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chan-capi/README.Diva.qsig

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+===================================================================+
| QSIG Abstraction |
+===================================================================+

+-------------------------------------------------------------------+
| QSIG supplementary services |
+-------------------------------------------------------------------+

The QSIG network differentiates between four different types of call transfers,
two unassisted and two assisted.
The type of invoked unassisted call transfer depends on the call state.
The type of assisted call transfers depends on the type of the switching
equipment Dialogic(R) Diva(R) interfaces as well.
The coding of the messages and the type of the transfer invoked, depends
on the QSIG dialect and on the vendor-specific implementation of QSIG dialect.

+-------------------------------------------------------------------+
| Use Diva QSIG abstraction with chan_capi |
+-------------------------------------------------------------------+

To use Diva QSIG abstraction please add 'divaqsig=1' to configuration
of CAPI controller (capi.conf).

+-------------------------------------------------------------------+
| QSIG abstraction |
+-------------------------------------------------------------------+

Dialogic(R) Diva(R) System Release Software abstraction allows to write
QSIG applications independent of the used QSIG dialect.

Name and Display information elements
Name (Calling Pary Name, Called Party Name, Connected Party Name,
Busy Party Name) and Display information elementss are converted to protocol
independent format and delivered to (received from) application using
Diva manufacturer extensions. Information elements encoded as facility array
(for example in CONNECT_REQ) are converted in accordance with rules of active
QSIG protocol.

Unassisted call transfer:
The application can use CAPI call deflection. The Diva System Release software
will automatically translate the call deflection request in the appropriate
QSIG primitives. The translation depends on the Diva System Release software
configuration and on the call state.
You can invoke this feature in any call state, but the request may fail in
case the used switching equipment does not support the required service.

Assisted call transfer:
The application can use CAPI Explicit Call Transfer (ECT). The Diva System Release
software will automatically translate ECT in the appropriate QSIG primitive.
The translation depends on the Diva System Release configuration.

+-------------------------------------------------------------------+
| Conclusion |
+-------------------------------------------------------------------+
If reviewed in short form, you can use any ETSI application with QSIG and without
the need to change any code to access QSIG call transfers. There is no need to deal
with details of the underlying network.
The same is true not only for QSIG but for all supported signaling protocols.
The same interface can be used to access basic and supplementary services for
ETSI, QSIG, SS7 ISUP, 5ESS, R2, RBS/CAS, ...

+-------------------------------------------------------------------+
| QSIG path replacement |
+-------------------------------------------------------------------+

There are three parties involved in the path replacement procedure;
The party that initiated the call (party A), the party that initially received and
transferred the call (party B) and the party that finally received the
call after the call transfer (party C).

The goal of the call replacement procedure is to free switching equipment resources
by the replacement of the chain A->B->C with chain A->C.
To achieve this, party B will short cut the D-channel link between A and C and
let A and C exchange D-channel messages. In most cases, party B will short
cut the B-channel between A and C as well and preserve this connection until the path
replacement is complete. If the path replacement will not proceed (not supported, ...),
party B will preserve the D-channel and B-channel interconnections for the entire
duration of the call.

After party B completes the call transfer procedure, one transfer complete message
will be sent (Diva System Release softwre configuration option) and will invoke the path
replacement procedure (Diva System Release configuration option). As part of this procedure,
party A will prepare an alternative resource and send information about this resource over
the D-channel to C through B.
After the information about the alternative resource is received, C will establish a new call
directly from C to A and replace A->B->C by C->A (A->B->C still running in parallel).
After the new connection is established, A and C will establish a new B-channel connection
and will exchange D-channel messages over B and release connections A->B and B->C.
After the release is complete, C->A is preserved during the duration of the call.

The Diva System Release software supports all three parties A, B, and C in the above mentioned
path replacement procedure.

+-------------------------------------------------------------------+
| Support at party A and C endpoints |
+-------------------------------------------------------------------+

The support at A and C endpoints is transparent to the applications.
The Diva System Release software will replace one connection with another in
a fully transparent way to the application.
The data streaming between the application and the bearer resource will not be interrupted
during this operation. Only one notification about the change of the B-channel and
about the completion of the path replacement procedure is provided to the application but
does not require any action from the application (in certain environments
applications will use this notification to issue RESET_B3 REQ and restart the voice
message if any. PBX applications do not need to perform any action).

Please note that party C responds to the call replacement procedure only if the change of the
connection is supported by the underlying protocol. This change is not possible if the fax or
modem session is already in progress. In this case, C will ignore the path replacement and
the chain A->B->C will be preserved for the entire duration of the call.
The same is true if the path replacement procedure fails for any reason.

The M-Board is required to provide the path replacement operation at A and B and it is
responsible for moving the call between different connections transparently for application.
The path replacement can be performed only between Dialogic(R) Diva(R) interfaces
that belong to the same M-Board.

+-------------------------------------------------------------------+
| Support at the party B endpoint |
+-------------------------------------------------------------------+

Party B is the party that uses ECT to perform the assisted QSIG call transfer.
The type of call transfer and the messages sent after the call transfer is completed
are specified by the Diva System Release software configuration. The software detects if
compatible QSIG dialects are used for both parties of ECT and will automatically
establish the D-channel bridge.
The application is responsible to establish the B-channel bridge. The best practice is to
establish the B-channel bridge (using CAPI line interconnect command) before issuing
the CAPI ECT command. The Dialogic(R) Diva(R) CAPI will atomatically maintain the D-channel bridge.

If the M-Board is used at the party B endpoint, it is possible to activate "ECT Emulation".
If active, the M-Board will automatically establish and maintain the B-channel and D-channel bridge
once the ECT command is sent by the application. In this case, there is no need to maintain the B-channel
bridge by the application. The M-Board will maintain all necessary resources until the path
replacement procedure is completed or for the entire duration of the call.
This option is available only for calls that belong to the same M-Board.

+-------------------------------------------------------------------+
| Call state of involved in the ECT calls |
+-------------------------------------------------------------------+

In case of QSIG, it is not necessary to put one of the calls, involved in the ECT, on hold.
Moreover, it is possible to invoke the ECT if the consultation call is in alerted state
(if supported by the switching equipment).
To achieve this, independent from the state of the primary and of the consultation call operation
of the ECT, it is necessary to set the CAPIECTPLCI variable to PLCI (getplci commang provides it in
CAPIPLCI variable) of the primary call before invoking the ECT.

Example: The application accepts one call, creates the consultation call and once the alert is
received, the consultation call starts the playback of message on the first call. After an
additional command is received, the application proceeds with ECT, independent from the state
of the consultation call.
It is even possible to play the message to the first call until the path replacement is completed
and parties A and C are connected directly.

ECT Example:
/////////////////////////////////////////////////////////////////////
[macro-capiect]
; Activate suppressor of ambient noise for consultation call
exten => s,1,capicommand(noisesuppressor,yes)
; Invoke ECT command
exten => s,n,capicommand(ect)

[isdn-in]
; Send progress message on incoming call
exten => 12345,1,Progress()
exten => 12345,n,Set(TIMEOUT(digit)=1) ; Set Digit Timeout to 5 seconds
exten => 12345,n,Set(TIMEOUT(response)=5) ; Set Response Timeout to 10 seconds
; Play message to incoming call using early media mode
exten => 12345,n,Playback(demo-enterkeywords,noanswer,us)
; Accept incoming call
exten => 12345,n,Answer
; Activate suppressor of ambient noises for incoming call
exten => 12345,n,capicommand(noisesuppressor,yes)
; Save PLCI of incoming call to CAPIPLCI variable
exten => 12345,n,capicommand(getplci)
; Set CAPIECTPLCI variable to PLCI of incoming call
; and allow to export this variable to consultation call
exten => 12345,n,Set(_CAPIECTPLCI=${CAPIPLCI})
; Create consultation call and invoke ECT
; ECT procedure will detect CAPIECTPLCI is set and use saved in this variable value
; to identify the ECT party and invoke ECT independent from the state of the primary call
exten => 12345,n,Dial(CAPI/ISDN1/100,10,M(capiect))
exten => 12345,n,Hangup()
/////////////////////////////////////////////////////////////////////