Computer Network

UNIT-I: Basic Concepts and Models

Components of data communication, distributed processing, standards and organizations. Line configuration, topology, transmission mode, and categories of networks. OSI and TCP/IP Models: Layers and their functions, comparison of models. Digital Transmission: Interfaces and Modems: DTE-DCE Interface, Modems, Cable modems.

UNIT-II: Transmission Media

Guided and unguided media, attenuation, distortion, noise, throughput, propagation speed and time, wavelength, Shannon capacity, comparison of media.

UNIT-III: Telephony, Multiplexing, and Data Link Control

Telephony: Multiplexing, error detection and correction: Many to one, One to many, WDM, TDM, FDM, Circuit switching, packet switching and message switching. Data link control protocols: Line discipline, flow control, error control, synchronous and asynchronous protocols, character and bit oriented protocols, Link access procedures. Point to point controls: Transmission states, PPP layers, LCP, Authentication, NCP. ISDN: Services, Historical outline, subscriber’s access, ISDN Layers and broadcast ISDN.

UNIT-IV: Networking Devices and the Network Layer

Devices: Repeaters, bridges, gateways, routers. The Network Layer: Design issues, Routing algorithms, Congestion control Algorithms, Quality of service, Internetworking, Network Layer in the internet.

UNIT-V: Transport and Upper Layers in OSI Model

Transport layer functions, connection management, functions of session layers, presentation layer and application layer.

UNIT-I: Basic Concepts

1. Components of Data Communication

Data communication refers to the exchange of data between devices using a transmission medium. The essential components of data communication include:

Sender: The device that sends data.
Receiver: The device that receives data.
Transmission Medium: The physical path between the sender and receiver (e.g., cables, wireless).
Message: The actual data that is transmitted.
Protocol: Rules that govern data communication.

Example Diagram:

                [Sender] ---> [Transmission Medium] ---> [Receiver]
                (Message)
                (Protocol governs the exchange)
            

2. Distributed Processing

Distributed processing involves dividing tasks among multiple computers that communicate over a network.

Example Diagram:

                [Client 1] [Client 2]
                \ /
                \ /
                [Distributed Server Cluster]
            

3. Standards and Organizations

Some key standard organizations are ISO, IEEE, ITU, and IETF, which ensure interoperability and compatibility in communication systems.

Example Diagram:

                Organizations: [ISO] [IEEE] [IETF] [ITU]
                |
                Define
                |
                [Protocols & Standards]
            

4. Line Configuration

Defines how devices are connected in a communication line.

Example Diagram:

                Point-to-Point: [Device A] ----- [Device B]
                Multipoint: [Device A]
                |
                ---------------
                | | |
                [Device B][Device C][Device D]
            

5. Topology

Defines the structure of a network.

Example Diagram:

                Star Topology:
                [Switch]
                / | \
                [PC1] [PC2] [PC3]

                Ring Topology:
                [PC1]---[PC2]---[PC3]
                \ /
                ---[PC4]---
            

6. Transmission Mode

Simplex: One way only

Half-Duplex: Two-way, one at a time

Full-Duplex: Two-way simultaneously

Example Diagram:

                Simplex: [A] ---> [B]
                Half-Duplex: [A] <--- [B] (One direction at a time) Full-Duplex: [A] <--> [B] (Both directions
                    simultaneously)
            

7. Categories of Networks

Classification based on geographic spread.

Example Diagram:

                PAN: [Smartphone] <--> [Laptop]
                    LAN: [PC1] --- [PC2] --- [Printer] (Same building)
                    MAN: [Campus Network] across a city
                    WAN: [Internet: Connects cities/countries]
            

8. OSI and TCP/IP Models

OSI Model: 7 Layers

TCP/IP Model: 4 Layers

Example Diagram:

                OSI Model: TCP/IP Model:
                ----------------- ----------------
                Application Application
                Presentation |
                Session |
                Transport Transport
                Network Internet
                Data Link Network Access
                Physical
            

9. Digital Transmission: Interfaces and Modems

Digital communication often uses modems and interface standards.

Example Diagram:

                [Computer] --(DTE)--> [Modem] --(DCE)--> [Telephone Line] --> [Remote Modem] --> [Server]
            

UNIT-II: Transmission Media

1. Guided and Unguided Media

Guided Media involves physical cables through which signals are guided.

Twisted Pair Cable
Coaxial Cable
Fiber Optic Cable

Unguided Media transmits signals through air or vacuum (wireless).

Radio Waves
Microwaves
Infrared

Example Diagram:

                Guided Media:
                [Device A] ---- Twisted Pair ---- [Device B]

                Unguided Media:
                [Device A] ))))) Radio Signal ))))) [Device B]
            

2. Attenuation

Attenuation refers to the loss of signal strength as it travels through the medium.

Example: A signal sent at 100 dB might be received at 70 dB.

                Signal Strength Decrease:
                100 dB --> 90 dB --> 80 dB --> 70 dB
            

3. Distortion

Distortion occurs when the signal changes its form or shape due to delay in different components of the signal.

                Sent Signal: /\/\/\/\/\
                Received: /\_/\/\__\
            

4. Noise

Noise is unwanted energy that alters or interferes with the original signal.

Thermal Noise
Intermodulation Noise
Crosstalk
Impulse Noise

                Clean Signal: 10101010
                With Noise: 10111000
            

5. Throughput

Throughput is the actual rate at which data is successfully transmitted over the channel.

Example: A channel with a bandwidth of 10 Mbps might only transmit 8 Mbps due to overhead and noise.

6. Propagation Speed and Time

Propagation Speed is the rate at which a signal travels through the medium (close to speed of light).

Propagation Time is the time it takes for a signal to reach the receiver.

Formula:

                Propagation Time = Distance / Propagation Speed
                Example: 3000 km / (2 x 10^8 m/s) = 0.015 s
            

7. Wavelength

Wavelength is the distance between two consecutive peaks of a signal.

Formula: λ = Propagation Speed / Frequency

                Example:
                Frequency = 2 GHz, Speed = 3x10^8 m/s
                λ = 3x10^8 / 2x10^9 = 0.15 meters
            

8. Shannon Capacity

Maximum data rate of a noisy channel.

Formula:

                C = B * log2(1 + S/N)
                Where:
                C = Channel Capacity (bps)
                B = Bandwidth (Hz)
                S = Signal Power
                N = Noise Power

                Example:
                B = 3000 Hz, S/N = 1000
                C = 3000 * log2(1 + 1000) ≈ 3000 * 9.97 = 29.9 kbps
            

9. Comparison of Media

Media Type	Bandwidth	Noise Resistance	Cost	Usage
Twisted Pair	Low	Low	Low	LANs, Telephones
Coaxial Cable	Medium	Medium	Medium	Cable TV
Fiber Optic	High	High	High	Backbone, Long-distance
Radio Waves	Medium	Low	Low	Wireless LANs
Microwaves	High	Medium	Medium	Cellular, Satellite

UNIT-III: Telephony

1. Multiplexing

Multiplexing is the process of combining multiple signals for transmission over a single medium.

Many to One: Combines many sources into one line (e.g., many calls over one wire).
One to Many: One source is distributed to many destinations.

Types of Multiplexing:

WDM (Wavelength Division Multiplexing): Used in fiber optics. Each signal is assigned a different wavelength (color of light).
TDM (Time Division Multiplexing): Each signal is assigned a time slot.
FDM (Frequency Division Multiplexing): Each signal is transmitted in a separate frequency band.

                Example (TDM):
                Time Slots: | A | B | C | A | B | C | ...
                Each device sends in its time slot.
            

2. Switching Techniques

Circuit Switching: A dedicated path is established for the duration of the communication. (e.g., Telephone calls)
Packet Switching: Data is broken into packets and sent independently. (e.g., Internet)
Message Switching: Whole messages are stored and forwarded. No dedicated path needed.

                Circuit: A ──────── B (reserved line)
                Packet: A → (packet 1) → B
                → (packet 2) → B
                Message: A → Store → Forward → B
            

3. Error Detection and Correction

Detection: Identifies the presence of an error (e.g., Parity Check, CRC).
Correction: Locates and corrects the error (e.g., Hamming Code).

                Example:
                Original: 1010 → Transmitted: 1010 → Received: 1110 (Error detected)
            

4. Data Link Control Protocols

Line Discipline: Determines which device can send and when.
Flow Control: Manages data rate between sender and receiver (e.g., Stop-and-Wait, Sliding Window).
Error Control: Ensures error-free delivery using ACKs and retransmissions.

Types:

Synchronous: Blocks of data transmitted with synchronization bits.
Asynchronous: Data sent character by character with start/stop bits.
Character-Oriented: Uses characters for control (e.g., ASCII).
Bit-Oriented: Uses bit patterns for control (e.g., HDLC).

5. Link Access Procedures

Define how a device accesses the link, used in WAN protocols. Examples include:

LAPB – used in X.25 networks
LAPD – used in ISDN

6. Point-to-Point Protocol (PPP)

PPP is used to establish a direct connection between two nodes.

Transmission States:

Link Establishment
Authentication
Network Layer Protocol Configuration

PPP Layers:

LCP (Link Control Protocol): Establishes and configures the link.
Authentication: PAP/CHAP used to verify identity.
NCP (Network Control Protocol): Configures network layer protocols like IP.

                PPP Communication:
                | LCP | → | Authentication | → | NCP | → | Data Transfer |
            

7. ISDN (Integrated Services Digital Network)

Services: Voice, Video, Text, and Data over a single line.
Historical Outline: Introduced to replace analog telephone systems with digital.
Subscriber's Access: Uses B (Bearer) and D (Delta) channels.
ISDN Layers: Similar to OSI model; physical, data link, and network layers.
Broadcast ISDN: Extension of ISDN to support broadcasting like video conferencing.

                Basic ISDN:
                - 2B (64 kbps) + 1D (16 kbps) = 144 kbps
                Primary Rate:
                - 23B + 1D (North America)
                - 30B + 2D (Europe)
            

UNIT-IV: Network Devices & The Network Layer

1. Devices

Repeaters: Regenerate weak signals to extend transmission distance. Operate at the Physical Layer.
Bridges: Connect and filter traffic between two LAN segments. Operate at the Data Link Layer.
Routers: Direct data packets between different networks. Operate at the Network Layer.
Gateways: Connect networks using different protocols. Work at multiple OSI layers including the Application Layer.

                Diagram Example:
                [PC] ── [Repeater] ── [Bridge] ── [Router] ── [Gateway] ── [Internet]
            

2. Network Layer

The Network Layer is responsible for delivery of packets from source to destination across multiple networks.

Main Functions:

Logical addressing (IP address)
Routing and forwarding
Packet switching

3. Design Issues in the Network Layer

Packet delivery
Routing efficiency
Congestion control
Error handling and diagnostics

4. Routing Algorithms

Routing is the process of selecting paths in a network along which to send data packets.

Static Routing: Predefined routes, no change during transmission.
Dynamic Routing: Adapts routes based on network changes (e.g., RIP, OSPF).

Examples of Algorithms:

Shortest Path (Dijkstra's Algorithm)
Flooding: Packet sent to all possible paths
Distance Vector (e.g., RIP)
Link State (e.g., OSPF)

                Example:
                A --1-- B --1-- C
                Shortest Path A to C: A → B → C (Total cost = 2)
            

5. Congestion Control Algorithms

Used to prevent too much traffic in the network which leads to performance degradation.

Open Loop: Prevent congestion before it occurs (e.g., traffic shaping).
Closed Loop: Detect and respond to congestion (e.g., feedback mechanisms).

6. Quality of Service (QoS)

QoS refers to the performance level of a service like delay, jitter, bandwidth, and packet loss.

Traffic shaping
Resource reservation
Prioritization

                Example:
                Video Call → High QoS (low latency)
                Email → Low QoS needed
            

7. Internetworking

Internetworking connects multiple distinct networks into a larger network (like the internet).

Devices involved: Routers and Gateways

8. Network Layer in the Internet

Uses the Internet Protocol (IP) to route packets globally.

IPv4: 32-bit addressing
IPv6: 128-bit addressing

Other protocols:

ICMP – error reporting
ARP – address resolution

UNIT-V: Transport and Upper Layers in OSI Model

1. Transport Layer Functions

The Transport Layer ensures reliable data transfer between end systems. It acts as a source-to-destination delivery service.

Segmentation and Reassembly: Divides data into segments and reassembles them at the destination.
Connection Control: Can be connection-oriented (TCP) or connectionless (UDP).
Flow Control: Ensures sender doesn't overwhelm receiver (e.g., TCP's sliding window).
Error Control: Detects and retransmits lost or corrupted segments.
Multiplexing: Multiple applications use the same network connection using port numbers.

                Example:
                TCP port 80 → HTTP

                TCP port 443 → HTTPS
            

2. Connection Management

Connection management involves establishing, maintaining, and terminating connections.

Connection Establishment: 3-way handshake (SYN, SYN-ACK, ACK in TCP)
Connection Maintenance: Managing data flow and error handling
Connection Termination: Using FIN and ACK packets

                Example (TCP Handshake):
                Client → SYN → Server

                Server → SYN-ACK → Client

                Client → ACK → Server

3. Session Layer Functions

The Session Layer manages sessions (continuous exchanges of information) between applications.

Establishes, maintains, and terminates sessions
Synchronizes data with checkpoints
Controls dialog (e.g., full or half-duplex communication)

                Example:
                Video conference software uses sessions to keep the stream active and in sync.
            

4. Presentation Layer Functions

This layer handles syntax and data format translation between communicating systems.

Data conversion (e.g., ASCII to EBCDIC)
Encryption and decryption
Compression and decompression

                Example:
                Encrypting data before sending → Decryption at the receiver side
            

5. Application Layer Functions

The Application Layer is the closest to the user. It provides network services to applications.

Provides services like email, file transfer, and browsing
Examples: HTTP, FTP, SMTP, DNS, SNMP

                Example:
                - Web Browsing → HTTP

                - Email → SMTP

                - File Transfer → FTP

Diagram: OSI Model (Layers 4 to 7)

                | Layer 7 | Application | Email, HTTP, FTP |
                | Layer 6 | Presentation| Encryption, Encoding |
                | Layer 5 | Session | Dialog Control |
                | Layer 4 | Transport | TCP, UDP (Reliable transfer) |
            