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Configuring H.323 gatekeeper settings

To configure gatekeeper settings, go to Settings > H.323.

You can configure the MCU to use a gatekeeper, which can make it easier for end-users to join conferences using directory numbers rather than requiring them to know the IP address or host name of the MCU. The MCU can register up to 100 IDs with the gatekeeper; these IDs comprise conferences' Numeric IDs, the MCU service prefix, and the H.323 ID. If you need to register more than 100 IDs, use a prefix for MCU registrations to route calls to the MCU, rather than registering individual conferences with the gatekeeper. The use of prefixes is described further in the table below.

On this page:

Gatekeeper settings

Refer to this table for assistance configuring the gatekeeper settings. After making any configuration changes, click Apply changes.


Field Field description Usage tips
H.323 gatekeeper usage

Enables the MCU to use an H.323 gatekeeper for registration of numeric identifiers for its conferences and/or auto attendants.

When set to Disabled then no gatekeeper registrations are attempted (and existing registrations are torn down), regardless of other gatekeeper or per-conference settings.

When set to Enabled registrations with the gatekeeper are attempted, and the gatekeeper is contacted for incoming and outgoing calls. If the gatekeeper does not respond, calls are still connected if possible. When set to Required registrations with the gatekeeper are attempted but calls are not connected if the gatekeeper cannot be contacted.

H.323 gatekeeper address

Identifies the network address of the gatekeeper to which MCU registrations should be made.

This can be specified either as a host name or as an IP address.

This field will have no effect if H.323 Gatekeeper usage (see above) is set to Disabled.

The gatekeeper can be either the built-in gatekeeper enabled on the Gatekeeper page (see Displaying the built-in gatekeeper registration list) or an external gatekeeper. To use the built-in gatekeeper enter "". For an external gatekeeper, enter its host name or IP address. Note that square brackets are mandatory for IPv6 addresses.

Gatekeeper registration type

Controls how the MCU identifies itself when registering with its configured gatekeeper.

Cisco recommends that you use the Terminal / gateway option unless you are using a service prefix (in this case, use Gateway). Only use a different option if you are:

  • having specific problems
  • using the VCS as a gatekeeper (with or without a service prefix), in which case use MCU (standard)
  • using the Cisco Gatekeeper (with or without a service prefix), in which case use Gateway (Cisco GK compatible)
  • using the VCON MXM Gatekeeper (with or without a service prefix), in which case use MCU (compatible)

Refer to the Knowledge Base in the Support section of the web site for more details about interoperability with gatekeepers.

Ethernet port association

Whether a call involves consultation with the configured gatekeeper also depends on the Port A and Port B settings. For all incoming calls, and outgoing calls dialed by address rather than by E.164 phone number, the gatekeeper will be used to validate the connection only if the network port over which the connection is made is selected here.

The check boxes that are available here depend on which interfaces are enabled.

Check the boxes of the interface(s) and IP version(s) that you want to be registered to the gatekeeper.

(Mandatory) H.323 ID to register

Specifies an identifier that the MCU can use to register itself with the H.323 gatekeeper.

Before the MCU can register any IDs with the H.323 gatekeeper, it must make a unit-wide/blade-wide registration.

This field is required for the gatekeeper registration.

This will have no effect if H.323 gatekeeper usage is disabled.

Use password

If the configured gatekeeper required password authentication from registrants, select the Use password check box and type the password.

Note that where password authentication is used, the (Mandatory) H.323 ID to register will be used as the username.

Prefix for MCU registrations

Specifies an optional group of digits that are added to the beginning of each conference or auto attendant's numeric identifier before registering it with the H.323 gatekeeper.

Conferences and auto attendants registered with a gatekeeper have a numeric identifier. The numeric identifier is a unique sequence of digits entered from a video-conferencing endpoint to connect directly to the conference or auto attendant. This eliminates the need for users to navigate additional menus or to know the IP address of the MCU.

To usefully partition the dialing space, you might need to ensure that all registrations from a single MCU start with the same sequence of digits.

Using registration prefixes also can benefit large-scale dial plan changes. For example, you can change all MCU registrations to begin with "121" instead of "11" by changing a single MCU configuration field rather than individually amending every conference or auto attendant's associated numeric identifier.

If H.323 gatekeeper usage is disabled, this field will have no effect.

Note that if you are also intending to use the MCU service prefix (see below), Cisco recommends that you set both prefixes to the same number.

MCU service prefix

If required, specify a group of digits which the H.323 gatekeeper may use to identify calls to be routed to the MCU.

This field is optional. If set, users dialing any number beginning with this prefix will have their call directed to the MCU. This might be useful if you want to create conferences in response to unknown E.164 numbers.

Any numbers following the prefix will be identified by the MCU as a conference or auto attendant number. For example, if a conference has Numeric ID "3333" and you have set the service prefix to be "121", then a user dialing "1213333" will be connected to that conference.

This field will have no effect if H.323 gatekeeper usage is disabled.

Note that if you are also intending to use the Prefix for MCU registrations (see above), Cisco recommends that you set both prefixes to the same number.

If the MCU is unable to match a call to a conference or auto attendant, the action for Incoming calls to unknown E.164 number will be applied. This is a setting on the Settings > Conferences page (see Configuring global conference settings). This action can be set to Create new ad hoc conference.

Allow numeric ID registration for conferences

This setting controls whether conferences' configured numeric IDs are allowed to be registered with the gatekeeper.

This setting is the global control that allows or disallows conferences to be registered with the gatekeeper.

Individual conferences will be registered or not depending on the per-conference Numeric ID registration setting which is on the Add conference page for scheduled conferences and for ad hoc conferences it is in the ad hoc conference template.

This would normally be Enabled; by setting it to Disabled, an administrator can prevent users from adding to the set of IDs registered with the configured gatekeeper, even if those users enable the gatekeeper Numeric ID registration setting for conferences they control. This may be desired when working with certain types of H.323 gatekeeper whose behavior in some modes is to disconnect active calls when the set of registered IDs changes.

This setting affects both the registration of numeric IDs configured for scheduled conferences and the registration of ad hoc conferences.

This field will have no effect if H.323 Gatekeeper usage is set to Disabled.

Send resource availability indications

Select this option if you want the MCU to inform the gatekeeper about its availability or non-availability. This information will be used by the gatekeeper when it is selecting where to place ad hoc conferences.

Only use this option where multiple MCUs are registered with the same MCU service prefix on the same gatekeeper.

If you select this option, you must configure the thresholds for conferences and/or video ports.


  • Conferences: Enter any number of conferences between 0 and 200. (A value of 0 will mean that the MCU will always indicate 'unavailable'.)
  • Video ports: Enter a number between 0 and the number of video ports on your MCU; for example, on an MCU 4205, there are 12 video ports, so enter a number between 0 and 12. (A value of 0 will mean that the MCU will always indicate 'unavailable'.)

The ability of the MCU to send resource availability messages is useful in a network where there are multiple MCUs or where there are several media blades in an MSE.

In an environment with multiple conferencing devices registered with the same gatekeeper, that gatekeeper should favor devices in the available state when choosing where to place new calls.

For example, when one MCU sends the gatekeeper a message indicating that it is not available, the gatekeeper will then attempt to use a different MCU for new ad hoc conferences.

Resource availability indications are most useful where the thresholds are configured such that the MCU informs the gatekeeper that it is unavailable when its resources are nearly used up.

Conferences without any active participants do not contribute to the conference count; any video port in use is added to the video port count.

When either threshold is equaled or exceeded, the MCU sends a message to indicate that it is not available; when the resource usage drops such that neither threshold is equaled or exceeded, the MCU sends a message indicating that it is available.

You might choose to only configure one of the thresholds. You are probably aware of how your video conferencing resources tend to be used by participants and you need to consider this when configuring the thresholds. For example, you could have four people who have each started an ad hoc conference; you might know that it is usual for such conferences to end up having ten participants. In this case, on a 40-port MCU you could set the conference threshold to 4 to indicate that it will be out-of-resources very soon. On the same MCU if you set the video port threshold to 35 and left the conference threshold empty, another four or more people could begin ad hoc conferences on this MCU before the participants expected in the original four conferences had dialed in.

When switching between Standard and High Definition mode on your MCU 4501 or MSE Media2 blade, if the video ports availability value is higher than the number of video ports available, the MCU will change the value to reflect the number of video ports.

Gatekeeper status

The MCU also displays brief status information about its registrations with the configured gatekeeper.

To display a complete list of all IDs that the MCU is attempting to register with the configured H.323 gatekeeper, click the details link in the Number of active registrations row of the gatekeeper status table; this takes you to the Active registrations page.


Field Field description Usage tips
H.323 gatekeeper status

Displays the IP address of the gatekeeper currently being used by the MCU.

This information might be useful if the gatekeeper has been specified with a host name rather than with an IP address.

If the MCU has been unable to reach the configured gatekeeper and has instead registered with an alternate gatekeeper, the status displayed here will be "registered with alternate gatekeeper <IP address>".

Registered address

Displays the local IP address and port number that the MCU has registered with the gatekeeper.

This information might be useful if the MCU has more than one IP address, for instance if both Ethernet interfaces are in use.

Alternate gatekeepers available

Displays the number of 'alternate' gatekeepers configured on the H.323 gatekeeper. This figure comes from the gatekeeper itself; if there are any 'alternate' gatekeepers configured, the gatekeeper tells the MCU their IP addresses.

Where the configured gatekeeper has told the MCU about any configured 'alternate' gatekeepers and if the MCU loses contact with the configured gatekeeper, the MCU will attempt to register with each of the 'alternates' in turn. If none of the 'alternate' gatekeepers responds, the MCU will report that the registration has failed.

If the MCU successfully registers with an 'alternate' gatekeeper:

  • the H.323 gatekeeper status will indicate that registration is with an 'alternate'
  • the list of 'alternates' received from the new gatekeeper will replace the previous list
  • the MCU will only revert back to the original gatekeeper if the 'alternate' fails and only if the original gatekeeper is configured as an 'alternate' on the current gatekeeper's list of 'alternates'

Note that if the MCU registers with an 'alternate' that does not itself supply a list of 'alternates', the MCU will retain the original list and if it loses contact with the current gatekeeper, each one will be attempted from the top again as before.

Resource availability status

Displays whether the gatekeeper is configured to send resource availability indications and if it is, it displays the current state of the resource availability status of the MCU.

The possible statuses are:

  • resources available
  • resources unavailable
  • <indications not configured>
Number of active registrations

Displays the number of E.164 numbers plus H.323 IDs plus prefixes that the MCU has registered with the gatekeeper.

It also shows how many registrations are in progress but are not fully registered yet.

Full information on the gatekeeper registrations being made by the MCU can be seen by clicking on details; this takes you to the Active registrations page.

H.323 ID registration

Displays the identifier that the MCU has used to register itself with the H.323 gatekeeper.

For more information about the H.323 ID, refer to the table above.

MCU service prefix

Displays the identifier that the gatekeeper has registered for calls to be routed to the MCU.

For more information about this prefix, refer to the table above.

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