📘 PAPER 6 – DATA COMMUNICATION & NETWORKS (UNIT 1 – INTRODUCTION & PHYSICAL LAYER) university of allahabad

📘 PAPER 6 – DATA COMMUNICATION & NETWORKS

🔴 UNIT 1 – INTRODUCTION & PHYSICAL LAYER

1️⃣ Introduction to Data Communication

✅ Definition

Data Communication is the process of transferring data from one device to another using a transmission medium.

Components of Data Communication

Characteristics of Data Communication

✔ Delivery
✔ Accuracy
✔ Timeliness
✔ Jitter-free communication

2️⃣ Goals of Computer Networks

✔ Resource sharing
✔ Communication
✔ Reliability
✔ Cost reduction
✔ Scalability

3️⃣ Network Structure & Architecture

Network Architecture:

Defines how network is designed and how devices communicate.

4️⃣ OSI Reference Model

OSI has 7 Layers

Layer	Name	Function
7	Application	User interface
6	Presentation	Encryption
5	Session	Session control
4	Transport	Reliable delivery
3	Network	Routing
2	Data Link	Framing
1	Physical	Transmission

👉 Exam Tip:

Remember as:
A-P-S-T-N-D-P

5️⃣ Services Provided by OSI Model

✔ Data transmission
✔ Error control
✔ Flow control
✔ Connection management

6️⃣ Network Topologies

🔹 1. Bus Topology

Single cable
Low cost
Difficult troubleshooting

🔹 2. Star Topology

Central hub
Easy maintenance
High reliability

🔹 3. Ring Topology

Circular connection
Data flows in one direction

🔹 4. Mesh Topology

Each node connected to every other
High cost
Highly reliable

7️⃣ Network Design

Network Design Factors:

✔ Delay
✔ Bandwidth
✔ Cost
✔ Reliability

8️⃣ Physical Layer

Functions:

✔ Bit transmission
✔ Electrical specifications
✔ Data rate control

9️⃣ Transmission Media

🔹 Guided Media

1. Twisted Pair Cable

UTP
STP
✔ Cheap
❌ Noise sensitive

2. Coaxial Cable

✔ Better shielding
✔ Used in cable TV

3. Optical Fiber

✔ High speed
✔ Long distance
✔ Secure

🔹 Unguided Media

✔ Radio waves
✔ Microwave
✔ Infrared

🔟 Switching Techniques

🔹 Circuit Switching

Dedicated path
Used in telephone network

🔹 Packet Switching

Data divided into packets
Used in Internet

🔹 Message Switching

Store and forward technique
Not used now

📌 EXAM IMPORTANT QUESTIONS (UNIT 1)

✔ OSI model with diagram
✔ Transmission media
✔ Network topology
✔ Switching techniques
✔ Physical layer functions