2.2 The internet

# Wired and wireless networking
# Wired
### Implications of use of wired media
#### Benifits
- Reliability: more reliable and stable connection since it is less susceptible to interference and signal Loss
- Security: provide better security as the physical cables make it more difficult for unauthorized users to intercept
- Higher Bandwidth: can support higher bandwidths, making it suitable for applications that require fast and high-volume data transfer, sch as Large File transfers, video streaming, and online gaming.
#### Drawbacks
- Infrastructure Cost: higher upfront infrastructure costs, including the installation of cables, connectors, switches, and routers Limited
- Mobility: restricts mobility as devices need to be physically connected to the network
## Copper cable/Coaxial Cable
- Cable made up of central copper core, insulation, copper mesh and outside insulation
### Characteristics
- Structure: consists of a central conductor, surrounded by an insulating layer, a metallic shield, and an outer insulating layer.
- Signal Transmission: capable of transmitting analog and digital signals at high freqnencies
- Bandwidth: offers a relatively high bandwidth, allowing for the transmission of large amounts of data
- Interference Resistance: The metallic shield in coaxial cable provides excellent protection against electromagnetic interference （EMI） and radio frequency interference (RFI).
- Distance: can transmit signals over long distance without significant Loss of quality, for very long distance repeaters are needed
- installation and maintain: copper cabling is less expensive and easier to install, because it is more flexible. it is easier to make terminations using copper cabling.
- Applications: commonly used in cable TV systems, Ethernet networks, and high-speed data transmission
## fibre-optic Cable
- Cable made up of glass fibre wires which use pulses of light (rather than electricity) to transmit data
### Characteristics
- Structure: consists of a thin strand of glass or plastic (Fiber) surrounded by a protective sheath
- Signal Transmission uses Light signals to transmit data, allowing for high-speed and Long-distance communication
- Bandwidth: incredibly high bandwidth, enabling the transmission of large amounts of data simultaneously.
- Interference Resistance: immune to electromagnetic interference (EMI) and radio Frequency interference (RFI).
- Distance: can transmit signals over very Long distances with minimal signal loss, as the light signals experience less attenuation
- installation and maintain :  is higher, cable / hardware is more expensive to buy per metre,  the electronics at both ends are more complex. Specialists / trained personnel are needed to install / maintain
- Appolications: used in telecommunications networks, internet backbone infrastructure, and high-speed data transmission
# Wireless
## Implications of use of wireless media
### Benifits
- Mobility and Flexibility:
  - Less hard-wiring/hardware is required: Reduced cost of setting up the network
  - Users and computers can be mobile: The network can be accessed from anywhere within range of an access point
- Easy Deployment and Scalability: easy deployment and expansion of networks as there is no need for physical cabling infrastructures 
### Drawbacks
- Interference and Signal Quality: susceptible to interference from other wireless devices operating on the same frequency range, Signal quality can be affected by obstacles like walls, furniture, or enviromental conditions
- Bandwidth may be limited: As more devices connect the bandwidth can be reduced so access may be slow.  provides lower bandwidth and slower data transfer speeds compared to wired media. 
- Limited range: users can easily move out of range
- Transmissions may be less secure: more easier to unauthorized access and interception since the signals
### Wifi (Wireless Fidelity)
- wireless connectvity that uses radio waves, microwaves 
- allows devices to-connect tor a network or the internet without cables
#### Characteristics
- Wireless networking technology that allows devices to connect to a Local area network （LAN） or the internet without using physical cables.
- Uses radio wares to transmit and receive data over Short distances Provides high-speed and convenient wireless connectivity for devices sch as smartphones, Laptops, and IOT devices
- Supports various encryption and security protocols to protect data during transmission
- Wi-Fi networks can operate in different frequency bands, sch as 2.4 GHz and 5 GHz, offering different levels of speed and ranges
### Radio waves
- Electromagnetic wares used for wireless communication and broadcasting, with Long wavelengths and Low frequencies.
#### Characteristics
- Electromagnetic wares with long wavelengths and low frequencies in the electromagnetic spectrum
- Used for various communication purposes, including radio broadcasting, television transmission, wireless networking (eg., Wi-Fi), and mobile communications (eg, Cellular networks).
- Can travel throngh the atmosphere and other materials, such as buildings, with relatively low attenuation
- Interference From other electronic devices and physical obstacles can affect the quality of radio ware communication
- Different frequency bands are allocated for specific applications to avoid interference
### Microwave
- Subset of the electromagnetic spectrum with shorter wavelengths and higher frequencies than radio wares
- Used in applications sch as microware ovens, wireless communication, and radar systems.
#### Characteristics
- Uses shorter wavelengths than radio waves.
- Operates in the frequency range of 300 MHz to 300 GHz.
- Can be used for short-range or long-range communication.
- Widely applied in microware ovens, wireless communication (eg, Wi-Fi, cellular networks), radar systems, and satellite communication
- Capable of achieving high data transfer rates.
### Satellite
- Satellite transmission media refers to the use of artificial objects called satellites to-transmit signals and data between different Locations on Earth or in space
- These satellites orbit the Earth and act as relay stations, receiving signals From one location and transmitting them to another.
- Satellite transmission media enable long-distance communication, global coverage, and various applications sch as satellite television, satellite internet, and satellite-based navigation systems like GPS.
#### Characteristics
- Artificial objects placed in orbit around the Earth, used for various purpose, including communication, navigation, weather monitoring, and scientific research.
- Enable long-distance communication by relaying signals between ground-based stations or other satellites
- Communication satellites receive signals from one location, amplify them, and transmit them back to a different Location Can provide wide coverage area, including remote or inaccessible regions
- Used for applications sch as satellite television, satellite internet, global positioning systems（GPS）, and satellite imagery.
- Require line-of-sight communication, and atmospheric conditions can affect signal quality.
### Router in a network
- Receives and sends data between two networks operating on the same protocol
- Allows internal connections between LANs OR allows external connection from the main LAN to a WAN
- find destination of packets using the IP address
- forward packets to the destination
- assign private IP addresses to devices on LAN
- store/update/maintain a routing table
- find most efficient path to destination
- maintain table of MAC and IP addresses
- provides the LAN with a public IP address
- performs protocol conversion
- acts as a firewall
# LAN-supporting hardware
## Switch
  - Connected to all devices in a LAN and can simultaneously broadcast information to all devices
## Server
  - device/software provides specific functions for computers in the network
## Network Interface Card (NIC)
  - Provides each device (an end-system) in the wired LAN with a unique (MAC) address to uniquely identify it on the network
  - Allows each individual device to connect to network
## Wireless Network Interface Card (WNIC): 
  - Hardware component that allows a device to connect to a wireless network
  - Provides a MAC address to the device to identify it on the wireless network
  - Provide interface to wireless network as an antenna 
  - Receives analogue radio waves convert them to digital / binary 
  - Checks incoming transmissions for correct MAC / IP address ignore transmissions not intended for it 
  - Encrypts / encodes the data 
  - Decrypts / decodes the data 
  - Takes digital/binary input and converts to analogue waves sends the radio waves via the antenna
## Wireless Access Points (WAP):
  - Hardware component that provides radio communication from the central device to nodes on the network (and vice versa)
  - Usually built into router
## Cables
  - A wired transmission medium that allows communication in wired networks
## Bridge
  - Connects two LANs which work use the same protocol, which can be two segments of the same network
  - Stores network addresses for all devices (end-systems) between the 2 networks
  - A bridge looks for the receiving device before it sends the message.
## Repeater
  - Connects two cables
  - regenerates the sent data signal over the same network before the signal weakens (attenuation) to prevent it from being corrupted
### Ethernet
- A protocol (suite)
- For data transmission over standard / universal wired / cabled network connections
- Uses Carrier Sense Multiple Access / Collision Detection (CSMA/CD)
- Data is transmitted in frames, each frame has a source and destination (IP/MAC) address and error checking data (so damaged frames can be resent)
#### Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)
- A workstation / node (wishing to transmit) listens to the communication channel
- data is only sent when the channel is free
- Because there is more than one computer connected to the same transmission medium.
- two workstations can start to transmit at the same time, causing a collision
- If a collision happens, the workstations send a (jamming) signal / abort transmission and each waits a random amount of time before attempting to resend.
### Bit streaming
- Sequence of digital signals (bits) transferred over a communication path at high speeds
- Requires a fast broadband connection and some form of buffers (short-term memory)
- Bits arrive in the same order they are sent
#### Benefits
- no need to wait for a whole file to be downloaded
- no need to store large files on user's computer
- allows on demand playback
- no specialist software is required for playback in browser
#### Drawbacks
- video stops / hangs if very slow Internet / broadband speed low
- video stops / hangs if inadequate buffering capacity
- loss of Internet means can't access films / files
- may require specific software to run the files / films
- viruses can be downloaded from the websites
#### On-demand
- digital video tape, analogue video tape, or digital files are converted to bit streaming format for broadcasting on the net; this is known as encoding these encoded streaming video files are then uploaded to a dedicated server
- a link for the encoded video is placed on a web site
- a user clicks on the link to download the encoded streaming video; the streamed video is then broadcast to the user as and when they require it
- can be paused / can go back and re-watch / fast-forward, etc.
#### Real-time
- an event is captured live with a video camera
- the video camera is connected to a computer
- the video signal is converted to streaming media files (encoded) on the computer
- the encoded feed is then uploaded from the computer to a dedicated streaming server via cable, DSL, or a high-speed internet connection
- the server then sends the live images it to all users requesting it as real-time video streaming
- cannot be paused etc.
#### Importance of high broadband speed / bit-rate
- User has to download and display bits at same time
- If media is of higher quality, then higher broadband speed needed since each “frame” is of a larger size
- Real-time needs faster broadband speeds as compared to on-demand, since there are a greater number of users simultaneously requesting same data
#### World Wide Web (WWW)
- Collection of web pages stored on websites
- uses HTTP protocol to transfer web pages/data
- web pages are written in HTML
- URLs specify the location of the web pages
- web documents are accessed using browsers over Internet
#### Internet (Interconnected network)
- is Infrastructe//Massive network of networks/interconnected network of computer devices
- Internet stands for Interconnected Networks
- Uses TCP/IP protocol, which uses IP addresses to identify devices connected to the interne
##### Internet-supporting hardware
- Modems
  - Allows a device to connect to the Internet via a telephone line.
  - A transmitter uses a modem to convert digital signals (from the transmitting device) to analogue signals sent down the telephone line.
  - A receiver uses a modem on the other end to convert the analog signals to digital signals so the receiving device can understand the data.
- PSTN (Public Switched Telephone Network)
  - Refers to all telephone networks
  - Channel used between 2 endpoints for the call duration via circuit switching
  - Lines active even during a power outage
  - Bi-directional communication
  - The communication passes through different switching centres
- Dedicated lines
  - Telecommunication path between endpoints
  - Not shared with multiple users; it’s bought/leased
  - Able to host websites as well as carry phone calls
  - Allows continuous, uninterrupted access on Web
  - faster connection / communication / transmission of data
  - More consistent transmission speed
  - Improved security
  - Expensive to set-up / maintain Disruption to the dedicated line would leave no alternative
- Cell phone network
  - Wireless networks spread over land areas divided into (hexagonal) ‘cells’
  - Each cell is served by at least one base station (transceiver), which uses a different frequency range, as compared to adjacent cells, to transmit data
  - Larger capacity possible since same frequencies can be used, in non-adjacent cells
  - Radio waves are usually used for transmission
  - Can be broadcast in all directions over a wide area
  - Portable transceivers (e.g. mobile phones) are able to communicate and access internet via base stations
##### IP address
- Gives each device on a network an identifier // IP address used to locate a device on a network
- Each address is unique within the network 
- Allows a device/gateway/node to send data to the correct destination / a specific device/gateway/node
##### IPv4:
- Four groups of denary or Hexadecimal integers separated by dots
- Numbers between 0 and 255 / 0 and FF
- Each stored in 1 byte / 8 bits // the whole is stored in 32 bits / 4 bytes
123.234.5.35
##### IPv4 functionality
- IP address is made up of a network ID and a host ID 
- Each device in a subnetwork has the same network ID // Each subnetwork has a different network ID 
- Every device in each subnetwork has a different host ID but the same network ID // the host ID uniquely identifies the device within the subnetwork
##### IPv6:
- 128-bits/16bytes address format
- Eight groups of hexadecimal digits separated by colons
- Each stored in 2 bytes/16bits
- Eg: 3ffe:1900:4545:3a7b:200a:f8ff:fe2i:67cf
##### IPv6 Compression:

Step1: Remove Leading Zeros
```
67A1:0045:0010:0052:0001:0012:8000 => 67A1:45:10:52:1:12:8000
```
Step 2:Remove Inline Zeros
```
67A1:0000:0000:0000:0001:0012:8000 => 67A1::1:12:8000
```
**This can be used anywhere in an address, start, middle or end
However this::can only be used once in one address
```
eg: 8055:F2F2:0000:0000:FFF1:0000:0000:DD04
=> 8055:F2F2::FFF1:0000:0000:DD04
OR => 8055:F2F2:0000:0000:FFF1::DD04
```

| **Public IP Address**                                           | **Private IP Address**                                                  |
| --------------------------------------------------------------- | ----------------------------------------------------------------------- |
| Assigned by Internet Service Providers  (ISPs）                  | Assigned by router for private use                                      |
| Globally unique and accessible on the  internet                 | Not globally unique and accessible only  within a network               |
| Required for devices to communicate  over the internet          | Used for internal communication within  a network                       |
| Can be directly accessed and targeted  by the internet          | Not directly reachable or visible from  the internet                    |
| Typically used for servers, routers,  and public-facing devices | Used for regular devices within a  private network                      |
| Limited in number due to the scarcity  of IPv4 addresses        | Abundant in number as they are used  within private networks            |
| Subject to security risks and potential  attacks                | Generally more secure as they are not  directly exposed to the internet |
| Managed and allocated by ISPs                                   | Managed and allocated by network  administrators                        |
##### Static IP address
A fixed, unchanging network identifier assigned to a device, often used for consistent hosting or management purposes.
##### Dynamic address
An automatically assigned network identifier that changes periodically as devices connect and disconnect

| **Static**                                                   | **Dynamic**                                                  |
| ------------------------------------------------------------ | ------------------------------------------------------------ |
| IP address never changes.                                    | IP address will change at regular time periods.              |
| Static IP addresses are useful when websites need to remember a device for a long time. Eg) VPNs whitelisting | Dynamic IP address is relatively more secure, hence used where data privacy is important |
| Faster upload/download speeds                                | Maintaining cost of dynamic IP address is lesser             |

##### Subnetting
- Practice of dividing a network into two or more networks
- IP addresses are broken down to 3 parts by not changing the netID but partitioning the host ID into a subnet ID and host ID
- These subnet ID bits are used to identify each subnet within the network.
- Subnet masks are numbers that hides (masks) the netID of a system's IP address and leaves only the host part as the machine identifier, allowing data to be routed within the subnet to the appropriate host.
##### Network Address Translation(NAT)
- NAT allows multiple devices in a private network to access the internet using a single public IP address.
##### Benefits of subnetting a network
- Reduce amount of traffic in a network // improve network speed
	- … by localising network communications // by dividing data between segments
	- … so that devices are not flooded with data
	- … because data sent between devices on the same subnet stays within the subnet
- Data stays in its subnet so it does not travel as far
- Improves network security
	- … so that devices do not receive unintended data
	- … so that a compromised device does not expose the whole network
	- ... so not all devices can access all segments
- To make the network management easier
	- … because faults can be isolated more efficiently
- Allows for easier maintenance
- because only one subnetwork may need taking down/changing while the rest of the network can continue
- To make the network easier to expand // For better control of network growth
	- … by allowing for greater range of IP addresses to be available
  
# URL (Uniform Resource Locator) 
Syntax - Protocol://websiteaddress/path/filename
- Unique reference address for the exact location of an internet resource on the WWW 
- Protocol: enables browser to know what protocol is used to access info in domain 
- Hostname: Domain name 
- Location of server: path 
## Domain Name Service (DNS) 
- naming system used for computers or resources having internet connection 
- Consists of a hierarchy of DNS servers which have a URLs database of and their corresponding  IP addresses 
### Describe how the browser uses the Domain Name Service (DNS) to display the web page. 
- URL is a reference address to a resource on the Internet. 
- The URL is passed to the nearest Domain Name Server (by browser software). 
- DNS server stores a database / list of URLs and matching IP addresses. 
- DNS (Name Resolver) looks for the URL in its database. 
- Finds the matching IP address and returns it to the originator. 
- Or if it cannot find it, it forwards to another Domain Name Server at a higher level. 
- (Original) DNS server adds the returned IP address to its cache. 
- (Original) DNS server returns the IP address to the browser. 
### How a URL is converted into its matching IP address 
- URL is parsed to obtain the Domain name 
- Domain name is sent to the nearest Domain Name Server (DNS)  
- DNS holds a list of Domain names and matching IP addresses 
- DNS name resolver searches its database for the Domain name 
- If DNS does not find the Domain name, the request is forwarded to a higher level DNS  
- If the Domain name is found, the IP address is returned 
- If the Domain name is not found, the request is passed to a higher level server 
- If the Domain name is finally not found, an error message is generated