What is OSI 7 layers model

7. Application Layer

Application layer is seventh (7^th) layer of Open System Interconnection (OSI) Model. It is human and PC interaction layer. It is closed to the end user.  In this layer protocols allows software to send and receive data and present meaningful data to users. Web browser (Google Chrome, Firefox, Safari), Telnet, File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), Domain Name System (DNS) and email client are examples of Application layer.

6. Presentation Layer

The presentation layer is Sixth (6^th) and very important layer of Open System Interconnection (OSI) Model. It is also called translated layer. On this layer, ASCII and EBCDIC are used to present human readable text. It converts data into text. Encryption, Decryption, Conversion of data is performing on this layer. Examples of presentation layer protocols are ASCII (American Standard Code for Information Interchange), EBCDIC (Extended Binary Coded Decimal Interchange Code), MIDI (Musical Instrument Digital Interface), MPEG (Moving Picture Expert Group), TDI (Tabbed Document Interface), TLS (Transport Layer Security), XDR (External Data Representation), SSL (Secure Sockets Layer), HTTP (Hyper Text Transfer Protocol) and HTML (Hyper Text Manipulating Language).

5. Session Layer

The session layer is the fifth (5^th) layer of Open System Interconnection (OSI) Model. It is responsible for creating session, maintain safe and secure connection and terminating them when communication ends. Session ID is attached on this layer. It provides checkpoints during communication, whenever the session is break, devices can resume data transfer from the last checkpoint. Examples of session layer are ADSP (Apple talk Data Stream Protocol), RTCP (Real-Time Transport Control Protocol), PPTP (Point-to-Point Tunneling Protocol), PAP (Password Authentication Protocol), RPC (Remote Procedure Call Protocol), NFS (Network File System Protocol), SQL and Net Bios.

4. Transport Layer

The transport layer is the fourth (04^th) layer of Open System Interconnection (OSI) model. It takes data transferred in the 5^th layer (session layer) and breaks into small segments on the transmitting end. Transport layer control the segmentation. If the data reaches out of order, it can reorder the data by the help of segment numbering and present the data in the right order. Flow control performs on this layer. It can store data in Buffer, by default using FIFO (First in First Out) algorithm. If the buffer becomes full, it stops to receive data from sender.

Services of Transport Layer:

Connection oriented communication

Same Order Delivery

Flow Control

Reliability

Congestion Avoidance

Port Multiplexing

Popular protocols of Transport Layer

User Datagram Protocol (UDP)

Transmission Control Protocol (TCP)

Multi Path Transmission Control Protocol (MPTCP)

Structure Stream Transport (SST)

3. Network Layer

Network layer is the third (3^rd) layer of Open System Interconnection (OSI) model and performs two main functions:

1. Segments converts into packets
2. Path selection

It takes segments (data) transferred in the 4^th layer (transport layer) and breaks into packets. It added source IP address and destination IP address to the data packets. It transfer network packet from source address to destination address. If the packet is too large then it breaks the packet into small packets. It decides the route for data packet from source to destination (Path selection) using routing protocol e.g Routing Information Protocol (RIP), Enhance Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First Protocol (OSPF) etc.

Protocols of Network Layer

IP Version 4 (32 bits address)

IP Version 6 (128 bits address)

Internet Protocol Security (IPSec)

Internetwork Packet Exchange Protocol (IPX)

Internet Control Message Protocol (ICMP)

Internet Grouping Management Protocol (IGMP)

Devices of Network Layer

1. Router
2. Layer 3 Switch

2. Data Link Layer

Data Link Layer is the second (2^nd) layer of Open System Interconnection (OSI) model. The data link layer creates and end a connection between two physically-connected nodes on a network. Switch and bridge devices are used on this layer and both devices MAC (Media Access Control) address of 48 bits (6 bytes), Mac address is also called Physical address. It breaks up packets into frames (attached MAC address with data) and sends them from source (MAC address) to destination (MAC address). It use Address Resolution Protocol (ARP) to convert IP (internet protocol) address to MAC (media access control) address. This Layer is divided on two parts:

1. Logical Link Control (LLC)

LLC identifies protocols, error detection and acknowledgement.

2. Media Access Control (MAC)

MAC sub layer to connect devices and allowed to transmit and receive data.

Functions of the Data Link Layer

1. Framing
2. Addressing
3. Error Control
4. Flow Control
5. Access Control

Protocols of Data Link Layer

1. Address Resolution Protocol (ARP)
2. Synchronous Data Link Protocol (SDLC)
3. High-level Data Link Protocol (HDLC)
4. Serial Line Interface Protocol (SLIP) for encoding
5. Point to Point Protocol (PPP)
6. Link Control Protocol (LCP)
7. Link Access Procedure (LAP)
8. Network Control Protocol (NCP)                                                                                            1. Physical Layer

The Physical is the First (1^st) layer of Open System Interconnection (OSI) model. It is combination of Hardware and Software programming. Power plug, connectors, receiver, cables components are used on this layer. It sends data bits (0’s, 1’s) from one device to another device.

Function of Physical Layer:

1. Maintain Data Rate
2. Synchronization of bits
3. Physical and wireless connection between nodes
4. Point to Point and Multi Point configuration provides
5. Modulization

Protocols of Physical Layer:

1. Ethernet with 1000 Base-T
2. Ethernet with 1000 Base-SX
3. Synchronous Digital Hierarchy / Optical Synchronization
4. Physical Layer Variations in 802.11
5. Bluetooth
6. Network for controller
7. S Serial Bus

Devices of Physical Laye:

Hub and Ethernet  

What is OSI 7 layers model.

What is OSI 7 layers model