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Lecture 2 - Weeks 2 3.pptx
Lecture_2_-_Weeks_2___3.pptx
Showing 67-70 out of 70
Lecture 2 - Weeks 2 3.pptx-Data Communication an...
Lecture_2_-_Weeks_2___3.pptx-Data Communication and Computer Networks 2.
Lecture 2 - Weeks 2 3.pptx-Data C...
Lecture_2_-_Weeks_2___3.pptx-Data Communication and Computer Networks 2.
Page 67
Application Layer A 2-67
POP3 protocol
authorization phase
❖
client commands:
▪
user:
declare
username
▪
pass:
password
❖
server responses
▪
+OK
▪
-ERR
transaction phase,
client:
❖
list:
list message
numbers and there sizes
❖
retr:
retrieve message
by number
❖
dele:
delete
❖
quit
C:
list
S: 1 498
S: 2 912
S: .
C:
retr
1
S: <message 1 contents>
S: .
C:
dele
1
C: retr 2
S: <message 1 contents>
S: .
C: dele 2
C:
quit
S:
+OK
POP3 server signing
off
S:
+OK
POP3 server ready
C:
user
bob
S:
+OK
C:
pass
hungry
S:
+OK
user successfully logged
on
Page 68
Application Layer A 2-68
IMAP
❖
with POP3 user can manage downloaded
messages into folders in local machine
❖
search can be done on that file system
❖
This hierarchy however is on the local machine
only
▪
cannot be seen on the server, or from different
machines, which may be very inconvenient
IMAP
❖
keeps all messages in one place: at server
❖
allows user to create folders and organize
messages in them
❖
keeps user state across sessions:
▪
names of folders and mappings between
message IDs and folder name
Page 69
Application Layer A 2-69
IMAP
❖
messages are assigned into folders
▪
new messages are associated with INBOX folder
❖
Protocol provide commands to
▪
allow user to create folders and move messages to
them,
▪
remotely, search folders for messages matching
some criteria
▪
delete, manipulate messages, …
❖
unlike, POP3, IMAP maintains state
▪
i.e. created folders keep their names across multiple
IMAP sessions
❖
permits user to obtain components of a
message
▪
i.e. obtain only the header or just a part of a
multipart
MIME
message
▪
this is useful, especially under low
Page 70
Application Layer A 2-70
Webmail via HTTP
❖
users can access e-mail through web browsers
▪
Hotmail introduced web-based e-mails in mid 1990s
❖
user agent is an ordinary web browser
❖
browsers communicate with their remote
mailboxes via HTTP
❖
when a user accesses his/her mailbox, the e-
mail messages are sent from the server to the
browser via HTTP
instead of POP3 or IMAP
❖
when a user wishes to send an e-mail, the e-
mail is sent from the browser to the user’s
mail server through HTTP
instead of SMTP
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