Give some advantages and disadvantages of combining the session, presentation, and application layer in the OSI model into one single application layer in the Internet model?

Session layer in the OSI model

1.     Dialog Control : This layer allows two systems to start communication with each other in half-duplex or full-duplex.

2.     Synchronization : This layer allows a process to add checkpoints which are considered as synchronization points into stream of data. Example: If a system is sending a file of 800 pages, adding checkpoints after every 50 pages is recommended. This ensures that 50 page unit is successfully received and acknowledged. This is beneficial at the time of crash as if a crash happens at page number 110; there is no need to retransmit 1 to100 pages

Presentation layer in the OSI model

1.     Translation : Before being transmitted, information in the form of characters and numbers should be changed to bit streams. The presentation layer is responsible for interoperability between encoding methods as different computers use different encoding methods. It translates data between the formats the network requires and the format the computer.

2.     Encryption : It carries out encryption at the transmitter and decryption at the receiver.

3.     Compression : It carries out data compression to reduce the bandwidth of the data to be transmitted. The primary role of Data compression is to reduce the number of bits to be 0transmitted. It is important in transmitting multimedia such as audio, video, text etc.

Application layer in the OSI model

1.     Mail Services : This layer provides the basis for E-mail forwarding and storage.

2.     Network Virtual Terminal : It allows a user to log on to a remote host. The application creates software emulation of a terminal at the remote host. User’s computer talks to the software terminal which in turn talks to the host and vice versa. Then the remote host believes it is communicating with one of its own terminals and allows user to log on.

3.     Directory Services : This layer provides access for global information about various services.

4.     File Transfer, Access and Management (FTAM) : It is a standard mechanism to access files and manages it. Users can access files in a remote computer and manage it. They can also retrieve files from a remote computer.