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| author | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
|---|---|---|
| committer | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
| commit | 4bfd864f10b68b71482b35c818559068ef8d5797 (patch) | |
| tree | e3989f47a7994642eb325063d46e8f08ffa681dc /doc/rfc/rfc2355.txt | |
| parent | ea76e11061bda059ae9f9ad130a9895cc85607db (diff) | |
doc: Add RFC documents
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diff --git a/doc/rfc/rfc2355.txt b/doc/rfc/rfc2355.txt new file mode 100644 index 0000000..acacd17 --- /dev/null +++ b/doc/rfc/rfc2355.txt @@ -0,0 +1,2131 @@ + + + + + + +Network Working Group B. Kelly +Request for Comments: 2355 Auburn University +Obsoletes: 1647 June 1998 +Category: Standards Track + + + TN3270 Enhancements + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (1998). All Rights Reserved. + +Abstract + + This document describes a protocol that more fully supports 3270 + devices than do traditional 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 is negotiated under the TN3270E Telnet Option, and is + unrelated to the Telnet 3270 Regime Option as defined in RFC 1041 + [1]. + +TABLE OF CONTENTS + + 1. Introduction ............................................... 2 + 1.1 Changes to RFC 1647 .................................... 4 + 2. TN3270E OVERVIEW ........................................... 5 + 3. COMMAND NAMES AND CODES .................................... 6 + 4. COMMAND MEANINGS ........................................... 7 + 5. DEFAULT SPECIFICATION ...................................... 9 + 6. MOTIVATION ................................................. 9 + 7. TN3270E SUB-NEGOTIATION RULES .............................. 9 + 7.1 DEVICE-TYPE Negotiation ................................ 9 + 7.1.1 Device Pools ...................................... 10 + 7.1.2 CONNECT Command ................................... 12 + + + +Kelly Standards Track [Page 1] + +RFC 2355 TN3270 Enhancements June 1998 + + + 7.1.3 ASSOCIATE Command ................................. 12 + 7.1.4 Accepting a Request ............................... 13 + 7.1.5 REJECT Command .................................... 13 + 7.2 FUNCTIONS Negotiation .................................. 14 + 7.2.1 Commands .......................................... 14 + 7.2.2 List of TN3270E Functions ......................... 16 + 8. TN3270E DATA MESSAGES ...................................... 16 + 8.1 The TN3270E Message Header ............................. 18 + 8.1.1 DATA-TYPE Field ................................... 18 + 8.1.2 REQUEST-FLAG Field ................................ 19 + 8.1.3 RESPONSE-FLAG Field ............................... 19 + 8.1.4 SEQ-NUMBER Field .................................. 20 + 9. BASIC TN3270E .............................................. 20 + 9.1 3270 Mode and NVT Mode ................................. 21 + 10. DETAILS OF PROCESSING TN3270E FUNCTIONS .................... 22 + 10.1 The SCS-CTL-CODES Function ............................. 22 + 10.2 The DATA-STREAM-CTL Function ........................... 23 + 10.3 The BIND-IMAGE Function ................................ 24 + 10.4 The RESPONSES Function ................................. 25 + 10.4.1 Response Messages ................................. 26 + 10.5 The SYSREQ Function .................................... 28 + 10.5.1 Background ........................................ 28 + 10.5.2 TN3270E Implementation of SYSREQ .................. 29 + 11. THE 3270 ATTN KEY .......................................... 30 + 12. 3270 STRUCTURED FIELDS ..................................... 31 + 13. IMPLEMENTATION GUIDELINES .................................. 31 + 13.1 3270 Data Stream Notes ................................. 31 + 13.2 Negotiation of the TN3270E Telnet Option ............... 32 + 13.3 A "Keep-alive" Mechanism ............................... 32 + 13.4 Examples ............................................... 32 + 14. SECURITY CONSIDERATIONS .................................... 36 + 15. REFERENCES ................................................. 36 + 16. AUTHOR'S NOTE .............................................. 37 + 17. AUTHOR'S ADDRESS ........................................... 37 + 18. Full Copyright Statement ................................... 38 + +1. Introduction + + Traditionally, support for 3270 terminal emulation over Telnet has + been 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 + method of negotiating 3270 terminal support by defining the 3270 + Regime Telnet Option. Very few developers and vendors ever + implemented RFC 1041. + + + + + +Kelly Standards Track [Page 2] + +RFC 2355 TN3270 Enhancements June 1998 + + + This document will refer to the existing practice of negotiating + these three Telnet Options before exchanging the 3270 data stream as + "traditional tn3270". Traditional tn3270 is documented in [10]. + + 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]. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119. + + There were several shortcomings in traditional tn3270; among them + were the following: + + - It provided no capability for Telnet clients to emulate the 328x + class of printers. + + - There was no mechanism by which a Telnet client could 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 were not universally supported. + + - There was 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. + + + + + + +Kelly Standards Track [Page 3] + +RFC 2355 TN3270 Enhancements June 1998 + + + - There was no mechanism by which the client could access the SNA + Bind information. The Bind image contains a detailed description + of the session between the Telnet server and the host application. + + - There was no mechanism by which the server could determine whether + a client supported 3270 structured fields, or a client could + request that it receive them. + +1.1 Changes to RFC 1647 + + This document replaces RFC 1647; the following is a summary of the + changes that have been incorporated: + + - Reworded the Introduction to refer to traditional tn3270 in the + past tense. + + Affected sections: 1. + + - Added this section documenting changes to RFC 1647 + + Affected sections: 1.1 + + - Clarified the specification of numeric literals contained in the + document. + + Affected sections: 3. (first paragraph) + + - Extensively revised several sections to + + 1) clarify the motivation behind and use of the ASSOCIATE + command + 2) remove restrictive wording regarding the organization + and use of server maintained device pools + 3) distinguish between device-names and resource-names in the + TN3270E device-type negotiation, and define a maximum length for + device-names and resource-names + + Affected sections: 4. (DEVICE-TYPE REQUEST command) and 7.1.1 + through 7.1.6 + + - Corrected the erroneous specification of the format of the + function-list sent during TN3270E functions negotiation. + + Affected sections: 7.2.1 (first paragraph) + + + + + + + +Kelly Standards Track [Page 4] + +RFC 2355 TN3270 Enhancements June 1998 + + + - Added a statement addressing what a client or server should do + if an impasse is reached during TN3270E functions negotiation. + + Affected sections: 7.2.1 (last paragraph) + + - Added a DATA-TYPE of PRINT-EOJ with a value of 0x08 to support + the end-of-job indication for printers. + + Affected sections: 8.1.1, 10.1, 10.2 + + - Clarified the description of the SEQ-NUMBER Field to state that + + 1) the field should be sent in network byte order (big endian) + 2) either byte that contains a 0xff must be doubled to 0xffff + before sending, and stripped back to 0xff after receipt. + + Affected sections: 8.1.4 + + - Defined the format and maximum length of the Bind image. + + Affected sections: 10.3 (fourth paragraph) + + - Clarified the misleading wording regarding allowable DATA-TYPEs + when BIND-IMAGE has been negotiated and a BIND has been sent. + + Affected sections: 10.3 (last paragraph) + + - Clarified the use of the SEQ-NUMBER field in regards to when it + should be reset to zero. + + Affected sections: 10.4 (last paragraph) + + - Clarified the format of the data when the DATA-TYPE field is + SSCP-LU-DATA. + + Affected sections: 10.5.2 (fourth paragraph) + + - Reworded the Security section to refer to Kerberos. + + Affected sections: 14. + +2. TN3270E Overview + + In order to address these issues, this document proposes a new Telnet + Option - TN3270E. 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 + + + +Kelly Standards Track [Page 5] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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 + + Please note that all numeric literals in this document specify + decimal values, unless they are preceded by "0x", in which case a + hexadecimal value is represented. + + TN3270E 40 + ASSOCIATE 00 + CONNECT 01 + DEVICE-TYPE 02 + FUNCTIONS 03 + IS 04 + REASON 05 + REJECT 06 + REQUEST 07 + SEND 08 + + Reason-codes + CONN-PARTNER 00 + DEVICE-IN-USE 01 + INV-ASSOCIATE 02 + INV-NAME 03 + + + +Kelly Standards Track [Page 6] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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 + + Refer to the Telnet Protocol Specification [8] for the meaning of + IAC, DO, WILL, etc. + + 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. + + 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. + + + + +Kelly Standards Track [Page 7] + +RFC 2355 TN3270 Enhancements June 1998 + + + IAC SB TN3270E DEVICE-TYPE REQUEST <device-type> + [ [CONNECT <resource-name>] | [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 must be followed by + <resource-name> and ASSOCIATE must be followed by <device-name>. + (See the section entitled "DEVICE-TYPE Negotiation" 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 and to return the + server-defined device-name. + + 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 "FUNCTIONS Negotiation" 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. + + + + + + + +Kelly Standards Track [Page 8] + +RFC 2355 TN3270 Enhancements June 1998 + + +5. Default Specification + + WON'T TN3270E + + DON'T TN3270E + + i.e., TN3270E will not be used. + +6. Motivation + + See the section entitled "Introduction". + +7. TN3270E Sub-negotiation Rules + + 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 names are NVT ASCII strings, all upper case. + + 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 resource-name or device-name request. + + Valid device-types are: + + erminals: IBM-3278-2 IBM-3278-2-E (24 row x 80 col display) + IBM-3278-3 IBM-3278-3-E (32 row x 80 col display) + IBM-3278-4 IBM-3278-4-E (43 row x 80 col display) + IBM-3278-5 IBM-3278-5-E (27 row x 132 col display) + IBM-DYNAMIC (no pre-defined display size) + + 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. The intention is to simplify the + device-type negotiation (in comparison to traditional tn3270) by + minimizing the number of possible device-types, and by breaking the + association of a specific piece of IBM hardware with a related set of + data stream capabilities. For example, negotiation of device-type + + + +Kelly Standards Track [Page 9] + +RFC 2355 TN3270 Enhancements June 1998 + + + IBM-3278-2-E does NOT in and of itself preclude the use of any of the + functions associated with a physical 3279 model S2B. A client's + ability to support the more advanced functions of the 3270 data + stream will be indicated not by negotiation of an IBM device type and + model number, but rather by the combination of Read Partition Query + and Query Reply. + + All of the terminal device-types support a "primary" display size of + 24 rows by 80 columns. The "-3", "-4" and "-5" types each support an + "alternate" display size as noted in the above list. The IBM-DYNAMIC + device-type implies no pre-defined alternate display size; this value + will be passed from the client to host applications as part of the + Query Reply structured field, and it can represent any display size + the client and the host application can support. + + 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. + + Clients that negotiate a terminal device-type with the "-E" suffix or + the DYNAMIC type, 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. + + In a VTAM/SNA environment, negotiation of IBM-DYNAMIC as the device- + type should result in a Bind in which the Presentation Services Usage + screen field (the eleventh byte in the logmode's PSERVIC field) is + set to 0x03, indicating that the alternate screen size will be + determined by the Query Reply (Usable Area). + +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. Definition of a few terms is also in + order. + + The terms "device-name", "LU name" and "network name" can be + considered interchangeable in this document. They refer to a + specific terminal or printer device. + + + + + +Kelly Standards Track [Page 10] + +RFC 2355 TN3270 Enhancements June 1998 + + + The term "resource-name" is less specific; it may refer to a device- + name, but it may also be the name of a pool of printer or terminal + devices. Such a named pool could serve to group devices with similar + operational or administrative characteristics. In fact, this + document places no restrictions on how a server makes use of + resource-names, so long as the server can take a resource-name + specified by the client and use it to come up with a device-name to + assign to the session. Note, however, that servers must avoid + allowing ambiguity; for example, they must not allow the definition + of a device-name with the same name as that of a pool of devices. + + Device-names and resource-names are specified as NVT ASCII strings in + which upper and lower case are considered equivalent. The length of + device-names and resource-names should not exceed 8 bytes. + + A "generic session request" is one which includes neither the CONNECT + nor the ASSOCIATE command, while a "specific session request" is one + that includes either the CONNECT or the ASSOCIATE command. + + If a TN3270E server wishes to support traditional tn3270 clients, it + must maintain a set of terminal device-names that can be used to + satisfy requests from such clients for terminal sessions. This same + pool could be used to satisfy generic requests for terminal sessions + from TN3270E clients. + + The server may also maintain any number of other pools of device- + names. For example, there could be a pool of terminal device-names + reserved for a specific department within the organization, or a pool + of terminal device-names that have access to certain applications on + the host. + + For any of these terminal device pools, the TN3270E server may also + have defined a "partner" or "paired" printer device for each terminal + in the pool. There should be a unique, one-to-one mapping between a + terminal and its associated 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 one or more pools + 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 + + + +Kelly Standards Track [Page 11] + +RFC 2355 TN3270 Enhancements June 1998 + + + example, when the userid of the person signed on to a terminal + determines the print destination). It is also possible that a pool + of printer device-names could be maintained to satisfy generic + requests for printers (i.e., those that specify neither CONNECT nor + ASSOCIATE). + +7.1.2 CONNECT Command + + CONNECT can be used by the client in two ways: if the resource-name + it specifies is a device-name, then the client is requesting a + specific device-name. If the specified resource-name is not a + device-name, then the client is requesting any one of the device- + names associated with the resource-name. + + In either case, the resource indicated by the specified resource-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 a device-name defined at the host as a terminal, then + the server must deny the request. Further, if the requested + resource-name is a device-name already associated with some other + Telnet session, or if it is not defined to the server, the server + must 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, and the specified device-name must be + that of a terminal that was returned by the server in a previous + DEVICE-TYPE IS <device-type> CONNECT <device-name> command. + + 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 must deny + the request. Also, if the server does not have defined a partner + printer for the specified terminal, it must deny the request. + + The use of the ASSOCIATE command is to be as follows: A client first + connects and requests a terminal from one of the terminal pools; it + then uses the terminal device-name returned by the server (see + "Accepting a Request", section 7.1.4 below) in a second session + request, this time asking for the printer that is paired with the + terminal session it just established. This allows clients to + associate a printer session with a terminal rather than having to + have prior knowledge of a printer device-name. + + + + + + +Kelly Standards Track [Page 12] + +RFC 2355 TN3270 Enhancements June 1998 + + +7.1.4 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 session. + + Normally, the client should accept any DEVICE-TYPE IS <device-type> + CONNECT <device-name> sent by the server. An exception to this would + be if the client must (e.g., to satisfy local-site policy) be + connected to a specific LU name and is presented with a device-name + which does not match the one requested by the client (this could + happen, for example, if the client requested what it thought was a + device-name, but what was defined at the server as the name of a pool + of devices). In this case, the client should reject the DEVICE-TYPE + IS command by terminating TN3270E negotiations. + +7.1.5 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-NAME The resource-name or 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 + session. + + TYPE-NAME-ERROR The requested device-name or + resource-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 + + + +Kelly Standards Track [Page 13] + +RFC 2355 TN3270 Enhancements June 1998 + + + server does not have any such pools of + device-names defined to it, or the + 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 must + 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 must 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 a DEVICE-TYPE IS command that is + acceptable), the client must 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 TN3270E + functions that the sender would like to see supported on this + session. All functions not in the list are to be considered + unsupported. The list is terminated by the IAC code that precedes + + + +Kelly Standards Track [Page 14] + +RFC 2355 TN3270 Enhancements June 1998 + + + the SE command. Functions may appear in any order in the list. + + 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, both parties must not 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. + + If an impasse is reached during FUNCTIONS negotiation (for example, + if a client requested and was granted a DEVICE-TYPE representing a + printer, but refuses to accept either the SCS-CTL-CODES or DATA- + STREAM-CTL function), then the "offended" party should terminate + the negotiation by sending an IAC DON'T (or WON'T) TN3270E. + + + + + + + + + + + + + + +Kelly Standards Track [Page 15] + +RFC 2355 TN3270 Enhancements June 1998 + + +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 + 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. + + If in the process of functions negotiation an unrecognized function + code is recieved, the recipient should simply remove that function + code from the list and continue normal functions negotiation. + +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 + + + +Kelly Standards Track [Page 16] + +RFC 2355 TN3270 Enhancements June 1998 + + + the last byte transmitted (note that this discussion disregards SNA + chaining). The Telnet EOR command is used to delimit these natural + blocks of 3270 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> + + 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 bytes containing decimal 255 + will be treated as one data byte with a value of decimal 255. + + It is strongly recommended that Telnet commands (other than IAC IAC) + should be sent between TN3270E data messages, with no header and no + trailing IAC EOR. If a TN3270E data message containing either IAC IP + (to be interpreted as 3270 Attention) or IAC AO (to be interpreted as + SYSREQ) is received, the receiver should defer processing the command + until the 3270 data has been processed (see the appropriate sections + for discussion of 3270 Attention and SYSREQ). If a TN3270E data + message containing any other IAC-command sequence (other than IAC + IAC) is received, it is implementation dependent when the IAC-command + sequence will be processed, but it must be processed. The receiver + may process it immediately, which in effect causes it to be processed + as if it had been received before the current TN3270E data message, + or the processing may be deferred until after the current TN3270E + data message has been processed. It is because of this ambiguity + that the presence of Telnet commands within a TN3270E data message + (i.e., between the header and the trailing IAC EOR) is not + recommended; neither clients nor servers should send such data. + + + + + + + + + + + +Kelly Standards Track [Page 17] + +RFC 2355 TN3270 Enhancements June 1998 + + +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. + + SSCP-LU-DATA 0x07 The data portion of the message is + data from the SSCP-LU session. + + + + +Kelly Standards Track [Page 18] + +RFC 2355 TN3270 Enhancements June 1998 + + + PRINT-EOJ 0x08 There is no data portion present in + the message. This value can be sent + only by the server, and only on a + printer session. + +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. + + + +Kelly Standards Track [Page 19] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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: + + 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. This field must be sent in network byte + order ("big endian"). If either byte contains a 0xff, it should be + doubled to 0xffff before sending and stripped back to 0xff upon + receipt; this is standard IAC escaping. See the section entitled + "The RESPONSES Function" for further information on the use of the + SEQ-NUMBER field. 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. + + + + +Kelly Standards Track [Page 20] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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. + +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. + + + + + + + + + +Kelly Standards Track [Page 21] + +RFC 2355 TN3270 Enhancements June 1998 + + +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 with regard to 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. + +10.1 The SCS-CTL-CODES Function + + This function can only be supported on a 3270 printer session. + + Agreement to support this function requires that the party support + the following TN3270E header values: + + Header field Value + ------------ ----- + DATA-TYPE SCS-DATA + DATA-TYPE PRINT-EOJ + + 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 must + 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. + + The server should send a TN3270E message with DATA-TYPE set to + PRINT-EOJ at the end of each print job to indicate to the client that + it may now take whatever action is appropriate for its environment + (e.g., close a disk or spool file, etc.). The server may have + multiple criteria for determining when it should send a PRINT-EOJ, + + + +Kelly Standards Track [Page 22] + +RFC 2355 TN3270 Enhancements June 1998 + + + such as receipt of SNA End Bracket from the host application, or + expiration of a pre-defined timeout value. + +10.2 The DATA-STREAM-CTL Function + + This function can only be supported on a 3270 printer session. + + Agreement to support this function requires that the party support + the following TN3270E header values: + + Header field Value + ------------ ----- + DATA-TYPE 3270-DATA + DATA-TYPE PRINT-EOJ + + 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. + + The server should send a TN3270E message with DATA-TYPE set to + PRINT-EOJ at the end of each print job to indicate to the client that + it may now take whatever action is appropriate for its environment + (e.g., close a disk or spool file, etc.). The server may have + multiple criteria for determining when it should send a PRINT-EOJ, + such as receipt of SNA End Bracket from the host application, or + expiration of a pre-defined timeout value. + + + + + + + + + + + + + + +Kelly Standards Track [Page 23] + +RFC 2355 TN3270 Enhancements June 1998 + + +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 + DATA-TYPE SSCP-LU-DATA + + 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. The format and + maximum length of this bind image are defined in [6]. + + When an SNA session between the server and a host application is + terminated, the server must 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 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 or SCS-DATA are not allowed + before the first BIND-IMAGE is received by the client; only SSCP-LU- + 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, + + + +Kelly Standards Track [Page 24] + +RFC 2355 TN3270 Enhancements June 1998 + + + in addition to SSCP-LU-DATA, now include 3270-DATA and/or SCS-DATA, + depending on whether a terminal or printer device-type was + negotiated, and whether a printer client agreed to DATA-STREAM-CTL or + SCS-CTL-CODES, or both. (See the section entitled "The SYSREQ + Function" for further discussion of the SSCP-LU session in an SNA + environment.) + +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 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 TN3270E + session. This counter should start at zero for the first such + message, and be incremented by one for each subsequent message. Note + that this counter is independent of any SNA sequence numbers, and + should not be reset to zero as a result of Bind or Unbind. If the + counter reaches the maximum of 32767, it should be restarted at zero. + The sender must 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. + + + + + + + +Kelly Standards Track [Page 25] + +RFC 2355 TN3270 Enhancements June 1998 + + +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. + + Normally only the client 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 a 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: + + 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"). + + + + +Kelly Standards Track [Page 26] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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 an SNA positive 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. + + 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. + + + +Kelly Standards Track [Page 27] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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 SSCP-LU-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 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; normal 3270 data stream orders are not allowed in this + data. 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 + + + +Kelly Standards Track [Page 28] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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. + + 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 exchanged between the client and + server should have the DATA-TYPE flag set to SSCP-LU-DATA; the data + stream will be as defined in [7], specifically the section entitled + + + +Kelly Standards Track [Page 29] + +RFC 2355 TN3270 Enhancements June 1998 + + + "Operation in SSCP-SLU Session." + + 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 (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 + + + +Kelly Standards Track [Page 30] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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 structured field(s) 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, the DYNAMIC terminal type, or 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). + +13. Implementation Guidelines + +13.1 3270 Data Stream Notes + + Implementors of TN3270E clients should note that the command codes + for the various 3270 Read and Write commands have different values + depending on how the server is connected to the host (local versus + remote, SNA versus non-SNA). Clients should be coded to check for + the various possible values if they wish to be compatible with the + widest range of servers. See [7] for further details. + + + +Kelly Standards Track [Page 31] + +RFC 2355 TN3270 Enhancements June 1998 + + +13.2 Negotiation of the TN3270E Telnet Option + + Since TN3270E is a Telnet Option governed by [8], both client and + server are free to attempt to initiate negotiation of TN3270E by + sending a DO TN3270E command. However, just as is usually the case + with the Telnet DO TERMINAL-TYPE, it is anticipated that the server + will normally be the one sending the DO TN3270E, and the client will + be responding with a WILL or a WON'T TN3270E. + +13.3 A "Keep-alive" Mechanism + + In many environments, it is very helpful to have in place a mechanism + that allows timely notification of the loss of a 3270 session. + TN3270E does not require that any form of keep-alive mechanism be + employed by either clients or servers, but implementors wishing to + support such a mechanism should consider the following guidelines. + + There are at least three possible means of providing a keep-alive + mechanism in TN3270E: the TCP Keepalive, the Telnet IAC NOP command + [8], and the Telnet DO TIMING-MARK option [9]. Each method has its + advantages and disadvantages. It is recommended that TN3270E clients + and servers that support keep-alives should support all three + methods, and that both sides should always respond to TIMING-MARKs. + + Note that both clients and servers could be configured to "actively" + implement keep-alives. That is, both sides could send a TIMING-MARK + or a NOP or issue a TCP Keepalive in order to determine whether or + not the partner is still alive. Alternatively, network + administrators may wish to configure only one side to send keep- + alives; in this case, the other side would be a "passive" participant + which simply responds to the keep-alives it receives. + + Implementors who want their code to be capable of being an "active" + keep-alive participant should make their client or server + configurable so that administrators can set which, if any, keep-alive + mechanism should be employed, and how often it should be used. + + Upon failure of a session on which keep-alives are used, both parties + should make the proper notifications. A client should give the user + some indication of the failure, such as an error code in the Operator + Information Area of the screen. A server should notify the host + application that the session has been terminated, for example by + sending an UNBIND with type CLEANUP in an SNA environment. + +13.4 Examples + + The following example shows a TN3270E-capable server and a + traditional tn3270 client establishing a connection: + + + +Kelly Standards Track [Page 32] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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-E + CONNECT myterm IAC SE + Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-5-E CONNECT + myterm IAC SE + Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES + BIND-IMAGE IAC SE + Server: IAC SB TN3270E FUNCTIONS IS RESPONSES BIND-IMAGE + 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 resource-name and is returned a device-name chosen by the + server: + + + + +Kelly Standards Track [Page 33] + +RFC 2355 TN3270 Enhancements June 1998 + + + 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-E + CONNECT pool1 IAC SE + Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-5-E CONNECT + term0013 IAC SE + Client: IAC SB TN3270E FUNCTIONS REQUEST BIND-IMAGE IAC SE + Server: IAC SB TN3270E FUNCTIONS IS BIND-IMAGE 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: + + 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 + Server: IAC SB TN3270E FUNCTIONS REQUEST DATA-STREAM-CTL + RESPONSES IAC SE + Client: IAC SB TN3270E FUNCTIONS REQUEST DATA-STREAM-CTL IAC + Server: IAC SB TN3270E FUNCTIONS IS DATA-STREAM-CTL IAC SE + + + +Kelly Standards Track [Page 34] + +RFC 2355 TN3270 Enhancements June 1998 + + + (3270 data stream is exchanged) + + The following example shows a TN3270E-capable server and a TN3270E- + capable client establishing first a specific 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 CONNECT + termxyz 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) + . . + . . + (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) + + The following example shows a TN3270E-capable server and a TN3270E- + capable client establishing first a terminal session where a + resource-name was requested and a server chosen device-name was + returned, 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-3278-5 CONNECT + poolxyz IAC SE + Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3278-5 CONNECT + terma IAC SE + Client: IAC SB TN3270E FUNCTIONS REQUEST RESPONSES IAC SE + + + +Kelly Standards Track [Page 35] + +RFC 2355 TN3270 Enhancements June 1998 + + + Server: IAC SB TN3270E FUNCTIONS IS RESPONSES IAC SE + (3270 data stream is exchanged) + . . + . . + (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 terma IAC SE + Server: IAC SB TN3270E DEVICE-TYPE IS IBM-3287-1 CONNECT + terma'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. Security Considerations + + These extensions to telnet do not provide any security features + beyond that of ordinary telnet; so a TN3270E session is no more + secure than an ordinary telnet session. Once standard authentication + and/or privacy mechanisms for telnet have been defined, these may + also be usable by TN3270E. One of the important uses of + authentication would be to answer the question of whether or not a + given user should be allowed to "use" a specific terminal or printer + device-name. + +15. References + + [1] Rekhter, J., "Telnet 3270 Regime Option", RFC 1041, January 1988. + + [2] VanBokkelen, J., "Telnet Terminal-Type Option", RFC 1091, + February 1989. + + [3] Postel, J., and J. Reynolds, "Telnet Binary Transmission", STD + 27, RFC 856, May 1983. + + [4] Postel, J., "Telnet End of Record Option", RFC 885, 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. + + + + +Kelly Standards Track [Page 36] + +RFC 2355 TN3270 Enhancements June 1998 + + + [7] "3174 Establishment Controller Functional Description", + publication number GA23-0218, IBM Corporation. + + [8] Postel, J., and J. Reynolds, "Telnet Protocol Specification", STD + 8, RFC 854, May 1983. + + [9] Postel, J., and J. Reynolds, "Telnet Timing Mark Option", STD 31, + RFC 860, May 1983. + + [10] J. Penner, "TN3270 Current Practices", RFC 1576, January, 1994. + +16. 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 1993 IETF meetings. + + - Discussions on the "TN3270E" list, 1993-94 and 1997. + +17. Author's Address + + Bill Kelly + Division of University Computing + 144 Parker Hall + Auburn University, AL 36849 + + Phone: (334) 844-4512 + EMail: kellywh@mail.auburn.edu + + + + + + + + + + + + + + + + + +Kelly Standards Track [Page 37] + +RFC 2355 TN3270 Enhancements June 1998 + + +18. Full Copyright Statement + + Copyright (C) The Internet Society (1998). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + + + + + + + + + + + + + + + + + + + + + + + +Kelly Standards Track [Page 38] + |