Physical Layer

• Functionality:

  1. Hardware Specification:

     • Details of physical cables, network interface cards, wireless radios.
     • Examples: Coaxial Cable, Hybrid Cable, Wireless Card, Network Card.

     

  2. Encoding and Signalling:

     • How bits are encoded in the medium.
     • Modulation techniques, e.g., Binary Phase Shift Keying.

     

  3. Data Transmission and Reception:

     • Responsible for the transfer of each bit of data.
     • Transmission is not completely reliable, and there is no error correction.

  4. Topology and Network Design:

     • Integral part of the physical layer.
     • Involves network design, placement of routers, switches, hubs, server locations, and choosing network topologies (ring, bus, star).

     

Data Link Layer

• Functionality:

  1. Framing:

     • Breaks input data into frames, cares about frame boundaries and size.

  2. Acknowledgment:

     • Sent by the receiver to inform the source about error-free frame reception.

  3. Sequence Numbering:

     • Acknowledges which frame was received.

  4. Error Detection:

     • Deals with damaged, lost, or duplicated frames.

  5. Retransmission:

     • Retransmits the packet if the source doesn't receive acknowledgment.

  6. Flow Control:

     • Regulates the flow of information between fast transmitters and slow receivers.

     

Network Layer

• Functionality:

  1. Routing:
     • Determines how packets are routed from source to destination.
     • Types: Static (based on static tables), Dynamic (follows different routes), Semi-Dynamic (chosen at the start of each conversation).

  

  1. Services:

     • Connectionless Service: Treats each packet independently.
     • Connection-Oriented Service: Establishes a connection before all packets follow the same route.

  2. Congestion Control:

     • Manages congestion, minimizes packet dropping, and informs the source of dropped packets.

  3. Internetworking:

     • Connects multiple networks, acts as one large network.
     • Uses routers, switches, and bridges for connectivity.

     

Transport Layer

• Functionality:

  1. Multiplexing / Demultiplexing:

     • Creates distinct network connections for each transport connection.
     • May multiplex several transport connections onto the same network connection.

  2. Fragmentation and Re-assembly:

     • Splits data into smaller units for transmission and re-assembles at the receiving end.

     

  3. Types of Service:

     • Decides the type of service provided to the session layer.
     • May be perfectly reliable, reliable within tolerances, or unreliable.

  4. Error Control:

     • Performs error detection and recovery for reliable services.

  5. Flow Control:

     • Regulates the flow of information between fast and slow hosts.

  6. Connection Establishment / Release:

     • Establishes and releases connections across the network.
     • Requires a naming mechanism for communication.

Session Layer

• Concept of Sessions:
  • Authentication required when a user logs in to a remote server.
  • Establishes and maintains sessions for data transfer.
• Session Management:
  • Re-establishes connection if a session breaks down.
  • Ensures transparent data transfer restarts from the point of interruption.
• Synchronization:
  • Introduces checkpoints in case of broken connections.
  • Ensures transactions on a database are not lost even if the user has not committed.
• Dialogue Control:
  • Determines whose turn it is to speak in a session.
  • Useful in video conferencing.

Presentation Layer

• Syntax and Semantics:
  • Concerned with the syntax and semantics of transmitted information.
  • Defines data structures in an abstract way with standard encoding.
• Data Exchange:
  • Manages abstract data structures and allows the exchange of higher-level structures.
  • Encodes data in a standard agreed-upon network format.
• Compatibility:
• Additional Functions:

Application Layer

• User Network Access: