Telnet Binary Transmission(1)

　　Network Working Group J. Postel

　　Request for Comments: 856 J. Reynolds

　　ISI

　　Obsoletes: NIC 15389 May 1983

　　TELNETBINARY TRANSMISSION

　　This RFCspecifies a standard for the ARPA Internet community. Hosts on　the ARPA Internet are expected to adopt and implement this standard.

　　1. Command Name and Code

　　TRANSMIT-BINARY 0

　　2. Command Meanings

　　IAC WILL TRANSMIT-BINARY

　　The sender of this command REQUESTS permission to begin　transmitting, or confirms that it will now begin transmitting　characters which are to be interpreted as 8 bits of binary data by　the receiver of the data.

　　IAC WON'T TRANSMIT-BINARY

　　If the connection is already being operated in binary transmission　mode, the sender of this command DEMANDS to begin transmitting　data characters which are to be interpreted as standard NVT ASCII characters by the receiver of the data. If the connection is not　already being operated in binary transmission mode, the sender of　this command REFUSES to begin transmitting characters which are to　be interpreted as binary characters by the receiver of the data　(i.e., the sender of the data demands to continue transmitting　characters in its present mode).

　　A connection is being operated in binary transmission mode only　when one party has requested it and the other has acknowledged it.

　　IAC DO TRANSMIT-BINARY

　　　　IAC DON'T TRANSMIT-BINARY

　　If the connection is already being operated in binary transmission　mode, the sender of this command DEMANDS that the sender of the　data start transmitting characters which are to be interpreted as　RFC856May 1983　standard NVT ASCII characters by the receiver of the data (i.e.,　the party sending this command). If the connection is not already　being operated in binary transmission mode, the sender of this　command DEMANDS that the sender of data continue transmitting　characters which are to be interpreted in the present mode.

　　A connection is being operated in binary transmission mode only　when one party has requested it and the other has acknowledged it.

　　3. Default

　　WON'T TRANSMIT-BINARY

　　DON'T TRANSMIT-BINARY

　　The connection is not operated in binary mode.

　　4. Motivation for the Option

　　It is sometimes useful to have available a binary transmission path　within TELNET without having to utilize one of the more efficient,　higher level protocols providing binary transmission (such as the　File Transfer Protocol). The use of the IAC prefix within the basic　TELNET protocol provides the option of binary transmission in a　natural way, requiring only the addition of a mechanism by which the　parties involved can agree to INTERPRET the characters transmitted　over a TELNET connection as binary data.

　　5. Description of the Option

　　With the binary transmission option in effect, the receiver should　interpret characters received from the transmitter which are not　preceded with IAC as 8 bit binary data, with the exception of IAC　followed by IAC which stands for the 8 bit binary data with the　decimal value 255. IAC followed by an effective TELNET command (plus　any additional characters required to complete the command) is still　the command even with the binary transmission option in effect. IAC　followed by a character which is not a defined TELNET command has the　same meaning as IAC followed by NOP, although an IAC followed by an　undefined command should not normally be sent in this mode.