Patent Publication Number: US-2007118881-A1

Title: Application control at a policy server

Description:
FIELD OF THE INVENTION  
      This invention relates to signalling within a packet-based communications system to establish a connection.  
     BACKGROUND TO THE INVENTION  
      Communications networks are increasingly being used to deliver a range of multimedia communications traffic via packet-based delivery protocols.  
      It is generally preferred that packet-based networks use some form of admission control which controls access to the shared network and helps to maintain a particular quality of service (QoS) for the traffic that is permitted access to the network. Admission control can be performed by policy controllers in the network, with enforcement occurring at policy enforcement points (PEP). Admitted traffic can also be policed by the PEP, during the duration of a connection, to ensure that the parameters agreed at the beginning of the connection are adhered to.  
       FIG. 1  shows a communications system which is based around a packet-based network  30 . Terminals  10 ,  20  are connected to network  30  via policy enforcement points, such as media gateways or routers, which police connections. When setting up a connection across a packet-based network, signalling  15  occurs between an endpoint  10  and an Application Manager  40 . The Application Manager  40  determines capabilities of the endpoints  10 ,  20 , such as the types of codec that each endpoint supports. The Application Manager  40  makes a selection of certain parameters (e.g. selecting what it determines is the best codec and hence bandwidth for the connection) and submits a connection request to the policy server  50 . The policy server  50  determines whether a connection, with the requested parameters, can be supported and returns a reply to the Application Manager. If the connection cannot be supported, then the Application Manager  40  can either submit a further connection request or it can return an error message to the endpoint  10 . If the connection cannot be supported then further requests can be submitted by the Application Manager, which can result in a high volume of signalling messages between the Application Manager and policy server.  
      The present invention seeks to provide an alternative architecture which is more efficient.  
     SUMMARY OF THE INVENTION  
      A first aspect of the present invention provides a method of establishing a connection between first and second endpoints in a packet-based communication system which comprises an application manager and a policy server, the method comprising, at the application manager:  
      receiving information about the required connection;  
      sending, to the policy server, application control related information for the required connection;  
      receiving, from the policy server, at least one application control parameter selected by the policy server.  
      By sending application control information to the policy server, such as the list of codecs available at the endpoints, the policy server can use this information to decide certain application control parameters relating to the connection, such as selecting which codecs should be used by the endpoints. Making application control selections at the policy server, rather than at the application manager, can significantly reduce signalling between the application manager and the policy server compared to existing methods. This is because the policy server is better placed to make the selection.  
      The application control information can be carried between the application manager and policy server in various ways. The information can be carried by an application control protocol, such as the Session Initiation Protocol (SIP), or it can be carried by modified forms of policy control protocols such as the Common Open Policy Service (COPS), Diameter, SOAP/XML or Parlay. Conventionally, application control protocols are not used to interface with a policy server, and policy control protocols do not carry application control parameters such as a list of supported codecs.  
      Further aspects of the invention relate to a method performed by a policy server. Still further aspects of the invention relate to an application manager and a policy server which implement these methods.  
      The functionality described here can be implemented in software, hardware or a combination of these. Accordingly, further aspects of the invention provide a computer program product for implementing any combination of the steps of the methods according to the invention. It will be appreciated that the software can be installed on the host apparatus (e.g. the application manager or policy server) at any point during the life of the equipment. 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 directly to the host via a network connection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the invention will be described with reference to the accompanying drawings in which:  
       FIG. 1  shows a generalised architecture of a packet-based communications system;  
       FIG. 2  shows an equivalent architecture to  FIG. 1  for a PacketCable system;  
       FIG. 3  shows the network of  FIG. 1  with the addition of media proxy control;  
       FIG. 4  shows an equivalent architecture to  FIG. 1  for a 3G wireless system; 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      Referring again to  FIG. 1 , this shows a general overview of a system which includes a packet-based network  30 . Although not shown, network  30  includes routers which are interconnected by communication links in a conventional manner. The network  30  can be implemented by wireline, wireless or a combination of both wireline and wireless technologies. Although shown as one overall network, network  30  can comprise a number of individual networks which are interconnected. Several specific architectures for PacketCable and 3G wireless networks are described later, and these share the same general features shown here.  
      Endpoints  10 ,  20  can be terminals which support a packet-based connection. Alternatively, endpoints  10 ,  20  can be Media Gateways which perform conversion between the circuit-switched domain, which is used to serve terminals (such as conventional telephone terminals) local to the gateway, and the packet-switched domain used across network  30 .  
      An Application Manager  40  is a network entity which defines service control policies and co-ordinates subscriber-initiated requests for application sessions with access to the network resources that are required to meet those requests. The Application Manager  40  communicates  15 ,  25  with end points  10 ,  20  using a signalling protocol such as the Session Initiation Protocol (SIP).  
      The Application Manager  40  authenticates and authorizes client requests based on Service Control Domain policies. This ensures that clients making a request are entitled to use the requested services. For client requests that pass these checks, the Application Manager  40  determines the particular QoS parameters necessary to deliver the service to the client, based on its knowledge of the requested service. The Application Manager  40  communicates with a Policy Server  50  across an interface  45 . The Application Manager  40  sends a request for the required resources to the appropriate Policy Server  50  via interface  45 . The Policy Manager  50  may deny the request, based on network policies, or it may process (forward) the request to entities within network  30 . This process can include communicating  35 ,  36  with Policy Enforcement Points (PEPs)  31 ,  32  that are responsible for admission control and enforcement. A connection between endpoints  10 ,  20  may require the policy server  50  to communicate with a larger number of PEPs, particularly if the connection spans several differently owned/operated networks. Policy decisions can be based on a number of factors, such as: parameters associated with the request and the status of available resources; the identity of the particular client and associated profile information; application parameters; security considerations.  
      Policy Enforcement Points (PEPs)  31 ,  32  within the network  30  act as gates, allowing certain traffic flows to pass. As part of a call establishment process, policy server  50  communicates with PEPs to ensure that sufficient resources are available to meet the request received from the Application Manager  40 . If resources are available, then the Policy Server  50  returns an acknowledgement message to the Application Manager  40  across interface  45 . A communication path is then established between the endpoints  10 ,  20  which includes path  12 , between client  10  and PEP  31 , a path across network  30 , and a path  22  between PEP  32  and the remote client  20 .  
      Various protocols have been proposed for use across interface  45  between the Application Manager  40  and Policy Sever  50 .  FIG. 2  shows a system according to the PacketCable Multimedia Specification (PKT-SP-MM-I01-030627). A cable modem  110  equates to the endpoint  10 . The interface  15  between the cable modem  110  and the Application Manager  40  is called the ‘pkt-mm7’ interface and the interface  45  between the Application Manager  40  and Policy Server  50  is called the ‘pkt-mm-3’ interface. It has been recommended that the Common Open Policy Service (COPS) is used across the pkt-mm3 interface  45 . The Common Open Policy Service (COPS) is defined in RFC 2748, to which the skilled reader is directed for further information. Policy Server  50  communicates with a Cable Modem Termination System (CMTS)  130  via a ‘pkt-mm2’ interface  135  using COPS. CMTS  130  authorizes resource requests.  
      Operation of the network using COPS messaging on interface  45  will now be described in more detail. Conventionally, COPS sends information on a per-flow basis. A requested service between endpoints  10 ,  20  may comprise several related flows of traffic. As an example, a video conferencing service will include conversational voice, real-time video and data representing slides to be discussed during the conference. As part of a connection establishment process, Application Manager  40  receives parameters of the requested service, the capabilities of the endpoints  10 ,  20 , and determines what bandwidth is required. Application Manager  40  individually issues requests for each of the required flows, even if they are related to one another as part of a common service. Each request includes information about the required bandwidth, QoS and Class of service. The required bandwidth is determined by finding the codecs available at each endpoint  10 ,  20  and choosing a preferred combination (often, but not necessarily, a codec common to both endpoints  10 ,  20  which offers the best quality (greatest bandwidth)). Once the codec has been selected, this is translated into a required bandwidth which is used in the request. To give several examples, a G.711 codec with a packetisation rate of 10 ms over an IP transmission network has a bandwidth requirement of 102 kbps whereas a G.729 codec with the same 10 ms packetisation rate over an IP transmission network has a bandwidth requirement of 46 kbps.  
      Policy Server  50  verifies each request against network policies, determines whether network resources are available to meet the request and replies to the Application Manager  40  with an acknowledgement message.  
      In accordance with an embodiment of the invention, the Application Manager  40  issues a request across interface  45  which includes information for the group of related flows. This can be carried by a modified form of COPS messaging. This allows the Policy Server to consider all of the related flows (e.g. voice, video and data) at the same time, and to request/reserve network resources based on the combination of flows. In addition, the Application Manager  40  does not select the preferred codec itself, but passes a list of supported codecs to the Policy Sever  50 . The list of codecs can be a list of codecs which is common to both endpoints (i.e. the AS looks at the codecs supported by both endpoints and only sends these), or it can be the list of codecs supported by each endpoint.  
      The Policy Server  40  inspects the codec information and submits a request for resources based on a particular policy.  
      As the Policy Server  50  interacts with the network entities responsible for reserving bandwidth, it is better placed to make a decision on what bandwidth can be supported by the network and hence what codecs can be used. If the network  30  can support the group of flows, the Policy Server  50  returns an acknowledgement message to the Application Manager  40 . The acknowledgement includes a codec, selected by the Policy Server  50 , which is appropriate for the bandwidth reserved on network  30 . If there is more than flow, then the acknowledgement includes a selected codec for each flow. By considering a set of related flows together, and knowing the candidate codecs for each flow, the Policy Server  50  can adjust the resource reservation by choosing appropriate codecs for each flow. This is more efficient than repeated signalling exchanges between the Application Manager  40  and Policy Server  50  across interface  45  which specify single bandwidth values on a per-flow basis.  
      In accordance with an embodiment of the invention, the Policy Server  50  also takes part in Media Proxy control.  FIG. 3  shows a similar network to  FIG. 1 , with the addition of a Media Proxy  70  within network  30 . As part of the connection establishment process, Application Manager  40  sends the address and port(s) of the endpoints  10 ,  20  of the requested connection to the Policy Server  50 . Policy Server  50  selects a suitable media proxy  35  for the requested flow(s) and passes an address and port of the media proxy  70  that should be used by the endpoints  10 ,  20 . The reason for doing this is because the Policy Server  50  has a view of the network which the application server does not, so it can select the optimal media proxy based on available resources (e.g. bandwidth).  
      The above description refers to COPS. Standards bodies in other areas have considered other kinds of protocol for the interface  45  between the Application Manager  40  and Policy Server  50 .  FIG. 4  shows a Third Generation (3G) wireless network. An endpoint is represented by a Session Initiation Protocol (SIP) client  310 . The Application Manager  40  is represented by a Proxy Call Session Control Function (P-CSCF)  340  which performs a similar function of authenticating a user&#39;s requests for services. The interface between the P-CSCF 340 and Policy Server  50  is called the Gq interface. Further information about the Gq interface can be found in the documents: 3 rd  Generation Partnership Project; Technical Specification Group Services and System Aspects; End-to-end Quality of Service (QoS) concept and architecture (3GPP TS 23.207) and 3 rd  Generation Partnership Project; Technical Specification Group Core Network; Policy control over Gq interface (3GPP TS 29.209). The 3GPP intend to use the Diameter protocol for the Gq interface, having considered the protocols SOAP/XML, COPS and Parlay. In the same manner as described above for COPS, the Diameter protocol similarly lacks support for passing call control information such as codec types between the Application Manager  40  and Policy Server  50 .  
      In a further alternative of the invention, a Session Initiation Protocol (SIP) invite message is sent between the Application Manager  40  and the Policy Server  50  to pass application (call) control to the Policy Server. SIP messages carry application control related information to the Policy Server  50 , which the Policy Server  50  can use to make selections of application control parameters.  
      The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention.