Chapter 2: Communications

Devices that are inter-connected and communicate between each other.

- Easily transfer data, like files between devices
- Devices can share resources, such as hardware, printers, or same software
- Store data in drives connected to the network

Local Are Network (LAN) and Wider Area Network (WAN)

- Small geographical region
- Private ownership
- Wi-Fi, Copper, and Coaxial mediums
- High speed
- Low congestion

- Large geographical region
- Private/Public ownership
- PSTN or satellite mediums
- Low speed
- High congestion

The server stores all the data and performs the tasks requewsted by the client

client (sends request) --> server (returns results) --> client (receives results)

e.g:
- web pages
- emails
- company storing files on central server
- print/file/email server

Pros:
- Increases security as only the server has higher privileges
- Increased performance of individuals computers
- Central management of data and software so there is always a backup and each device has consistent software
Cons:
- All operations depend on the main server, if server is down then the others are down too
- Difficult to scale and expensive
- Speed of networks decreases exponentially based on the number of devices connected.

Provides input to the server and receives an output from the server

Carriest out some processing on its own before/after sending/receiving data to the server

All devices on the netwrok are of equal status, each computer has access to all the data and resources of another device, thus each device is responsible for its own safety.

Pros:
- Setup cost is cheap
- Each device has complete access to any device on t he network
- No central server dependancy
Cons:
- Reduced security, vulnerable to viruses from other devices on the network
- Reduced performance, other devices might also be attempting to access data on a device.
- No central backup of files, if one computer has data and loses it, they all lose access to it.

The way devices are connected on a network:
- Bus
- Star
- Mesh
- Hybrid

All devices connected to a central cable, has terminators at the end
- Only onecommunication can take place at a time
- Data terminators are needed to prevent a network crash from data collision

All devices connected to a switch / router independantly
- No collisions can occur and data can be sent out simultaneously
- You can use hub instead of switch but its slower

All devices on a network are connected to each other
- The internet itself is an example of mesh topology

A combination of topologies used together

Applications and services that deliver over the internet. A third party hosts the data for the user that they can then use. Can exist for public, where it can be used by anyone online, and private use, where it is made specifically for use by a company

Pros:
- Free for small quantities
- Can access data from anywhere if you have internet
- Likely better security and recovery options
Cons:
- Internet access is required to acces it
- Long upload and download time limits access to data
- No control over security and backups

- Wired
- Twisted pair / Copper cable
- Fiber-optic cable
- Wierless
- Radio waves
- Micro waves
- Satellites

Twisted pair of copper wires that carry data as electrical signals

Glass/Plastic cables that rely on total internal reflection to transmit data as light

- Slow
- Travels short distances; needs repeaters
- Higher risk of interference
- Less safe (lower security)
- High durability
- Low price

- Fast
- Travels long distances
- Low risk of interference
- Safe (better security)
- Low durability
- High price

An electromagnetic wave that carries data wirelessly; Wi-Fi

An electromagnetic wave that is used to communicate with satellites

A communication device that orbits the Earth and sends / receives data

- Cheap
- Other radio waves are its obstacles
- Travels long distances
- Lower size

- Expensive
- Physical objects are its obstacles
- Travels shorter distances
- High size

- Expensive
- High risk of obstacles
- Travels long distances
- High size

- Switch
- Server
- Network Interface Card (NIC)
- Wireless Network Interface Card (WNIC)
- Wireless Access Point (WAP)
- Cables
- Bridge
- Repeater

Connects all devices on a network and simultaneously brodcasts information to those devices

A specialized high-speed computer that handles requests from clients or other computers on the network

- A hardware component that provides each device a unique MAC address so that it can be identified on a wrieless network.
- It provides an interface by acting as an antenna to a Wi-Fi network. It receives analogue radio waves that it decodes and converts into digital data, and it sends signal data, that it encrypts and converts into analogue waves, via the antenna.
- It checks incoming transmissions to check if they match the device's IP / MAC address and ignores them if they're not.

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

Hardware component that provides radio communication from the central device to nodes on the network (and vice versa)

• To receive packets from devices or the Internet
• To forward / route packets to the destination
• To find the destination of the packet
• To assign / allocate private IP addresses to devices on LAN
• To store / update / maintain a routing table
• To find the most efficient path to the destination
• To maintain a table of MAC and IP addresses

Physical means of sending and receiving data on a network

A device that interconnects two or more LANs together and forwards data packets

Restores the digital signal so it can be transmitted over greater distances

Receives and sends data between two networks operating on the same protocol
- Can be used to segment a network

- Maintain a table of MAC and IP addresses
- Assign private IPs to a device on a network
- Routes packets to their destination but doesn not direct packets to each device attached to it
- To receive packets from devices or the Internet

The most common form of wired connection used in LAN and WAN that is based on Bus topology.
- Due to this it is possible for data collisions to occur, hence a Carrier Sense Multiple Access / Collision Detection (CSMA/CD) is used.

-A workstation listens to the communication channel, when it receives a request first it will check if the line is empty, if empty sends data.
-- If a collision occurs because both devices checked if the line was empty at the same time, then the workstation will send an abort signal and the data will be sent back.
--- And a random wait time is assigned to each device before resending

- Faster
- More stable
- More secure
- Restricted movement
- High cabling
- Difficult to expand

- Slower
- Less stable
- Less secure
- Free movement
- Less cabling
- Easy to expand

- Modem
- Public Switch Telephone Network (PSTN)
- Dedicated lines
- Cell phone network

A device that allows users to connect to the internet via telephone line; converts analogue signals into digital signals.

Full duplex form of communication over wire via circuit swtiching that remains active during power outages

A permanent connection for communication that is expensive but faster and more secure/consistent

A wireless connection that relies on mobile connection and cell towers that use radio waves

- A video is compressed and is then sent as a continuous stream of bits. When it is downloaded the server sends the data to the buffer which then sends a continuous stream of data to the user
- Higher bit-rate speed and broadband speed means users can stream the video faster and with less buffering

- Real time
- On demand

Used when watching a live stream of events that are currently taking place. The event is captured live with a video camera connected to a computer, and it cannot be paused or rewound.

Used when watching an event that has taken place in the past. Existing media are encoded to bit streaming format and uploaded to a server. It can be paused and rewound.

• Temporal - Sequence of consecutive pixels have the same value on a frame
• Spatial - Sequence of consecutive pixels between frames have the same value

A collection of websites that are available on the internet. When you access a website, you are using both the internet and the world wide web because the website is stored on WWW but the internet provides the necessary infrastructure.

- The unique address that identifies a device a network and to allow router to send data from the internet to the device.
- It has two formats:
• IPv4
• IPv6

- 4 groups
- Group range: 0-255
- Separator = .
- Size is 32 bits
- Example : 192.168. 1.1

- 8 groups
- Group range = 0-65535
- Separator = :
- Size is 64 bits
- Example : fe80:d4a8:6435:d2d8:d9f3b11

- Public
- Private
- Static
- Dynamic

Assigned by the IP visible on the internet, must be unique on the internet.

Only the router has a public IP address, devices on the netwrok do not as all data passes through the router, which also protects the device from external threats.

Assigned by the router that is visible to devices on the network, must be unique on that specific network.

Remains constant, whenever a device connects to the internet. Webpages need Satatic IP addresses so the DNS does not need to be updated everytime which can cause delays and errors.

A new IP address is allocated every time a device connects to the internet.

Dividing a network into smaller groups

- Reduces traffic
- More secure

Uniform Resource Locator, easier way to remember IP addresses for websites.
- e.g, Duck.com = 52.250.42.157, Google.com = 2a00:1450:4019:80c::200e

Domain Name Server, the DNS looks up the URL within a table, if it finds the corresponding IP address, it's then returned to the client. If it's unable to find it, the request is forwarded to a higher DNS.