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CS2033: Data Communication and Networks - Introduction

By Malindu — 2025-07-13

Understanding How Computers Talk: The Real Start of Networking

I used to think computers just magically sent stuff to each other. Like, I type a message, press send, and boom - it appears on the other side of the world. Done. Fast-forward to CS2033, and now I know it’s not magic. It’s engineering. Systems. Layers. Rules. Wires. And a whole bunch of clever tricks working together.

This article is my attempt to capture exactly what we covered in Lecture 0 of our Data Communication and Networks module. Think of it as that friend who goes, “Here’s what the slides really meant.” If you're just starting out and have zero clue about networks, you're in the right place.

1. What Is Communication?

At its core, communication is just sending information from one place to another. But when it comes to computers and electronics, it gets a bit more technical.

Imagine you're sending a text. You're basically:

  • Turning your message into electrical signals
  • Passing those signals through a physical medium (like a wire or air, if it's wireless)
  • Having the other side decode it back into readable data

That's communication - not with emotions, but with signals.

2. Types of Communication

Now, not all communication is the same. Here’s how it breaks down:

Based on Content Type

  • Video
  • Text
  • Voice
  • Data
  • Multimedia (mix of the above)

Based on Direction of Flow

  • One-way: Like watching a YouTube video. You get data, but you don’t send anything back.
  • Interactive (Non-Real Time): Think emails. You reply, but not instantly.
  • Interactive (Real-Time): Video calls, gaming - it's back and forth right now.

Based on Number of People

  • Two-party: Just two devices or users talking.
  • Multi-party: Group calls, online classrooms, multiplayer games.

3. What Is a Network?

A network is basically the system that makes all this communication possible.

It connects devices so they can exchange information. Examples?

  • PSTN: The classic landline telephone network
  • LAN (Local Area Network): Your home or school Wi-Fi
  • Television Networks
  • Vehicular Networks: Smart cars talking to each other
  • Internet: The biggest network of them all

A network isn’t just “computers talking” - it’s any system where data flows from A to B (or more).

4. Building Blocks of a Network

Let’s break a network down into parts:

  • Terminals: These are your endpoints - laptops, phones, servers, etc.
  • Switching Equipment: Routers, switches - devices that figure out where to send your data
  • Transmission Media: Cables, fiber optics, or air (if wireless). This is the “road” the data travels on.

5. The Big Challenge

Why is networking tricky?

Because devices are all different. They may have:

  • Different architectures (Intel vs ARM, Windows vs Linux)
  • Different languages (binary formats, encoding styles)
  • Different data formats (JPEG, MP4, DOCX)
  • Different communication rates (one device talks fast, another talks slow)

To make all of them work together, we need a common system.

6. The Solution: Layered Architecture

This is where things get smart.

Instead of one messy system doing everything, networking is designed in layers. Each layer has a specific job, and they all work together like a team.

Advantages?

  • You can change one layer without breaking the whole system
  • Testing becomes easier
  • Systems become modular and standardized

Two popular models that use this approach:

  • OSI Model (Open Systems Interconnection)
  • TCP/IP Model

For now, we’re focusing on the OSI model.

7. OSI Model: The Networking Cake

The OSI Model splits network communication into 7 layers. Each layer handles part of the job, and together they make data communication possible.

Here’s the idea:

You send a message. It goes down your OSI layers (application to physical), across the network, and then up the receiver’s OSI layers.

The 7 Layers Are:

  1. Physical
  2. Data Link
  3. Network
  4. Transport
  5. Session
  6. Presentation
  7. Application

Let’s look at each one like a nosy detective.

1. Physical Layer

This is the lowest layer. It deals with the actual hardware and signals.

  • What it does: Sends raw bits (0s and 1s) across a medium

  • How it does it: Using electrical pulses, light signals, or radio waves

  • Stuff it includes:

    • Cables and connectors
    • Network interface cards (NICs)
    • Wireless radios
    • Topology (how the network is physically arranged)

Think of this layer as the roads and wires.

2. Data Link Layer

Now we get a bit smarter.

  • What it does: Makes sure the message gets across one link without errors

  • Features:

    • Framing: Organizing raw bits into frames
    • Error Detection: Checking if bits got messed up in transit
    • Flow Control: Making sure data isn’t sent too fast
    • Addressing: At the hardware level (like MAC addresses)

3. Network Layer

Here’s where the actual routing happens.

  • Goal: Deliver packets from one host to another

  • Functions:

    • Logical Addressing: Who the packet is for (IP addresses)
    • Routing: Which path to take
    • Encapsulation: Wrapping data in packets
    • Congestion Control: Managing traffic jams
    • Quality of Service (QoS): Prioritizing data (e.g. video > email)

If the Data Link layer is the “street,” this is the GPS system.

4. Transport Layer

Now we go from host to host to application to application.

  • What it does: Ensures complete, reliable delivery of data

  • Tricks up its sleeve:

    • Connection setup and teardown (TCP)
    • Multiplexing: Multiple conversations over one line
    • Error checking
    • Flow control
    • QoS (again): Just like the Network layer, but finer control

This is where TCP and UDP live.

5. Session Layer

Honestly, this layer is like the forgotten middle child.

  • What it does: Manages sessions between apps

  • Helps with:

    • Dialog control (who speaks when)
    • Token passing
    • Sync points and recovery in case of failure

Modern systems often skip it or merge it with other layers.

6. Presentation Layer

Data goes through here for a quick wardrobe change.

  • Goal: Make sure sender and receiver understand each other

  • What it does:

    • Translation (e.g., EBCDIC to ASCII)
    • Compression
    • Encryption

In practice, these features are done at the app level, so this layer often isn’t separate.

7. Application Layer

Finally, the part we see.

  • Provides services like:

    • File transfers
    • Email
    • Browsing (HTTP, FTP, SMTP)
    • Messaging
    • DNS lookups

Apps use the network through this layer. This is your WhatsApp, Gmail, Chrome, etc.

8. OSI Model in Action

Here’s how it flows:

  • You write an email (Application Layer)
  • It gets formatted (Presentation Layer)
  • A session is started (Session Layer)
  • It’s sent across (Transport → Network → Data Link → Physical)
  • On the other side, it goes back up those layers in reverse

It’s like passing a secret message through seven layers of security and transformation.

9. What CS2033 Covers

Here’s what the course will focus on:

  • Physical Layer - in-depth (wires, signals, encodings, etc.)
  • Touches Data Link Layer - just enough to understand how to move beyond bits
  • Briefly introduces Network and Application Layers

You won’t get too deep into Transport or above layers this semester, but you’ll have a solid foundation to build on.

Final Thoughts

This lecture wasn’t just an intro - it was an eye-opener.

We now know that networking isn’t just cables and IP addresses. It’s a well-thought-out system with layers, standards, and logic.

If you ever feel lost, just remember: every bit that travels across the world goes through this journey. And now, so will you.

Let the networking begin.

References

  1. Lecture Slides: Rathnayake, S. CS2033: Data Communication and Networks - Lecture 0: Introduction. Department of Computer Science and Engineering, University of Moratuwa, 2025. (Developed based on original slides by Prof. Gihan Dias and Dr. Sulochana Suriyaarachchi)

  2. OSI Model Overview:

    • ISO/IEC 7498-1:1994. Information technology — Open Systems Interconnection — Basic Reference Model: The Basic Model.
    • Wikipedia contributors. OSI model. Wikipedia, The Free Encyclopedia. Accessed July 2025.

  3. TCP/IP Model and Layered Architecture Concepts:

    • Tanenbaum, A. S., & Wetherall, D. J. (2011). Computer Networks (5th ed.). Pearson.
    • Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson.

  4. Networking Fundamentals: