Network Model: OSI and TCP/IP Model (ET: 2.5 Hours)
OSI and TCP/IP Model
    • 1
      OSI Model OSI Introduction
      OSI Model Basic Introduction: Theory and Video Tutorial
      Watch Video: OSI Model Explanation
      OSI Model — Open Systems Interconnection Model
      Definition: The OSI (Open Systems Interconnection) Model is a conceptual 7-layer reference model developed by the International Organization for Standardization (ISO) to describe how data is communicated between different computers and network devices. It helps us understand how data moves from one end device to another through a network.
      The OSI Model was introduced in 1984 and consists of seven layers:
      7. Application Layer → 6. Presentation Layer → 5. Session Layer → 4. Transport Layer → 3. Network Layer → 2. Data Link Layer → 1. Physical Layer
      Each layer performs a specific group of networking functions and works with protocols and services related to that layer. The OSI Model is mainly a reference model; real-world networking protocols do not always fit perfectly into only one OSI layer.
      Why is the OSI Model Needed?
      Imagine two computers running different operating systems, such as Microsoft Windows and macOS. They still need to communicate over a network. Communication is possible because networking uses standardized protocols, addressing methods, data formats and transmission rules.
      The OSI Model divides the complicated communication process into seven manageable layers. Each layer performs particular tasks and provides services to the layer above it.
      Important Concept: Protocols
      A protocol is a set of rules and conventions used for communication between network devices. Each OSI layer is associated with particular networking functions and protocols.
      For example, HTTP/HTTPS is associated with the Application layer, TCP/UDP with the Transport layer, IP with the Network layer, and Ethernet with the Data Link/Physical layers.
      7. Application Layer
      The Application Layer is the topmost layer of the OSI Model. It provides network services directly to network-aware applications and acts as the interface between applications and network services.
      Important: Application Layer does not mean that applications such as Chrome, Firefox or Outlook themselves are the OSI layer. Rather, these applications use application-layer protocols and services.
      Main functions:
      • Provides network services to applications.
      • Supports web browsing, email, file transfer and other network activities.
      • Provides services such as resource sharing and remote access.
      Examples of Application-layer protocols:
      • HTTP/HTTPS — Web communication
      • FTP — File transfer
      • SMTP — Sending email
      • DNS — Domain name resolution
      • SSH/Telnet — Remote access
      6. Presentation Layer
      The Presentation Layer is responsible for how data is represented, encoded and transformed so that different systems can understand it.
      Main functions:
      1. Translation: Converts data between different representation formats or character encodings when required. For example, conversion between different character-code representations.
      2. Data Compression: Reduces the amount of data that needs to be transmitted or stored. Compression may be lossless or lossy.
      3. Encryption and Decryption: Protects data by transforming readable information into an encoded form and recovering it at the receiving side.
      Remember: The traditional OSI description commonly associates Translation, Compression and Encryption/Decryption with the Presentation Layer. In modern TCP/IP networking, these functions are often implemented by application protocols and libraries rather than as a separate universal layer.
      5. Session Layer
      The Session Layer is responsible for establishing, managing and terminating communication sessions between applications.
      Main functions:
      • Establishes communication sessions.
      • Maintains and manages sessions.
      • Terminates sessions when communication is complete.
      • Provides synchronization and, conceptually, checkpoints for long data exchanges.
      Examples historically associated with Session-layer services include NetBIOS and other session-management mechanisms.
      Authentication and Authorization: These concepts are important in network communication, but they are not exclusively Session-layer functions. In modern networks, authentication and authorization can be handled by application-layer protocols, security protocols, operating systems and dedicated identity systems.
      4. Transport Layer
      The Transport Layer provides end-to-end communication between applications running on different hosts. It is responsible for delivering data to the correct application and, depending on the protocol, providing reliability and flow control.
      Data Unit: Segment is commonly used for TCP. UDP uses the term datagram.
      Main functions:
      1. Segmentation: Large application data can be divided into smaller units for transmission.
      2. Port Addressing: Port numbers identify the destination application or service on a host.
      3. Flow Control: Helps prevent a sender from overwhelming a receiver. TCP uses mechanisms such as the receive window for flow control.
      4. Error Control and Reliability: TCP can detect missing or corrupted data and use acknowledgments, retransmission and sequencing to provide reliable delivery.
      5. Ordering and Reassembly: TCP uses sequence numbers so that received data can be reconstructed in the correct order.
      Major Transport-layer protocols:
      TCP (Transmission Control Protocol): Connection-oriented and reliable.
      UDP (User Datagram Protocol): Connectionless and has no built-in guarantee of delivery, ordering or retransmission.
      TCP is commonly used for: Web traffic, email, file transfer and other applications where reliable delivery is important.
      UDP is commonly used for: DNS queries, real-time audio/video, online gaming and applications where low overhead or timeliness is important. Modern protocols such as QUIC use UDP while implementing reliability and other functions above UDP.
      3. Network Layer
      The Network Layer is responsible for delivering data packets between different networks. This is the layer most closely associated with IP addressing and routing.
      Data Unit: Packet
      Main functions:
      1. Logical Addressing: Uses logical addresses such as IPv4 and IPv6 to identify source and destination interfaces/hosts at the network layer.
      2. Routing: Determines how packets should be forwarded toward their destination across interconnected networks.
      3. Path Determination: Routing protocols help network devices learn or calculate suitable paths through a network.
      Layer 3 device: Router
      Examples of routing protocols: OSPF, BGP and IS-IS.
      2. Data Link Layer
      The Data Link Layer provides node-to-node delivery over a particular local or link-level network. It organizes network-layer packets into frames and controls how frames are transmitted over a specific link.
      Data Unit: Frame
      Major functions:
      1. Framing: Encapsulates a Network-layer packet inside a Data Link-layer frame.
      2. Physical/MAC Addressing: Ethernet and Wi-Fi commonly use MAC addresses for local link delivery.
      3. Media Access Control: Defines how devices share or access a transmission medium.
      4. Error Detection: Many Data Link technologies use mechanisms such as Frame Check Sequence (FCS) to detect errors in frames.
      5. Link-level delivery: Provides communication between devices on the same network link.
      1. Physical Layer
      The Physical Layer is the lowest layer of the OSI Model. It is responsible for transmitting and receiving raw bits over a physical medium.
      Data Unit: Bits
      Main functions:
      • Represents bits as physical signals.
      • Defines characteristics of the transmission medium.
      • Defines signaling, connectors, pin arrangements and transmission characteristics where applicable.
      • Transmits signals through copper, fiber or wireless media.
      Examples:
      • Copper cable: Electrical signals
      • Optical fiber: Light signals
      • Wireless: Radio-frequency electromagnetic signals
      At the receiving side, the Physical Layer receives the physical signal and converts it into a bit stream that can be processed by the Data Link Layer.
      Data Encapsulation in OSI Model
      When data travels from the sender's application toward the network, each lower layer adds its own control information.
      Application → Data
      Transport → Segment / Datagram
      Network → Packet
      Data Link → Frame
      Physical → Bits
      At the receiving side, the reverse process occurs. Each layer removes or processes the information added by its corresponding layer. This process is called decapsulation.
      OSI Layers at a Glance
      LayerNameMajor FunctionData Unit
      7ApplicationNetwork services for applicationsData
      6PresentationTranslation, compression, encryptionData
      5SessionSession establishment, management and terminationData
      4TransportEnd-to-end delivery, ports, reliability/flow control depending on protocolSegment / Datagram
      3NetworkLogical addressing and routingPacket
      2Data LinkFraming, MAC addressing, link access, error detectionFrame
      1PhysicalTransmission of raw bits as signalsBits
      Easy Way to Remember the 7 Layers
      Top to Bottom: All People Seem To Need Data Processing
      A — Application
      P — Presentation
      S — Session
      T — Transport
      N — Network
      D — Data Link
      P — Physical
      Bottom to Top: Please Do Not Throw Sausage Pizza Away
      P — Physical
      D — Data Link
      N — Network
      T — Transport
      S — Session
      P — Presentation
      A — Application

    • 2
      OSI Model OSI Introduction
      Why Do We Need the OSI Model in Networking?
      In the early days of networking, communication between computers was very limited. Computers were large, expensive, and mostly worked independently without much interaction.
      As networking technology expanded, different companies developed their own proprietary communication methods. These methods only worked within the same company or environment.
      For example, a computer made by one company could not easily communicate with a system developed by another company. There was no common structure, standard rules, or shared communication method. This created major compatibility problems, especially when organizations tried to connect systems from different vendors.
      Solves Compatibility Issues
      The absence of standardization made data exchange difficult and costly. Different networks used different protocols, rules, and data formats, making communication unreliable and complicated.
      The OSI model solved this issue by dividing the communication process into multiple logical layers.
      Each layer performs a specific function and communicates only with its neighboring layers. This layered structure makes networking systems easier to understand, manage, and control.
      Creates a Universal Framework
      The main goal of the OSI model was to create a universal framework that all vendors and organizations could follow.
      The OSI model introduced the concept of Interoperability, allowing different heterogeneous systems to communicate smoothly even if they use different technologies.
      Each Layer Can Be Studied Independently
      Another important purpose of the OSI model is to simplify networking education.
      Networking includes hardware, software, signals, protocols, and applications working together. Studying all these concepts at once can be difficult for beginners.
      By dividing communication into layers, the OSI model allows learners to study one layer at a time. This makes learning more organized and logical.
      Useful in Troubleshooting
      The OSI model is very useful for troubleshooting network problems.
      When a network issue occurs, engineers often identify the problem by referring to a specific layer, such as “Layer 1 issue” or “Layer 7 issue.”
      This troubleshooting approach is based directly on the OSI model.

    • 3
      OSI Model OSI Introduction
      Explain the Importance of Layered Architecture in the OSI Model
      Layered architecture is the main concept behind the OSI model. Instead of creating one large and complex communication system, the OSI model divides the communication process into smaller and manageable layers.
      Each layer performs a specific task and works independently without affecting other layers. A layer provides services to the layer above it and receives services from the layer below it.
      Benefits of Layered Architecture
      • Modularity: If changes are made in one layer, other layers do not need modification. For example, introducing fiber optic transmission mainly affects the physical layer only.
      • Fault Isolation: If a network problem occurs, engineers can check each layer separately to identify the exact source of the problem quickly.
      • Independent Development: Different network protocols can be developed independently while still working together properly.


    • 4
      OSI Model OSI Introduction
      Expain the Layers of the OSI Model
      The OSI model consists of seven layers arranged from bottom to top according to their functions. Each layer performs a specific task in the communication process.
      1. Physical Layer − Transmits individual bits from one device to another through a physical medium.
      2. Data Link Layer − Provides reliable transfer of data frames between directly connected nodes.
      3. Network Layer − Handles addressing and routing to deliver packets from source to destination.
      4. Transport Layer − Ensures complete delivery of messages from source host to destination host.
      5. Session Layer − Establishes and manages communication sessions between users.
      6. Presentation Layer − Handles translation, compression, and encryption of data.
      7. Application Layer − Provides network services and APIs to end users and applications.
      The lower layers mainly deal with hardware and data transmission, while the upper layers focus on software and user interaction.
      When sending data, it moves from the Application Layer down to the Physical Layer. When receiving data, it moves from the Physical Layer up to the Application Layer.

    • 5
      OSI Model OSI Introduction
      Describe the Network Support Layers, Transport Layer, and User Support Layers of the OSI Model.
      What are Network Support Layers in the OSI Model?
      The bottom three layers of the OSI model are called Network Support Layers. These layers are responsible for the actual transmission of data across the network.
      • Physical Layer − Transmits raw bits through physical media and defines cables, signals, and transmission methods.
      • Data Link Layer − Ensures reliable data transfer between directly connected devices using frames and MAC addresses.
      • Network Layer − Handles logical addressing and routing to deliver packets from source to destination.
      These layers together ensure physical and logical communication over the network.
      What is the Role of the Transport Layer in the OSI Model?
      The Transport Layer acts as a bridge between the network support layers and user support layers.
      It provides end-to-end communication, divides messages into segments, controls flow, and handles error detection and retransmission.
      Protocols like TCP and UDP operate at this layer.
      What are User Support Layers in the OSI Model?
      The top three layers of the OSI model are known as User Support Layers because they interact closely with users and application software.
      • Session Layer − Manages communication sessions between systems.
      • Presentation Layer − Handles data translation, compression, and encryption.
      • Application Layer − Provides services like email, web browsing, and file transfer to users.

    • 6
      OSI Model OSI Introduction
      Advantages and Disadvantages of OSI model
      Advantages of OSI Model
      • The OSI model supports both connection-oriented and connectionless services.
      • Users can choose connectionless services for faster communication and connection-oriented services for reliable communication.
      • The OSI model supports a wide variety of networking protocols.
      • Its layered structure makes networking easier to understand and troubleshoot.
      Disadvantages of OSI Model
      • The Session Layer and Presentation Layer are considered less useful compared to other layers.
      • Some services are repeated in different layers, such as Transport Layer and Data Link Layer functions.
      • Layers cannot work simultaneously because each layer depends on data from the previous layer.

    • 7
      OSI Model OSI Introduction
      How Data Travels from One Computer to Another Through the OSI Layers

      When data is sent from one computer to another, it passes down through the OSI layers at the sender, travels through the network as bits, and then moves up through the layers at the receiver.

      Application Layer (Layer 7): The sender creates the original Data.
      Transport Layer (Layer 4): Adds a TCP header containing port numbers, creating a Segment.
      Network Layer (Layer 3): Adds an IP header containing source and destination IP addresses, creating a Packet.
      Data Link Layer (Layer 2): Adds MAC addresses and a CRC trailer, creating a Frame.
      Physical Layer (Layer 1): Converts the frame into Bits (0s and 1s) and transmits them through the network.

      At the receiving computer, the process happens in reverse:

      Bits → Frame → Packet → Segment → Data

      The receiver removes each layer's header/trailer (decapsulation) until the original data reaches the Application Layer.

    • 8
      OSI Model OSI Introduction
      Protocol used in different layer of OSI model
      OSI LayerProtocols
      ApplicationDNS, HTTP, HTTPS, FTP, POP3, SMTP, SNMP, IMAP
      PresentationJPEG, TIFF, MPEG, MIDI, SSL, TLS
      SessionPPTP, NETBIOS, SCP, SQL
      TransportUDP, TCP
      NetworkIP, IPV6, IPX, RIP, ICMP, IGMP
      Data LinkFDDI, ARP, CDP, MPLS, STP, PPP
      PhysicalDSL, Bluetooth, WiFi, 802.11

    • 9
      TCP/IP Model TCP/IP Model Introduction
      TCP/IP Model Basic Introduction: Theory and Video Tutorial
      Watch Video: TCP/IP Model Explanation
      TCP/IP Protocol Suite — Exam Notes
      TCP/IP: Transmission Control Protocol / Internet Protocol.
      Definition: TCP/IP is a practical network model/protocol suite designed to support communication between computers, including computers from different manufacturers.
      Important: TCP/IP is not only TCP and IP; it consists of many protocols arranged into different layers.
      Why Protocols Are Needed
      Protocol is an agreed set of rules that makes communication between computers possible. Computers need common rules for message format, data, addressing and communication.
      TCP/IP Layers
      LayerMain FunctionImportant Protocols / Data Unit
      ApplicationProvides network services to user applications.HTTP, HTTPS, FTP, DNS, DHCP, SMTP, POP3, IMAP
      TransportEnd-to-end communication, segmentation, reliability and flow/congestion control.TCP Segment / UDP Datagram
      Network / InternetLogical addressing, routing and path determination.IP Packet
      Data LinkFraming, MAC addressing, media access and error detection.Ethernet Frame
      PhysicalTransmits bits as physical signals through the medium.Bits
      ⭐ Data Encapsulation
      At the sender side, each lower layer encapsulates the data received from the layer above.
      Application → Message → Transport → Segment/Datagram → Network → IP Packet → Data Link → Ethernet Frame → Physical → Bits
      At the receiver side, the corresponding headers are removed layer-by-layer. This process is called Decapsulation.
      Physical Layer
      Function: Actual transmission of data takes place at the Physical Layer.
      It converts binary 0s and 1s into physical signals and transmits them through the medium.
      Copper/LAN Cable → Electrical Signal
      Optical Fiber → Light Signal
      Wireless/Air → Radio Signal
      Important: The signal depends on the type of transmission medium.
      Data Link Layer
      Data Unit: Ethernet Frame.
      The Data Link Layer is divided into two sublayers:
      MAC: Medium Access Control
      LLC: Logical Link Control
      MAC Sublayer Functions: Data encapsulation and media access.
      The MAC sublayer adds a header and trailer to the IP packet. The header contains source and destination MAC addresses, while the trailer contains error-checking information.
      MAC Address: A traditional Ethernet MAC address is a 6-byte link-layer address associated with a network interface.
      Important: Traditional shared Ethernet used CSMA/CD for media access.
      Network Layer
      Main Functions:
      1. Logical Addressing
      2. Routing
      3. Path Determination
      The Network Layer adds IP addresses to TCP segments or UDP datagrams to form IP packets and uses routers to forward them between networks.
      Logical Address: IP Address.
      Data Unit: IP Packet.
      Important Protocol: IP.
      ⭐ Routing vs Path Determination
      Routing: Moving an IP packet from source to destination across different networks.
      Path Determination: Choosing the best possible path for data delivery.
      Examples: OSPF, BGP, IS-IS.
      ⭐ Same Network vs Different Network
      SituationWhat Happens?
      Same NetworkDestination MAC can be resolved locally; routing between networks is not required.
      Different NetworkPacket is forwarded through a router; the MAC address changes at each link/hop while the destination IP remains the same for the end-to-end communication.
      ⭐ ARP
      ARP (Address Resolution Protocol) is used to obtain a MAC address corresponding to an IP address on the local network.
      Key Point: When the destination is on another network, the sender normally uses the router/default gateway's MAC address for the local Ethernet frame rather than the remote host's MAC address.
      Transport Layer
      The Transport Layer receives messages from the Application Layer and uses either TCP or UDP.
      TCP — Transmission Control Protocol
      TCP is: Connection-oriented and reliable.
      TCP Data Unit: Segment.
      Major Features:
      • Segmentation
      • Reliable delivery
      • Ordered delivery
      • Error detection
      • Retransmission of lost data
      • Duplicate detection/discarding
      • Flow/congestion control
      ⭐ TCP Three Main Phases
      1. Connection Establishment → Three-Way Handshake
      2. Data Transfer → Reliable and ordered data transmission
      3. Connection Termination → Four-Way Handshake
      ⭐ TCP Three-Way Handshake
      Client → Server: Connection Request
      Server → Client: Acknowledgement
      Client → Server: Final Acknowledgement
      Remember: TCP connection establishment = 3-Way Handshake.
      UDP — User Datagram Protocol
      UDP is: Connectionless and generally faster/lower overhead than TCP.
      UDP Data Unit: Datagram.
      Important: UDP does not guarantee delivery or correct ordering of datagrams.
      Common Uses: DNS, DHCP, SNMP, RIP and streaming applications.
      ⭐ TCP vs UDP
      TCPUDP
      Connection-orientedConnectionless
      ReliableNo built-in delivery guarantee
      Ordered deliveryNo built-in ordering guarantee
      RetransmissionNo built-in retransmission
      Generally higher overheadGenerally lower overhead
      Data Unit: SegmentData Unit: Datagram
      Application Layer
      The Application Layer provides network services used by applications such as web browsers and email programs.
      ProtocolFunction
      DNSDomain Name System; translates domain names and IP addresses.
      DHCPAutomatically assigns IP configuration to network devices.
      FTPFile Transfer Protocol; used for file transfer.
      HTTPUsed for web communication.
      HTTPSSecure HTTP communication.
      SMTPUsed for sending email.
      POP3Used by email clients to retrieve messages.
      IMAPUsed for accessing and managing email messages on a server.
      IRCInternet chat protocol.


    • 10
      TCP/IP Model TCP/IP Model Introduction
      What is TCP/IP Model?

      The TCP/IP Model provides a standardized set of protocols to ensure that data transmission is efficient, secure, and error-free. It is a concise version of the OSI Model with only four layers, in contrast to the OSI Model's seven layers. This four-layer approach makes TCP/IP more practical for modern networking needs and aligns closely with how real-world networking works.

      Layers of the TCP/IP Model

      1. Application Layer
      2. Transport Layer
      3. Network/Internet Layer (IP)
      4. Network Access Layer

    • 11
      TCP/IP Model TCP/IP Model Introduction
      Draw relation to TCP/IP Protocol Suite to OSI Reference Model
      Watch Video: Relation OSI and TCP/IP

    • 12
      TCP/IP Model TCP/IP Model Introduction
      OSI vs TCP/IP
      Watch Video: OSI vs TCP/IP

Topic Wise Question Bank
All Topics
    • ☆
      1
      Computer NetworkOSI/TCP-IP
      Draw a tabular representation of the TCP/IP Model. Explain the function of each layer, protocols related to each layer, and associated devices and software. Describe different types of Network Firewalls. Explain the advantages of Next-Generation Firewall (NGFW) over a Traditional Firewall.
      CB, AE(IT)/AME, 24 | AME/ANE/AE

      TCP/IP Model (Tabular Representation)

      Types of Network Firewall

      • Packet Filtering Firewall: Filters packets based on IP, port, protocol.
      • Stateful Inspection Firewall: Tracks connection state and allows valid traffic.
      • Proxy Firewall: Acts as intermediary between user and internet.
      • Application Firewall: Filters traffic at application layer.
      • Next-Generation Firewall (NGFW): Advanced firewall with deep inspection and security features.

      Advantages of NGFW over Traditional Firewall

      • Deep Packet Inspection: Analyzes full packet content, not just headers.
      • Application Awareness: Identifies and controls specific applications.
      • Intrusion Prevention (IPS): Detects and blocks attacks in real-time.
      • Better Security: Protects against modern threats like malware and phishing.
      • User-Based Control: Policies based on user identity, not just IP.

    • ☆
      2
      Computer NetworkOSI/TCP-IP
      What is OSI model? Explain the functions of each layer with examples.
      Combined Bank, SO(IT-23), 26 | Senior Officer (IT)

      The OSI (Open Systems Interconnection) Model is a reference framework that explains how data travels from one device to another over a network. It divides the entire communication process into seven layers. Each layer has its own specific job and passes data to the next layer. It helps developers and network engineers understand and troubleshoot network problems easily.

      The Seven Layers of the OSI Model

      1. Physical Layer

      This is the lowest layer. It deals with the actual physical connection between devices. It transmits raw bits (0s and 1s) through cables, switches, and hubs.

      Function: Bit transmission, voltage levels, cable types, and signal timing.

      Devices: Cables, hubs, repeaters, and network interface cards (NIC).<

      Example: An Ethernet cable carrying electrical signals between a computer and a router.

      2. Data Link Layer

      This layer handles data transfer between two directly connected devices on the same network. It makes sure data is delivered without errors.

      Function: Framing, MAC addressing, error detection, and flow control.

      Devices: Switches and bridges.

      Example: A switch uses MAC addresses to send data to the correct computer in a local network.

      3. Network Layer

      This layer is responsible for moving data from one network to another. It finds the best path (routing) for the data to reach its destination.

      Function: Logical addressing (IP), routing, and path selection.

      Devices: Routers.

      Example: A router uses IP addresses to send a packet from your home network to a website server on the internet.

      4. Transport Layer

      This layer ensures data is delivered completely and correctly. It breaks large data into smaller segments and reassembles them at the other end.

      Function: Segmentation, error recovery, and flow control.

      Protocols: TCP and UDP.

      Example: TCP breaks an email into small parts, sends them, and puts them back together in the right order at the receiver.

      5. Session Layer

      This layer creates, manages, and ends communication sessions between two devices. It keeps the conversation active and organized.

      Function: Session establishment, maintenance, and termination.

      Example: When you log into a video call, the session layer sets up and keeps the call active until you hang up.

      6. Presentation Layer

      This layer acts like a translator. It formats, encrypts, and compresses data so the application layer can understand it.

      Function: Data translation, encryption, decryption, and compression.

      Example: SSL/TLS encryption on a website that keeps your password safe during login.

      7. Application Layer

      This is the top layer where users directly interact with the network. It provides services like email, file transfer, and web browsing.

      Function: User interface and network services for applications.

      Protocols: HTTP, FTP, SMTP, DNS.

      Example: A web browser using HTTP to load a webpage when you type www.google.com.

      Summary Table:

      LayerNameMain FunctionExample
      7ApplicationUser services like web and emailBrowser loading a website
      6PresentationEncryption and data formattingSSL encrypting login password
      5SessionManage connection sessionsKeeping a video call active
      4TransportReliable data deliveryTCP sending email in parts
      3NetworkRouting and IP addressingRouter sending packet to server
      2Data LinkError-free local deliverySwitch using MAC address
      1PhysicalRaw bit transmissionEthernet cable carrying signal

    • ☆
      3
      Computer NetworkOSI/TCP-IP
      Draw and explain the seven layers of the OSI model.
      CB, ANE, 2026 | Assistant Network Engineer
    • ☆
      4
      Computer NetworkOSI/TCP-IP
      What is OSI model? Describe briefly about OSI model layer? Difference between OSI and TCP IP layer?
      SPCBL, SAME, 22 | AME/ANE/AE

      The OSI (Open Systems Interconnection) Model is a conceptual framework that standardizes the functions of a network communication system by dividing it into seven distinct layers. These layers ensure seamless communication between different systems and networks by defining protocols and packet transfer processes.

      osi_model_function_en

      Difference Between OSI and TCP/IP Model:

      osi_vs_tcpip



    • ☆
      5
      Computer NetworkOSI/TCP-IP
      Difference between OSI model and TCP/IP model. Relation between Data, Segment, Packet and Bit in OSI model. 10
      CB, SO(IT), 23 | Senior Officer (IT)

      Difference between OSI Model and TCP/IP Model

      osi_vs_tcpip

      Relation between Data, Segment, Packet and Bit in OSI Model

      As data moves down through the OSI layers, it changes its form. This process is called encapsulation.

      • Data: At the Application, Presentation, and Session layers, information is called Data.
      • Segment: At the Transport layer, data is divided into Segments (TCP) or Datagrams (UDP).
      • Packet: At the Network layer, segments are encapsulated into Packets.
      • Frame: At the Data Link layer, packets are converted into Frames.
      • Bit: At the Physical layer, frames are transmitted as Bits (0s and 1s).

      Flow: Data → Segment → Packet → Frame → Bit


    • ☆
      6
      Computer NetworkOSI/TCP-IP
      At which layer of the OSI model does a standard Router primarily operate, and what is the specific name of the Protocol Data Unit (PDU) at this layer? A router has four contiguous /24 routing table entries: 10.1.0.0/24, 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24. If you summarize these into a single route, what will be the new CIDR notation?
      CB, AME/AE(IT-23), 26 | AME/ANE/AE

      A standard router primarily operates at the Network Layer, which is Layer 3 of the OSI model.

      The Protocol Data Unit (PDU) at the Network Layer is called a Packet.

      Given Routing Entries:
      10.1.0.0/24
      10.1.1.0/24
      10.1.2.0/24
      10.1.3.0/24

      These four networks are continuous or contiguous because their network addresses increase sequentially.

      First Network: 10.1.0.0/24
      Range: 10.1.0.0 to 10.1.0.255

      Second Network: 10.1.1.0/24
      Range: 10.1.1.0 to 10.1.1.255

      Third Network: 10.1.2.0/24
      Range: 10.1.2.0 to 10.1.2.255

      Fourth Network: 10.1.3.0/24
      Range: 10.1.3.0 to 10.1.3.255

      Together, these four networks cover addresses from:
      10.1.0.0 to 10.1.3.255

      Each /24 network contains 256 addresses.

      So total addresses become:
      256 + 256 + 256 + 256 = 1024 addresses

      To represent 1024 addresses, 10 host bits are required.

      Since IPv4 address contains 32 bits:
      32 − 10 = 22

      Therefore, the summarized CIDR notation becomes:
      10.1.0.0/22

      Final Answer:
      Router Layer = Network Layer / Layer 3
      PDU Name = Packet
      Supernet = 10.1.0.0/22


    • ☆
      7
      Computer NetworkOSI/TCP-IP
      Differentiate between OSI Model and TCP/IP Model. Draw the diagram of 4 Layers of TCP/IP Model including the main function of each layer and related protocols. List some basic functions performed at MAC layer.
      Rupali, ANE, 23 | AME/ANE/AE

      OSI vs TCP/IP Model

      osi_vs_tcpip

      TCP/IP Layer with protocol

      a

      Basic Functions Performed at MAC Layer

      • Frame Encapsulation: Converts data into frames for transmission.
      • MAC Addressing: Uses physical (MAC) addresses to identify devices.
      • Error Detection: Detects transmission errors using CRC.
      • Medium Access Control: Controls access to the shared transmission medium.
      • Collision Handling: Manages data collision in shared networks.
      • Frame Synchronization: Identifies start and end of data frames.


    • ☆
      8
      Computer NetworkOSI/TCP-IP
      Mention the layer of OSI Model and Function of each layer.
      Combined Bank, O(IT-22), 26 | Officer (IT)

      OSI Model Layers and Their Functions

      1. Physical Layer: Responsible for the transmission of raw bits over a physical medium. It defines cables, connectors, voltage levels, and data rates.

      2. Data Link Layer: Ensures error-free data transfer between two directly connected nodes. It handles framing, error detection, and MAC addressing.

      3. Network Layer: Manages logical addressing and routing of data packets across different networks.
      Example: IP addressing.

      4. Transport Layer: Provides reliable data transfer between end systems. It handles segmentation, flow control, and error recovery.
      Example: TCP, UDP.

      5. Session Layer: Manages sessions between applications. It establishes, maintains, and terminates communication sessions.

      6. Presentation Layer: Translates data formats, handles encryption/decryption, and data compression.

      7. Application Layer: Provides network services directly to end users and applications.
      Example: HTTP, FTP, SMTP.


    • ☆
      9
      Computer NetworkOSI/TCP-IP
      In order to prevent that the company decided to add end to end encryption techniques which layer of the OSI model is suitable to work in considering parameters like development time, software maintainability and development cost, Give reasons for your concepts.
      BB, AP, 23 | Assistant Programmer

      Suitable OSI Layer for End-to-End Encryption

      To implement end-to-end encryption (E2EE) while considering development time, software maintainability, and development cost, the most suitable layer of the OSI model is the Application Layer (Layer 7).

      Reasons for Choosing the Application Layer

      • Faster Development Time: Encryption at the application layer can be implemented directly within the application logic. Developers do not need to modify lower-level networking protocols, which significantly reduces development time.
      • Better Software Maintainability: Application-layer encryption is easier to update, debug, and maintain. Changes can be made without affecting the underlying network infrastructure or operating system.
      • Lower Development Cost: No changes are required in routers, switches, or transport-layer implementations. This avoids hardware upgrades and reduces overall implementation cost.
      • True End-to-End Security: Data is encrypted at the sender’s application and decrypted only at the receiver’s application. Intermediate systems (routers, proxies, servers) cannot read the data.
      • Platform Independence: Application-layer encryption works across different networks, protocols, and platforms without compatibility issues.

      Why Not Lower Layers?

      • Transport Layer (e.g., TLS): Requires certificate management and protocol-level integration, increasing complexity and cost.
      • Network/Data Link Layers: Require hardware or OS-level changes, leading to high cost and poor maintainability.

      Considering development time, cost efficiency, and long-term maintainability, implementing end-to-end encryption at the Application Layer is the best and most practical choice.


    • ☆
      10
      Computer NetworkOSI/TCP-IP
      Write down the functionality of OSI model.
      CB, AP, 20 | Assistant Programmer
    • ☆
      11
      Computer NetworkOSI/TCP-iP
      Synthia wants to send an email to her friend. He sends the email through the application and transport layer.

      (a)Mention the protocol of application layer and transport layer

      (b)Draw a diagram from the above scenario.
      BB, AD(ICT), 25 | Bangladesh Bank

      Protocols used in Application Layer and Transport Layer:

      Application Layer: The protocol commonly used here for sending emails is SMTP (Simple Mail Transfer Protocol).

      Transport Layer: This layer is responsible for the reliable transmission of data between applications. The commonly used protocol at this layer is TCP (Transmission Control Protocol), which ensures that the data is delivered accurately and in order.

      ব্যাখ্যা দেখুন:

      Application Layer Protocol :Simple Mail Transfer Protocol(SMTP)

      ইমেইল পাঠানোর জন্য Application Layer-এ SMTP ব্যবহৃত হয়। SMTP এর কাজ হলো একটি কম্পিউটার থেকে অন্য কম্পিউটারে ইমেইল মেসেজ পাঠানো। এটি ব্যবহারকারীকে সহজে ইমেইল লিখে পাঠানোর সুযোগ দেয় এবং সার্ভারগুলোর মধ্যে মেসেজ ট্রান্সফার পরিচালনা করে।

      Transport Layer Protocol :TCP (Transmission Control Protocol)

      Transport Layer-এর মূল কাজ হলো ডেটা নির্ভরযোগ্যভাবে (reliably) গন্তব্যে পৌঁছে দেওয়া।

      TCP (Transmission Control Protocol) ব্যবহার করা হয় কারণ:

      • এটি ডেটাকে ছোট ছোট অংশে (segments) ভেঙে পাঠায়।
      • প্রতিটি অংশ ঠিকভাবে এবং সঠিক ক্রমে (in order) পৌঁছেছে কিনা তা যাচাই করে।
      • ডেটা হারিয়ে গেলে পুনরায় পাঠানোর ব্যবস্থা করে।

      ইমেইল একটি গুরুত্বপূর্ণ যোগাযোগ মাধ্যম। যদি মেসেজের কোনো অংশ হারিয়ে যায় বা এলোমেলোভাবে পৌঁছে যায়, তাহলে ইমেইলটি অপূর্ণ বা ভুল হয়ে যাবে। এজন্য Application Layer-এ SMTP ইমেইল পাঠানোর নিয়ম ঠিক করে দেয়, আর Transport Layer-এ TCP ডেটা সঠিকভাবে, সম্পূর্ণভাবে এবং নির্ভরযোগ্যভাবে পৌঁছানো নিশ্চিত করে।

      (b) Answer:
      The diagram illustrates the process of sending an email from the sender to the receiver

      ব্যাখ্যা দেখুন:

      Sender’s Device → Sender’s Mail Server এর সাথে SMTP protocol ব্যবহার করে যোগাযোগ করে।
      Sender’s Mail Server → ইন্টারনেটের মাধ্যমে SMTP ব্যবহার করে ইমেইলটি Receiver’s Mail Server-এ পাঠায়।
      Receiver’s Mail Server → ইমেইলটি Receiver’s Device-এ পৌঁছে দেওয়ার জন্য POP3 অথবা IMAP protocol ব্যবহার করে।


  • What is the OSI Model? (Definition + Introduced By)
  • Why is the OSI Model Needed? + Importance of Layered Architecture
  • Explain All 7 Layers of the OSI Model (Function Shortly)
  • PDU in Every OSI Layer
  • Protocols Used in Different OSI Layers
  • Network Support Layers, Transport Layer & User Support Layers
  • Advantages and Disadvantages of the OSI Model
  • What is the TCP/IP Model? (Definition)
  • Explain All 4 Layers of the TCP/IP Model (Function Shortly)
  • Protocols Used in Different TCP/IP Layers
  • OSI Model vs TCP/IP Model (Layer, Architecture & Protocol Comparison)
  • Mapping of TCP/IP Protocol Suite to the OSI Reference Model
  • Encapsulation and Decapsulation in OSI/TCP-IP Models
  • Practical Example: How Data Travels from One Computer to Another Through the Layers
PRACTICE MODE
Sheet11
0 of 123 answered
MCQ OSI, TCP/IP 123 questions
Q1
MCQ OSI, TCP/IP

Which statement about PDU naming is most accurate?

Q2
MCQ OSI, TCP/IP

Which PDU is normally associated with UDP at the Transport Layer?

Q3
MCQ OSI, TCP/IP

Which statement correctly compares a TCP segment and an IP packet?

Q4
MCQ OSI, TCP/IP

Which sequence correctly represents the data units as information moves downward from Transport to Physical Layer?

Q5
MCQ OSI, TCP/IP

Which OSI layer is responsible for flow control between directly connected devices at the Data Link level?

Q6
MCQ OSI, TCP/IP

Which statement best distinguishes Data Link error control from Transport reliability?

Q7
MCQ OSI, TCP/IP

Which OSI layer can provide segmentation and reassembly of application data?

Q8
MCQ OSI, TCP/IP

Why is segmentation useful at the Transport Layer?

Q9
MCQ OSI, TCP/IP

Which OSI layer is responsible for multiplexing multiple application processes over a host-to-host connection using port numbers?

Q10
MCQ OSI, TCP/IP

Which statement about TCP/IP and OSI is most accurate?

Q11
MCQ OSI, TCP/IP

Which mapping is correct between OSI and the common four-layer TCP/IP model?

Q12
MCQ OSI, TCP/IP

Which mapping is correct?

Q13
MCQ OSI, TCP/IP

Which mapping is correct for the upper OSI layers?

Q14
MCQ OSI, TCP/IP

Which statement about the OSI Application Layer and TCP/IP Application Layer is correct?

Q15
MCQ OSI, TCP/IP

Which layer would most likely be investigated if a user can reach a server by IP address but cannot resolve its domain name?

Q16
MCQ OSI, TCP/IP

A computer can ping another computer on the same LAN but cannot establish a TCP connection to a specific service. Which layer should be investigated after basic IP connectivity is confirmed?

Q17
MCQ OSI, TCP/IP

A host successfully creates an Ethernet frame but the frame cannot be transmitted because the network interface has no physical link. Which layer is the likely problem?

Q18
MCQ OSI, TCP/IP

Which scenario most clearly represents a Layer 3 problem?

Q19
MCQ OSI, TCP/IP

Which scenario most clearly represents a Layer 4 problem?

Q20
MCQ OSI, TCP/IP

Which layer is responsible for logical communication between hosts rather than direct physical transmission?

Q21
MCQ OSI, TCP/IP

Which layer provides node-to-node or hop-to-hop delivery on a local link?

Q22
MCQ OSI, TCP/IP

Which layer provides process-to-process communication?

Q23
MCQ OSI, TCP/IP

Which layer provides services directly to network applications such as web browsers and email clients?

Q24
MCQ OSI, TCP/IP

Which protocol-layer combination is correct?

Q25
MCQ OSI, TCP/IP

Which protocol-layer combination is incorrect?

Q26
MCQ OSI, TCP/IP

Why can OSI troubleshooting be performed from lower layers upward?

Q27
MCQ OSI, TCP/IP

Which order is most appropriate for basic layered troubleshooting?

Q28
MCQ OSI, TCP/IP

Which statement about the Physical Layer is correct?

Q29
MCQ OSI, TCP/IP

Which statement about the Network Layer is correct?

Q30
MCQ OSI, TCP/IP

Which statement about the Transport Layer is correct?

Q31
MCQ OSI, TCP/IP

Which statement about the Session Layer is correct?

Q32
MCQ OSI, TCP/IP

Which statement about the Presentation Layer is correct?

Q33
MCQ OSI, TCP/IP

Which statement about the Application Layer is correct?

Q34
MCQ OSI, TCP/IP

Which layer would handle a problem where two systems use incompatible data formats?

Q35
MCQ OSI, TCP/IP

Which layer would be most relevant if a communication session needs to resume from a synchronization point after interruption?

Q36
MCQ OSI, TCP/IP

Which layer is responsible for delivering a packet across multiple interconnected networks?

Q37
MCQ OSI, TCP/IP

Which statement correctly describes hop-to-hop and end-to-end communication?

Q38
MCQ OSI, TCP/IP

Which layer is responsible for selecting a route but not for determining which application receives the data?

Q39
MCQ OSI, TCP/IP

Which combination correctly identifies three different addressing levels?

Q40
MCQ OSI, TCP/IP

Which of the following best explains why a router does not normally use a destination port number to choose the basic IP route?

Q41
MCQ OSI, TCP/IP

Which statement best explains why a switch and router perform different forwarding tasks?

Q42
MCQ OSI, TCP/IP

Which situation demonstrates decapsulation?

Q43
MCQ OSI, TCP/IP

Which situation demonstrates encapsulation?

Q44
MCQ OSI, TCP/IP

Which statement best describes the relationship between protocols and the OSI model?

Q45
MCQ OSI, TCP/IP

Why is the OSI model still useful even though modern Internet protocols are based primarily on TCP/IP?

Q46
MCQ OSI, TCP/IP

What is the OSI Model?

Q47
MCQ OSI, TCP/IP

Why is the OSI Model needed in networking?

Q48
MCQ OSI, TCP/IP

How many layers are present in the OSI Model?

Q49
MCQ OSI, TCP/IP

Which OSI layer is responsible for logical addressing and routing?

Q50
MCQ OSI, TCP/IP

Which OSI layer is responsible for reliable end-to-end delivery of data?

Q51
MCQ OSI, TCP/IP

Which OSI layer is responsible for establishing, managing, and terminating communication sessions?

Q52
MCQ OSI, TCP/IP

Which OSI layer is responsible for data translation, encryption, and compression?

Q53
MCQ OSI, TCP/IP

Which OSI layer is closest to the end user?

Q54
MCQ OSI, TCP/IP

Which layer of the OSI Model is responsible for transmitting raw bits over a physical medium?

Q55
MCQ OSI, TCP/IP

Which OSI layer is responsible for framing?

Q56
MCQ OSI, TCP/IP

Which PDU is associated with the Network Layer of the OSI Model?

Q57
MCQ OSI, TCP/IP

Which PDU is associated with the Data Link Layer?

Q58
MCQ OSI, TCP/IP

What is the PDU of the Physical Layer?

Q59
MCQ OSI, TCP/IP

Which protocol is primarily associated with the Transport Layer?

Q60
MCQ OSI, TCP/IP

What is the TCP/IP Model?

Q61
MCQ OSI, TCP/IP

Which layer is the lowest layer of the TCP/IP Model?

Q62
MCQ OSI, TCP/IP

Which TCP/IP layer corresponds approximately to the OSI Network Layer?

Q63
MCQ OSI, TCP/IP

Which protocol is the primary protocol of the TCP/IP Internet Layer?

Q64
MCQ OSI, TCP/IP

Which TCP/IP layer contains HTTP, FTP, SMTP, and DNS?

Q65
MCQ OSI, TCP/IP

Which OSI layers are broadly combined into the TCP/IP Application Layer?

Q66
MCQ OSI, TCP/IP

Which statement correctly compares OSI and TCP/IP models?

Q67
MCQ OSI, TCP/IP

Which sequence correctly represents the OSI layers from Layer 1 to Layer 7?

Q68
MCQ OSI, TCP/IP

Which group contains only OSI layers considered Network Support Layers?

Q69
MCQ OSI, TCP/IP

Which OSI layer acts as the boundary between Network Support Layers and User Support Layers?

Q70
MCQ OSI, TCP/IP

Which three OSI layers are commonly called User Support Layers?

Q71
MCQ OSI, TCP/IP

A network engineer wants to troubleshoot whether an Ethernet frame is being delivered correctly on a local network. Which OSI layer should be examined first?

Q72
MCQ OSI, TCP/IP

Which layer is responsible for determining the best path for a packet between different networks?

Q73
MCQ OSI, TCP/IP

Two applications communicate reliably even though packets may travel through multiple routers. Which OSI layer primarily provides this end-to-end reliability?

Q74
MCQ OSI, TCP/IP

Which statement best explains why the OSI model uses layers?

Q75
MCQ OSI, TCP/IP

Which statement about OSI layers is most accurate?

Q76
MCQ OSI, TCP/IP

A host receives an Ethernet frame containing an IP packet. Which layer processes the Ethernet header before passing the packet upward?

Q77
MCQ OSI, TCP/IP

Which OSI layer adds logical source and destination addresses during encapsulation?

Q78
MCQ OSI, TCP/IP

Which addressing type is most closely associated with the Data Link Layer?

Q79
MCQ OSI, TCP/IP

Which addressing type is primarily associated with the Transport Layer?

Q80
MCQ OSI, TCP/IP

Which combination correctly matches an OSI layer with its common PDU?

Q81
MCQ OSI, TCP/IP

Which PDU is created when a Network Layer packet is encapsulated by the Data Link Layer?

Q82
MCQ OSI, TCP/IP

Which process occurs as data moves down the OSI layers on the sending computer?

Q83
MCQ OSI, TCP/IP

Which process occurs as data moves upward through the layers on the receiving computer?

Q84
MCQ OSI, TCP/IP

A user sends an HTTP request to a remote web server. At which OSI layer does the HTTP request originate conceptually?

Q85
MCQ OSI, TCP/IP

Which OSI layer is responsible for syntax and format translation of data between systems?

Q86
MCQ OSI, TCP/IP

Why can encryption be associated with the Presentation Layer in the OSI model?

Q87
MCQ OSI, TCP/IP

Which OSI layer is responsible for synchronization and dialog control between applications?

Q88
MCQ OSI, TCP/IP

What is the main purpose of checkpoints in the Session Layer?

Q89
MCQ OSI, TCP/IP

Which layer would be most directly concerned with converting data between different character encoding formats?

Q90
MCQ OSI, TCP/IP

Which of the following is NOT a primary responsibility of the Network Layer?

Q91
MCQ OSI, TCP/IP

Which of the following is NOT primarily a Data Link Layer function?

Q92
MCQ OSI, TCP/IP

Which protocol is commonly associated with the Data Link Layer in LAN communication?

Q93
MCQ OSI, TCP/IP

Which protocol is primarily responsible for logical addressing and routing in the TCP/IP architecture?

Q94
MCQ OSI, TCP/IP

Which protocol provides reliable connection-oriented transport service?

Q95
MCQ OSI, TCP/IP

Which protocol provides a connectionless transport service with lower overhead than TCP?

Q96
MCQ OSI, TCP/IP

Which protocol translates domain names into IP addresses?

Q97
MCQ OSI, TCP/IP

Which protocol is primarily used to transfer web resources using the traditional request-response model?

Q98
MCQ OSI, TCP/IP

Which protocol is primarily used for sending email between mail servers?

Q99
MCQ OSI, TCP/IP

Which protocol is used for file transfer and is associated with the TCP/IP Application Layer?

Q100
MCQ OSI, TCP/IP

Which protocol is commonly used to map an IPv4 address to a MAC address on a local network?

Q101
MCQ OSI, TCP/IP

Which protocol is used for network diagnostic and error-reporting functions in IP networks?

Q102
MCQ OSI, TCP/IP

Which OSI layer is most closely associated with ICMP?

Q103
MCQ OSI, TCP/IP

Which TCP/IP layer corresponds most closely to the OSI Physical and Data Link Layers?

Q104
MCQ OSI, TCP/IP

Which TCP/IP layer corresponds most closely to the OSI Transport Layer?

Q105
MCQ OSI, TCP/IP

Which OSI layers are combined into the TCP/IP Application Layer in the common four-layer comparison?

Q106
MCQ OSI, TCP/IP

Which statement about the TCP/IP model is correct?

Q107
MCQ OSI, TCP/IP

Which layer of TCP/IP is responsible for end-to-end process communication?

Q108
MCQ OSI, TCP/IP

Two applications on the same computer communicate using different port numbers. Which layer provides the addressing mechanism that distinguishes these application processes?

Q109
MCQ OSI, TCP/IP

A packet has reached the correct destination computer but must be delivered to the correct application. Which information is most important at the Transport Layer?

Q110
MCQ OSI, TCP/IP

Which address generally remains associated with the destination host across routers, while the Data Link destination address can change at each hop?

Q111
MCQ OSI, TCP/IP

Which statement best distinguishes MAC addressing from IP addressing?

Q112
MCQ OSI, TCP/IP

If a switch receives an Ethernet frame and forwards it based on the destination MAC address, which OSI layer is primarily involved?

Q113
MCQ OSI, TCP/IP

If a router examines an IP destination address to select the next hop, which OSI layer is primarily involved?

Q114
MCQ OSI, TCP/IP

Which device is most closely associated with Layer 2 forwarding?

Q115
MCQ OSI, TCP/IP

Which device is primarily associated with Layer 3 packet forwarding?

Q116
MCQ OSI, TCP/IP

Which OSI layer is responsible for controlling the physical characteristics of data transmission such as signal representation?

Q117
MCQ OSI, TCP/IP

Which OSI layer is most directly affected when a damaged Ethernet frame is detected using a frame check mechanism?

Q118
MCQ OSI, TCP/IP

Why is the OSI Model called a reference model?

Q119
MCQ OSI, TCP/IP

Which is a major disadvantage of the OSI Model compared with the TCP/IP architecture?

Q120
MCQ OSI, TCP/IP

Which is an advantage of the OSI layered approach?

Q121
MCQ OSI, TCP/IP

Which statement best describes interoperability as an advantage of layered networking?

Q122
MCQ OSI, TCP/IP

A sender's application creates data and passes it down through the OSI stack. Which statement is correct?

Q123
MCQ OSI, TCP/IP

At the receiving host which layer removes the Data Link header and trailer from an incoming Ethernet frame?

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