The VCS supports the H.323 protocol: it is an H.323 gatekeeper,
and will provide interworking between H.323 and SIP calls. In
order to support H.323, the

H.323 mode

must be enabled.

Call Time to Live

Once the endpoint is in a call, the VCS will periodically poll it to
confirm whether it is still in the call. If the endpoint does not
respond, the call will be disconnected.
The VCS allows you to configure the interval at which the
endpoints are polled, known as the

Call Time to Live

Configuring H.323 Ports

The VCS allows you to configure the listening port for H.323
registrations and call signaling, and the range of ports to be
used by H.323 calls once they are established.
The default VCS configuration uses standard port numbers so
you can use H.323 services out of the box without having to first
set these up.

Using the VCS as an H.323 Gatekeeper

As an H.323 gatekeeper, the VCS accepts registrations from
H.323 endpoints and provides call control functions such as
address translation and admission control.

H.323 Overview

Time to Live

H.323 endpoints must periodically re-register with the VCS in
order to confirm that they are still functioning. The VCS allows
you to configure the interval between these re-registrations,
known as the

Time to Live

Some older endpoints do not support the ability to
periodically re-register with the system. In this case, and
in any other situation where the system has not had a

confirmation from the endpoint within the specified period, it will
send an IRQ to the endpoint to verify that it is still functioning.

The system will poll endpoints in a call regardless of
whether the call type is traversal or non-traversal.

H.323 Endpoint Registration

Auto Discover

The VCS has an

Auto Discover

setting which determines whether

it will respond to the Gatekeeper Discovery Requests sent out by
endpoints.
To prevent H.323 endpoints being able to register automatically
with the VCS, set

Auto Discover

Off.

This will mean that

endpoints will be able to register with the VCS only if they have
been configured with the VCS’s IP address.

Overview

H.323 endpoints in your network must register with the VCS in
order to use it as their gatekeeper.
There are two ways an H.323 endpoint can locate a VCS
with which to register: manually or automatically. The option
is configured on the endpoint itself under the

Gatekeeper

Discovery

setting (consult your endpoint manual for how to

access this setting).

If the mode is set to automatic, the endpoint will try to

•

register with any VCS it can find. It does this by sending out
a Gatekeeper Discovery Request, to which eligible VCSs will
respond.
If the mode is set to manual, you must specify the IP address

•

of the VCS with which you wish your endpoint to register, and
the endpoint will attempt to register with that VCS only.

Registration Conflict Mode

An H.323 endpoint may attempt to register with the VCS using
an alias that has already been registered on the VCS from
another IP address. The reasons for this could include:

two endpoints at different IP addresses are attempting to

•

alias. The IP address allocated to the endpoint then changes,
and the endpoint is attempting to re-register using the same
alias.

You can determine how the VCS will behave in this situation by
configuring the

Registration Conflict Mode

. The options are:

Reject

•

: denies the new registration.

Overwrite

•

: deletes the original registration and replaces it

with the new registration.