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E-mail: Ouyang@china-pub.com
Translator: Gu Guofei (GGFEI GGFEI@263.net)
Translation time: 2001-4-2
Copyright: This Chinese translation copyright belongs to China Interactive Publishing Network. Can be used for non-commercial use free reprint, but the translation and copyright information of this document must be retained.
Network Working Group J. Postel
Request for Comments: 856 J. Reynolds
ISI
Obsoletes: NIC 15389 May 1983
RFC856 Telnet binary transmission
(RFC856 - Telnet Binary Transmission)
This RFC specifies the standards on ARPA Internet Community. All hosts on the ARPA Internet should adopt and implement this standard.
table of Contents
Command and code 1
2. Command meaning 1
3. By default 2
4. The reason for the option 2
5. Option Description 2
6. Realize the problem 3
Command and code
TRANSMIT-BINARY 0
2. Command meaning
* Iac Will Transmit-binary
The sender request of this command request starts to transmit, or determines that the data to be transmitted now is interpreted in an eight-bit binary.
* Iac Won't transmit-binary
If the connection has been connected in a binary mode, the command is sent to request the recipient to recover the original NVT ASCII mode to interpret data. If it is not yet in the binary mode, the sender refusal to transmit the recipient to interpret the character of binary data (that is, the data transmitter requires continues to be transmitted now). Binary transmission is only possible if both parties agree.
* Iac Do Transmit-binary
The sender requires transferring data, or determines that the data will be transmitted, which is interpreted as 8-bit binary.
* Iac Don't transmit-binary
If it is now in a binary state, the command sender requires the data sender to perform standard NTV ASCII transmission. If the connection is not in the binary state, the issuer requests the data sender to send data according to the current state. Binary transmission is only possible if both parties agree.
3. By default
The default is: won't transmit-binary and don't transmit-binary, the connection is not in the binary state.
4. The reason for the appearance of options
Sometimes binary transmission on Telnet will be more efficient, this is the root cause. And both parties can complete this option as long as they change the interpretation of the data, so it is more convenient.
5. Option description
After starting binary transmission, the recipient explains the data that does not have IAC starts with binary. The IAC is behind a standard telnet command. If the command behind the IAC is unrecognizable, it is the same as the IAC NOP command.
6. Realize problems
Implement binary transmission cannot be transmitted for other modes, which is foreseeable. However, if both parties understand they are in binary transmission modes or, for example, they are in Echo mode, if they have negotiated this, they will not have any problems.
We see that the meaning of the above command can notice that Won't and don't meaning should be seen in binary transmission mode now, suppose now in eBCDIC mode, and one side does not know any binary transfer command, if It receives the do transmit-binary, it doesn't know what this is, so returns Won't transmit-binary, if the default value for Won't transmit-binary is NVT ASCII, sending the Do Transmit-binary may wish to receive the square transfer To NVT ASCII, but if you receive the Do Transmit-binary, you may not do this.
Therefore, we have such a rule: When the connection is not in the binary state, the default value (that is, the explanation for WON 'T and DON't) is to maintain the status, whether it is in NVT ASCII, EBCDIC or other state. . However, this rule is not used when the connection is in a binary state. This requires the connection between the two sides to maintain a stack that holds all available connection status, so that Won't and don't can be explained correctly. In the binary state, WON't and don n't returns the state to NVT ASCII.
Because Telnet is a two-way channel, it must ensure that the two-way data stream is binary. This rule has a description in the Telnet protocol when implementing rules that prevent cycles. Let's take a look at the situation from one process and terminal or receiving binary transfer:
a. Start binary transmission from the terminal
The implementation should consider how to generate 8 valid data in the binary state, where there is something such as a check bit.
b. binary transfer to the process
Implementors should consider how to receive all binary data in binary states. For example, TOPS-20 will explain some specific characters (eg, ETX, interrupt CONTROL-C) in the terminal stage without transmitting them to the process.
c. Binary transmission starting from the process
The implementator should consider how the transmitted characters do not interpret the other characters as other characters. For example, TOPS-20 converts non-print characters to an arrow and a printable character.
d. binary transmission to the terminal
Implementors should consider how the received data is transmitted to the local terminal. Some characters, check operations, or character translations that should be added locally should be added.
RFC 856 Telnet Binary Transmission RFC 856 Telnet Binary Transmission
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