INTRODUCTION TO CLIENT SERVER | CLIENT SERVER MODEL (REPORTS)

Client-server model

A networking architecture where client computers request services or resources from a more powerful centralized server.

• Open applications

• Retrieve files

• Maintain consistency across devices

Client-server model enables multiple clients to?

LAN

more secure, local

WAN / Internet

broader access, but requires stronger security

Thin clients

rely heavily on server for processing

Thick clients

process data independently, minimal server assistance

Hybrid clients

handle local processing but use server for storage or heavy tasks

Database servers

host structured data like spreadsheets, accounting records etc.

Application servers

deliver apps without requiring local installation

Web servers

facilitate client access to web content

Computing servers

provide extra processing power or storage

Web proxy servers

act as intermediaries between user and browser

DNS servers

translate domain names to IP addresses

One Tier

Everything runs on a single device no network is needed and minimal traffic

Two Tier

Client handles GUI, server hosts business logic and often built using Java or C++

Three Tier

Split across:

Presentation layer (UI)

Application layer (processing/services)

Data layer (database)

N Tier

Multiple layers across different machines, for better scalability and separation of concerns, can be open (free communication) or closed (strict layer hierarchy)

Centralization

o Easier updates and access management

o Reduced network redundancy

Enhanced Security

o Central point for enforcing cybersecurity

o Simplifies backups and data protection

Scalability

o Horizontal scaling: add more servers to distribute load

o Vertical scaling: enhance server capabilities with more RAM or stronger hardware

Accessibility

o Secure remote access with proper credentials

o Supports remote working

Improved Management

o Streamlined data tracking

o Coordinated updates and feature deployment

o Simultaneous handling of multiple requests

o Lower maintenance costs

Single Point of Failure

If the server goes down or experiences downtime, all clients lose access to the web application.

Single Point of Failure

This can lead to service disruptions and negatively impact user experience.

Server Overload

High traffic or many client requests at the same time can overload the server.

Server Overload

This results in slow response times, crashes, or unavailability

Scalability Challenges

Scaling a traditional client-server setup requires adding more resources (hardware, servers, etc.).

Scalability Challenges

This can be costly and complex to implement, especially for rapidly growing web applications.

Security Risks

The server is a central target for cyberattacks (e.g., DDoS attacks, data breaches).

Security Risks

Sensitive data in transit between client and server can also be intercepted if not encrypted

Social Media (Facebook, Instagram, TikTok)

Client (app/browser) — sends request for posts/messages

Server — processes request and sends back feed, notifications, or messages.

E-commerce (Shopee, Lazada)

Client (Shopee app) — searches for an item Server — returns product list, prices, and stock info.

Online Banking

Client (banking app) — login request

Server — verifies credentials and sends account info.

Gaming (Mobile Legends, Valorant)

Client (game app) — sends player actions (move, attack)

Server — processes actions and updates the game for all players

Cloud Computing

Data and apps stored in cloud servers (Google Drive, iCloud, Dropbox)

Microservices

Systems split into smaller services (Netflix - one service for recommendations, another for video streaming, another for payments)

Mobile & IoT Growth

More devices (phones, smartwatches, smart home devices) acting as clients.

Request services and display information

What is the main function of the client in a client–server model?

Servers are central targets for cyberattacks

Why is security a challenge in the client–server model?

If there is no server to process client requests in a web application, the application will fail to function properly.

What will happen if there is no server to process client requests in a web application?

HyperText Transfer protocol (HTTP)

It is the foundational protocol used by the World Wide Web browsers (clients) and web servers.

HyperText Transfer protocol (HTTP)

developed by Tim Berners-Lee and his team between 1989-1991

HyperText Transfer protocol (HTTP)

It started as a simple protocol for sharing files in a lab and evolved into flexible system that powers today’s rich web content like images, videos, and 3D media

HTTP 0.9

1991 was the first simple version, supporting only basic web page requests

HTTP 1.0

1996 added headers and status codes for better communication

HTTP 1.1

1997/1999 improved speed with persistent connections and caching

HTTP 2.0

2015 made web pages load faster by allowing multiple requests at once

HTTP 3

uses Google’s QUIC protocol to enhance speed and reliability on modern networks.

HTTP Methods

instructions that tell a web server what action the client wants to perform on a resource

GET “Give me this resource“

Used to request data from a server without changing anything

POST “Here’s some data, please process it“

Used to send data to the server, usually to create something new

PUT “Update this resource with my data“

Used to update existing data on the server

DELETE “Remove this resource“

Used to delete specified resource from the server

HEAD “Retrieves“

Like GET, but only returns headers, not the body

OPTIONS “Check responsibilities“

its like checking what you’re allowed to do before you actually do it

TRACE “Debug“

is used for diagnostic purposes

It asks the server to send back the exact HTTP request it received, so the client can see how the request looks when it reaches the server

CONNECT “Open a tunnel“

used to establish a network tunnel to a server, typically for secure HTTPS connections through a proxy

Status code

This is a 3-digit number that tells your browser whether the request was successful, failed, redirected, or had some other issue

1xx

Informational

The request was received, and the process is contuining

100 Continue

Server says “keep sending your request“

2xx

Success

the request worked as expected

200 OK

Success everything went well

3xx

Redirection

The resource has moved; the client should try another location

301

Moved permanently

4xx

Client errors

Something went wrong with the request from the client side

404 Not Found

The requested page doesn’t exist

5xx

Server Errors

the server failed to fulfill a valid request

500 Internal Server Error

Something went wrong on the server

HyperText Transfer Protocol Secure (HTTPS)

the secure version of the HTTP, the standard communication protocol used for transferring data between a web browser(client) and a web server

HyperText Transfer Protocol Secure (HTTPS)

establishes the communication between the browser and the web server

Secure Socket Layer (SSL) and Transport Layer Security (TLS)

HTTPS uses the ___________ and ____________ protocols for establishing the communications.

Transport Layer Security (TLS)

newer version of the SSL

HyperText Transfer Protocol Secure (HTTPS)

It keeps the information on websites safe from being easily viewed or stolen by anyone who might be spying on the network.

Secure Socket Layer (SSL)

Ensures that the data transfer between the communicating systems is secure and reliable.

Secure Socket Layer (SSL)

It is the standard security technology that is used for encryption and decryption of data during the transmission of requests.

Transport Layer Security (TLS)

A protocol that secures communication on the internet by encrypting data, authenticating websites, and ensuring that information is not altered during transmission.

Secure Communication

Data Integrity

Privacy and Security

Faster Performance

Advantages of HTTPS

Secure Communication

HTTPS establishes a secure communication link between the communicating system by providing encryption during transmission.

Data Integrity

By encrypting the data, HTTPS ensures data integrity. This implies that even if the data is compromised at any point, the hackers won't be able to read or modify the data being exchanged.

Privacy and Security

HTTPS prevents attackers from accessing the data being exchanged passively, thereby protecting the privacy and security of the users.

Faster Performance

TTPS encrypts the data and reduces its size. Smaller size accounts for faster data transmission in the case of HTTPS.

HyperText Transfer protocol (HTTP)

URL begins with "http://".

HyperText Transfer protocol (HTTP)

Works at the Application Layer

HyperText Transfer protocol (HTTP)

speed is faster than HTTPS

HyperText Transfer Protocol Secure (HTTPS)

URL starts with "https://".

HyperText Transfer Protocol Secure (HTTPS)

works at Transport Layer

HyperText Transfer Protocol Secure (HTTPS)

speed is slower than HTTP

TCP/IP (Transmission Control Protocol/Internet Protocol) model

a conceptual framework used to understand and design how data is transmitted over a network, especially the Internet.

TCP/IP (Transmission Control Protocol/Internet Protocol) model

It defines how computers communicate by breaking down the communication process into layers, each with specific functions.

TCP/IP (Transmission Control Protocol/Internet Protocol) model

create a robust, fault-tolerant communication system that could survive even if parts of the network failed

TCP/IP (Transmission Control Protocol/Internet Protocol) model

was developed from real-world networking experiments, making it easier to implement.

Application Layer

Provides services and applications for the end user (e.g., web browsing, email, file transfer).

Application Layer

OSI Equivalent: Combines Application + Presentation + Session layers of OSI

Transport Layer

Ensures reliable communication between devices. Handles error checking, data segmentation, and flow control.

TCP (Transmission Control Protocol)

Reliable, connection-oriented

UDP (User Datagram Protocol)

Fast, connectionless, but no guarantee of delivery.

Internet Layer

Determines how data is addressed and routed across networks. Ensures packets find the correct destination.

Internet Layer

OSI Equivalent: Network Layer

Network Access Layer (or Link Layer)

Deals with the physical transmission of data on the network. Defines how data is formatted into frames and transmitted over hardware like Ethernet, Wi-Fi, etc.

Network Access Layer (or Link Layer)

OSI Equivalent: Data Link + Physical Layers