Introduction to Networking
A network is a group of interconnected devices that can send and receive data. This guide covers the history of the internet, core networking components, topologies, the OSI and TCP/IP models, reliable network design, and current trends.
Overview
A network is a group of interconnected devices that can send and receive data. Network Architecture refers to the technologies that support infrastructure protocols that move data across the network.
A large group of interconnected networks that spans the globe, enabling communication between billions of devices.
The collection of pages, multimedia, and documents residing on computers connected to the internet. If the internet is the plumbing, the web is the water.
Brief History of the Internet and World Wide Web
1973 — ARPANET: The first computer network, created by the US Defence Advanced Research Projects Agency, using the TCP/IP Protocol Suite.
1989 — World Wide Web: Tim Berners-Lee proposed the WWW at CERN in Geneva, connecting pages through hyperlinks and the HTTP protocol.
1989–1993 — Commercial ISPs: Dial-up ISPs such as AOL brought the internet to the public. The Mosaic browser arrived in 1993.
1994–1995 — Browser Wars: Netscape (1994) and Internet Explorer (1995) launched, kicking off the Web 1.0 era.
Life Noggin. (2014). History of the Internet. YouTube. https://youtu.be/h8K49dD52WA
CrashCourse. (2017). The Internet: Crash Course Computer Science #29. YouTube. https://youtu.be/AEaKrq3SpW8
Networking Components
Hosts (End Devices / Nodes)
An end device (or node) is where a message originates or is received — a switch, router, or computer. Every computer on a network can be a host, acting as either a server or a client.
Provide information. A web server delivers documents to other computers on request and runs continuously, waiting for new requests.
Request information. A web browser is a client that requests web pages from a server and renders them for display.
Intermediary Network Devices
Intermediary devices interconnect end devices, manage data flow, regenerate signals, maintain pathway information, and notify other devices of errors. Routers, switches, wireless routers, and firewalls are all intermediary devices.
Network Media
- Metal Wires
- Copper, Cat5, or Cat6 cables transmit data as electrical impulses.
- Fiber Optics
- Transmit data in the form of light pulses, offering higher bandwidth over longer distances.
- Radio Frequency (Wireless)
- Transmit data as electromagnetic waves; used by Wi-Fi and cellular networks.
- Infrared
- Short-range wireless transmission using infrared light.
Ethernet Connections
Connects devices of the same type (e.g. computer-to-computer, switch-to-switch).
Connects devices of different types (e.g. computer-to-switch, switch-to-router).
Ethernet Standards
1000BASE-T— supports up to 1,000 Mbps (Gigabit Ethernet)100BASE-T— supports up to 100 Mbps10BASE-T— supports up to 10 Mbps
Devices on a shared Ethernet segment are identified by Layer 2 MAC addresses. Any device can send a frame to all others (broadcast). A collection of devices on shared media is called a Local Area Network (LAN).
Network Topologies & Representations
A network's structure can be described through physical and logical diagrams — analogous to road maps vs. traffic-flow maps. Physical diagrams show where devices are located; logical diagrams show IP addresses, ports, and routing information.
PowerCert Animated Videos. (2018). Network Topologies. YouTube. https://youtu.be/zbqrNg4C98U
| Topology | Advantage | Disadvantage |
|---|---|---|
| Mesh Every host connected to all others. Can be full or partial mesh. |
Good redundancy; if one node fails others are unaffected. Popular for IoT and smart-home devices. | Requires many connections; can be inefficient on large networks. |
| Ring Adjacent hosts connected in a circle. Legacy topology. |
Data flows in one direction, reducing packet collision. Suitable for small networks. | If any host disconnects, the ring breaks. Not common in modern networks. |
| Star Central device connects all others. |
Common today; provides a central point of administration. | Single point of failure — if the central device fails, the whole network fails. |
| Hybrid Combination of two or more topologies. |
Increased flexibility, fault tolerance, and easy expansion. | Can inherit the weaknesses of the topologies it combines. |
| Tree Bus network of star networks. Stars connected to a main bus. |
High scalability and fault tolerance. Easier to identify faults. | Requires extensive cabling. Hub failure can take down entire segments. |
| Bus All nodes connected to a single main cable. |
Efficient for small networks. Requires less cable and is cost-effective. | Many points of failure; not suitable for larger networks. |
Common Network Types
PowerCert Animated Videos. (2018). Network Types: LAN, WAN, PAN, CAN, MAN, SAN, WLAN. YouTube. https://youtu.be/4_zSIXb7tLQ
| Network Type | Description |
|---|---|
| LAN (Local Area Network) | Covers a small or limited area (e.g. home or office). High-speed connections, single administration. May have gateways to a WAN. |
| WAN (Wide Area Network) | Covers a wide geographical area; typically administered by multiple service providers; generally slower than LAN. WANs can be made up of interconnected LANs. |
| VPN (Virtual Private Network) | Method of connecting to a private network through an insecure network (the internet). |
| VLAN (Virtual LAN) | Extension of traditional LAN; groups devices based on administrator-defined boundaries such as departments or floors. |
| WLAN (Wireless LAN) | Connects multiple wireless devices using access points. |
| MAN (Metropolitan Area Network) | Spans a city, connecting city infrastructure. |
| PAN (Personal Area Network) | Commonly uses Bluetooth-connected personal devices. |
| WMN (Wireless Mesh Network) | Connects multiple wireless access points together to expand wireless coverage. |
| Small Home | A few PCs connected to each other and the internet. |
| SOHO (Small Office / Home Office) | Home PC connected to a corporate network via DSL, cellular, or satellite. |
| Other Types | CAN (Campus Area Network), SAN (Storage Area Network), EPN (Enterprise Private Network), POLAN (Passive Optical LAN). |
Network Models & Perspectives
A network model defines how and where resources are shared and how access to those resources is regulated.
Concerned with how devices are interconnected across a network for data flow.
Concerned with a layered model (like the OSI model) where each layer sits above or below another.
Decentralised — each device acts as both client and server. No central authority.
Centralised host provides services (web server, mail server) to client devices.
Modern networks carry multiple services — voice, data, and video — over a single infrastructure using the same standards and rules. This convergence simplifies management and reduces cost.
Packet Switching vs. Circuit Switching
Circuit switching (traditional telephone): two nodes establish a dedicated channel before communicating. If the chain of connections is saturated, the call cannot be placed.
Message switching (early internet): messages are routed node-by-node; each node chooses the next hop. Replaced by packet switching for efficiency.
Packet switching (current internet): binary messages are divided into fixed-length packets, each carrying destination address and length. Packets may take different paths and arrive out of order; the receiver reassembles them. This guarantees message acceptance even under partial network failure.
Source: The Power of Algorithm, Springer — Chapter 5.2 (Ausiello & Petreschi)
CrashCourse. (2017). Computer Networks: Crash Course Computer Science #28. YouTube. https://youtu.be/3QhU9jd03a0
Network Layers
Computers communicate by structuring data using networking models. The OSI model and TCP/IP model are the two primary reference frameworks.
Both are layered architectures with similar functionality. OSI has 7 layers and separates services, interfaces, and protocols clearly and is protocol-independent. TCP/IP has 4 layers, does not clearly separate these concerns, and is protocol-dependent. OSI supports a vertical approach; TCP/IP supports a horizontal approach.
| Layer # | Example Protocols | OSI Model | TCP/IP Model | PDU |
|---|---|---|---|---|
| Layer 7 | FTP, HTTP/S, SMTP, SSH, SNMP, DHCP, RTP, DNS; Modbus, BACnet, OpenADR | Application | Application | Data |
| Layer 6 | Compression & encryption protocols (TLS, SSL) | Presentation | ||
| Layer 5 | NFS, SQL, SMB, RPC, SIP, H.323 | Session | ||
| Layer 4 | TCP (reliable), UDP (fast) | Transport | Transport | Segment |
| Layer 3 | IP (IPv4, IPv6), ARP, IGMP, ICMP | Network | Internet | Packet |
| Layer 2 | Ethernet, LAN, WAN, UTP cables (Cat5/6), DSL, Fiber Optic | Data Link (LLC & MAC) | Network Access | Frame |
| Layer 1 | Physical | Bits |
Layer Responsibilities at a Glance
- Layer 7 (Application): Actual data to be transferred — email content, file download, webpage.
- Layer 6 (Presentation): Encryption, compression, serialisation, encoding/decoding.
- Layer 5 (Session): Tracks ongoing conversations; opens/closes sessions; manages tunnels.
- Layer 4 (Transport): Breaks data into chunks; detects successful receipt; routes to correct application.
- Layer 3 (Network): Routes between networks using IP addresses; ARP resolves IP to MAC.
- Layer 2 (Data Link): Local connections; MAC addressing (e.g. Ethernet).
- Layer 1 (Physical): Electricity in copper, light in fibre, radio waves in Wi-Fi.
Reliable Networks
A reliable network exhibits four key attributes: fault tolerance, scalability, quality of service, and security.
- Fault Tolerance
- Multiple paths for data transmission (packet switching). If one path fails, data reroutes automatically — unlike circuit switching which dedicates a single path. Example: backup routers.
- Scalability
- Allows additional devices to be added without degrading performance for existing users.
- Quality of Service (QoS)
- Prioritises time-sensitive traffic such as voice and live video over bulk data transfers. Routers with a QoS policy can manage and shape data flows accordingly.
- Network Security
- Addresses both physical security and information security. Three core goals: Confidentiality (data read only by intended recipient), Integrity (data not altered in transit), and Availability (timely, reliable access for authorised users).
A network that is highly available but insecure is not truly reliable. All four pillars must be addressed together.
Network Trends
Emerging trends shaping modern networking include:
Bring Your Own Device — employees using personal laptops, phones, and tablets on corporate networks.
Video communication platforms (Webex, Zoom) enabling distributed teams to collaborate in real time.
Storing, processing, and backing up data over the internet via data centres. Available as public (Gmail), private, or hybrid cloud.
IoT, Sensors, Ad-hoc, Software Defined Networking (SDN), LPWAN, WPAN/WBAN, Content Delivery Networks (CDN), cellular, and mobile networks are all reshaping how we think about network architecture.