43 Diagrams Explain Computer Networks: Complete Visual Guide with PDF

Computer Network Overview

A computer network connects hosts, while the internet connects multiple networks, making it a network of networks. A computer network consists of three main parts: computers (clients and servers), network devices (routers, switches, firewalls), and transmission media (wired and wireless).

Internet Service Providers (ISP)

ISPs obtain IP addresses from internet management organizations, own communication lines and routing equipment, and provide internet access to individuals or organizations for a fee. The current internet has a multi-level ISP structure: backbone ISPs, regional ISPs, and local ISPs. Internet Exchange Points (IXPs) allow two ISPs to connect directly without a third ISP.

Host Communication Modes

1. Client-Server (C/S)

The client requests services; the server provides services.

2. Peer-to-Peer (P2P)

No distinction between client and server; each node can act as both.

Delay Components

Total delay = transmission delay + propagation delay + processing delay + queuing delay.

Computer Network Architecture

Three common layered models:

OSI: Application, Presentation, Session, Transport, Network, Data Link, Physical (7 layers)

Five-layer protocol: Application, Transport, Network, Data Link, Physical (5 layers)

TCP/IP: Application, Transport, Internet, Network Interface (4 layers)

Passband Modulation

Analog signals are continuous; digital signals are discrete. Passband modulation converts digital signals into analog signals for transmission over analog media.

Data Link Layer

Framing

Encapsulates network-layer packets by adding headers and trailers to mark frame boundaries.

Transparent Transmission

Ensures data appears as if the transmission medium does not exist; uses escape sequences to handle special bit patterns.

Error Detection

Widely uses Cyclic Redundancy Check (CRC) to detect bit errors.

Virtual LAN (VLAN)

VLANs create logical groups independent of physical location. Only members of the same VLAN receive broadcast traffic. For example, hosts A1–A4 in one VLAN receive broadcasts from A1, while other stations do not.

File Transfer Protocol (FTP)

FTP uses TCP at the transport layer and establishes two parallel TCP connections: a control connection (port 21) that stays open throughout the session, and a data connection (port 20) that closes after data transfer completes.

Common Port Numbers

Reference diagram listing well-known port numbers for common services.