1、INTERNATIONAL TELECOMMUNICATION UNION#)44 1 THE INTERNATIONALTELEGRAPH AND TELEPHONECONSULTATIVE COMMITTEE34!%G0G0 G0G0$%3#2)04)/.G0G0 or the maximum number of B-channels per ISDN number are in use; the number of calls per ISDN number counter has not reached its maximum value; the number of waiting
2、calls per ISDN number counter has not reached its maximum value.When the network invokes Call Waiting and the counters defined in 1.3.4 are supported, the network shallincrement the number of calls per ISDN number counter and the number of waiting calls per ISDN number counter.If all three condition
3、s are not met, then the call shall be offered using normal call offering procedurescontained in 5.2 of Recommendation Q.931.1.5.2.1.3.2 Notification of Call WaitingAs a network option, an indication may be sent to the calling party that their call is a waiting call.Notification description, “call is
4、 a waiting call”, shall be sent in the notification indicator information elementin the ALERTING message.6 Recommendation Q.9531.5.2.1.3.3 Operation of Call WaitingWhen the network has determined that the CW supplementary service shall be applied for a particular waitingcall, the network shall send
5、to the called ISDN user a SETUP message with channel identification “no channel”.The call offering timers shall be the same for call waiting as for the call offering procedure inRecommendation Q.931.The called user has the choice of accepting, rejecting, or ignoring the waiting call, using the proce
6、durescontained in Recommendation Q.931. If the call is to be accepted, the channel negotiation procedures, which aredescribed below, are to be used. The network treatment given due to multiple ISDN users responding to the samewaiting call on the same interface shall be the same (except for the chann
7、el negotiation procedures) as the procedures inRecommendation Q.931.1.5.2.1.3.3.1 Called user accepts the waiting callIf the called user is to accept the waiting call, the non-rejecting messages that may be sent in response to aSETUP message are CALL PROCEEDING (see 1.4.1.2), ALERTING (see 1.4.1.1),
8、 or CONNECT (see 1.4.1.3).The procedures for the receipt of a CALL PROCEEDING and/or ALERTING message are as described inRecommendation Q.931 with the exception of the procedures associated with the channel identification informationelement.The channel negotiation procedures allow the user to design
9、ate a channel in the CONNECT message, ratherthan restricting channel designation to a given ISDN users first response to the SETUP message. A channel designationin either a CALL PROCEEDING or ALERTING message may be ignored by the network for the CW supplementaryservice operation. It is a network op
10、tion to act upon the contents of the channel identification information element.If the called user responding to the waiting call has a call on a channel, that user shall make a channel availableby using the call clearing procedures contained in 5.3 of Recommendation Q.931, before returning a CONNEC
11、Tmessage to attempt to answer the waiting call. It is also possible that another user that is not contending for the incomingcall and has a call on a channel, can make a channel available by using the call clearing procedures. The cleared channelis not reserved by the network for the waiting call. I
12、t is a network option to reserve the identified channel for theresponding user. When a call is cleared and the counters defined in 1.3.4 are supported, the number of calls per ISDNnumber counter shall be decremented for the ISDN number that cleared the call.The called user may also make a channel av
13、ailable by holding an existing call (see 1.6.15).The user can return a CONNECT message with any of the following channel designations:a) channel is indicated, no acceptable alternative;b) channel is indicated, any alternative is acceptable;c) any channel is acceptable; ord) no channel designation pr
14、esent in the CONNECT message.When the network receives a CONNECT message from the called ISDN user, the channel designation shall bechecked: If the designated channel is not available and is indicated as in case a), the network shall initiate callclearing to the responding user following the procedu
15、res in Recommendation Q.931, using CCITT causevalue No. 44, “requested circuit channel not available”. If the designated channel is available and is indicated as in case a), the network shall return a CONNECTACKNOWLEDGE message (Table 1-2/Q.953) with the channel designation, and follow procedurescon
16、tained in 5.2.8 (receipt of active indication) and 5.2.9 (to clear non-selected users) ofRecommendation Q.931. In some networks, the channel identification information element may not beincluded in the CONNECT ACKNOWLEDGE message.Recommendation Q.953 7 If the designated channel is available and is i
17、ndicated as in case b), the network shall return a CONNECTACKNOWLEDGE message (Table 1-2/Q.953) with the channel designation, and follow procedurescontained in 5.2.8 (Active indication) and 5.2.9 (non-selected user clearing) of RecommendationQ.931. If the designated channel is not available, is indi
18、cated as in case b), and another channel is available, thenetwork shall return a CONNECT ACKNOWLEDGE message with the channel designation, and followprocedures contained in 5.2.8 and 5.2.9 of Recommendation Q.931. If a channel is available and is indicated as in case c) or d), the network shall retu
19、rn a CONNECTACKNOWLEDGE message with the channel designation, and follow procedures contained in 5.2.8and 5.2.9 of Recommendation Q.931.In some networks, if the channel is indicated as in case d) and the network had received the channeldesignation, “channel is indicated, no acceptable alternative”,
20、in the first response to the SETUP message(e.g., the ALERTING message), the Channel identification information element may not be included inthe CONNECT ACKNOWLEDGE message. If no channel is available, the network shall initiate call clearing to the responding user following theprocedures in Recomme
21、ndation Q.931 using CCITT cause value No. 34, “No circuit/channel available”.After the network has sent a CONNECT ACKNOWLEDGE message, the number of waiting calls countershall be decremented if the counters defined in 1.3.4 are supported.The user shall not connect to any B-channel until receiving a
22、CONNECT ACKNOWLEDGE message. Theuser shall connect to the B-channel specified in the CONNECT ACKNOWLEDGE message.1.5.2.1.3.3.2 Called user rejects waiting callIf the called user rejects the waiting call, the procedures contained in 5.2.5.3 of Recommendation Q.931 shallbe followed.When the waiting ca
23、ll is cleared and the counters defined in 1.3.4 are supported, the number of calls counterand number of waiting calls counter shall be decremented.1.5.2.1.3.3.3 Called user ignores waiting callIf the called user ignores the waiting call, the procedures contained in 5.2.5.4 of Recommendation Q.931sha
24、ll be followed.When the waiting call is cleared and the counters defined in 1.3.4 are supported, the number of calls counterand number of waiting calls counter shall be decremented.1.5.2.2 Exceptional proceduresIf any error conditions exist that are not contained in 1.5.2.1.3.3, the appropriate proc
25、edures inRecommendation Q.931 shall be followed. If the waiting call is cleared and the counters defined in 1.3.4 aresupported, the number of calls counter and number of waiting calls counter shall be decremented.1.6 Interactions with other supplementary services1.6.1 Call WaitingNot relevant.1.6.2
26、Call TransferNo applicable interaction at this time.1.6.3 Connected Line Identification PresentationNo interaction.8 Recommendation Q.9531.6.4 Connected Line Identification RestrictionNo interaction.1.6.5 Calling Line Identification PresentationIf the CLIP procedures allow the calling number to be p
27、resented, the calling number shall be sent in theSETUP message containing the call waiting indication.1.6.6 Calling Line Identification RestrictionNo interaction.1.6.7 Closed User GroupNo interaction.1.6.8 Conference CallingNo applicable interaction at this time.1.6.9 Direct-dialling-InNo interactio
28、n.1.6.10 Call Diversion Services1.6.10.1 Call Forwarding BusyNo applicable interaction at this time.1.6.10.2 Call Forwarding No ReplyNo applicable interaction at this time.1.6.10.3 Call Forwarding UnconditionalNo applicable interaction at this time.1.6.11 Line HuntingNo applicable interaction at thi
29、s time.1.6.12 Three-Party ServiceNo applicable interaction at this time.1.6.13 User-to-User Signalling1.6.13.1 Service 1User-user information is delivered in the SETUP message which contains the call waiting indication accordingto the procedures contained in User-to-User service 1.1.6.13.2 Service 2
30、No interaction.1.6.13.3 Service 3No interaction.1.6.14 Multiple Subscriber NumberNo interaction.Recommendation Q.953 91.6.15 Call HoldWhen a call is offered to an ISDN number using Call Waiting and the user has also subscribed to Call Hold,the called party may use the Call Hold supplementary service
31、 in conjunction with the CW supplementary service.Instead of having to clear a call on a channel, the user could make a channel available for a waiting call byapplying the Call Hold service to an established circuit-mode call. A channel may be reserved for the terminal thatinvoked the Call Hold serv
32、ice.After a channel has been made available, the called user shall then be able to send a CONNECT message (withor without sending a CALL PROCEEDING message and/or an ALERTING message) to answer the waiting call asdescribed in 1.5.2.1.3.3.All procedures of the Call Hold service can be used.1.6.16 Adv
33、ice of ChargeNo applicable interaction at this time.1.6.17 Sub-addressingNo interaction.1.6.18 Terminal PortabilityNo interaction.1.6.19 Call Completion to Busy SubscriberNo applicable interaction at this time.1.6.20 Malicious Call IdentificationNo applicable interaction at this time.1.7 Interaction
34、s with other networks1.7.1 Procedures for interworking with private ISDNs1.7.1.1 Served user is on a private ISDNWhen the CW supplementary service operation occurs within a private network, the notification description,“call is a waiting call”, shall be returned in the notification indicator informa
35、tion element in the ALERTING message,when available.1.7.1.2 Calling user is on a private ISDNWhen available, the notification description, “call is a waiting call” shall be sent in the notification indicatorinformation element in the ALERTING message to the calling user.1.8 Signalling flowsExample s
36、ignalling flows are included to illustrate a subset of the CW supplementary service operation. Thesefigures assume that the terminals are compatible with the incoming call as defined in Recommendation Q.931.1.9 Parameter values (timers)No states beyond those defined in Recommendation Q.931 are neede
37、d for the CW supplementary serviceoperation.No timers beyond those defined in Recommendation Q.931 are needed for the CW supplementary serviceoperation.10 Recommendation Q.9531.10 Dynamic description (SDLs)1.10.1 UserSame as in Recommendation Q.931.1.10.2 NetworkSame as in Recommendation Q.931.T1124
38、350-90Callingparty NetworkTEI 1(B1, CR1)TEI 2(B2, CR2) TEI3SETUPALERTCW notification(Note)CONNSETUP(CR3, No channel)ALERT (CR3)ALERT (CR3)ALERT (CR3)DISC (CR1)REL (CR1)REL COM (CR1)CONN (CR3)REL (CR3)REL (CR3)CRTEICall referenceTerminal endpoint identifierNote Notification of call waiting is a netwo
39、rk option.FIGURE 1-2/Q.953Call Waiting Call acceptance by clearing an existing callCONN ACK (CR3, B1)Recommendation Q.953 11T1124360-90Callingparty NetworkTEI 1(B1, CR1)TEI 2(B2, CR2) TEI3SETUPALERTCW notification(Note)CONNALERT (CR3)ALERT (CR3)ALERT (CR3)HOLD (CR1)HOLD ACK (CR1)CONN (CR3)REL (CR3)REL (CR3)CRTEICall referenceTerminal endpoint identifierNote Notification of call waiting is a network option.FIGURE 1-3/Q.953Call Waiting Call acceptance by placing an existing call on holdCONN ACK (CR3, B1)SETUP (CR3, No channel)
