Introduction to Computer Networks
# Definition
A computer network is a collection of interconnected computing devices that
can exchange data and share resources through a communication medium.
These devices, also called nodes or hosts, include computers, servers, printers,
routers, and switches.
# Working Principles
Computer networks function by establishing connections between devices using
hardware (network adapters, cables, routers) and software (protocols, operating
systems, applications). They transmit data in packets following standardized
protocols that ensure reliable delivery regardless of the types of devices
involved.
# Key Uses and Functions of Computer Networks
1. Resource Sharing
- Hardware Sharing : Printers, scanners, storage devices
- Software Sharing : Applications, databases, file systems
- Data Sharing : Files, information, and content distribution
2. Communication
- Email : Asynchronous message exchange between users
- Video Conferencing : Real-time audio and video communication
- Instant Messaging : Text-based real-time communication
- Voice over IP (VoIP) : Telephone services over networks
3. Business Applications
- E-commerce: Online buying and selling of products
- Enterprise Resource Planning (ERP) : Integrated management of business
processes
- Customer Relationship Management (CRM) : Managing customer
interactions
- Supply Chain Management: Coordinating production, inventory, and
distribution
4. Entertainment
- Streaming Services: Video and audio content delivery
- Online Gaming: Interactive multiplayer games
- Social Media: Platforms for social interaction and content sharing
5. Distributed Processing
- Cloud Computing : Delivery of computing services over the internet
- Grid Computing : Distributed computing across multiple locations
- Parallel Processing : Breaking down tasks to be processed simultaneously
Network Topologies
# Definition
Network topology refers to the physical or logical arrangement of network
devices and connections between them. It defines how devices are
interconnected and how data flows within the network.
# Types of Network Topologies
1. Bus Topology
Definition : A single cable (backbone) connects all devices in the network.
Working : All data is transmitted along a single transmission medium. When a
device sends data, it travels along the entire length of the cable in both
directions until it reaches the intended recipient.
Functions :
- Simple and inexpensive to implement
- Easy to extend by adding more devices
- Works well for small networks
Advantages :
- Easy installation and configuration
- Requires less cable than other topologies
- Cost-effective for small networks
Disadvantages :
- Vulnerable to cable failures
- Limited cable length and number of stations
- Performance degrades as more devices are added
- Difficult to troubleshoot
2. Ring Topology
Definition : Devices are connected in a circular fashion, with each device
having exactly two neighbours.
Working : Data travels in one direction (clockwise or counterclockwise) from
one device to another until it reaches its destination. Each device acts as a
repeater, regenerating the signal before passing it to the next device.
Functions :
- Provides equal access to all devices
- Avoids collision due to unidirectional data flow
- Suitable for networks where each node needs equal priority
Advantages :
- Easy to install and configure
- Performs better under heavy loads than bus topology
- No data collision due to token passing
- Equal access for all devices
Disadvantages :
- Failure of one device can affect the entire network
- Adding or removing devices disrupts the network
- More difficult to troubleshoot than star topology
3. Star Topology
Definition : All devices are connected to a central hub or switch.
Working : The central hub acts as a signal repeater or switch. All data must
pass through the hub before reaching its destination.
Functions :
- Centralizes network administration
- Provides fault isolation
- Simplifies troubleshooting
Advantages :
- Easy to install and manage
- Failure of one node doesn't affect others
- Easy to add or remove devices
- Centralized monitoring and management
Disadvantages :
- Dependent on the central hub (single point of failure)
- Requires more cable than bus or ring
- More expensive due to hub/switch requirements
4. Mesh Topology
Definition : Every device is connected directly to every other device in the
network.
Working : Data can take multiple paths from source to destination, providing
redundancy and fault tolerance.
Functions :
- Provides maximum reliability and redundancy
- Supports heavy traffic loads
- Ensures data privacy and security
Advantages :
- Highly reliable and robust
- No traffic congestion issues
- Provides privacy and security
- No single point of failure
Disadvantages :
- Very expensive to implement
- Complex to configure and manage
- Difficult to install and troubleshoot
- Requires substantial cabling
5. Tree/Hierarchical Topology
Definition : A combination of bus and star topologies arranged in a
hierarchical structure.
Working : Devices are connected to a central bus, with groups of devices
connected in star arrangements to form branches.
Functions :
- Supports hierarchical organization of networks
- Allows for easy expansion of existing networks
- Provides centralized control with distributed management
Advantages :
- Supports scalability
- Easy management of different sections
- Suitable for large organizations
- Balance of performance and management
Disadvantages :
- Dependent on the root bus
- Complicated wiring
- Difficult to configure
6. Hybrid Topology
Definition : Combination of two or more different topology types.
Working : Integrates the advantages of multiple topologies to meet specific
network requirements.
Functions :
- Addresses varying requirements across the network
- Optimizes performance, reliability, and cost
- Provides flexibility in network design
Advantages :
- Flexible and efficient
- Reliable and scalable
- Can be optimized for specific needs
Disadvantages :
- Complex to design and implement
- Can be costly
- Requires advanced management skills
ISO-OSI Reference Model
# Definition
The Open Systems Interconnection (OSI) model is a conceptual framework
developed by the International Organization for Standardization (ISO) that
standardizes the functions of a telecommunication or computing system into
seven distinct abstraction layers.
# Layered Architecture
Purpose : The layered architecture breaks down the complex process of
network communication into smaller, more manageable functions, with each
layer responsible for a specific aspect of data transmission.
Working : Each layer provides specific services to the layer above it and uses
services provided by the layer below it. This modular approach simplifies
design, implementation, and troubleshooting.
# Peer-to-Peer Processes
Definition : Peer-to-peer communication refers to the logical interaction
between corresponding layers on different systems.
Working : While data physically moves up and down through layers within
each system, logically, each layer communicates with its peer layer in the other
system. For example, the transport layer in one system communicates with the
transport layer in another system.
Functions :
- Creates the illusion of direct communication between corresponding layers
- Enables standardization of layer protocols
- Allows different implementations at each layer as long as interfaces remain
consistent
# Encapsulation
Definition : Encapsulation is the process of adding control information
(headers and sometimes trailers) to data as it moves down through the layers of
the OSI model.
Working :
1. At the sender, each layer adds its own header (and sometimes trailer) to the
data received from the layer above
2. As data moves down the stack, it accumulates headers from each layer
3. At the receiver, each layer removes and processes the header meant for it
before passing the data to the higher layer
Functions :
- Provides addressing information for routing
- Adds error detection and correction mechanisms
- Includes sequencing information for reassembly
- Carries control information for protocol operations
Functions and Services of OSI Layers
# 1. Physical Layer
Definition : The lowest layer of the OSI model that deals with the physical
connection between devices and the transmission and reception of raw binary
data over a physical medium.
Working : Converts the digital bits into electrical, radio, or optical signals for
transmission over the network media. Concerned with mechanical, electrical,
functional, and procedural characteristics of physical links.
Functions and Services :
- Bit transmission: Sending bits as electrical or optical signals
- Bit synchronization: Ensuring sender and receiver are synchronized
- Physical topologies: Defining how devices are physically arranged
- Transmission mode: Defining simplex, half-duplex, or full-duplex
transmission
- Multiplexing: Combining multiple signals over a single medium
Protocols and Standards :
- RS-232, RS-449
- V.35, X.21
- Ethernet (physical specifications)
- USB, Bluetooth physical specifications
- DSL, ISDN
# 2. Data Link Layer
Definition : The second layer of the OSI model that provides reliable transit of
data across a physical link and handles errors that may occur at the physical
layer.
Working : Creates frames from bits received from the physical layer, handles
flow control between adjacent network nodes, and manages error detection and
correction.
Functions and Services :
- Framing: Encapsulating packets into frames with start/stop delimiters
- Physical addressing (MAC): Identifying devices on the same network
- Flow control: Managing data rate to prevent overwhelming receivers
- Error control: Detecting and retransmitting damaged or lost frames
- Access control: Determining which device has control of the link at any time
Sublayers :
- Media Access Control (MAC): Manages access to the shared medium
- Logical Link Control (LLC): Provides error and flow control
Protocols and Standards :
- Ethernet, Token Ring
- PPP (Point-to-Point Protocol)
- HDLC (High-level Data Link Control)
- Frame Relay
- ATM (Asynchronous Transfer Mode)
# 3. Network Layer
Definition : The third layer of the OSI model that provides functional and
procedural means of transferring variable-length data sequences from a source
host on one network to a destination host on a different network.
Working : Handles logical addressing and routing of data packets across
multiple networks, making decisions about the most appropriate path for data
delivery.
Functions and Services :
- Logical addressing: Assigning unique addresses to devices across different
networks
- Routing: Determining the best path for data to travel from source to
destination
- Path determination: Selecting routes based on various metrics (distance, cost,
etc.)
- Packet forwarding: Moving packets from input to output interfaces
- Traffic management: Controlling congestion in the network
- Fragmentation and reassembly: Breaking large packets into smaller ones if
needed
Protocols and Standards :
- IP (Internet Protocol)
- ICMP (Internet Control Message Protocol)
- IGMP (Internet Group Management Protocol)
- Routing protocols: RIP, OSPF, BGP
# 4. Transport Layer
Definition : The fourth layer of the OSI model that provides transparent
transfer of data between end systems and is responsible for end-to-end error
recovery and flow control.
Working : Segments data from the session layer, establishes end-to-end
connections, and ensures reliable data delivery with appropriate quality of
service.
Functions and Services :
- Segmentation and reassembly: Breaking data into segments and reassembling
at destination
- Connection control: Establishing, maintaining, and terminating connections
- Flow control: Preventing sender from overwhelming receiver
- Error control: Ensuring error-free data delivery
- Congestion control: Preventing network congestion
- Multiplexing: Allowing multiple applications to use the same transport
connection
Protocols and Standards :
- TCP (Transmission Control Protocol): Connection-oriented, reliable
- UDP (User Datagram Protocol): Connectionless, best-effort
- SCTP (Stream Control Transmission Protocol)
- DCCP (Datagram Congestion Control Protocol)
# 5. Session Layer
Definition : The fifth layer of the OSI model that establishes, maintains, and
terminates sessions (logical connections) between applications.
Working : Manages the dialogue control between devices, establishing
checkpoints for recovery and controlling the communication process.
Functions and Services :
- Session establishment, maintenance, and termination
- Session support: Full-duplex, half-duplex, or simplex operation
- Dialogue control: Determining whose turn it is to transmit
- Synchronization: Adding checkpoints to data streams for recovery
- Token management: Preventing simultaneous critical operations
Protocols and Standards :
- NetBIOS (Network Basic Input/Output System)
- RPC (Remote Procedure Call)
- SQL (Structured Query Language)
- ASP (AppleTalk Session Protocol)
- PPTP (Point-to-Point Tunneling Protocol)
# 6. Presentation Layer
Definition : The sixth layer of the OSI model that is concerned with the syntax
and semantics of the information exchanged between systems.
Working : Transforms data from the application layer into a format that can be
sent over the network, handling data representation, encryption, and
compression.
Functions and Services :
- Data translation: Converting between different data formats
- Character code translation: ASCII to EBCDIC, etc.
- Data compression: Reducing the size of data for transmission
- Encryption/decryption: Ensuring data privacy and security
- Data formatting: Managing data structures used by applications
Protocols and Standards :
- SSL/TLS (Secure Sockets Layer/Transport Layer Security)
- MIME (Multipurpose Internet Mail Extensions)
- XDR (External Data Representation)
- JPEG, MPEG, GIF, TIFF (compression formats)
# 7. Application Layer
Definition : The topmost layer of the OSI model that provides a means for
applications to access network services.
Working : Provides interfaces for applications to use network services,
including user authentication, resource allocation, and data synchronization.
Functions and Services :
- Network virtual terminal: Remote access to a computer
- File transfer, access, and management
- Email services and directory services
- Network management functions
- Resource sharing and application services
Protocols and Standards :
- HTTP/HTTPS (Hypertext Transfer Protocol/Secure)
- FTP (File Transfer Protocol)
- SMTP (Simple Mail Transfer Protocol)
- DNS (Domain Name System)
- DHCP (Dynamic Host Configuration Protocol)
- SSH (Secure Shell)
- Telnet
Types of Digital Signaling Techniques :
1. Unipolar Encoding
- Definition : Uses a single positive voltage level to represent one binary
value and zero voltage to represent the other
- Working : Typically, voltage present = 1, no voltage = 0
- Advantages : Simple implementation
- Disadvantages : DC component, no error detection, synchronization issues
2. Polar Encoding
- Definition : Uses positive voltage for one binary value and negative
voltage for the other
- Types :
- NRZ (Non-Return to Zero) : Signal does not return to zero between bits
- RZ (Return to Zero) : Signal returns to zero between bits
- Manchester Encoding : Combines clock and data signals, transition in
middle of each bit
- Advantages : Better DC balance, improved synchronization
- Disadvantages : Requires more bandwidth than unipolar
3. Bipolar Encoding
- Definition : Uses three voltage levels: positive, negative, and zero
- Working : Usually, alternate 1s are represented by positive and negative
voltages, while 0s are represented by zero voltage
- Types :
- AMI (Alternate Mark Inversion)
- B8ZS (Bipolar with 8-Zero Substitution)
- HDB3 (High-Density Bipolar 3)
- Advantages : Excellent error detection, no DC component
- Disadvantages : More complex implementation
4. Multilevel Encoding
- Definition : Uses more than two signal levels
- Types :
- 2B1Q (2 Binary, 1 Quaternary) : Maps pairs of bits to one of four voltage
levels
- MLT-3 (Multilevel Transmission-3) : Uses three voltage levels with a
specific transition rule
- Advantages : More bits per symbol, reduced bandwidth
- Disadvantages : More susceptible to noise, more complex circuitry
# Transmission Impairments
Definition : Transmission impairments are unwanted factors that distort the
signal during transmission, causing the received signal to differ from the
transmitted signal.
Working : These impairments degrade signal quality, introduce errors, and
limit the effective data rate of communication channels.
Types of Impairments :
1. Attenuation
- Definition : The weakening of signal strength as it travels through the
transmission medium
- Working : Signal power decreases exponentially with distance due to
resistance of the medium
- Effects : Reduced signal-to-noise ratio, increased bit error rate
- Mitigation : Amplifiers or repeaters to boost signal strength
2. Distortion
- Definition : Alteration of the signal waveform during transmission
- Working : Different frequency components of a signal travel at different
speeds, causing them to arrive at different times
- Types :
- Delay distortion/phase distortion : Different frequencies travel at different
speeds
- Amplitude distortion : Different frequencies experience different amounts
of attenuation
- Mitigation : Equalizers to adjust the characteristics of the channel
3. Noise
- Definition : Unwanted electrical signals that get added to the transmitted
signal
- Types :
- Thermal noise : Generated by thermal agitation of electrons in conductors
- Intermodulation noise : Result of signals of different frequencies sharing
the same medium
- Crosstalk : Unwanted coupling between signal paths
- Impulse noise : Irregular pulses of high energy (e.g., from lightning,
electrical switches)
- Mitigation : Shielding, twisted pair cables, error detection and correction
techniques
4. Jitter
- Definition : Variation in the timing of signal edges from their ideal
positions
- Working : Caused by phase noise, timing drift, and other timing
imperfections
- Effects : Sampling errors, synchronization problems
- Mitigation : Phase-locked loops, timing recovery circuits
# Maximum Data Rate of a Channel
Definition : The maximum rate at which data can be transmitted over a given
communication channel with an acceptable error rate.
Working : The data rate is limited by the channel bandwidth, signal-to-noise
ratio, and the encoding scheme used.
Shannon's Theorem
Definition : A theorem formulated by Claude Shannon that establishes the
theoretical maximum data rate for a noise-limited channel.
Formula : C = B × log₂(1 + S/N)
Where:
- C = Channel capacity in bits per second (bps)
- B = Bandwidth of the channel in Hertz (Hz)
- S/N = Signal-to-noise ratio (power ratio)
Working :
- Higher bandwidth allows more data to be transmitted
- Better signal-to-noise ratio increases the reliable data rate
- The formula establishes an upper bound that cannot be exceeded regardless of
the encoding or modulation technique
Example : For a channel with 3 kHz bandwidth and a signal-to-noise ratio of
31 (15 dB):
C = 3000 × log₂(1 + 31) = 3000 × log₂(32) = 3000 × 5 = 15,000 bps
Nyquist Theorem
Definition : A theorem formulated by Harry Nyquist that establishes the
maximum data rate for a noiseless channel with limited bandwidth.
Formula : C = 2B × log₂M
Where:
- C = Channel capacity in bits per second (bps)
- B = Bandwidth of the channel in Hertz (Hz)
- M = Number of signal levels used
Working :
- For binary signaling (M=2), the maximum rate is 2B bits per second
- Using more signal levels increases the data rate but makes the system more
susceptible to noise
- This theorem provides a hard limit even in ideal, noiseless conditions
Example : For a channel with 3 kHz bandwidth using 4 signal levels:
C = 2 × 3000 × log₂(4) = 6000 × 2 = 12,000 bps
Transmission Media
# Definition
Transmission media are the physical paths or channels through which data is
transmitted from one device to another in a network.
# Types of Transmission Media
1. Guided Media (Wired)
Definition : Physical media that provide a conduit for data signals to travel
along a specific path.
Types :
# a. Twisted Pair Cable
Definition : Consists of pairs of insulated copper wires twisted together to
reduce electromagnetic interference.
Working : The twisting cancels out electromagnetic interference from external
sources and crosstalk between adjacent pairs.
Types :
- Unshielded Twisted Pair (UTP) : No additional shielding, categorized from
Cat1 to Cat8
- Shielded Twisted Pair (STP) : Additional metallic shield to reduce
interference
Characteristics :
- Bandwidth: 100 MHz to 2000+ MHz (depending on category)
- Data rate: 10 Mbps to 40 Gbps
- Distance: Up to 100 meters for most categories
- Cost: Inexpensive
- Applications: Ethernet networks, telephone systems
*Different types of twisted pair cables including UTP and STP*
# b. Coaxial Cable
Definition : Consists of a central copper conductor surrounded by an
insulating material, a conductive mesh, and an outer jacket.
Working : The central conductor carries the signal, while the mesh acts as a
ground and shield against interference.
Types :
- Baseband : Used for digital transmissions (e.g., Ethernet)
- Broadband : Used for analog transmissions (e.g., cable TV)
Characteristics :
- Bandwidth: 500 MHz to 1 GHz
- Data rate: Up to 10 Gbps
- Distance: Up to 500 meters
- Cost: Moderate
- Applications: Cable television, broadband internet, older Ethernet networks
# c. Fiber Optic Cable
Definition : Consists of a core of thin glass or plastic fibers that transmit data
using light pulses.
Working : Data is converted to light pulses, which travel through the fiber by
total internal reflection.
Types :
- Single-mode : Has a small core and carries one ray of light
- Multi-mode : Has a larger core and carries multiple rays of light
Characteristics :
- Bandwidth: Extremely high (THz range)
- Data rate: From 100 Mbps to hundreds of Tbps
- Distance: From 2 km (multi-mode) to 100+ km (single-mode)
- Cost: Expensive
*Comparison of single-mode and multi-mode fiber optic cables*
2. Unguided Media (Wireless)
Definition : Media that transmit signals without physical conductors, using
electromagnetic waves or radio frequencies.
Types :
# a. Radio Waves
Definition : Electromagnetic waves with frequencies ranging from 3 kHz to 1
GHz.
Working : Information is modulated onto a carrier wave and transmitted
through the air.
Types :
- Low-frequency (LF): 30-300 kHz
- Medium-frequency (MF): 300 kHz-3 MHz
- High-frequency (HF): 3-30 MHz
- Very high-frequency (VHF): 30-300 MHz
- Ultra high-frequency (UHF): 300 MHz-3 GHz
Characteristics :
- Can penetrate walls and buildings
- Susceptible to interference
- Applications: AM/FM radio, maritime communications, mobile phones
# b. Microwaves
Definition : High-frequency radio waves with frequencies ranging from 1
GHz to 300 GHz.
Working : Uses directional antennas to transmit high-frequency signals in a
line-of-sight path.
Types :
- Terrestrial microwave: Ground-based transmitters and receivers
- Satellite microwave: Communication via satellites
Characteristics :
- Line-of-sight transmission
- High data rates
- Affected by weather conditions
- Applications: Wireless LANs, cellular networks, satellite communications
# c. Infrared
Definition : Electromagnetic waves with frequencies ranging from 300 GHz
to 400 THz.
Working : Uses light-emitting diodes (LEDs) or lasers to transmit data as
infrared light pulses.
Characteristics :
- Short-range, line-of-sight transmission
- Cannot penetrate walls or obstacles
- Immune to electromagnetic interference
- Applications: Remote controls, wireless keyboard/mouse, device-to-device
data transfer
# d. Bluetooth
Definition : A wireless technology standard for exchanging data over short
distances using UHF radio waves.
Working : Uses frequency-hopping spread spectrum technology in the 2.4
GHz band.
Characteristics :
- Range: Typically 10-100 meters
- Data rate: Up to 50 Mbps (Bluetooth 5.0)
- Low power consumption
- Applications: Wireless peripherals, IoT devices, audio streaming
# e. Wi-Fi
Definition : A technology for wireless local area networking based on the
IEEE 802.11 standards.
Working : Uses radio waves to provide wireless high-speed internet and
network connections.
Characteristics :
- Range: Up to 100 meters indoors
- Data rate: Up to several Gbps (depending on standard)
- Uses 2.4 GHz and 5 GHz frequency bands
- Applications: Wireless internet access, home and business networks
*Different types of wireless transmission media and their applications*
Switching Techniques
# Definition
Switching is the process of establishing a temporary connection between the
source and destination for data transfer in a network.
# Types of Switching
1. Circuit Switching
Definition : A dedicated physical path is established between sender and
receiver for the entire duration of the communication session.
Working :
1. Connection setup: A physical path is established and reserved
2. Data transfer: Information is transmitted over the dedicated path
3. Connection teardown: The path is released after communication ends
Characteristics :
- Guaranteed bandwidth
- Fixed delays
- Connection-oriented
- Inefficient use of bandwidth
- Examples: Traditional telephone networks, ISDN
Advantages :
- Guaranteed bandwidth once connection is established
- Predictable performance with fixed delays
- No overhead once connection is established
Disadvantages :
- Inefficient use of network resources
- Connection setup takes time
- Costly for bursty data transmission
*Circuit switching establishes a dedicated path between sender and receiver*
2. Packet Switching
Definition : Data is divided into packets that are individually routed through
the network to the destination.
Working :
1. Message is broken into packets
2. Each packet contains addressing information
3. Packets are independently routed through the network
4. Packets may take different paths
5. Destination reassembles packets
Types :
- Datagram Packet Switching : Connectionless service, each packet routed
independently
- Virtual Circuit Packet Switching : Connection-oriented service, all packets
follow the same path
Characteristics :
- Efficient use of network resources
- Variable delays
- Better suited for bursty traffic
- Examples: Internet (IP), X.25
Advantages :
- Efficient bandwidth utilization
- Resilient to network failures
- Cost-effective for data transmission
- Better handling of congestion
Disadvantages :
- Variable and unpredictable delays
- Overhead due to packet headers
- Potential for packet loss and out-of-order delivery
*Packet switching divides data into packets that may take different paths*
3. Message Switching
Definition : An entire message is transmitted as a unit from source to
destination, stored and forwarded at each intermediate node.
Working :
1. Complete message is transmitted to the first switching node
2. The message is stored until resources are available
3. The entire message is forwarded to the next node when possible
4. This store-and-forward process continues until the message reaches its
destination
Characteristics :
- Store-and-forward technique
- No dedicated path
- Suitable for non-real-time applications
- Examples: Email, SMS
Advantages :
- No call setup required
- Efficient use of network resources
- Messages can be prioritized
- Useful when network connectivity is intermittent
Disadvantages :
- High delivery delays
- Requires significant storage at switching nodes
- Not suitable for real-time applications
- Possible network congestion with large messages
*Message switching stores and forwards entire messages at each intermediate
node*
# Virtual Circuit
Definition : A logical connection established between two devices in a packet-
switched network that provides a seemingly dedicated path for data transfer.
Working :
1. Connection setup: A virtual circuit is established before data transfer
2. Data transfer: All packets follow the same path through the network
3. Connection teardown: The virtual circuit is terminated after communication
ends
Types :
- Permanent Virtual Circuit (PVC) : Established permanently by network
administrators
- Switched Virtual Circuit (SVC) : Established on demand when needed and
terminated when communication ends
Characteristics :
- Connection-oriented service
- Predetermined route for all packets
- Guaranteed sequence of packet delivery
- Examples: Frame Relay, ATM, MPLS
Advantages :
- Guaranteed in-sequence packet delivery
- Lower routing overhead for individual packets
- Can provide QoS guarantees
Disadvantages :
- Connection setup overhead
- Less resilient to network failures
- Less efficient for very bursty traffic
*Virtual circuit packet switching establishes a fixed logical path for all packets*
Introduction to ISDN and Its Components
# Definition
Integrated Services Digital Network (ISDN) is a set of communication
standards for digital transmission of voice, video, data, and other network
services over the traditional circuits of the public switched telephone network.
# Working
ISDN digitizes the telephone network to allow digital transmission of voice and
data over ordinary telephone copper wires. It provides a digital alternative to the
analog PSTN (Public Switched Telephone Network).
# Key Components of ISDN
1. Channels
Definition : Communication paths for carrying data, voice, and control
signals.
Types :
- B-Channel (Bearer Channel) : Carries user data at 64 Kbps
- D-Channel (Delta Channel) : Carries control and signaling information
- 16 Kbps for Basic Rate Interface
- 64 Kbps for Primary Rate Interface
2. Reference Points
Definition : Conceptual points between functional groups in ISDN.
Types :
- R : Reference point between non-ISDN equipment and a terminal adapter
- S : Reference point between user terminals
