Post office protocols version - application layer, Computer Networking

Assignment Help:

Post Office  Protocols Version

In computing  the post office protocol  version 3 (POP3) is an  application layer internet standard  protocols  used by  local e mail  clients  to retrieve e mail  from a remote  server over  a TCP/ IP connection. POP3 and IMAP4 ( internet  message access protocols ) as the  two most  prevalent internet  standard protocol for e mail  retrieval. Virtually all modern  mail  clients  and servers  support both.

POP3 begins when  the user starts the mail   reader.  The mail  reader calls  up the ISP ( unless there  is already a connection ) and establishes a TCP connection  with the  message transfer agent  at part 110once  the connection has been  established the POP  3 protocol  goes through  three  states in sequence.

a. Authorization

b.Transactions

c.Update

During   the first  phase authorization  the user  agent sends a username and a password  to authenticate the user. During  the second  phase transaction the user agent  retrieves message, also  during  this phase the user agent can mark message for deletion remove deflection  marks. And obtain mail  statistics. The third  phase update occurs after the client has issued the quit command ending the POP3  session at this  time the mail  server deletes the  message  that were  marked  for deflection.

The  authorization phase  has two  principal  commands  user < user name> and pass  to illustrate these  two commands  we suggest that the telnet  is directly applied to a POP3 server using  port 110 and  issue these  commands. Suppose that  mail server is  the name  of your mail  server. You will see something  like  telnet  mail server 110.

S:

 C :

S : + ok POP 3  serer ready

C : USER Harish

 S : + ok  user accepted

 C :  pass vegetables

 S : ok login  successful

Note :  the line  marked  c are from  the client  and those  marked  s are from the  server.

In  transaction phase, the  user agent issues  commands and the  server responds to each  command  with a  reply. There  are two  possible  responses + ok  used by  the server  to indicate that the  previous  command was fine  and ERR used by  the server to  indicate that something  was wrong  with the  previous command. A user agent  using POP3 can often  be configured ( by the  user) to download and delete or to download and keep. The sequence of commands  issued by a POP3. User agent  depends on which  of these  two  mode  the user agent  is operating in. In  the download  and delete  mode  the user agent will issue  the LIST   RETR and DELE commands. As an example  suppose user has two  message in his her mailbox.

C: LIST

 S: + ok  2 messages

S : 1 120

 S : 2 200

S:

 C: RETER 1

 S: < the POP3 server sends  message 1>

 S: .

 C:  DELE 1

 S: ok  message 1 deleted

 C: RETR 2

 S : + ok

 S: < the  POP3  server sends  message >

 C: Quit

 S : + ok Dewey POP3  server signing off ( Mail drop empty)

 C: < close connection >

After  processing the quit  command, the POP3 server enters  the update phase and removes  message 1 and 2  from the mailbox.

A problem  with download  and  delete  mode is  that the  recipient. Harish  of group of people  want  to access  his mail message from  multiple  machines for example  his office PC, his home PC and his portable computer. This mode  partitions  Harish  mail message over these  three  machines  if Harish  first reads a message on his office PC he will  not be able  to read the message  from his  portable at home  late in the evening. In the download and keep  mode the user agent leaves the message  on the mail  server after downloading  them. In this  case Harish  can reread messaged from  different  machines  he can access  a message  from  work  and access  it again  again  later the  week  from home. 


Related Discussions:- Post office protocols version - application layer

Network and system administration, The goal of this assignment is to provid...

The goal of this assignment is to provide an exposure to Network and System Administration issues. For the project, you are required to design/configure/implement/test/review a Net

Explain the term - primary memory and hard disk, Explain the term - primary...

Explain the term - primary memory and hard disk A peculiar situation arises when the existing server arrives at a stage when it cannot handle the requests quickly and most of i

Routing table - network layer and routing , Routing Table Each  router ...

Routing Table Each  router now  uses the  shortest path tree to construct its routing table . each  router  uses the same algorithm and the same link state  database its own sh

Mention different categories of computer networks, Mention different catego...

Mention different categories of computer networks (on the basis of scale) and distinguish one from the other. Local Area Network (LAN): Metropolitan Area Network (MAN): W

Plot way forms for the modulation schemes, Plot way forms for the following...

Plot way forms for the following modulation schemes using Mathlab: a) 2 ASK   4 ASK                       b)  BFSK     4 FSK                             c) BPSK 4

What is unacknowledged connectionless service, What is Unacknowledged conne...

What is Unacknowledged connectionless service This service is a datagram-style service. It is a very simple service that does not involve any of the flow- and error-control mec

Which applications of computer network will be categorized, Q. What are the...

Q. What are the main categories based on which applications of computer network will be categorized? Ans: The main areas under which the applications for computer network will

State the specification of high-end server, State the specification of high...

State the specification of high-end server A mid-range or high-end server with the following specifications would be sufficient for a medium to large organisation: A Pentiu

Define csma/cd, CSMA/CD - A Simple Definition A netwo...

CSMA/CD - A Simple Definition A network station wishing to broadcast will first check the cable plant to make sure that no other station is currently transmit

What is intranet security, What is Intranet security Every company star...

What is Intranet security Every company starts its operations with a genuine and honest thinking. As time passes, based on the needs of its employees as well as customers, a nu

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd