RFC 121 (rfc121) - Page 2 of 13
Network on-line operators
Alternative Format: Original Text Document
RFC 121 Network On-Line Operators April 1971
In all operations involving the On-Line System Network operators,
there are certain conventions concerning the format of the data sent
and received. The data is grouped in 'messages' consisting of three
fields, op code, length, an text, in that order. The op code is one
byte in length and is a code which indicates how the text field is to
be interpreted. The length field is two bytes long, and gives the
length, in bits, of the text field, which contains the actual data.
(The op code and length fields together are termed a header.)
The following op codes are presently defined:
op code meaning
0 This op code is a NOP. No text field exists, and the
contents of the length field are unpredictable. (This
op code is used mainly as a delimiter.)
1 The text field contains EBCDIC characters, one
character per byte. The On-Line System operators
consider the characters as intended for display as
soon as the text field has been received.
2 The text contains codes for keypushes, one byte per
key. The On-Line operators consider the keys as
intended for execution as soon as the text field has
been received.
3 The same as for an op code of 2, except that the On-
Line operators consider that the execution of the keys
will be delayed until all data for that receive
operation has been received.
The standard format of data sent or received by the On-Line System
operators is a string of messages, with the last message indicated by
a header with a NOP op code, called a trailer. These conventions are
the default situation; any of them may be overridden by appropriate
programming. Following is a description of each operator, its
function and key sequence.
(1) OPEN
By invoking this operator, the user requests that the specified
local socket be removed from the closed state and thus be prepared
to participate in data transfer. There are three distinct
operations that can be performed by this operator and these are
described below:
Krilanovich