Abstract:
The present invention relates to a system and method of communicating operating capabilities in a telecommunication network or networks. The present invention stems from the realisation that mobile telecommunication network resources can be utilised with greater efficiency by maintaining mobile station attributes or operating capabilities at a network node associated with the mobile station. Preferably, the network node is a Visitor Location Register VLR. Additionally, the network node may be a Home Location Register HLR, a Mobile Switching Centre MSC or a Gateway Mobile Switching Centre GMSC. In particular, the invention may provide the creation of a list of operating capabilities at a network node upstream from the mobile station. Having done this, a comparison of this list with another list received from a remote telecommunication element to negotiate operating capabilities at a call set up is achieved without involving communication resources between the mobile station and the network node.

Description:
FIELD OF INVENTION 
   In general, the present invention relates to a system and method of communicating operating capabilities in a telecommunication network or networks. 
   In one aspect, the present invention relates to a method of negotiating operating capabilities between telecommunication subscribers, and more particularly relates to a method of enabling codec compatibility between a first mobile station in a public land mobile network (PLMN) and a network node either located in a fixed network or in a different PLMN or in the same PLMN, although, it is to be appreciated, however, that the invention is not limited to use in that application, only. 
   In another aspect, this invention relates to a method of providing operating capabilities at a telecommunications network node, and more particularly relates to a method of providing operating capabilities at a telecommunications network node during a call set-up procedure between a mobile station in a mobile telecommunications network and a network element. 
   BACKGROUND OF INVENTION 
   In general, when a subscriber having a mobile station (MS) or terminal located within a first PLMN wishes to contact another subscriber having a mobile station or terminal located in a different PLMN, the first mentioned subscriber&#39;s MS must transmit to its serving mobile switching centre (MSC) operating capabilities, such as, a codec or a list of codecs on which it can transmit information or messages. Negotiation must then be initiated, typically, over a fixed switched network, such as PSTN, or ISDN, IP or ATM with the other mobile station or terminal. Once operating capabilities are negotiated between the two mobile stations then the call may proceed using those capabilities. All of this negotiation requires a lot of signalling to take part between the originating mobile station and its serving MSC each time a call needs to be established. 
   As mobile networks are becoming more and more advanced and requiring the transmission of greater amounts of data between nodes of the network or across other networks such as a PSTN or ISDN fixed network, this creates a burdensome task for nodes within the network to process all the data. Furthermore, the signalling process takes place relatively slowly. It would therefore be desirable to remove extra data, where possible, especially between an MS and its serving MSC, in order to increase the speed of signalling and reduce the signalling load between the MS and MSC, especially for example, at call set-up. By reducing the amount of signalling data that needs to be transmitted between an originating mobile station and its serving MSC, the network resources could be more efficiently used. 
   In one particular arrangement, developed by the present applicant, a Bearer Independent Call Control (BICC) protocol is used for negotiating operating capabilities, and in particular codec negotiation. The BICC protocol is particularly suitable for third generation mobile networks, such as UMTS, wherein non-TDM transport technologies are used. However, the proposed BICC codec negotiation is not fully optimised for mobile environments. In particular, it is not optimised for fast selection of operating capabilities for mobile terminated calls when, for efficiency reasons, transcoders are placed in the edge of the core network at the GMSC. 
   The present invention seeks to overcome or substantially ameliorate at least one of the disadvantages of the prior art. 
   SUMMARY OF INVENTION 
   In one aspect the present invention provides a method of communicating in a telecommunication system including at least one mobile station, the method including the step of providing operating capabilities of the mobile station at a node associated with the mobile station wherein the node is upstream in a communication path from the mobile station. 
   In another aspect the present invention provides a telecommunication system including at least one mobile station and at least one node associated with the mobile station, the node including storage means for providing operating capabilities of the mobile station wherein the node is upstream in a communication path from the mobile station. 
   In essence, the present invention stems from the realisation that mobile telecommunication network resources can be utilised with greater efficiency by maintaining mobile station attributes or operating capabilities at a network node associated with the mobile station. Preferably, the network node is a Visitor Location Register VLR. Additionally, the network node may be a Home Location Register HLR, a Mobile Switching Centre MSC or a Gateway Mobile Switching Centre GMSC. In particular, the invention may provide the creation of a list of operating capabilities at a network node upstream from the mobile station. Having done this, a comparison of this list with another list received from a remote telecommunication element to negotiate operating capabilities at a call set up is achieved without involving communication resources between the mobile station and the network node. 
   In a further aspect, the present invention seeks to overcome or substantially ameliorate any of the abovementioned disadvantages by providing a method of negotiating operating capabilities between a mobile station and a network node whereby the amount of signalling required between the originating mobile station and its serving MSC is reduced. 
   Accordingly, in this aspect, the present invention provides a method of negotiating operating capabilities between a mobile station in a mobile telecommunications network and a network node, wherein said mobile telecommunications network includes a storage means associated with a switching centre serving said mobile station;
         the method including the step of:   transmitting a list of one or more operating capabilities from said mobile station to the switching centre for storage in said storage means as part of a non-call based signal.       

   The method may further include the step of updating said storage means with another list of operating capabilities, such as codecs, for use by said mobile station when said mobile station moves from one location area to another location area by sending a message to said switching centre for subsequent storage in the storage means. The message may be a location update message or any existing or new message. 
   The network node may be located in a fixed network, such as PSTN or ISDN or in a mobile network, or it may be a mobile station located in another mobile telecommunications network. 
   The one or more operating capabilities may be prioritised such that a list of preferred operating capabilities is supplied by the mobile station. Operating capabilities may include security algorithms, or codecs, in which case the storage means will receive the list of algorithms supported by the MS for subsequent storage. 
   Thus, the signalling load is reduced between the MS and MSC at call set-up as the operating capabilities of the MS are already stored in the storage means associated with the switching centre and the MS does not need to transmit the operating capabilities each time it needs to establish a call. Furthermore, the MS does not need to receive the list of operating capabilities in the set-up message from the switching centre every time it receives a call. 
   In yet another aspect, the present invention seeks to overcome or substantially ameliorate any of the abovementioned disadvantages by providing a method of making available the list of operating capabilities to be used between a mobile station and a network node during a call set-up procedure between the mobile station and the network node. Accordingly, in this aspect, the present invention provides a method of providing operating capabilities of a mobile station at a telecommunications network node to a telecommunications element during a call set-up procedure between the mobile station and said telecommunications element, and wherein said telecommunications element transmits to the telecommunications network node a list of operating capabilities of the telecommunications element as part of the call set-up procedure, the method including the steps of:
         transmitting a list of operating capabilities of said mobile station from a switching centre serving said mobile station to said telecommunication network node;   providing said list of operating capabilities at said telecommunications network node;   such that on initiation of a communication from said network element to said mobile station, said telecommunications network node internally selects one or more operating capabilities common to both the mobile station and the network element.       

   In this manner, the invention advantageously accelerates the selection of operating capabilities for mobile terminated calls wherein negotiation on the operating capabilities to be used between the mobile station and network node is no longer required at call set-up. 
   The network element is preferably another mobile station, but may alternatively be a telecommunications terminal device or node. The list of operating capabilities of the mobile station may be transmitted to the network node in response to an information retrieval message sent from the network node to the switching centre. The list of operating capabilities of said mobile station may have been previously stored in a storage means, such as a VLR, associated with the switching centre serving the mobile station. The telecommunications network node may be a node located in the same telecommunications network or PLMN as the mobile station. The telecommunications network node may be a node located in a fixed network which is traversed in establishing a call between the network element and the mobile station. Alternatively the telecommunications network node may be a node of a different network to that where the mobile station is located and is preferably at the home network of the mobile station. The node, when located in one of the PLMNs is preferably a GMSC. The list of operating capabilities of both the network element and the mobile station may be prioritised in the sense that preferred operating capabilities, such as codecs, are specified. 
   A list of operating capabilities of the network element may be stored at a network node serving the network of said network element. Preferably during the call set up the list of operating capabilities of the network element is transmitted from the network node serving the network of the network element to the telecommunications network node. 
   Thus, the selection of operating capabilities to be used is accelerated between the mobile station and the network element by the prior storage of the list of operating capabilities in the telecommunications network node. Codec operating capability negotiation need not take place as part of the call set-up between the mobile station and network element as the particular operating capabilities, such as codecs to be used, can be automatically selected by the telecommunications network node. 

   
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A preferred embodiment of the invention will be hereinafter described, by way of example only, with reference to the drawings wherein: 
       FIG. 1  is a schematic diagram of a telecommunication system used in accordance with the present invention; 
       FIG. 2  is a signalling diagram showing the signalling messages that are conducted between two mobile stations in the telecommunications system of  FIG. 1  in accordance with a first embodiment of the present invention. 
       FIG. 3  is a signalling diagram showing signalling messages that are passed between an originating mobile station and a destination mobile station using the telecommunications system of  FIG. 1  in accordance with a second embodiment of the present invention; 
       FIG. 4  is a signalling diagram of the second embodiment of the present invention, showing the messages signalled between a switching centre serving a destination mobile station and a telecommunications network node, being in this case a GMSC located in a home network of the destination mobile station. 
   

   In general the present invention provides operating capabilities of a mobile station at a network node capable of storing the operating capabilities and thereafter negotiation of operating capabilities can proceed with a remote telecommunication element where negotiation does not need to take place between the mobile station and the node, which is upstream of the mobile station. When negotiating operating capabilities, a stored list is compared with the operating capabilities of the remote element, which can also be provided prior to a call set up and stored at a node upstream from the remote element. Preferably in the negotiation of operating capabilities, a selection is made based on operating capabilities common to both lists of operating capabilities stored at each node. Preferably, the remote telecommunication element is another mobile station, a terminal device or a node. 
   First Embodiment 
   In  FIG. 1  there is shown a first mobile station MS  4  in a location area  6  (LA 1 ), of a first PLMN  2 , which is controlled by base station controller  8 . The mobile switching centre  10  is in communication with each of the BSC  8  and a further BSC  9 . The MSC  10  has an associated storage means in the form of a visitor location register (VLR)  12  in which is stored details of mobile subscribers and their mobile units that are temporarily located within its serving area, in this case LA 1  and LA 2 . A gateway MSC (GMSC)  14  provides an interface between other networks such as a PSTN or ISDN  16 . A further storage means  18  in the form of a home location register (HLR) provides permanent storage of subscriber details and keeps continuous track of the location of a subscriber whether that subscriber is in a MSC service area or in a different PLMN. This information is used by the GMSC  14  when receiving a call from another network. The PLMN  2  also has other MSCs such as MSC  20  with its own VLR  22  and whereby the MSC  20  serves BSCs  24  and  26 . 
   When MS  4  wishes to contact a further mobile station  28  located in another PLMN  30  a set-up message will be transmitted from MS  4  to its serving MSC  10 . Thereafter negotiation of operating capabilities, such as codecs or security algorithms, takes place between the MSC  10  and the PLMN  30  and in particular an MSC  29  that is serving between MS  28 . An initial address message (IAM) is used to signal between the MSC  10  and MSC  29  of PLMN  30 . The negotiation continues to take place and when an operating capability has been agreed upon between the MS  28  and MS  4  to transmit the data, then such data can be transmitted. 
   The MSC  10  or equivalently a Bearer Independent Call Control (BICC) node has the capability to separate the ISUP signal into a Call Control (CC) portion and a Bearer Control (BC) portion where the call control portion of ISUP carries the initial address message (IAM). 
   According to the present invention MS  4  regularly transmits to its serving MSC  10 , via a message, such as a location update message or any other existing or new message, a list of operating capabilities applicable to MS  4  which is subsequently stored in the VLR  12  associated with that MSC. The list of operating capabilities may be updated at predetermined times for example on polling by the serving MSC  10  or when the mobile station  4  for example changes its location area say from LA 1  to LA 2 . Alternatively a special procedure may be set up between the MS  4  and the MSC  10 /LVR  12  to update the capabilities. The updated list of operating capabilities is then subsequently stored in the VLR  12  associated with MSC  10 . By doing this, negotiation is handled between the MSC  10  and the MSC  29  as to which is a compatible operating capability on which both mobile stations  28  and  4  can communicate. The controlling MSCs of MS  4  and MS  28  know the operating capability options that each MS can support and the MSCs handle the negotiation on behalf of the MSs. Equivalently, the MS  28  has a list of operating capabilities stored in VLR  31  which it can use. In so doing, this creates less signalling at call set-up for example between the MS  4  and the MSC  10  and between the MS  28  and MSC  29 . In practice when a MS  4  requires to initiate a call the MSC  10  will automatically select an operating capability from the list of operating capabilities stored in the VLR  12  and then the subsequent negotiation takes place between the MSC  10  and the MSC  29 . The updated list of operating capabilities may be in order of priority so that if the most preferred operating capability cannot be negotiated then the next most preferred operating capability is attempted for compatibility. 
   The IAM originating from the serving MSC  10  of MS  4 , includes the list of operating capabilities that the originating MS  4  prefers to use and once an operating capability is agreed by the BICC node  29  serving the receiving or destination MS  28 , then the receiving MS  28  will answer by node  29  confirming a selected operating capability to use. 
   If the MS  4  crosses over into a further location area LA 3  then the VLR  22  associated with the MSC  20  which oversees BSC  24  which in turn oversees LA 3  will be updated with the new temporary records of MS  4  as well as HLR  18 . Consequently any negotiation that is to take place on initiation from a call from a mobile station  4  while it is in the location area LA 3  is done through the VLR  22  and the VLR  31  of the terminating subscriber as the new VLR  22  will have the updated list of operating capabilities. 
   An example of signalling that takes place between mobile stations during call set-up is shown in  FIG. 2 . MS  4  in PLMN  2  initiates a call set-up message at  40 . This is received at the serving MSC  10  wherein an Initial Address Message (IAM) is transmitted by way of example over the core network  16  to the MSC  29  serving the terminating subscriber&#39;s MS  28 . Signalling of the IAM is shown at  42 . The IAM contains a list of operating capabilities, which may be prioritised, on which the MS  4  can transmit. The set-up message  44  is used for signalling between the MSC  29  of the terminating subscriber and MS  28 . MS  28  then, through its serving MSC  29 , responds by MSC  29  negotiating or providing a list of operating capabilities on which MS  28  can transmit to the MSC  10  at step  46 . An update may be transmitted at various times or instances from MS  28  to VLR  31  at  45 . Negotiation then takes place at  47  between the MSC  10  and the MSC  29 . Once agreement is reached on which operating capability is to be used between the mobile stations  4  and  28 , at  48 , a ringing signal is initiated and an alert message is sent at  50  and then the MSC  29  serving MS  28  sends an address complete message at  52  to the MSC  10 . The MSC  29  also sends a call progress message at  56  in response to receiving the alert message. On receipt of this message, an ALERT message is sent at  54  to MS  4  which responds by generating a ringing tone. 
   If the subscriber of MS  28  answers, that terminal sends a connect message at  58  which in turn is acknowledged by its serving MSC which forwards on an answer message at  60  to the MSC  10  which in turn sends a connect message  62  to MS  4 . Conversation can then take place between the two mobile subscribers at  64 . 
   It is to be understood that, although this embodiment has been described in relation to a GSM network, the invention equally applies to third generation PLMN networks and other second generation PLMNs including PDC, D-AMPS, UMTS, CDMAOne and CDMA2000, having similar architectures. In the 3G networks negotiations with respect to operating capabilities, such as codecs may be done by nodes in the core networks such as a public switched network. Furthermore, the MS  28  in PLMN  30  may suitably be replaced by a network node either located in the fixed PSTN/ISDN network  16  or in the same PLMN  30 . Thus such capability negotiation may take place between mobile stations in the same mobile network. 
   Second Embodiment 
   In accordance with a second embodiment of the present invention, using the telecommunication system of  FIG. 1 , there is shown a network element, hereinafter referred to as an originating mobile station  4  located in a first PLMN  2  which mobile station  4  is controlled by Base Station Controller or BSC  8 . A Mobile Switching Centre (MSC)  10  directly controls or is linked to the BSC  8  and has an associated storage means in the form of a VLR  12 . A GMSC  14  provides an interface between other networks such as a PSTN or ISDN  16 . The GMSC  14  is directly linked to the MSC  10  and a further MSC  20  which has an associated VLR  22 . Each of the VLRs store details of mobile subscribers and their mobile units that are temporarily located within the serving area of the associated MSC. A further storage means  18  in the form of a Home Location Register (HLR) provides permanent storage of subscriber details and keeps continuous track of the location of a subscriber whether that subscriber is in an MSC service area or in a different PLMN. This information is used by the GMSC  14  when receiving a call from another network. 
   When the mobile station  4  wishes to initiate a communication or a call with a mobile station, hereinafter referred to as a destination mobile station, MS  28  located in a further PLMN  30 , a list of operating capabilities of originating MS  4  is already stored in the VLR  12  associated with the MSC  10  serving MS  4 . The destination mobile station MS  28  is serviced by base station controller BSC  27  which in turn is linked to and controlled by MSC  29 . Associated with the MSC  29  is a storage means in the form of a VLR  31  which stores a list of operating capabilities of MS  28 . The MSC  29  is linked directly to a GMSC  32  which in turn is linked to a further network such as the PSTN/ISDN  16 . A set-up message is transmitted from MS  4  to the MSC  10 . Thereafter an Initial Address Message (IAM) is sent from the MSC  10  to the GMSC  32  which may traverse other nodes such as the GMSC  14  and the fixed network  16 . Included in this message are the operating capabilities, including, for example, the list of codecs that the MS  4  can use. At this stage on receipt by the GMSC  32  of the IAM from MSC  10 , the GMSC  32  will send an information retrieval message in the form of a routing information retrieval signal to the MSC  29 /LVR  31  requesting identification of the destination mobile station by the MSISDN or IMSI, in which case the MSC  29 /LVR  31  will respond by sending the Mobile Subscriber Roaming Number (MSRN). This is sent back to the GMSC  32  for call routing purposes and a list of supported operating capabilities of the MS  28  is returned to the GMSC  32 . The GMSC  32  is then in a position to select a codec or other operating capabilities for use and compatibility between the originating MS  4  and the destination MS  28 . A further Initial Address Message or (IAM) is sent from the GMSC  32  to the MSC  29  including the selected codec whereupon a call is set up between the destination MS  28  and the originating MS  4 . The list of supported operating capabilities, including codecs, by MS  28  is initially obtained from the VLR  31  for use in the return routing information retrieval message from the MSC  29  to the GMSC  32 . 
   The MSC  10  or equivalently a BICC node has capability to separate an ISDN user part (ISUP) signal into a Call Control (CC) portion and a Bearer Control (BC) portion to where the Call Control (CC) portion of the ISUP carries the initial address message IAM. By separating out the CC and BC portions via ISUP, the BC portion can allow the transmission at non-PCM levels particularly across the fixed network  16  which generally operates at 64 kbit/s. For example, channels only require 8 kbit/s or 16 kbit/s can be used so that when the MS  4  communicates with the MS  28 , the selected codec may reflect the transmission at non-PCM levels such as 13 kbit/s for example. 
   Referring to  FIG. 3 , MS  4  in the originating PLMN  2  sets up the call through the set-up signal  34  which is received by the MSC  10 . From there the MSC  10  sends an IAM  36  with a list of the operating capabilities of the MS  4 , which may for example contain a list of codecs X, Y, Z that the MS  4  may use. This is transmitted to the GMSC  32 , which by way of example is transmitted over a core network  16 . The GMSC  32  then sends the routing information retrieval message  38  to the MSC  29 /LVR  31  and when that signal is received a signal is returned to the GMSC  32  including the list of supported codecs and other operating capabilities of MS  28 . In this particular example these supported codecs are identified as X, Y and W. The GMSC  32  then selects an appropriate codec, in this example X, for use by both MS  4  and MS  28  and forwards an IAM  44  to the MSC  29  including the listed codec X and from there a set-up signal  42  is transmitted from the MSC  29  to the MS  28 . At the same time the retrieval message  38  is being sent to the MSC  29 , a call processing signal  46  is sent from the MSC  10  to the MS  4  so as to inform the MS  4  of progress of the call. A message  48 , in the form of an application transport message (APM), containing the selected codec X is transmitted from GMSC  32  to the MSC  10  which in turn transmits a further progress call  50  to the MS  4  containing the selected codec X in this case. Radio Access Bearer (RAB) channels are then set up between the mobile stations and their respective MSCs at steps  52  and  54  respectively. An alert signal  56  is then sent from the destination MS  28  to the originating MS  4  as an in-band tone. On receipt of the alert message, the MS  4  responds by generating a ringing tone and if the subscriber of mobile station  28  answers, that MS sends a connect message at  58  to the MSC  29 . The connection is then acknowledged by the MSC  29  in a return signal  60  to the MS  28  and then the MSC  29  forwards an answer message  62  to the GMSC  32  which is then forwarded at  64  on to the MSC  10 . A connect message  66  is then transmitted from the MSC  10  to the MS unit  4  and connection is acknowledged by the MS  4  in a signal  68  back to the MSC  10 . Thereafter conversation can then take place between the two mobile subscribers. 
   With reference to  FIG. 4  the routing information retrieval message is sent by the GMSC  32  to the Home Location Register (HLR)  33  as a signal  70 . This signal is sent using the Mobile Application Part (MAP) protocol and contains information requesting the identity of the mobile subscriber  28 , such as the MSISDN or IMSI, from the HLR  33 . The HLR  33  then forwards on a signal  72  using MAP to the visited network, in this case MSC  29  and VLR  31  of the MS  28 . The signal  72  includes the request for the MS  28  to provide a roaming number or IMSI (International Mobile Subscriber Identity). Once received by the MSC  29  it responds with a signal  74  containing an acknowledgement of the signal  72  and transmits the mobile subscriber roaming number applicable to the MS  28  together with a list of operating capabilities, including a list of codecs, to be used by the MS  28 . This list is retrieved from the VLR  31 . That gets transmitted to the HLR  33  which in turn forwards a signal  76  to the GMSC  32  containing the routing information acknowledgement and the MSRN and the list of operating capabilities of the mobile station  28 . 
   It will be appreciated that the list of operating capabilities included in the IAM  36  may be incorporated in the MAP message  70  sent from the GMSC  32  to the HLR  33 , and then in the MAP message  72  from the HLR  33  to the MSC  29 /LVR  31 . The selected operating capability may then be returned to the GMSC  32  from the MSC  29 /VLR  31  via MAP messages  74  and  76 . In this case, codec selection takes place in the MSC  29 /LVR  31 . 
   Although this particular embodiment has been described with respect to a GSM network, the invention equally applies to third generation PLMN networks and other second generation PLMN networks, having similar architectures. Furthermore the telecommunications network node in this preferred embodiment has been identified as GMSC  32 . It may equally be a further GMSC in the network identified as the home network of the destination mobile station MS  28 . Alternatively it may be any other node in either a PLMN or a node located in the fixed network  16 . Furthermore the call may not necessarily be established across a fixed network  16  but may be from one mobile network to another mobile network or the originating mobile station and destination mobile station may be located within the same PLMN. 
   With the foregoing description in mind, it is to be appreciated that the speed and efficiency at which operating capabilities, such as codecs and security algorithms, may be substantially accelerated from mobile terminated calls where a list of operating capabilities of the mobile station are stored at a selected telecommunications node such that the requirement for negotiating operating capabilities out of band towards the terminating mobile station is substantially reduced or not needed at all. Furthermore the GMSC serving the originating mobile station may have forwarded to it a list of operating capabilities of the originating mobile station or network element which is sent from the designated VLR associated with the originating mobile station or network element. 
   It will also be appreciated that various modifications and alterations may be made to the preferred embodiments above, without departing from the scope and spirit of the present invention.