> For the complete documentation index, see [llms.txt](https://technobureau.com/llms.txt).
> Use it to discover all available pages before exploring further.
# Introduction to Computer Networks
A comprehensive guide to computer networks covering topology, nodes, devices, and data transmission fundamentals.
## What is a Computer Network?
A **computer network** (or data network) is a telecommunications network that allows computers to exchange data. In computer networks, networked computing devices pass data to each other along different data connections using encoding and decoding standards.
**Network Nodes** are devices that originate, route, and terminate data. They include hosts (PCs, phones, servers) and networking hardware (routers, switches).
### Network Applications
Access to World Wide Web and web-based applications.
Shared use of servers, printers, storage, and applications.
Email, instant messaging, video calls, and conferencing.
Computing resources across network to accomplish tasks.
## Network Packets
A **network packet** is a formatted unit of data carried by a packet-switched network. When data is formatted into packets, the bandwidth can be better shared among users compared to circuit-switched networks.
```mermaid
graph LR
A[Data] --> B[Segmentation]
B --> C[Packet 1]
B --> D[Packet 2]
B --> E[Packet 3]
C --> F[Header + Payload]
D --> G[Header + Payload]
E --> H[Header + Payload]
F --> I[Transmission]
G --> I
H --> I
I --> J[Reassembly]
J --> K[Original Data]
```
Contains control information: source/destination addresses, error detection codes, sequencing information.
The actual user data being transmitted between network nodes.
Optional footer containing error-checking data (CRC, checksum).
## Network Topology
**Network topology** is the arrangement of elements (links, nodes, etc.) of a computer network. It can be depicted physically or logically:
- **Physical Topology** - Placement of components, device locations, cable installation
- **Logical Topology** - How data flows within the network, regardless of physical design
### Common Network Topologies
All nodes connected to a common backbone cable. Used in early Ethernet (10BASE5, 10BASE2). Simple but single point of failure.
Here are each of the topologies split into standalone Mermaid diagrams (one per graph):
```mermaid
graph TB
A1[Node1] --- A2[Node2] --- A3[Node3] --- A4[Node4]
```
All nodes connected to a central hub/switch. Common in Wireless LANs and modern Ethernet. Easy to manage, hub is single point of failure.
```mermaid
graph TB
B1[Central Hub] --- B2[Node1]
B1 --- B3[Node2]
B1 --- B4[Node3]
B1 --- B5[Node4]
```
Each node connected to left and right neighbors. Used in FDDI. Data travels in one direction.
```mermaid
graph TB
C1[Node1] --- C2[Node2]
C2 --- C3[Node3]
C3 --- C4[Node4]
C4 --- C1
```
Nodes connected to multiple neighbors. Provides redundancy and fault tolerance. Expensive due to many connections.
```mermaid
graph TB
D1[Node1] --- D2[Node2]
D1 --- D3[Node3]
D1 --- D4[Node4]
D2 --- D3
D2 --- D4
D3 --- D4
```
Hierarchical arrangement of nodes. Scalable and easy to expand. Root node failure affects entire network.
```mermaid
graph TB
E1[Root] --- E2[Branch1]
E1 --- E3[Branch2]
E2 --- E4[Leaf1]
E2 --- E5[Leaf2]
E3 --- E6[Leaf3]
```
## Network Nodes and Devices
A **node** is a connection point, redistribution point, or communication endpoint in a network. Physical network nodes are active electronic devices capable of sending, receiving, or forwarding information.
### Network Device Types
```mermaid
graph LR
subgraph "Layer 1 - Physical"
A[Repeaters]
B[Hubs]
end
subgraph "Layer 2 - Data Link"
C[Bridges]
D[Switches]
end
subgraph "Layer 3 - Network"
E[Routers]
end
subgraph "Other Devices"
F[Modems]
G[Firewalls]
H[NIC Cards]
end
A --> C
C --> E
D --> E
F --> E
G -.-> E
H -.-> A
```
Network Interface Controller (NIC) provides physical connection to network. Has unique MAC address (6 octets) for Ethernet networks.
Receives, cleans, and regenerates signals to extend network distance. Works at Physical Layer (Layer 1).
Multi-port repeater. Broadcasts incoming data to all ports. Mostly obsolete, replaced by switches.
Connects and filters traffic between network segments at Data Link Layer (Layer 2). Types: Local, Remote, Wireless.
Forwards and filters Layer 2 datagrams based on MAC addresses. Learns MAC-to-port mappings. More efficient than hubs.
Forwards packets between networks using Layer 3 (IP) addresses. Uses routing tables for path determination.
Modulates/demodulates signals for transmission over analog media (telephone lines). DSL technology example.
Controls network security and access rules. Rejects unauthorized access while allowing recognized sources.
## OSI Model and Device Layers
```mermaid
graph TB
subgraph "Application Layers"
A7[Layer 7 - Application]
A6[Layer 6 - Presentation]
A5[Layer 5 - Session]
end
subgraph "Transport Layers"
A4[Layer 4 - Transport]
end
subgraph "Network Layers"
A3[Layer 3 - Network
Routers]
A2[Layer 2 - Data Link
Switches, Bridges]
A1[Layer 1 - Physical
Hubs, Repeaters, Cables]
end
A7 --> A6
A6 --> A5
A5 --> A4
A4 --> A3
A3 --> A2
A2 --> A1
```
Understanding which layer each device operates at helps in troubleshooting network issues and designing efficient network architectures.