SNA Functions, Telnet Server Functions, BC-252

Overview of IBM Networking

CMCC Adapter Features for SNA Environments

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

•Telnet Server Functions

Figure 113 TN3270 Implementation

TN3270

server

27990

TN3270

client

SNA

TCP/IP

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.

Cisco IOS Bridging and IBM Networking Configuration Guide