DCCN PPT ONOSI REFERNCE(7LAYER)MODEL BY Bhargavi and group DECE
An open system is a set of protocols that allow two different systems to communicate regardless of theirOpen Systems Interconnection Open Systems Interconnection (OSI) it is a networking model which is fundamental to all communications between network devicesIt is now the theoretical model for how communication takes place between network devices.
The OSI reference model is an arbitrary hierarchical stratification (layering) of computer networking functions. The stratification consists of seven layers.
The OSI Reference ModelThe OSI reference model consists of seven layers, not including layer 8, the end user’s application, and layer 0 the physical transmission media. 8. O/S or User Application 0. Physical Transmission Media
LAYER 1: PHYSICAL The physical layer deals with the physical characteristics of the transmission medium. and it sends the data in the form of raw bits It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. .
FUNCTIONSIt controls the define voltages and bit rates needed for transmission This layer manages the interface between the computer and the network medium (coaxial cable, twisted pair) It is the bottom layer of the OSI model
Layer 2 : DATA LAYERThis layer takes the data frames (or) messages from the layer and provides their actual transmission A message is a block statement such as ok (or) yes, which denotes positive (or) negative acknowledgement (or) request for repeating such as “come again” (or) pardon me . At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
Data Link Layer synchronization To take packets from the upper layer and converting them into frames To take bits from lower and converting them into packet Error detection and control Framing 010110110101 10110000001 0110001011
LAYER 3: NETWORK Defines end-to-end delivery of packets. It receives the packets from transport layer and converts them into frames Defines how routing works and how routes are learned so that the packets can be delivered. It is responsible for sending the data to destination node by choosing the data
Establishing the connection Releasing the connections Sending the data This layer also handles packet switching and network congestion control
LAYER 4: TRANSPORT If once it receives the data from session layer it splits the data into packets After dividing it adds sequence to the packets It is responsible for error control and flow control
ERROR CONTROL: while transmitting the data if they are errors in the data which is been sent to the destination node it detects and controls the error and resends the data to the node FLOW CNTROL: when the data is sent . The form of data sending should be maintained currently for acknowledgement
LAYER 5: SESSION LAYER When once the data is received from the presentation layer it is converted in the form of sessions Again this sessions are divided into sub sessions It avoids the retransmission by adding the checking point feature if the system craches (or) power failures last checking point substation re-trasnmitts the left data but not the entire data again At destination side it receives the data from the transport layer and handovers the data to the presentation layer Whenever it is divided into substations it adds the sequence number
The Session Layer Responsibilities: establishes, manages, and terminates sessions between applications. service location lookup
Responsible for security and access control to session information (via session participant identification) Responsible for synchronization services (checkpoints)
LAYER 6: PRESENTATION It provides compression of data It is concerned with Semantics and syntax of the information Provides compression of data It is responsible for Data Encoding Data Compression Data conversion
The Presentation Layer Responsibilities: data encryption data compression data conversion
Data Encoding: The data is encoded i.e if one node (source node) supports ASCII format, Destination node may support UNICODE format and at this time the data is transmitted in the form of UNCODE even the source node supports ASCII format Compression: The data is compressed before sending it to the destination node, here the data is compressed in the destination layer This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression.
LAYER 7: APPLICATION The top layer of the OSI model The container which contains various types of protocols i.e www, http is called application layer If once it is connected to the protocol it handovers to the presentation layer
The application layer is the closest to the user. It provides network access to the user. It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs.
Sending Computer Receiving ComputerUser UserApplication Application 7 Application 7 Application 6 Presentation 6 Presentation 5 Session 5 Session Transmission Media 4 Transport 4 Transport 3 Network 3 Network 2 Data Link 2 Data Link 1 Physical 1 Physical