Configuring Sip And H.323 Interworking - Cisco TelePresence Administrator's Manual

Configuring SIP and H.323 interworking

The Interworking page (VCS configuration > Protocols >
the VCS acts as a gateway between SIP and H.323 calls. The translation of calls from one protocol to the
other is known as "interworking".
By default, the VCS acts as a SIP-H.323 and H.323-SIP gateway but only if at least one of the endpoints that
are involved in the call is locally registered. You can change this setting so that the VCS acts as a SIP-H.323
gateway regardless of whether the endpoints involved are locally registered. You also have the option to
disable interworking completely.
The options for the H.323 <-> SIP interworking mode are:
Off: the VCS does not act as a SIP-H.323 gateway.
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Registered only: the VCS acts as a SIP-H.323 gateway but only if at least one of the endpoints is locally
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registered.
On: the VCS acts as a SIP-H.323 gateway regardless of whether the endpoints are locally registered.
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You are recommended to leave this setting as Registered only (where calls are interworked only if at least
one of the endpoints is locally registered). Unless your network is correctly configured, setting it to On (where
all calls can be interworked) may result in unnecessary interworking, for example where a call between two
H.323 endpoints is made over SIP, or vice versa.
Calls for which the VCS acts as a SIP to H.323 gateway are
Searching by protocol
When searching a zone, the VCS first performs the search using the protocol of the incoming call. If the
search is unsuccessful the VCS may then search the zone again using the alternative protocol, depending on
where the search came from and the Interworking mode. Note that the zone must also be configured with
the relevant protocols enabled (SIP and H.323 are enabled on a zone by default).
If the request has come from a neighboring system and Interworking mode is set to Registered only, the
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VCS searches the Local Zone using both protocols, and all other zones using the native protocol only
(because it will interwork the call only if one of the endpoints is locally registered).
If Interworking mode is set to On, or the request has come from a locally registered endpoint, the VCS
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searches the Local Zone and all external zones using both protocols.
Enabling SIP endpoints to dial H.323 numbers
SIP endpoints can only make calls in the form of URIs — such as name@domain. If the caller does not
specify a domain when placing the call, the SIP endpoint automatically appends its own domain to the
number that is dialed.
So if you dial 123 from a SIP endpoint, the search will be placed for 123@domain. If the H.323 endpoint
being dialed is just registered as 123, the VCS will not be able to locate the alias 123@domain and the call
will fail. The solutions are to either:
Ensure all your endpoints, both H.323 and SIP, register with an alias in the form name@domain.
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Create a pre-search transform on the VCS that strips the @domain portion of the alias for those URIs that
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are in the form of number@domain.
See the pre-search transforms
the stripping @domain for dialing to H.323 numbers
Cisco VCS Administrator Guide (X7.2)
section for information about how to configure pre-search transforms, and
section for an example of how to do this.
Interworking) lets you configure whether or not
traversal calls.
Protocols
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