Configuring TN3270 Server on the Channel Interface Processor 5
Cisco’s Implementation of TN3270 on a Channel Interface Processor
Configuring TN3270 Server on the ChannelInterface Processor
This chapter describes TN3270 server support provided by the Channel Interface Processor (CIP)
cardfor Systems Network Architecture (SNA) devices. For a complete description of the commands
mentioned in this chapter, refer to the “TN3270 Server Commands” update chapter.

Cisco’s Implementation of TN3270 on a Channel Interface Processor

The TN3270 server feature on a CIP card provides mapping between an SNA 3270 host and a
TN3270client connected to a TCP/IP network as shown in Figure 1. Functionally, it is useful to view
the TN3270 server from two different perspectives: SNA functions and Telnet Server functions.
•SNA Functions
From the perspective of an SNA 3270 host connected to the CIP, the TN3270 server is an SNA
device that supports multiple physical units (PUs), with each PU supporting up to 255 logical
units (LUs). The LU can be Type 1, 2, or 3. The SNA host is unaware of the existence of the
TCP/IP extension on the implementation of these LUs.
The LUs implemented by TN3270 server are dependent LUs. To route these dependent LU
sessionsto multiple virtual telecommunications access method (VTAM) hosts connected to the
serverin the CIP card, rather than routing in the VTAM hosts, the TN3270 server implements a
SNAsession switch with end node dependent LU requester (DLUR) function. Using the DLUR
isoptional so that the TN3270 server can be used with VTAMversions prior to version 4.2, which
provide no APPN support.
SNA session switch allows you to eliminate SNA subarea routing between hosts of TN3270
traffic by establishing APPN links with the primary LU hosts directly.
•Telnet Server Functions
From the perspective of a TN3270 client, the TN3270 server is a Telnet server that can support
approximately 8000 (CIP1) or 16000 (CIP2) concurrent Telnet sessions. The server on the CIP
cardsupports Telnet connection negotiation and data format as specified in RFC 1576 (referred
to as “traditional TN3270”) and RFC 1647 (referred to as “TN3270E”).
Figure 1 TN3270 Implementation
Becausethe TN3270 server configuration is performed after an interface is configured for CIP SNA
(CSNA)support, TN3270 configuration issues and tasks are addressed separately from the interface
configurationtasks. The description of TN3270 configuration issues and tasks begins in the section
“Configuring TN3270 on a Channel Interface Processor,” later in this chapter.
Router Router Token
Ring
SNA TCP/IP
TN3270
client
S4735