Binary Transfer Protocol


What Does Binary File Transfer (BFT) Mean?

Binary file transfer (BFT) describes the syntax and semantics required to represent data files that are transferred using fax modems. Binary file transfer is a standard used to transmit data files through protocols of different telematic services, including Telefax Group 3 and 4, Teletex and Data Transfer and Manipulation (DTAM) normal mode.

Binary files hold data types encoded in binary form for computer processing and storage. Binary files are made up of byte sequences where the binary digits are grouped in eights. They may contain text, images and compressed versions of other files or sounds. A few binary files have headers within them. If they do not contain headers, they are called flat binary files.

In order to transfer binary files through systems that do not permit certain data values, they have to be translated into plain text format. Such a translation increases the file size by 30 percent. Files are translated back into binary after being received at the destination.

Transmitted binary data messages consist of sequences of certain attributes, which include the file data itself. The sequence of the name component is the file name of type graphic string. If more than one element is encoded, the first element is the file name and the remaining elements represent file name prefixes. Another attribute, called the permitted action attribute, defines the set of actions performed on the file. These include read, insert, replace, extend, erase, etc.

The content type attribute contains the abstract data type of the file contents and the structuring information necessary for maintaining the complete file structure and the semantics during the binary file transfer. The storage account attribute denotes the authority responsible for accumulated file storage charges. The value of the storage account attribute is of type graphic string. Date and time attributes indicate the time when the file was created. The value of this attribute type is generalized time. Date and time related to the last modification attribute indicate when the file contents were last modified. The recipient attribute indicates the final user destination of the binary file transfer. The character set attribute indicates the international character set to be used for rendering the character data included in the attribute data-file content. The compression attribute indicates an optional compression added to the contents of the data-file content. The access control syntax defines conditions under which access to the file is valid.

The FTP protocol defines two ways of transferring files: ASCII (Text) and Binary.

A binary transfer creates a byte-for-byte identical copy of the transferred file.

An ASCII transfer is intended for files which contain only plain text, and will attempt to convert the line endings from those of the sending system to those of the receiving system.

By default, Transmit runs in Automatic mode, which means that Transmit will make a decision about whether to use ASCII or binary for each file based on its file type extension. For example, an “html” file would be sent in ASCII mode and a “png” file would be sent in binary mode.

Leave Transmit in automatic mode unless you know of a specific reason that a different mode should be used.

To change transfer modes:

  1. Connect to an FTP server
  2. Choose Transfer > Mode
  3. Choose ASCII (Text), Binary, or Auto

That transfer mode will be used for all subsequent transfers.

In automatic mode, Transmit assumes all files should be sent in binary mode unless they are specifically listed as known ASCII file types.

To add or remove a file type from the list of known ASCII file types:

  1. Choose Transmit > Preferences…
  2. Click Transfers
  3. Click  or  in the ASCII File Extensions section to add or remove ASCII types


A binary file mistakenly sent in ASCII mode will very likely become corrupted. For example, a png image uploaded in ASCII mode will likely become un-viewable. Always use binary mode for these types of files.

An ASCII text file mistakenly sent in binary mode will retain the line endings from the originating system. If the two systems use the same type of line ending characters, the file will be the same on both sides. However if the line endings differ between the two systems, the transferred file will become either double-spaced or compressed onto a single very long line, unless you use ASCII mode.

FTP is the only protocol that distinguishes between ASCII and binary files. Other protocols, such as SFTP, always create a byte-for-byte (binary mode) copy of the file.


binary transfer protocol is a communication protocol which utilizes all values of a byte, as opposed to text-based protocol which only uses values corresponding to human-readable characters in ASCII encoding. … Binary protocols have the advantage of terseness, which translates into speed of transmission and interpretation.


One of the advantages of binary files is that they are more efficient. In terms of memory, storing values using numeric formats such as IEEE 754, rather than as text characters, tends to use less memory. In addition, binary formats also offer advantages in terms of speed of access.

Using FTP allows you to transfer multiple directories at one time. If you regularly transfer files, you know how advantageous this feature can be. Instead of sending single files or even single directories at a time, you can send numerous directories all at once.


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