Before an endpoint can register with a VCS, it must determine which VCS it can or should be
registering with. This setting is configured on the endpoint, and the process is different for SIP and
H.323.

SIP

SIP endpoints must find a SIP Registrar with which to register. The SIP Registrar maintains a
record of the endpoint’s details against the endpoint’s Address of Record (AOR). When a call is
received for that AOR, the SIP Registrar refers to the record in order to find the endpoint to which
it corresponds. (Note that the same AOR can be used by more than one SIP endpoint at the same
time.)
The SIP Registrar will only accept registrations for domains for which it is authoritative.
There are two ways a SIP endpoint can locate a Registrar with which to register: manually or
automatically. The option is configured on the endpoint itself under the SIP

Server Discovery

option

(consult your endpoint user guide for how to access this setting).

If the

•

Server Discovery

mode is set to automatic, the endpoint will send a REGISTER message to

its SIP Server. This will be forwarded (via DNS if necessary) to the Registrar that is authoritative
for the domain with which the endpoint is attempting to register. For example, if an endpoint
is attempting to register with a URI of

[email protected]

, the request will be sent to the

Registrar authoritative for the domain

example.com

If the

•

Server Discovery

mode is set to manual, the user must specify the IP address or FQDN of

the Registrar with which they wish to register, and the endpoint will attempt to register with that
Registrar only.

The VCS is a SIP Server for endpoints in its local zone, and can also act as a SIP Registrar.

If the VCS is acting as the endpoint’s SIP Server and SIP Registrar, when the registration request

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is received from the endpoint it will be accepted by the VCS and the endpoint will be registered
and able to receive inbound calls. See

Using the VCS as a SIP Registrar

for more information.

If the VCS is acting as the endpoint’s SIP server but is not a SIP Registrar, it will proxy the

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registration request. See

Proxying registration requests

for more information.

H.323

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

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your endpoint to register, and the endpoint will attempt to register with that VCS only.

Auto discover
On

: The VCS will respond

to Gatekeeper discovery
requests.

Off

: The VCS will reject

Gatekeeper discovery
requests. H.323 endpoints
will be able to register
with the VCS only if their

Gatekeeper Discovery

setting

Manual

and they have

entered the IP address of the
VCS.

Preventing automatic registrations

You can prevent H.323 endpoints being able to register automatically with the VCS by disabling

Auto Discovery

on the VCS. The

Auto Discovery

setting determines whether the VCS responds to

the Gatekeeper Discovery requests sent out by endpoints.

To configure the Auto Discovery setting:

VCS Configuration > Protocols > H.323

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You will be taken to the

H.323

page.

H323 Gatekeeper AutoDiscover

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