Scribd
Upload
319 views28 pages

23-1 Architecture: TCP/IP Protocol Suite

The document describes four scenarios of increasing complexity for email architecture. The simplest involves a single sender and receiver on the same mail server using two user agents. The most common scenario today involves senders and receivers connected to mail servers over LAN/WAN using two user agents, two pairs of MTAs, and a pair of MAAs. The key components of an email system are user agents, message transfer agents which use SMTP, and mail access agents. Web-based email allows access through websites like Hotmail, Yahoo, and Gmail.

Uploaded by

Amran Hossain
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
319 views28 pages

23-1 Architecture: TCP/IP Protocol Suite

The document describes four scenarios of increasing complexity for email architecture. The simplest involves a single sender and receiver on the same mail server using two user agents. The most common scenario today involves senders and receivers connected to mail servers over LAN/WAN using two user agents, two pairs of MTAs, and a pair of MAAs. The key components of an email system are user agents, message transfer agents which use SMTP, and mail access agents. Web-based email allows access through websites like Hotmail, Yahoo, and Gmail.

Uploaded by

Amran Hossain
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 28

23-1 ARCHITECTURE

To explain the architecture of e-mail, we give four


scenarios. We begin with the simplest situation and
add complexity as we proceed. The fourth scenario
is the most common in the exchange of e-mail.

TCP/IP Protocol Suite 1


Topics Discussed in the Section

ü  First Scenario
ü  Second Scenario
ü  Third Scenario
ü  Fourth Scenario

TCP/IP Protocol Suite 2


Figure 23.1 First scenario

2
1

TCP/IP Protocol Suite 3


Note

When the sender and the receiver of an


e-mail are on the same mail server,
we need only two user agents.

TCP/IP Protocol Suite 4


Figure 23.2 Second scenario

5
1

2 3 4

TCP/IP Protocol Suite 5


Note

When the sender and the receiver of an


e-mail are on different mail servers,
we need two UAs and a pair of MTAs
(client and server).

TCP/IP Protocol Suite 6


Figure 23.3 Third scenario

3
7

5
4 6

TCP/IP Protocol Suite 7


Note

When the sender is connected to the


mail server via a LAN or a WAN, we
need two UAs and two pairs of MTAs
(client and server).

TCP/IP Protocol Suite 8


Figure 23.4 Fourth scenario

1 9

2
8

5
4 6

TCP/IP Protocol Suite 9


Note

When both sender and receiver are


connected to the mail server via a LAN
or a WAN, we need two UAs, two pairs of
MTAs (client and server), and a pair of
MAAs (client and server). This is the
most common situation today.

TCP/IP Protocol Suite 10


23-2 USER AGENT

The first component of an electronic mail system is


the user agent (UA). It provides service to the user to
make the process of sending and receiving a
message easier.

TCP/IP Protocol Suite 11


Note

Some examples of GUI-based user


agents are Eudora, Outlook,
And Netscape.

TCP/IP Protocol Suite 12


Figure 23.6 Format of an email

TCP/IP Protocol Suite 13


Figure 23.7 E-mail address

TCP/IP Protocol Suite 14


23-3 MESSAGE TRANSFER AGENT

The actual mail transfer is done through message
transfer agents (MTAs). To send mail, a system must
have the client MTA, and to receive mail, a system
must have a server MTA. The formal protocol that
defines the MTA client and server in the Internet is
called Simple Mail Transfer Protocol (SMTP). As we
said before, two pairs of MTA client-server programs
are used in the most common situation (fourth
scenario). Figure 23.8 shows the range of the SMTP
protocol in this scenario.

TCP/IP Protocol Suite 15


Figure 23.8 SMTP range

TCP/IP Protocol Suite 16


Figure 23.9 Commands and responses

TCP/IP Protocol Suite 17


TCP/IP Protocol Suite 18
TCP/IP Protocol Suite 19
Figure 23.10 Connection establishment

220 service ready 1


2 HELO: deanza.edu

250 OK 3

TCP/IP Protocol Suite 20


Figure 23.11 Message transfer

TCP/IP Protocol Suite 21


Figure 23.12 Connection termination

1 QUIT

221 service closed 2

TCP/IP Protocol Suite 22


Figure 23.13 Pop3 and IMAP4

TCP/IP Protocol Suite 23


Figure 23.14 Pop3

TCP/IP Protocol Suite 24


23-6 WEB-BASED MAIL

E-mail is such a common application that some


websites today provide this service to anyone who
accesses the site. Three common sites are Hotmail,
Yahoo, and Google. The idea is very simple. Let us
go through two cases:

TCP/IP Protocol Suite 25


Figure 23.19 Web-based e-mail, case 1

1
HTTP
transactions
3
2 4

TCP/IP Protocol Suite 26


Figure 23.20 Web-based e-mail, case 2

HTTP HTTP
transactions transactions

1 2 3

TCP/IP Protocol Suite 27


TCP/IP Protocol Suite 28

You might also like