Abstract:
Call placement to or from satellite UEs is optimized by reducing IMS message exchanges, the originating party has control over QoS parameters, a HPA subscription service is made available, and calls to a terminating satellite UE that is shielded from satellite coverage are completed by selectively employing HPA pages. For a call request without preconditions, an IMS node associated with an originating UE uses the NRSCPA on Offer instead of using the standard terminating node initiated NRSCPA on Answer. An IMS node associated with a terminating UE checks for HPA subscription by the user. If subscribed, the terminating INVITE request is for a “Conversational” or “Interactive” service, and the terminating UE is in PMM_IDLE state, the satellite RAN pages the terminating UE using HPA.

Description:
[0001]    This application is a continuation of U.S. application Ser. No. 12/872,474, filed Aug. 31, 2010, now pending, which claims priority to U.S. Provisional Patent Application No. 61/246,212, filed Sep. 28, 2009 and U.S. Provisional Patent Application No. 61/250,631, filed Oct. 12, 2009., the disclosure of which is incorporated herein by reference application 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to telecommunication systems, and in particular to a satellite RAN and IMS network operative to establish certain calls with reduced latency and selectively using HPA pages to reach satellite UE. 
       BACKGROUND 
       [0003]    The IP Multimedia Subsystem (IMS), as defined by the 3 rd  Generation Partnership Project (3GPP) standards body, merges telephony and Internet technology by providing an all-IP based architecture for the telecommunications industry. The IMS is based on the Session Initiation Protocol (SIP) and makes heavy use of the protocols defined within the IETF. IMS offers a network of servers and databases that assist a user agent with the task of establishing and managing sessions. IMS uses the term sessions because the connections between users are no longer limited to voice services (a phone call). Sessions may be voice, video, text, or other services connecting two or more user agents together. A representative IMS network is depicted in  FIG. 1 . 
         [0004]    Communications between nodes within an IMS network utilize the Session Initiation Protocol (SIP). SIP is a signaling protocol for Internet conferencing, telephony, presence, events notification, instant messaging, and the like. SIP signaling uses a long-term stable identifier, the SIP Universal Resource Indicator (URI). User equipment (UE) in an IMS refers to a device that contains the SIP User Agent that will initiate or terminate SIP sessions. In particular, one form of UE is a mobile terminal operative to send and receive data across a defined air interface, such as Wideband Code Division Multiple Access (WCDMA). 
         [0005]    SIP signaling packets in an IMS network are processed by SIP servers or proxies collectively called Call Session Control Function (CSCF). Different types of CSCFs perform specific functions. 
         [0006]    A Proxy-CSCF (P-CSCE) is a SIP proxy that is the first point of contact for an IMS terminal (UE). The P-CSCF may reside in the terminal&#39;s H-PLMN or a V-PLMN. In either case, a P-CSCE is assigned to a UE during registration, which does not change for the duration of the registration. All SIP messages to and from the UE pass through the P-CSCE, which can inspect them. The P-CSCF performs authentication and security functions for the UE, and maintains records of communications for billing. 
         [0007]    A Serving-CSCF (S-CSCF) is the central SIP proxy in a UE&#39;s H-PLMN that performs SIP services and session control, Based on information from a Home Subscriber Server (HSS) database, the S-CSCF handles SIP registrations, in which it binds the UE IP address to a SIP address. The S-CSCF also can intercept and inspect all SIP messages to and from the UE. The S-CSCF decides to which AS SIP messages will be forwarded, to obtain their services. The S-CSCF also provides routing services, typically using Electronic Numbering (ENUM) lookups, and it enforces network operator policies. 
         [0008]    An Interrogating-CSCF (I-CSCF) is a SIP proxy located at the edge of an administrative domain. The IP address of the I-CSCF is published in the Domain Name System (DNS) of the domain, so that remote servers can find it, and use it as a forwarding point for SIP packets into the I-CSCF&#39;s domain. The I-CSCF retrieves the subscriber location from the HSS and then routes SIP requests to its assigned S-CSCF. 
         [0009]    An IMS network includes a Home Subscriber Server (HSS) that stores the relevant user data including authentication information and service data. As part of the user profile, initial Filter Criteria (iFC) are defined to indicate which application servers are to be invoked based on information in the signaling plane. 
         [0010]    An IMS network also includes one or more Application Servers (AS) providing various services, such as audio and video broadcast or streaming, push-to-talk, videoconferencing, games, file sharing, e-mail, and the like. Application Servers are invoked based on the iFCs that are stored in the user profile. The S-CSCF will pass signaling onto an AS if the criteria defined in the iFC are met. Once invoked, the AS can take part in the session and provide additional capabilities. 
         [0011]      FIG. 1  is a simplified functional block diagram of an IMS network  10 . A UE  12  has associated with it one or more CSCFs (e.g., a P-CSCF, S-CSCF, and/or I-CSCF)  14 . The CSCF  14  is connected to various AS  16 ,  18  providing services. A HSS  20  provides information for Authentication, Authorization and Accounting (MA) functions. 
         [0012]    The Diameter protocol is an advanced, extensible AAA protocol, derived fro the industry standard RADIUS (Remote Authentication Dial-In User Service) protocol. Diameter includes numerous enhancements to RADIUS, such as error handling and message delivery reliability, It extracts the essence of the AAA protocol from RADIUS and defines a set of messages that are general enough to form the core of a Diameter base protocol. The various applications that require AAA functions can define their own extensions on top of the Diameter base protocol, and can benefit from the general capabilities provided by the Diameter base protocol. 
         [0013]      FIG. 2  depicts a representative prior art call flow for a UE to UE call, in which preconditions are used to avoid a problem known as “ghost ringing.” This is accomplished by ensuring that radio resources are reserved on the calling party&#39;s side (UE #1) before alerting the called party (UE #2) The call flow with preconditions of  FIG. 2  is extracted from section 5.1.2.3 of 3GPP TR 24.930 V.7.5.0, the disclosure of which is incorporated herein by reference in its entirety. 
         [0014]    When the called and calling UEs are mobile satellite terminals, the call flow of  FIG. 2  presents several problems. First, if the called UE is located where there is no satellite coverage, such as inside a building, the SIP INVITE message at step  207  will never reach the UE unless the satellite initiates a High Penetration Alert (HPA) page. A HPA page is a paging message transmitted at much higher power than a normal page. The HPA page directs the UE to display a message asking the called party to exit the building (or otherwise move into an area of satellite coverage) to receive the call. One solution is for the satellite Radio Access Network (RAN) to send a HPA page on every SIP INVITE, regardless of session establishment type (voice calls, messaging). However, this approach severely impacts radio resources. 
         [0015]    Additionally, the codec negotiation of steps  217  to  232  result from Network Requested Secondary POP Context Activation (NRSCPA) on Answer—that is, no POP context is established until the called party is reached via initial SIP signaling. While NRSCPA on Answer has some advantages in terrestrial networks, such as ensuring that network resources are available and reserved prior to connecting the call, it entails extensive SIP messaging between the two UEs. When a call is established over a satellite, the voluminous exchange of SIP messages not only consumes satellite link bandwidth, it also increases the call setup time. 
       SUMMARY 
       [0016]    According to one or more embodiments of the present invention described and claimed herein, call placement to or from satellite UEs is optimized by reducing IMS message exchanges, the originating party has control over QoS parameters, a HPA subscription service is made available, and calls to a terminating satellite UE that is shielded from satellite coverage are completed by selectively employing HPA pages. For a call request without preconditions, an IMS node associated with an originating UE uses the NRSCPA on Offer instead of using the standard NRSCPA on Answer, An IMS node associated with a terminating UE checks for HPA subscription by the user. If subscribed, the terminating INVITE request is for a “Conversational” or “Interactive” service, and the terminating UE is in PMM_IDLE state, the satellite RAN pages the terminating UE using HPA. 
         [0017]    One embodiment relates to a method of establishing a telecommunication session with a mobile satellite terminal having an IMS client. An IMS POP context activation is established by a P-CSCF associated with the calling UE prior to exchanging any SIP signaling with a proxy associated with the called UE. A HPA is directed to the called UE only if the called UE subscribes to a HPA service, and only for calls having a conversational or interactive traffic class. 
         [0018]    Another embodiment relates to an IMS network node operative to receive a SIP INVITE message from an originating UE and, in response to the contents of the SIP INVITE message, establish an IMS POP context activation prior o exchanging any SIP signaling with a proxy associated with a terminating UE 
         [0019]    Yet another embodiment relates to an IMS network node operative to receive a SIP INVITE message from another IMS node and, in response to the contents of the SIP INVITE message and further in response to a called party identified in the SIP INVITE message subscribing to a HPA paging service, page a UE associated with the called party using a HPA page. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a functional block diagram of a conventional IMS network. 
           [0021]      FIG. 2  is a call flow diagram of conventional call setup in an IMS network. 
           [0022]      FIG. 3  is a functional block diagram of a satellite RAN integrated with an IMS network. 
           [0023]      FIGS. 4A-4F  depict a call flow diagram of a satellite call setup according to one embodiment of the present invention. 
           [0024]      FIG. 5  is a table of call setup latencies in prior art call setup techniques. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 3  depicts an integrated satellite/IMS network  22 . The network  22  connects satellite mobile terminals  24  with each other, with application servers  26  or other resources in an IMS network, or with communication terminals in other networks, such as the Public Switched Telephone Network (PSTN)  30 . Traffic to and from the mobile terminals  24  is transmitted by one or more satellites  32 , with access controlled by a satellite Radio Access Network (RAN)  34 . The satellite RAN  34  is communicatively coupled to a terrestrial wireless IP Connectivity Access Network (IP-CAN)  36 , In the embodiment depicted in  FIG. 3 , the wireless IP-CAN  36  is a Wideband Code Division Multiple Access (WCDMA) network with General Packet Radio Service (GPRS) comprising at least a Gateway GPRS Service Node (GGSN)  38  and a Serving GPRS Support Node (SGSN)  40 . The WCDMA IP-CAN  36  is connected to an IMS core network comprising a Policy and Charging Rule Function (PCRF)  42 , a P-CSCF  44 , a S-CSCF  46 , and application servers  26 . 
         [0026]    The IMS network additionally comprises a Home Location Register (HLR)  48  and HSS  50 , a Media Resource Function  52  comprising a Media Resource Function Controller (MRFC) and a Media Resource Function Processor (MRFP), and a server  54  performing address lookup and translation functions such as DNS, Electronic Numbering (ENUM), and Dynamic Host Configuration. Protocol (DHCP). The IMS network further includes a Media Gateway Controller Function (MGCF) and Signaling Gateway (SGW)  56  connected to a Media Gateway (MGW)  58  across a H.248 interface. The structure and operation of the IMS network is well defined, and is not further explained herein. Those of skill in the art will further recognize the existence of a packet core, comprising switches and routers (not shown), that carries bearer traffic between the GGSN  38  and MGW  58 . 
         [0027]      FIG. 3  depicts a voice or interactive call directed to a satellite mobile UE located in a building  60 . A High Penetration Alert (HPA) page is selectively employed to reach the called UE  24 . The HPA displays a message, such as that depicted, that the user has an incoming call, and requesting the user to exit the building  60  to receive the call from the satellite  32 . According to embodiments described and claimed herein, the HPA is selectively employed based on the type of call, the state of the called UE  24 , and whether the called user subscribes to a HPA service. 
         [0028]    The operation of embodiments of the present invention is described in the context of a voice call from one satellite UE  24  (identified as user “A”) to another satellite UE  24  (identified as user “B”), when user B is in a building. Both the originating mobile satellite UE  24  and the terminating mobile satellite UE  24  typically include a special codec to optimize the transmission of voice packet over the satellite link, In this case, the standard IMS call flow with preconditions can be enhanced to: give the originating mobile satellite UE  24  full control in providing Quality of Service (QoS) for various end user services; increase successful call establishment rate without wasting satellite radio resources by using HPA paging only for selected bearer services (e.g., only voice and interactive calls); and charge mobile satellite subscribers for subscribing to HPA as a service. 
         [0029]    First, the originating mobile satellite UE  24  uses the Network Requested Secondary PDP Context Activation (NRSCPA) on Offer instead of using the standard terminating-UE  24  initiated Secondary PDP Context Activation procedure (NRSCPA on Answer). This method eliminates preconditions and reduces the number of messaging exchanges between the originating mobile UE  24  and the terminating mobile UE  24  in half (i.e., no PRACK, UPDATE, and corresponding 200 OKs). In addition, NRSCPA on Offer gives the operator full control in providing QoS for various end user services as the network instructs the UE  24  which QoS parameter values to use, thus avoiding pre-provisioning of terminals. 
         [0030]    Second, the terminating PCRF  42  checks for HPA subscription before initiating NRSPCA which triggers HPA., thus allowing mobile satellite operators to charge subscribers for using HPA. 
         [0031]    Third, the satellite RAN  34  sends HPA to the terminating UE  24  only when the terminating INVITE request is for a “Conversational” or “Interactive” (e.g., a voice call or a push-to-talk request), thus optimizing page channel resource usage. 
         [0032]    The service logic in the IMS nodes P-CSCE  44 , PCRF  42 , GGSN  38 , SGSN  40 , and the satellite RAN  34  required to support NRSPCA on Offer is described below, for both the originating and terminating sides. For the purpose of explanation, both the originating mobile UE  24  (user “A”) and terminating mobile UE  24  “B” (user “B”) are considered as mobile satellite subscribers as the most general case. However, in general, either of them could be a PSTN or PLMN subscriber and the logic for the other subscriber remains unchanged. 
       Originating Side Service Logic 
       [0033]    Mobile satellite subscriber A is making a voice call to mobile satellite subscriber B. Upon receiving the originating SIP INVITE message ( FIG. 4 , step  1 ), subscriber A&#39;s P-CSCF  44  executes the following logic, If the Require header field and the Supported header field in the INVITE message do not contain preconditions, the SDP portion of the INVITE message does not contain “desired QoS” and “current QoS,” and a configurable system parameter, such as NRSPCA_ON_OFFER is set to “Y” in A&#39;s P-CSCF  44 , then the following steps occur: 
         [0034]    A&#39;s P-CSCF  44  requests that A&#39;s PCRF  42  perform preliminary QoS authorization for an incoming voice call by sending a Diameter AAR (Authorize and Authenticate Request) message (SERVICE_INFO_STATUS: PRELIMINARY_SERVICE_INFORMATION, Media-Component-Description: Code-Data: “uplink” “offer” . . . ) to PCRF  42  ( FIG. 4 , step  3 ), Alternatively, the AAR can include a new Attribute-Value Pair (AVP) such as NRSPCA_ON_OFFER to indicate to PCRF  42  that this is a call which requires NRSPCA on Offer. Therefore, PCRF  42  will delay sending AAA back to P-CSCF  44  ( FIG. 4 , step  19 ) until PCRF  42  receives an indication of successful secondary POP context activation from GGSN  38  ( FIG. 4 , step  18 ). 
         [0035]    A&#39;s PCRF  42  requests that A&#39;s GGSN  38  perform NRSPCA for a voice call by sending a Diameter RAR (Re-Auth-Request) message to GGSN  38  ( FIG. 4 , step  4 ). 
         [0036]    A&#39;s GGSN  38  requests that A&#39;s SGSN  40  create a secondary POP context for a voice call ( FIG. 4 , step  7 ). 
         [0037]    A&#39;s SGSN  40  sends Request POP Context Activation message to A ( FIG. 4 , step  7 ). 
         [0038]    A&#39;s GGSN  38 , A&#39;s SGSN  40 , and UE A  24  together complete the NRSPCA procedure, as depicted in  FIG. 4 , steps  9 - 17 . A&#39;s GGSN  38  then notifies A&#39;s PCRF  42  of the successful secondary POP context activation ( FIG. 4 , step  18 ), which sends an AAA to A&#39;s P-CSCF  44  ( FIG. 4 , step  19 ). 
         [0039]    Note that, as an alternative to A&#39;s PCRF  42  sending a AAA to A&#39;s P-CSCF  44  at step  19 —that is, at the completion of secondary POP context activation—A&#39;s PCRF  42  could send the AAA immediately upon receipt of AAR at step  3 . A&#39;s PCRF  42  would send RAR to A&#39;s GGSN  38 , and receive a RAA in response, as depicted at  FIG. 4 , steps  4 - 5 . Then, after successful secondary POP context establishment, following  FIG. 4 , step  17 , A&#39;s GGSN  38  would send a CCR (Update) to A&#39;s PCRF  42 , which would respond with CCA. A&#39;s PCRF  42  would then send RAR to A&#39;s P-CSCF  44 , to notify the P-CSCF  44  that the resource reservation procedure is complete. 
         [0040]    In any event, following the completion of the NRSPCA procedure and notifications thereof, A&#39;s P-CSCF  44  sends an INVITE to B&#39;s I-CSCF ( FIG. 4 , steps  20 - 27 ), which interacts with HSS and B&#39;s S-CSCF to route the call to B&#39;s P-CSCF ( FIG. 4 , steps  28 - 37 ). 
         [0041]    If the NRSPCA_ON_OFFER parameter is not set, or if the INVITE message includes preconditions, then the conventional originating P-CSCF  44  service logic applies, as depicted in  FIG. 2 . That is, A&#39;s P-CSCF  44  sends a SIP INVITE message to the terminating P-CSCF  44  via the IMS core ( FIG. 2 , steps  203 - 206 ) and initiates the QoS authorization procedure ( FIG. 2 , step  214 ) upon receiving a  183  Session Progress from the called UE  24  ( FIG. 2 , steps  212 - 213 ). 
       Terminating Side Service Logic 
       [0042]    When B&#39;s P-CSCF  44  receives the terminating INVITE message ( FIG. 4 , step  36 ), B&#39;s P-CSCF  44  executes the following service logic, If the Require header and the Supported header in the SIP INVITE message do not contain preconditions, the SDP portion of the INVITE does not contain “desired QoS” and “current QoS”, and a configurable system parameter such as NRSPCA_ON_OFFER is set to “Y” in B&#39;s P-CSCF  44 , then the following steps occur: 
         [0043]    B&#39;s P-CSCF  44  requests that B&#39;s PCRF  42  perform preliminary QoS authorization for an incoming voice call by sending a Diameter AAR message to B&#39;s PCRF  42 , the AAR message including a new AVP named NRSPCA_ON_OFFER ( FIG. 4 , step  38 ). 
         [0044]    B&#39;s PCRF  42  checks for B&#39;s HPA subscription. 
         [0045]    If B has an HPA subscription, B&#39;s PCRF  42  requests that B&#39;s GGSN  38  perform NRSPCA with HPA for an incoming voice call by sending a Diameter RAR message (Traffic Class: Conversational, Allocation. Retention Priority (ARP): 1) to GGSN  38  ( FIG. 4 , step  39 ), Note that ARP value selections are arbitrary for HPA and non-HPA calls, The requirement is that the chosen ARP for HPA must be unique. 
         [0046]    If, on the other hand, B does not have an HPA subscription, B&#39;s PCRF  42  requests that B&#39;s GGSN  38  perform NRSPCA for an incoming voice call without HPA by sending a Diameter RAR message (Traffic Class: Conversational, Allocation Retention Priority: 2 or 3) to GGSN  38  ( FIG. 4 , step  39 ), B will receive the INVITE message if B is not inside a building. 
         [0047]    B&#39;s GGSN  38  requests that B&#39;s SGSN  40  create a secondary POP context for a terminating voice call by sending an initiate POP Context. Activation Request message to B&#39;s SGSN  40  ( FIG. 4 , step  42 ). 
         [0048]    If B is inside a building or otherwise out of satellite coverage), B&#39;s UE  24  Packet Mobility Management (PMM) state should be PMM_IDLE. Therefore, B&#39;s SGSN  38  sends a Page message (Cause IE: “Terminating High Priority Signaling”) to the satellite RAN  34  ( FIG. 4 , step  43 ). 
         [0049]    In response to the Paging Cause Information Element (IE) being set to “Terminating High Priority Signaling,” the RAN  34  sends an HPA page to B&#39;s UE  24  ( FIG. 4 , step  44 ). 
         [0050]    B&#39;s UE  24  displays a message to the effect that “There is an incoming voice call for you. If you are inside a building, please step outside the building to answer it.” 
         [0051]    User B steps outside the building to receive the SIP INVITE message, and send Page Response ( FIG. 4 , steps  45 - 46 ). 
         [0052]    B&#39;s GGSN  38 , B&#39;s SGSN  40 , and B&#39;s UE  24  together complete the NRSPCA procedure ( FIG. 4 , steps  47 - 58 ). 
         [0053]    Note that, as an alternative to B&#39;s PCRF  42  sending a AAA to B&#39;s P-CSCF  44  at step  58 —that is, at the completion of secondary POP context activation, B&#39;s PCRF  42  could send the AAA immediately upon receipt of AAR at step  38 . Then, after successful secondary POP context establishment, B&#39;s PCRF  42  would send RAR to B&#39;s P-CSCE  44  (e.g., at  FIG. 4 , step  57 ) to notify B&#39;s P-CSCF  44  of the event. 
         [0054]    B&#39;s P-CSCF  44  sends INVITE to B&#39;s UE  24  ( FIG. 4 , step  59 ). 
         [0055]    B&#39;s UE  24  sends  100  Trying ( FIG. 4 , step  60 ), and will then send a 183 Session Progress response all the back to UE A via IMS (indicated generally at  FIG. 4 , step  61 ). B&#39;s UE  24  then sends 180 Ringing ( FIG. 4 , step  62 ), and 200 OK (INVITE) with SDP ( FIG. 4 , step  71 ). 
         [0056]    B&#39;s PCRF  42  performs final QoS authorization ( FIG. 4 , steps  72 - 75 ). 
         [0057]    B&#39;s P-CSCF  44  relays the 200 OK (INVITE) to A&#39;s P-CSCF  44  ( FIG. 4 , steps  76 - 82 ), which requests that A&#39;s PCRF  42  perform final QoS authorization ( FIG. 4 , steps  83 - 87 ). 
         [0058]    The call is then established bet seen As UE  24  and B&#39;s UE  24 , as depicted in the remaining steps of  FIG. 4 . 
         [0059]    if the NRSPCA_ON_OFFER parameter is riot set in B&#39;s P-CSCF  44 , or if the received SIP INVITE message includes preconditions, then the conventional terminating P-CSCF  44  service logic applies, as depicted in  FIG. 2 . That is, B&#39;s P-CSCF  44  sends a SIP INVITE message to the terminating UE  24  ( FIG. 2 , steps  207 ) and initiates the QoS authorization procedure ( FIG. 2 , step  211 ) upon receiving a  183  Session Progress from the called UE  24  ( FIG. 2 , step  183 ). 
         [0060]    The following table shows an example of the mapping between Traffic Class and Allocation Retention Priority (ARP) to Paging Cause Information Element (IE) in the SGSN  40 . 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Paging Cause 
                   
               
               
                 Case 
                 IE 
                 RAN Action 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 NRSPCA/ 
                 Traffic Class is 
                 ARP is 1 
                 Terminating 
                 HPA 
               
               
                 Downlink 
                 Conversational 
                   
                 High Priority 
               
               
                 Payload 
                   
                   
                 Signaling 
               
               
                   
                   
                 ARP is 2 
                 Terminating 
                 Normal 
               
               
                   
                   
                   
                 Conversational 
                 Page 
               
               
                   
                   
                   
                 Call 
               
               
                   
                   
                 ARP is 3 
                 Terminating 
                 Normal 
               
               
                   
                   
                   
                 Conversational 
                 Page 
               
               
                   
                   
                   
                 Call 
               
               
                   
                 Traffic Class is 
                 N/A 
                 Terminating 
                 Normal page 
               
               
                   
                 Streaming 
                   
                 Streaming Call 
               
               
                   
                 Traffic Class is 
                 ARP is 1 
                 Terminating 
                 HPA 
               
               
                   
                 Interactive 
                   
                 High Priority 
               
               
                   
                   
                   
                 Signaling 
               
               
                   
                 Traffic Class is 
                 ARP is 2 
                 Terminating 
                 Normal 
               
               
                   
                 Interactive 
                   
                 Interactive Call 
                 Page 
               
               
                   
                 Traffic Class is 
                 ARP is 3 
                 Terminating 
                 Normal 
               
               
                   
                 Interactive 
                   
                 Interactive Call 
                 Page 
               
               
                   
                 Traffic Class is 
                 N/A 
                 Terminating 
                 Normal 
               
               
                   
                 Background 
                   
                 Background 
                 Page 
               
               
                   
                   
                   
                 Call 
               
               
                 Downlink 
                 HLR or SGSN 
                 N/A 
                 Terminating 
                 Normal 
               
               
                 Signaling 
                 Initiated 
                   
                 Low Priority 
                 Page 
               
               
                   
                 Detach 
                   
                 Signaling 
               
               
                   
                 GGSN or 
                 N/A 
                 Terminating 
                 Normal 
               
               
                   
                 SGSN Initiated 
                   
                 Low Priority 
                 Page 
               
               
                   
                 PDP Context 
                   
                 Signaling 
               
               
                   
                 Deactivation 
               
               
                   
                 GGSN 
                 N/A 
                 Terminating 
                 Normal 
               
               
                   
                 Initiated PDP 
                   
                 Low Priority 
                 Page 
               
               
                   
                 Context 
                   
                 Signaling 
               
               
                   
                 Modification 
               
               
                   
                 MT-SMS 
                 N/A 
                 Terminating 
                 Normal 
               
               
                   
                   
                   
                 Low Priority 
                 Page 
               
               
                   
                   
                   
                 Signaling 
               
               
                   
               
               
                 Note that in this example HPA is only activated when the ARP is 1, and the Traffic Class is Conversational or Interactive. 
               
             
          
         
       
     
         [0061]    According to embodiments of the present invention, satellite radio resources usage is optimized and successful call establishment rate is increased by using Network Request Secondary PDP Context Activation on Offer and HPA to set up mobile satellite UE  24  to mobile satellite UE  24  or PSTN/PLMN to mobile satellite UE  24  call. Furthermore, the number of SIP message exchanges required to set up a mobile satellite UE  24  to mobile satellite UE  24  calls over IMS is significantly reduced, resulting in both decreased traffic over the satellite RAN  34 , and decreased latency in call establishment.  FIG. 5  depicts the processing time for a standard Mobile to PSTN call without NRSPCA on Offer, requiring 5 seconds delay. By using NRSCPA on Offer, the call setup time can be reduced by a minimum of 2 seconds, For a mobile UE  24  to mobile UE  24  call, the setup time saving will be even greater due to elimination of PRACK/200OK and UPDATE/200OK SIP message exchanges over the radio link to the terminating mobile UE  24 . 
         [0062]    Additionally, embodiments of the present invention give the operator full control in providing QoS for various end user services, thus avoiding QoS configuration in a variety of terminals from different vendors. Additionally, a method is provided for mobile satellite service providers to charge subscribers for subscribing to HPA. 
         [0063]    The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.