TCP/IP Tutorial and Technical Overview - IBM Redbooks

Because the 3278 and 3287 are commonly used devices, device-types are
restricted to 3278 and 3287 terminal and printer types to simplify the negotiation.
This does not mean that other types of devices cannot be used. Simply, the
device-type negotiation determines the generic characteristic of the 3270 device
that will be used. More advanced functions of 3270 data stream supported by the
client are determined by the combination of read partition query and query reply.
The -E suffix indicates the use of extended attributes, such as partition, graphics,
extended colors, and alternate character sets. If the client and the server have
agreed to use extended attributes and negotiated on a device with the -E suffix,
such as an IBM-DYNAMIC device or printer, both sides must be able to handle
the 3270 structured field. The structured field also allows 3270 Telnet clients to
issue specific 3270 data stream to host applications that the client is capable of
using.
From the point of TN3270E client, it is not always possible or easy to know
device names available in the network. The TN3270E server must assign the
proper device to the client. This is accomplished by using a device pool that is
defined on the TN3270E server. Basically, these device pools contain SNA
network devices, such as terminals and printers. In other words, the TN3270E
implementation maps TN3270 sessions to specific SNA logical unit (LU) names,
thus effectively turning them into SNA devices. The device pool not only defines
SNA network devices but also provides some other important functions for a
TN3270E session. Some of these are:
► It is possible to assign one or more printers to a specific terminal device.
► It is possible to assign a group of devices to a specific organization.
► A pool can be defined that has access to only certain types of applications on
the host.
The TN3270E client can issue CONNECT or ASSOCIATE commands to connect
or associate the sessions to certain types of resources. However, this resource
must not conflict with the definition on the server and the device-type determined
during the negotiation.
13.2 Remote Execution Command protocol (REXEC and
RSH)
Remote Execution Command Daemon (REXECD) is a server that allows the
execution of jobs submitted from a remote host over the TCP/IP network. The
client uses the REXEC or Remote Shell Protocol (RSH) command to transfer the
job across to the server. Any standard output or error output is sent back to the
client for display or further processing.
Chapter 13. Remote execution and distributed computing 495