Core Notes
CY403 Computer Networks
Structured notes designed for understanding concepts and writing RGPV examination answers.
Unit I
Introduction to Computer Networks & Network Models
Computer networking deals with the communication of information between
interconnected devices. A network can be designed for resource sharing,
communication, remote access and distributed services.
Network Components
SenderDevice that generates and sends data.
ReceiverDevice that receives transmitted data.
Transmission MediumPath through which signals travel.
Network DevicesSwitches, routers, hubs, gateways and access points.
ProtocolsRules governing communication between devices.
MessagesInformation exchanged between network entities.
Types of Networks
- PAN: Personal Area Network for devices around an individual.
- LAN: Local Area Network covering a limited geographic area.
- MAN: Metropolitan Area Network covering a city or large campus.
- WAN: Wide Area Network covering large geographic regions.
OSI Reference Model
The OSI model divides network communication into seven conceptual layers.
Each layer provides services to the layer above it and uses services of the
layer below it.
7. ApplicationNetwork services used by applications.
6. PresentationTranslation, encryption and compression.
5. SessionSession establishment and management.
4. TransportEnd-to-end delivery and reliability.
3. NetworkLogical addressing and routing.
2. Data LinkFraming, MAC addressing and error control.
1. PhysicalTransmission of raw bits over a medium.
TCP/IP Model
The TCP/IP model is the practical networking architecture used by the
Internet. Its commonly described layers are Application, Transport,
Internet and Network Access.
Exam Tip: For an OSI-model question, draw all seven layers
in order and write at least one major function of every layer.
Unit II
Data Link Layer
The Data Link Layer provides node-to-node delivery and is responsible for
framing, physical addressing, error detection and, depending on the protocol,
flow control and medium access.
Framing
Framing divides a continuous stream of bits into manageable data units
called frames. Common approaches include character count, byte stuffing
and bit stuffing.
Error Detection
ParityAdds a parity bit to detect certain bit errors.
ChecksumUses arithmetic over data blocks for error detection.
CRCPolynomial-based technique widely used for detecting transmission errors.
Flow Control
- Stop-and-Wait: Sender transmits a frame and waits for acknowledgement.
- Sliding Window: Multiple frames can be transmitted before acknowledgements are required.
MAC & Ethernet
Media Access Control deals with access to a shared communication medium.
Ethernet is a major LAN technology and uses MAC addresses for local delivery.
Transmission efficiency depends on frame size, propagation delay,
transmission rate, acknowledgements and the selected flow-control protocol.
Unit III
Network Layer
The Network Layer is responsible for logical addressing, packet forwarding
and routing between different networks.
IP Addressing
IP addressing identifies network interfaces logically. IPv4 uses 32-bit
addresses, while IPv6 uses 128-bit addresses.
IPv4 Example:
192.168.1.10 is an example of an IPv4 address written in dotted-decimal notation.
Routing
Routing determines a suitable path for packets from a source network to a
destination network. Routing approaches include static routing and dynamic
routing.
Common Routing Concepts
- Routing table
- Next hop
- Metric
- Default route
- Distance-vector routing
- Link-state routing
IPv4 vs IPv6
| Feature | IPv4 | IPv6 |
|---|
| Address length | 32 bits | 128 bits |
| Notation | Dotted decimal | Hexadecimal separated by colons |
| Address space | Smaller | Very large |
| Header | Variable length | Fixed base header |
Unit IV
Transport Layer
The Transport Layer provides process-to-process communication and can offer
reliability, flow control, congestion control and multiplexing through port
numbers.
TCP
- Connection-oriented transport protocol.
- Provides reliable, ordered byte-stream delivery.
- Uses acknowledgements and retransmission mechanisms.
- Supports flow control and congestion control.
UDP
- Connectionless transport protocol.
- Lower protocol overhead than TCP.
- Does not provide TCP-style reliable ordered delivery.
- Useful where low overhead and application-level control are important.
TCP vs UDP
| Feature | TCP | UDP |
|---|
| Connection | Connection-oriented | Connectionless |
| Reliability | Reliable delivery mechanisms | No TCP-style reliability |
| Ordering | Maintains ordered byte stream | No ordered delivery guarantee |
| Overhead | Higher | Lower |
Three-Way Handshake
SYN → SYN-ACK → ACK
TCP uses a three-step handshake to establish a connection and synchronise
sequence information before normal data transfer.
Unit V
Application Layer
The Application Layer provides network services directly to user applications.
Common protocols support web access, name resolution, email, file transfer
and remote communication.
HTTP / HTTPSWeb communication and secure web communication.
DNSMaps domain names to network addresses.
FTPFile transfer between networked systems.
SMTPUsed for sending email between mail systems.
DHCPAutomatically provides network configuration.
SSHSecure remote login and command execution.
DNS
The Domain Name System provides a hierarchical naming system that allows
users to access services using domain names instead of remembering numerical
network addresses.
Network Security Relevance
- HTTPS protects web traffic using cryptographic mechanisms.
- SSH provides secure remote administration.
- Firewalls control network traffic according to defined rules.
- Intrusion detection systems analyse traffic for suspicious behaviour.