1 Call Waiting (CW)

24.0833GPPCall Waiting (CW) and Call Hold (HOLD) supplementary servicesRelease 17Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

1.1 Waiting call indication and confirmation

When this service is activated for the controlling subscriber B and the B‑subscriber has calls only in states U10 (Active) or U26 (MO Modify) as defined in 3GPP TS 24.008, the arrival of an incoming call from subscriber C shall, if no other call is waiting be signalled to the mobile station B by a normal call indication. In that case the network and the mobile station shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (C‑B) allocated to the waiting call and must not be the same as the transaction identifier (A‑B) for the already existing call (see figure 1.1). In the CALL CONFIRMED message sent to the network the Cause information element shall be included with cause #17 "user busy" (see figure 1.1). When the ALERTING message is received by the network the call waiting timer T2 shall be started or if call forwarding on no reply is activated for the B‑subscriber the no reply condition timer T3 shall be started.

If the network received a non‑zero SS Screening indicator from the calling users mobile station the ALERTING/FACILITY message sent to a calling mobile user shall include the Facility information element with an invoke of the Notification operation indicating that the call is waiting (see figure 1.2). If the network did not receive a non‑zero SS Screening indicator from the calling users mobile station it shall not send a notification, i.e. either the ALERTING message does not include the Notification operation or the FACILITY message is omitted.

MS Network

SETUP

<————————————————————————————————————————

…..Transaction identifier(C-B)…..

CALL CONFIRMED

————————————————————————————————————————>

…..Transaction identifier(C-B)…..

…..Cause #17 (user busy)…..

ALERTING

————————————————————————————————————————>

…..Transaction identifier(C-B)….. start T2/T3

NOTE: The SETUP message shall include a "Signal Information" element with value #7 (call waiting tone on). This shall be used by the MS to generate an appropriate call waiting indication.

Figure 1.1: Call indication to the mobile station on arrival of an incoming call
and call confirmation from the mobile station

MS Network

SETUP

————————————————————————————————————————>

CALL PROCEEDING

<————————————————————————————————————————

ALERTING/FACILITY

<————————————————————————————————————————

Facility (Invoke = NotifySS (CW, CallIsWaiting-Indicator))

NOTE: If possible, the ALERTING message shall be used as the carrier message for the Call Waiting notification. Otherwise the FACILITY message shall be used.

Figure 1.2: Notification to a calling mobile station that the call is in the waiting state

1.2 Normal operation with successful outcome

1.2.1 Waiting call accepted; existing call released

If the mobile user B before expiry of timer T2 determines to accept the waiting call and release the existing call the mobile station shall release the existing call firstly and accept the waiting call secondly.

For the release of the existing call the mobile station and the network shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (A‑B) of the already existing call. The Cause information element in the first clearing message shall indicate cause #16 "normal clearing".

For the acceptance of the waiting call the mobile station and the network shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (C‑B) of the waiting call.

When the network receives the CONNECT message the timer T2 or if applicable the timer T3 shall be stopped.

1.2.2 Waiting call accepted; existing call on hold

If the mobile user B before expiry of timer T2 or if applicable timer T3 determines to accept the waiting call and put the existing call on hold the mobile station shall put the existing call on hold firstly and accept the waiting call secondly.

In case there is one active call (A‑B) and another call (D‑B) on hold and call (C‑B) waiting, and the mobile user B wants to accept the waiting call (C‑B) and put the active call (A‑B) on hold, the held call (D‑B) has to be released first, either by user B or user D, in accordance with 3GPP TS 24.008.

To put the existing call on hold the mobile station and the network shall act in accordance with clause 2. The hold function shall be initiated by the mobile station and the transaction identifier shall be the transaction identifier (A‑B) of the existing call (see figure 1.3).

When the network receives the CONNECT message the timer T2 or if applicable the timer T3 shall be stopped.

MS Network

HOLD

————————————————————————————————————————>

…..Transaction identifier(A-B)…..

HOLD ACKNOWLEDGE

<————————————————————————————————————————

…..Transaction identifier(A-B)…..

HOLD REJECT

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

…..Transaction identifier(A-B)…..

…..Cause #29 (facility rejected)…..

or #50 (requested facility not subscribed)

or #69 (requested facility not implemented)

CONNECT

————————————————————————————————————————>

…..Transaction identifier(C-B)….. stop T2/T3

CONNECT ACKNOWLEDGE

<————————————————————————————————————————

…..Transaction identifier(C-B)…..

Figure 1.3: Existing call on hold and acceptance of waiting call by the mobile station

1.2.3 Existing call released by user A; waiting call accepted

If user A before the expiry of timer T2 or if applicable timer T3 determines to release the existing call then the existing call shall by released by the network firstly and the waiting call may be accepted by the mobile station secondly.

For the release of the existing call the network and the mobile station shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (A‑B) of the existing call.

When the network receives the CONNECT message the timer T2 or if applicable the timer T3 shall be stopped.

1.3 Normal operation with unsuccessful outcome

1.3.1 Waiting call released by subscriber B

For the release of the waiting call the mobile station and the network shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (C‑B) of the waiting call.

* If the B subscriber indicates UDUB by the sending of the first clearing message with cause information element #17 (User Busy), and call forwarding on mobile subscriber busy is activated for the B subscriber the call shall be forwarded by the network. If call forwarding is not active the call will be cleared.

* If any other causes are given in the first clearing message the call will be released.

1.3.2 Waiting call released by calling user C

If the calling user C, before the expiry of timer T2 or timer T3 (if applicable), releases the waiting call then the network shall release the waiting call against the mobile station.

For the release of the waiting call the network and the mobile station shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (C‑B) of the waiting call.

When the network initiates clearing by sending a clearing message to the mobile station the timer T2 or, if applicable, the timer T3 shall be stopped.

1.3.3 Waiting call times out

If the timer T2 expires the network shall release the waiting call. The network and the mobile station shall act in accordance with 3GPP TS 24.008. The transaction identifier shall be the transaction identifier (C‑B) of the waiting call. The Cause information element in the first clearing message shall indicate cause #102 "recovery on timer expiry".

1.3.4 No reply condition timer expires

If call forwarding on no reply is activated for the B‑subscriber and the no reply condition timer expires the waiting call shall be forwarded in accordance with 3GPP TS 24.082. The network shall clear the waiting call towards the B‑subscriber as in subclause 1.3.3.

1.4 Activation

Activation of the supplementary service call waiting will be performed by the subscriber. The network will send a return result indication of acceptance of the request (see figure 1.4).

If the network cannot accept an activation request, an error indication is returned to the served mobile subscriber. Error values are specified in 3GPP TS 24.080 (see figure 1.4).

If the mobile subscriber does not indicate a specific basic service group the activation of call waiting is valid for all applicable basic services (see figure 1.4).

Normal outgoing call procedures apply when this service is activated.

MS Network

————————————————————————————————————————>

Facility (Invoke = ActivateSS (CW, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = ActivateSS (BasicServiceCode))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: If the BasicServiceCode is not included the activation is valid for all applicable basic services.

Figure 1.4: Activation of call waiting

1.5 Deactivation

Deactivation of the supplementary service call waiting will be performed by the subscriber. The network will send a return result indication of acceptance of the request (see figure 1.5).

If the network cannot accept a deactivation request, an error indication is returned to the served mobile subscriber. Error values are specified in 3GPP TS 24.080 (see figure 1.5).

If the subscriber does not indicate a specific basic service group the deactivation of call waiting is valid for all applicable basic services (see figure 1.5).

MS Network

————————————————————————————————————————>

Facility (Invoke = DeactivateSS (CW, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = DeactivateSS (BasicServiceCode))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: If the BasicServiceCode is not included the deactivation is valid for all applicable basic services.

Figure 1.5: Deactivation of call waiting

1.6 Interrogation

Status check

The mobile subscriber can request the status of the supplementary service call waiting and be informed whether the service is supported in the network and if so, a list of all basic service groups to which the call waiting supplementary service is active (see figure 1.6).

If a mobile subscriber interrogates the network on the status of call waiting, and the network supports call waiting but the service is not active for any basic service groups then an SS‑Status parameter shall be returned indicating "deactivated" (see figure 1.6).

If a mobile subscriber interrogates the network on the status of call waiting, whilst the network does not support call waiting, the network shall return an error indication (see figure 1.6).

MS Network

————————————————————————————————————————>

Facility (Invoke = InterrogateSS (CW))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = InterrogateSS (BasicServiceCode(s))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = InterrogateSS (SS-Status)

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

Figure 1.6: Interrogation of call waiting

1.7 Invocation

Invocation of call waiting causes no signalling on the radio path.

1.8 Registration and erasure

Registration and erasure of the supplementary service call waiting are not applicable.