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 had a communications controller that connected to a point-to-point SNA/SDLC leased line running at 19,200bps. This line extended to a remote site where it connected to an IBM (or Perle) remote controller, which in turn supported multiple twinaxially-attached terminals and printers. While this type of connection proved extremely reliable, it had one key shortcoming. An SNA/SDLC line supports only the SNA/SDLC protocols. It does not readily support TCP/IP, and therefore could not 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, TCP/IP connectivity between all offices of the enterprise is assumed. However, there continue to be remote workstation controllers (and associated "dumb" terminals and printers) that must be supported. It is unrealistic to think that all of these devices can be replaced overnight by LAN-based PC's running TCP/IP or thin clients. So, I/T managers often face a tough question. How does one support legacy controllers, terminals and printers over their high-speed TCP/IP network?
Fortunately, there are many ways to solve this problem without a wholesale replacement of the installed workstation controllers, terminals, and printers. Cisco routers (with the right IOS) 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. A Cisco router 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 FLG Networking Services a call.
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