OSI Model(Extra) Flashcards
Physical Layer (Layer 1)
Purpose: The Physical Layer is responsible for the physical transmission of raw data (bits) over a communication medium, like cables, fiber optics, or wireless signals.
Key Functions:
* Defines hardware specifications (cables, connectors, etc.)
* Manages bit-level transmission (1s and 0s)
* Manages electrical, optical, or radio signals to transmit data
* Deals with physical network topology (how devices are connected)
Devices: Hubs, repeaters, network cables, wireless transmission mediums.
Data Link Layer (Layer 2)
Purpose: The Data Link Layer ensures reliable data transfer across the physical link by handling framing, addressing, and error detection/correction.
Key Functions:
* Divides data into frames for transmission
* Performs error detection and correction at the frame level
* Provides flow control to ensure efficient data transmission
* Manages MAC (Media Access Control) addressing for devices on the same network
* Handles how data is accessed and sent over the network medium (e.g., Ethernet)
Devices: Switches, bridges, network interface cards (NICs).
Network Layer (Layer 3)
Purpose: The Network Layer handles logical addressing and routing, ensuring that data packets are sent from the source to the destination across multiple networks.
Key Functions:
* Manages logical IP addressing (e.g., IPv4, IPv6)
* Determines the best path for data using routing protocols
* Handles packet forwarding between different networks (internetworking)
* Fragmentation and reassembly of packets if necessary
Devices: Routers, layer 3 switches.
Transport Layer (Layer 4)
Purpose: The Transport Layer ensures end-to-end communication and reliability of data transfer between devices.
Key Functions:
* Divides data into segments and reassembles them at the destination
* Provides reliable data transfer using error correction and flow control (e.g., TCP)
* Supports connection-oriented (TCP) and connectionless (UDP) communication
* Ensures data is delivered in sequence and without duplication or errors
Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
Session Layer (Layer 5)
Purpose: The Session Layer manages and controls the dialog between two devices, establishing, maintaining, and terminating connections.
Key Functions:
* Establishes, manages, and terminates sessions between applications
* Manages dialog control (half-duplex or full-duplex communication)
* Provides synchronization for data exchanges (e.g., checkpoints for long transfers)
* Manages session restoration if connections are interrupted
Example: A web browser maintaining a session with a server.
Presentation Layer (Layer 6)
Purpose: The Presentation Layer ensures that the data is in a usable format and handles data translation, encryption, and compression.
Key Functions:
* Translates data between different formats (e.g., EBCDIC to ASCII)
* Handles encryption and decryption for security
* Manages data compression to reduce the size of transmitted data
* Ensures that data sent by the application layer of one system is readable by the application layer of another system
Examples: JPEG image format, SSL/TLS encryption.
Application Layer (Layer 7)
Purpose: The Application Layer is the top layer that interacts directly with the user and provides network services to applications.
Key Functions:
* Provides network services directly to user applications (e.g., web browsing, email)
* Handles application-level protocols for different services (e.g., HTTP for web, SMTP for email, FTP for file transfers)
* Ensures proper communication between applications by enabling access to the network
Examples of Protocols: HTTP, FTP, SMTP, DNS, Telnet.
