1 Call waiting (CW)

03.833GPPCall Waiting (CW) and Call Hold (HOLD) supplementary servicesStage 2TS

1.1 Handling of call waiting

1.1.1 Activation

The call waiting supplementary service is activated at the request of the user. The activation request indicates the basic services to which the activation request refers.

The information flow for activation of call waiting is shown in figure 1.1.

MS MSC VLR HLR 
+—+ +—+ +—+ +—+
| | Activate CW | | | | | |
| +—————>| | | | | |
| | | | Activate CW | | | |
| | | +————->| | | |
| | | | | | Activate CW | |
| | | | | +————->| |
| | | | | | | |
| | | | | | Acknowledge | |
| | | | | |<————-| |
| | | | Acknowledge | | | |
| | | |<————-| | | |
| |Release Complete| | | | | |
| |<—————| | | | | |
| | /Facility | | | | | |
| | | | | | | |
| | | | | | | |

Figure 1.1: Activation of call waiting

1.1.2 Deactivation

The call waiting supplementary service is deactivated at the request of the user. The deactivation request indicates the basic services to which the deactivation request refers.

The information flow for deactivation of call waiting is shown in figure 1.2.

MS MSC VLR HLR 
+—+ +—+ +—+ +—+
| |Deactivate CW | | | | | |
| +—————>| | | | | |
| | | |Deactivate CW | | | |
| | | +————->| | | |
| | | | | |Deactivate CW | |
| | | | | +————->| |
| | | | | | | |
| | | | | | Acknowledge | |
| | | | | |<————-| |
| | | | Acknowledge | | | |
| | | |<————-| | | |
| |Release Complete| | | | | |
| |<—————| | | | | |
| | /Facility | | | | | |
| | | | | | | |
| | | | | | | |

Figure 1.2: Deactivation of call waiting

1.1.3 Interrogation

Status check

The status check procedure enables the mobile subscriber to obtain information about the status of the call waiting supplementary service with respect to subscribed basic service groups.

The interrogation of call waiting is for all applicable basic services.

The information flow for interrogation of call waiting is shown in figure 1.3.

MS MSC VLR HLR 
+—+ +—+ +—+ +—+
| |Interrogate CW | | | | | |
| +—————>| | | | | |
| | | |Interrogate CW| | | |
| | | +————->| | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | Acknowledge | | | |
| | | |<————-| | | |
| |Release Complete| | | | | |
| |<—————| | | | | |
| | /Facility | | | | | |
| | | | | | | |
| | | | | | | |

Figure 1.3: Interrogation of call waiting

1.2 Functions and information flows

GSM 04.08 specifies the procedures for call control. These shall also be used for waiting calls when applicable.

The following Mobile Additional Function has been identified for the call waiting service:

MAF013

Call waiting related authorizations examination

The ability of a PLMN component to determine the authorizations relating to call waiting. See figure 1.4.

Location: VLR

Definitions:

Subscriber B:

The subscriber who is provided by the network with the call waiting supplementary service. The subscriber B is always a mobile subscriber.

User B:

The user who reacts to call waiting at subscriber B. The user B is always a mobile user.

User C:

The user who has originated a call to subscriber B which causes the call waiting supplementary service to be invoked. The user C may be a mobile user.

User A:

The user who is engaged in a call with user B. The user A may be a mobile user.

Timer T1:

This timer corresponds to T303 + T310 (as defined in GSM 04.08).

Timer T2:

Call Waiting Timer. This shall limit the duration of the call in the waiting condition.

Timer T3:

No Reply Condition Timer (see GSM 02.82).

CFNRc:

Call Forwarding on Not Reachable (see GSM 02.82).

CFNRy:

Call Forwarding on No Reply (see GSM 02.82).

CW:

Call Waiting.

The overall SDL diagram of call waiting is shown in figure 1.5. This represents the network as a whole.

The information flows are shown in figure 1.6. In these flows it is assumed that user A and user C are fixed users and that user B is a mobile user. Functions to be performed by the fixed ISDN are not shown in the information flows. Only the functions to be performed by the PLMN are shown.

1.2.1 Description of overall SDL-diagram of call waiting

In the SDL-diagrams the states are dimensioned in two dimensions. The first dimension is a normal basic call state, e.g. null or active. The second dimension is an auxiliary state associated with hold, e.g. idle or held. Active call is represented by (active, idle) state, held call by (active, held) state.

When call waiting is active and the subscriber is connected to at least one call (active or held), the arrival of a subsequent incoming call from user C to user B shall, if no other call is waiting, be signalled to the mobile equipment at B as described in GSM 04.08. The network shall then await an acknowledgement from the mobile termination at user B within a specific time period T1. In figure 1.5, the mobile terminated call from user C is described as being in the "Pending Ack" state during this period. The call waiting service is suspended for further incoming calls.

1.2.1.1 Behaviour during the "Pending Ack" state

Expiry of call control timers in T1

If no acknowledgement is received by the network from the mobile termination at user B within the time period T1 (timer T1 expires) then the network shall initiate clearing towards the calling user C and served user B in accordance with GSM 04.08. Following the expiry of call control timers in T1 the call waiting service shall be resumed for further incoming calls.

Release of active call

User A or B may release the active call between them in the normal manner. This does not change the state of the call from user C. Note that the MS has to indicate a normal ringing tone to the served subscriber.

Release of call by user C

User C may release the call to user B. In this case, call clearing shall take place in the normal manner, and the call waiting service shall be resumed for further incoming calls.

Call hold service

User B can operate the call hold service on any active calls in the normal manner.

Indication of UDUB

User B may release the call from user C using the indication of UDUB. In this case, if CFB is active the call from user C shall be forwarded, if CFB is not active the call from user C shall be cleared. The call waiting service is resumed for further incoming calls.

Rejection of call from user C

User B may reject the call from user C. In this case, the call from user C shall be cleared. The call waiting service is resumed for further incoming calls.

Acknowledgement of call from user C

If the mobile termination at user B acknowledges the incoming call within the time period T1, a call is waiting indication shall be sent towards calling user C. Timer T1 is stopped. Upon reception of alerting the network shall await an acceptance from the controlling user B within the time period T2. In figure 1.5, the mobile terminated call is described as being in the "Waiting" state during this period. In case the controlling subscriber B has call forwarding on no reply active the network shall await an acceptance from user B within the time period T3 < T2. The call waiting service is still suspended for further incoming calls.

1.2.1.2 Behaviour during the "Waiting" State

Expiry of Timer T3

If no acceptance is received by the network within the time period T3 (timer T3 expires) the waiting call shall be forwarded on no reply and clearing shall be initiated towards the controlling user B. The call waiting service is resumed for further incoming calls.

Expiry of Timer T2

If call forwarding on no reply is not active and no acceptance is received within the time period T2 (timer T2 expires), the waiting call shall be cleared by the network towards the controlling user B and the calling user C. The call waiting service is resumed for further incoming calls.

Other Events

The following events are treated as described in subclause 1.2.1.1:

– release of active call;

– release of call by user C;

– call hold service;

– indication of UDUB;

– rejection of call from user C.

Acceptance of waiting call

A precondition for the acceptance of the waiting call is that there is no other call in the (active, idle) state. The user can achieve this by releasing active calls, or using the call hold service. When user B accepts the call from user C it becomes the (active, idle) call. Timer T2 or T3 is stopped. The call waiting service is resumed for further incoming calls.

Figure 1.4: MAF013 Call waiting related authorisations examination (VLR)

Figure 1.5 (sheet 1 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 2 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 3 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 4 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 5 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 6 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 7 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 8 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 9 of 10): Overall SDL diagram of call waiting

Figure 1.5 (sheet 10 of 10): Overall SDL diagram of call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CHANNEL NOT AVAILABLE | | | | | | | | | |
| | | | | | | | | | | | | |
|subscriber C wants to set up connection C-B | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | set-up | | | | | | | |
| | | | | |———>| |interrogation | | | | | |
| | | | | | | |————-> | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | acknowledge | | | | | |
| | | | | | | |<————- | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | set-up | | | | | |
| | | | | | | |—————————┼——┼———>| | | |
| | | | | | | | | | | | | |
| | | | | | | | | | info req | | | |
| | | | | | | | | |<———| | | |
| | | | | | | | |MAF013| | | | |
| | | | | | | | | | info ack | | | |
| | | | | | | | | |———>| | set-up | |
| | | | | | | | | | |start |———>| |
| | | | | | | | | | |timer | | |
| | | | | | | | | | | T1 | | |
| | | | | | | | | | | | | |
|WAITING ACKNOWLEDGMENT | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|WAITING ACKNOWLEDGMENT | | | | | | | | | |
| | | | | | | | | | | | | |
|B being informed | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | |stop |call-conf | |
| | | | | | | | | | |timer |<———| |
| | | | | | | | | | | T1 | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | alert | |
| | | | | | | | notify C | | |start |<———| |
| | | | | | | |<————————–┼——┼———-|timer | | |
| | | | | | | | (call waiting C-B) | | | T2 or| | |
| | | | | | | | | | | T3 | | |
| | | | | | notify C | | | | | | | |
| | | | | |<———| | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD or | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|WAITING ACKNOWLEDGMENT | | | | | | | | | |
| | | | | | | | | | | | | |
|timer T1 expires | | | | | | | | | |
| | | | | | | | | | | T1 | | |
| | | | | | | | disconnect demand | | |expires | |
| | | | | | | |<————————–┼——┼———-| | | |
| | | | | | | | (no user responding)| | | | | |
| | | | | | | | | | | | | |
| | | | | |disconnect| | | | | | | |
| | | | | | demand | | | | | | | |
| | | | | |<———| | | | | | | |
| | | | | |no user | | | | | | | |
| | | | | |responding| | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CHANNEL NOT AVAILABLE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 1: info req: information request info ack: information acknowledge

Figure 1.6 (sheet 1 of 7): Information flow for call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD or | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|timer T2 expires | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | T2 | demand | |
| | | | | |disconnect| | disconnect demand | | expires| (C-B) | |
| | | | | | demand | |<————————–┼——┼———-| |———>| |
| | | | | |<———| | (user alerting, no answer)| | | |(recovery | |
| | | | | |user alerting, | | | |after timer |
| | | | | |no answer | | | | | | expiry)| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CHANNEL NOT AVAILABLE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B WAITING | | | | | | | | | |
| | | | | | | | | | | | | |
|timer T2 expires | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | T2 | demand | |
| | | | | | | | disconnect demand | | expires| (C-B) | |
| | | | | | | |<————————–┼——┼———-| +———>| |
| | | | | | | | (user alerting, no answer)| | | |(recovery | |
| | | | | |disconnect| | | | | |after time| |
| | | | | | demand | | | | | | expiry)| |
| | | | | |<———| | | | | | | |
| | | | | |user alerting, | | | | | |
| | | | | |no answer | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|IDLE | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD or | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|B rejects incoming call from C | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | | reject | |
| | | | | | | | | | | |<———| |
| | | | | | | | disconnect demand | | | |(user busy) |
| | | | | |disconnect| |<————————–┼——┼———-| stop | | |
| | | | | | demand | | (user busy) | | | T2 or| | |
| | | | | |<———| | | | | T3 | | |
| | | | | |(user busy) | | | (note 2) | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CHANNEL NOT AVAILABLE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 2: The call shall be forwarded on mobile subscriber busy at this stage if activated.

Figure 1.6 (sheet 2 of 7): Information flow for call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD or | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|C releases waiting call | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | |disconnect| | | | | | | |
| | | | | | demand | | | | | | | |
| | | | | |———>| | disconnect demand | | | | | |
| | | | | | | |—————————┼——┼———>| stop |disconnect| |
| | | | | | | | | | | T2 or| demand | |
| | | | | | | | | | | T3 |———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | | ack | |
| | | | | | | | | | | |<———| |
| | | | | | | | disconnect acknowledge | | | | | |
| | | | | |disconnect| |<————————–┼——┼———-| | | |
| | | | | | ack | | | | | | | |
| | | | | |<———| | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CHANNEL NOT AVAILABLE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B WAITING | | | | | | | | | |
| | | | | | | | | | | | | |
|B rejects incoming call from C | | | | | |connection| |
| | | | | | | | | | | | reject| |
| | | | | | | | | | | |<———| |
| | | | | | | | | | | |(user busy) |
| | | | | | | | disconnect demand | | | stop | | |
| | | | | | | |<————————–┼——┼———-| T2 or| | |
| | | | | |disconnect| | (user busy) | | | T3 | | |
| | | | | | demand | | | | (note 3) | |
| | | | | |<———| | | | | | | |
| | | | | |(user busy) | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|IDLE | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B WAITING | | | | | | | | | |
| | | | | | | | | | | | | |
|C releases waiting call | | | | | | | | | |
| | | | | |disconnect| | | | | | | |
| | | | | | demand | | | | | | | |
| | | | | |———>| | disconnect demand | | | stop | | |
| | | | | | | |—————————┼——┼———>| T2 or|disconnect| |
| | | | | | | | | | | T3 | demand | |
| | | | | | | | | | | |———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | | ack | |
| | | | | | | | | | | |<———| |
| | | | | | | | disconnect acknowledge | | | | | |
| | | | | | | |<————————–┼——┼———-| | | |
| | | | | |disconnect| | | | | | | |
| | | | | | ack | | | | | | | |
| | | | | |<———| | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|IDLE | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 3: The call shall be forwarded on mobile subscriber busy at this stage if activated.

Figure 1.6 (sheet 3 of 7): Information flow for call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|subscriber B wants to hold active call and connect the waiting call | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | hold A-B | |
| | | | | | | notify A (call A-B held by B) | | |<———| |
| | | |<———┼-┼———-┼—————————–┼——┼———-| | | |
| | notify A | | | | | | | | | | connect | |
| |<———| | | | | | | | | | waiting | |
| | call A-B | | | | | | | | | | call | |
| | held by B| | | | | | connection demand | | | stop |<———| |
| | | | | | | |<————————–┼——┼———-| T2 or| | |
| | | | | |connection| | | | | T3 |connection| |
| | | | | | demand | | | | | | ack (C-B)| |
| | | | | |<———| | | | | +———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B ACTIVE | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|subscriber B wants to terminate active or held call and connect waiting call | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | | demand | |
| | | | | | | | | | | | (A-B) | |
| | | | | | | | disconnect demand (A-B) | | | |<———| |
| | | |<———┼-┼———-┼-┼—————————┼——┼———-| | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | |ack (A-B) | |
| | | | | +———>| |
| | CONTINUE A-B AS NORMAL CALL CLEARING | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | | demand | |
| | | | | | | | | | | | (C-B) | |
| | | | | | | | connection demand (C-B) | | | stop |<———| |
| | | | | |connection| |<————————–┼——┼———-| T2 or| | |
| | | | | | demand | | | | | T3 | | |
| | | | | |<———| | | | (note 4) | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | | ack (C-B)| |
| | | | | | | | | | | +———>| |
| | | | | | | | | | | | | |
|CALL C-B ACTIVE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 4: If T2 or if applicable T3 expires before reception of connection demand in the MSC then call c-b shall be released with cause no reply and if it was T3 which expired the waiting call from C shall be forwarded on no reply.

Figure 1.6 (sheet 4 of 7): Information flow for call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|subscriber A disconnects active or held call | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| |disconnect| | | | | | | | | | | |
| | demand | | | | | | | | | | | |
| +———>| | | | | | disconnect demand (A-B) | | | |disconnect| |
| | | +———-┼-┼———-┼-┼—————————┼——┼———>| | demand | |
| | | | | | | | | | | | (A-B) | |
| | | | | | | | | | | +———>| |
| | | | | | | | | | | | | |
| | CONTINUE A-B AS NORMAL CALL CLEARING | | | |disconnect| |
| | | | | | | | | | | |ack (A-B) | |
| | | | | | | | | | | |<———| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | | demand | |
| | | | | | | | | | | | (C-B) | |
| | | | | | | | connection demand (C-B) | | | stop |<———| |
| | | | | |connection| |<————————–┼——┼———-| T2 or| | |
| | | | | | demand | | | | | T3 | | |
| | | | | |<———| | | | (note 5) | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | |ack (C-B) | |
| | | | | | | | | | | +———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B ACTIVE | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B WAITING or | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING or | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD | | | | | |
| | | | | | | | | | | | | |
|timer T3 expires | | | | | | | | | |
| | | | | | | | | | |T3 | | |
| | | | | |disconnect| | disconnect demand | | |expires | |
| | | | | | demand | |<————————–┼——┼———-| |disconnect| |
| | | | | |<———| | (user alerting, no answer)| | (note 6) demand | |
| | | | | |(user alerting, | | | | (C-B) | |
| | | | | |no answer)| | | | | |———>| |
| | | | | | | | | | | |(recovery | |
| | | | | | | | | | | | after | |
| | | | | | | | | | | |timer expiry)
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|B wants to retrieve held call | | | | | |retrieve | |
| | | | | | | | | | | | req (A-B)| |
| | | | | | | | | | | |<———| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |retrieve | |
| | | | | | | | | | | | ack (A-B)| |
| | | | | | | | | | | |———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |retrieve | |
| | | | | | | | | | | | reject | |
| | | | | | | | | | | | (A-B)| |
| | | | | | | | | | | |———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 5: The call shall be forwarded on mobile subscriber busy at this stage if activated.

NOTE 6: The call shall be forwarded on no reply.

Figure 1.6 (sheet 5 of 7): Information flow for call waiting

TEa LEa TEc LEc VLR MSC MS
+-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | |
|B wants to connect waiting call | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |connection| |
| | | | | | | | | | | | demand | |
| | | | | | | | | | | | (C-B)| |
| | | | | | | | | | | stop |<———| |
| | | | | | | | connection demand (C-B) | | | T2 or| | |
| | | | | |connection| |<————————–┼——┼———-| T3 | | |
| | | | | | demand | | | | | | | |
| | | | | |<———| | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B HELD/CALL C-B ACTIVE | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD | | | | | |
| | | | | | | | | | | | | |
|B wants to terminate active call | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | | | | | | | | | | |demand (A-B)|
| | | | | | | | disconnect demand (A-B) | | | |<———| |
| | | |<———┼-┼———-┼-┼—————————┼——┼———-| | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | |disconnect| |
| | CONTINUE A-B AS NORMAL CALL CLEARING | | | | |ack (A-B) | |
| | | | | | | | | | | +———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B WAITING/CALL D-B HELD (note 7) | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD | | | | | |
| | | | | | | | | | | | | |
|A disconnects active call| | | | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| |disconnect| | | | | | | | | | | |
| | demand | | | | | | | | | | | |
| +———>| | | | | | | | | | | |
| | | | | | | | disconnect demand (A-B) | | | | | |
| | | +———-┼-┼———-┼-┼—————————┼——┼———>| |disconnect| |
| | | | | | | | | | | |demand (A-B)|
| | | | | | | | | | | |———>| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
| | CONTINUE A-B AS NORMAL CALL CLEARING | | | | |disconnect| |
| | | | | | | | | | | |ack (A-B) | |
| | | | | | | | | | | |<———| |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |
|CALL C-B WAITING/CALL D-B HELD (note 7) | | | | | | |
| | | | | | | | | | | | | |
| | | | | | | | | | | | | |

NOTE 7: This state can be treated as CALL C-B WAITING/CALL A-B HELD.

Figure 1.6 (sheet 6 of 7): Information flow for call waiting

TEa LEa TEc LEc TEd LEd VLR MSC MS
+-+ +-+ +-+ +-+ +-+ +-+ +——+ +——+ +-+
| | | | | | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD | | | | | |
| | | | | | | | | | | | | | | | | |
|B wants to terminate held call | | | | | | | |
| | | | | | | | | | | | | | | |disconnect| |
| | | | | | | | | | | | | | | |demand (D-B)|
| | | | | | | | | | | | disconnect demand (D-B) | | | |<———| |
| | | | | | | | | | | |<————————–| | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | |disconnect| | | | | |disconnect| |
| | | | | | | | | | demand | | | | | |ack (D-B) | |
| | | | | | | | | |<———| | | | | |———>| |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | CONTINUE D-B AS NORMAL CALL CLEARING | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |

| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING/CALL D-B HELD | | | | | |
| | | | | | | | | | | | | | | | | |
|D wants to terminate held call | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | |disconnect| | | | | | | |
| | | | | | | | | | demand | | | | | | | |
| | | | | | | | | |———>| | | | | | | |
| | | | | | | | | | | | disconnect demand (D-B) | | | | | |
| | | | | | | | | | | |——————————————–>| |disconnect| |
| | | | | | | | | | | | | | | |demand (D-B)|
| | | | | | | | | | | | | | | |———>| |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |disconnect| |
| | | | | | | | | | | | | | | | ack (D-B)| |
| | | | | | | | | | | | | | | |<———| |
| | | | | | | | | | | | | | | | | |
| | CONTINUE D-B AS NORMAL CALL CLEARING | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |
|CALL A-B ACTIVE/CALL C-B WAITING | | | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | |

Figure 1.6 (sheet 7 of 7): Information flow for call waiting

1.3 Information stored in the HLR

Call waiting may have the following logical states (refer to GSM 03.11 for an explanation of the notation):

Provisioning State Registration State Activation State HLR Induction State

(Not Provisioned, Not Applicable, Not Active, Not Induced)

(Provisioned, Not Applicable, Not Active, Not Induced)

(Provisioned, Not Applicable, Active and Operative, Not Induced)

The activation state may be different for each applicable elementary basic service group.

The provisioning state shall be on a per subscriber basis, and hence the same for all basic service groups.

The HLR shall store the logical state of the call waiting service (which shall be one of the valid states listed above) on a per elementary basic service group.

1.4 State transition model

The following figure shows the successful cases of transition between the applicable logical states of call waiting. The state changes are either caused by actions of the service provider or the mobile user.

Note that error cases are not shown in the diagram as they normally do not cause a state change. Additionally, some successful requests may not cause a state change. Hence they are not shown in the diagram.

The diagram only shows operations on elementary basic service groups.

Figure 1.7: State transition model for call waiting

1.5 Transfer of information from HLR to VLR

If the provisioning state for call waiting is "Provisioned" then, when the subscriber registers on a VLR, the HLR shall send that VLR information about the logical state of call waiting.

If the logical state of call waiting is changed while a subscriber is registered on a VLR, then the HLR shall inform the VLR of the new logical state of call waiting.

1.6 Information stored in the VLR

For call waiting, the VLR shall store the service state information received from the HLR.

1.7 Handover

Handover will have no impact on the control procedures and the operation of the service.