TN3270E Support in VM TCP/IP 310
TN3270E is an extension to the Telnet 3270 protocol and is described in
RFC 1647. In VM TCP/IP Level 310, we have added support for some aspects
of the protocol extensions. In particular, we support 328x printers using
3270 data streams. We do not support TN3270E for display terminals.
Essentially, we negotiate to support a subset of TN3270E for printers,
define a logical 3287 device to represent the printer, invoke an exit
to attach the device to the appropriate service machine (for example,
and handle the data streams that flow between the server and the printer.
Allowable TN3270E printer connections are defined by the
TN3270E and EndTN3270E statements in the TCP/IP
configuration file. Each printer definition gives an IP address, LU
name, user identifier, and virtual address. The LU name may be used
by the IP address to establish a TN3270E session and is associated
with the user identifier and virtual address.
| || Implications for TN3270E Clients|
When a TN3270E server receives a connection, it goes through negotiation
with the client to determine the characteristics of the session. Because
it supports TN3270E printer sessions, the VM Telnet server must start
its negotiation by asking the client if it wants to use TN3270E protocol.
A client that accepts this offer eventually supplies a terminal type
to the server. If the type is not associated with a printer, the server
backs out of the original TN3270E negotiation and attempts to negotiate
a regular TN3270 session.
Some clients do not support this part of the TN3270 negotiation protocol
properly. That is, they do not recognize that the server might change its
mind. Instead, they usually respond to the protocol back-out in one of
three inappropriate ways, as follows:
- They terminate the connection with the server.
- They ignore the negotiation and try to use TN3270E protocols anyway .
- They crash.
In all cases, the connection is unusable.
Some clients have a settable option to control their use of TN3270E. For
a VM terminal session, this option should (or, might as well) be off,
since it adds no function to the environment.
Some clients that claim to support TN3270E for printing do not support
them in 3270 data stream mode. Instead, they assume that SCS data streams
will be acceptable to the server and fail in some inconvenient way when
that assumption turns out to be incorrect.
If clients do not have the ability to disable their own use of
TN3270E, the NoTN3270E option of the InternalClientParms
statement can be specified in the TCPIP stack machine configuration
file (PROFILE TCPIP). This option disables TN3270E for all clients.
Unfortunately, it also prevents using printers via TN3270E, although
they can be used (as they can be with previous levels of VM TCP/IP)
via LPR, either directly or through RSCS.
IBM cannot recommend or even comment about TN3270 clients offered by
other companies. While we have tested some of these clients with our
server, reported any problems we have found, and provided diagnostic
assistance when asked, repairing the problems and verifying correct
operation is up to the individual client product owners. We have
successfully used IBM Personal Communications on OS/2, Windows 95, and
other platforms together with our server, both for printer and terminal
sessions. It does not require any special configuration settings to work
properly, although installing the most current level of the package for
your platform is advisable.
Using selective trace features introduced in TCP/IP FL310 (via the
TraceOnly and EndTraceOnly statements) you can use the
- Trace Telnet
- MoreTrace Telnet
to collect diagnostic information for sessions originating from a
particular IP address. This trace information is sufficient to determine
where a negotiation or protocol problem exists. If you need assistance
to collect, interpret, or explain a trace, call the IBM Support Center
and ask for TCP/IP Level 2 support.
For information on configuring RSCS TN3270E support see
RSCS Common Problems and Solutions