Briefly describe the function of application layer in OSI model.
The application layer is the top-most layer of OSI model. It provides services directly to user applications. It enables the to access the network. It provides user interfaces and support for services such as email, remote file access and transfer, shared database management and other types of distributed information services.
1. File Transfer: It allows a user to access, retrieve and manage files in a remote computer.
2. Mail services: It provides the basis for email forwarding and storage facilities.
3. Directory services: It provides distributes database sources and access for global information about various objects and services.
Explain the function of presentation layer in OSI model.
The presentation layer performs data reformatting, data compression and encryption.
- Data Reformatting: When two computers exchange data, the data is changed to bit streams before it is transmitted. The computers may use different encoding techniques. The presentation layer at sending computer changes data according to the sender’s format. The presentation layer at receiving computer change data according to the receiver’s format.
- Encryption: The presentation layer encrypts data before transmission. It means that the sender transforms the original information to another from and sends resulting message over the network. The receiver again transforms the message back to its original form. It is called decryption.
- Compression: Data compression reduces the number of bits to be transmitted. The presentation layer compresses a large amount of data into small size.
What is the function of session layer works in OSI model?
The session layer establishes, manages, and terminates user connections. A session is an exchange of message between computers. It synchronizes user tasks.
Synchronization involves the use of Checkpoints in data stream. If a failure occurs only the data from the last checkpoint is retransmitted. Suppose we want to send 1000 pages of data. Check point can be used after each 100 pages. If there is an error at page 320’ the pages from 301 will be retransmitted. Pages from 1 to 300 will not be retransmitted.
Explain the function of transport layer.
The transport layer controls the flow of data. It ensures that message is delivered error free. It divides large message into small packets for efficient transmission. These packets are reassembled, checked for error and acknowledged at receiving side. If there are errors in transmission, the data is re-transmitted.