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Structure Of Network

Structure of Network

  • In this section we will learn the models that are used in today's networking technology and their layers.

OSI Model

  • It stands for Open Systems Interconnection Modal.

  • There are 7 layers in this model:

              - Application Layer
          - Presentation Layer
          - Session Layer
          - Transport Layer
          - Network Layer
          - Data Link Layer
          - Physical Layer

Application Layer

  • It is implemented in the application itself.
  • This is the only layer the user directly interacts with.
  • Some protocols used are HTTP, FTP, etc.
  • The application layer will give data to next layer which is Presentation Layer.

Presentation Layer

  • This layer handles encryption, encoding, translation, etc of the data received by the application layer.
  • This layer assumes that the next layer which is Session Layer will convert the data by itself for further processing.
  • SSL (Secure Socket Layer) is used for encryption and encoding in this layer.

Session Layer

  • This layer focuses on setting up the connection and managing it and then enabling processing of data followed by termination of the connected sessions.
  • This layer assumes that the next layer which is transport layer will send the data once the connection is established.

Transport Layer

  • This layer divides the data into segments which have a sequence number attached to them to align them sequentially in the received device.
  • This layer has Flow Control which manages the upload speed of the sending device according to the receiving device so we do not lose any data packet during the data sending process.

Network Layer

  • This layer takes data segments from transport layer and then transports it from uploading device to the downloading device.
  • Router is a part of network layer.
  • The function of this layer is logical addressing.

Data Link Layer

  • This takes data packet from network layer and does logical address and physical addressing.
  • MAC Address is used for physical addressing.
  • A frame is the data unit that is has the MAC Address to it added by the data link layer.
  • After creating these data frames, all the above layers can access these frames and control how they are placed and received.
  • Adds MAC Address to frames or data segments received from network layer.

Flowchart

  • This flow shows how a packet goes layer by layer from uploading device to downloading device.

  • Application => Message formed by the user and this layer sends it to presentation layer.

  • Presentation => Transports the message by modifying it (encoding, encrypting, decrypting, etc).

  • Session => Creates a connection between devices and sends the message to transport layer.

  • Transport => Makes the message into packets and segments and sends it to network layer.

  • Network => Bundles and assigns IP Addresses to packets and sends it to Data Link layer.

  • Data Link => Adds MAC Address to the received frames and sends it to physical layer.

  • Physical => Sends the data to physical router.

Real World Example

  • ME => A => P => S => T => N => D => P => Router => P => D => N => T => S => P => A => MY FRIEND.

TCP/IP Model

  • Internet Protocol Suite.

  • This model has 5 layers: - Application Layer - Transport Layer - Network Layer - Data Link Layer - Physical Layer

  • The working of the layers is same as OSI Model but with few exceptions.

  • OSI model's Application, Presentation, Session are merged together into Application.

  • This is used practically and OSI is used for theory and concepts.