Data Communications
Data Communications & Networks
Data communication is the process of transferring data from one device to another using a communication medium (wire or wireless).
Example: Sending a WhatsApp message from your mobile phone to another phone.
Components of Data Communication
There are five basic components of data communication:
| Component | Meaning | Example |
|---|---|---|
| Sender | Device that sends data | Computer, Mobile |
| Receiver | Device that receives data | Another computer |
| Message | Data to be sent | Text, Image, Video |
| Transmission Medium | Path for data | Cable, Wi-Fi |
| Protocol | Set of rules for communication | TCP/IP, HTTP |
Without protocol, communication is impossible.
Characteristics of Data Communication
For effective data communication, the system must have the following characteristics:
1. Delivery: Data must reach the correct destination
2. Accuracy: Data must be error-free
3. Timeliness: Data must be delivered on time
4. Jitter
- Variation in packet arrival time should be minimal
- Important for audio and video calls
Real-Life Example: Smooth video calling needs low jitter and timely delivery.
Data Representation
Data can be represented in different forms:
| Type | Description | Example |
|---|---|---|
| Text | Characters using ASCII/Unicode | Emails |
| Numbers | Binary format | OTP numbers |
| Images | Pixels | Photos |
| Audio | Sound signals | Voice calls |
| Video | Sequence of images | YouTube videos |
Data Flow
Data flow refers to the direction of data transmission between devices.
Types of Data Flow
| Type | Description | Example |
|---|---|---|
| Simplex | One-way communication | Keyboard → Computer |
| Half Duplex | Both directions, but one at a time | Walkie-talkie |
| Full Duplex | Both directions at the same time | Mobile phone call |
Computer Networks
A computer network is a group of interconnected devices that share resources and information.
Example: Computers connected in a college lab.
Types of Networks
1. LAN (Local Area Network)
| Feature | Description |
|---|---|
| Area | Small (office, building) |
| Speed | High |
| Cost | Low |
| Ownership | Private |
Example: Network in a computer lab or office.
2. MAN (Metropolitan Area Network)
| Feature | Description |
|---|---|
| Area | City-wide |
| Speed | Medium |
| Ownership | Private or Public |
Example: Cable TV network in a city.
3. WAN (Wide Area Network)
| Feature | Description |
|---|---|
| Area | Large (country/world) |
| Speed | Comparatively low |
| Cost | High |
Example: The Internet.
Comparison Table (Exam-Friendly)
| Feature | LAN | MAN | WAN |
|---|---|---|---|
| Area Covered | Small | City | Large |
| Speed | High | Medium | Low |
| Cost | Low | Medium | High |
| Example | Office network | City cable network | Internet |
Network Topologies
Network topology refers to the physical or logical arrangement of computers in a network.
1. Bus Topology
- Single main cable (backbone)
- All devices connected to it
Advantages:
- Low cost
- Easy to install
Disadvantages:
-
Failure of main cable affects entire network
Example: Old school computer labs.
2. Star Topology
-
All devices connected to a central hub or switch
Advantages:
- Easy fault detection
- High performance
Disadvantages:
-
Hub failure stops network
Example: Modern office networks.
3. Ring Topology
-
Devices connected in a circular manner
Advantages:
-
No data collision
Disadvantages:
-
Failure of one node affects whole network
Example: Token Ring networks.
4. Mesh Topology
-
Every device connected to every other device
Advantages:
-
High reliability
Disadvantages:
-
Expensive and complex
Example: Military or banking networks.
Topology Comparison Table
| Topology | Cost | Reliability | Example |
|---|---|---|---|
| Bus | Low | Low | Old LANs |
| Star | Medium | High | Office LAN |
| Ring | Medium | Medium | Token Ring |
| Mesh | High | Very High | Banking systems |
Important Exam Questions
- Define data communication and its components
- Explain characteristics of data communication
- What is data flow? Explain its types
- Compare LAN, MAN, and WAN
- Explain different network topologies with advantages and disadvantages
Protocols, Network Devices & Transmission Media
Protocols and Standards
A protocol is a set of rules that decides how data is sent, received, and understood between network devices.
Real-life example: Just like traffic rules help vehicles move safely, protocols help data move correctly in a network.
ISO-OSI Model (7-Layer Model)
The OSI (Open Systems Interconnection) model is a 7-layer conceptual model developed by ISO to understand network communication.
OSI Layers (Bottom to Top)
| Layer No. | Layer Name | Function (Simple Language) | Example |
|---|---|---|---|
| 7 | Application | Interface for user applications | Email, Browser |
| 6 | Presentation | Data formatting, encryption | JPG, MP3 |
| 5 | Session | Session management | Login session |
| 4 | Transport | Reliable data transfer | TCP, UDP |
| 3 | Network | Routing and logical addressing | IP |
| 2 | Data Link | Error detection, MAC address | Ethernet |
| 1 | Physical | Actual data transmission | Cables |
Mnemonic (Exam Friendly): All People Seem To Need Data Processing
Advantages of OSI Model
- Easy to understand
- Standard reference model
- Helps in troubleshooting
TCP/IP Model
The TCP/IP model is a practical model used on the Internet.
TCP/IP Layers
| TCP/IP Layer | OSI Equivalent | Function |
|---|---|---|
| Application | Application + Presentation + Session | User services |
| Transport | Transport | Reliable delivery |
| Internet | Network | Routing |
| Network Access | Data Link + Physical | Physical transmission |
Difference Between OSI and TCP/IP
| Basis | OSI Model | TCP/IP Model |
|---|---|---|
| Layers | 7 | 4 |
| Nature | Conceptual | Practical |
| Developed by | ISO | DARPA |
| Usage | Teaching & learning | Real Internet use |
Network Connecting Devices
1. Hub
- Works at Physical Layer
- Broadcasts data to all devices
- No intelligence
Example: Old LAN setups.
2. Bridge
- Works at Data Link Layer
- Divides network into segments
- Reduces traffic
Example: Connecting two LAN segments.
3. Switch
- Works at Data Link Layer
- Sends data only to intended device
- Faster than hub
Example: Modern office networks.
4. Router
- Works at Network Layer
- Connects different networks
- Uses IP address
Example: Home Wi-Fi router.
5. Gateway
- Works at all layers
- Connects different types of networks
- Protocol converter
Example: Email gateway between different mail systems.
Comparison Table (Exam Ready)
| Device | Layer | Function |
|---|---|---|
| Hub | Physical | Broadcast |
| Bridge | Data Link | Segment network |
| Switch | Data Link | Intelligent forwarding |
| Router | Network | Route packets |
| Gateway | All | Protocol conversion |
Transmission Media
Transmission media is the path through which data travels.
Guided Media (Wired Media)
| Type | Description | Example |
|---|---|---|
| Twisted Pair | Two wires twisted together | Telephone cables |
| Coaxial Cable | Single copper core | Cable TV |
| Optical Fiber | Light-based transmission | Internet backbone |
Advantages:
- High security
- Less interference
Unguided Media (Wireless Media)
| Type | Description | Example |
|---|---|---|
| Radio Waves | Long-distance communication | FM radio |
| Microwaves | Line-of-sight communication | Mobile communication |
| Infrared | Short-range | TV remote |
| Satellite | Large area coverage | GPS, DTH |
Classification and Arrangement of LANs
1. Wired LAN
- Uses cables
- High speed and secure
Example: Computer labs.
2. Wireless LAN (WLAN)
- Uses radio waves
- Flexible and easy to install
Example: Wi-Fi in homes, colleges.
Wired vs Wireless LAN
| Feature | Wired LAN | Wireless LAN |
|---|---|---|
| Speed | High | Medium |
| Security | High | Lower |
| Mobility | No | Yes |
| Cost | Medium | Low |
Important Exam Questions
- Explain OSI model with functions of each layer
- Compare OSI and TCP/IP models
- Explain Hub, Switch, Router and Gateway
- Discuss guided and unguided transmission media
- Compare wired and wireless LANs