Basic call state model
Basic call state model (BCSM) is used to describe the actions and different phases of the call processing in the MSC/GMSC/VMSC. The BCSM consists of two sets of call processing logics, i.e., originating BCSM (O-BCSM) and terminating BCSM (T-BCSM). The DP and points in call are two main components of a BCSM. Figure 8-12 illustrates the BCSM components.
O-BCSM. O-BCSM is used to describe the actions taken by the serving MSC to handle a call invoked by a subscriber with active O-CSI. This can also be used to describe actions of the MSC/GMSC for the forwarded calls. Figure 8-13 shows PIC and DP at different phases of a call.
On receiving a setup message from an MS, if the serving MSC/VMSC finds an active CAMEL subscription information (CSI) in its VLR, the MSC suspends the call and initiates the dialogue with the gsmSCF in the subscriber’s HPLMN.
Figure 8-12 BCSM components.
Figure 8-13 O-BCSM.
This dialogue contains an initial DP message indicating that a statically armed DP2, i.e., collected info, has been encountered. The gsmSCF requests the serving MSC to monitor the detection points DP7, O answer, and DP9, O disconnect. The gsmSCF then instructs the MSC to continue call processing. In the case of a successful call scenario, when terminating party answers the call, the MSC sends a notification, i.e., DP7, O answer. The MSC continues to process and monitor the call under instructions from the gsmSCF. When either calling or called party terminates the call, the MSC reports back to the gsmSCF, indicating that DP9, O disconnect, has been encountered.
The detection points for the originating BCSM are described in Table 8-9
TABLE 8-9 O-BCSM DPs
|
CAMEL DP |
Description |
|
Collected info |
This DP indicates that O CSI is active and has been analyzed. The dialed number has been received in the setup message sent by the initiating subscriber but is not yet analyzed. |
|
Analyzed information |
Indicates that the routing address and the nature of address is available and analyzed. |
|
Route select failure |
Indicates that call establishment failed because of the failure to select the route for the call. |
|
O busy |
A busy indication is received by the terminating party, i.e., ISUP REL message has been received by the serving MSC with the release cause code "busy." |
|
O no answer |
Indicates that one of the following events has occurred. ■ Serving MSC has received ISUP REL message with release cause code "no answer." ■ An application timer associated with O no answer has been triggered. |
|
O term seized |
An alerting indication is received from the terminating party, i.e., ISUP ACM has been received by the serving MSC. |
|
O answer |
Indication that the call is accepted and answered by the terminating party, i.e., an ISUP ANM message has been received by the serving MSC. |
|
O midcall |
Indication that a service feature request is received from the calling party via in-band DTMF signaling. |
|
O change of position |
Indication that the originating party has changed position. |
|
O disconnect |
Indication that either a disconnect message has been received from the originating party or a ISUP REL message with release cause code "normal release" has been received from the terminating side. |
|
O abandon |
Indication that a disconnect message has been received from the originating party during the call establishment phase. |
T-BCSM. In the case of mobile-terminating call, the IPLMN GMSC examines the called party MSISDN to identify its home PLMN. The GMSC then sends a request to the HPLMN HLR to get routing information, using the send routing information procedure. The HLR responds with the subscriber routing information, including the CSI of the called party. The GMSC checks the received CSI and acts accordingly. If the T-CSI is active and the trigger criterion of a DP is met, the call processing is suspended in order to get further instructions from the gsmSCF. An initial DP message is sent, informing the gsmSCF that a statically armed DP12 message, i.e., terminating attempt authorized was encountered in the T-BCSM. The gsmSCF requests the GMSC to monitor the DP’s T answer and T disconnect. The gsmSCF then asks GMSC to continue the call processing. Once the called party answers, the GMSC sends the notification to the gsmSCF on DP T answer.
Figure 8-14 T-BCSM.
The call processing continues in accordance with gsmSCF, and the GMSC continues monitoring state call and notifies the gsmSCF on call disconnection by the calling or the called party.
Figure 8.14 describes possible PICs and DPs at different phases of a call.
The detection points for T-BCSM are described in Table 8-10.
CAMEL information flow
The following tables describe the information flow between CAMEL nodes to support circuit-switched calls, USSD, SMS, supplementary service invocation, and mobility management.
CAMEL operation for circuit-switched calls. Table 8-11 lists the operations in a CAMEL circuit-switched call.
CAMEL operation for USSD. Table 8-12 lists the CAMAL IF operations for USSD.
CAMEL operation for GPRS interworking. Table 8-13 lists the CAMEL operations for GPRS interworking.
CAMEL operation for short message services. Table 8-14 lists the CAMEL information flow for short message service.
TABLE 8-10 T-BCSM DPs
|
CAMEL DP |
Description |
|
Terminating attempt authorized |
Indicates that the T-CSI/VT-CSI is active and analyzed. |
|
T busy |
Indicates that a busy indication is received from the destination exchange. |
|
T no answer |
This indicates that an application timer associated with the T no answer DP has expired. |
|
Call accepted |
This indicates that the called party is alerted. |
|
T answer |
This indicates that the call is answered by the terminating party. |
|
T midcall |
Indication that a service feature request is received from the terminating party via in-band DTMF |
|
signaling. | |
|
T change of position |
Indicates that the terminating party has changed its position. |
|
T disconnect |
A disconnect indication is received from the originating or the terminating party. |
|
T abandon |
Indication that a disconnect message is received from the originating party during the call establishment phase. |
TABLE 8-11 CAMEL Information Flow for a Circuit-Switched Call
|
CAMEL operation / information flow (IF) |
Description |
 | |
|
Activity test ack |
Response of IF activity test. |
|
Apply charging report |
A report in response to the apply charging request. |
|
Call information report |
Specific call information in response to the call information request. |
|
Disconnect leg ack |
Successful response to the disconnect leg IF. |
|
Entity released |
Sent to the gsmSCF to inform it of the release of a logical entity caused by exceptions/errors. |
|
Event report BCSM |
Used to notify about a call-related event once it has occurred—for example, events like answer and disconnect. |
|
Initiate call attempt ack |
The successful response to the initiate call attempt. |
|
Initial DP |
The gsmSSF uses this IF to request instructions from the gsmSCF when a trigger is detected at a DP in BCSM. |
|
Move leg ack |
The successful response to the move leg request. |
|
Split leg ack |
The successful response to the split leg IF. |
 | |
|
Activity test |
Used to check if the gsmSCF and the gsmSSF relationship is in existence. Appropriate actions are taken to recover the relationship if no response is received. |
|
Apply charging |
Used to instruct the gsmSSF to apply charging mechanisms to control the call duration. |
|
Call gap |
Used to control the number of service requests sent to a gsmSCF |
|
Call information request |
This is used to instruct the gsmSSF to record specific information about a single call party and report back. |
|
Cancel |
Request to cancel all event DPs and report. |
|
Connect |
Request to the gsmSSF to perform call processing actions required to route a call to the destination. |
|
Connect to resource |
Request to connect a call to a specialized resource, i.e., gsmSRF. |
|
Continue |
Request to the gsmSSF to continue a previously suspended call. |
|
Continue with argument |
Request to the gsmSSF to continue a previously suspended call but with modified call setup information. |
|
Disconnect forward connection |
Request to disconnect a connection with the gsmSRF. |
|
Disconnect forward connection with argument |
Request to disconnect a connection with the gsmSRF. This is used to explicitly disconnect a connection that was previously established with a connect to resource or an establish temporary connection message. |
|
Disconnect leg |
Request to the gsmSSF to release a specific leg of a call while retaining all other legs of that call. |
|
Establish temporary connection |
Request to create a connection between an initiating gsmSSF and an assisting gsmSSF as a part of the assist procedure. It is also used to establish a connection between a gsmSSF and a gsmSRF. |
|
Furnish charging information |
Request to the gsmSSF to include call-related information in the CAMEL-specific logical call record. |
|
Initiate call attempt |
Request to the gsmSSF to establish a new call or add a new party to an existing established call. |
TABLE 8-11 CAMEL Information Flow for a Circuit-Switched Call
|
CAMEL operation / information flow (IF) |
Description |
 | |
|
Move leg |
Request to the gsmSSF to move a call leg to another call segment. |
|
Play tone |
Request to play a sequence of tones to a particular leg or call segment. |
|
Release call |
Request to tear down a call. |
|
Request report |
Request to the gsmSSF to monitor for a call-related |
|
BCSM event |
event and then send notification back on event detection. |
|
Reset timer |
Request to reset a specific timer. |
|
Send charging information |
Charging information to be sent to MS. |
|
Split leg |
Request to move a call leg from one call segment to another existing call segment or newly created call segment. |
 | |
|
Activity test |
Used to check if the gsmSCF and the gsmSRF relationship is in existence. Appropriate actions are taken to recover the relationship if no response is received. |
|
Cancel |
Request to the gsmSRF to cancel a correlated previous information flow. |
|
Play announcement |
A request to play a single announcement/tone or sequence of announcements for the in-band interaction. |
|
Prompt and collect user information |
Used to interact with the calling party by announcement/ tone and to collect information such as digits or speech. |
 | |
|
Activity test ack |
Response to the IF activity test. |
|
Assist request instructions |
Sent by the gsmSRF or by the assisting gsmSSF to associate the assist request with the initial DP. |
|
Prompt and collect user information ack |
Response to the IF prompt and collect user information. |
|
Specialized resource report |
Response to the request for resources by the gsmSCF in a play announcement message or a prompt and collect user information message. |
 | |
|
Activity test |
This is used to check if the gsmSCF and the assist SSF relationship is in existence. Appropriate actions are taken to recover the relationship if no response is received. |
|
Cancel |
Request to cancel a correlated information flow. |
|
Connect to resource |
Request to connect a call to a specialized resource, i.e., gsmSRF. |
|
Disconnect forward connection |
Used to disconnect a previously established connection using a connect to resource message. |
|
Play announcement |
A request to play a single announcement/tone or sequence of announcements for the in-band interaction. |
|
Prompt and collect user information |
Used to interact with the calling party by announcement/ tone and to collect information such as digits or speech. |
|
Rest timer |
A request to reset a specific timer. |
TABLE 8-11 CAMEL Information Flow for a Circuit-Switched Call
|
CAMEL operation / information flow (IF) |
Description |
 | |
|
Activity test ack |
A response to IF activity test. |
|
Assist request instructions |
This is sent by the gsmSRF or by the assisting gsmSSF to associate the assist request message with the initial DP. |
|
Prompt and collect user information ack |
A response to the IF prompt and collect user information. |
|
Specialized resource report |
Response to the request for resources by the gsmSCF in a play announcement message or a prompt and collect user information message. |
 | |
|
Delete subscriber data |
Used by the HLR to delete CAMEL subscription data from a VLR. |
|
Insert subscriber data |
The HLR uses this IF to update the VLR with subscriber specific data. CAMEL-specific subscriber information such as O-CSI and T-CSI are transferred by this procedure. |
|
Provide subscriber info |
The HLR can request anytime information on a subscriber currently roaming in a VPLMN. The VLR sends a response with roamer information such as subscriber location, IMEI, and SW version. |
|
Provide roaming number |
Used by the HLR to get the roaming number assigned to a roamer in a visited network. |
 | |
|
Insert subscriber data ack |
Response to the IF insert subscriber data. |
|
Provide subscriber info ack |
Response to the IF provide subscriber info. |
|
Update location |
Used by the VLR to provide information about supported CAMEL phases to the HLR. |
|
Restore data |
Used by the VLR to provide information about supported CAMEL phases to the HLR. |
 | |
|
Send routing info ack |
Response to the IF send routing info. The HLR transfers routing information to enable the GMSC to route call to the destination MSC. |
 | |
|
Send routing info |
GMSC uses this operation to request information from the HLR to route an MT call. |
 | |
|
Resume call handling |
Request to the GMSC to take over handling the call. |
TABLE 8-11 CAMEL Information Flow for a Circuit-Switched Call
|
CAMEL operation / information flow (IF) |
Description |
 | |
|
Send info for ICA |
Used to request the VLR to provide information to handle an outgoing call leg created by the gsmSCF. |
|
Send info for incoming call |
Used to request the VLR to provide information to handle an incoming call. |
|
Send info for MT reconnected call |
The MSC uses this to request the VLR to provide information to handle a reconnected MT call. |
|
Send info for outgoing call |
Used to request the VLR to provide information to handle an outgoing call. |
|
Send info for reconnected call |
The MSC uses this to request the VLR to provide information to handle a reconnected MO call. |
 | |
|
Complete call |
Request to MSC to continue the connection of a call. |
|
Continue CAMEL handling |
Request to MSC to continue CAMEL-specific handling. |
|
Process call waiting |
Request to MSC to continue the connection of a waiting call. |
|
Send info for ICA negative response |
Negative response to indicate that the outgoing call leg for which the MSC requested subscription information will not be connected, given for a reason such as bearer service not allowed or call barred. |
|
Send info for incoming call ack |
Used to indicate that the incoming call for which the MSC requested subscription information should be forwarded. |
|
Send info for incoming call negative response |
Used to indicate that the incoming call for which the MSC requested subscription information should not be connected. |
|
Send info for MT reconnected call ack |
Used to instruct the MSC to continue the connection of a reconnected MT call. |
|
Send info for MT reconnected call negative response |
Used to indicate that the reconnected MT call for which the MSC requested subscription information should not be connected. |
|
Send info for reconnected call ack |
Request to MSC to continue the connection of a reconnected MO call. |
|
Send info for reconnected call negative Ack |
Used to indicate that the reconnected call for which the MSC requested subscription information should not be connected. |
|
Internal MSC | |
|
Perform Call forwarding ack |
This IF is used to inform the MSC that the call forwarding is taking place. |
 | |
|
Send routing info |
A request for information from the HLR to route a gsmSCF-initiated call. |
 | |
|
Send routing info ack |
Response for IF send routing info. |
TABLE 8-12 CAMEL Information Flow for Short Message Service
|
CAMEL operation |
Description |
 | |
|
Unstructured SS request |
Used to request data from the MS via the HLR. |
|
Unstructured SS notify |
Used to send data to the MS via the HLR. |
|
Process unstructured SS data ack |
Used to send a response to the MS via the HLR for the MS-initiated request. |
 | |
|
Unstructured SS request ack |
MS response to the gsmSCF-initiated IF unstructured SS request. The response is sent to the gsmSCF via the HLR. |
|
Unstructured SS notify ack |
Used by the MS to acknowledge to the gsmSCF the receipt of notification. |
|
Process unstructured SS data |
The MS requests data from the gsmSCF via the HLR. |
|
Process unstructured SS request |
The MS requests data from the gsmSCF via the HLR. |
|
Begin subscriber activity |
Used by the HLR to start subscriber activity toward the gsmSCF for USSD. |
CAMEL operation for SS notification. Table 8-15 lists the CAMEL information flow for SS notification.
CAMEL operation for mobility management. Table 8-16 lists the CAMEL information flow for mobility management.