Cisco TelePresence Administrator's Manual page 95

Registration control
one or more H.323 IDs
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one or more E.164 aliases
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one or more URIs
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Users of other registered endpoints can then call the endpoint by dialing any of these aliases.
You are recommended to register your H.323 endpoints using a URI. This facilitates interworking between
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SIP and H.323, as SIP endpoints register using a URI as standard.
You are recommended to not use aliases that reveal sensitive information. Due to the nature of H.323, call
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setup information is exchanged in an unencrypted form.
SIP
When registering, the SIP endpoint presents the VCS with its contact address (IP address) and logical
address (Address of Record). The logical address is considered to be its alias, and will generally be in the
form of a URI.
H.350 directory authentication and registrations
If the VCS is using an H.350 directory service to authenticate registration requests, the Source of aliases
for registration setting is used to determine which aliases the endpoint is allowed to attempt to register with.
See Using an H.350 directory service lookup via LDAP [p.120]
Attempts to register using an existing alias
An endpoint may attempt to register with the VCS using an alias that is already registered to the system.
How this is managed depends on how the VCS is configured and whether the endpoint is SIP or H.323.
H.323: an H.323 endpoint may attempt to register with the VCS using an alias that has already been
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registered on the VCS from another IP address. You can control how the VCS behaves in this situation by
configuring the Registration conflict mode, on the
SIP: a SIP endpoint will always be allowed to register using an alias that is already in use from another IP
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address. When a call is received for this alias, all endpoints registered using that alias will be called
simultaneously. This SIP feature is known as "forking".
Blocking registrations
If you have configured the VCS to use a
add all the aliases used by that endpoint to the Deny List.
Removing existing registrations
After a restriction policy has been activated, it controls all registration requests from that point forward.
However, any existing registrations may remain in place, even if the new list would otherwise block them.
Therefore, you are recommended to manually remove all existing unwanted registrations after you have
implemented a restriction policy.
To manually remove a registration, go to
want to remove, and click Unregister.
If the registered device is in an active call and its registration is removed (or expires), the effect on the call is
dependent on the protocol:
H.323: the call is taken down.
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SIP: the call stays up by default. This SIP behavior can be changed but only via the CLI by using the
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command xConfiguration SIP Registration Call Remove.
Cisco VCS Administrator Guide (X8.1.1)
for more information.
H.323 page
Deny List, you will have an option to block the registration. This will
Status > Registrations > By
(Configuration > Protocols >
device, select the registrations you
About registrations
H.323).
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