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Overview of IBM Networking
CMCC Adapter Features for SNA Environments
BC-249
Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02
The TN3270 server feature offers an attractive solution when the following conditions need to be
supported in an SNA environment:
• Maintaining an IP backbone while providing support for SNA 3270-type clients.
• Offloading mainframe CPU cycles when using a TN3270 host TCP/IP stack with a TN3270 server.
• Providing support for high session density or high transactions per second.
The TN3270 server feature on a CMCC adapter card provides mapping between an SNA 3270 host and
a TN3270 client connected to a TCP/IP network as shown in Figure 113. Functionally, it is useful to view
the TN3270 server from two different perspectives:
• SNA Functions, page 249
• Telnet Server Functions, page 249
Figure 113 TN3270 Implementation
SNA Functions
From the perspective of an SNA 3270 host connected to the CMCC adapter, the TN3270 server is an
SNA device that supports multiple PUs, with each PU supporting up to 255 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 the TN3270 server are dependent LUs. To route these dependent LU sessions
to multiple VTAM hosts connected to the TN3270 server in the CMCC adapter card, rather than routing
in the VTAM hosts, the TN3270 server implements a SNA session switch with EN DLUR function. SNA
session switching allows you to eliminate SNA subarea routing between hosts of TN3270 traffic by
establishing APPN links with the primary LU hosts directly.
Using the DLUR function is optional so that the TN3270 server can be used with VTAM versions prior
to version 4.2, which provide no APPN support. In these non-APPN environments, access to multiple
hosts is accomplished using direct PU configuration in the TN3270 server.
Telnet Server Functions
From the perspective of a TN3270 client, the TN3270 server is a high-performance Telnet server that
supports Telnet connections, negotiation and data format. The server on the CMCC adapter card supports
Telnet connection negotiation and data format as specified in RFC 1576 (referred to as Traditional
TN3270) and RFC 2355 (referred to as TN3270 Enhancements).
Unless the TN3270 server uses a Token Ring connection to a FEP, or other LLC connectivity to the
mainframe host, it requires CSNA or CMPC support. For more information about configuring CSNA or
CMPC support, see the “Configuring CSNA and CMPC” chapter in this publication.
SNA TCP/IP
TN3270
server
TN3270
client
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