📄 rfc1205.txt
字号:
Network Working Group P. Chmielewski
Request for Comments: 1205 IBM Corporation
February 1991
5250 Telnet Interface
Status of this Memo
This RFC is being distributed in order to document the interface to
the IBM 5250 Telnet implementation. This information is being
provided for hosts on the Internet that want to support the 5250 work
station data stream within the Telnet protocol. This memo provides
information for the Internet community. It does not specify any
standard. Distribution of this memo is unlimited.
1. Introduction
This RFC describes the interface to the IBM 5250 Telnet
implementation. The purpose of this memo is to describe the details
of the interface so that a person wanting to implement a client
Telnet which emulates an IBM 5250 work station would be able to do
so. This memo does not describe all of the 5250 commands, aid codes,
and other information specific to the 5250 data stream. That
information is contained in the IBM 5250 Information Display System,
Functions Reference Manual, IBM publication number SA21-9247.
Corrections and additions to this manual are documented in this RFC
in section 5.
2. Telnet Options
No new Telnet options are defined for 5250 mode of operation.
However, to enable 5250 mode, both the client and server must agree
to at least support the Binary, End-Of-Record (EOR), and Terminal-
Type Telnet options. The complete list of 5250 terminal types is
maintained in the Assigned Numbers RFC and includes the following:
IBM-5555-C01 24 x 80 Double-Byte Character Set color display
IBM-5555-B01 24 x 80 Double-Byte Character Set (DBCS)
IBM-3477-FC 27 x 132 color display
IBM-3477-FG 27 x 132 monochrome display
IBM-3180-2 27 x 132 monochrome display
IBM-3179-2 24 x 80 color display
IBM-3196-A1 24 x 80 monochrome display
IBM-5292-2 24 x 80 color display
IBM-5291-1 24 x 80 monochrome display
IBM-5251-11 24 x 80 monochrome display
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RFC 1205 5250 Telnet Interface February 1991
An example of a typical negotiation process to establish 5250 mode of
operation is shown below. In this example, the server initiates the
negotiation by sending the DO TERMINAL-TYPE request.
Server: IAC DO TERMINAL-TYPE
Client: IAC WILL TERMINAL-TYPE
Server: IAC SB TERMINAL-TYPE SEND IAC SE
Client: IAC SB TERMINAL-TYPE IS IBM-5251-11 IAC SE
(The client has specified its terminal-type is an IBM-5251-11)
Server: IAC DO END-OF-RECORD
Client: IAC WILL END-OF-RECORD
Server: IAC WILL END-OF-RECORD
Client: IAC DO END-OF-RECORD
(The server and client have both agreed to transmit EORs)
Server: IAC DO TRANSMIT-BINARY
Client: IAC WILL TRANSMIT-BINARY
Server: IAC WILL TRANSMIT-BINARY
Client: IAC DO TRANSMIT-BINARY
(The server and client have both agreed to binary transmission)
3. Data Stream Format
The actual data stream that is exchanged between the client and
server is composed of a header followed by the 5250 work station data
stream. For information about the 5250 work station data stream
refer to the IBM 5250 Information Display System, Functions Reference
Manual (SA21-9247). The header which prefixes the 5250 data stream
was originally designed for the 5250 Display Station Pass-Through
(DSPT) application. 5250 DSPT is an application similar to Telnet
which runs on the IBM AS/400, System/36, and System/38 over an SNA
network. This header is designed to be variable in length and is
composed of two parts. The first, fixed part is always 6 octets long
and has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Logical Record Length | Record Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Logical Record Length: 16 bits
This field indicates the length, in octets, of this logical record
including the header length. The length is calculated BEFORE
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RFC 1205 5250 Telnet Interface February 1991
doubling any IAC characters in the data stream. The length does
not include the <IAC><EOR> that is appended to the end of the data
stream to mark the end of this logical record. The length is
specified with the most significant octet first. For example, a
length of 36 (decimal) would be specified as '0024'X.
Record Type: 16 bits
This field indicates the SNA record type. It should always be set
to '12A0'X to indicate the General Data Stream (GDS) record type.
Reserved: 16 bits
This field is currently not used.
The second part of the header is designed to be variable in length.
The length of this variable part is specified in the first octet.
Currently this portion of the header will always be 4 octets long and
has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |E|A| | | |S|T|H| | |
| Var Hdr Len |R|T| | | |R|R|L| | Opcode |
| |R|N| | | |Q|Q|P| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Var Hdr Len: 8 bits
The length, in octets, of the variable portion of the header.
Currently this is always '04'X.
Flags: 16 bits
Bit 0: ERR This bit is set to indicate a data stream
output error. The negative response code
is sent as data following the opcode field.
Bit 1: ATN This bit is set to indicate that the 5250
attention key was pressed.
Bits 2-4: * These bits are reserved (set to zero).
Bit 5: SRQ This bit is set to indicate that the 5250
System Request key was pressed.
Bit 6: TRQ This bit is set to indicate that the 5250
Test Request key was pressed.
Bit 7: HLP This bit is set to indicate the Help in
Error State function. The error code is
sent as data following the header and is
Chmielewski [Page 3]
RFC 1205 5250 Telnet Interface February 1991
a four digit packed decimal number. For
example, an error code of '0005'X indicates
the operator attempted to type in an area of
the display that is not enabled for input.
Bits 8-15: * These bits are reserved (set to zero).
Opcode: 8 bits
This field contains the operation code. It is set to indicate the
type of operation requested by the sender. The following are the
valid values:
'00'X: No Operation
'01'X: Invite Operation
'02'X: Output Only
'03'X: Put/Get Operation
'04'X: Save Screen Operation
'05'X: Restore Screen Operation
'06'X: Read Immediate Operation
'07'X: Reserved
'08'X: Read Screen Operation
'09'X: Reserved
'0A'X: Cancel Invite Operation
'0B'X: Turn On Message Light
'0C'X: Turn Off Message Light
The actual 5250 work station data stream will immediately follow the
opcode field in the header and will be terminated by the <IAC><EOR>
pair. For some operations the header will be immediately followed by
an <IAC><EOR> without any 5250 work station data stream in between.
For example, the following request to turn on the message light could
be sent by the server:
000A 12A0 0000 0400 000B FFEF
| | | | | | |
| | | | | | End Of Record marker
| | | | | |
| | | | | Opcode = Turn On Message Light ('0B'X)
| | | | |
| | | | Flags = '0000'X
| | | |
| | | Variable Header Length = '04'X
| | |
| | Reserved - Set to '0000'X
| |
| Record Type = General Data Stream ('12A0'X)
|
Logical Record Length = '000A'X for this record
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RFC 1205 5250 Telnet Interface February 1991
In this example the requested operation is indicated by the opcode
and there is no associated work station data stream.
4. Data Flow Examples
The following examples illustrate the flow of data between the client
and server for some of the more common operations. These examples
are intended to show the order in which the logical records are sent
between the client and server and the content of those records. The
hex representation of the records which are exchanged between the
client and server is shown. The way in which a client implements the
various operations will differ between implementations and those
details are not discussed here. In these examples, when the value of
a field is dependent on the length of the screen data for a
particular logical record, it will be represented as 'LLLL'.
4.1 Query Device Example
A Query command may be sent by the server system in order to
determine the attributes of the device it is talking to. When a
client receives a Query command, it must send the Query Reply back to
the server. See section 5 for a complete description of the format
for the Query command and Query Reply.
Server: Sends Write Structured 001112A0 00000400 000304F3 0005D970
Field Query command. 00FFEF
Client: Responds with a Query 004712A0 00000400 00000000 88003AD9
Reply, in this case, 70800600 01030000 00000000 00000000
for a 3180-2. 00000000 00000001 F3F1F8F0 F0F0F202
00000061 50000100 00000018 11000000
00000000 000000FF EF
4.2 Cancel Invite Example
The server will send a Cancel Invite when it needs to reverse the
normal flow direction. When a client receives a Cancel Invite, it
should reply with a Cancel Invite and not send any user data until
the server has once again "invited" the work station. A work station
is said to be "invited" when the server has sent a read command to
the client. The Cancel Invite flow is as follows:
Server: Sends header with the 000A12A0 00000400 000AFFEF
Opcode = Cancel Invite.
Client: Sends header with the 000A12A0 00000400 000AFFEF
Opcode = Cancel Invite
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RFC 1205 5250 Telnet Interface February 1991
to indicate that the
work station is no
longer invited.
4.3 System Request Example
The 5250 System Request operation is invoked when a client wants to
interrupt the server job to perform some function. The typical
scenario would be for a user to press the system request key, or
whatever key is mapped to a system request key, which would cause the
client Telnet to initiate the following flow:
Client: Sends header with the 000A12A0 00000404 0000FFEF
System Request bit set.
Note: It is possible for a client to include user data in this
record following the header. This data would be interpreted by the
server as an option to be selected from the system request menu. If
this were the case, the server would not send the system request menu
and the flow would continue based on the option selected. For this
example, the client does not send any user data and the flow would
continue as follows:
Server: Sends header with the 000A12A0 00000400 000AFFEF
Opcode = Cancel Invite.
Client: Sends header with the 000A12A0 00000400 000AFFEF
Opcode = Cancel Invite
to indicate that the
work station is no
longer invited.
Server: Sends Save (Immediate) 000C12A0 00000400 00040402 FFEF
command with
Opcode = Save Screen.
Client: Sends the screen image LLLL12A0 00000400 00040412
to be saved. <Screen Image> FFEF
Server: Sends System Request LLLL12A0 00000400 0003
menu with <System Request Menu> FFEF
Opcode = Put/Get.
Client: Sends User Input to LLLL12A0 00000400 0000
the Sys Req menu. <User Input> FFEF
Note: What happens next will depend on the System Request option
selected by the user. After any System Request processing has
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