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TN3270 Enhancements Working Group B. Kelly
Internet Draft Auburn University
October 1993
TN3270 Enhancements
(filename: draft-ietf-tn3270e-enhancements-02.txt)
Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a
"working draft" or "work in progress."
Please check the 1id-abstracts.txt listing contained in the
internet-drafts Shadow Directories on ds.internic.net,
nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
current status of any Internet Draft.
Abstract
This document describes a protocol that more fully supports 3270
devices than do the existing tn3270 practices. Specifically, it
defines a method of emulating both the terminal and printer members
of the 3270 family of devices via Telnet; it provides for the
ability of a Telnet client to request that it be assigned a
specific device-name (also referred to as "LU name" or "network
name"); finally, it adds support for a variety of functions such as
the ATTN key, the SYSREQ key, and SNA response handling.
This protocol would be negotiated and implemented under a new
Telnet Option and would be unrelated to the Telnet 3270 Regime
Option as defined in RFC 1041 [1].
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TABLE OF CONTENTS
1. INTRODUCTION ............................................... 2
2. TN3270E OVERVIEW ........................................... 4
3. COMMAND NAMES AND CODES .................................... 4
4. COMMAND MEANINGS ........................................... 5
5. DEFAULT SPECIFICATION ...................................... 7
6. MOTIVATION ................................................. 7
7. IMPLEMENTATION RULES ....................................... 7
7.1 DEVICE-TYPE Negotiation ................................ 7
7.1.1 Device Pools ...................................... 8
7.1.2 CONNECT Command ................................... 9
7.1.3 ASSOCIATE Command ................................. 9
7.1.4 Device Selection Rules ............................ 10
7.1.5 Accepting a Request ............................... 11
7.1.6 REJECT Command .................................... 11
7.2 FUNCTIONS Negotiation .................................. 12
7.2.1 Commands .......................................... 12
7.2.2 List of TN3270E Functions ......................... 13
8. TN3270E DATA MESSAGES ...................................... 14
8.1 The TN3270E Message Header ............................. 15
8.1.1 DATA-TYPE Field ................................... 15
8.1.2 REQUEST-FLAG Field ................................ 16
8.1.3 RESPONSE-FLAG Field ............................... 16
8.1.4 SEQ-NUMBER Field .................................. 17
9. BASIC TN3270E .............................................. 17
9.1 3270 Mode and NVT Mode ................................. 18
10. DETAILS OF PROCESSING TN3270E FUNCTIONS .................... 18
10.1 The SCS-CTL-CODES Function ............................. 19
10.2 The DATA-STEAM-CTL Function ............................ 19
10.3 The BIND-IMAGE Function ................................ 20
10.4 The RESPONSES Function ................................. 21
10.4.1 Response Messages ................................. 22
10.5 The SYSREQ Function .................................... 24
10.5.1 Background ........................................ 24
10.5.2 TN3270E Implementation of SYSREQ .................. 25
11. THE 3270 ATTN KEY .......................................... 26
12. 3270 STRUCTURED FIELDS ..................................... 27
13. EXAMPLES ................................................... 28
14. REFERENCES ................................................. 30
15. AUTHOR'S NOTE .............................................. 30
16. AUTHOR'S ADDRESS ........................................... 31
1. Introduction
Currently, support for 3270 terminal emulation over Telnet is
accomplished by the de facto standard of negotiating three separate
Telnet Options - Terminal-Type [2], Binary Transmission [3], and
End of Record [4]. Note that there is no RFC that specifies this
negotiation as a standard. RFC 1041 attempted to standardize the
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method of negotiating 3270 terminal support by defining the 3270
Regime Telnet Option. Unfortunately, very few developers and
vendors ever implemented RFC 1041.
This document will refer to the existing practice of negotiating
these three Telnet Options before exchanging the 3270 data stream
as "traditional tn3270".
NOTE: Except where otherwise stated, this document does not
distinguish between Telnet servers that represent SNA devices and
those that represent non-SNA 3270 devices.
All references in this document to the 3270 data stream, 3270 data
stream commands, orders, structured fields and the like rely on
[5]. References to SNA Request and Response Units rely on [6].
References to SNA versus non-SNA operation rely on [7].
There are several shortcomings in traditional tn3270; among them
are the following:
- It provides no capability for Telnet clients to emulate the 328x
class of printers.
- There is no mechanism by which a Telnet client can request that
a connection be associated with a given 3270 device-name. This
can be of importance when a terminal session is being
established, since many host applications behave differently
depending on the network name of the terminal. In the case of
printer emulation, this capability is an absolute necessity
because a large number of host applications have some method of
pre-defining printer destinations.
- The 3270 ATTN and SYSREQ keys are not universally supported.
- There is no support for the SNA positive/negative response
process. This is particularly important if printer emulation is
to function properly, but is also useful for some terminal
applications. A positive response is used to indicate that
the previously received data has been successfully processed.
A negative response indicates some sort of error has occurred
while processing the previously received data; this could be
caused by the host application building a 3270 data stream that
contains an invalid command, or by a mechanical error at the
client side, among other things.
- There is no mechanism by which the client can access the SNA
Bind information. The Bind image contains a detailed
description of the session between the Telnet server and the
host application.
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- There is no mechanism by which the server can determine whether
a client supports 3270 structured fields, or a client can
request that it receive them.
2. TN3270E Overview
In order to address these issues, this document proposes a new
Telnet Option - TN3270E (option number has yet to be assigned).
Telnet clients and servers would be free to negotiate support of
the TN3270E option or not. If either side does not support TN3270E,
traditional tn3270 can be used; otherwise, a sub-negotiation will
occur to determine what subset of TN3270E will be used on the
session. It is anticipated that a client or server capable of both
types of 3270 emulation would attempt to negotiate TN3270E first,
and only negotiate traditional tn3270 if the other side refuses
TN3270E.
Once a client and server have agreed to use TN3270E, negotiation of
the TN3270E suboptions can begin. The two major elements of
TN3270E sub-negotiation are:
- a device-type negotiation that is similar to, but somewhat
more complicated than, the existing Telnet Terminal-Type Option.
- the negotiation of a set of supported 3270 functions, such as
printer data stream type (3270 data stream or SNA Character
Stream), positive/negative response exchanges, device status
information, and the passing of BIND information from server to
client.
Successful negotiation of these two suboptions signals the
beginning of 3270 data stream transmission. In order to support
several of the new functions in TN3270E, each data message must be
prefixed by a header. This header will contain flags and
indicators that convey such things as positive and negative
responses and what type of data follows the header (for example,
3270 data stream, SNA Character Stream, or device status
information).
3. Command Names and Codes
TN3270E (to be assigned)
ASSOCIATE 00
CONNECT 01
DEVICE-TYPE 02
FUNCTIONS 03
IS 04
REASON 05
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REJECT 06
REQUEST 07
SEND 08
Reason-codes
CONN-PARTNER 00
DEVICE-IN-USE 01
INV-ASSOCIATE 02
INV-DEVICE-NAME 03
INV-DEVICE-TYPE 04
TYPE-NAME-ERROR 05
UNKNOWN-ERROR 06
UNSUPPORTED-REQ 07
Function Names
BIND-IMAGE 00
DATA-STREAM-CTL 01
RESPONSES 02
SCS-CTL-CODES 03
SYSREQ 04
4. Command Meanings
IAC WILL TN3270E
The sender of this command is willing to send TN3270E
information in subsequent sub-negotiations.
IAC WON'T TN3270E
The sender of this command refuses to send TN3270E information.
IAC DO TN3270E
The sender of this command is willing to receive TN3270E
information in subsequent sub-negotiations.
IAC DON'T TN3270E
The sender of this command refuses to receive TN3270E
information.
Note that while they are not explicitly negotiated, the equivalent
of the Telnet Binary Transmission Option [3] and the Telnet End of
Record Option [4] is implied in the negotiation of the TN3270E
Option. That is, a party to the negotiation that agrees to support
TN3270E is automatically required to support bi-directional binary
and EOR transmissions.
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IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Only the server may send this command. This command is used to
request that the client transmit a device-type and, optionally,
device-name information.
IAC SB TN3270E DEVICE-TYPE REQUEST <device-type>
[CONNECT | ASSOCIATE <device-name>] IAC SE
Only the client may send this command. It is used in response
to the server's SEND DEVICE-TYPE command, as well as to suggest
another device-type after the server has sent a DEVICE-TYPE
REJECT command (see below). This command requests emulation of
a specific 3270 device type and model. The REQUEST command may
optionally include either the CONNECT or the ASSOCIATE command
(but not both). If present, CONNECT and ASSOCIATE must both be
followed by <device-name>. (See the section entitled
"Implementation Rules" for more detailed information.)
IAC SB TN3270E DEVICE-TYPE IS <device-type> CONNECT
<device-name> IAC SE
Only the server may send this command. This command is used to
accept a client's DEVICE-TYPE REQUEST command.
IAC SB TN3270E DEVICE-TYPE REJECT REASON <reason-code> IAC SE
Only the server may send this command. This command is used to
reject a client's DEVICE-TYPE REQUEST command.
IAC SB TN3270E FUNCTIONS REQUEST <function-list> IAC SE
Either side may send this command. This command is used to
suggest a set of 3270 functions that will be supported on this
session. It is also sent as an implicit rejection of a previous
FUNCTIONS REQUEST command sent by the other side (see the
section entitled "Implementation Rules" for more information).
Note that when used to reject a FUNCTIONS REQUEST command, the
function-list must not be identical to that received in the
previous REQUEST command.
IAC SB TN3270E FUNCTIONS IS <function-list> IAC SE
Either side may send this command. This command is sent as a
response to a FUNCTIONS REQUEST command and implies acceptance
of the set of functions sent to it in the REQUEST command. Note
that the list of functions in the FUNCTIONS IS command must
match the list that was received in the previous FUNCTIONS
REQUEST command.
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5. Default Specification
WON'T TN3270E
DON'T TN3270E
i.e., TN3270E will not be used.
6. Motivation
See the section entitled "Introduction."
7. Implementation Rules
All TN3270E commands and parameters are NVT ASCII strings in which
upper and lower case are considered equivalent.
Once it has been agreed that TN3270E will be supported, the first
sub-negotiation must concern the DEVICE-TYPE (and possibly
DEVICE-NAME) information. Only after that has been successfully
negotiated can the client and server exchange FUNCTIONS
information. Only after both DEVICE-TYPE and FUNCTIONS have been
successfully negotiated can 3270 data stream transmission occur.
7.1 DEVICE-TYPE Negotiation
Device-type (and device-name) negotiation begins when the server
transmits the DEVICE-TYPE SEND command to the client. The
client responds with the DEVICE-TYPE REQUEST command, which must
include a device-type and may include a device-name request.
Valid device-types are:
terminals: IBM-3278-2 IBM-3278-2-E
IBM-3278-3 IBM-3278-3-E
IBM-3278-4 IBM-3278-4-E
IBM-3278-5 IBM-3278-5-E
printers: IBM-3287-1
Note that the use of '3278' and '3287' is not intended to
exclude any particular device capabilities; they are used here
only because they are commonly known designations for a terminal
and a printer member of the 3270 family of devices. A client's
ability to support the more advanced functions of the 3270 data
stream will be indicated via means other than an IBM device type
and model number.
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Terminal device-types with the "-E" suffix should only be
negotiated by clients that are willing to support some subset of
the 3270 "extended data stream." This usually includes at a
minimum support for extended colors and highlighting, but may
also include a number of other functions, such as graphics
capability, alternate character sets, and partitions.
TN3270E clients that negotiate a terminal device-type with the
"-E" suffix, as well as those that negotiate a printer
device-type, must be able to accept and respond to a Read
Partition Query command (see the section entitled "3270
Structured Fields"). This allows the client to indicate to host
applications which subsets of the 3270 extended data stream the
client is willing to support.
7.1.1 Device Pools
An explanation of the CONNECT and ASSOCIATE commands first
requires a discussion of the organization of terminal and
printer device pools that the server maintains and from which it
selects device-names to assign to session requests. (The terms
"device-name", "LU name" and "network name" can be considered
interchangeable in this document.) Also, for the purposes of
this discussion, the term "generic session request" will be used
to describe a request for a session by a Telnet client (either
traditional or TN3270E) that does not include a request for a
specific device-name. The term "specific session request" will
be used to describe a request for a session by a TN3270E client
that includes a request for a specific device-name (either via
CONNECT or ASSOCIATE).
As is the case with traditional tn3270, the TN3270E server must
maintain a set of terminal device-names. A generic request for
a terminal session would result in the server selecting any
available device-name from this pool. The server, however, may
also maintain a separate pool of terminal device-names which can
only be used to satisfy specific terminal session requests.
This is to ensure that a terminal device that has some
significance to host applications (and is therefore likely to be
the target of a specific session request) is not "accidentally"
assigned to a generic request and winds up associated with a
client that has no use for it. Note that the reverse situation
is allowed. That is, a specific terminal session request could
ask for a device-name that happens to be in the "generic
terminal pool."
For each terminal device (in both the "generic" and the
"specific" pools), the TN3270E server could also have defined a
"partner" or "paired" printer device. There should be a unique,
one-to-one mapping between a terminal and its associated
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printer. The reasoning behind such a configuration is to allow
for those host applications that produce printed output bound
for a printer whose device-name is determined by the device-name
of the terminal that initiated the print request. These printer
devices can only be assigned to specific printer session
requests that use the ASSOCIATE command (see below).
In addition, the TN3270E server may also maintain a pool of
printer device-names that are not associated with any terminal.
These printer devices can only be assigned to specific printer
session requests that use the CONNECT command (see below). This
allows for those host applications that generate printed output
bound for a printer whose device-name is determined by something
other than the device-name of the terminal that initiated the
print request (for example, when the userid of the person signed
on to a terminal determines the print destination).
Finally, it is possible that a pool of printer device-names
could be maintained and used only to satisfy generic requests
for printers.
7.1.2 CONNECT Command
CONNECT is used by the client to request that the server assign
a specific device-name to this Telnet session; it may be used
when requesting either a terminal or a printer session. The
specified device-name must not conflict with the device-type;
e.g., if the client requests DEVICE-TYPE IBM-3287-1 (a printer)
and specifies CONNECT T1000001, but T1000001 is defined at the
host as a terminal, then the server should deny the request.
Further, if the requested device-name is already associated with
some other Telnet session, or if it is not defined to the
server, the server should deny the request.
7.1.3 ASSOCIATE Command
ASSOCIATE can be used by the client only when requesting a
DEVICE-TYPE that represents a printer. The ASSOCIATE command
requests that this session be assigned the device-name of the
printer that is paired with the terminal named in the request.
If the device-type does not represent a printer, or if the
device-name is not that of a terminal, then the server should
deny the request. It is anticipated that the device-name
specified in this request would be one returned by the server
when accepting a previous terminal session request (see the IS
command below). Since no means of authentication has been
provided for, it is possible that the printer paired with the
terminal specified in the ASSOCIATE command has already been
assigned to some other Telnet session; in this case, the server
should deny the request.
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7.1.4 Device Selection Rules
To summarize, assume a TN3270E server has the following device
pools defined to it (device-names that begin with a "T" are
terminal devices; those that begin with a "P" are printers):
Generic Terminal Pool Specific Terminal Pool
--------------------- ----------------------
TG000001 <--> PTG00001 TS000001 <--> PTS00001
TG000002 <--> PTG00002 TS000002 <--> PTS00002
TG000003 <--> PTG00003 TS000003 <--> PTS00003
Generic Printer Pool Specific Printer Pool
-------------------- ----------------------
PG000001 PS000001
PG000002 PS000002
PG000003 PS000003
Note that the only pool that absolutely must be defined to the
server is the generic terminal pool. The absence of other pools
(or of partner printers for a terminal pool) simply means that
the server is unable to satisfy as wide a variety of requests as
would be possible if all pools were defined to it.
Given the above configuration, the following rules apply:
- a generic terminal request can only be satisfied from the
generic terminal pool (device-names TG000001 - TG000003).
- a specific terminal request (allowable only via the CONNECT
command) can be satisfied from either the generic or the
specific terminal pool, although it is anticipated that the
majority of such requests would ask for terminals in the
specific terminal pool (TS000001 - TS000003).
- a generic printer request can only be satisfied from the
generic printer pool (device-names PG000001 - PG000003).
- a specific printer request may come in one of two forms:
via ASSOCIATE: the request can only be satisfied using the
partner of the specified terminal, which
may be in the generic or the specific
terminal pool; therefore, devices in the
ranges PTG00001 - PTG00003 and PTS00001 -
PTS00003 can be used to satisfy the request.
via CONNECT: the request can be satisfied either from
the generic or the specific printer pools
(although, as with specific terminal requests,
it is likely that most such requests will name
printers in the specific printer pool); this
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request cannot be satisfied with the partner
printer of a terminal in either the specific or
the generic terminal pools.
7.1.5 Accepting a Request
The server must accept the client's request or deny it as a
whole - it cannot, for example, accept the DEVICE-TYPE request
but deny the CONNECT portion.
If the server wishes to accept the request, it sends back the
DEVICE-TYPE IS command confirming the requested device-type and
the CONNECT command specifying the device-name of the terminal
or printer assigned to this Telnet session. This device-name
may be the one directly requested (via CONNECT) by the client,
the one indirectly requested (via ASSOCIATE) by the client, or
one chosen by the server if the client specified neither CONNECT
nor ASSOCIATE.
7.1.6 REJECT Command
If the server wishes to deny the request, it sends back the
DEVICE-TYPE REJECT command with one of the following
reason-codes:
Reason code name Explanation
---------------- -----------------------------------
INV-DEVICE-TYPE The server does not support the
requested device-type.
INV-DEVICE-NAME The device-name specified in the
CONNECT or ASSOCIATE command is
not known to the server.
DEVICE-IN-USE The requested device-name is
already associated with another
Telnet session.
TYPE-NAME-ERROR The requested device-name is
incompatible with the requested
device-type (such as terminal/
printer mismatch).
UNSUPPORTED-REQ The server is unable to satisfy
the type of request sent by the
client; e.g., a specific terminal
or printer was requested but the
server does not have such a pool of
device-names defined to it, or the
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ASSOCIATE command was used but no
partner printers are defined to the
server.
INV-ASSOCIATE The client used the ASSOCIATE
command and either the device-type
is not a printer or the device-name
is not a terminal.
CONN-PARTNER The client used the CONNECT command
to request a specific printer but
the device-name requested is the
partner to some terminal.
UNKNOWN-ERROR Any other error in device type or
name processing has occurred.
The process of negotiating a device-type and device-name that
are acceptable to both client and server may entail several
iterations of DEVICE-TYPE REQUEST and DEVICE-TYPE REJECT
commands. The client should make use of the reason-code
specified by the server in any DEVICE-TYPE REJECT command(s) to
minimize the amount of negotiation necessary. For example, if
the client initially requests that it be assigned a specific
terminal device-name via the CONNECT command, and the server
rejects the request with a reason-code of UNSUPPORTED-REQ, the
client should make no further specific terminal requests in the
negotiations. If at any point in the process either side wishes
to "bail out," it can simply send a WON'T (or DON'T) TN3270E
command to the other side. At this point both sides are free to
negotiate other Telnet options (including traditional tn3270).
7.2 FUNCTIONS Negotiation
Once the DEVICE-TYPE negotiation has successfully completed
(i.e, when the client receives the DEVICE-TYPE IS command), the
client should initiate the FUNCTIONS negotiation by sending the
FUNCTIONS REQUEST command to the server. After this initial
REQUEST command, both sides are free to transmit FUNCTIONS
REQUEST and FUNCTIONS IS commands as needed.
7.2.1 Commands
The FUNCTIONS REQUEST command contains a list of the 3270
functions that the sender would like to see supported on this
session. All functions not in the list are to be considered
unsupported. The function-list consists of a string of 2-byte
entries separated from one another by a single space character.
The list is terminated by the IAC code that precedes the SE
command. Functions may appear in any order in the list.
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Upon receipt of a FUNCTIONS REQUEST command, the recipient has
two choices:
- it may respond in the positive (meaning it agrees to support
all functions in the list, and not to transmit any data
related to functions not in the list). To do this, it sends
the FUNCTIONS IS command with the function-list exactly as it
was received. At this point, FUNCTIONS negotiation has
successfully completed.
- it may respond in the negative by sending a FUNCTIONS
REQUEST command in which the function-list differs from the
one it received (and not simply in the order of appearance
of functions in the list; at least one function must have
been added to, or removed from, the list).
To avoid endlessly looping, neither party should add to the
function-list it receives any function that it has previously
added and that the other side has removed.
The process of sending FUNCTIONS REQUEST commands back and forth
continues until one side receives a function-list it is willing
to live with. It uses the FUNCTIONS IS command to accept the
list, and, once this command is received by the other side, all
necessary negotiation has been completed. At this point, 3270
data stream transmission can begin.
Note that it is possible that the function-list agreed to is
null; this is referred to as "basic TN3270E." See the section
entitled "Basic TN3270E" for more information.
7.2.2 List of TN3270E Functions
The following list briefly describes the 3270 functions that may
be negotiated in the function-list:
Function Name Description
------------- -----------
SCS-CTL-CODES (Printer sessions only). Allows the use
of the SNA Character Stream (SCS) and SCS
control codes on the session. SCS is
used with LU type 1 SNA sessions.
DATA-STREAM-CTL (Printer sessions only). Allows the use
of the standard 3270 data stream. This
corresponds to LU type 3 SNA sessions.
RESPONSES Provides support for positive and
negative response handling. Allows the
server to reflect to the client any and
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all definite, exception, and no response
requests sent by the host application.
BIND-IMAGE Allows the server to send the SNA Bind
image and Unbind notification to the
client.
SYSREQ Allows the client and server to emulate
some (or all, depending on the server) of
the functions of the SYSREQ key in an SNA
environment.
See the section entitled "Details of Processing TN3270E
Functions" for a more detailed explanation of the meaning and
use of these functions.
8. TN3270E Data Messages
3270 device communications are generally understood to be block
oriented in nature. That is, each partner buffers data until an
entire "message" has been built, at which point the data is sent to
the other side. The "outbound message" (from host to device)
consists of a 3270 command and a series of buffer orders, buffer
addresses, and data, while the "inbound message" contains only
buffer orders, addresses and data. The end of a message is
understood to be the last byte transmitted (note that this
discussion disregards SNA chaining). The Telnet EOR command is
used to delimit these natural 3270 blocks of data within the Telnet
data stream.
In TN3270E, each 3270 message must be prefixed with a TN3270E
header, which consists of five bytes and whose format is defined
below (see the section entitled "The TN3270E Message Header").
A "data message" in TN3270E therefore has the following
construction:
<TN3270E Header><data><IAC EOR>
It should be noted that it is possible that, for certain message
types, there is no data portion present. In this case, the TN3270E
data message consists of:
<TN3270E Header><IAC EOR>
Note also that Telnet commands may appear anywhere in the Telnet
stream. For this reason, if either side wishes to transmit the
decimal value 255 and have it interpreted as data, it must "double"
this byte. In other words, a single occurrence of decimal 255 will
be interpreted by the other side as an IAC, while two successive
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bytes containing decimal 255 will be treated as one data byte with
a value of decimal 255.
8.1 The TN3270E Message Header
As stated earlier, each data message in TN3270E must be prefixed
by a header, which consists of five bytes and is formatted as
follows:
-----------------------------------------------------------
| DATA-TYPE | REQUEST-FLAG | RESPONSE-FLAG | SEQ-NUMBER |
-----------------------------------------------------------
1 byte 1 byte 1 byte 2 bytes
8.1.1 DATA-TYPE Field
The DATA-TYPE field indicates how the data portion of the
message is to be interpreted by the receiver. Possible values
for the DATA-TYPE field are:
Data-type Name Code Meaning
-------------- ---- ---------------------------------
3270-DATA 0x00 The data portion of the message
contains only the 3270 data stream.
SCS-DATA 0x01 The data portion of the message
contains SNA Character Stream data.
RESPONSE 0x02 The data portion of the message
constitutes device-status information
and the RESPONSE-FLAG field indicates
whether this is a positive or negative
response (see below).
BIND-IMAGE 0x03 The data portion of the message is
the SNA bind image from the session
established between the server and the
host application.
UNBIND 0x04 The data portion of the message is
an Unbind reason code.
NVT-DATA 0x05 The data portion of the message is to
be interpreted as NVT data.
REQUEST 0x06 There is no data portion present in
the message. Only the REQUEST-FLAG
field has any meaning.
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8.1.2 REQUEST-FLAG Field
The REQUEST-FLAG field only has meaning when the DATA-TYPE field
has a value of REQUEST; otherwise, the REQUEST-FLAG field must
be ignored by the receiver and should be set to 0x00 by the
sender. Possible values for the REQUEST-FLAG field are:
Request-Flag Name Code Meaning
----------------- ---- ---------------------------------
ERR-COND-CLEARED 0x00 The client sends this to the server
when some previously encountered
printer error condition has been
cleared. (See the section entitled
"The RESPONSES Function" below.)
8.1.3 RESPONSE-FLAG Field
The RESPONSE-FLAG field only has meaning for certain values of
the DATA-TYPE field. For DATA-TYPE field values of 3270-DATA
and SCS-DATA, the RESPONSE-FLAG is an indication of whether or
not the sender of the data expects to receive a response. In
this case the possible values of RESPONSE-FLAG are:
Response-Flag Name Code Meaning
------------------ ---- ---------------------------------
NO-RESPONSE 0x00 The sender does not expect the
receiver to respond either
positively or negatively to this
message. The receiver must
therefore not send any response
to this data-message.
ERROR-RESPONSE 0x01 The sender only expects the
receiver to respond to this message
if some type of error occurred, in
which case a negative response must
be sent by the receiver.
ALWAYS-RESPONSE 0x02 The sender expects the receiver to
respond negatively if an error
occurs, or positively if no errors
occur. One or the other must
always be sent by the receiver.
For a DATA-TYPE field value of RESPONSE, the RESPONSE-FLAG is an
actual response to a previous data message (which must by
definition have had a DATA-TYPE of either 3270-DATA or SCS-DATA
and a RESPONSE-FLAG value of either ERROR-RESPONSE or
ALWAYS-RESPONSE). In this case the possible values of
RESPONSE-FLAG are:
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Response-Flag Name Code Meaning
------------------ ---- ---------------------------------
POSITIVE-RESPONSE 0x00 The previous message was received
and executed successfully with
no errors.
NEGATIVE-RESPONSE 0x01 The previous message was received
but an error(s) occurred while
processing it.
Accompanying status information will be found in the data
portion of the message.
For any other values of the DATA-TYPE field, the RESPONSE-FLAG
field must be ignored by the receiver and should be set to 0x00
by the sender.
8.1.4 SEQ-NUMBER Field
The SEQ-NUMBER field is only used when the RESPONSES function
has been agreed to. It contains a 2 byte binary number, and is
used to correlate positive and negative responses to the data
messages for which they were intended. See the section entitled
"The RESPONSES Function" for further information. When the
RESPONSES function is not agreed to, this field should always be
set to 0x0000 by the sender and ignored by the receiver.
9. Basic TN3270E
As has been stated earlier, whether or not the use of each of the
TN3270E functions is allowed on a session is negotiated when the
connection is established. It is possible that none of the
functions are agreed to (in this case, the function-list in the
FUNCTIONS REQUEST and FUNCTIONS IS commands is null). This mode of
operation is referred to as "basic TN3270E." Note that, since
neither the SCS-CTL-CODES function nor the DATA-STREAM-CTL function
is agreed to, basic TN3270E refers to terminal sessions only.
Basic TN3270E requires the support of only the following TN3270E
header values:
Header field Value
------------ -----
DATA-TYPE 3270-DATA
DATA-TYPE NVT-DATA
The REQUEST-FLAG, RESPONSE-FLAG and SEQ-NUMBER fields are not used
in basic TN3270E.
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9.1 3270 Mode and NVT Mode
At any given time, a TN3270E connection can be considered to be
operating in either "3270 mode" or "NVT mode." In 3270 mode,
each party may send data messages with the DATA-TYPE flag set to
3270-DATA; sending a DATA-TYPE flag set to NVT-DATA constitutes
a request to switch modes. In NVT mode, each party may send
data messages with the DATA-TYPE flag set to NVT-DATA; sending
3270-DATA is a request to switch modes. The connection is
initially in 3270 mode when TN3270E operation is successfully
negotiated. When a party receives a message with a DATA-TYPE
different from the mode it is operating in, the mode of
operation for the connection is switched. Switching modes
results in the client performing the equivalent of a 3270
Erase/Reset operation, as described in [5], using the default
partition (screen) size. The server cannot assume the client
preserves any attributes of the previous environment across a
mode switch.
Note that even when sending NVT-DATA, each side should buffer
data until an entire message is built (for the client, this
would normally mean until the user presses Enter). At that
point, a complete TN3270E data message should be built to
transmit the NVT data.
Typically, NVT data is used by a server to interact with the
user of a client. It allows the server to do this using a
simple NVT data stream, instead of requiring a 3270 data stream.
An example would be a server which displays a list of 3270
applications to which it can connect the client. The server
would use NVT data to display the list and read the user's
choice. Then the server would connect to the application, and
begin the exchange of 3270 data between the application and the
client.
10. Details of Processing TN3270E Functions
Agreement by both parties to a specific function in the FUNCTIONS
REQUEST function-list implies agreement by each party to support a
related set of values in the TN3270E header. It also implies a
willingness to adhere to the rules governing the processing of data
messages as regards the agreed upon function. Either party that
fails to accept header values associated either with agreed upon
functions or with basic TN3270E, or attempts to use header values
associated with a function that is not a part of basic TN3270E and
was not agreed upon, will be considered non-conforming and in
violation of the protocol. The following sections detail for each
TN3270E function the associated header values and processing
rules.
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10.1 The SCS-CTL-CODES Function
This function can only be supported on a 3270 printer session.
If either party receives this function in a FUNCTIONS REQUEST
function-list when the previously negotiated device-type
represents a terminal, it must remove the SCS-CTL-CODES function
from the list before responding with a FUNCTIONS REQUEST of its
own.
Agreement to support this function requires that the party
support the following TN3270E header values:
Header field Value
------------ -----
DATA-TYPE SCS-DATA
A client representing a printer device uses this function to
indicate its willingness to accept a data stream that includes
SCS control codes. For the purposes of NVT mode versus 3270
mode, SCS-DATA should be treated exactly like 3270-DATA (i.e.,
it can cause a switch from NVT mode to 3270 mode).
When a printer device-type has been negotiated, either the
SCS-CTL-CODES function or the DATA-STREAM-CTL function, or both,
must be negotiated. This enables the server to know when it
should and should not accept a session with a host application
on behalf of the client. If only the SCS-CTL-CODES function is
agreed to, then the server will not establish sessions with host
applications that would send 3270 data stream control. If both
SCS-CTL-CODES and DATA-STREAM-CTL are agreed to, then the server
will establish sessions both with host applications that would
send SCS control codes and with those that would send 3270
orders.
10.2 The DATA-STREAM-CTL Function
This function can only be supported on a 3270 printer session.
If either party receives this function in a FUNCTIONS REQUEST
function-list when the previously negotiated device-type
represents a terminal, it must remove the DATA-STREAM-CTL
function from the list before responding with a FUNCTIONS
REQUEST of its own.
Agreement to support this function requires that the party
support the following TN3270E header values:
Header field Value
------------ -----
DATA-TYPE 3270-DATA
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A client representing a printer device uses this function to
indicate its willingness to accept a data stream that includes
3270 orders and attributes.
When a printer device-type has been negotiated, either the
SCS-CTL-CODES function or the DATA-STREAM-CTL function, or both,
must be negotiated. This enables the server to know when it
should and should not accept a session with a host application
on behalf of the client. If only the DATA-STREAM-CTL function
is agreed to, then the server will not establish sessions with
host applications that would send SCS control codes in a data
stream. If both SCS-CTL-CODES and DATA-STREAM-CTL are agreed
to, then the server will establish sessions both with host
applications that would send SCS control codes and with those
that would send 3270 orders.
10.3 The BIND-IMAGE Function
This function can only be supported when the TN3270E server
represents SNA terminals and printers.
Agreement to support this function requires that the party
support the following TN3270E header values:
Header field Value
------------ -----
DATA-TYPE BIND-IMAGE
DATA-TYPE UNBIND
When BIND-IMAGE is in effect, the server must inform the client
when an SNA session has been established with a host
application, and when such a session has been terminated. It
uses DATA-TYPE values of BIND-IMAGE and UNBIND to convey this
information.
When establishing an SNA session on behalf of a client, the
server will receive a Bind RU from the host application. It
will also receive a Start Data Traffic RU. Once both of these
have been responded to positively by the server, it must then
inform the client of the presence of this session by sending it
a data message with the DATA-TYPE flag set to BIND-IMAGE. The
data portion of this message must contain the bind image exactly
as it was received in the Bind RU that the server accepted on
behalf of the client.
When an SNA session between the server and a host application is
terminated, the server should send a data message to the client
with the DATA-TYPE flag set to UNBIND. If the server was
notified of the session termination via an SNA Unbind RU, it
should include the Unbind reason code in the data portion of the
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message it sends to the client. If the server itself requested
the SNA session termination (for example, as part of SYSREQ key
processing), it should set the data portion of the UNBIND
message to 0x01, indicating "normal end of session."
Another aspect of the BIND-IMAGE function alters the allowable
DATA-TYPE flag values slightly from the behavior described in
the section entitled "Basic TN3270E." When BIND-IMAGE is in
effect, data messages with DATA-TYPE set to 3270-DATA are not
allowed before the first BIND-IMAGE is received by the client;
only SCS-DATA or NVT-DATA can be used to transmit user-oriented
data. The same applies to data messages exchanged after an
UNBIND is sent and before another BIND-IMAGE is received by the
client. Once the client receives a BIND-IMAGE data message, the
allowable DATA-TYPE values (while in 3270 mode, as opposed to
NVT mode) are determined by the following:
- for terminal sessions, only 3270-DATA is allowed unless the
SYSREQ function has been negotiated (see the section entitled
"The SYSREQ function").
- for printer sessions, either 3270-DATA or SCS-DATA, or both,
may be allowed, depending on which types were negotiated. See
the sections entitled "The SCS-CTL-CODES Function" and "The
DATA-STREAM-CTL Function" for more information.
10.4 The RESPONSES Function
This function can be supported for both terminal and printer
sessions connected to both SNA and non-SNA servers.
Agreement to support this function requires that the party
support the following TN3270E header values:
Header field Value
------------ -----
DATA-TYPE RESPONSE
DATA-TYPE REQUEST
RESPONSE-FLAG -all values-
REQUEST-FLAG ERR-COND-CLEARED
SEQ-NUMBER binary values from 0-32767
Whenever a data message is sent with a DATA-TYPE of either
SCS-DATA or 3270-DATA, the sender must set the RESPONSE-FLAG
field to either NO-RESPONSE, ERROR-RESPONSE, or ALWAYS-RESPONSE.
It is anticipated that the client side will normally set
RESPONSE-FLAG to NO-RESPONSE. The server, if it represents an
SNA device, should set RESPONSE-FLAG to reflect the response
value set in the RH of the RU that generated this data message -
Definite Response resulting in a RESPONSE-FLAG value of
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ALWAYS-RESPONSE, Exception Response resulting in ERROR-RESPONSE
being set, and No Response causing a setting of NO-RESPONSE. A
non-SNA server should set RESPONSE-FLAG to ERROR-RESPONSE.
In addition, the sender must keep a count of the messages with a
DATA-TYPE of 3270-DATA or SCS-DATA that it sends on a given
session. This counter should start at zero for the first such
message, and be incremented by one for each subsequent message.
If the counter reaches the maximum of 32767, it should be
restarted at zero. The sender should place this value in the
SEQ-NUMBER field of the TN3270E header before it sends the
message. Note that the SEQ-NUMBER field must be set regardless
of the value of the RESPONSE-FLAG field.
10.4.1 Response Messages
Whenever a data message with a DATA-TYPE of either SCS-DATA or
3270-DATA is received, the receiver must attempt to process the
data in the data portion of the message, then determine whether
or not it should send a data message with a DATA-TYPE of
RESPONSE. If the data message it has just processed had a
RESPONSE-FLAG value of NO-RESPONSE, or if it had a value of
ERROR-RESPONSE and there were no errors encountered while
processing the data, then no RESPONSE type message should be
sent. Otherwise, a data message should be sent in which the
header DATA-TYPE field is set to RESPONSE, and in which the
SEQ-NUMBER field is a copy of the SEQ-NUMBER field from the
message to which this response corresponds. The RESPONSE-FLAG
field in this header must have a value of either
POSITIVE-RESPONSE or NEGATIVE-RESPONSE. A POSITIVE-RESPONSE
should be sent if the previously processed message's header
specified ALWAYS-RESPONSE and no errors were encountered in
processing the data. A NEGATIVE-RESPONSE should be sent when
1) the previously processed message specified ERROR-RESPONSE
or ALWAYS-RESPONSE and
2) some kind of error occurred while processing the data.
Please keep in mind that it is normally only the client that
will be constructing and sending these RESPONSE messages. A
negative response sent by the client to the server is the
equivalent of a Unit Check Status [7]. All references to device
status and sense codes in this section rely on [7].
The data portion of this RESPONSE message must consist of one
byte of binary data. The value of this byte gives a more
detailed account of the results of having processed the
previously received data message. The possible values for this
byte are:
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For a RESPONSE-FLAG value of POSITIVE-RESPONSE -
Value Meaning
----- -------
0x00 Successful completion (when sent by the client,
this is equivalent to "Device End").
For a RESPONSE-FLAG value of NEGATIVE-RESPONSE -
Value Meaning
----- -------
0x00 An invalid 3270 command was received
(equivalent to "Command Reject").
0x01 Printer is not ready (equivalent to
"Intervention Required").
0x02 An illegal 3270 buffer address or order
sequence was received (equivalent to
"Operation Check").
0x03 Printer is powered off or not connected
(equivalent to "Component Disconnected").
When the server receives any of the above responses, it should
pass along the appropriate information to the host application.
The appropriate information is determined by whether the server
represents an SNA or a non-SNA device.
An SNA server should pass along a POSITIVE-RESPONSE from the
client as a positive SNA Response Unit to the host application.
It should translate a NEGATIVE-RESPONSE from the client into an
SNA negative Response Unit in which the Sense Data Indicator bit
is on and which contains one of the following sense codes:
RESPONSE-FLAG Equivalent SNA Sense Code
------------- ---------- --------------
0x00 Command Reject 0x10030000
0x01 Intervention Required 0x08020000
0x02 Operation Check 0x10050000
0x03 Component Disconnected 0x08310000
A non-SNA server should pass along a POSITIVE-RESPONSE from the
client by setting the Device End Status bit on. It should
reflect a NEGATIVE-RESPONSE from the client by setting the Unit
Check Status Bit on, and setting either the Command Reject,
Intervention Required, or Operation Check Sense bit on when
responding to the Sense command.
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In the case of Intervention Required or Component Disconnected
being passed by the server to the host application, the host
would normally refrain from sending any further data to the
printer. If and when the error condition at the client has been
resolved, the client must send to the server a data message
whose header DATA-TYPE field is set to REQUEST, and whose
REQUEST-FLAG is set to ERR-COND-CLEARED. Note that this message
has no data portion. Upon receipt of this message, the server
should pass along the appropriate information to the host
application so that it may resume sending printer output.
Again, the form of this information depends on whether the
server represents an SNA or a non-SNA device.
An SNA server should reflect an ERR-COND-CLEARED to the host
application by sending an SNA LUSTAT RU with one of the
following sense codes:
- if the previous error condition was an Intervention
Required, the server should send sense code 0x00010000
- if the previous error condition was Component
Disconnected, the server should send sense code 0x082B0000
A non-SNA server should set the corresponding bits in the Ending
Status and Sense Condition bytes.
10.5 The SYSREQ Function
This function can only be supported when the TN3270E server
represents SNA devices.
Agreement to support this function requires that the party
support the following TN3270E header values:
Header field Value
------------ -----
DATA-TYPE SCS-DATA
The 3270 SYSREQ key can be useful in an SNA environment when the
ATTN key is not sufficient to terminate a process. (See the
section entitled "The 3270 ATTN Key" for more information.)
10.5.1 Background
In SNA, there is a session between the host application (the
PLU, or Primary Logical Unit) and the TN3270E server
representing the client (the SLU, or Secondary Logical Unit).
This is referred to as the PLU-SLU session, and it is the one on
which normal communications flow. There is also a session
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between the host telecommunications access method (the SSCP, or
System Services Control Point) and the SLU, and it is referred
to as the SSCP-LU session. This session is used to carry
various control information and is normally transparent to the
user. For more information, refer to [7].
The terminal display and keyboard are usually "owned" by the
PLU-SLU session, meaning any data the user types is sent to the
host application. The SYSREQ key is used to toggle ownership of
the keyboard and display between the PLU-SLU session and the
SSCP-LU session. In other words, the user is able to press
SYSREQ and then communicate directly with the host SSCP. The
user may then enter any valid Unformatted Systems Services
commands, which are defined in the USS table associated with the
SLU. The most common USS command users employ is "LOGOFF,"
which requests that the SSCP immediately terminate the PLU-SLU
session. The usual reason for requesting such an action is that
the host application (the PLU) has stopped responding
altogether.
Whenever the keyboard and display are owned by the SSCP-LU
session, no data is allowed to flow in either direction on the
PLU-SLU session. Once "in" the SSCP-LU session, the user may
decide to switch back to the PLU-SLU session by again pressing
the SYSREQ key.
10.5.2 TN3270E Implementation of SYSREQ
The design of some TN3270E servers allows them to fully support
the SYSREQ key because they are allowed to send USS commands on
the SSCP-LU session. Other TN3270E servers operate in an
environment which does not allow them to send USS commands to
the SSCP; this makes full support of the SYSREQ key impossible.
For such servers, TN3270E provides for emulation of a minimal
subset of functions, namely, for the sequence of pressing SYSREQ
and typing LOGOFF that many users employ to immediately
terminate the PLU-SLU session.
The Telnet Abort Output (AO) command is the mechanism used to
implement SYSREQ key support in TN3270E because, in a real SNA
session, once the user presses the SYSREQ key, the host
application is prevented from sending any more output to the
terminal (unless the user presses SYSREQ a second time), but the
user's process continues to execute.
In order to implement SYSREQ key support, TN3270E clients that
have agreed to the SYSREQ function should provide a key (or
combination of keys) that is identified as mapping to the 3270
SYSREQ key. When the user presses this key(s), the client
should transmit a Telnet AO command to the server.
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Upon receipt of the AO command, a TN3270E server that has agreed
to the SYSREQ function should enter what will be loosely termed
"suspended mode" for the connection. (If a server that has not
agreed to the SYSREQ function receives an AO command, it should
simply ignore it.) Any attempt by the host application to send
data to the client while the connection is "suspended" should be
responded to by the server with a negative response, sense code
0x082D, indicating an "LU Busy" condition. The server should
not transmit anything to the client on behalf of the host
application. While the connection is "suspended," any data
messages (except TN3270E responses) exchanged between the client
and server should have the DATA-TYPE flag set to SCS-DATA.
At this point, the behavior of the server depends upon whether
or not it is allowed to send USS commands on the SSCP-LU
session. Servers that have this ability should simply act as a
vehicle for passing USS commands and responses between the
client and the SSCP.
Servers that are not allowed to send USS commands on the SSCP-LU
session should behave as follows:
- if the user transmits the string LOGOFF (upper or lower case),
the server should send an Unbind SNA RU to the host
application. This will result in termination of the PLU-SLU
session. If the BIND-IMAGE function was agreed upon, then
the server should also send a data message to the client with
the DATA-TYPE flag set to UNBIND and the data portion set to
0x01.
- if the user transmits anything other than LOGOFF, the server
should respond with the string "COMMAND UNRECOGNIZED" to the
client. The server should not send anything to the host
application on behalf of the client.
Regardless of which kind of server is present (i.e., whether or
not it may send USS commands on the SSCP-LU session), while the
connection is suspended, the user may press the "SYSREQ" key
again. This will result in the transmission of another AO to
the server. The server should then send to the host application
an LUSTAT RU with a value of 0x082B indicating "presentation
space integrity lost." The server will then "un-suspend" the
Telnet connection to the client, meaning it will allow the host
application to once again send data to the client.
11. The 3270 ATTN Key
The 3270 ATTN key is interpreted by many host applications in an
SNA environment as an indication that the user wishes to interrupt
the execution of the current process. The Telnet Interrupt Process
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(IP) command was defined expressly for such a purpose, so it is
used to implement support for the 3270 ATTN key. This requires two
things:
- TN3270E clients should provide as part of their keyboard
mapping a single key or a combination of keys that map to
the 3270 ATTN key. When the user presses this key(s), the
client should transmit a Telnet IP command to the server.
- TN3270E servers should translate the IP command received from
a TN3270E client into the appropriate form and pass it along
to the host application as an ATTN key. In other words, the
server representing an SLU in an SNA session should send
a SIGNAL RU to the host application.
The ATTN key is not supported in a non-SNA environment; therefore,
a TN3270E server representing non-SNA 3270 devices should ignore
any Telnet IP commands it receives from a client.
12. 3270 Structured Fields
3270 structured fields provide a much wider range of features than
"old-style" 3270 data, such as support for graphics, partitions and
IPDS printer data streams. It would be unreasonable to expect all
TN3270E clients to support all possible structured field functions,
yet there must be a mechanism by which those clients that are
capable of supporting some or all structured field functions can
indicate their wishes.
The design of 3270 structured fields provides a convenient means to
convey the level of support (including no support) for the various
structured field functions. This mechanism is the Read Partition
Query command, which is sent from the host application to the
device. The device responds with a Query Reply(s) structured
field, listing which, if any, structured field functions it
supports.
The Query Reply is also used to indicate some device capabilities
which do not require the use of structured fields, such as extended
color support and extended highlighting capability. Most host
applications will use Read Partition Query to precisely determine a
device's capabilities when there has been some indication that the
device supports the "extended data stream."
Therefore, all TN3270E clients that negotiate a terminal
device-type that contains a "-E" suffix, as well as those that
negotiate a printer device-type, must be able to respond to a Read
Partition Query command. Note that these clients must support both
the Read Partition Query (Type 02), and all forms of the Read
Partition Query List (Type 03).
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13. Examples
The following example shows a TN3270E-capable server and a
traditional tn3270 client establishing a connection:
Server: IAC DO TN3270E
Client: IAC WON'T TN3270E
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-3278-2 IAC SE
Server: IAC DO EOR IAC WILL EOR
Client: IAC WILL EOR IAC DO EOR
Server: IAC DO BINARY IAC WILL BINARY
Client: IAC WILL BINARY IAC DO BINARY
(3270 data stream is exchanged)
The following example shows a TN3270E-capable server and a
TN3270E-capable client establishing a generic pool (non-specific)
terminal session:
Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3278-2 IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-2 CONNECT
anyterm IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES IAC SE
Server: IAC SB TN3270E FUNCTIONS IS RESPONSES IAC SE
(3270 data stream is exchanged)
The following example shows a TN3270E-capable server and a
TN3270E-capable client establishing a terminal session where the
client requests a specific device-name:
Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3278-5
CONNECT myterm IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-5 CONNECT
myterm IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES IAC SE
Server: IAC SB TN3270E FUNCTIONS IS RESPONSES IAC SE
(3270 data stream is exchanged)
The following example shows a TN3270E-capable server and a
TN3270E-capable client attempting to establish a terminal session;
multiple attempts are necessary because the device-name initially
requested by the client is already in use:
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Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3278-5
CONNECT myterm IAC SE
Server: IAC SB TN3270E DEVICE-TYPE REJECT REASON
DEVICE-IN-USE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3278-2
CONNECT herterm IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-2 CONNECT
herterm IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES IAC SE
Server: IAC SB TN3270E FUNCTIONS IS RESPONSES IAC SE
(3270 data stream is exchanged)
The following example shows a TN3270E-capable server and a
TN3270E-capable client establishing a printer session where the
client requests a specific device-name, and where some amount
of 3270 function negotiation is required before an agreement is
reached:
Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3287-1 CONNECT
myprt IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3287-1 CONNECT
myprt IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST DATA-STREAM-CTL IAC SE
Server: IAC SB TN3270E FUNCTIONS REQUEST DATA-STREAM-CTL
RESPONSES IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST DATA-STREAM-CTL IAC SE
Server: IAC SB TN3270E FUNCTIONS IS DATA-STREAM-CTL IAC SE
(3270 data stream is exchanged)
The following example shows a TN3270E-capable server and a
TN3270E-capable client establishing first a generic terminal
session, then a printer session where the "partner" printer for
the assigned terminal is requested:
Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3278-2 IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-2 CONNECT
termXYZ IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES IAC SE
Server: IAC SB TN3270E FUNCTIONS IS RESPONSES IAC SE
(3270 data stream is exchanged)
. .
. .
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Internet Draft TN3270 Enhancements October 1993
(user decides to request a printer session,
so client again connects to Telnet port on server)
Server: IAC DO TN3270E
Client: IAC WILL TN3270E
Server: IAC SB TN3270E SEND DEVICE-TYPE IAC SE
Client: IAC SB TN3270E DEVICE-TYPE REQUEST IBM-3287-1
ASSOCIATE termXYZ IAC SE
Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3287-1 CONNECT
termXYZ's-prt IAC SE
Client: IAC SB TN3270E FUNCTIONS REQUEST SCS-CTL-CODES
RESPONSES IAC SE
Server: IAC SB TN3270E FUNCTIONS IS SCS-CTL-CODES RESPONSES
IAC SE
(3270 data stream is exchanged)
14. References
[1] Rekhter, J., "Telnet 3270 Regime Option", RFC 1041, IBM
Corporation, January 1988.
[2] VanBokkelen, J., "Telnet Terminal-Type Option", RFC 1091,
FTP Software, Inc., February 1989.
[3] Postel, J., and J. Reynolds, "Telnet Binary Transmission",
RFC 856, USC/Information Sciences Institute, May 1983.
[4] Postel, J., "Telnet End of Record Option", RFC 885, USC/
Information Sciences Institute, December 1983.
[5] "3270 Information Display System - Data Stream Programmer's
Reference", publication number GA24-0059, IBM Corporation.
[6] "SNA Formats", publication number GA27-3136, IBM Corporation.
[7] "3174 Establishment Controller Functional Description",
publication number GA23-0218, IBM Corporation.
15. Author's Note
Portions of this document were drawn from the following sources:
- A White Paper written by Owen Reddecliffe, WRQ Corporation,
October 1991.
- Experimental work on the part of Cleve Graves and Michelle
Angel, OpenConnect Systems, 1992 - 1993.
- Discussions at the March 1993 IETF meeting.
- Discussions on the "TN3270E" list, Spring/Summer 1993.
B. Kelly Expires March 1994 [Page 30]
16. Author's Address
Bill Kelly
Division of University Computing
144 Parker Hall
Auburn University, AL 36849
Phone: (205) 844-4512
Email: kellywh@mail.auburn.edu
B. Kelly Expires March 1994 [Page 31]