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Chapter 26

SMTP

and

FTP

26.1 Electronic Mail26.1 Electronic Mail

Sending/Receiving Mail

Addresses

User Agent

MIME

Mail Transfer Agent

Mail Access Protocols

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Figure 26.1 Format of an email

Figure 26.2 Email address

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Figure 26.3 User agent

Some examples of command-driven

user agents are mail, pine, and elm.

NoteNote::

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Some examples of GUI-based user

agents are Eudora, Outlook, and

Netscape.

NoteNote::

Figure 26.4 MIME

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Figure 26.5 MIME header

Table 26.1Table 26.1 Data types and subtypes in MIMEData types and subtypes in MIME

General binary data (8-bit bytes)Octet-Stream

Adobe PostScriptPostScriptApplication

Single-channel encoding of voice at 8 KHzBasicAudio

Video is in MPEG formatMPEGVideo

Video is in GIF formatGIF

Image is in JPEGJPEGImage

Body is a reference to another messageExt. Body

Partial

RFC822

Alternative

Digest

Parallel

Mixed

PlainSubtype

Body is a fragment of a bigger message

Body is an encapsulated message

Message

Parts are different versions of the same message

Similar to mixed, but the default is message/RFC822

Same as above, but no order

Body contains ordered parts of different data types

Multiport

Unformatted textTextDescriptionType

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Table 26.2Table 26.2 ContentContent--transfer encodingtransfer encoding

Non-ASCII characters are encoded as an equal sign followed by anASCII code

6-bit blocks of data are encoded into 8-bit ASCII characters

Non-ASCII characters with unlimited-length lines

Non-ASCII characters and short lines

ASCII characters and short lines

Description

Base64

Binary

8bit

7bit

Type

Category

Figure 26. 6 Base64

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Table 26.3Table 26.3 Base64 encoding tableBase64 encoding table

2

1

0

z

y

x

w

v

u

t

s

Code

63

62

61

60

59

58

57

56

55

Value

/

+

9

8

7

6

5

4

3

Code

43

42

41

40

39

38

37

36

35

34

33

Value

r

q

p

o

n

m

l

k

j

i

h

Code

54

53

52

51

50

49

48

47

46

45

44

Value

V

U

T

S

R

Q

P

O

N

M

L

Code

32

31

30

29

28

27

26

25

24

23

22

Value

g

f

e

d

c

b

a

Z

Y

X

W

Code

21

20

19

18

17

16

15

14

13

12

11

Value

K

J

I

H

G

F

E

D

C

B

A

Code

9

10

6

7

8

3

4

5

2

1

0

Value

Figure 26.7 Quoted-printable

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Figure 26.8 MTA client and server

Figure 26.9 Commands and responses

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Figure 26.10 Email delivery

Figure 26.11 POP3

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26.2 File Transfer26.2 File Transfer

Connections

Communication

File Transfer

User Interface

Anonymous

FTP uses the services of TCP. It needs

two TCP connections. The well-known

port 21 is used for the control

connection, and the well-known port

20 is used for the data connection.

NoteNote::

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Figure 26.12 FTP

Figure 26.13 Using the control connection

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Figure 26.14 Using the data connection

Figure 26.15 File transfer

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Example 1Example 1

Figure 26.16 (next slide) shows an example of how a file is stored.

1. The control connection is created, and several control

commands and responses are exchanged.

2. Data are transferred record by record.

3. A few commands and responses are exchanged to close the

connection.

Figure 26.16 Example 1

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Table 26.4Table 26.4 List of FTP commands in UNIXList of FTP commands in UNIX

!, $, account, append, ascii, bell, binary, bye, case, cd, cdup,close, cr, delete, debug, dir, discount, form, get, glob, hash, help,

lcd, ls, macdef, mdelete, mdir, mget, mkdir, mls, mode, mput,nmap, ntrans, open, prompt, proxy, sendport, put, pwd, quit,quote, recv, remotehelp, rename, reset, rmdir, runique, send,status, struct, sunique, tenex, trace, type, user, verbose,?

Commands

Example 2Example 2

We show some of the user interface commands that accomplish the same task as in

Example 1. The user input is shown in boldface. As shown below, some of the commands

are provided automatically by the interface. The user receives a prompt and provides only

the arguments.

$ ftp challenger.atc.fhda.edu

Connected to challenger.atc.fhda.edu220 Server ready

Name: forouzan

Password: xxxxxxxftp > ls /usr/user/report

200 OK150 Opening ASCII mode

......................

226 transfer complete

ftp > close221 Goodbye

ftp > quit

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Example 3Example 3

We show an example of using anonymous FTP. We connect to internic.net, where weassume there are some public data available.

$ ftp internic.netConnected to internic.net220 Server readyName: anonymous331 Guest login OK, send "guest" as passwordPassword: guestftp > pwd257 '/' is current directoryftp > ls200 OK150 Opening ASCII modebin

...ftp > close221 Goodbyeftp > quit