14.6 Providing tones or announcements

23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS

It shall be assumed that the MGW selected for the call has the capabilities to provide announcements and tones.

14.6.1 Preconditions when providing in-band information to the calling subscriber

For a mobile terminating/forwarded call, announcements/tones may be provided to the calling subscriber only when both of the following conditions are satisfied:

1. Either:

a. The incoming IAM indicated that the Continuity message will follow, and a Continuity message has been received, or

b. The incoming IAM did not indicate that the Continuity message will follow;

2. Notification indicating successful completion of the incoming side bearer set-up has been received from the MGW using the Bearer Established procedure.

For a mobile originating call, the traffic channel assignment shall be completed before providing the in-band information to the calling subscriber.

14.6.2 Preconditions when providing in-band information to the called subscriber

The called party is selected by the calling party, or a supplementary service (call forwarding, call deflection, CAMEL redirection etc), or a call is initiated by the gsmSCF using the Initiate Call Attempt procedure. The called party may also be in the PSTN.

Announcements/tones may be provided to the called subscriber only when both of the following conditions are satisfied:

1. The called party has answered and is still active in the call.

2. Notification indicating successful completion of the outgoing side bearer set-up has been received from the MGW using the Bearer Established procedure.

14.6.3 Preconditions when providing in-band information to multiple subscribers

The gsmSCF may instruct the MSC‑S/gsmSSF to provide announcements or tones for multiple subscribers. For each calling and called subscriber the precondition for calling and called subscriber (respectively) shall be fulfilled. If the preconditions are not fulfilled for all subscribers (e.g. one of the called parties is in the alerting phase), then the announcements/tones shall not be played to the subscribers who do not meet the preconditions, but the announcements/tones shall be played to the subscribers (if any) who meet the preconditions.

14.6.4 Request to play an announcement/tone

The (G)MSC server/gsmSSF/gsmSRF provides the MGW with the announcement/tone identification and optionally requests the MGW to notify the announcement/tone completion using the Play Announcement or Send Tone procedure (bullet 1 in figure 14.13).

14.6.5 Stopping an announcement/tone

The (G)MSC server/gsmSSF/gsmSRF can order the MGW to stop the current announcement/tone using the Stop Announcement or Stop Tone procedure (bullet 2 in figure 14.13).

14.6.6 Announcement/tone completed

If notification of the announcement/tone completion was requested in the Play Announcement or Send Tone procedure, the MGW notifies the (G)MSC server/gsmSSF/gsmSRF when the announcement/tone has been completed using the Announcement Completed or Tone Completed procedure (bullet 3 in figure 14.13).

14.6.7 Example 1

Figure 14.12 shows the network model for providing in-band information to the calling subscriber where the (G)MSC-S requests to play the announcement/tone directly on the desired termination from which the signal shall be sent. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The bearer termination Tx is used for the bearer towards the preceding MGW (calling subscriber).

A bearer termination Ty may exist in the same context towards the succeeding MGW (called subscriber) and may be both-way connected and through-connected with Tx. In that case, the exchange of media streams between the terminations Tx and Ty is assumed to be normally interrupted during playing the announcement in the direction towards which the announcement is played.

Figure 14.12: Providing in-band information
(Network model)

Figure 14.13 shows the message sequence example for providing the calling party with an announcement/tone. In the example the (G)MSC server requests the MGW to play an announcement/tone and to notify the announcement/tone completion. The (G)MSC server may stop the announcement while the current announcement/tone is ongoing.

Figure 14.13: Playing an announcement/tone (message sequence chart)

14.6.8 Example 2

Figure 14.6.8/1 shows the network model for providing in-band information to the calling subscriber where the (G)MSC-S requests to play the announcement/tone on another termination in the context connected via topology information to the desired termination(s). E.g. during the call setup, the MSC-S requests the MGW to send a ring back tone to the calling subscriber when receiving the indication that the called subscriber is being alerted.

The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The in-band information applied on the T0 termination is forwarded to the bearer termination(s) towards which the topology association is either ‘oneway’ or ‘bothway’, i.e. towards the Ta termination in this example.

Figure 14.6.8/1: Proving in-band information
(Network model)

Figure 14.6.8/2 shows the message sequence example for providing the calling party with the announcement/tone. In the example the MSC requests the MGW to play an announcement/tone by seizing a new ephemeral announcement/tone termination with the indication that a tone or announcement shall be forwarded internally to the bearer termination(s) towards which the topology association is either ‘oneway’ or ‘bothway’.

Figure 14.6.8/2: Playing an announcement/tone (message sequence chart)