Microsoft KB Archive/138483

Current Limitations of TN3270

PSS ID Number: Q138483 Article last modified on 11-01-1995

2.11

WINDOWS

= SUMMARY =

TN3270 Server provides access to IBM Mainframes for TN3270 clients using TCP/IP as the network transport.

In regards to this fact, RFC 1576 states the following:

“Existing complex IBM 3270 display terminal networks are not easily integrated with the increasing number of multi-platform networking environments, specifically TCP/IP. These complex networks include terminals attached to a 3270 host using SNA (Systems Network Architecture) and non-SNA connections. To address the issue of easily connecting display terminals to 3270 hosts using IP networks, several vendors have introduced telnet servers that provide TCP/IP users a connection to existing IBM mainframes by supporting display terminal emulation using a subset of the existing telnet protocol. Telnet servers may exist on the host itself, or be connected to the host using SNA or non-SNA methods.”

= MORE INFORMATION =

TN3270 Server has the following limitations.


 * No printing support.
 * ATTN and SYSREQ keys are not universally supported.
 * There is no mechanism by which the client can access the SNA Bind information.
 * TN3270 clients cannot request a specific SNA resource (for example, 3270 LU)

For a more detailed explanation refer to RFC 1647. RFC 1647 also describes TN3270E which addresses these limitations.

Excerpt from RFC 1647:

&quot;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.
 * 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.&quot;

KBCategory: kbnetwork kbinterop KBSubcategory: ntnetserv ntprotocol Additional reference words: prodsna 2.11

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================================================================ Copyright Microsoft Corporation 1995.