The AT&T Software Defined Network (SDN) is a flagship network product in the AT&T nodal architecture. SDN provides customers with the ability to achieve a corporate virtual private network (VPN) while using the facilities of the AT&T Switched Network. SDN is a customer's VPN that resides in the AT&T 4ESS? based switched Worldwide Intelligent Network and provides networked-based features and management capabilities that are usually not found in private networks. Some of the networked-based features are customized routing, advance numbering plans, call screening, authorization codes, remote access, security codes and customized billing.

SDN is compatible with most private networks and PBXs and, as such, protects these existing investments. Since SDN does not require a sophisticated PBX base, businesses can choose tariffed access or dial-up. The service fully supports analog data transmission at up to 28.8 Kbps and end-to-end digital data transmission at 56/64 Kbps.


SDN provides several optional features which enables a company to customize the service to meet its needs.

Major offerings among these features are:

  • Software Defined Data Network (SDDN) - a virtual private data network that lets users negotiate data calls on demand (dial-up). It gives customers fast access to transmit data at 56 and 64 Kbps restricted, 64 Kbps clear channel, 384 Kbps, and Nx64 Kbps.
  • SDN International (SDN-I) - is available for companies that operate in the global arena. Callers can transmit voice, data, fax, graphics, and video using either dedicated or switched access.
  • SDN Voice Mail - is a network-based service designed for applications in which geographically dispersed associates need to be in contact with each other and with centralized managers. Sales forces, technicians, associates on the move, and dispersed communities of interest can increase their communication through SDN Voice Mail.
  • SDN Cellular Calling - gives subscribers the capability to pre-subscribe to cellular service so that their SDN can carry long distance calls originating from their cell phones. The caller will be able to transfer data at the rates supported by the cellular service provider.
  • Global SDN (GSDN) - In contrast to SDN-I, GSDN is a voice-only international offering between a company's United States sites and its foreign location. GSDN is the most cost-effective high-volume international switched voice service. However, it can be particularly cost effective for businesses with as little as 2 hours of calling time per day to a given international location during peak rate periods. Access to the service can be direct or switched.

AT&T's SDN is an extremely feature-rich service offering. The above features are a limited sampling. Please contact your AT&T account executive for further information.


SDN supports a number of access arrangements from a customer's location to the AT&T Switched Network.

Below is a summary of the most frequently used arrangements. Contact your account representative for details and for additional access arrangements.

  • Dedicated Access - also referred to as Special Access. With this arrangement access is provided over Voice Grade Private Line (VGPL - analog), T1, T45, digital 56/64 DS0 Local Channel Service, or ISDN.
  • Switched Access - also referred to as Local Exchange Service Access (LESA) for voice. This approach is used to bring onto the network low-volume locations that can not justify dedicated access. LESA is available through a Local Exchange Carrier (LEC) or an independent provider's equal access end office.
  • SDDN Switched Access for Data - is an equal access (10ATT) arrangement in which data calls are passed through the LEC to an AT&T office over Feature Group D trunks. These trunks are dedicated to switched data traffic.
  • SDN Cellular Calling - a business can pre-subscribe to up to 5000 cellular numbers for SDN. Calls are placed through the cellular carrier's network and completed on SDN.
  • Network Remote Access - this access is useful for remote locations with occasional SDN traffic and for associates who travel. NRA provides access to SDN from non-SDN stations. Callers are required to enter a valid authorization code before SDN will complete the call. A telecommunications manager decides which call destinations are valid for NRA users.


Optional features are available free of charge to ensure service integrity in the event of an outage due to natural disasters, such as storms or floods. Among these features are:

  • Flexible Routing - in the event of damaged lines or circuits, the customer's calls are re-routed to ensure a high percentage of call completion. Although not instantaneous, flexible routing can be accomplished rapidly.
  • Off-Network Overflow on Terminating Busy - calls routed to busy or disabled SDN stations (on-net) are re-routed to predefined non-SDN stations (off-net).

To qualify, an organization must notify AT&T within 72 hours of the disaster. This service is available for up to 6 months from the occurrence of the disaster or until the service is restored, whichever is less. For further information, please contact your AT&T account executive.


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.


To share with customers the richness of these services and to keep them abreast of the goings-on, AT&T supports and fully participates in the SDN Users Forum. Annually, AT&T hosts a Forum Meeting to give customers a close-up look at some of the latest killer applications.

ISDN Vendor testing program is currently suspended