Abstract:
The present invention relates to a method of transmitting data between a content server ( 11 ) and a terminal ( 17 ) belonging to a discontinuous coverage network, said terminal ( 17 ) moving from a first radio coverage area ( 14, 161 ) to a second radio coverage area ( 14, 162 ) over an area ( 14   a ) comprising no radio coverage. Said method is characterized by the following steps: terminating ( 100 ) one or more protocols used by said content server ( 11 ) for the data transmission with the terminal ( 17 ) within a proxy, wherein said proxy is seen as the entry point of the discontinuous coverage network by said content server ( 11 ), using a caching mechanism provided within said discontinuous coverage network for forwarding ( 200 ) data from said proxy to said terminal ( 17 ).

Description:
[0001]     The invention is based on a priority application EP05292605.2 which is hereby incorporated by reference.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a method of transmitting data between a content server and a terminal belonging to a discontinuous coverage network, said terminal moving from a first radio coverage area to a second radio coverage area over an area comprising no radio coverage.  
         [0003]     The present invention further relates to a discontinuous coverage network comprising one or more radio coverage areas and being capable of transmitting data received from a content server to a terminal that moves between and/or resides in said radio coverage areas.  
       BACKGROUND OF THE INVENTION  
       [0004]     Discontinuous coverage networks are radio access networks which do not provide a continuous radio coverage contrary to conventional second or third generation radio access networks as GSM or UMTS. Such discontinuous coverage networks are constituted by islands of radio coverage supporting very high bit rates and low power cells. Such networks are commonly referred as fourth generation (4G) access networks They inter alia provide video/audio streaming services and fast downloads or uploads of large data volumes.  
         [0005]     The islands having radio coverage are nevertheless separated by areas without any radio coverage so that applying usual handover procedures between cells according to common techniques is not possible.  
         [0006]     In such networks, mobile terminals have a reduced mobility. They cannot leave the radio coverage area without loosing the connection.  
         [0007]     A fast mobile IP solution is currently investigated at the IETF for solving this problem. Mobile IP solutions consist in introducing a home agent between the content server and the access controller. The IP address of the moving terminal is modified during terminal mobility. The current IP address of the moving terminal is stored at the home agent together with a permanent IP address. The mobility is totally transparent for the content server which sends the content to the permanent IP address. The translation is performed at the home agent which in turn identifies the access controller under the coverage of which the moving terminal is currently located. This solution enables it to support mobility in IP networks. Nevertheless, even if the speed of the process is accelerated, such a solution do not provide an efficient answer to the need for providing very high rate streaming services to a moving terminal leaving temporarily the zone of radio coverage.  
         [0008]     Furthermore, if the time during which the terminal resides in an area without radio coverage is too long, the data transmission between the terminal and an external network element such as a content provider may be negatively affected in that the behaviour of an application related to the data transmission is modified. For instance, an ongoing communication could completely be stopped or a network interface might appear to be unavailable.  
       SUMMARY OF THE INVENTION  
       [0009]     Therefore, it is an object of the present invention to provide an improved method and network of the above mentioned type, which avoid at least some of the discussed disadvantages of prior art.  
         [0010]     According to the present invention, regarding said method this object is achieved by the following steps: 
        terminating one or more protocols used by said content server for the data transmission with the terminal within a proxy, wherein said proxy is seen as the entry point of the discontinuous coverage network by said content server,     using a caching mechanism provided within said discontinuous coverage network for forwarding data from said proxy to said terminal.        
 
         [0013]     The inventive termination of one or more network protocols used for the data transmission between said content server and said terminal within the proxy enables to maintain a data transmission session with said terminal even if the terminal is currently not within a radio coverage area of the network.  
         [0014]     Even a standard delivery of data to the terminal may be simulated to the content server according to a preferred embodiment of the inventive method. In this case, the content server is not notified of the fact that the terminal is temporarily out of a radio coverage area or unavailable due to any other reason. Consequently, the content server may advantageously proceed with its data transmission to the terminal via the inventive proxy without experiencing any discontinuity that would require an additional overhead such as retransmissions of data packets and the like.  
         [0015]     Data which has been received from said content server within said discontinuous coverage network may be forwarded by the inventive proxy either directly to said terminal or via a radio access point or an access controller or any other network element capable of temporarily storing or forwarding said data to the terminal.  
         [0016]     The functionality of the inventive proxy is advantageously implemented in a network element of said discontinuous coverage network, in particular within an access controller and/or a radio access point of said discontinuous coverage network.  
         [0017]     According to a further advantageous embodiment of the present invention, data which is to be forwarded from said proxy to said terminal is partitioned into cache units, preferably numbered cache units, which may e.g. be consumed by the terminal according to their respective numbers, whereby a particularly secure handling and delivery of cached data to the terminal is accomplished.  
         [0018]     The cache units may e.g. be stored within an access controller and/or a radio access point of said discontinuous coverage network.  
         [0019]     According to a further advantageous embodiment of the present invention, said terminal performs a request to said access controller and/or said radio access point in order to determine whether cache units are available for said terminal. Said request is preferably at least performed whenever the terminal enters a new area of radio coverage.  
         [0020]     A further solution to the object of the present invention is given by a discontinuous coverage network according to claim  11 .  
         [0021]     Other advantageous embodiments of the present invention are defined by the dependent claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     Further advantages and features of the present invention are described in the following detailed description with reference to the drawings in which:  
         [0023]      FIG. 1   a - FIG. 1   c  show an implementation of the present invention in the context of a discontinuous coverage radio access network supporting micro mobility,  
         [0024]      FIG. 2   a - FIG. 2   b  show an implementation of the present invention in the context of a mobile IP based discontinuous coverage radio access network supporting macro mobility, and  
         [0025]      FIG. 3  shows a simplified flowchart of an embodiment of a method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]      FIGS. 1   a  to  1   c  show an implementation of the present invention in the context of a discontinuous coverage radio access network.  FIGS. 1   a  to  1   c  illustrate an example of network architecture for such fourth generation radio access networks where the present invention may be implemented.  
         [0027]     The radio access network comprises a content server  11 , one or more access controllers  14 , radio access points  161 ,  162  and terminals  17 . Content server  11  and access controller  14  are connected to an IP network  13 , access controller  14  and radio access points  161 ,  162  are connected to a transmission network  15 . Terminals  17  are accessible from radio access points  161 ,  162  through an radio-based air interface.  
         [0028]     Each pair of access controller and radio access point  14 ,  161 ;  14 ,  162  defines a respective zone of radio coverage. In the present example the radio coverage is discontinuous, i.e. there are also areas  14   a  without any radio coverage. These areas  14   a  without radio coverage are situated between two areas of radio coverage  14 ,  161 ;  14 ,  162 . It will be understood by the person skilled in the art that the present invention may also apply to mixed continuous and discontinuous networks.  
         [0029]      FIG. 1   a  represents the case where said terminal  17  is within a first radio coverage area  14 ,  161 . The terminal  17  includes a cache memory (not shown).  Figure 1   b  represents the case where said terminal  17  is in an area  14   a  without radio coverage.  FIG. 1   c  represents the case where said terminal  17  is entering a second radio coverage area  14 ,  162 . The depicted scenario illustrates a so-called micro-mobility case, in which two consecutive coverage areas  14 ,  161 ;  14 ,  162  visited by said terminal  17  are serviced by the same access controller  14 .  
         [0030]     According to the present invention, the access controller  14 —additionally to its basic functions—implements a proxy functionality which enables the access controller  14 , to terminate one or more protocols used by said content server  11  for the data transmission with the terminal  17 .  
         [0031]     The respective step  100  of terminating is illustrated in the simplified flow chart of  FIG. 3 .  
         [0032]     Since said proxy is usually seen as the entry point of the discontinuous coverage network by said content server  11 , the inventive process of terminating  100  certain protocols enables to maintain a data transmission between the content server  11  and the network even if the terminal  17  itself is currently not within a radio coverage area  14 ,  161 ;  14 ,  162  and thus the terminal  17  is not able to respond to any data transmissions of the content server  11 .  
         [0033]     Advantageously, said responding and the like is taken over by the proxy, and in general, a standard delivery of data to the terminal  17  is simulated to the content server  11  by the proxy.  
         [0034]     For instance, if a real time streaming protocol (RTP) is used for a data transmission between said content server  11  and said terminal  17 , according to the present invention, the access controller  14  in its inventive proxy function may terminate the RTP protocol and may accordingly immediately return corresponding RTCP (realtime transport protocol control protocol) RR (receiver report)-messages to the content server  11 . In turn, the proxy inhibits any RR-message which may have been sent from the terminal  17  to the content server  11 .  
         [0035]     Thus, performing the inventive method e.g. enables the proxy to timely supply the content server  11  with RR-messages which are necessary to maintain the data transmission with the content server  11 , independent of the state and/or availability of the terminal  17 .  
         [0036]     A further inventive measure symbolized by step  200  of the flow chart of  FIG. 3  consists in using a caching mechanism provided within said discontinuous coverage network for forwarding data from said proxy to said terminal  17 .  
         [0037]     I.e., simultaneously to the handling of e.g. RR-messages and other protocol-related operations which are necessary to maintain a data transmission or communication, respectively, with the content server  11 , data received from the content server  11  which is to be forwarded to the terminal  17  is forwarded using a caching mechanism of the network. Thus it is guaranteed that said data will successfully be forwarded to the terminal  17  even if it is currently not within any of the radio coverage areas  14 ,  161 ;  14 ,  162 .  
         [0038]     Data from the content server  11  may e.g. be forwarded from the proxy to a radio access point  161 ,  162  or to an access controller  14  which may temporarily store said data and later on forward it to the terminal  17 .  
         [0039]     However, according to the present invention, it is also possible for the proxy to directly forward said data to a radio access point  161 ,  162  of the radio coverage area  14 ,  161 ;  14 ,  162  the terminal  17  presently resides in.  
         [0040]     It is also possible for the proxy to directly forward said data to a radio access point  162  of the radio coverage area  14 ,  162  the terminal  17  is expected to visit in future.  
         [0041]     Should the current position of the terminal  17  be known in the proxy, the data received from the content server  11  may also be directly forwarded to the terminal  17 .  
         [0042]     Generally, caching data to be transmitted to the terminal according to the present invention may be performed by any network element that is capable of temporarily storing said data.  
         [0043]     A further particularly advantageous embodiment of the present invention provides for partitioning data which is to be forwarded from said proxy to said terminal  17  into cache units, preferably numbered cache units. As described above, said cache units may e.g. be stored within an access controller  14  and/or a radio access point  161 ,  162  of said discontinuous coverage network. The numbering of said cache units ensures a secure handling and delivery to the terminal  17 .  
         [0044]     Advantageously, said terminal  17  performs a request to said access controller  14  and/or said radio access point  161 ,  162  in order to determine whether cache units are available for said terminal  17 . Said request is preferably performed whenever said terminal  17  leaves an area  14   a  without radio coverage and enters a new radio coverage area  14 ,  161 ;  14 ,  162 . If there are cache units available, the terminal  17  may receive them and directly consume them or cache them for future use.  
         [0045]     Preferably, the terminal  17  also comprises a local cache memory and fills said local cache memory with data, in particular prior to leaving a radio coverage area  14 ,  161 ;  14 ,  162  said terminal  17  presently resides in.  
         [0046]      FIGS. 2   a ,  2   b  show an implementation of the present invention in the context of a mobile IP based discontinuous coverage radio access network supporting macro mobility.  FIG. 2   a  illustrates an example of a network configuration for such fourth generation radio access networks where the present invention may be implemented.  
         [0047]     The radio access network comprises a content server  11 , access controllers  141 ,  142 , and radio access points  161 ,  162 ,  163 ,  164 . Content server  11  and access controllers  141 ,  142  are connected to an IP network  13  which supports the mobile IP functionality thanks to Home Agent (HA)  12  and thanks to Foreign Agents (FA) each associated to one access controller. The HA is associated to the service provided by content server  11  and provides for a unique IP address for the terminal  17  seen from content server  11 . The FA are adapted to take in charge the mobility of the terminal by sending updated information to a table located in HA which registers under the control of which access controller  141 ,  142 , terminal  17  is currently located. Consequently, a translation between the unique IP address used by content server  11  and the local IP address can take place and the data destined to terminal  17  are routed to the appropriate access controller  141 ,  142 .  
         [0048]     Access controllers  141 ,  142  and radio access points  161 , . . . ,  164  are connected to a transmission network  15 . The terminals  17  are accessible from radio access points  161 , . . . ,  164  via an air interface.  
         [0049]     Each pair access controller, radio access point ( 141 ,  161 ), ( 141 ,  162 ), ( 142 ,  163 ), ( 142 ,  164 ) defines a zone of radio coverage. In the example described below the radio coverage is discontinuous so that there remain areas  14   a  of non radio coverage between two areas of radio coverage. It will be understood by the person skilled in the art that the present invention may also apply to mixed continuous and discontinuous networks.  
         [0050]      FIG. 2   a  represents the case where the terminal  17  is under the radio coverage of the coverage area ( 141 ,  162 ).  FIG. 2B  represents the case where the terminal  17  has moved to a new coverage area ( 142 ,  163 ). This case illustrates the macro-diversity case (i.e. the consecutive coverage areas visited by terminal  17  are serviced by different access controller  141 ,  142 ).  
         [0051]     The inventive method of providing proxy functionality and of simulating a standard data delivery to the content server  11  as already described above with respect to the network scenario of  FIG. 1   a  to  1   c , may also be applied to the network scenario of  FIG. 2   a ,  2   b , i.e. in a macro-diversity case.  
         [0052]     The proxy functionality may for instance also be implemented within the HA  12 .  
         [0053]     The present invention enables to benefit from a continuous session control regarding the data transmission between the content server  11  and the terminal  17  even if the terminal  17  is temporarily out of a radio coverage area and if the TCP is used.