7 layer of OSI model

7 layer of OSI Model | 7 Layer OSI model in Computer Network

7 layers of OSI model are application layer, presentation layer, session layer, transport layer, network layer, data link layer, and physical layer.

7 layers of OSI model

1. Application Layer

The Seventh layer contains the application protocols with which the user gains access to the network.

The function of the application layer are:

• The application layer provides the basis for Email forwarding and storage.
• It allows a user to log on to a remote host. It creates software emulation of a terminal at the remote host. Users Computer talks to the software terminal which in turn talks to the host and vice versa. then the remote hist believes it is communicating with one in its own terminals and allows a user to log on
• This layer provides access to global information about various services.
• lt is a standard mechanism to access files and manages it.

• Users can access files on a remote computer and manage it. They can also retrieve files from a remote computer.

In the 7 layers OSI model, the protocols used by the application layer are HTTPS, FTP, DNS, SNMP, Telnet.

2. Presentation Layer

The sixth layer in the 7 layers of OSI model is the presentation layer. 

This layer is concerned with the syntax and semantics of the information

transmitted. The primary goal of this layer is to take care of the syntax and semantics of the information exchanged between two communicating systems- Presentation layer takes care that the data is sent in such a way that the receiver will understand the information (data) and will be able to use the data.

Languages (syntax) can be different from the two communicating systems- Under this condition presentation layer plays a role translator.

The function of the presentation layer are:

• Before being transmitted, the information in the form of characters and numbers should be changed to bitstreams. the presentation layer is responsible for interoperability between encoding methods as different computers use different encoding methods. It translates data between the formats the network requires and the format the computer uses.
• The presentation layer carries out encryption at the transmitter and decryption at the receiver.
• The presentation layer carries out data compression to reduce the bandwidth of the data to be transmitted. The primary role if the data compression is to reduce the number of bits to be transmitted. it is important in transmitting multimedia such as audio, video, text, etc.

The protocols used by the presentation layer in the 7 layer OSI model are SSL and TLS

3. Session Layer

The main aim of the session layer in the 7 layer OSI model is to establish, maintain and synchronize between communicating systems. The session layer manages and synchronizes the conversation between two different applications.

The function of the session layer are :

• The Session layer deals with the concept of Sessions i.e. when a user logins to the remote server he should be authenticated before getting access to the files and application programs. If during the transfer of data between two machines the session breaks down, it is the session layer that re-establishes the connection.
• It also ensures that the data transfer starts from where it breaks keeping it transparent to the end-user.
• Dialogue Contol: It determines whose turn is to speak in a session. It is useful in video conferencing.

The protocols used by the session layer in the 7 layer OSI model is NetBIOS.

4. Transport Layer

In, 7 layers of OSI model, the main aim of the transport layer is to be

delivered the entire message from source to destination. The transport layer ensures the whole message arrives intact and in order, ensuring both error control and flow control at the source to destination level. lt decides if data transmission should be on a parallel path or single path.

Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer and ensures that

the message arrives in order by checking error and flow control.

The transport layer uses Port numbers to identify the process in the destination machine to communicate with. An example includes HTTP -port 80, FTP- port 21, SMTP- port 25.

The function of the transport layer are :

• Transport Layer header includes service point address which is port address. This layer gets the message to the correct process on the computer unlike the network layer, which gets each packet to the correct computer.
• A message is divided into segments; each segment contains a sequence number, which enables this layer in reassembling the message. Message reassembled correctly upon arrival art destination and replaces packets that were lost in transmission.
• Flow control is performed end to end.
• Error Control is performed end to end in this layer to ensure that the complete message arrives at the receiving transport layer without any error.

The protocols used by the transport layer in the 7 layer osi model are TCP and UDP.

5. Network Layer

The main aim of this layer is to deliver packets from source to destination across multiple links (networks). If two computers (system) are connected to the same link then there is no need for a network layer. lt routes the signal through different channels to the other end and acts as a network controller.

It also divides the outgoing messages into packets and to assemble incoming packets into messages for higher

levels.

Its basic functions are routing and congestion control.

The protocols used by the network layer in the 7 layer osi model are lP,lPv4,lPv6, IPSec, ICMP, IGMP.

6. Data Link Layer

The second layer in the 7 layers osi model is the physical layer. This layer provides reliable transmission of a packet by using the services of the physical layer that transmits bits over the medium in an unreliable fashion.

The function of the data link layer are :

• 
  

  Framing: Breaking input data into frames and caring about the frame boundaries and the size of each frame.
• Acknowledgment: Sent by the receiving end to inform the source that the frame was received without any error.
•  Sequence Numbering: To acknowledge which frame was received.
• Error Detection: The frames may be damaged, lost or duplicated leading to errors. The error control is on the link to link basis.
• Retransmission: The packet is retransmitted if the source fails
  to receive an acknowledgment.
• Flow Control: Necessary for a fast transmitter to keep pace with
  a slow receiver.
• Access Control: Protocols of this layer determine which
  of the devices has to control over the link at any given time, when two or more devices are connected to the same link.

Datalink layer

The protocols used by the data link layer in the 7 layer osi model are PPP, ATM, Ethernet.

7. Physical  Layer

This layer is the lowest layer in the 7 layers OSI model. lt helps in the transmission of data between two machines that are communicating through a physical medium, which can be optical fibers, copper wire or

wireless, etc.

The function of the physical layer are :

Hardware Specification: The details of the physical cables, network interface cards, wireless radios, etc- are a part of this layer.

Encoding and Signaling: How are the bits encoded in the medium is also decided by this layer.

For example, on the copper wire medium, we can use different voltage levels for a certain time interval to represent '0' and '1'.

Data Transmission and Reception: The transfer of each bit of data is the responsibility of this layer. This layer assures the transmission of each bit with a high probability.

Transmission Modes: Physical Layer defines the direction of transmission between two devices: Simplex, Half Duplex, and Full Duplex.

Synchronization: lt deals with the synchronization of the transmitter and receiver. The sender and receiver are synchronized at a bit level.

The protocols used by the physical layer in the 7 layer OSI model are USB, Bluetooth, etc.

tags: 7 layers of osi model, 7 layer osi model, OSI reference model, OSI model