Networking Model Types:
1. Protocol Model (TCP/IP)

Protocol implementation.

Horizontal approach.

No standardization for connection between computers

Functionalities to interface human network with data network
2. Reference Model (OSI)

Conceptual framework for understanding and designing networks.

Vertical approach.

Provides standardization of networking functions across devices.

For understanding the functions and processes involved in network
communication.
Open System Interconnection (OSI)

Developer: International Organization for Standardization.

Describes 7 layers that computers use to communicate over a network.
1. Physical Layer:
o
Units of Data: Bits/Signals
o
Hardware -> Nodes. Nodes are connected in different topologies.
o
Encodes binary data into physical signal at sender’s side by the process
of modulation
o
Decodes physical signal to binary data at the receiver’s side by the
process of demodulation
o
Define physical characteristics of transmission Eg: Copper and Optical
Fiber Cables, Hubs, Ethernet, etc.
2. Data Link Layer:
o
Units of Data: Frame
o
Sender:
 Encapsulates frame around the packet i.e. adds data link header and
trailer around the packet
 Adds source and destination MAC address
 Provides efficient communication between directly connected nodes.
 Uses both LLC and MAC sublayers
o
Receiver:
 Checks received frame’s MAC addressing and frame information
 Decapsulates the packet from the frame i.e. removes the Data Link
header and trailer around the packet
 Performs relevant error checking.
o
Error free and efficient communication between the 2 nodes
o
2 sublayers:
1. Logical link control (LLC):
 Provides logic to the data link layer
 Services: synchronization, flow control and error handling
 Eg: Checksums, cyclic redundancy checks.
2. Media Access Control (MAC):
 Used to identify physical address of a device on a network
 Usually added when device is manufactured
 Unlike IP address it does not change in the network
o
Eg: MAC addresses, switches, etc.
3. Network Layer:
o
Unit of Data: packets
o
Sender:
 Adds source and destination IP address to data packets
 Routes packets through the networks.
o
Receiver:
 Examines the IP of the destination address
 Processes the packet and removes the Network-layer information.
o
Eg: IPv4 and IPv6 addressing, routers, etc.
4. Transport Layer
o
Unit of data: message
o
Uses transport protocols like TCP and UDP.
o
Responsible for:
 End to end connection
 Segmentation and reassembly
 Flow and Error control
o
TCP: establishes a connection, numbers/acknowledges data, retransmits
lost data, and controls the flow -> reliable but more overhead.
o
UDP: sends datagrams directly without establishing a connection or
guaranteeing delivery/order -> faster with less overhead.
o
Eg: TCP, UDP, etc.
5. Sessions:
o
Unit of data: Data
o
Responsible for:
 Establishing and terminating sessions
 Managing communication sessions
 Dialog control
 Synchronization and checkpoints
o
Establishes, maintains, and terminates communication between
applications.
o
Synchronization: Creates checkpoints so communication can resume from
the last checkpoint after a failure.
o
Eg: RPC (Remote Procedure Call), NetBIOS Session Service, PPTP, SQL
sessions / database sessions, etc.
6. Presentation:
o
Sender
 Formats/encodes data into a form suitable for transmission.
 May perform encryption and compression.
o
Receiver
 Decodes/translates the data into a form understandable by the
application.
 May perform decryption and decompression.
o
Eg: Encryption, Decryption, etc.
7. Application:
o
Provides interface between application and network communication
o
Eg: HTTPS, SMTP, FTP, etc.
Networking Components & Device
Hub (Layer 1 Physical)
Definition:

Device at physical layer of OSI Model

Connect multiple device/segments in a LAN

Does not examine destination MAC address -> cannot intelligent which port
should receive the data

Receives incoming data from 1 of the port and regenerates and sends to all
other connecting ports


Hubs are getting obsolete but active and intelligent hubs are still used today.
Types:
1. Active Hub:

Transmits weak incoming signals in all ports after regenerating and amplifying it

Also called power hubs for its performance as multi-port repeater

Prevents signal degradation and attenuation thus increasing usable signal
distance
2. Passive Hubs:

Central connection point between device

No power supply -> no signal regeneration and amplification -> no compensation to
signal degradation

Largely obsolete in modern networks
3. Intelligent Hubs:

Advanced/managed type hub

Support functions using Simple Network Management Protocol (SNMP) which is
an Application Layer protocol:
o Network & device monitoring
o Collecting and managing information
o Error detection and reporting
o Basic traffic monitoring/filtering
o Limited QoS-related capabilities
o UDP 161: handling requests and queries
o UDP 162: traps and notifications
Disadvantages:

Collision possibilities especially if devices transmit simultaneously via halfduplex Ethernet

Increase competition on shared bandwidth with addition of more devices

Unnecessary traffic since signal is sent to all ports unintelligently

Mostly half-duplex environment operations

Less efficient to switches
Repeater (Layer 1 Physical)
Definition:

Device operating at the Physical Layer (Layer 1) of the OSI Model.

Receives a weak/incoming signal which contains data frame at one port,
regenerates it, and retransmits it via another port.

Used to extend the transmission distance of a network.

It does not connect 2 LANs but is used to connect segments within the same
LAN.

Since each LAN can have its own network protocol so same different LANs
would need different Repeater

Used to overcome the problem of attenuation.
Attenuation:

Attenuation = weakening/loss of signal strength as it travels over distance.

Greater transmission distance generally results in greater attenuation.

Repeater regenerates the weakened signal, helping it travels a longer distance.
Working:

Weak signal -> Repeater -> Regenerated signal -> Longer distance
Modem or Modulator-&-Demodulator (Layer 1 Physical)
Definition:

Connects a computer/home network to an Internet Service Provider (ISP).


Modem = MOdulator + DEModulator.

Signal translator, converting signals between forms suitable for transmission
and forms that the computer/network can understand.

A modem is primarily associated with the Physical Layer (Layer 1) because it
deals with signal transmission.

A router is generally placed after modem as it passes the network packets it
received from internet to all the other devices within the LAN as per the
destination IP address.
How does a Modem work?
1. Modulation:

Converts digital data from the computer into a signal suitable for transmission
over the communication medium.

The data is encoded onto a carrier signal.

Common characteristics that can be varied during modulation include amplitude,
frequency and phase.
2. Transmission:

The modulated signal travels through the communication medium to the
receiving side.
3. Demodulation:

The modem at the receiving side extracts the original data from the
transmitted signal and converts it back into a form that the receiving computer
can understand.
Types of Modems:
1. Dial-up Modem:

Uses a telephone line to establish an Internet connection.

Converts between digital computer data and signals suitable for the telephone
line.

Older technology and much slower than modern broadband connections.
2. DSL Modem:

DSL = Digital Subscriber Line.

Provides Internet access over telephone lines.

Uses different frequency bands so voice and data can operate simultaneously on
the same telephone line.
3. Cable Modem:

Uses coaxial cable / cable-TV infrastructure to provide Internet access.

Commonly used for broadband Internet connections.
4. Satellite Modem:

Provides connectivity through satellite communication.

Converts data into signals suitable for transmission to/from satellite systems.
5. Optical Modem:

Uses optical fibre as the transmission medium.

Converts digital data into light pulses for transmission through optical fiber.
Modes of Communication (Layer – 1 Physical):
Based on Data Flow:
Simplex:

Unidirectional communication

One device always sends information and other always receive it

Advantage: simple, easy to implement, lower installation and maintenance cost,
use entire bandwidth, suitable for broadcast type operations, etc.

Disadvantages are lack of: error reporting from receiver, confirmation of
successful delivery, etc.

Eg: mouse, keyboard, TV broadcast, radio broadcast, etc.
Half Duplex:

Both parties can communicate with each other but not in the same time

At a specific point of time communication can be done only in 1 direction

Advantages: more flexibility to simplex, cost effective to full-duplex, whole
bandwidth is used, suitable for controlled communication environments, etc.

Disadvantage: no simultaneous 2 way communication, possible delay due to turnbased transmission, performance decreases with heavy traffic, risk of collision
if control mechanisms fail, etc.

Eg: radio walkie-talkie, etc.
Full Duplex:

Communication in both directions simultaneously

Capacity of the network divided between the 2 directions devices or separate
channels are used for uplink and downlink.

Advantages: Faster data transfer rate, no waiting time between transmission,
improved communication efficiency, suitable for interactive applications, etc.

Disadvantages: Higher installation cost, more complex hardware, greater
bandwidth need, etc.

Most common real time communication.

Eg: Telephone, cell phone, etc.
Based on Connectivity:
Point-to-Point:

Dedicated link between the 2 devices

Entire capacity of network reserved for transmission between the devices.

Advantage: simplicity, reliability, repairability, scalability, better control, fault
isolation, etc.

Eg: TV remote control, content delivery network like Cloudflare, and akamai, etc.
Multipoint:

Multiple devices share a common link:

Sharing can be:
 Spatial: Sharing within same point of time
 Temporarily: 1 device operate on the common link only within allotted time
slot
Based on Geography:
Local Area Network (LAN):

Collection of devices connected in one physical location like a office building,
office, house etc.

Coverage depends on:
 Network topology
 Type of media used for transmission
1. Ethernet Cable (IEEE 802.3): can carry data up to 100 m. (e.g.: computer,
switches, etc.)
2. WiFi (IEEE 802.11): Typically, 20–50 m indoors and up to 100–300 m
outdoors, depending on the standard, obstacles, antenna, and
environment.
3. Optical Fiber Cables:
1) Multimode Fibre (MMF): up to 2km or more
2) Single Mode Fibre (SMF): 10-100km or even more depending on the
network transmission technology involved and equipment used
 Network equipment capacity
Metropolitan Area Network (MAN):

Network that connects multiple LANs within a city or metropolitan area.

Covers a larger area than LAN but smaller than WAN.

Used to connect offices, campuses, or buildings across a city.

Eg: City-wide government networks, cable TV networks.

Typically uses fibre-optic cables or high-speed wireless links.
Wide Area Network (WAN):

Connects networks over a large geographical area, such as countries or
continents.

Collection of LANs and MANs connected over long distances.

Used for long-distance transmission of data such as audio, images, video, and
files.

Uses technologies such as leased lines, fibre-optic links, satellite, and cellular
networks.

The Internet is the largest example of a WAN.
Network Topology:

Way in which the network is laid out physically

2/more devices form a link

2/more links form a topology

Network Topology: geometric form of all the links and linking devices

Types
1. Mesh Topology:
o
Every device has a dedicate point-to-point link with other devices
o
For n nodes, every node is connected to n-1 nodes.
o
Total number of connections: n(n-1)
o
High fault tolerance and reliability due to presence of multiple
alternate routes
o
High complexity and cost
2. Star Topology:
o
All nodes are individual connected to a central point a hub/switch.
o
Point-to-point between device and the central node
o
Devices are not directly linked to one another
o
Does not allow direct traffic flow between devices
o
If device wants to connect one another it sends data to the controller
3. Bus topology:
o
Devices linked to single shared coaxial cable -> backbone of the
network
o
Suitable for smaller network
o
Single point of failure
o
Dropline: Device to main cable connection
o
Tap: connector
4. Ring Topology:
o
Each devices have point-to-point network connection between devices
on either side

o
Signals are passed in 1 direction
o
Each device uses a repeater
o
Adding/deleting a connection only requires changing 2 connections
Diagram:
Network Interface Card (Layer 2 Data Link)
Definition:

Interface between device and network medium

Provide both wired and wireless network connectivity

Each NIC has its own MAC address that handles layer 2 communication

Helps create, send and receive network frames

Receives frames from the network and passes the relevant data to the device.

Works with the Data Link and Physical layers for transmission and reception
Types:
1. Wired NIC:

Connects a device to the network using a physical cable, commonly Ethernet.

Commonly uses an Ethernet port.
2. Wireless NIC:

Connects a device to a network wirelessly using Wi-Fi.

Uses radio signals instead of a physical Ethernet cable.
MAC Address:

Physical/hardware address associated with a network interface.

Standard Ethernet MAC address = 48 bits / 6 bytes.

Usually represented as 12 hexadecimal digits, e.g. 00: 1A: 2B: 3C: 4D: 5E.

First 24 bits -> OUI (Organizationally Unique Identifier), generally identifying
the manufacturer.

Remaining 24 bits -> interface-specific identifier assigned by the manufacturer.
Switch (Layer 2 Data Link):
Definition:

Connect multiple devices in a LAN

Data link layer (Layer 2) operation primarily but sometimes Network Layer
operation (Layer 3) too

Uses MAC address to identify destination device

Receives frame and forwards it to the appropriate port (unlike Hub that
forwards everywhere)

Maintains MAC Address table

Local network segmentation and traffic management

Each switch port: separate collision domain

Supports VLANS, QoS, and security depending on switch

Network layer switches also provide routing capabilities
Types:
1. Unmanaged Switch:

Plug and play

Little or no configuration required

Common in home or simple networks
2. Managed Switch:

Allows configuration and monitoring

Provides greater control over network security and performance
3. Network Layer (Layer 3) Switch:

Combines data link layer (layer 2) switching and data link layer (layer 3) routing

Route traffic between different network/VLANs
Advantages:

Reduces collisions

Better bandwidth utilization than hubs

More efficient frame forwarding

Supports full-duplex communication

Provides network segmentation and scalability
Bridge (Layer 2 – Data Link)
Definition:

Connections 2/more LAN segments to allow them to communicate as single
extended network

Data Link Layer (Layer 2)

Uses MAC address of source and destination devices to decide whether to
forward or a filter a frame and maintains the MAC address table for future
filtering decisions.

Divide LAN segments into smaller network segments or collision domains,
reducing unnecessary traffic and collisions

Unlike Hub, it does not blindly send a frame to every segment, it filters a
traffic and forwards it only when it is required

It can generally connect networks using same or similar protocols
Working:

When a frame arrives, it generally examines the destination MAC address

If the destination is on the same segment, the frame is filtered and not
forwarded to another segment.

If the destination is on a different segment, the bridge forwards the frame.

If the destination MAC address is unknown, the bridge may flood the frame to
other segments.

Performs frame forwarding, address learning and traffic filtering.
Types:
1. Transparent Bridge:

Automatically learns MAC addresses and maintains its forwarding table.

Hosts do not need to know that a bridge exists -> transparent.

Uses frame forwarding, address learning and loop resolution.

Broadcast and multicast frames are generally flooded across the bridge.
2. Source Routing Bridge:

The source determines/specifies the route that the frame should take.

Uses source-routing information to determine the path.

Commonly associated with Token Ring networks.
3. Translational Bridge:

Connects different types of networks by translating between their different
frame formats/protocols.

Example: Ethernet <-> Token Ring.
4. Wireless Bridge:

Connects two networks wirelessly, allowing network segments to communicate
without a physical cable connection.
Advantages:

Reduces network traffic by filtering unnecessary frames.

Divides a LAN into separate collision domains.

Improves network performance by reducing collisions and congestion.

Uses MAC addresses for intelligent frame forwarding.

Allows expansion of a LAN by connecting different network segments.

Provides basic traffic filtering between network segments.
Disadvantages:

Traditional bridges have limited functionality compared with routers.

Cannot make complex IP-based routing decisions.

Broadcast traffic can still pass across bridge segments.

Multiple bridges can create loops; loop-resolution mechanisms such as Spanning
Tree Protocol (STP) are used to prevent them.

Bridges are largely replaced by switches, which are essentially multiport bridges
with greater performance and scalability.
Access Point (Networking Layer – Layer 2)
Definition:

Allows wireless devices to connect to a wired LAN.

Bridge between wireless devices and the wired network.

Data Link Layer (Layer 2)

Uses Wi-Fi / IEEE 802.11 for wireless communication

Allows multiple wireless devices such as laptops, smartphones and tablets to
connect to the network.

Generally, provides a wireless access area within which devices can connect to
the LAN.
Working:

Wireless Device -> Wi-Fi/802.11 -> Access Point -> Wired LAN ->
Router/Internet

AP receives wireless frames from connected devices.

It forwards/bridges the traffic between the wireless network and wired LAN.

It also transmits data received from the wired network to the appropriate
wireless device.

AP therefore provides connectivity between wireless and wired network
segments.
Wireless Access Point vs Wi-Fi Router:
Access Point:

Primarily provides wireless access to an existing LAN.

Acts mainly as a Layer-2 bridge.

Usually does not need to perform routing, NAT or DHCP when deployed as a
standalone AP.

Multiple APs can be deployed to provide wider wireless coverage.
Wi-Fi Router:

Combines several functions, commonly including routing + wireless access point +
switch.

Connects the local network to another network/Internet.

May provide DHCP, NAT and firewall functions depending on the device.
Router (Layer 3 – Networking)
Definition

Connects different networks.

In a typical home network, the router connects the local LAN to external
networks such as the ISP/Internet.

Operates primarily at Layer 3 — Network Layer.

Uses IP addresses to determine where packets should be forwarded.
Working
1. Receives a packet.
2. Examines the destination IP address.
3. Checks its routing table.
4. Selects the appropriate route/next hop.
5. Forwards the packet toward the destination.
Key Functions

Routing — determines the path for packets.

Packet forwarding — forwards packets to the next hop.

Inter-network communication — connects different networks/subnets.

Logical addressing — works with IP addresses.

Modern routers may additionally provide NAT, DHCP, firewalling, etc.
Advantages

Connects different networks.

Enables communication between different IP networks/subnets.

Determines efficient routes using routing information.

Reduces broadcast traffic between networks because routers form broadcast
boundaries.

Can provide additional services such as NAT, DHCP and firewalling, depending on
the device.
Disadvantages

Generally, more complex and expensive than a basic switch.

Routing decisions introduce processing overhead.

Requires configuration and maintenance.

Can become a bottleneck if overloaded or poorly configured.

Router failure can disrupt communication between the networks it connects.
Networking Protocol (Layer 3 onwards):

Set of instructions for connecting device to communicate & exchange
information across networks easily and safely

Standardized by below institutes:
1. Institute of Electric and Electronics Engineers (IEEE)
2. Internet Engineer Task Force (IETF)
Internet Protocol/IP (Layer 3 – Network):

Network-layer protocol

Logical addressing and routing packets across the network

Identifies the source and destination.

Forwards packets but does not guarantee arrival of packets to destination

Eg: IPv4, IPv6, etc.

It has 2 parts:
1. Header:
o
Information added by the IP in front of the packet
o
Source and destination IP address
o
Other information like packet size, versions, header length, time to
live, etc.
2. Data Payload:
o

Actual information to be transferred
Header, TCP and Data payload together consist of IP datagram
Transmission Control Protocol /TCP (Layer 3 – Network):

Transport Layer Protocol

Communication standard that allows applications and programs to reliably
transport messages over the network

Responsible for breaking data that is obtained by the HTTPs request into
smaller packets

Adds a sequence number to each packet

The sequence number ensures that the packets can be properly reassembled in
the correct order at the receiving end

Provides services like reliable delivery, sequencing, acknowledgements,
retransmission, flow-control, error-detection, connection management, etc.

Eg: web traffic, email, file-transfer, etc.
Port (Layer 4 – Transport):

It is the logical communication endpoint used to identify a particular application
or service on a device.

Each of them acts like a private channel for two-way communication.

A server can listen for incoming connection requests on a particular port.

When the client connects, it specifies the server’s IP address and port number.

The server can then accept or reject the connection.

Once connection is accepted, TCP and IP get to work in data transmission
How to TCP/IP model works along with Port:


Example: Sending a Picture
o
Suppose a client wants to send an email with a picture to a server.
o
A picture is usually too large to be sent as one single packet.
o
TCP breaks the picture into multiple smaller IP packets.
o
TCP assigns a sequence number to each packet.
o
The packets may travel through the network and arrive at the
destination.
o
TCP uses the sequence numbers to put the packets back in the correct
order.
o
Once all packets are received, the original picture can be properly
reassembled.
Hypertext Transfer Protocol Secure /HTTPS (Layer 7 - Application):

Protocol that secures communication and data transfer between the user and
the website

Protects users from eavesdropping and man-in-the-middle attacks.

Relies both on TCP and IP for message transmission

HTTPS is secure version of HTTP that uses TLS encryption to provide
confidentiality, integrity and authentication between client and web-server.
File Transfer Protocol/ FTP (Layer 7 - Application):

Protocol to transfer files to the website

Eg: uploading files in webpage

Application Layer Protocol

Uses TCP for reliable delivery
Gateway (Layer – Technically Everywhere):
Definition

Connects different networks or systems.

Entry/exit point between networks.

Depending on its implementation, it can perform protocol, data-format, or
communication-function translation.
Working
1. Receives data from one network/system.
2. Examines the requirements of the destination system.
3. Performs the required conversion/translation.
4. Forwards the resulting data toward the destination.
Key Functions

Protocol translation — allows systems using different protocols to communicate.

Data-format translation — converts data into a format the destination can
understand.

Network interconnection — connects different networks/systems.

Routing/forwarding — may perform network-level forwarding depending on
implementation.

Entry/exit point — provides a path from one network/system to another.
Advantages

Enables communication between different or incompatible systems.

Supports protocol conversion.

Provides interoperability between heterogeneous networks.

Can provide additional services depending on implementation.
Disadvantages

More complex than basic networking devices.

Translation can introduce processing overhead.

Configuration and maintenance can be complicated.

Failure of a gateway can disrupt communication between connected systems.