VOTE UP THE ANSWERS:

ANSWER:

Services of Application Layers

• Network Virtual terminal: An application layer allows a user to log on to a remote host. To do so, the application creates a software emulation of a terminal at the remote host. The user’s computer talks to the software terminal, which in turn, talks to the host. The remote host thinks that it is communicating with one of its own terminals, so it allows the user to log on.

• File Transfer, Access, and Management (FTAM): An application allows a user to access files in a remote computer, to retrieve files from a computer and to manage files in a remote computer. FTAM defines a hierarchical virtual file in terms of file structure, file attributes and the kind of operations performed on the files and their attributes.

• Addressing: To obtain communication between client and server, there is a need for addressing. When a client made a request to the server, the request contains the server address and its own address. The server response to the client request, the request contains the destination address, i.e., client address. To achieve this kind of addressing, DNS is used.

• Mail Services: An application layer provides Email forwarding and storage.

• Directory Services: An application contains a distributed database that provides access for global information about various objects and services.

Authentication: It authenticates the sender or receiver’s message or both.

m1: Send an email from a mail client to a mail server :

-> SMTP:

• SMTP stands for Simple Mail Transfer Protocol and it is an application layer protocol.

. SMTP is used to send an email from a mail client to a mail server.

• SMTP uses port 25.

m2: Download an email from mailbox server to a mail client:

–> POP:

• POP stands for Post Office Protocol and it is also an application layer protocol.

• POP allows an email client to download an email from an email server.

m3: Checking email in a web browser:

–> HTTP:

The Hypertext Transfer Protocol (HTTP) is an Application Layer protocol and is used to check email in a web browser.