Introducing the H.323 Dial Plan used by Gatekeepers and Endpoints.


The purpose of this paper is to explain in greater detail the concept of an H.323 Dial Plan used by Gatekeepers and H.323 Endpoints in initiating services used in Video Conferences. It discusses the H.323 User Number (E.164 number) and explains how it is used by the Gatekeeper to identify the end-user (Endpoint) being called.

It is assumed that the reader has a general knowledge of Video Conferencing systems and the standards involved. However, the following technical papers are available to provide more information on these topics:

H.323 User Number (E.164 number):

When initiating an H.323 Video Conference, we need some means of identifying the User or H.323 Endpoint that we wish to conference with. The thought of having to remember IP addresses is daunting enough; but the use of DHCP to dynamically allocate the IP address of an Endpoint means that this method is impractical. Hence the concept of a Dial Plan and the use of an H.323 User Number.

A Dial Plan is simply a method of allocating a unique number to an H.323 Endpoint. This number is referred to as the H.323 User Number and when registered with a Gatekeeper, such as that embedded in Edgewater Networks EdgeProtect 4550, we have a means of translating this User Number into an IP address.

Basically, when an H.323 Endpoint registers, the Gatekeeper places an entry into a look-up table that maps the H.323 User Number to the current IP address of the corresponding Endpoint. Hence, it does not matter if the H.323 Endpoint uses DHCP to dynamically allocate an IP address as if it changes, it would automatically get updated when it re-registered with the Gatekeeper.

The endpoints H.323 User Number is also loosely referred to as its E.164 number. This is because the Telecommunications Sector of the International Telecommunications Union, (ITU-T) has created a recommendation that has a similar goal; recommendation E.164 - The International Public Telecommunications Numbering Plan, defines the E.164 number as the number used by the calling party to establish a call to the end user. The ITU recommend length of the E.164 number is 17 digits.

Dial Plan Structure:

As stated earlier, the Dial Plan is simply a method of allocating a unique number to an H.323 Endpoint. In determining what the Dial Plan should be and how it is to be structured, you have to decide how this number is to uniquely vary, how it will identify the H.323 Endpoint and how it will be publicised to users who want to identify you and/or the video conferencing system you use.

Probably the most common way of uniquely identifying a person, group or team within an organisation is their telephone extension number. This number is also published and updated within the organisation. Therefore, an obvious form of Dial Plan would be to simply use the endusers telephone extension number, or prefix this with numbers that identifies the equipment type, location and as being used for Video Conferencing.

In the above example, the Dial Plan identifies the equipment as an HDX7000 located in Design.

The Dial Plan is subjective and there are no set rules on how you create your unique plan.