14.1 Customised Applications for Mobile network Enhanced Logic (CAMEL)

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

If the gsmSRF is co-located with the (G)MSC server, the gsmSRF is divided into a gsmSRF server and an MGW. The gsmSRF server terminates the CAP protocol and signals over the Mc interface to instruct its MGW to provide the required resource. All the logic of the gsmSRF is located in the gsmSRF server. The MGW provides only simple resources for playing a single announcement or tone, or detection of single DTMF tone pair. If one single resource in the MGW does not fulfil the requirement of the gsmSCF, the gsmSRF server has to use different resources in sequence to fulfil the whole requirement.

The gsmSSF uses the capabilities of the (G)MSC server and the MGW to play announcements or send tones to the server.

NOTE 1: In the subsequent figures within clause 14.1, the "Connect To Resource" scenario is used. However the other CAMEL Intelligent Peripheral (IP) scenarios are not intended to be excluded. No impacts are identified when applying these other CAMEL scenarios.

NOTE 2: The gsmSRF functionality may be deployed within the MSC server, and either the current serving MGW or any MGW resource under the control of the current MSC server.

14.1.1 Play Announcement/Send Tone

The playing of an announcement or sending of a tone shall be performed in accordance with 3GPP TS 23.078 [10]. It is assumed that the MGW selected for the call has the capabilities to provide announcements and tones.

When the gsmSCF requests the gsmSRF to play a specified announcement or tone, the gsmSRF orders the MGW to play the announcement or tone as described in clause 14.6.

After the gsmSRF has received the announcement or tone completed notification from its MGW, it reports the announcement or tone completion to the gsmSCF.

If the gsmSCF requests the gsmSRF to cancel the earlier started announcement or tone, the gsmSRF orders the MGW to stop playing the announcement or tone as described in clause 14.6.

14.1.1.1 Example of playing announcement by the gsmSRF

Figure 14.1: CAMEL Announcement Playing (message sequence chart)

14.1.2 User Interaction

The user interaction shall be performed in accordance with 3GPP TS 23.078 [10]. It shall be assumed that the MGW selected for the call has the capabilities to provide announcements. In bearer independent CS core network the DTMF digits can be propagated inband or out-of-band.

14.1.2.1 Play announcement

When the gsmSCF requests the gsmSRF/SSF to play a specified announcement and to collect digits that are sent by the user the gsmSRF/SSF requests the MGW to play the announcement as described in clause 14.6.

14.1.2.2 Detect DTMF tones

The gsmSRF/gsmSSF starts detecting DTMF tones, as describes in clause 14.4.2, before it receives the announcement or tone completed notification (see clause 14.6).

14.1.2.3 Report DTMF tones

The DTMF tones are reported to the gsmSRF/SSF as described in clause 14.4.2. After all requested digits are received the gsmSRF/SSF reports the digits to the gsmSCF.

14.1.2.4 Cancel prompt and collect user information

If the gsmSCF requests the gsmSRF to cancel the prompt and collect user information procedure, which had been started earlier, the gsmSRF orders the MGW to stop playing the announcement or sending tone, if they are still in progress , using the Stop Announcement or the Stop Tone procedure. The gsmSRF shall also order the MGW to stop detecting DTMF tones using the Stop DTMF Detection procedure.

Figure 14.2: CAMEL User Interaction (message sequence chart)

NOTE: Since gsmSRF don not know whether DTMF digits are provided inband or out-of-band the gsmSRF has to be able to collect DTMF tones both inband and out-of-band.

14.1.3 Call Party Handling (CPH)

The procedures specified in 3GPP TS 23.078 [10] for Call Party Handling (CPH) shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network.

In contrast with HOLD and MPTY, the call parties created on instruction from the gsmSCF are not seen as separate calls in the Mobile Station, i.e. all call parties in a CPH configuration use the same transaction id towards the MS. In addition, CPH may take place in an MSC‑S different from the one where the CAMEL served subscriber is registered. Furthermore, in CPH it is possible to have multiple call parties in separate call segments whereas the call hold supplementary service has a limit of one held call party and one active call.

The gsmSCF always triggers the elementary procedures which are described in this clause. CPH elementary procedures can be used in more complex procedures to provide useful services, but the more complex procedures are out of scope of this specification.

NOTE: For simplicity, the figures below which show network models do not show the gsmSCF. The gsmSCF is in the HPLMN of the served (CAMEL) party. The GMSC‑S is in the interrogating network (IPLMN). The MSC‑S is in the VPLMN of the served party.

Use of a multi-party (conference) bridge

When the gsmSCF invokes a CPH procedure which requires the connection of three or more legs in a multi-party configuration, the MSC server selects an MGW which provides multi-party bridge capabilities. The timing of the selection of the MGW with the multi-party bridge capabilities is vendor specific. If the selected MGW is not the MGW which is used for the active call, the MSC server requests the MGW(s) to connect the bearer terminations of the participants to the selected MGW. The bearer terminations are connected together.

14.1.3.1 Call Party Handling concepts

The relationship between Call Segments and voice connections is explained in 3GPP TS 23.078 [10] clause 4.5.1.

14.1.3.2 Initiate Call Attempt procedure

The Initiate Call Attempt (ICA) procedure is used either:

– To create a new call (out-of-the-blue), in which case the gsmSCF makes the initial contact with the MSC‑S, or

– To create an additional call party in an existing call. The new call party is always created in a new call segment. The existing call may have triggered contact with the gsmSCF based on CAMEL subscription information (MO or MT in VMSC, MT in GMSC, call forwarding etc), or the gsmSCF may have initiated the contact using the ICA procedure (out-of-the-blue).

The gsmSCF may create additional call parties before it establishes the bearer to the calling party. The MSC‑S/GMSC‑S shall establish bearers to the additional call parties independently of the other parties, including the calling party.

The leg which is created by the Initiate Call Attempt procedure is initially in the held state.

14.1.3.2.1 Example

Figure 14.1.3/1 shows an example network model for the Initiate Call Attempt procedure with an establishment of a new call leg. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The MSC‑S seizes a new context with one bearer termination in the MGW which is used for the new call leg.

Figure 14.1.3/1 Initiate Call Attempt procedure (Network model)

Figure 14. 1.3/2 shows an example message sequence for the Initiate Call Attempt procedure.

In this example a new call leg to the C-party is established.

Figure 14. 1.3/2 Information flow for Initiate Call Attempt (message sequence chart)

14.1.3.3 Move Leg procedure

The Move Leg procedure is used to move a leg from its current call segment to the (existing) target call segment.

Using Move Leg to add a leg to a call segment which already includes 2 call legs requires the establishment of a multiparty call (if it does not already exist for the served CAMEL subscriber) as described in clause 13.7. Other call parties may be involved in independent Multiparty calls due to MPTY SS or CPH. If the call segment to which the specified leg is added is already using a multi-party bridge, the MSC server requests the MGW to establish the connection between the specified leg and the multi-party bridge.

Example

Figure 14. 1.3/3 shows an example network model for the Move Leg procedure. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer

Figure 14. 1.3/3 Move Leg procedure (Network model)

Figure 14. 1.3/4 shows an example message sequence for the Move Leg procedure.

In this example the leg of the C-party is moved to an existing call segment. The MSC‑S requests the MGW to move the bearer termination for the C-party to the same Context which contains the bearer termination for the A-party

Figure 14. 1.3/4 Information flow for Move Leg (message sequence chart)

14.1.3.4 Split Leg procedure

The Split Leg procedure is used to separate a call leg from a source call segment and place it in a (new) target call segment.

When the gsmSCF uses the Split Leg procedure to put a call leg on hold, the MSC server instructs the MGW to interrupt the connection between the specified call leg and the other party/parties in the call segment. If the call segment is using a multi-party bridge, the connection from the specified call leg to the multi-party bridge is interrupted.

Example

Figure 14. 1.3/5 shows an example network model for Split Leg procedure. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer.

Figure 14. 1.3/5 Split Leg procedure (Network model)

Figure 14. 1.3/6 shows an example message sequence for the Split Leg procedure.

In this example the leg of the B-party is moved to a new call segment. The MSC‑S requests the MGW to move the bearer termination for the B-party in the active call to a new context.

Figure 14. 1.3/6 Information flow for Split Leg (message sequence chart)

14.1.3.5 CAMEL User interaction procedure

In accordance with 3GPP TS 23.078 [10] the gsmSCF may order the MSC‑S/gsmSSF to play an announcement or control user interaction as specified in clauses 14.1.1 and 14.1.2 respectively. The tones are provided in accordance with clause 14.6 of the present document. As part of Call Party Handling, announcements or tones can be played to an individual party or to all the parties connected in the call segment.

The gsmSCF may also instruct the MSC‑S to establish a temporary connection to an external device which provides the user interaction.

14.1.3.6 Failure handling in the MSC‑S

If resources for Call Party Handling cannot be allocated in any of the MGWs assigned to the MSC‑S, then the MSC‑S shall reject the request for the Call Party Handling procedure.