Page 272 - Informatics_Practices_Fliipbook_Class12
P. 272

SMTP:  An  email  usually  has  some  text  and  may  optionally  include  text  or  multimedia  attachments.  Also,  an
        email may be sent to multiple recipients. SMTP is a TCP/IP (Transmission Control Protocol/ Internet Protocol)
        based protocol. It involves a User Agent (UA) and a mail transfer agent (MTA). UA is responsible for packing the
        message into an envelope on the client side and unpacking the message from the envelope on the receiving side.
        MTA is responsible for the transmission of messages between the mail servers. As MTA on the receiver side may
        use a protocol different from the sender side, a gateway can establish compatibility by making the necessary
        transformation. The SMTP protocol requires the email server at the recipient end to be online. However, if the
        email server is not on, repeated efforts will be made to deliver the email. If the email server remains inaccessible
        for several days, the email message will be discarded and an intimation of this effect will be sent to the sender.
        Fig 7.7 shows the SMTP components. On receiving an email, the SMTP server places it in the recipient's mailbox.
        Subsequently, the recipient can access the email from his/her mailbox.

                               Sender    UA                                  UA    Receiver
                               (Client)                                             (Server)



                                         MTA             Gateway             MTA

                                                  Fig 7.7 SMTP Components
        POP3: Post Office Protocol version 3 (POP3) is an email protocol for receiving emails from a remote server and
        sending them to a local email client. Thus, POP3 allows us  to save email messages to our local device (computer,
        tablet, mobile phone, etc.) and read them. Once a message is delivered to an email client, Internet is not required
        to view it.
        In POP3, the workstation intended to receive mail need not be online all the time. An SMTP server receives emails on
        behalf of all organisations' users and provides a mail drop facility. Subsequently, the users can retrieve the messages
        from the server. Fig 7.8 shows email transfer using POP3.
                                                     Inquiring for mail




                                  Client             Downloading Mail            Server
                                                       Fig 7.8 POP3



               Simple Mail Transfer Protocol (SMTP) and Post Office Protocol Version 3 (POP3) : They are used for exchange of
               emails over the Internet.


        7.1.6 Protocols for Chat and VoIP

        Several protocols define rules for communication for chatting with someone, i.e. exchanging text, audio, and video
        messages. Examples of chat protocols include IRC and VoIP.
        Internet Relay Chat (IRC): IRC is the most commonly used text-based chat protocol. It allows two or more users
        to form a (logical) chat room for communicating with each other. When a node (source) wishes to send a message
        to the destination node(s), the source sends the message to the IRC server, which relays it to the destination
        node(s).
        Voice  over  Internet  Protocol  (VoIP):  VoIP  allows  us  to  make  calls  using  an  Internet  connection.  You  may  use  an
        application program such as Skype from your computer or smartphone to make a call. You can also use a traditional
        landline phone for making a VoIP call, provided you have a VoIP adapter. A VoIP call converts an analog voice signal to
        a digital signal before sending it to the desired destination (IP address) over the internet.

          258  Touchpad Informatics Practices-XII
   267   268   269   270   271   272   273   274   275   276   277