Cisco Cisco Expressway Maintenance Manual
Configuring SIP and H.323 interworking
The
Interworking
page (
Configuration > Protocols > Interworking
) lets you configure whether or not the
Expressway acts as a gateway between SIP and H.323 calls. The translation of calls from one protocol to
the other is known as “interworking”.
the other is known as “interworking”.
The Expressway always takes the media for SIP–H.323 interworked calls so that it can independently
negotiate payload types on the SIP and H.323 sides and Expressway will re-write these as the media
passes.
negotiate payload types on the SIP and H.323 sides and Expressway will re-write these as the media
passes.
Also in a SIP SDP negotiation, multiple codec capabilities can be agreed (more than one video codec can be
accepted) and the SIP device is at liberty to change the codec it uses at any time within the call. If this
happens, because Expressway is in the media path it will close and open logical channels to the H.323
device as the media changes (as required) so that media is passed correctly.
accepted) and the SIP device is at liberty to change the codec it uses at any time within the call. If this
happens, because Expressway is in the media path it will close and open logical channels to the H.323
device as the media changes (as required) so that media is passed correctly.
Searching by protocol
When searching a zone, the Expressway first performs the search using the protocol of the incoming call. If
the search is unsuccessful the Expressway 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).
the search is unsuccessful the Expressway 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).
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.
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 Expressway will not be able to locate the alias 123@domain and
the call will fail. The solutions are to either:
being dialed is just registered as 123, the Expressway will not be able to locate the alias 123@domain and
the call will fail. The solutions are to either:
n
Ensure all your endpoints, both H.323 and SIP, register with an alias in the form name@domain.
n
Create a pre-search transform on the Expressway that strips the @domain portion of the alias for those
URIs that are in the form of number@domain.
See the
URIs that are in the form of number@domain.
See the
section for information about how to configure pre-search transforms, and
the stripping @domain for dialing to H.323 numbers section for an example of how to do this.
Cisco Expressway Administrator Guide (X8.5.2)
Page 107 of 403
Protocols
Configuring SIP and H.323 interworking