Seven layers

The specific description for each layer is as follows:
Layer 7: Application Layer
Defines interface to user processes for communication and data transfer in network
Provides standardized services such as virtual terminal, file and job transfer and operations

Layer 6:Presentation Layer
Masks the differences of data formats between dissimilar systems
Specifies architecture-independent data transfer format
Encodes and decodes data; Encrypts and decrypts data; Compresses and decompresses data

Layer 5:Session Layer
Manages user sessions and dialogues
Controls establishment and termination of logic links between users
Reports upper layer errors

Layer 4:Transport Layer
Manages end-to-end message delivery in network
Provides reliable and sequential packet delivery through error recovery and flow control mechanisms
Provides connectionless oriented packet delivery

Layer 3:Network Layer
Determines how data are transferred between network devices
Routes packets according to unique network device addresses
Provides flow and congestion control to prevent network resource depletion

Layer 2:Data Link Layer
Defines procedures for operating the communication links
Frames packets
Detects and corrects packets transmit errors

Layer 1:Physical Layer
Defines physical means of sending data over network devices
Interfaces between network medium and devices
Defines optical, electrical and mechanical characteristics
There are other network architecture models,. Those models will be discussed in separate documents.
The OSI 7 layer model is defined by ISO in document 7498 and ITU X.200, X.207, X.210, X.211, X.212, X.213 , X.214, X.215, X.217 and X.800. The protocols defined by ISO based on the OSI 7 layer mode.