Abstract:
An Application Server entity in an IP Multimedia Subsystem (IMS) network comprises an interface for interfacing with an application and control logic which is arranged to inspect signaling information received from the application via the interface in the form of Extensible Markup Language (XML). The received signaling information is compared with stored rule data which specifies a relationship between an element in the signaling information and an action that should be taken and output data is generated based on the comparison. The Application Server can output operational measurements and/or charging information which more accurately reflect usage made of the Application Server resources. The need for a separate OSA/Parlay-X gateway can be avoided.

Description:
FIELD OF THE INVENTION 
     This invention relates to an IP Multimedia Subsystem (IMS) communications network and to implementing applications within such a network. 
     BACKGROUND TO THE INVENTION 
     The IP Multimedia Subsystem (IMS) is a Next Generation Networking (NGN) architecture for telecom operators, standardised by the Third Generation Partnership Project (3GPP), which can provide multimedia services to mobile and fixed terminals. IMS uses SIP (Session Initiation Protocol) based signaling and Internet Protocol (IP) connectivity. 
     A number of CSCF (Call Session Control Function) entities are used to establish a session within the IMS network and process SIP signaling packets. The CSCF entities are the Proxy-CSCF (P-CSCF), Interrogating-CSCF (I-CSCF) and Serving-CSCF (S-CSCF).  FIG. 1  shows part of an IMS network which includes the S-CSCF. The S-CSCF is responsible for handling registration processes, making routing decisions and maintaining session states. 
     Application servers (AS) within an IMS network can host and execute applications which provide services. An Application Server interfaces with the S-CSCF via an IMS Service Control (ISC) interface  24  which uses SIP signaling. Services can include call related services such as Call waiting, Call holding, Call forwarding, Call transfer, Call blocking services. Applications can also provide services such as notifying a user of particular information, such as stock prices or football results. Applications can be provided by the operator of the IMS network, with the application being hosted and executed by a SIP Application Server within the IMS network. 
     Alternatively, an application can be provided by a third party service provider external to the IMS network, as shown in  FIG. 1 . An Application Server  30  within the IMS network, called an Open Service Architecture Service Capability Server (OSA SCS), can provide IMS network resources to implement the external service. The S-CSCF communicates with the OSA-SCS over an IMS Service Control (ISM), SIP-based, signaling interface  24 . An OSA gateway  14  acts as an intermediary between the OSA SCS  30  and an Application  42  in the IT environment  40 . An Application can interface directly with the OSA Gateway  14  via an OSA Application Programming Interface (OSA API), which typically uses Parlay over CORBA. Application  41  interfaces with OSA Gateway  14  in this manner. For Applications which use XML, a Parlay-X interface is used and a Parlay-X gateway  16  is required. Application  42  uses a Parlay-X interface to communicate with the Parlay-X gateway  16 . The Parlay-X gateway uses a Parlay interface to communicate with the OSA gateway  14 . IT-based applications or web-based services typically exchange data in an XML format, and so the arrangement of gateways  14 ,  16  is usually required. It can be seen that, with the current architecture, two gateway elements are required whenever an application  42  which uses an XML messaging format is connected to the IMS network. This considerably increases the complexity of implementing services provided by third parties. 
     An Application Server  30  may be dedicated to a single service, or it may be shared by several services (as shown by ‘Application A’  41  and ‘Application B’  42  in  FIG. 1 ). Multiple Application Servers  30  can participate in a single session. For example, a particular call between two users may involve a call transfer service and a music-on-hold service. 
     Currently, Application Server billing triggers are all related to SIP and ISUP protocols and are resident at the CSCF (Call Session Control Function) plane. A disadvantage with this approach is that it is not possible to properly track the IMS network resources used by an IT-based service external to the IMS network. This problem can arise, for example, where an Application Server is used by multiple third parties. While conventional mechanisms can monitor use of the Application Server resources as a whole, they cannot monitor use by particular external applications. 
     Accordingly, the present invention seeks to reduce, or overcome, this problem. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention provides an Application Server entity for use in an IP Multimedia Subsystem (IMS) network, the Application Server comprising: 
     an interface for interfacing with an application; and, 
     control logic arranged to:
         inspect signaling information received from the application via the interface in the form of Extensible Markup Language (XML);   compare the received signaling information with stored rule data which specifies a relationship between an element in the signaling information and an action that should be taken; and,   generate output data on the basis of the comparison.       

     Web services exchange XML information streams to co-ordinate and action services. By providing an interface and control logic at the Application Server which can inspect XML flows, it is now possible to more accurately monitor usage of the Application Server resources by other entities, especially external applications. Preferably, the control logic outputs operational measurements and/or charging information. A further advantage of providing functionality at the Application Server which can inspect XML data is that the need for a separate OSA/Parlay-X gateway can be avoided. 
     The incoming XML streams are inspected by the Application Server for key information elements. Comparing the information elements with the stored rules allows the application server to generate a trigger to begin the billing and charging capture process. The capture process acquires the relevant information for use in charging a subscriber for the service. Inspecting XML streams at this point in the network can also ensure that the external applications adhere to limits imposed by the operator of the network. 
     Preferably, the charging information output by the Application Server is in a form which is compatible with a charging or billing entity in the IMS network. The charging information is preferably compliant with the 3GPP Rf standard as defined in 3GPP TS 32.260. For an offline charging scheme, the charging information can take the form of an Accounting Request for sending to a Charging Data Function (CDF) entity. For an online charging scheme, the charging information can take the form of a Credit Control Request (CCR) for sending to an Online Charging System (OCS). 
     As the control logic compares received XML data with stored rules, it can generate separate output messages, such as individual Accounting Request messages. Alternatively, the control logic can collate information during the process of comparing the received signaling information with stored rule data, and can output a collated batch of information. 
     The stored rule data can represent rules for multiple parties, such as: rules of the network operator; rules for a subscriber and rules for governance of the application. 
     The Application Server can be an Open Service Architecture Service Capability Server (OSA SCS), which interfaces to an external (third party) application. 
     A further aspect of the present invention provides a method of generating charging information in an IP Multimedia Subsystem (IMS) network, the method comprising, at an Application Server: 
     receiving signaling information via an interface from an application; and, 
     inspecting the received signaling information in the form of Extensible Markup Language (XML); 
     comparing the received signaling information with stored rule data which specifies a relationship between an element in the signaling information and an action that should be taken; and, 
     generating output data on the basis of the comparison. 
     The functionality described here can be implemented in software, hardware or a combination of these. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. Accordingly, another aspect of the invention provides software for implementing the method. The software may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium. The software may be delivered as a computer program product on a machine-readable carrier or it may be downloaded to the Application Server via a network connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows part of a conventional IMS network which supports applications provided by external parties; 
         FIG. 2  shows an IMS network according to an embodiment of the present invention; 
         FIG. 3  shows a rule checking function performed by the Application Server of  FIG. 2  which collates charging information in a charging data record; 
         FIG. 4  shows a rule checking function performed by the Application Server of  FIG. 2  which uses rules relating to different parties. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows the provision of services within an IMS network  20  in accordance with an embodiment of the present invention. For clarity, only those parts of the IMS network  20  relevant to the present invention are shown in detail. In this example embodiment it is assumed that a service is provided to a call session involving a user equipment (UE)  12  which accesses the IMS network via an access network  10 . Although not shown in detail, access network  10  will typically comprise a Radio Access Node (RAN) supporting a wireless connection with the user equipment  12 , and a connection will be established with the IMS network  20  via a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). An IMS session will involve a Proxy-Call Session Control Function (P-CSCF) and an Interrogating Call Session Control Function (I-CSCF), both shown generally as part  21  of the IMS network  20 , and a Serving-Call Session Control Function (S-CSCF)  22 . All of these features are well known. The Serving-Call Session Control Function (S-CSCF)  22  communicates with an Application Server (AS)  30  via an IMS Service Control (ISC) interface  24  which uses SIP-based signaling. Application Server  30  provides processing resources for implementing the service. As described above, the processing resources of an Application Server can be used to implement an Application  41 ,  42  provided by some entity external to the IMS network  20 . 
     In accordance with this invention, the interface  44  between the Application Server  30  and the external Applications Servers in the IT environment  40  hosting applications  41 ,  42  uses signaling messages in the Extensible Markup Language (XML) format. The XML data can be carried as, for example, XML over SOAP. 
     An Application Server incorporates control logic  32  which inspects the incoming XML data stream received over the interface  44  and compares information elements in the received XML data with stored data. The stored data can take the form of rules which specify an action that should be taken in response to a particular information element being received in the received XML data. Stated another way, the control logic  32  performs a filtering action on the received data. 
     A rule can instruct the control logic to look for a particular information element in the received data and to compare the value with a condition, such as a limit, or a range, which is specified in the rule. As an example, a rule can specify a number of messages that a user is allowed to send at a particular tariff and a tariff for the message (e.g. first ten messages per day free of charge, next ten messages per day at a price of $X per message). The inspection process can use rules which include multiple inspection criteria. Alternatively, or additionally, the inspection process can use multiple rules. The control logic  32  can use sets of rules which relate to different parties, such as the operator of the network  20 , the subscriber (UE  12 ), and the provider of the external applications  41 ,  42 . The rules can be stored  34  at the Application Server  30 , at a centralised database  31  in the IMS network  20 , or at individual databases ( 102 ,  104 ,  106 ,  FIG. 4 ). Where rules are stored at a database externally of the Application Server  30 , the Application Server  30  can perform a query to the database in real-time. The set, or multiple sets, of stored rules can be configured and updated as necessary. 
     One function which the control logic  32  can perform is a Charge Triggering Function (CTF). The control logic  32  compares information elements in the received data with stored data (billing triggers) which are indicative of charging events where charging information should be generated. The inspection process uses a set of rules. When received data matches one or more of the stored billing triggers (e.g. a condition specified in a rule) the control logic creates an information flow that captures any relevant information and creates an Accounting Request. The Charge Data Function (CDF) will act on this request to generate a charging record which is typically known as a Charging Data Record (CDR). An output function  33  of the Application Server  30  packages the charging information into the required output format. Preferably, the Accounting Request issued by the Application Server is compliant to the 3GPP Rf interface standard as defined in 3GPP TS 32.260 (3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Telecommunication management; Charging management; IP Multimedia Subsystem (IMS) charging). 3GPP TS 32.260 also defines how each Accounting Request is acknowledged by an Accounting Answer (ACA). It can be seen that because the CTF control logic  32  at the Application Server  30  is now inspecting XML flows, it is now possible to more accurately monitor usage of the AS resources by external applications. 
     One example of a rule is a simple instruction for the control logic to look for a particular information element in the received data, such as a particular subscriber identity (e.g. john@nortel.com), a called party, a calling party, or any other information carried in an XML signaling message carried across the interface, and to create an Accounting Request. 
     The Accounting Requests  35  are sent to a Charging Data Function (CDF)  50  over an interface  36 . The Charging Data Function  50  is a part of the IMS architecture which collates the accounting requests received from the AS, and the accounting requests received from other entities, such as accounting requests  25  received from the S-CSCF  22 . The CDF  50  creates a Charging Data Record (CDR) and sends it to a Charging Gateway Function (CGF)  52 . The CGF  52  subsequently issues billing information, via an interface  55 , to a billing system  56 . The billing system will add a charge to a subscriber&#39;s account. 
     In cases where the comparison process compares the XML data with multiple rules, a separate Accounting Request can be generated on each occasion where a rule instructs the control logic to generate charging information.  FIG. 3  schematically illustrates an alternative scheme performed by the control logic  32  at an Application Server  30  in which the comparison process compares all of the XML data in a particular signaling flow against a set of rules, and issues a single Accounting Request which collates all of the charging information which results from the comparison. This can reduce network signaling overheads and the burden of subsequently processing the multiple accounting requests. Application XML data is received by the Rule check function  60 . The rule check function  60  checks the XML data against a set of rules (Rule 1, Rule 2, . . . Rule N) stored in rules database  34 . On the first occasion when a comparison of a rule with the XML data results in a match, a create billing record function  61  is invoked. As an example, a rule may state: 
                                             If (/incomingData@address=‘john@nortel.com’)           {             billingRecord=new(billingRecord)           }                        
which creates a new Accounting Request based on match between a particular address stated in the rule with the same address appearing in the received XML data. The rule check function  60  proceeds to compare other rules in the database  34  against the received XML data. On each subsequent occasion when a rule matches the XML data, further data is appended to the Accounting Request by an append data to Accounting Request function  62 . A subsequent rule may state, for example:
 
                                             If(/incomingData@applicationRequested=’EffectiveCallRoute’)           {             append(billingRecord,EffectiveCallRoute)           }                        
If the incoming XML data structure called incomingData has the field applicationRequested then it is inspected to see if it has the value of ‘EffectiveCallRoute. If there is a match, then the incoming information is appended to the Accounting Request which is here called ‘billingRecord.’
 
     At the end of the rule checking process, the Accounting Request is closed by a close Accounting Request function  63  and the combined Accounting Request is sent from the Application Server via an output  33 . 
     Charging in an IMS network can be ‘offline’ or ‘online’. The present invention can be applied to either offline or online charging schemes. In an offline charging scheme, charging information is collected as a service is provided for the purpose of later charging a user for the use of that service (e.g. a charge is added to a monthly bill). Offline charging is implemented as described above, with an AS inspecting incoming XML data, comparing elements in the XML data with rules, and issuing Accounting Requests which are sent to a CDF. 
     In an online charging scheme, a user has an account which defines an amount of credit and a check is made, in real-time, whether the user has sufficient credit before granting or denying access to a service. In an online charging implementation of the present invention, the Application Server  30  inspects incoming XML data and compares elements in the XML data with rules using the control logic  32 , and then generates a Credit Control Request (CCR) to an Online Charging System (OCS)  54 . The CCR is preferably sent via the Ro interface as defined in 3GPP 32.360. The OCS  54  will compare the request with the subscriber&#39;s available credit and will reply with a Credit Control Authorisation (CCA) if sufficient credit exists. As the authorised credit is used up, or as stored rules are triggered at the control logic  32 , further credit control requests may be sent from the control logic  32  to the OCS  54 . At the end of the session, the control logic  32  will inform the OCS  54  to allow it to release any unused credit. The OCS  54  is responsible for keeping the Billing System informed of the usage of credit to allow billing records to be generated. 
       FIG. 3  schematically illustrates the inspection and comparison processes performed by Application Server  30 , using multiple rule sets. An Application  41  provides a score of a sports match (e.g. soccer game) each time a goal is scored. Application  41  is provided by a party who is independent of the operator of the IMS network  20 , such as a television company providing sports coverage. Typically, a subscriber will subscribe to the service at some point in time and the service provider will initiate delivery of a message within a predetermined time period of the score in a match changing. Application  41  sends a message  43  over interface  44  which includes XML data. The control logic  32  is shown implementing rules for three separate parties: the IMS network operator; the subscriber and the provider of the external Application. At stage  101 , an operational rules database  102  is consulted. The received XML data is compared against the set of operational rules. As a result of checking the operational rules, operational measurement data is captured. Stage  101  shows an example of an operational rule which counts the number of messages received which can be used as an operational measurement for the purposes of network management and may also be used to charge on a per-message basis. 
     At stage  103  a Home Subscriber Server (HSS)  104  is consulted. This invokes a set of rules which are particular to the subscriber, such as a list of applications that the subscriber wishes to receive messages from. The HSS can provide transparent data that is relevant to the specific application and which would only be valid in the scope of the application. Data captured at this stage could be used for charging or operational reasons. If an online charging scheme is used, at stage  103  a credit check can be performed by issuing a Credit Control Authorisation (CCA) message to the Online Charging System  54 . 
     At stage  105  a governance rules database  106  is consulted. This invokes a set of rules which govern the use that Application  41  can make of the IMS network, such as a maximum number of messages that the IMS network will deliver in response to instructions from that Application. The IT application rules can be used to handle and capture data that is related to the governance of the application within the overall network. A particular application may be limited to sending a certain number of messages per day, and this needs to be captured to guarantee the governance. Information captured at this stage can be sent to any interested parties. 
     Each of the stages described above can be used to capture, and output, operational data or charging information. At each of the stages  101 ,  103 ,  105  data can be generated as a result of comparing the received XML data with the rules. The data can be sent after that stage has been completed, or the data can be collated as described above. If generated data is destined for different entities (e.g. charging information destined for a charging entity, operational measurements destined for a network management entity) then the generated data can be collated based on the entity to which that data is destined. Charging information can be based upon the capture of operational data. As an example, if a session lasts for 3 minutes then this is in effect an operational data capture, which can be used to calculate the charging information. The operational data required for charging can be collected by the Application Server. 
     Although the above description has shown a wireless subscriber  12 , the invention is not limited to providing services to wireless subscribers. Any form of access network can be used to connect a user equipment to the IMS network. 
     The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention.