Explain About OSI Layer

Long Questions

Q#4: Explain About OSI Layer?
ANS:LAYERS IN THE OSI MODEL:

1: Physical Layer: 

                                         The Physical Layer is responsible for moments of individual bits from one hop (node) to the next. The physical layer coordinates the functions required to carry a bit stream over a physical medium. It deal with the mechanical and electrical specifications of interface and transmission medium. It also defines the procedures and

function that physical device and interface have to perform for transmission to occur.

2: Data Link Layer: 

                                              The Data Link layer is responsible for moving frames from one hop (node) to the next. The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. It other responsibilities of the data link layer include the following:

A: Framing:

                       The data link layer divides the stream of bits received from the network layer into manageable data units called frames.

B: Access control: 

                                  When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time.  

3: Network Layer: 

                                          The Network Layer responsible for the delivery of individual packet from, the source host to the destination host . The Network Layer is responsible for sure to destination delivery of a packet possibly networks (links) whereas the data link layer overseas the delivery of packet between the two system on some network (links). The network layer ensures that each packet gets from its point to origin to its final destination.

4: Transport Layer: 

                                              The Transport Layer is responsible for process to process delivery of the entire message. The transport layer is responsible for the delivery of a message from one process to another.

The transport layer is responsible for the delivery of a message from one process to another.

A: Flow control: 

                              Like the data link layer, the transport layer is responsible for flow control. However, flow control at this layer is performed end to end rather than across a single link.

B: Error control: 

                                Like the data link layer, the transport layer is responsible for error control. However, error control at this layer is performed process-to-process rather than across a single link.

5: Session Layer: 

                                       The services provided by the first three layers (physical, data link, and network) are not sufficient for some processes. The session layer is the network dialog controller. It establishes, maintains, and synchronizes the interaction among communicating systems. The Session Layer is responsible for dialog control and synchronization. Specific responsibilities of the session layer include the following:

A: Dialog control: 

                                   

The session layer allows two systems to enter into a dialog. It allows the communication between two processes to take place in either half duplex (one way at a time) or full-duplex (two ways at a time) mode.

6: Presentation Layer: 

                                                   The Presentation Layer is responsible for translation, compression and encryption. The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.                                    Specific responsibilities of the presentation layer include the following:

A: Encryption: 

                           To carry sensitive information, a system must be able to ensure privacy. Encryption means that the sender transforms the original information to another form and sends the resulting message out over the network. Decryption reverses the original process to transform the message back to its original form.

B: Compression:

                                Data compression reduces the number of bits contained in the information. Data compression becomes particularly important in the transmission of multimedia such as text, audio, and video.

7: Application Layer: 

                                                The Application Layer is responsible for providing services to the user. The application layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as electronic mail, remote file access and transfer, shared database management, and other types of distributed information services. The application layer is responsible for providing services to the user. Specific services provided by the application layer include the following:

A: Mail service: 

                             This application provides the basis for e-mail forwarding and storage.

B: Directory service:

                                       This application provides distributed database sources and access for global information about various objects and services.