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Briefs

 

Support for Legacy (SNA/SDLC) Systems

Prior to the universal acceptance of TCP/IP as a communications protocol, many systems used vendor proprietary protocols such as SNA. IBM, the developer of SNA, still supports the SNA and SDLC protocols to connect remote workstation controllers to both large systems (S/390 series mainframes) and midrange systems (AS/400).

For example, an AS/400 system might have a communications controller that connects to a point-to-point SNA/SDLC leased line running at 19,200bps. This line extends to a remote site where it connects to an IBM (or Perle) remote controller, which in turn supports multiple twinaxially-attached terminals and printers. While this type of connection has proven extremely reliable, it has one key shortcoming. An SNA/SDLC line supports only the SNA/SDLC protocols. It does not readily support TCP/IP, and therefore cannot be used to provide TCP/IP connectivity between a LAN at the remote site and the LAN at the central site.

In today's world, it is desirable to have TCP/IP connectivity between all offices of the enterprise. A few of the benefits of TCP/IP connectivity to all sites are:

  • All remote sites can share a single Internet connection & firewall, making it possible to enforce the corporate Internet policies.
  • Users at different remote sites can exchange email with each other, as well as with users at the central site.
  • The central site can establish an internal web server for corporate communications.
  • The central site can establish an FTP server as a repository for large files.

However, it is unrealistic to think that all remote workstation controllers (and associated "dumb" terminals and printers) can be replaced overnight by LAN-based PC's running TCP/IP. Further, there are many user applications that are arguably delivered the most effectively using "dumb" terminals. So, I/T managers often face a dilemma. How does one support high-speed TCP/IP LAN-to-LAN connectivity while continuing to support the legacy terminals and printers? (Hint: Paying for two lines to the remote site isn't the answer.)

Fortunately, there are many ways to solve this problem without a wholesale replacement of the installed workstation controllers, terminals, and printers. And, you don't need to pay for two communication lines. Today's routers can support legacy SNA/SDLC equipment while simultaneously supporting LAN-to-LAN TCP/IP traffic -- over the same frame-relay or point-to-point circuit. Networking equipment from Cisco, Motorola, or Nortel can be configured using a variety of different techniques, including serial tunneling (STUN), bridging, and Data-Link Switching (DLSW), to provide this support reliably and effectively.

FLG Networking Services has designed and installed several wide-area networks providing support for legacy equipment. To see how this can be accomplished for your company, give ITS Networking Services a call.

 

To discuss your networking requirements, email us at waltermorris3@yahoo.com OR call (408) 842-8630.

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