Introduction to Networks

• Two or more computers or electronic devices are connected for communication.

• Can be connected by a wired medium (such as cables), or by a wireless medium (such as Wi-Fi)

• Stand-alone is A computer or device not connected to a network.

Examples of Devices Connected to a Network

• Desktop computers, laptops, smartphones, smartwatches, fitness trackers, car engine management systems, internet-enabled fridges, intelligent personal assistants, and media boxes.

Advantages of Using Networks

1. Software and File Sharing

• Users share software and files with other users.

2. Hardware Sharing

• Users share hardware, such as printers.

3. Communication

• Users communicate via email, chat, or video.

4. Roaming Access

• Users sign in to any computer on the network to access their files.

5. Centralised Maintenance and Updates

• Network managers can apply software updates across the network, removing the need for users to do so.

6. Centralised Security

• Anti-virus software and firewalls can be implemented across a network, protecting user files from risks.

7. User Monitoring

• Network managers can monitor what users do on a network.

8. Levels of Access

• Different users can be given different access rights, restricting or granting permissions as needed.

Disadvantages of Networks

1. Cost

• Additional equipment is needed to allow computers to communicate.

2. Management

• Larger networks require management by specialist staff, such as a network manager.

3. Spread of Malware

• Viruses and other forms of malware can easily spread across an improperly secured network.

4. Hacking

• Once a device is connected to another device, data may be accessed without the device owner's permission.

Local Area Networks (LANs) and Wide Area Networks (WANs)

• Two classifications of network.

Local Area Network (LAN)

- Geographically confined to a single site (e.g., small businesses, schools, homes).

- Connected by wired (cables) or wireless (Wi-Fi) mediums.

- Owned and maintained by the organization.

Wide Area Network (WAN)

- Spread over a wide geographical area, covering more than one site.

- Made up of two or more LANs.

- Used by organizations with multiple branches (e.g., banks) for communication and data sharing.

- Communication through national telephone infrastructures or wireless transmission.

- The internet is a massive, international WAN.

Wired and Wireless Connectivity

Wired Networks

• Use copper or fiber optic cables.

• Fiber optic cables provide greater bandwidth and faster transfer speeds.

Advantages of Wired Networks

- Faster data transfer.

- Less interference compared to wireless.

- Harder for unauthorized users to intercept data.

Disadvantages of Wired Networks

- Expensive installation and reconfiguration.

- Limited mobility for devices.

Wireless Networks

• Use radio signals or other methods like infrared light.

• Allow easy addition of new nodes and user mobility.

Advantages of Wireless Networks

- Easy addition of new nodes.

- User mobility without loss of connection.

Disadvantages of Wireless Networks

- Limited range.

- Susceptible to electromagnetic interference and obstacles.

- Bandwidth is shared among connected nodes, slowing communication with more nodes.

- Security risks due to potential interception; encryption is needed.

- Expensive installation and reconfiguration.

- Limited mobility for devices.

Network Data Speeds

• Measured in bits per second (bps).

• 1 Mbps = 1,000,000 bits per second.

• 1 Gbps = 1,000,000,000 bits per second.

Formula for Calculating Transmission Time

time = size of file (in bits) / network speed (in bits).

Protocols

• Rules that govern communication, including transmission speed, error checking, and addressing.

Network Protocols

Ethernet - Used in wired LANs.

Wi-Fi - Used in wireless LANs.

TCP/IP - Enables communication over the internet.

HTTP/HTTPS - Governs web server and client communication; HTTPS includes secure encryption.

FTP - Governs file transmission across a network and the internet.

Email Protocols

SMTP - Governs sending email to a mail server.

POP3/IMAP - Also known as Post Office Protocol and Internet Message Access Protocol; Governs retrieving emails from servers (IMAP is the newer standard).

Network Layering

Layering - Breaking up message sending into components/activities.

IP Addressing - Uses IPv4 (32 bits) and IPv6 (128 bits) for node addresses.

Four layers to be considered in a network:

Application Layer - Encodes/decodes messages (uses HTTP, FTP, SMTP).

Transport Layer - Breaks messages into packets, and assigns numbers for reassembly.

Internet Layer - Adds IP addresses for routing and is sometimes called the network layer.

Link Layer - Handles physical transfer of packets between nodes.

Packet Switching

- Breaking messages into packets for transmission.

Two parts of a packet:

Header - Includes sender/recipient IP, packet number, total packets, and protocol details.

Payload - Part of the message itself.

Network Topologies

• the arrangement, or pattern, in which all nodes on a network are connected together. The major network topologies are Bus, Ring, Star, and Mesh.

Node

• Any device connected to a network

• All nodes are connected to the network either by cables or wirelessly.

Bus Networks

• All nodes joined to a single cable. At each end of the cable, a terminator is fitted to stop signals reflecting back down the bus.

• Advantages: Easy and cheap to install.

• Disadvantages: Main cable failure disrupts the network, data collisions slow performance, and security risk.

Star Networks

• Nodes connected through one or more switches/hubs. The switch or hub acts as a central point through which all communications are passed.

• Hub: Broadcasts a message across the whole network.

• Switch: Sends the message to the intended recipient only.

• Advantages: Isolated node/link failure, easy addition of nodes, high performance.

• Disadvantages: Switch failure disrupts the network, expensive due to cabling.

Mesh Networks

• Nodes connected to multiple other nodes. There is no central connection point.

• Fully Connected Mesh: Every node is connected to every other node.

• Partial Mesh: Nodes connected to some, not all.

• Advantages: Reliable, multiple communication routes, simultaneous transmission/reception, easy node addition.

• Disadvantages: Expensive setup, high maintenance.

Mesh Topologies in Use

• Applications: Military, city monitoring, emergency services, utility companies, the internet.