List of FTP Features
The main purpose of the FTP protocol is to provide fast data transfer. However, the list of its features covers more than that. Below we have gathered the main features of the FTP protocol.
Representation of data
There are two main types of files used when transferring files using the FTP protocol: ASCII
and binary. However, one can also use EBCDIC. ASCII files contain plain text. These files can be without extension or with a .txt extension. Binary files are programs and other non-text files saved in the format of the application that created them, or in the format of archived or compressed files. As for EBCDIC transfer type, well it is recommended for exchanging files between systems that support EBCDIC. This will avoid double conversion from ASCII to EBCDIC and vice versa.
File organization and Data structures
Both structured and nonstructured files can transfer via FTP. Non-structured files are byte streams and are usually marked with EOF at the end. The structure record file is divided into records for text files and is marked with EDR at the end. The page structure file is divided into pages, each page has a page number and a page title. Random access or sequential access can be performed.
FTP transfer mode has 3 modes, namely streaming mode, block mode, and compressed mode.
Data is transmitted as a stream of bytes in the default settings of FTP. the data is divided into segments by TCP. There is no need to specify EOF while closing data. However, in case the file is divided into records EOR and EOF are required.
The file is transferred as a block, and the block has its own 3-byte header. Main bytes include 16-bit values and 8-bit description subcodes.
In the compressed mode, since the data is compressed, there are many advantages to increasing the throughput. While compressing text files blank spaces are removed. Whereas while compressing binary files, the null characters are removed.
There is no point in an extra mechanism of recovery after errors, as FTP uses TCP for data transfer.
There is a secure mechanism for accessing the system via password and the name of the user.
Based on a client-server architecture, by default, FTP uses 2 TCP connections for performing data transfer. One is a control connection the other is a data connection.
The control connection is established as a normal client-server connection. The server makes a passive open to a well-known FTP port (21) and waits for a connection request from the client. The client does an active open on TCP port 21 to establish a control connection. The control connection exists as long as the client communicates with the server. This connection is used to send commands from the client to the server and to send responses from the server. The IP service type for the control connection is set to get the "lowest latency" since commands are usually entered by the user.
Opens every time a file is transferred between the client and the server and closes every time after the data has been sent. Transfer data can occur between the data transfer processes of a DTP server and a DTP and a client, or between a DTPS of two servers. FTP port (20) is used. The IP service type of the data connection should be "maximum bandwidth" because that connection is used for file transfers.