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OSI_Model.md

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OSI Model

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The OSI model is composed of seven ordered layers: physical (layer 1), data link (layer 2), network (layer 3), transport (layer 4), session (layer 5), presentation (layer 6), and application (layer 7).

  • Open system interconnection model
  • 7 Layers
  • Developed by ISO

OSI Model Diagram

Layer number Name
7 Application layer
6 Presentation layer
5 Session layer
4 Transport layer
3 Network layer
2 Data link layer
1 Physical layer

Basic working

  • Application Layer : Layer consists many protocols such as file transfer protocol FTP , web service HTTP & HTTPS and for emails SMTP.

  • Presentation Layer : Presentation layer handles translation to binary , compresion & encryption/decryption.

  • Session Layer : Creates , manages & ends session. Authentication is also done here. Tracks received and sent data packerts.

  • Transport Layer : DIvided data into segments and keeps track where to send data . Also do flow control means speed at data travels to application. Also handles error controls. Have protocols like TCP & UDP.

  • Network Layer : Handles transmission. Handles logical addressing , path determination and routing. Data handles in terms of packets. Protocols like IPv4 , IPv6 , ICMPv4 & ICMPv6.

  • Data Link Layer : physical addressing like MAC done here. Also does framing i.e. creating frames.

  • Physical Layer : Handles data conversion such as signal to bits . Determines types of media like light i.e. optical fiber, voltage like cable or signal like wifi.

Function

Application Layer

  • Network Virtual Terminal : To allow remote user to get software version of physical terminal
  • File transfer , access and management : To access files in a remote host , change or update file on system
  • Email : Email forwarding and storage
  • Directory services : Distributed database sources and access gloabal information

Presentation Layer

  • Translation : Converts information so system can understand it.
  • Encryption : Encryptes outgoing traffic and decryptes incoming data
  • Compression : Compression and decompression of data for efficient data transfer.

Session Layer

  • Dialog control : Allows two processes to take place either in half duplex or full duplex mode.
  • Synchronization : Adds checkpoints into stream of data for control flow.

Transport Layer

  • Service-point addressing : Identifies and differentiate services using Ports .
  • Segmentation and reassembly : Messages are divided into segments for transmission and reassembled upon arriving.
  • Connection control : Connectionless or connection-oriented services for better transmission policy.
  • Flow control : To control flow of data for end to end transmission.
  • Error control : To avoid errors and cover up errors if it happens.

Network Layer

  • Logical Addressing : Logical addressing using IP to distinguish multiple devices on internet.
  • Routing : Transfer of packets from one device to other.

Data link Layer

  • Framing : Divide packets into frames for manageable data units.
  • Physical addressing : Physical addressing using MAC address.
  • Flow control : Control flow of data transfer
  • Access control : Determine access to link for two or more devices.
  • Error control : Add trailer to achieve error control.

Physical Layer

  • Physical characteristics : Defines transmission media
  • Representation of bits : Bit length and encoding
  • Data rate and synchronization : Synchronize data transfer and manage data rate
  • Physical topology : Topology
  • Transmission mode : Either simplex , half duplex or duplex

OSI

Detailed OSI

Sources :