About the Global Dialing Scheme (GDS)

All active elements of an H.323 videoconferencing network (endpoints, conferences, multipoint control units, and gateways) typically have a name ("H.323 name") and number ("E.164 number" or "H.323 extension") as well as an IP address. These H.323 elements can register with a service called an H.323 gatekeeper, which provides H.323 name and/or E.164 number resolution to a specific IP address. Like DNS servers, gatekeepers can be hierarchically interconnected to allow uniform dialing among systems registered to different gatekeepers. Indiana University participates in the Global Dialing Scheme (GDS), a voluntary numbering plan for the H.323-based global video and Voice over IP (VoIP) network, developed by ViDeNet and now managed by the Internet2 Commons. GDS resembles the international telephone system numbering plan, with some exceptions.

Each GDS number consists of four parts:

  • International Access Code (IAC): Also called the world gatekeeper prefix, this is defined as 00.
  • Country Code (CC): This follows the ITU international access code system. For instance, the country code for the United States is 1. Switzerland's code is 41.
  • Organizational Prefix (OP): Many national research organizations are assigned a unique OP number by the Internet2 Commons. For instance, IU currently has the organizational prefix 1439.
  • Endpoint Number (EN): An EN is a unique number that is assigned to a particular endpoint or conference within the organization. The EN can be of varying length, but must be unique. For instance, a conference on IU's Video Bridge that includes the "Copybird" uses the EN 23200.

The whole numeric code therefore follows this format:


For example, the code for the IU Copybird is:

  00(IAC) 1(CC) 1439(OP) 23200(EN)

Typed into your videoconferencing endpoint, the number would look like:

At IU, if you are asked to dial an E.164 number that begins with a double zero (00), dial it. If the remote system or conference is ready to receive calls, you will connect.

For information on IU's H.323 numbering plan, see Configure your H.323 videoconferencing endpoint with a qualified GDS E.164 number at IU.

For help or to learn more, contact UITS Classroom & Conferencing Support (cthelp@iu.edu, 812-856-2020, Skype for Business/Lync: cthelp).

This is document aurw in the Knowledge Base.
Last modified on 2019-01-03 11:31:37.

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