We recently won a contract with a customer that had a national leased line WAN with IBM remote controllers running SDLC at the branch offices and an IBM AS400 at the head office. The problem was that this network only supported the IBM SDLC protocol and could not support the IP protocol.

Our solution was to design and build a new Cisco based IP network that could also support the legacy IBM protocols. The legacy protocols were supported using the Cisco STUN (Serial Tunneling) feature. This not only transported the SDLC frames over the IP network, but also spoofed a lot of the acknowledgements. These local protocol acknowledgements saved a considerable amount of bandwidth. Another enhancement was the introduction of data compression. When using leased lines this technology (standard issue on Cisco routers) can effectively double the available bandwidth.

The result was a network that supported a gradual migration from legacy systems over to IP based systems without incurring further recurring telecom costs.