TCP/IP Animation , Email
EmailIf we want to send or receive email, we must contract with ISP or enroll webmail service and use the server they manage. So email is always sent to the destination through the server of ISP or webmail provider. Of these servers, the server which we send email to is called SMTP server. And the server which we receive email from is called POP or IMAP server.Before PC accesses the serer PC, it must get own global IP address and target global IP address. So as to get them, it is necessary to use DHCP, NAT and DNS. The explanation of them is in 'LAN, DHCP, NAT' scene or 'DNS' scene.After getting the both IP address, PC can access the server and send or receive email. The communication between them is according to TCP.* Differences between POP and IMAPPOP : Client PC manages email. After downloading all email, users view the email with mailer.IMAP : Server manages email. Users view the email on the server with mailer.So when using IMAP, PC downloads the only selected email temporarily. When PC doesn't connect to internet, it can display past email only at using POP.
Send emailSending email1.PC A : Sends email to Mr. B.2.PC A : (SYN) Requests TCP connection.3.ISP X : (ACK) Connection OK.(SYN) I Request TCP connection, too.4.PC A : (ACK) Connection OK.5.PC A : (PSH) Sends the email.6.ISP X : (ACK) Received the email.7.PC A : The email has been sent.8.ISP X : (SYN) Requests TCP connection.9.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.10.ISP X : (ACK) Connection OK.11.ISP X : (PSH) Sends the email.12.ISP Y : (ACK) Received the email.13.ISP X : The email has been sent.(Omit finishing the connection)Send email (AUTH)Sending email with authentication (SMTP-AUTH) 1.PC A : Sends email to Mr. B.2.PC A : (SYN) Requests TCP connection.3.ISP X : (ACK) Connection OK.(SYN) I Request TCP connection, too.4.PC A : (ACK) Connection OK.5.PC A : (PSH) Sends ID and password before sending email.6.ISP X : (ACK)+(PSH) The user was identified.7.PC A : (ACK)+(PSH) Sends email to Mr. B.8.ISP X : (ACK) Received the email.9.PC A : The email has been sent.10.ISP X : (SYN) Requests TCP connection.11.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.12.ISP X : (ACK) Connection OK.13.ISP X : (PSH) Sends the email.14.ISP Y : (ACK) Received the email.15.ISP X : The email has been sent.(Omit finishing the connection)Send webmailSending webmail (Example:Gmail,Hotmail)1.PC A : Sends email to Mr. B by webmail.2.PC A : (SYN) Requests TCP connection to the webmail site.3.ISP X : (ACK) Connection OK.(SYN) I Request TCP connection, too.4.PC A : (ACK) Connection OK.5.PC A : (PSH) Accesses the webmail site.6.ISP X : (ACK)+(PSH) Returns the webmail data such as the received email and draft.7.PC A : (ACK)+(PSH) Conducts to create email and sends it.8.ISP X : (ACK) Received the webmail data.9.ISP X : (PSH) Passes the email to the local or internal SMTP server.(Omit connection) 10.PC A : The email has been sent.11.ISP X : (SYN) Requests TCP connection.12.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.13.ISP X : (ACK) Connection OK.14.ISP X : (PSH) Sends the email.15.ISP Y : (ACK) Received the email.16.ISP X : The email has been sent.(Omit finishing the connection)Receive email (POP)Receiving email with simple function. Client manages email.1.ISP Y : (PSH) Email is sent from the external SMTP server.(Omit connection) 2.ISP Y : (ACK) The email was stored.3.PC B : Confirms the email box provided by ISP which Mr. B contracts.4.PC B : (SYN) Requests TCP connection.5.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.6.PC B : (ACK) Connection OK.7.PC B : (PSH) Confirms the email box. Accesses with ID and password.8.ISP Y : (ACK)+(PSH) Permits login and sends all the stored email.9.PC B : (ACK) Received the email.10.ISP Y : (PSH) Sends the next email.11.PC B : (ACK) Received all the email.12.PC B : After this, PC holds these email and can display them at offline.Receive email (IMAP)Receiving email with advanced function. Server manages email.1.ISP Y : (PSH) Email is sent from the external SMTP server.(Omit connection) 2.ISP Y : (ACK) The email was stored.3.PC B : Confirms the email box provided by ISP which Mr. B contracts.4.PC B : (SYN) Requests TCP connection.5.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.6.PC B : (ACK) Connection OK.7.PC B : (PSH) Confirms the email box. Accesses with ID and password.8.ISP Y : (ACK)+(PSH) Permits login and sends the email that the user selects.9.PC B : (ACK) Received the selected email temporarily.10.PC B : At using IMAP, if PC is offline, it can't display the email.Receive webmailReceiving webmail (Example:Gmail,Hotmail)1.ISP Y : (PSH) Email is sent from the external SMTP server.(Omit connection) 2.ISP Y : (ACK) The email was stored.3.PC B : Confirms the webmail provided by webmail service corporation.4.PC B : (SYN) Requests TCP connection to the webmail site.5.ISP Y : (ACK) Connection OK.(SYN) I Request TCP connection, too.6.PC B : (ACK) Connection OK.7.PC B : (PSH) Accesses the webmail site.8.ISP Y : (PSH) Gets email from the local or internal POP server.9.ISP Y : (ACK)+(PSH) Returns the received webmail data.10.PC B : (ACK) Received the webmail data.
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