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

