Network Layers & Terminology

Before diving into protocols and models, you need to understand the basic vocabulary and concepts of networking.

Network Layers Concept

Networks operate in layers — each layer builds on the one below it. Think of it like building — you need a foundation before walls, and walls before a roof.

Why Layers?

• Separation of concerns — each layer has a specific job
• Modularity — you can understand one layer without knowing all details of others
• Standards — different vendors can implement layers differently, but they still work together

Key Network Terminology

1. Node Any device connected to the network:

• Servers, computers, phones, IoT devices, routers, switches
• Identified by an IP address

2. Host An active device that participates in network communication:

• Has an IP address assigned
• Can initiate or respond to network requests
• Examples: Web server, laptop, database server

3. Link/Network Link The connection between two nodes:

• Can be physical (Ethernet cable) or wireless (WiFi)
• Operates at Layer 1 (Physical Layer)

4. Network Segment A group of devices connected together:

• Shares the same network address prefix
• Can be local (LAN) or wider (WAN)

5. End-to-End Communication The path from a source node to a destination node:

• May pass through multiple intermediate nodes (routers, switches)
• Each layer adds its own headers (encapsulation)

Network Topologies

The physical or logical arrangement of network nodes:

Star Topology

• All nodes connect to a central hub or switch
• Common in modern networks
• If hub fails, entire network goes down

Mesh Topology

• Every node connects to every other node
• Highly redundant but expensive
• Used in critical systems

Ring Topology

• Nodes form a circle; data flows one direction
• Older technology; rarely used today

Bus Topology

• All nodes share a single communication line
• Simple but has limitations
• Rarely used in modern networks

Tree Topology

• Hierarchical arrangement with a root and branches
• Common in enterprise networks

Bandwidth vs. Latency

Bandwidth

• How much data can flow through a connection per unit time
• Measured in bits per second (bps): Kbps, Mbps, Gbps
• Think of it like a pipe's width

Latency

• The time it takes for data to travel from source to destination
• Measured in milliseconds (ms)
• Think of it like how long it takes water to flow through a pipe
• Lower latency is better

Throughput

• The actual amount of data successfully transmitted
• Often less than bandwidth due to overhead, retransmissions, etc.

Network Types

LAN (Local Area Network)

• Limited geographic area (building, office)
• High bandwidth, low latency
• Usually managed by one organization

WAN (Wide Area Network)

• Large geographic area (multiple cities, countries)
• Lower bandwidth, higher latency
• Often uses public/rented infrastructure

MAN (Metropolitan Area Network)

• Intermediate size (city)
• Bridges LAN and WAN concepts

Packets and Encapsulation

Packet

• Unit of data transmitted across a network
• Contains:
  • Header — source/destination addresses, protocol info
  • Payload — actual data being transmitted
  • Trailer/Footer — checksums for error detection

Encapsulation

• Process of wrapping data with protocol-specific headers
• Each layer adds its own header:
  • Application layer: HTTP header + data
  • Transport layer: TCP/UDP header + application data
  • Network layer: IP header + transport data
  • Link layer: Ethernet header + network data

Network Interfaces

NIC (Network Interface Card)

• Physical or virtual hardware that connects a device to a network
• Each NIC has a unique MAC address
• Can have multiple NICs (multi-homed device)

Virtual Network Interface

• Software-based network interface (no physical hardware)
• Used in containers, VMs, cloud environments
• Functions the same way as a physical NIC

Key Concepts to Remember

• Networks operate in layers for modularity and standards
• Nodes are devices; hosts are active devices
• Bandwidth is capacity; latency is delay; throughput is actual data rate
• Encapsulation wraps each layer's data with its own headers
• Understanding terminology lays the foundation for all networking knowledge