Information Technology: Network Basics and Communication Systems

A network is broadly defined as a system that links things together. In technology, a communication network (also known as a communication system) specifically links devices so that data and information can be shared among them.
As a network user, it is essential to consider the concept of control, which directly affects your personal privacy and security.
In 1948, Claude Shannon, an engineer at Bell Labs, published a landmark article describing a communication system model. This model is applicable to networks of all types and illustrates the essential components and functions of a network.

Networks are classified based on their size and geographic scope. The primary categories include PAN, LAN, and WAN.
PAN (Personal Area Network):
- Connects smart devices or consumer electronics within a very short range, typically about $30\,\text{feet}$ ( $10\,\text{meters}$ ).
- These networks generally do not use wires or cables.
- The term "personal" emphasizes that the network serves a single individual rather than multiple users.
LAN (Local Area Network):
- These are data communication networks that connect personal computers within a very limited geographical area, such as a single building.
- Common examples include school computer labs, home networks, and in-house networks operated by most businesses.
- Public Wi-Fi networks found in airports and coffee shops are also classified as LANs.
WAN (Wide Area Network):
- Covers a large geographical area and often consists of several smaller networks.
- These smaller networks might utilize different computer platforms and various network technologies.
- The Internet is the world’s largest WAN.
- Other examples of public WANs include telephone systems, cable television systems, and satellite-based communication systems.

A communication channel is the specific medium used to transport information from one network device to another. These are categorized into wired and wireless channels.
Wired Channels: These transport data through physical wires and cables. Examples include:
- Twisted pair wires: Used for traditional telephone landlines.
- Category 6 cables: The standard used for most modern LANs.
- Coaxial cables: Used primarily for cable television networks.
- Fiber-optic cables: Used for high-capacity trunk lines.
Wireless Channels: These transport data from one device to another without the use of physical cables. The most common methods are:
- Radio Signals (RF signals): Most wireless networks transport data as radio waves. These are sent and received by transceivers.
- Microwaves: These are electromagnetic signals that can be aimed in a single direction. They have more carrying capacity than standard radio waves and are typically used for large corporate network installations (not to be confused with microwave ovens).

Wired Connections:
- Pros: Highly secure because a device must be physically connected to join the network. They are reliable because carrying capacity and speed are not affected by interference from weather (rain, snow) or other electrical devices. Cables can be protected from damage using shielding and strong outer covers.
- Cons: Mobility is limited for tethered devices. Installation in WANs is costly due to the need for poles or burying cables underground. Cables can be unsightly, tangle easily, and collect dust. Running them through walls or floors is challenging. They can also carry electrical surges (sudden increases in power) that may damage equipment.
Wireless Connections:
- Pros: Provide mobility for laptops, tablets, and handheld devices. There are no unsightly cables. They are less susceptible to power spikes compared to wired systems.
- Cons: Generally slower than wired connections. The range is limited/weakens when passing through walls or obstacles. They are easier to hack if not properly protected. Some wireless frequencies require legal licensing to use.

Bandwidth refers to the transmission capacity of a communication channel.
Broadband: Network channels capable of moving at least $25\,\text{megabits}$ of data per second ( $25\,\text{Mbps}$ ).
Narrowband: Channels that operate at speeds slower than $25\,\text{Mbps}$ .

Topology refers to the structure and layout of network components, including computers, cables, and wireless signal paths.
Star Topology: Connects multiple devices to a single central device.
Mesh Topology: Connects multiple devices to each other. This can be a full mesh (all devices connected to all others) or a partial mesh.
Bus Topology: A less popular configuration where devices are connected in a linear sequence.

Any device connected to a network is called a node. These are classified as either DTE or DCE.
DTE (Data Terminal Equipment): Any device that stores or generates data.
DCE (Data Communication Equipment): Devices that manage the network's operation, including:
- Controlling data speed.
- Converting signals (e.g., from cable to wireless).
- Checking for corrupted data.
- Routing data to its specific destination.
Specific Network Devices:
- Router: Controls the flow of data within a network and acts as a gateway to pass data between different networks (e.g., home network to the Internet) using IP addresses.
- Modem: Converts data-carrying signals from a digital device into signals that can travel over various communication channels.
- Hub: Connects multiple devices in a network by broadcasting data to all connected devices, which can cause unnecessary traffic.
- Switch: Connects devices in a network more efficiently than a hub by using MAC addresses to send data only to the intended device.
- Bridge: Connects two network segments and reduces traffic by filtering based on MAC addresses.
- Repeater: Extends the distance of a signal by regenerating or boosting weak signals over long distances.
- WAP (Wireless Access Point): Provides Wi-Fi access to a wired network, acting as a bridge between wireless devices and the wired infrastructure.

A communication protocol is a defined set of rules for efficiently transmitting data between network nodes. This interaction process is called handshaking.
A collection of protocols used by a network is known as a protocol stack.
Types of Protocols:
- Physical Protocols: Specify the cable and signal standards for the channels used to carry data.
- Transport Protocols: Ensure data reaches its destination by establishing standards for dividing data into chunks, assigning addresses, and performing error correction.
- Arrival Protocols: Convert data into standard formats for use by applications like email, web browsers, and Skype.
Error Correction: This is a primary responsibility of protocols. Digital networks monitor signals to determine if interference has corrupted data, allowing for corrections to be made.