HK1096795B - Sessions in a communication system - Google Patents

Description

Sessions in a communication system

Technical Field

The present invention relates to communication systems, and in particular to policy control associated with sessions provided by means of communication systems.

Background

A communication system may be seen as a facility that enables communication sessions between two or more entities, such as user equipment and/or other nodes associated with the communication system. The communication may include, for example, communication of voice, data, multimedia, and so on. The user equipment may be equipped with two-way telephone calls or multi-way conference calls, for example. The user equipment may also be provided with a connection to an Application Server (AS), for example a service provider server, thereby enabling the use of the services provided by the application server.

A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define whether a user, or more precisely a user equipment, is equipped with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters applicable to the connection may also be defined. In other words, a specific set of "rules" on which the communication can be based needs to be defined to enable communication by means of the system.

Communication systems providing wireless communication for user equipment are known. An example of a wireless system is a Public Land Mobile Network (PLMN). PLMNs are typically based on cellular technology. In cellular systems, a Base Transceiver Station (BTS) or similar access entity serves wireless User Equipment (UE), also known as a Mobile Station (MS), via a radio interface between these entities. The communication over the wireless interface between the user equipment and the communication network element may be based on a suitable communication protocol. The operation of the base station apparatus and other apparatuses required for the communication may be controlled by one or several control entities. The various control entities may be interconnected.

One or more gateway nodes may also be provided for connecting the mobile network to other networks, for example to the Public Switched Telephone Network (PSTN) and/or other communication networks such as an IP (internet protocol) and/or other packet switched data networks. For example, if the requested service is provided by a service provider located in another network, the service request is routed to the other network via the mobile network and then to the service provider.

An example of a service that may be provided for a user, e.g. a subscriber of a communication system, is a so-called multimedia service. An example of a communication system capable of providing multimedia services is an Internet Protocol (IP) multimedia network. IP Multimedia (IM) functionality may be provided by means of an IP multimedia Core Network (CN) subsystem or simply an IP Multimedia Subsystem (IMs). The IMS includes various network entities for providing multimedia services.

The third generation partnership project (3GPP) has defined the use of General Packet Radio Service (GPRS) as the backbone communication system for providing IMS services. GPRS will therefore be used in this description as an example of a possible backbone communication system capable of implementing multimedia services. The third generation partnership project (3GPP) has also defined a reference architecture for the third generation (3G) core network, which will provide users of user equipment with access to multimedia services. This core network may be divided into three main domains. These are the Circuit Switched (CS) domain, the Packet Switched (PS) domain and the internet protocol multimedia (IM) domain.

The latter of these main domains, the IM domain, is used to ensure that multimedia services are adequately managed. The 3G IM domain supports the Session Initiation Protocol (SIP) developed by the Internet Engineering Task Force (IETF). Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying, and terminating sessions with one or more participants (endpoints).

SIP enables the establishment, modification and termination of multimedia sessions such as conferences. However, the details of the session, such as media type, codec or sampling rate, cannot be depicted. Instead, the SIP message body contains a session description encoded in the Session Description Protocol (SDP) format. A mechanism, called offer/answer mode, has been defined that enables two entities to agree on a multimedia session between them using SDP. In this mode, one participant provides a description of the intended conversation from its perspective to the other, while the other participants respond to the intended conversation from their perspective. The other participants may, for example, reduce the offer. The 3GPP allows operators of IP multimedia subsystems to define allowed media parameters for sessions in their networks; these parameters are either generic local policies or media policies, or subscription-based constraints. In these networks, only allowed media can be established. SDP violating the policy is rejected by the network.

Although the processing of SIP requests containing SDPs has been described for 3GPP, the processing of SIP responses, e.g., payload responses, has not been investigated. SIP allows for sending the SDP in a SIP response. However, if the SDP violates media policies, e.g. policies set by the operator but not known to the user, it is not possible to reject such a response.

Disclosure of Invention

Embodiments of the present invention aim to address one or several of the above problems.

According to one embodiment of the present invention, a method for handling a response to a message in a communication system is provided. The method comprises the following steps: sending a message from a first party to a second party; sending a response to the message, the response including at least one parameter that violates a policy for communication between the parties; detecting in the network controller that the response includes at least one parameter that violates the policy; and modifying the at least one parameter to be consistent with the policy.

According to another embodiment, a controller for a communication system is provided, the controller configured to process responses and requests between parties of a communication session, forward a message from a first party to a second party, check whether a response to the message includes at least one parameter that violates a policy for communication between the parties, and modify the at least one parameter to be consistent with the policy.

According to yet another embodiment, there is provided a communication system for providing communication sessions between parties connected thereto, the communication system comprising: a controller configured to process responses and requests between parties of a communication session, forward a message from a first party to a second party, check whether a response to the message includes at least one parameter that violates a policy for communicating between the parties, and modify the at least one parameter to be consistent with the policy.

In a more specific embodiment, at least one parameter is modified by the controller. In another embodiment, the at least one parameter is modified by the first party. The response may be passed from the second party to the first party without modification. It may be checked by the controller whether a further message from the first party in response to the response comprises at least one parameter violating the policy.

Embodiments may provide advantages when handling sessions with non-admissible parameters. The processing may be compatible. The system can better anticipate the various possible scenarios caused by conflicting policies.

Drawings

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 illustrates one embodiment of the present invention;

FIG. 2 is a signaling flow diagram illustrating the operation of one aspect of the present invention; and

fig. 3 is a signaling flow diagram illustrating the operation of another aspect of the present invention.

Detailed Description

Certain embodiments of the present invention will be described hereinafter, by way of example, with reference to an exemplary architecture of a third generation (3G) mobile communication system. However, it should be understood that the embodiments may be applied to any suitable communication system.

Referring to fig. 1, there is shown an example of a network architecture in which the present invention may be implemented. In fig. 1, an IP multimedia network 45 is provided for providing IP multimedia services to IP multimedia network subscribers.

As described above, IP Multimedia (IM) functionality may be provided by means of a mobile communication system. A mobile communication system is typically arranged to serve a plurality of mobile user equipment, typically via a wireless interface between the user equipment and at least one base station of the communication system. A mobile communication system may be logically divided into a Radio Access Network (RAN) and a Core Network (CN).

In the system, the base stations 31 and 40 are arranged to transmit/receive signals to/from mobile user equipment 30, 41 of mobile users, i.e. subscribers, via a wireless interface between the user equipment and the radio access network. Thus, the mobile user equipment is able to transmit/receive signals to/from the radio access network via the radio interface.

In the arrangement shown, the user equipment 30, 41 may access the IMS network 45 via access networks associated with the base stations 31, 40, respectively. It should be understood that although fig. 1 shows only two base stations for reasons of simplicity, a typical communication network system typically includes a plurality of base stations.

The mobile user equipment may comprise any suitable mobile user equipment suitable for Internet Protocol (IP) communications to connect to a network. For example, a mobile user may access a cellular network by means of a Personal Computer (PC), a Personal Data Assistant (PDA), a Mobile Station (MS), or the like. The following examples are described in the context of a mobile station.

Those skilled in the art are familiar with the features and operation of a typical mobile station. It is therefore sufficient to note that a user may use a mobile station for tasks such as for making and receiving phone calls, for receiving/sending data from/to a network, and for experiencing multimedia content or otherwise using multimedia services. The mobile station may comprise an antenna for wirelessly receiving/transmitting signals from/to a base station of the mobile communication network. The mobile station may also be provided with a display for displaying images and other graphical information to the user of the mobile user equipment. A camera device may be provided for capturing still or video images. Speaker means are also typically provided. The operation of the mobile station may be controlled by means of a suitable user interface, such as control buttons, voice commands, etc. Furthermore, the mobile station is provided with a processor entity and memory means.

It should be understood that although only two mobile stations are shown in fig. 1 for simplicity, multiple mobile stations may be in simultaneous communication with a base station of a mobile communication system.

The Core Network (CN) entities typically include various switching and other control entities and gateways for enabling communication via multiple radio access networks and also for interfacing a single communication system with one or more communication systems, such as other cellular systems and/or fixed line communication systems. In a 3GPP system, the radio access network controller is typically connected to one or more appropriate core network entities, such as, but not limited to, a serving general packet radio service support node (SGSN), see controllers 33 and 39 of fig. 1. The radio access network communicates with the serving GPRS support node via an appropriate interface, for example over the Iu interface. Although not shown, the SGSN typically has access to a designated subscriber database configured for storing information associated with subscriptions of the respective user equipment. The serving GPRS support node then communicates with the gateway GPRS support node, typically via the GPRS backbone network 32. This interface is typically a switched packet data interface.

In 3GPP networks, packet data sessions are established to carry traffic flows over the network. Such packet data sessions are often referred to as Packet Data Protocol (PDP) contexts. The PDP context may include: a radio bearer provided between the user equipment and the radio network controller; a radio access bearer provided between the user equipment, the radio network controller and the SGSN; and an exchange packet data channel provided between the serving GPRS service node and the gateway GPRS service node. Each PDP context typically provides a communication path between a particular user equipment and the gateway GPRS support node, and once established, each PDP context is typically capable of carrying multiple flows. Each flow normally represents, for example, a particular service and/or a media component of a particular service. A PDP context thus often represents a logical communication pathway for one or more flows traversing the network. In order to implement a PDP context between the user equipment and the serving GPRS support node, Radio Access Bearers (RABs) need to be established, which typically allow data transmission for the user equipment. The implementation of these logical and physical channels is known to those skilled in the art and is therefore not discussed further herein.

Communication systems have evolved in the direction in which user equipment is served by means of various functions of a data network handled by a controller entity, e.g. a server. For example, in the current third generation (3G) wireless multimedia network architecture, it is assumed that several different servers providing various control functions are used for service provision control. This includes functions such as Call State Control Functions (CSCFs) and the like. Call state control functions may be divided into various categories such as proxy call state control functions (P-CSCFs), interrogating call state control functions (I-CSCFs), and serving call state control functions (S-CSCFs). It should be understood that similar functions may be referred to by different names in different systems. For example, in some applications, a CSCF may be referred to as a call session control function.

A user wishing to use a service provided by the IMS system may first need to register with a serving controller, such as a serving call session control function (S-CSCF) 36. As shown in fig. 1, communications between the S-CSCF36 and the user equipment may be routed via at least one proxy call session control function (P-CSCF) 35. The proxy CSCF35 is thus used to proxy messages from the GGSN34 to the serving call session control function 36. The serving controller, CSCF36 in fig. 1, then provides the control entity with which the user equipment 30 needs to register. This registration is required to enable the user equipment to request services from the communication system.

A policy control entity 37 may also be provided. The policy control entity 37 may be configured to store the required policy information in its database 38. The network entity may query the policy control entity for various purposes, such as to obtain information related to the media policy of a particular user. The policy control entity may be provided by means of a Policy Decision Function (PDF) connected to the P-CSCF and the GGSN.

Fig. 1 also shows an application server 50. The user equipment may be connected via a GPRS network to an application server that is connected to one or more data networks, such as, but not limited to, an exemplary Internet Protocol (IP) network. It should be understood that a large number of application servers may be connected to each data network.

Although this is not always necessary, the system of figure 1 may be further arranged such that a user who has been provisioned with the required communication resources through the backbone network and registered with the service controller 36 must initiate use of the service provided by the application server 50 by sending a request for the desired service over the communication system to the service controller.

The examples are based on the recognition that: it may be advantageous if the predefined action can be taken after a breach of the media policy is detected. This action is preferably performed in a proxy network element, such as the P-CSCF 35.

More specific exemplary embodiments described below handle messages, such as SIP responses, that contain session parameters, such as offers that are inconsistent with the operator media policy stored in PDF37, and therefore require action to be performed in order to bring the at least one violating parameter into agreement with the policy.

As shown in fig. 2, the appropriate CSCF may modify the parameters before forwarding them. In response to the "INVITE" from the first user equipment 30, the 200OK sent from the second user equipment 41 contains an SDP offer that violates the media policy. The CSCF modifies the offer such that the SDP offer is in accordance with the media policy before being sent further as an SDP offer to the first user equipment 30. The acknowledgement in the ACK will be acceptable to the media policy.

If the reduced media is not satisfactory to the parties (in worse case it may happen that all media in the transaction is cancelled), they may initiate a new reINVITE. This is possible because the multimedia session is not released by the network.

According to an alternative shown in fig. 3, the appropriate CSCF may ignore the problem and forward the unmodified SIP message containing the SDP offer. The temporary response from the second user equipment to the INVITE from the first user equipment may contain an SDP offer that violates the media policy.

In other words, the SDP offer may be forwarded as accepted. The CSCF then waits for a modified and allowed session parameter answer from the other party. An SDP answer may be received in the PRACK request and the PRACK is then checked against the media policy. If not, the PRACK request is denied. The CSCF can thus reject the offer/answer if the final parameters still violate the media policy.

The rejection may contain an allowable media policy. This may be provided according to fig. 2.

A more specific example of the operation of the P-CSCF35 according to an embodiment will be described below. When the P-CSCF35 receives a SIP request containing SDP offer, the P-CSCF may check the media parameters in the received SDP. If the P-CSCF35 finds any media parameters that are not allowed on the network, e.g. due to local policies, the P-CSCF may return an "not acceptable here" response containing the SDP payload. The SDP payload may contain all media types, codecs and other SDP parameters allowed according to local policy, or a subset of these allowed parameters based on the configuration of the P-CSCF operator. This subset may depend on the content of the received SIP request.

When the P-CSCF receives a reliable provisional SIP response, e.g. the SIP183 message of fig. 3, containing the SDP offer, the P-CSCF may be configured not to check the media parameters in the received SDP offer. Thus, the SDP is allowed to pass transparently through the P-CSCF35, even though the offer contains media parameters that are not allowed by local policies on the network. This is advantageous since it may not be possible for the P-CSCF to reject the SIP response. Alternatively, the P-CSCF may take action based on a subsequent PRACK request containing an SDP answer to this offer, and so check this. If necessary, i.e. the SDP answer reduced by the User Equipment (UE) still violates the local policy, the P-CSCF may return a "not acceptable here" response containing the local policy as allowed SDP payload.

When the P-CSCF receives a 2xx final SIP response for an INVITE request in a dialog containing an acknowledgement of the SDP offer, i.e. for a reINVITE, the P-CSCF may check the media parameters in the received SDP offer. If the P-CSCF finds media parameters that are not allowed on the network, for example, by the local policy, the P-CSCF may intersect the SDP offer with the local policy, as shown in fig. 2. This approach may ensure that the SDP answer sent in the "ACK" request is allowed by local policy and is also a valid answer for the SDP offer initially received in the P-CSCF.

A more specific example will be described next in which operations according to embodiments are performed in the S-CSCF 36. When the S-CSCF36 receives a SIP request containing an SDP, the S-CSCF may check the media parameters in the received SDP. The S-CSCF may return an "not acceptable here" response containing the SDP payload if it finds any media parameters that are not allowed based on local policy or subscription. As above, the SDP payload may contain all media types, codecs and other SDP parameters allowed according to local policy and user subscription, or a subset of these allowed parameters based on the configuration of the S-CSCF operator. This subset may depend on the content of the received SIP request.

When the S-CSCF receives a reliable temporary SIP response containing the SDP offer, the S-CSCF may be configured not to check the media parameters in the received SDP offer. Thus, even media parameters that are not allowed on the network by local or other policies may still be allowed because it may not be possible to reject the SIP response. The P-CSCF may then check the subsequent PRACK request containing the SDP answer for this offer and continue the SIP request as described above if necessary, i.e. the SDP answer reduced by the User Equipment (UE) still violates local policy.

When the S-CSCF receives a 2xx final SIP response for an INVITE request in a confirmed dialog containing an SDP offer, the S-CSCF may verify the media parameters in the received SDP offer. If the S-CSCF finds any media parameters that the local policy does not allow on the network, the S-CSCF intersects the SDP offer with the local policy. This approach may ensure that the SDP answer sent in the ACK message is allowed by local policy and is also a valid answer for the SDP offer initially received in the S-CSCF.

According to one possibility, the communication system is configured such that the SIP200OK of the initial INVITE cannot contain SDP offers. In this case, either the initial INVITE request contains the offer or there may be a temporary reliable response with the SDP offer.

An inappropriate SDP model that the network may need to handle is briefly described below. According to one scenario, SDP offer is not answered according to the SDP offer/answer mode. In this case, the SDP offer may be discarded. In another case, there is no SDP payload in the SIP message, although the SDP offer/answer mode controls it. The intermediate server may then appear transparent. SIP messages may also contain invalid SDP offers, such as syntax semantic errors, or corrupt SDP offer/answer patterns. This may be considered a cancelled offer. The SIP message may also contain an invalid SDP answer. The corresponding offer is discarded and the P-CSCF does not send policy setup information to the policy decision function.

It should be appreciated that although embodiments of the present invention have been described with respect to user equipment, such as mobile stations, embodiments of the present invention are applicable to any other type of equipment.

Examples of the present invention have been described in the context of IMS systems and GPRS networks. The invention is also applicable to any other access technology including code division multiple access, frequency division multiple access or time division multiple access and any hybrids thereof. Furthermore, the given example is described in the context of a so-called all IP network with all IP entities. The invention is also applicable to any other suitable communication system, both wireless and fixed line systems, as well as standards and protocols. Examples of other possible communication systems capable of wireless data communication services include, but are not limited to, third generation mobile communication systems such as Universal Mobile Telecommunications System (UMTS), i-phone or CDMA2000 and digital trunked communication (TETRA) systems, enhanced data rates for GSM evolution (EDGE) mobile data networks. Examples of fixed line systems include various types of broadband technologies that provide internet access to users in different locations, such as homes and offices. Regardless of the standards and protocols used for the communication network, the present invention can be applied in all communication networks that require policy control in association with a session.

Embodiments of the present invention have been described in the context of proxy and serving call state control functions. Embodiments of the invention may be applied to other network elements where applicable.

It should also be noted that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.

Claims (19)

1. A method in a communication system for handling responses to messages, comprising:

in the communication system, a message from a first party is delivered to a second party;

receiving a response to the message from the second party, the response including at least one parameter that violates a policy for communicating between the first party and the second party;

communicating an unmodified response from the second party to the first party;

determining in the network controller that one or more of said at least one parameter violates the policy, wherein said determining comprises detecting at least one parameter that violates the policy in a further message sent from the first party to the network controller;

wherein the method further comprises:

in response to said detection, sending by the network controller to the first party a further message containing the payload allowed by the policy.

2. The method of claim 1, wherein the other message includes a definition of the policy.

3. The method of claim 1, wherein sending the other message comprises:

information of at least one parameter consistent with the policy is transmitted.

4. A controller for handling responses to messages in a communication system, comprising:

means for forwarding a message from a first party to a second party in the communication system;

means for communicating an unmodified response to the message from the second party to the first party, the response including at least one parameter that violates a policy for communicating between the first party and the second party;

means for determining in the network controller that one or more of said at least one parameter violates the policy, said determining comprising detecting the at least one parameter that violates the policy in a further message from the first party; and

means for sending another message to the first party containing a payload allowed by the policy in response to detecting that the at least one parameter violates the policy.

5. The controller of claim 4, wherein the another message includes a definition of the policy.

6. The controller of claim 4, wherein the means for sending the another message is configured to send information of the at least one parameter consistent with the policy.

7. A method in a communication system for handling responses to messages, comprising:

communicating a message from a first party to a second party in the communication system;

receiving a response comprising at least one parameter that violates a policy for communicating between the first party and the second party;

communicating an unmodified response from the second party to the first party;

receiving a further message from the first party, the further message comprising one or more of the at least one parameter that violates the policy;

detecting in the network controller that the further message comprises one or more of the at least one parameter that violates the policy; and

in response to detecting at least one parameter that violates the policy, another message is sent to the first party containing a payload allowed by the policy.

8. The method of claim 7, wherein the other message includes a definition of the policy.

9. A controller for handling responses to messages in a communication system, comprising:

means for forwarding a message from a first party to a second party in a communication system;

means for forwarding an unmodified response from the second party to the first party, the response comprising at least one parameter that violates a policy for communication between the first party and the second party;

means for receiving a further message from the first party, the further message comprising the at least one parameter that violates the policy;

means for detecting that the further message comprises the at least one parameter that violates the policy; and

means for sending another message to the first party containing a payload allowed by the policy in response to detecting at least one parameter that violates the policy.

10. The controller of claim 9, wherein the another message includes a definition of the policy.

11. A user equipment, comprising:

transmitting means for transmitting a message to another user equipment;

receiving means for receiving a response to the message from the further user equipment, the response comprising at least one parameter that violates a policy for communicating between the user equipment and the further user equipment; and

wherein the sending means is configured to further send a further message to the network controller, the further message comprising at least one parameter violating the policy, wherein the receiving means is further configured to receive the definition of the policy from the network controller, and wherein the sending means is further configured to send a further message to the further user equipment in accordance with the policy.

12. The user equipment of claim 11, wherein the network controller is further configured to modify at least one parameter in response to detecting that the at least one parameter violates the policy.

13. The user equipment of claim 11 or 12, wherein the network controller is configured to modify the at least one parameter to be consistent with a local policy.

14. A method in a user equipment, comprising:

sending, at a first user equipment, a message to a second user equipment;

receiving, at the first user equipment, a response to the message from the second user equipment, the response including at least one parameter that violates a policy for communication between the first user equipment and the second user equipment;

sending, at the first user equipment, a further message to a network controller, the further message comprising at least one parameter that violates the policy;

receiving a definition of the policy from the network controller; and

and sending a further message consistent with the policy to the second user equipment.

15. A method in a communication system for handling responses to messages, comprising:

forwarding the session initiation protocol message from the first user equipment to the second user equipment;

forwarding a session initiation protocol response from the second user equipment to the first user equipment without any modification, the session initiation protocol response containing a session description protocol offer, the session initiation protocol response including at least one parameter that violates a policy for communicating between the first party and the second party;

receiving a subsequent request from the first party and checking whether the request contains a session description protocol answer to the offer that violates a local policy; and

if the session description protocol reply violates the local policy, a response is returned that is unacceptable for the reply, the response containing the session description protocol payload allowed by the local policy.

16. The method of claim 15, wherein the first party is a user equipment and the session description protocol answer is reduced at the user equipment.

17. A network controller for handling responses to messages in a communication system, comprising:

means for forwarding a session initiation protocol request from a first user equipment to a second user equipment;

means for forwarding a session initiation protocol response from said second user equipment to said first user equipment without any modification, the session initiation protocol response containing a session description protocol offer, the session initiation protocol response comprising at least one parameter that violates a policy for communicating between the first party and the second party;

means for receiving a subsequent request from the first party and checking whether the request contains a session description protocol answer to the offer that violates a local policy; and

means for returning a response that the reply is unacceptable if the session description protocol reply violates the local policy, the response containing a session description protocol payload allowed by the local policy.

18. The network controller of claim 17, wherein the network controller is a proxy call session control function.

19. The network controller of claim 17, wherein the network controller is a serving call session control function.