No subject

Gary A. Thom gary.thom at
Wed Sep 12 10:36:21 EDT 2001

The current version of H.450.6 is such that in a GK-routed
environment, it becomes impossible for a GK to remain in
control of the Call Waiting service and still be able to
notify the served endpoint about the fact that there are
calls waiting.

The reason for this is that the Recommendation only
specifies a means for the served endpoint to notify the
calling users/endpoints about the fact that there call
"is waiting". The served endpoint uses incoming call setups
to implement the service.

As a result, a GK has no choice but to propagate call
setups to the served endpoint to let it know about incoming
calls. This means that both the GK and the served endpoint
implement Call Waiting, there will most likely be some
unwanted service interaction.

For this purpose I propose to make the following
modifications to H.450.6:

- 7.3 is split up into two parts (7.3.1 and 7.3.2).
- The text that is now in 7.3 goes into 7.3.1.
- The new section (7.3.2) will contain the following text:

--start of new text ---

"7.3.2 Call waiting notification to served user

A GK/Proxy may implement the Call Waiting service. In this
case, the GK/Proxy may send a cwNotification Invoke APDU
to the served endpoint. The GK/Proxy shall send the
cwNotification Invoke APDU in either a FACILITY message of
an existing call or in a SETUP message for a new call-
independent signalling connection. If a new call-independent
signalling connection is initiated, it shall be established
in accordance with the procedures specified in 6.2/H.450.1."

--end of text---

The ASN.1 to be added is the following:

---Start of ASN.1-----

cwNotification OPERATION ::=
{ -- Sent from GK to served endpoint

    ARGUMENT         cwNotificationArg
    CODE             local:xxx

cwNotificationArg ::= SEQUENCE
    nbOfCalls       NbOfCalls OPTIONAL,
    waitingCalls    SEQUENCE SIZE (0..65535) OF WaitingCall,
    extensionArg    SEQUENCE SIZE (0..255) OF MixedExtension OPTIONAL

WaitingCall ::= SEQUENCE
    waitingNumber     EndpointAddress OPTIONAL, -- if not present, waitingPosition must be present
    callId            CallIdentifier  OPTIONAL, -- to be used if waitingNumber is not present

NbOfCalls ::= INTEGER (0..65535)

---End of ASN.1---

Some carifications for the above ASN.1:

- Since the operation defines a notification, no (return)
  result is required.

- Because the GK/Proxy may have more than one calls waiting,
  a "nbOfParties" field is added. This field, when present,
  will contain the number of parties that the GK/Proxy has
  currently waiting for the served endpoint.

- Since it may be possible that presentation restrictions
  or screening apply to a call, it is possible to only
  convey the callId and not the calling party's "number"
  to the served endpoint.

- The "waitingParties" element contains a list of parties
  that are currently waiting. The number of calls that can
  be waiting is set at the same number as the maximum
  number of calls that can be parked according to the
  H.450.5 Recommendation.



Frank Derks                    |Tel  +31 35 6893238 |
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