Abstract:
The present invention relates to the information transmission rate between telecommunications nodes. More particularly the invention relates to the control of the rate at which information is transmitted between access nodes separated by a core network. The present invention provides an information rate control function adapted to authorize and/or establish a communication rate for transmission of information including: determining a plurality of maximum information transmission rates along a path of communication established between the plurality of access nodes; selecting a lowest one of the plurality of maximum information transmission rates, and; authorizing and/or establishing communication at a rate no greater than the selected lowest rate. The invention is suitable for use in the transmission of voice information to and from mobile terminals in third-generation mobile access networks across an ATM core network.

Description:
FIELD OF INVENTION 
   The present invention relates generally to the information transmission rate between telecommunications nodes. In one aspect, the present invention relates to the control of the rate at which information is transmitted across a core network, and in particular to the control of the rate at which information is transmitted to and from endpoints in access networks separated by a core network. The invention is suitable, in one aspect, for use in the transmission of voice information to and from mobile terminals in third-generation mobile access networks across an ATM core network and it will be convenient to hereinafter describe the invention in relation to that exemplary application. It should be appreciated, however, that the invention is not limited to that application, only. 
   BACKGROUND OF INVENTION 
   The evolution of mobile communications systems and broadband multi-service networks are generally expected to merge in third-generation mobile systems that will provide global multimedia access to the mobile user. The concept referred to in Europe as the Universal Mobile Telecommunication System (UMTS) and globally as International Mobile Telecommunications in the year 2000 (IMT-2000) includes high-level access to multimedia services and evolution from second-generation mobile systems as key components. Standardization of this new system is carried out mainly by the 3 rd  Generation Partnership Project (3GPP) and the International Telecommunication Union—Telecommunication Standardization Sector (ITU-T). 
   UMTS/IMT-2000 separates the access functionality from the core network functionality, providing a common core network to support various types of access networks. Access networks provide core-network-technology-independent access platforms for mobile and other terminals to all core networks and network services. In order to support the convergence of fixed and mobile telecommunications networks, a common core network for both fixed and mobile access is envisaged. 
   Bandwidth at the air interface in the mobile access networks, which can vary greatly during calls, remains a limiting factor in the volume of information that can be transmitted to and from the wireless mobile terminals 
   SUMMARY OF INVENTION 
   It would therefore be desirable to provide means for facilitating convergence of transmission of information between various nodes in access networks separated by a core network. 
   In one aspect the present invention provides in a telecommunication system having, a core network and a plurality of access nodes in communication with the core network, an information rate control function means adapted to authorise and/or establish a communication rate for transmission of information including: 
   determining means for determining a plurality of maximum information transmission rates along a path of communication established between the plurality of access nodes; 
   selecting means for selecting a lowest one of the plurality of maximum information transmission rates, and; 
   authorising and/or establishing means for authorising and/or establishing communication at a rate no greater than the selected lowest rate. 
   In another aspect the present invention provides a method of authorising and/or establishing a communication rate for transmission of information in a telecommunication system having a core network and a plurality of access nodes in communication with the core network, including the steps of: 
   determining a plurality of maximum information transmission rates along a path of communication established between the plurality of access nodes; 
   selecting a lowest one of the plurality of maximum information transmission rates, and; 
   authorising and/or establishing communication at a rate no greater than the selected lowest rate. 
   Unfortunately, the core network transport protocols of prior art systems, do not currently enable the comparison of the current maximum transmission rate supported by two air interfaces so that the transmission rate of information between mobile terminals or other endpoints within separated access networks cannot be optimized. 
   Therefore, in essence, the present invention stems from the realisation that a common core/backbone network can support fixed and/or mobile access by introducing a functionality that provides a communication rate for transmission based on a selection of the lowest maximum transmission rate in the communication. The maximum rate of transmission of information between wireless mobile terminals, for instance, is the current maximum transmission rate supported by whichever of the two associated air interfaces is the most congested. 
   Preferably, the communication rate is dynamically authorised and/or established during a communication session. 
   Preferably, wherein the communication rate is authorised and/or established at, or prior to, set up of a communication session. 
   Preferably, the information rate control function means is located in the access nodes. 
   Preferably, the information rate control function means is located in the core network. 
   Preferably, the information rate control function means operates in a Service Specific Convergence Sublayer of an AAL2 Adaption layer in the core network. 
   Preferably, the information rate control function means operates in an RTP Transport layer in the core network. 
   A communication system including the invention may include at least two access nodes communicating with endpoints, wherein the path of communication includes endpoint to endpoint communication. 
   One or more of the access nodes may be located in a radio access network. The radio access network may be a second or third generation cellular access network. At least one of the access nodes may be a radio network controller in a UMTS access network. One or more endpoints may be located in a Public Land Mobile Network PLMN. At least one of the endpoints may be a wireless MS. 
   The core network preferably includes a UMSC for mapping messages into an lu framing protocol for transport in the UMTS access network. 
   One or more of the access nodes may be located in a fixed access network, such as, for example, a PSTN, ISDN, or a PSTN/ISDN access network. 
   In one embodiment of the invention, the plurality of maximum information transmission rates are communicated across the core network as messages within I.366.2 Type 3 cells of an ATM AAL2 protocol. 
   In another embodiment of the invention, the plurality of maximum information transmission rates are communicated across the core network as messages within RTP packets of an IP protocol. 
   In another aspect the present invention provides a method for controlling the rate of information transmission between first and second endpoints which communicate with each other via access networks separated by a core network, information transmission to and from said first and second endpoints being respectively set by first and second telecommunications nodes, said first and second endpoints communicating with one of said access networks respectively across first and second interfaces, at least one of said interfaces having a variable maximum information transmission rate, the method including the steps of: 
   (a) said first and second telecommunications nodes respectively signalling to a remote node the maximum information transmission rate able to be supported by said first and second interfaces; 
   (b) comparing the maximum information transmission rates that can be supported by said first and second air interfaces; and 
   (c) setting the information transmission rate of each endpoint to not exceed that of the lower of the maximum information transmission rates. 
   Preferably, the remote node signalled by each of said first and second telecommunications nodes is the other of said first and second telecommunications nodes, the comparison of maximum information transmission rates being carried out in each of said first and second telecommunications nodes. 
   At least one endpoint may include a codec, wherein step (c) includes setting the rate of operation of the codec to the lower of the maximum information transmission rates. 
   In one embodiment of the invention, the core network may be an ATM core network. The ATM core network may include a Type 2 Adaptation layer. The Type 2 Adaptation layer may include an I.366.2 Service Specific Convergence Sub-Layer. I.366.2 Type 3 cells may be used to carry rate control information messages from each telecommunications node. 
   In another embodiment of the invention, the core network may be an IP network. The IP core network may include an RTP transport layer. RTP packets may be used to carry rate control information messages to and from each telecommunications node. 
   At least one of the interfaces may be an air interface. One or more of the access networks may be a radio access network, such as a UMTS access network. At least one of the telecommunications nodes may be a radio network controller forming part of the UMTS network. At least one of the endpoints may be a wireless mobile terminal. The core network may include a UMSC that acts to map rate control information into an lu framing protocol for transport in the UMTS access network. 
   One or more interfaces may alternatively be associated with a fixed access network, such as a PSTN/ISDN network. At least one telecommunications node may be, for example, a transcoder forming part of the fixed access network. At least one of the endpoints may be a fixed network terminal. 
   A further aspect of the present invention provides a telecommunications system including one or more access networks connected to a core network, first and second endpoints which communicate with each other via said access networks across said core network, information transmission to and from said first and second endpoints being respectively set by first and second telecommunications nodes, said first and second endpoints communicating with one of said access networks respectively across first and second interfaces, at least one of said interfaces having a variable maximum information transmission rate, wherein 
   said first and second telecommunications nodes respectively act to signal to a remote node the maximum information transmission rate able to be supported by said first and second interfaces, said remote node acting to compare the maximum information transmission rates that can be supported by said first and second interfaces, and wherein 
   the first and second telecommunications nodes respectively act to set the information transmission rate to and from said first and second endpoints to not exceed that of the lower of the maximum information transmission rates. 
   Yet another aspect of the present invention provides a first telecommunications node for use in a telecommunications system including a core network, one or more access networks connected to said core network, and a second endpoint, said first and second endpoints communicating with each other via said access networks across said core network, information transmission to and from said first and second endpoints being respectively set by first and second telecommunications nodes, said first and second endpoints communicating with one of said access networks respectively across first and second interfaces, at least one of said interfaces having a variable maximum information transmission rate, wherein 
   said first telecommunications node acts to signal to a remote node the maximum information transmission rate able to be supported by said first interface, said remote node acting to compare the maximum information transmission rates that can be supported by said first and second air interfaces, and wherein 
   the second telecommunications node acts to set the information transmission rate of said second endpoint to not exceed that of the lower of the maximum information transmission rates. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The following description refers in more detail to the various features of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the invention is illustrated in a preferred embodiment. It is to be understood, however, that the invention is not limited to the preferred embodiment as illustrated in the drawings. 
     In the drawings: 
       FIG. 1  is a schematic diagram illustrating a cellular system including an ATM core network interconnecting fixed and mobile access networks; 
       FIG. 2  is a timing diagram showing the exchange of rate control information between mobile terminals communicating with the mobile access networks of  FIG. 1 ; and 
       FIG. 3  is a schematic diagram showing the structure of a CPS-Cell used to transport rate control information messages between UMSC&#39;s over the AAL2 core network of  FIG. 1 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , there is shown generally a schematic representation of a third-generation cellular system  1  including an ATM core network  2  which has two parallel UMTS radio access networks  3  and  4  linked to it. Additionally, two fixed networks are linked to the ATM core network  2 , namely a PTSN/ISDN+ network  5  and an internet/intranet+ network  6 . The core network  2  acts to transport information between telecommunications nodes or endpoints forming part of or in communication with any of the networks  3  to  6 . 
   The ATM core network  2  includes at least a first Universal Mobile Telecommunications System Mobile Switching Center (UMSCa)  7  connected to the UMTS radio access network  3  across an lu-interface. The UMTS radio access network  3  includes at least a first Radio Network Controller (RNCa)  8  and Base Stations (BS)  9  connected to them. Mobile Terminals  10  communicate with the Base Stations  9  across an air interface  11 . Similarly, the ATM core network  2  also includes at least a second Universal Mobile Telecommunications System Mobile Switching Center (UMSCb)  12  connected to the UMTS radio access network  4  across an lu-interface. The UMTS radio access network  4  includes at least a first Radio Network Controller (RNCb)  13  and Base Stations (BS)  14  connected to them. Mobile Terminals  15  communicate with the Base Stations  14  across an air interface  16 . 
   The Base Stations  9  and  14  contain equipment for transmission and reception of information to and from the Mobile Terminals  10  and  15 , as well as equipment for encryption/decryption, signal strength measurement and for communication with the Radio Network Controllers  8  and  13 . The Radio Network Controllers  8  and  13  set up radio channels for voice and other traffic and for signaling to the UMSCs  7  and  12 , and monitor the access network portion of connections established. Notably, the Radio Network Controllers  8  and  13  respectively control the air interface resources, and monitor the availability of those resources, for calls made using the Mobile Terminals  10  and  15 . The UMSCs  7  and  12  serve as an interface to the ATM core network  2  and beyond to other access networks, and control the operation of the Radio Network Controllers  8  and  13 . Each of the Mobile Terminals  10 , 15  includes a Coder-Decoder (Codec) for converting analog sound, speech or video to and from digital information suitable for transport across a first of the access networks  3  to  6 , the ATM core network  2  and finally a second of the access networks  3  to  6 . 
   The digital information is transported to and from one of the Mobile Terminals  10  to one of the Mobile Terminals  15  across the ATM core network  2 . In this example, the ATM core network  2  uses the ATM Adaptation Layer Type 2 (AAL2) transmission protocol. The AAL2 transmission protocol provides for bandwidth-efficient transmission of low-rate, short and variable length cells in delay sensitive applications, and is divided into a Common Part Sub-Layer (CPS) and a Service Specific Convergence Sub-Layer (SSCS). The purpose of the SSCS is to convey narrow-band calls consisting of voice, voiceband data, or circuit mode data. Different SSCSs have been defined to support specific AAL2 user services, or groups of services. One such SSCS is defined in the ITU-T Recommendation I.366.2, otherwise known as I.trunk. 
   The desired encoding-decoding rate of information content can vary dramatically during a call. For example, upon detection of voiceband data traffic, it may be desirable to increase the rate of operation of the Codecs from a nominal to a higher rate in order to accommodate the voiceband data. If facsimile traffic is detected and facsimile encoding and decoding is supported by the Mobile Terminals  10 , 15 , the rate of operation of the Codecs may be further altered. Similarly, some voice or other information encoding algorithms are adaptive by nature and can use different information transmission rates depending upon the availability of network resources. It is therefore important to be able to adapt the information transmission rate to an optimal setting depending upon the Codec used and the information content transmitted between Mobile Terminals. 
   In accordance with the invention, the maximum information transmission rate is determined by the most congested link in the connections between one of the Mobile Terminals  10  and one of the Mobile Terminals  15 , namely the air interfaces  11  and  16 . During call set-up, each of the Radio Network Controllers  8  and  13  determines the maximum information transmission rate that the Codec of the remote Mobile Terminal must not exceed. As seen in  FIG. 2 , a rate control message containing this maximum information transmission rate is sent, at step  20 , from each Radio Network Controller  8 , 13  to its corresponding UMSC  7 , 12 . 
   For UMTS, the 3 rd  Generation Partnership Project is currently developing the lu-interface between RNCs and UMSCs. This framing protocol includes a rate control mechanism. The maximum information transmission rate contained in the rate control mechanism sent across the lu-interface is received at each UMSC  7  and  12 —sent respectively from the RNCs  8  and  13 —and mapped into an I.366.2 cell. By way of example, an I.366.2 Type 3 cell  30  is shown in  FIG. 3 . The I.366.2 Type 3 cell  30  includes a cell header  31 , a payload  32 , a message type field  33  and a cyclic redundancy check (CRC) field  34 . The I.366.2 SSCS makes explicit use of the User-to-User Indication (UUI) and implicit use of the Length Indicator (LI) contained in the cell header  31  to route the cell  30  across the ATM core network  2  between UMSCa  7  and UMSCb  12 . The maximum information transmission rate contained in the rate control mechanism sent across the lu-interface is mapped into the payload  32 , and a Rate Control Function code is created in the message type field  33 . The entire payload is protected by the 10-bit CRC. 
   At step  21 , when the UMSCb  12  receives a cell  30  sent from the UMSCa  7 , the UMSCb  12  detects the presence of a Rate Control Function code in the message type field  33  and then maps the payload of the cell  30  into the rate control message of the lu framing protocol for transport across the lu-interface to the Radio Network Controller  13 . Similarly, when the UMSCa  7  receives a cell  30  sent from the UMSCb  12 , the UMSCa  7  detects the presence of a Rate Control Function code in the message type field  33  and then maps the payload of the cell  30  into the rate control message of the lu framing protocol for transport across the lu-interface to the Radio Network Controller  8 . 
   Each Radio Network Controller then uses this rate control message received from the remote Radio Network Controller to control the operation of the Codec of its associated Mobile Terminal by comparing the maximum information transmission rate that can be supported by the air interfaces  11  and  16 , and then controlling the rate of operation of that Codec to not exceed the lower of the two maximum information transmission rates. 
   If a change in the radio channel capacity across one of the air interfaces  11 ,  16  is detected during the connection, the maximum information transmission rate of both Mobile Terminals may be altered. For example, if an altered radio channel capacity is detected across the air interface  11 , in step  22 , the Radio Network Controller  8  is able to compare the previously received maximum information transmission rate across the air interface  16  from the remote Radio Network Controller with the newly detected received maximum information transmission rate of the air interface  11 , and adjust the rate of operation to the Codec of its associated Mobile Terminal to not exceed the lower of the two maximum information transmission rates. 
   At the same time, at step  23 , the newly detected maximum information transmission rate across the air interface  11  is included in the rate control mechanism of the lu framing protocol and sent from the RNCa  8  across the lu-interface to the UMSCa  7 . This rate is then mapped into an I.366.2 Type 3 cell  30  and sent from the UMSCa  7  to the UMSCb  12 . Upon detection at the UMSCb  12  of the presence of a Rate Control Function code in the message type field  33 , the payload of the cell  30  is mapped into the rate control message of the lu framing protocol for transport across the lu-interface to the RNCb. That Radio Network Controller then uses this rate control message to compare the maximum information transmission rate that can now be supported by the air interfaces  11  and  16 , and controls the rate of operation of the Codec of its associated Mobile Terminal to not exceed the lower of the two maximum information transmission rates. 
   It should be understood that various modifications and/or additions may be made to the aforementioned method and system for controlling information transmission rate without departing from the ambit of the present invention. 
   In that regard, the cellular system shown in  FIG. 1  may include elements of second and/or third generation cellular systems, such as a GSM, D-AMPS, IS-136 or other radio access networks. Moreover, whilst a Type 2 Adaptation Layer is used in the exemplary ATM core network  2  described above, it is envisaged that other types of ATM adaptation layers may be used with the invention. 
   Other types of core networks may also be used in relation to the invention. For example, the core network  2  may instead be an Internet Protocol (IP) core network (i.e. a network having an IP network-layer protocol). The transport layer of the IP network may conform to the Real Time Transport-Layer Protocol (RTP). RTP is a framing protocol developed for transporting real-time data across IP networks and designed to be independent of the underlying transport and network layers. 
   Rate Control Messages sent from the RNCs  8 , 13  to the UMSCs  7 , 12  may be mapped into an RTP or RTP Control Protocol (RTCP) packet. An RTP packet includes a fixed RTP header and the payload. The RTP header includes a payload type (PT) field. The maximum information transmission rate contained in the rate control mechanism of the access networks of  FIG. 1  may be mapped into the RTP packet payload, and a Rate Control Function code created in the PT field of the RTP header, for transport across an IP core network. 
   Moreover, access networks communicating with endpoints other than the Mobile Terminals  10 , 15 , and including telecommunications nodes other than RNCs  8 , 13 , may be envisaged. For example, at least one telecommunications node may be a transcoder at the boundary between the core network  2  and the PSTN/ISDN access network  5 . 
   The skilled addressee will appreciate that various other types and combinations of access networks and core networks, and mechanisms for transporting rate control messages across such core networks, may be used in the context of the invention.