Abstract:
The subject matter described herein relates to methods, systems, and computer program products for providing Internet protocol multimedia subsystem (IMS) services in response to advanced intelligent network (AIN) triggers. According to one aspect, a method for providing an IMS service in response to an AIN trigger is provided. The method includes detecting the firing of an AIN trigger concerning an IMS registered non-IMS device. An IMS service to be provided in response to the AIN trigger is identified. The IMS service is provided.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/791,697, filed Apr. 13, 2006; the disclosure of which is incorporated herein by reference in its entirety. 
     This application is related to a commonly-assigned, co-pending U.S. Patent Application entitled Methods, Systems, and Computer Program Products for Providing Internet Protocol Multimedia Subsystem (IMS) Registration Services for Non-IMS Devices, filed on even date herewith, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The subject matter described herein relates to providing IMS services. More particularly, the subject matter described herein relates to methods, systems, and computer program products for providing Internet protocol multimedia subsystem (IMS) services in response to advanced intelligent network (AIN) triggers. 
     BACKGROUND 
     IP multimedia subsystem (IMS) networks allow IMS-compatible devices to establish voice calls and to receive call originating and call terminating services using IMS network elements. In an IMS network, an IMS-compatible subscriber device, such as an IMS-compatible handset, is homed to a serving call session control function (S-CSCF). When an IMS-compatible device connects to a network anywhere, the IMS-compatible device first obtains an IP address. The IP address may be obtained by static assignment or by a dynamic protocol, such as DHCP. The IMS device then registers with the home S-CSCF. Registration involves communicating the IMS device or subscriber identity and the corresponding IP address to the S-CSCF. For example, IMS devices may be identified by SIP URIs. An example of an IMS device identity that may be associated with an IMS subscriber&#39;s SIP phone is Dan@ Tekelec.com. The SIP phone may obtain an IP address of 196.10.10.1 when the phone connects to the network. Registration of the SIP phone involves communicating the association between 196.10.10.1 and Dan@ Tekelec.com to the subscriber&#39;s S-CSCF. Registration of IMS devices can be accomplished through SIP messaging between the devices and their respective S-CSCFs. 
     Once an IMS device is registered with its S-CSCF, the device can originate and terminate calls and receive call originating and call terminating services using IMS network elements. For example, when the IMS device originates a call, the S-CSCF is notified of the call origination and queries a database, referred to as a home subscriber server (HSS) database, to determining call originating services to be applied to the call. Examples of call originating services include prepaid calling services and number portability services. The S-CSCF may then obtain routing information and invite the terminating device to the join the call. If the IMS device is at the terminating leg of the call, the S-CSCF receives an invitation for the device to join the call, determines the terminating services to apply to the call, and signals with the originating S-CSCF to establish the call. 
     It may be desirable to establish calls and to provide services using IMS nodes to non-IMS devices, such as 2G mobile phones and PSTN phones or black phones. 2G mobile phones and black phones are incapable of receiving calls or services using IMS network elements because such devices are not identifiable to the IMS network. For example, black phones and 2G mobile phones are incapable of registering with the IMS network because they do not have registration signaling capabilities. As a result, such devices can receive calls and services only by relying on PSTN network elements. Consequently, such devices may be limited in the types of service that they can receive and may be charged more for such services than the corresponding services available via the IMS network. 
     An additional problem to providing IMS services to non-IMS devices is the inability to communicate AIN triggers to the IMS networks. Within the PSTN, AIN standards are defined to specify how a call origination triggered service and a call termination triggered service may be implemented. Typically, an end office switch may define and set AIN triggers that are fired upon a call origination attempt by a subscriber or a call termination attempt to a subscriber. A fired call origination attempt further may result in a generation of a TCAP origination attempt message, while a fired call termination attempt trigger may result in the generation of a TCAP termination attempt message. These TCAP messages may be transmitted to another AIN network element, such as a service control point (SCP), which may use the information contained in the messages to provide call control or other call related services. Because these triggers are fired in the PSTN domain, there is no mechanism for using these triggers to invoke IMS services. 
     Accordingly, in light of these difficulties, there exists a need for improved methods, systems, and computer program products for providing IMS services in response to AIN triggers. 
     SUMMARY 
     The subject matter described herein relates to methods, systems, and computer program products for providing IMS services in response to AIN triggers. According to one aspect, a method for providing an IMS service in response to an AIN trigger is provided. The method includes detecting the firing of an AIN trigger concerning an IMS registered non-IMS device. An IMS service to be provided in response to the AIN trigger is identified. The IMS service is provided. 
     In another aspect of the subject matter disclosed herein, a computer program product comprising computer executable instructions embodied in a computer readable medium for performing steps is provided. The steps include registering a non-IMS device with an IMS network by transmitting a registration message to an IMS network element detecting firing of an AIN trigger concerning an IMS-registered non-IMS device. An IMS service to be provided in response to the AIN trigger is identified. The IMS service is provided using IMS network elements. 
     As used herein, the term “AIN trigger” refers to logic implemented at a PSTN switching office to initiate either a call originating or call terminating service. Examples of AIN triggers include call originating attempt triggers and call terminating attempt triggers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the subject matter described herein will now be explained with reference to the accompanying drawings of which: 
         FIG. 1  is a network diagram illustrating an exemplary system for providing IMS registration services for non-IMS devices according to an embodiment of the subject matter described herein; 
         FIG. 2A  is a block diagram of the system illustrated in  FIG. 1  where IMS registration is triggered by presence status information updates according to an embodiment of the subject matter described herein; 
         FIG. 2B  is a block diagram of the system illustrated in  FIG. 1  where IMS registration is triggered by monitoring SS7 signaling messages involving a non-IMS device according to an embodiment of the subject matter described herein; 
         FIG. 2C  is a block diagram of the system illustrated in  FIG. 1  where IMS registration is triggered by subscriber action according to an embodiment of the subject matter described herein; 
         FIG. 3A  is a block diagram of a first portion of the system illustrated in  FIG. 1  showing SIP signaling for establishing a voice call with an IMS-registered, non-IMS device according to an embodiment of the subject matter described herein; 
         FIG. 3B  is a block diagram of a second portion of the system illustrated in  FIG. 1  showing ISDN user part (ISUP) signaling for establishing a voice call with an IMS-registered, non-IMS device according to an embodiment of the subject matter described herein; 
         FIG. 4  is a flow chart illustrating a process for registering non-IMS devices with an IMS network according to an embodiment of the subject matter described herein; 
         FIG. 5  is a flow chart illustrating a process for registering a non-IMS device with an IMS network by querying a presence server to identify activity involving the non-IMS device and for completing a call to the non-IMS device according to an embodiment of the subject matter described herein; 
         FIG. 6  is a flow chart illustrating a process for registering a non-IMS device with an IMS network by monitoring SS7 signaling messages associated with the non-IMS device to identify activity involving the non-IMS device and for completing a call to the non-IMS device according to an embodiment of the subject matter described herein; 
         FIG. 7  is a flow chart illustrating a process for registering a non-IMS device with an IMS network based on subscriber action according to an embodiment of the subject matter described herein; 
         FIG. 8  is a network diagram illustrating an exemplary system for AIN to IMS trigger mapping according to an embodiment of the subject matter described herein; 
         FIG. 9  is a network diagram illustrating in more detail the interaction with a home subscriber server (HSS) function in performing AIN to IMS trigger mapping according to an embodiment of the subject described herein; and 
         FIG. 10  is a flow chart illustrating an exemplary process for AIN to IMS trigger mapping according to an embodiment of the subject matter described herein. 
     
    
    
     DETAILED DESCRIPTION 
     In light of the problems associated with providing calls and services to non-IMS devices using IMS network elements, the subject matter described herein includes methods, systems, and computer program products for providing IMS registration services and AIN trigger mapping for non-IMS devices.  FIG. 1  illustrates an exemplary system  100  for providing IMS registration services for non-IMS devices according to an embodiment of the subject matter described herein. In  FIG. 1 , serving call session control functions (S-CSCF-1)  102  and S-CSCF-2  104  are shown interconnected via an IMS network  106 . S-CSCF-1  102  and S-CSCF-2  104  provide access points for subscriber devices seeking to communicate using IMS network  106 . An IMS-compatible SIP device  108  is shown connected to S-CSCF-1  102 . SIP device  108  may be any 3G or higher generation device, such as a 3G cell phone or a personal digital assistant (PDA). SIP device  108  may generate and respond to SIP signaling messages for call setup and teardown. SIP device  108  is assumed to be IMS compatible and thus capable of registering with IMS network  106  through its associated S-CSCF-1  102 . 
     A softswitch  110  is shown interconnecting S-CSCF-2  104  to an end office  122  and a mobile switching center (MSC)  123 . Softswitch  110  may convert signaling between a signaling system 7 (SS7 ) signaling interface with end office  122  and MSC  123  and a SIP signaling interface with S-CSCF-2  104 . Softswitch  110  may include or control media gateways (not shown) to send media stream communications between end subscribers that communicate using system  100 . 
     As stated above, it may be desirable to establish calls and provide other services to non-IMS devices using IMS network elements. Examples of non-IMS devices shown in  FIG. 1  are PSTN phones  116  and  118  and 2G mobile phone  120 . These devices have conventionally been incapable of registering with the IMS network. In order to register non-IMS devices  116 , 118 , and  120  with IMS network  106 , an IMS proxy  200  may be provided. IMS proxy  200  may have an IP address that can be used as an identity for non-IMS devices  116 ,  118 , and  120  with the IMS network. In addition, IMS proxy  200  may perform registration on behalf of non-IMS devices  116 , 118 , or  120 . It may be desirable to register a non-IMS device  116 ,  118 , and  120  with the IMS network if the subscriber has subscribed with his or her service provider to receive IMS services and to maintain that registration for a finite time period during which the device may seek to access the IMS services. In the IMS world, IMS compatible devices may be registered when they are turned on or when they enter a service area. In the PSTN world, registration may be triggered by predetermined activity involving a non-IMS device. Three examples of activity that may be used to trigger IMS registration include change in presence status of a non-IMS device, detection of PSTN signaling messages involving a non-IMS device, or detection of predetermined subscriber action to register a non-IMS device. Examples of how each of these activities can be used to trigger IMS registration of a non-IMS device will be described in detail below. An IMS registration may be maintained for a finite time period after the activity that triggered the registration or until deregistration is expressly triggered. 
     In one example, IMS proxy  200  may receive updates from presence server  201  regarding the status of non-IMS devices  116 , 118 , and  120  in order to identify activity regarding non-IMS devices  116 ,  118 , and  120  and trigger IMS registration for the devices.  FIG. 2A  illustrates such an embodiment. In  FIG. 2A , IMS proxy  200  has an IP address of 192.100.10.10. IMS proxy  200  receives an update message from presence server concerning PSTN telephone number 9194605500 associated with non-IMS device  116 . In the example illustrated in  FIG. 2A , it is assumed that IMS proxy  200  subscribes to the telephone number 9194605500 with presence server  201  to receive updates whenever the status of device  116  changes. For example, when a subscriber associated with device  116  initiates a call, a change in presence status and a corresponding update message may be generated. In an alternate embodiment, IMS proxy  200  may query presence server  201  for status updates regarding each non-IMS device  116 , 118 , and  120 . IMS proxy  200  may be provisioned with the identities of devices  116 , 118 , and  120  at the time the subscribers subscribe to receive IMS service with their telephone service provider. 
     In response to receiving the update message, IMS proxy  200  may generate a corresponding registration message. The registration message may correlate the telephone number, 9194605500 to the IP address of IMS proxy  200 . The registration message may be sent to S-CSCF  104  and the corresponding registration information may be stored in a registration database  202 . In the illustrated example, registration database  202  includes a table structure  204 . Table  204  includes a first column  206  that associates SIP to/from identifiers with corresponding IP addresses in column  208 . In the illustrated example, row  210  associates the PSTN identifier 9194605500 with IP address 192.100.10.10, which corresponds to IMS proxy  200 . The second row in table  204  associates the PSTN identifiers of non-IMS device  118  with the IP address of proxy  200 . The third row  214  indicates that PSTN device is provisioned with S-CSCF  104  but is not registered. The final row in table  204  contains a mapping between a URL associated with an IMS subscriber and the corresponding IP address of the subscriber&#39;s device. 
     In the example illustrated in  FIG. 2A , activity involving non-IMS devices is identified and IMS registration is triggered based on presence status update messages concerning non-IMS devices. In an alternate example, activity involving non-IMS devices  116 ,  118  and  120  may be identified and IMS registration may be triggered through monitoring SS7 signaling messages involving non-IMS devices.  FIG. 2B  illustrates such an embodiment. In  FIG. 2B , IMS proxy  200  may include an interface with end office  122  and/or signaling link probes  220  and  222  that monitor signaling links that connect end office  122  and MSC  123  to softswitch  110 . The signaling links monitored may be SS7 over TDM links or SS7 over IP links. Accordingly, the signaling messages that are monitored may be SS7 messages over MTP transport or SS7 messages over IP transport, including SS7 over SIGTRAN over IP transport. 
     In the illustrated example, when non-IMS phone  116  initiates a call, end office  122  generates an ISUP IAM message. The ISUP IAM message may be used to trigger IMS registration of device  116  so that IMS services may be provided to device  116 . In another example, when a PSTN phone, such as device  116  initiates a call, a TCAP message may be generated. The TCAP message may be used to trigger IMS registration of a non-IMS device. In yet another example, a mobile phone, such as 2G handset  120 , may register with the network. In response to the registration, MSC  123  may generate a location update or registration notification message, depending on the network protocol being used. The location update or registration notification message may be used to trigger IMS registration of a non-IMS mobile device, such as device  120 . In response to detecting the signaling messages, IMS proxy may generate a corresponding registration message and send the registration message to S-CSCF  104 . S-CSCF  104  may be update registration database  202  to associate the PSTN identifier of the non-IMS device with the IP address of IMS proxy  200 . 
     In yet another alternate example, the action that triggers registration of a non-IMS device may be predetermined subscriber action, such as the dialing of predetermined registration digits that trigger an IMS registration.  FIG. 2C  illustrates such an embodiment. In  FIG. 2C , the subscriber at non-IMS device  116  may dial predetermined digits, such as *99 that are recognized by end office  122  as a trigger for IMS registration. In response to receiving the * 99  digits, end office may send a message, such as a TCAP message with a payload indicating an IMS registration, to IMS proxy  200 . IMS proxy  200  may generate a corresponding registration message that registers the non IMS device with S-CSCF  104 . 
     Once a registration action occurs, it may be desirable to terminate a registration after a predetermined time period. For example, if no further activity has been detected from an IMS device within an operator configurable time period after an initial registration, an entry may be removed from registration database  202 . Such a timeout-based deregistration mechanism may be implemented using a deregistration timer at S-CSCF  104 . Each entry may have an associated timestamp. If the timestamp of an entry is older than a predetermined amount, an entry may be removed. The timestamp of an entry may be updated each time new activity that would trigger an IMS registration is detected. 
       FIGS. 3A and 3B  illustrate the use of system  100  to connect a voice call between SIP device  108  and non-IMS phone  116  using the registration information generated and stored within registration database  202 . In the message flow example illustrated in  FIG. 3A , a SIP INVITE message is received by S-CSCF-2  104 . The SIP INVITE message includes the non-IMS called party number in the destination “To:” field and the source email address in the source “From:” field. 
     Upon receipt of the SIP INVITE message, S-CSCF-2  104  may modify and forward the SIP INVITE message. By use of the information within routing table 204, the SIP INVITE message may be modified by addition of an IP address associated with 2G IMS proxy  200  within an “IP Dest. Add:” field. By performing a lookup within routing table 204 using the called party number which may be found within SIP To/From field  206  of row  210 , S-CSCF-2  104  may identify the IP address of 2G IMS proxy  200  within IP destination address field  208  and may add it to the SIP INVITE message. In the message flow example illustrated within  FIG. 3A , the SIP INVITE message as modified may be forwarded to softswitch  110 . 
       FIG. 3B  illustrates the receipt of the modified SIP INVITE message by 2G IMS proxy  200  within softswitch  110 . Upon receipt of the modified SIP INVITE message, 2G IMS proxy  200  may originate and forward an SS7 initial address message (IAM) to end office  112 . The IAM message may include the called party number of non-IMS subscriber  116  as the destination of the IAM message. End office  112  terminates the IAM message and rings non-IMS phone  116 . End office  112  formulates and forwards an address complete message (ACM) to softswitch  110  to indicate that a trunk has been reserved for the voice call and to indicate that non-IMS phone  116  is ringing. Softswitch  110  originates and forwards a SIP  180  RINGING message to S-CSCF-2  104 . 
     Returning to  FIG. 3A , S-CSCF-2  104  forwards the SIP  180  RINGING message toward SIP device  108 . Message forwarding may continue in this fashion until the SIP  180  RINGING message is received by SIP device  108 . Call setup continues with a SIP  200  OK message (not shown) originating from end office  112  when non-IMS phone  116  is answered. At that point, voice communication may proceed and call setup may be completed. 
     Accordingly, IMS capable devices may use SIP signaling within network system  100  to initiate voice calls with non-IMS devices that are registered using the IMS registration services described above. Because non-IMS phones are registered with the IMS network, IMS calls and other services can be provided to such devices. 
       FIG. 4  illustrates an exemplary process for registering non-IMS phones with an IMS network. In step  400 , activity involving a non-IMS subscriber terminal is identified. Examples of activity that may be identified are described above with respect to  FIGS. 2A-2C . 
     In step  402 , the process may, in response to identifying the activity involving non-IMS subscriber terminal, perform an IMS network registration operation on behalf of the non-IMS subscriber terminal. Registration may be affected using IMS proxy  200  as illustrated in  FIGS. 2A-2C . 
       FIG. 5  illustrates an exemplary process for registering a non-IMS phone with an IMS network by having a softswitch query a presence server for registration information for the non-IMS phone and for establishing a call with the non-IMS phone. Referring to  FIG. 5 , in step  500 , a presence server receives new presence information for a non-IMS phone. For example, the new presence information may be an indication that the non-IMS phone is initiating a new call. 
     In step  502 , the presence server is queried for status information for the non-IMS phone. For example, IMS proxy  200  may query presence server  201  for the status of IMS phone  116 . Alternatively, IMS proxy  200  may subscribe to a non-IMS phone with the presence server so that proxy  200  will be notified when presence information changes for a non-IMS phone. At decision point  504 , IMS proxy  200  waits for an update message to be received from presence server  201 . As described above, the update message may be in response to either a query or a subscription to IMS phone  116  with presence server  201 . In step  506 , once IMS proxy receives the update message, IMS proxy  200  sends registration information to an S-CSCF, such as S-CSCF-2  104 , to register the non-IMS phone within an IMS network. 
     Once registered with the IMS network, call setup SIP signaling messages may be processed on behalf of the non-IMS phone. Such messages may be processed by softswitch  110  using registration information received from S-CSCF  104 . At decision point  508 , the process may wait to determine whether a SIP INVITE message has been received for the non-IMS phone. When a determination is made that a SIP INVITE message has been received for the non-IMS phone, the process may generate an SS7 IAM message and forward the IAM message to an end office, such as end office  122 , to initiate a voice call to the non-IMS phone at step  510 . 
     At decision point  512 , the process may wait for an SS7 ACM message to be received from end office  122 . Upon receipt of an ACM message, the process may generate a provisional SIP  180  RINGING message and forward the message to S-CSCF-2  104  as a response to the SIP INVITE message at block  514 . At decision point  516 , the process may wait for an SS7 ANM message to be received. Upon receipt of an ANM message, the process may generate a success SIP  200  OK message and forward the message to S-CSCF-2  104  as a success response to the SIP INVITE message at block  518  and a voice call may be established with the non-IMS phone via a voice trunk. 
       FIG. 6  illustrates an exemplary process for registering a non-IMS by monitoring SS7 signaling messages associated with the non-IMS phone and for completing a call with the non-IMS phone. In steps  600  and  602 , the process may monitor SS7 signaling messages to identify activity involving a non-IMS device that is provisioned to receive IMS services. For example, IMS proxy  200  may monitor SS7 signaling messages until ISUP, TCAP, MAP, IMAP, or other messages involving a non-IMS phone that is provisioned to receive IMS service are detected. In response to detecting such messages, control proceeds to step  604  where proxy  200  sends a registration message to the S-CSCF to register the non-IMS phone. 
     Once registered with the IMS network, call setup SIP signaling messages may be processed on behalf of the non-IMS phone. The call setup signaling messages may be processed by softswitch  110  using registration information obtained from S-CSCF  104 . At decision point  606 , the process may wait to determine whether a SIP INVITE message has been received for the non-IMS phone. When a determination is made that a SIP INVITE message has been received for the non-IMS phone, the process may generate an SS7 IAM message and forward the IAM message to an end office, such as end office  122 , to initiate a voice call to the non-IMS phone at block  608 . 
     At decision point  610 , the process may wait for an SS7 ACM message to be received from end office  122 . Upon receipt of an ACM message, the process may generate a provisional SIP  180  RINGING message and forward the message to S-CSCF-2  104  as a response to the SIP INVITE message at block  612 . At decision point  614 , the process may wait for an SS7 ANM message to be received. Upon receipt of an ANM message, the process may generate a success SIP  200  OK message and forward the message to S-CSCF-2  104  as a success response to the SIP INVITE message at block  616  and a voice call may be established with the non-IMS phone via a voice trunk. 
       FIG. 7  is a flow chart illustrating an exemplary process for registering a non-IMS subscriber terminal with an IMS network in response to subscriber action according to an embodiment of the subject matter described herein. Referring to  FIG. 7 , in step  700 , DTMF digits are received from a non-IMS subscriber terminal. The DTMF digits may be predetermined digits that are associated with an IMS registration request. The DTMF digits may be received by end office  122 . In step  702 , in response to the DTMF digits, end office  122  may communicate a registration request to IMS proxy  200 . The registration request may be a TCAP message with a payload indicating that an IMS registration is requested. In step  704 , in response to the IMS registration request, a registration message is sent from IMS proxy  200  to S-CSCF  104 . In block  706 , S-CSCF  104  associates the non-IMS subscriber terminal identifier with the IMS proxy identifier in its registration database. The non-IMS subscriber terminal may be the PSTN directory number of the subscriber terminal. For mobile phones, the non-IMS subscriber terminal may be the IMSI or MSISDN number associated with the terminal. The IMS proxy identifier may be an IP address associated with the IMS proxy. 
     In the examples described above, it is assumed that the non-IMS subscriber terminal is provisioned to receive IMS services. In an alternate example, a subscriber may subscribe to receive IMS services from any non-IMS terminal that the subscriber desires to use to communicate. For example, a subscriber may wish to use IMS services from a black phone in a hotel. In order to use the services, the black phone in the hotel must be registered with the IMS network. In order to register the black phone, the subscriber may initiate an IMS registration using a process similar to that illustrated in  FIG. 7  where the subscriber communicates predetermined DTMF digits to initiate an IMS registration. In addition to the registration initiating digits, the subscriber may also communicate a subscriber identifier to the IMS network. The subscriber identifier may be an identifier that the IMS network recognizes as an identifier that is provisioned to receive IMS services. The subscriber identifier along with the directory number of the hotel black phone may be registered with the IP address of the IMS proxy in a serving call session control function, as described above. 
     AIN to IMS Trigger Mapping 
     As described above, an additional problem with connecting non-IMS devices to an IMS network is providing a mechanism for mapping AIN triggers to registered non-IMS devices to IMS triggers, so that the IMS network can provide AIN-like services to the registered devices.  FIG. 8  is a network diagram illustrating an exemplary system for providing AIN to IMS trigger mapping according to an embodiment of the subject matter described herein. Referring to  FIG. 8 , softswitch  110  includes a 2G-AIN inter-working function  800  that maps PSTN triggers, such as call origination attempt triggers to AIN triggers. Softswitch  110  may also include 2G/IMS proxy  200 , although proxy  200  is not illustrated in  FIG. 8  for simplicity. The IMS network may include one or more platforms  802 ,  804 , and  806  that provide AIN-like services to IMS registered devices. In the illustrated example, platform  802  comprises a prepaid platform for providing prepaid calling services to IMS-registered devices. The IMS network may also include a home subscriber server (HSS)  808  that stores profiles for IMS-registered devices. The IMS network may further include S-CSCF  104 , which includes registration database  202  described above. 
     In operation, when an IMS-registered device, such as black phone  116  goes off hook, a TCAP call origination attempt trigger message is generated by end office  112 . AIN/IMS inter-working function  800  receives the TCAP message. In an alternate example, the trigger message may be a MAP message, an INAP message, or a CAMEL-based message. AIN/IMS inter-working function  800  may translate, map, or encapsulate the AIN trigger and associated information, such as the subscriber identifier, into a form that may be communicated using a SIP message, such as a SIP invite, info, message, or other SIP message. In the illustrated example, a SIP invite message is used to communicate the call origination attempt trigger to the IMS network. 
     The resulting trigger carrying SIP message is forwarded to S-CSCF  104  that is associated with the 2G subscriber. The 2G subscriber is assumed to have been previously registered by IMS proxy  200  described above. In one implementation, S-CSCF  104  uses the 2G subscriber information in the SIP trigger message to query HSS  808 . HSS  808  stores information associated with origination and termination attempt that is to be performed for the 2G subscriber. S-CSCF  104  receives information associated with the specified origination or termination attempt processing application and invokes the specified service on behalf of the 2G subscriber. 
       FIG. 9  illustrates in more detail the database stored by HSS  808 . In  FIG. 9 , HSS  808  includes a database  900  that stores information that indicates the type of trigger to be performed for a particular subscriber. In this example, database  900  indicates that the subscriber corresponding to 9194605500 receives application one (APP1) origination service. HSS  808  communicates this information to S-CSCF  104 . S-CSCF  104  then queries platform  802  for the appropriate information. In the illustrated example, platform  802  is a prepaid application. The prepaid application may determine whether device  116  has sufficient prepaid credit to originate a call. 
     Returning to  FIG. 8 , once the subscriber is determined to have sufficient credit, S-CSCF  104  may generate a SIP message including the prepaid result. AIN/IMS inter-working function  800  may receive the SIP message and translate, map, or decapsulate payload information in the SIP message and generate a corresponding response to the originally received 2G AIN trigger message. In the illustrated example, the response is a TCAP response message indicating the prepaid result. The response message may be communicated to end office  112 . 
       FIG. 10  is a flow chart illustrating an exemplary process for providing an IMS service in response to an AIN trigger according to an embodiment of the subject matter described herein. Referring to  FIG. 10 , in step  1000 , the firing of an AIN trigger concerning an IMS registered non-IMS device is detected. For example, referring to  FIG. 8 , AIN/IMS inter-working function  18  may detect a call originating attempt trigger corresponding to a call originated by device  116 . 
     Returning to  FIG. 10 , in step  1002 , an IMS service to be provided in response to the AIN trigger is identified. Returning to  FIG. 8 , inter-working function  800  communicates the firing of the call origination attempt trigger to the S-CSCF  104 . S-CSCF  104  queries HSS  808  to determine the type of IMS service to be provided. HSS  808  may determine whether an originating or terminating attempt trigger is to be applied based on the leg of the call for which the trigger was generated and may select the appropriate service to be applied for the subscriber and the trigger type. In  FIG. 9 , the IMS service to be provided is identified as APP1 service or prepaid service. 
     Returning to  FIG. 10 , in step  1004 , the IMS service is provided. Returning to  FIG. 8 , in order to provide the IMS service, S-CSCF  104  queries prepaid platform  802  and receives a response indicating whether or not the call can be completed. S-CSCF  104  assumes a prepaid result message to inter-working function  800 , which generates a corresponding TCAP message indicating the prepaid result and communicates the TCAP message to end office  122 . 
     The subject matter described herein is not limited to providing IMS services in response to call originating attempt triggers. For example, IMS services may also be provided in response to call terminating triggers. 
     Examples of services that may be provided in response to call terminating trigger include call screening services. 
     It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the subject matter described herein is defined by the claims as set forth hereinafter.