TCP/IP Animation , FTP
FTPThere are several ways to upload or download a file between PC and Server PC. HTTP,FTP,SCP and so on are the concrete ways.1. FTPThis protocol uses 2 TCP connections. One is for control the other is for data communication. Data connection is established and finished at every file communication. The difference between 'active mode' and 'passive mode' is which side requests to establish data connection.2. FTPSFTPS is the same behavior as FTP. The difference is that the communication data at FTPS is encrypted with SSL.3. SCP and SFTPThey use one TCP connection. Communication data is encrypted with SSH by the exclusive application. And after receiving the data, it is restored by the exclusive application.4. HTTPThis uses one TCP connection. The way of communication is the same as website access. When a file is transmitted with HTTP, the data size is bigger than that of viewing website in many cases. This case is left out here.
FTP (active)Sending files with FTP active mode.1.PC : Downloads files with FTP active mode.2.PC : (SYN) Requests FTP control connection.3.Server : (ACK) Connection OK.(SYN) Requests FTP control connection, too.4.PC : (ACK) FTP control connection OK.5.PC : (PSH) Logins with ID and password. And then I am going to downloads two files.6.Server : (ACK) OK. Then we must establish a new connection for FTP data communication.7.Server : (SYN) Requests FTP data connection so as to send the file.8.PC : Firewall of OS or anti virus software blocks the request for connection from a server.9.PC : Firewall setting must be changed so that the communication may be permitted.10.PC : Setting is changed. Firewall Permits the request.11.Server : (SYN) Requests FTP data connection so as to send the file.12.PC : (ACK) Connection OK.(SYN) Requests FTP data connection, too.13.Server : (ACK) Connection OK.14.Server : (PSH) Sends the file.15.PC : (ACK) Received the file.16.Server : (FIN) Finishes the data connection.17.PC : (ACK) OK.18.PC : (FIN) Finishes the connection, too.19.Server : (ACK) OK.20.Server : (SYN) Requests FTP data connection again for the next file.21.PC : (ACK) Connection OK.(SYN) Requests FTP data connection, too.22.Server : (ACK) Connection OK.23.Server : (PSH) Sends the file.24.PC : (ACK) Received the file.25.Server : (FIN) Finishes the data connection.26.PC : (ACK) OK.27.PC : (FIN) Finishes the connection, too.28.Server : (ACK) OK.FTP (passive)Sending files with FTP passive mode.1.PC : Downloads files with FTP passive mode.2.PC : (SYN) Requests FTP control connection.3.Server : (ACK) Connection OK.(SYN) Requests FTP control connection, too.4.PC : (ACK) FTP control connection OK.5.PC : (PSH) Logins with ID and password. And then I am going to downloads two files.6.Server : (ACK) OK. Then we must establish a new connection for FTP data communication.7.PC : (SYN) Requests FTP data connection so as to send the file. Firewall doesn't block this.8.Server : (ACK) Connection OK.(SYN) Requests FTP data connection, too.9.PC : (ACK) Connection OK.10.Server : (PSH) Sends the file.11.PC : (ACK) Received the file.12.Server : (FIN) Finishes the data connection.13.PC : (ACK) OK.14.PC : (FIN) Finishes the connection, too.15.Server : (ACK) OK.16.PC : (SYN) Requests FTP data connection again for the next file.17.Server : (ACK) Connection OK.(SYN) Requests FTP data connection, too.18.PC : (ACK) Connection OK.19.Server : (PSH) Sends the file.20.PC : (ACK) Received the file.21.Server : (FIN) Finishes the data connection.22.PC : (ACK) OK.23.PC : (FIN) Finishes the connection, too.24.Server : (ACK) OK.FTPS (active) : ElementarySending files with FTP active mode and SSL.1.PC : Downloads files with FTPS active mode and SSL.2.PC : Requests FTPS control connection.3.Server : FTPS control connection OK.4.PC : Logins with ID and password. And then I am going to download a file.5.Server : Requests FTPS data connection so as to send the file.6.PC : FTPS data connection OK.7.Server : Sends the file.8.PC : Received the file.FTPS (passive) : ElementarySending files with FTP passive mode and SSL.1.PC : Downloads files with FTPS passive mode and SSL.2.PC : Requests FTPS control connection.3.Server : FTPS control connection OK.4.PC : Logins with ID and password. And then I am going to download a file.5.PC : Requests FTPS data connection so as to send the file.6.PC : FTPS data connection OK.7.Server : Sends the file.8.PC : Received the file.SCP,SFTPSending files with SSH. SCP and SFTP is similar composition.1.PC : Uploads files with SSH.2.PC : All communication data is encrypted with SSH by SSH application.3.PC : (SYN) Requests TCP connection.4.Server : The data is restored by SSH application.5.Server : After this, these encrypt and restore explanation is left out.6.Server : (ACK) Connection OK.(SYN) I Request TCP connection, too.7.PC : (ACK) Connection OK.8.PC : (PSH) Inputs ID and password for SSH authentication.9.Server : (ACK)+(PSH) Login OK.10.PC : (ACK)+(PSH) Now this PC can operate the server. Sends command with keyboard.11.Server : (ACK)+(PSH) Sends the response.12.PC : (ACK)+(PSH) Transmits a file.13.Server : (ACK) Received the file.14.PC : (FIN) Finishes the connection.15.Server : (ACK) OK.16.Server : (FIN) Finishes the connection, too.17.PC : (ACK) OK.
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