Done by: Mardonov B

APPLICATION LAYER
PRESENTATION LAYER
The presentation layer defines the format,
used for communication between nodes
network (you can call it a translator).
Level functions:
 data format conversion;
 data encoding/decoding, including
data compression and decompression;
 data encryption.
PRESENTATION LAYER
The task of the presentation layer is to
when transmitting information, convert the data into a format,
which is used in the information system
RS 2
UNIX File System
Presentation Layer
RS 1
DOS File System
Presentation Layer
Information System Data Formats
SESSION LAYER
The session layer determines the structure for managing the interaction of network subscribers, i.e. defines and controls the dialogue between network objects.
Performs the following functions:
 determines the beginning and end of a communication session (normal or emergency);
 determines the time, duration and mode of the communication session;
 defines synchronization points for intermediate control and recovery during data transfer;
 recognition of names and passwords;

• restores the connection after errors during the communication session without data loss.

Establishing a communication session includes procedures for checking the user name and password, determining access rights to certain system resources

TRANSPORT LAYER
The transport layer provides an efficient and reliable
transferring data between sessions objects (no errors, in
necessary sequence and without duplication). On this
level messages are repackaged - long break down into
multiple packs rather short are combined into one.
Transport layer functions:
 establishes and disconnects transport connections;
 controls the sequence of data transfer;
 manages the flow of data;
 detects and processes data transmission errors;
 establishes a correspondence between the transport (logical) and network addresses of subscribers;
allows multiplexing of transmitted messages or connections.
NETWORK LAYER
This level serves to form a single transport system that combines several networks with different principles of information transfer between end nodes.