PXS Gateways for Microsoft SNA Server

IBM mainframes with SNA are still in use. The huge investment required to replace distributed business applications using DB2 and Cobol, combined with the lack of qualified mainframe software developers, will ensure the mainframe's continuance.

Over the years, branch-offices have undergone major changes: special control unit emulators, a specialized server on a LAN, replaced IBM control units; LAN workstations replaced IBM terminals. Where distributed SNA applications were in use, SNA servers acting as agents to the mainframe replaced them. Microsoft's SNA server is one example.

Microsoft's SNA server supports 4 different interfaces:

1. Channel Interface to a 37XX communication controller, local to the mainframe
2. SDLC the native SNA link layer protocol (remote)
3. X.25 (non-native), with QLLC interface between SDLC and X.25 (remote)
4. IEEE 802 LLC, protocol used by IBM LANS (local or remote)

There are several PXS-based solutions:

1. Connected directly to 37XX communication controller, the PXS can tunnel the X.25 or SDLC traffic through TCP/IP to the remote SNA server. A PXS client module (software-only) at the remote site will remove the TCP/IP envelope and pass the traffic to the SNA server.
   
2. As above, but if X.25, the PXS can remove the X.25 protocol, and tunnel only the SDLC traffic.
3. The SNA server could reside inside the PXS, remove the SNA protocol, and forward only the user data via TCP/IP to a server or workstations. This will require that the SNA application use a socket interface.