here's an excerpt from ALEX :
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2.9 Network services
It is possible to execute network services both in pure H.323 private networks and in mixed H.323/ISDN private networks (scenarios with H.323/ISDN gateway nodes).
The procedure to request services is based both on ASB 501 04 Specific Protocol in UUI message and Information field, and on GFP (ISO QSIG). The aim of this twofold way of requesting some services is to assure interworking with existing ISDN tie lines: UUI assures interworking with previous ASB 501 04 releases, whilst GFP assures interworking with PABXes in the mixed H.323/ISDN scenarios mentioned above.
In case of a pure H.323 scenario, network services are only possible between ASB 501 04 systems and between ASB 501 04 and BusinessPhone systems.
The service information is included in H.225.0 messages by embedding Q.931 messages.
The same signalling procedures as in ISDN trunks are kept in H.323 trunks. Q.931 messages are embedded inside H.225.0 messages of the same message type, when possible.
The way some of the services (e.g., call diversion) are executed (in a proprietary way based either on UUI or on ISO QSIG) can be set in the destination configuration or, in some cases, can be chosen by means of the Application System Parameter PARNUM=223.
The following services make use of embedded UUI signalling:
Account code
Authorization code
Call Back
Call Deflection
Call Diversion
Call Extending
Call Offer
Called Party Number
Calling/Connected Line Identity
Calling/Connected Line Identity Restriction
Calling/Connected Name Identity
Customer Identity
Day/Night Service Notification
DNIS for ACD
FRL/TCM
Intrusion
Message Waiting Notification
Night Service Diversion
Priority Routing
Repeated Deflection
Rerouting
Transfer
Type of Party
Voice Mail facility
And these services are executed based on ISO QSIG standards:
Advice of Charge
Call Completion
Call Forwarding
Call Offer
Call Transfer
Calling/Connected Line Identity Restriction (only public number)
Calling/Connected Name Identity (without presentation rules)
Path replacement
Type of Party (through ISO common information)
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