constant access to a network, such as routers and servers, are assigned a static IP address
        
        Most devices have a dynamic IP address which they only have when they are online. If all the available addresses are in use, then a new device will have to wait to connect
        
        Domain Name System (DNS) - people can enter words instead of numbers for IP addresses, this is the first bit of a url, i.e: www.pearson.com
    - - A header contains:
        
        The source IP address
        
        The destination IP address
        
        The packet's sequence number
        
        The total number of packets being sent
        
        A checksum
      - What happens
        
        Data is broken into data packets according to an agreed set of protocols
        
        Packets are forwarded by the router to the ISP
        
        The ISP's router inspects the destination IP address and uses a routing table to determine where to send the packet next - it will often be forwarded many times from one router to another before reaching its destination
        
        Routers send packets different ways to avoid congestion
        
        Once a packet arrives, the generated checksum is compared to the one in the packet header, if they don't match, the destination will request the packet to be resent
        
        Packets from the same transmission can arrive in a different sequence, and will be reassembled using the sequence numbers once they have all arrived
- - - - Confidentiality - Only people authorised to do so should be able to access confidential data
      - Integrity - Only people authorised to do so should be able to update data, to prevent it from being incorrect
      - Availability - Data should be able to be accessed when people need it, a DoS attack aims to take servers offline
    - - To protect a network from internal and external threats. A security threat is an incident - malicious or unintended - that causes disruption, damage or data loss
  - - - Ethical hacking is when someone tries to hack their website to identify vulnerabilities - this is also Penetration Testing
      - Ethical hackers also test employees to ensure that they are aware of social engineering techniques, to ensure that they don't succumb to them
      - Ethical hackers then produce a report talking about the problems with the security, and how to fit them
  - - - Who can log into a network, what they can do etc.
      - Authentication is the process of checking whether someone is who they are
      - Multi-factor authorisation is now more commonly used: Something you have, are, and know
      - Principle of least privilege - employees can only do what they need to be able to do - not more
      - File permissions can also be used to control users
    - - Only authorised users are able to access critical areas, such as server rooms
      - Hackers could copy, modify, delete or install malware into the server if they get access
    - - Prevents hackers from being able to read the data even if they get access to it, as they do not have the right key
    - - A network security system that acts as a barrier between the network and the internet
      - Inspects incoming and outgoing traffic against a set of rules to decide what data comes through
      - Can stop protocols from being used, hackers from getting in, data from coming/going to certain network addresses
      - Can flag up suspicious activity, prevent the download of viruses, emails containing sensitive data, visiting bad websites and downloading viruses
      - Businesses with LANs are likely to have a firewall, and on each device, a software firewall should be downloaded, as well as having a network firewall
- - - - Defines how various user services operate such as web browsers and email
      - HTTP
        
        Defines how web pages are requested by a browser and served by a web server
        
        Hyper Text Transfer Protocol
      - HTTPS
        
        A secure version of HTTP with encryption
        
        Hyper Text Transfer Protocol Secure
      - FTP
        
        Defines how files are transferred across a network
        
        File Transfer Protocol
      - SMTP
        
        Defines how emails are sent between servers
        
        Simple Mail Transfer Protocol
      - POP3
        
        Defines how emails are deleted off a server once they are downloaded
        
        Post Office Protocol 3
      - IMAP
        
        Defines how emails are kept on the server/internet even when they are downloaded
        
        Internet Message Access Protocol
    - - Establishes a dedicated channel between the source and destination devices to transfer the data along.
      - Determines how outgoing data is split up into packets and how incoming packets are reassembled, but doesn't know what the data represents
      - TCP
        
        Delivers packets to the specified recipient
        
        Transmission Control Protocol
    - - Adds the source and destination IP addresses to the data packets received from the transport layer and routes them to the recipient
      - IP
        
        Obtains the address to which the data is sent
        
        Internet Protocol
    - - Defines how data is transferred from one device to another along the whole route from sender to recipient.
      - On a wired network, how the network card in the sending computer transmits the packets to the network switch and onwards. On a wireless network, how the Wi-Fi chip in the computer transmits data to the router and onwards
      - Ethernet
        
        Defines how data is transmitted on wired LANs
      - Wi-Fi
        
        Defines how data is transmitted on wireless LANs