Private networks, like AT&T's ESPCS and SBS's CNS-A, are comprised of transmission and switching systems and services dedicated to the internal communications requirements of a single corporation. These offerings are typified by dedicated access and long-haul transmission lines (paths) to carry on-net traffic while overflow and off-net traffic utilize switched public media.an average private network only addresses 30 to 50 percent of a corporation's traffic.he current interest by users in virtual offerings can be attributed to two factors: the shift in attitude by carriers to permit end-user access to the data base that controls the SDN, and the potential cost savings that switched service offers versus traditional dedicated networks.

In contrast, an SDN is a transport, switching and management service provided on a public switched network that is the functional equivalent of a private network. With these virtual network offerings, both on-net and off-net traffic traverse the carrier's switched network. Dedicated or switched access may be used to connect the user to the carrier's intelligent network nodes. It is these intelligent switches that allow the SDN to provide, via software, the same features and functions as a private network.

The service is available in both interstate and intrastate offerings throughout the United States. In addition, there is an international offering to more than 150 direct-dial countries around the world. Volume discounts can be offered on both international and domestic service.

Major offerings among these features are: Software Defined Data Network (SDDN) ,SDN International (SDN-I) , SDN Voice Mail,SDN Cellular Calling, Global SDN (GSDN)