Abstract:
A text-based information transmission is made complying with a greater number of transport-layer systems by performing the fragmentation and de-fragmentation of the information object at the application-layer side rather than at transport-layer domain. By this manner, the text-based information service is not restricted to transport-layer systems accommodating the maximum size of the information objects. Rather, it is possible to adjust the fragmentation size of the fragments into which the information objects are fragmented to the maximum transport packet content section size offered by the transport layer within the application layer. The fragment size may even vary in a time-varying manner responsive to instructions from the transport layer posed onto the transport layer in consequence of time-varying transmission channel characteristics, for example.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of copending International Application No. PCT/EP2010/054725, filed Apr. 9, 2010, which is incorporated herein by reference in its entirety, and additionally claims priority from European Application No. EP 09005332.3, filed Apr. 14, 2009, EP 09007012.9, filed May 26, 2009, all of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present application relates to a transmission scheme for text-based information such as, for example, data-carousel text-based information broadcasting an example for which is the XML-based low-profile information service Journaline (R). 
         [0003]    Text-based information signals carrying text-based information content distributed to information objects are used, for example, in data-carousel text-based information broadcasting systems, in data transmissions where the textual information contents are transferred on demand, or in address-based data transmissions directed to specified addressees which may or may not ordered the transmission by demand. 
         [0004]    Data carousel text-based information broadcasting, for example, enables text-based information to be distributed to a huge amount of users while keeping the technical overhead reasonably low. For example, no uplink or feedback signals from the receivers to the broadcast transmitter is needed. In order to enable the users to individually navigate through the information content provided by the broadcast signal according to their personal preferences, the whole information is divided-up into objects referring to other objects, thereby enabling interactively navigating through the resulting linked arrangement of objects. For example, menu objects enable the user to select, among menu items, in order to proceed from one object to the other. 
         [0005]    When considering the transmission of a text-based information signal, care should be taken to distinguish between the transport layer on the one hand and the application layer on the other hand. That is, the text-based information service provides for the text information objects into which the text-based information content is distributed. Obviously, these information objects may have different lengths. These information objects have to be transmitted to the service recipients. This falls into the responsibility of the transport layer system, i.e. the system interfacing the service transmitter and the service recipients/receivers. The transport layer defines the way the data to be transmitted or transported is to be passed on from the application layer to the transport layer and how the data is then passed on from the transport layer to the application layer at the recipient&#39;s side. For example, the transport layer may expect to receive the data to be transmitted in form of packets. Alternatively, the transport layer may allow a stream of data to be passed on to the transport layer at the transmission&#39;s side. In case of text-based information transmission by way of information objects, the service recipient expects to receive the application layer data in units of information objects. This, in turn, means that the transport layer has to be able to cope with the maximum size of the information objects, allowed by the text-based information service. That is, the transport layer has to be defined such that the information objects of maximum size fit into the content section of the transport packet of the transport layer, or the transport layer has to be able to handle inbound information objects having a size greater than the maximum size of the content section of the transport packets with then, at the recipient&#39;s side, re-combining the sub-portions of these information objects so that the fragmented transport is transparent for the service recipient. 
         [0006]    This, however, means that the information service and the respective service receivers are merely applicable in connection with transport layer systems which comply with the afore-mentioned requirements. This, however, restricts the applicability of the respective service. 
       SUMMARY 
       [0007]    According to an embodiment, an application-layer unit for receiving a text-information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units may have an extractor for inspecting each transport unit and extracting a fragment header and a corresponding fragment section therefrom so as to acquire a sequence of fragment sections with associated fragment headers; a de-fragmenter for de-fragmenting the sequence of fragment sections by use of the fragment headers to acquire the information objects with, at least for a part of the information objects, composing the respective information object from a sub-sequence of fragment sections of the sequence of fragment sections; and an information object handler for parsing the information object to acquire an object header and an object content section and processing the information objects according to the object header, wherein the fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections, wherein the de-fragmenter is configured to perform the de-fragmentation by a) checking the fragment header with which a current fragment section is associated as to whether the current fragment section is the first fragment section of a sub-sequence of fragment sections, b) if so, check the fragment header of the current fragment section and the fragment headers associated with a run of fragment sections immediately following the current fragment section and ending at the fragment section immediately preceding a fragment section comprising a fragment header associated therewith which indicates that its fragment section is the first fragment section of a sub-sequence of fragment sections, or at a fragment section that comprises a fragment header associated therewith that indicates that its fragment section is the last fragment section of a sub-sequence of fragment sections, whatever occurs first in the sequence of fragment sections, as to whether there is a discontinuity in the continuity index of these fragment headers; c) if there is a discontinuity in the continuity index of these fragment headers or if the run ends at a fragment section that comprises a fragment header associated therewith that does not indicate that its fragment section is the last fragment section of a sub-sequence of fragment sections, discarding the current fragment section on the run of fragment sections and resuming the de-frequentation at step a) with the fragment section immediately following the run of fragment sections as the current fragment section; and d) otherwise, composing the information object from the current fragment section and the run of fragment sections. 
         [0008]    According to another embodiment, a receiver for a text-information signal carrying text-based information content being distributed to information objects may have a transport-layer unit for receiving a transport signal so as to acquire a sequence of transport units; an application-layer unit for receiving a text-information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units which may have an extractor for inspecting each transport unit and extracting a fragment header and a corresponding fragment section therefrom so as to acquire a sequence of fragment sections with associated fragment headers; a de-fragmenter for de-fragmenting the sequence of fragment sections by use of the fragment headers to acquire the information objects with, at least for a part of the information objects, composing the respective information object from a sub-sequence of fragment sections of the sequence of fragment sections; and an information object handler for parsing the information object to acquire an object header and an object content section and processing the information objects according to the object header, wherein the fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections, wherein the de-fragmenter is configured to perform the de-fragmentation by a) checking the fragment header with which a current fragment section is associated as to whether the current fragment section is the first fragment section of a sub-sequence of fragment sections, b) if so, check the fragment header of the current fragment section and the fragment headers associated with a run of fragment sections immediately following the current fragment section and ending at the fragment section immediately preceding a fragment section comprising a fragment header associated therewith which indicates that its fragment section is the first fragment section of a sub-sequence of fragment sections, or at a fragment section that comprises a fragment header associated therewith that indicates that its fragment section is the last fragment section of a sub-sequence of fragment sections, whatever occurs first in the sequence of fragment sections, as to whether there is a discontinuity in the continuity index of these fragment headers; c) if there is a discontinuity in the continuity index of these fragment headers or if the run ends at a fragment section that comprises a fragment header associated therewith that does not indicate that its fragment section is the last fragment section of a sub-sequence of fragment sections, discarding the current fragment section on the run of fragment sections and resuming the de-frequentation at step a) with the fragment section immediately following the run of fragment sections as the current fragment section; and d) otherwise, composing the information object from the current fragment section and the run of fragment sections. 
         [0009]    According to another embodiment, an application-layer unit for transmitting a text-based information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units within a transport signal may have a fragmenter for fragmenting the information objects into a sequence of fragment sections with, at least for a part of the information objects, fragmentising the respective information objects into a sub-sequence of fragment sections of the sequence of fragment sections; and a header adder for providing each fragment section with a fragment header allowing a de-fragmentation of the fragment sections to acquire the information objects, each fragment section and the fragment header the respective fragment section is associated with, forming a transport unit, wherein the header adder is configured such that fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections. 
         [0010]    According to another embodiment, a transmitter for a text-based information signal carrying text-based information content being distributed to information objects may have an application-layer unit for transmitting a text-based information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units within a transport signal, which may have a fragmenter for fragmenting the information objects into a sequence of fragment sections with, at least for a part of the information objects, fragmentising the respective information objects into a sub-sequence of fragment sections of the sequence of fragment sections; and a header adder for providing each fragment section with a fragment header allowing a de-fragmentation of the fragment sections to acquire the information objects, each fragment section and the fragment header the respective fragment section is associated with, forming a transport unit, wherein the header adder is configured such that fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections; and a transport-layer unit for transmitting, transport unit-wise, the sequence of transport units within a transport signal. 
         [0011]    According to another embodiment, a transport signal may have a text-based information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units, each transport unit being comprising a fragment header and a corresponding fragment section, the fragment headers allowing a de-fragmentation of the sequence of fragment sections to acquire the information objects therefrom, wherein, at least for a part of the information objects, the respective information object is distributed to a sub-sequence of fragment sections of the sequence of fragment sections, wherein the fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections. 
         [0012]    According to another embodiment, a method for, at an application layer, receiving a text-information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units, may have the steps of inspecting each transport unit and extracting a fragment header and a corresponding fragment section therefrom so as to acquire a sequence of fragment sections with associated fragment headers; de-fragmenting the sequence of fragment sections by use of the fragment headers to acquire the information objects with, at least for a part of the information objects, composing the respective information object from a sub-sequence of fragment sections of the sequence of fragment sections; and parsing the information object to acquire an object header and an object content section and processing the information objects according to the object header, wherein the fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections, wherein the de-fragmentation is performed by a) checking the fragment header with which a current fragment section is associated as to whether the current fragment section is the first fragment section of a sub-sequence of fragment sections, b) if so, check the fragment header of the current fragment section and the fragment headers associated with a run of fragment sections immediately following the current fragment section and ending at the fragment section immediately preceding a fragment section comprising a fragment header associated therewith which indicates that its fragment section is the first fragment section of a sub-sequence of fragment sections, or at a fragment section that comprises a fragment header associated therewith that indicates that its fragment section is the last fragment section of a sub-sequence of fragment sections, whatever occurs first in the sequence of fragment sections, as to whether there is a discontinuity in the continuity index of these fragment headers; c) if there is a discontinuity in the continuity index of these fragment headers or if the run ends at a fragment section that comprises a fragment header associated therewith that does not indicate that its fragment section is the last fragment section of a sub-sequence of fragment sections, discarding the current fragment section on the run of fragment sections and resuming the de-frequentation at step a) with the fragment section immediately following the run of fragment sections as the current fragment section; and d) otherwise, composing the information object from the current fragment section and the run of fragment sections. 
         [0013]    According to another embodiment, a method for, at an application layer, transmitting a text-based information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units within a transport signal, may have the steps of fragmenting the information objects into a sequence of fragment sections with, at least for a part of the information objects, fragmentising the respective information objects into a sub-sequence of fragment sections of the sequence of fragment sections; and providing each fragment section with a fragment header allowing a de-fragmentation of the fragment sections to acquire the information objects, each fragment section and the fragment header the respective fragment section is associated with, forming a transport unit, wherein the provision of each fragment section with a fragment header is performed such that fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections. 
         [0014]    According to another embodiment, a computer program may have instructions for performing, when running on a computer, a method for, at an application layer, receiving a text-information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units, the method having the steps of inspecting each transport unit and extracting a fragment header and a corresponding fragment section therefrom so as to acquire a sequence of fragment sections with associated fragment headers; de-fragmenting the sequence of fragment sections by use of the fragment headers to acquire the information objects with, at least for a part of the information objects, composing the respective information object from a sub-sequence of fragment sections of the sequence of fragment sections; and parsing the information object to acquire an object header and an object content section and processing the information objects according to the object header, wherein the fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections, wherein the de-fragmentation is performed by a) checking the fragment header with which a current fragment section is associated as to whether the current fragment section is the first fragment section of a sub-sequence of fragment sections, b) if so, check the fragment header of the current fragment section and the fragment headers associated with a run of fragment sections immediately following the current fragment section and ending at the fragment section immediately preceding a fragment section comprising a fragment header associated therewith which indicates that its fragment section is the first fragment section of a sub-sequence of fragment sections, or at a fragment section that comprises a fragment header associated therewith that indicates that its fragment section is the last fragment section of a sub-sequence of fragment sections, whatever occurs first in the sequence of fragment sections, as to whether there is a discontinuity in the continuity index of these fragment headers; c) if there is a discontinuity in the continuity index of these fragment headers or if the run ends at a fragment section that comprises a fragment header associated therewith that does not indicate that its fragment section is the last fragment section of a sub-sequence of fragment sections, discarding the current fragment section on the run of fragment sections and resuming the de-frequentation at step a) with the fragment section immediately following the run of fragment sections as the current fragment section; and d) otherwise, composing the information object from the current fragment section and the run of fragment sections. 
         [0015]    According to another embodiment, a computer program may have instructions for performing, when running on a computer, a method for, at an application layer, transmitting a text-based information signal carrying text-based information content being distributed to information objects in form of a sequence of transport units within a transport signal, the method having the steps of fragmenting the information objects into a sequence of fragment sections with, at least for a part of the information objects, fragmentising the respective information objects into a sub-sequence of fragment sections of the sequence of fragment sections; and providing each fragment section with a fragment header allowing a de-fragmentation of the fragment sections to acquire the information objects, each fragment section and the fragment header the respective fragment section is associated with, forming a transport unit, wherein the provision of each fragment section with a fragment header is performed such that fragment headers associated with the sequence of the fragment sections are configured such that the fragment headers reveal as to whether the associated fragment section is the first fragment section of a sub-sequence of fragment sections into which an information object is fragmented; the fragment headers reveal as to whether the associated fragment section is the last fragment section of a sub-sequence of fragment sections into which an information object is fragmented; and the fragment headers of a sub-sequence of fragment sections into which an information object is fragmented comprise a continuity index continuously changing from the first to the last fragment section of the sub-sequence of fragment sections. 
         [0016]    The present invention is based on the finding that the text-based information transmission complies with a greater number of transport-layer systems when the fragmentation and de-fragmentation of the information object is performed at the application-layer side rather than at transport-layer domain. By this manner, the text-based information service is not restricted to transport-layer systems accommodating the maximum size of the information objects. Rather, it is possible to adjust the fragmentation size of the fragments into which the information objects are fragmented to the maximum transport packet content section size offered by the transport layer within the application layer. The fragment size may even vary in a time-varying manner responsive to instructions from the transport layer posed onto the transport layer in consequence of time-varying transmission channel characteristics, for example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Embodiments of the present invention are described in the following in more detail with regard to the Figs. In particular: 
           [0018]      FIG. 1   a  a schematic diagram of an illustrative application-layer system; 
           [0019]      FIG. 1   b  a schematic diagram of a illustrative tree-structure of information objects; 
           [0020]      FIG. 2  a block diagram for a text-based information signal according to an embodiment; 
           [0021]      FIG. 3  a block diagram of a receiver for a text-based information signal according to an embodiment; and 
           [0022]      FIG. 4   a  and  b , schematic diagrams of exemplary ways of transporting the fragment sections plus associated fragment header. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1   a  shows an application-layer system as an example where the present invention may be utilized. The application-layer system of  FIG. 1   a  is a text-based information service system where a text-based information signal carrying text-based information content is provided from a transmission side  10  to a receiving side  12 . The text-based information content may, for example, comprise news, advertisements or other textual information. The text-based information content is distributed to a plurality of information objects  14 . As shown in  FIG. 1   a , each object may, for example, comprise an object header  15  and an object content section  18 . Further, each object  14  may have associated therewith a unique object ID among a plurality of different object IDs. This object ID may, as shown in  FIG. 1   a , be contained within the object header, as shown at reference sign  20 . The text-based content of the respective object  14  is contained by the object content section  18  as shown at  22 . Some of the objects  14  may have links to other objects. Such a link item is shown in  FIG. 1   a  at reference sign  24  as being included within the object content section  18 . The link item  24  comprises a pointer  26  pointing or referring to an object ID different from the object ID  20  of the object to which pointer  26  belongs, as well as a label  28 . Both text portions  22  as well as labels  28  are dedicated for being presented to the user at the receiving side  12 . As it is described in more detail below, the user at the receiving side  12  is given the opportunity to activate the link item  24  represented by the label  28 , thereby navigating from the current object with a current object ID  20  to the object to which the pointer  26  of the activated link item  24  refers. The latter aspect is described in more detail below with respect to  FIG. 1   b.    
         [0024]    Of course, further syntax elements may be comprised by the object header  16  and/or the object content section  18  and/or the object itself. For example, the object header  16  may comprise the syntax element  30  specifying the type or structure of the object content section  18 . For example, manual objects, pure text objects, list objects and so forth may be distinguished. 
         [0025]    As shown in  FIG. 1   a , the transmission side  10  comprises a provider  32  being configured to provide the objects  14  to the receiving side. Provider  32  may be configured to provide the object  14  to the receiving side  12  in a data-carousel manner. That is, provider  32  may be configured to cycle through the object IDs wherein the repetition rate at which a certain object ID is visited, may be different between the individual object IDs. Alternatively, provider  32  may be configured to provide the objects  14  to the receiving side  12  on demand, i.e. responsive to a request from the receiving side  12  to provide a certain object with a determined object ID to the receiving side  12 . 
         [0026]    At the receiving side  12 , a processor  34  is configured to receive the information objects  14  provided by provider  32  and to parse them and handle them according to the specification within the object header  16  as it is described in more detail below. Several devices are connected with processor  34 . These devices comprise a presentation device  36 , an input device  38  and a memory  40 . In particular, processor  34  is configured to present the textual content within the object content section  18  of an object having a currently selected object ID  20  to the user via the presentation device  36 . The presentation device  36  may, for example, comprise a display, such as a graphical display or text display. However, it is also possible that the presentation device  36  comprises a loudspeaker with processor  34  performing a text-to-speech conversion in presenting the textual content of an object to the user. If present, processor  34  presents the label  28  of link items  24  to the user. The user, in turn, is given the opportunity to activate or select such link item  24  presented via presentation device  36 , by means of the input device  38 . For example, the input device  38  may comprise a toggle switch such as, for example, a 4-toggle switch, or a rotating knob or may comprise a touch screen capability, or a combination thereof. Even a speech recognition input capability enabling speech control would be feasible. In particular, in case of more than one link item  24  being present in the currently selected and presented object, processor  34  may be configured to highlight an actually selectable link item among these link items with the user being able to, via the input device  38 , change the currently selectable link item and activate the currently selectable link item, respectively. Responsive to a selection of a link item, processor  34  appoints the object ID referred to by the pointer  26  of the selected link item  24 , as the newly-selected object ID and obtains an object with that object ID and presents its textual content to the user via the presentation device  36 . In case of a data-carousel, processor  34  may obtain the object having the newly-selected object ID from the data-carousel text-based information signal provided by provider  32  or a precached version thereof stored within an object cache  42  within memory  40 . Alternatively, processor  34  may obtain the information object  14  having the newly-selected object ID by requesting same from provider  32 . 
         [0027]    In the above-described text-based information service system, the user is given the opportunity to navigate through the text-based information content of that service. To illustrate this, reference is made to  FIG. 1   b .  FIG. 1   b  shows an illustrative tree structure of information objects  14 , the tree structure being defined by the pointers  26  or link items  24 . In particular,  FIG. 1   b  distinguishes between objects  50  comprising one or more link items  24  which are illustrated by rectangles having rounded corners and being marked with “M”, and objects  52  having right-angled corners being marked with “T”. As already denoted above, each object  14  is assigned a unique object ID. In other words, the object  14  shown in  FIG. 1   b  each has a unique object ID associated therewith, which is different from the object ID of any other object  14  as shown in  FIG. 1   b . One of the link objects  50  may be associated with a specific object ID which is, in case of  FIG. 1   b , exemplarily the object ID 0x0000. This object  54  forms a root of the tree structure  56  into which the objects  14  are structured by the pointers  28 . A specific object ID of the root object  54  may be known at the receiving side  12  and may be initially presented to the user by processor  34  upon, for example, switching on processor  34 . The root object  54  forms a first hierarchy level of the hierarchical tree structure  56 . The pointers  26  of the link items  24  of the root object  54  point to objects  14  having different object IDs forming a second hierarchy level as illustrated by arrows starting from root object  54  and extending to objects  14  of the second hierarchy level. Objects  50  of the second hierarchy level in turn, have link items with pointers pointing to objects having a respective different object ID and so forth. The “hierarchy level” of an object  14  may be defined as the shortest possible path from the root object  54  to the respective object. Although the range of hierarchy levels may be unrestricted, according to an embodiment, the number of hierarchy levels may be restricted to a maximum value, such as 20 hierarchy levels. Similarly, the number of link items per object  50  may be unlimited or may be restricted to some maximum value. As shown in  FIG. 1   b , an object  14  may be referred to or pointed to by respective link items of more than one object  50 . Further, the pointer of the link item of a certain object  50  is not restricted to point to an object of the subsequent hierarchy level. Rather, the object  50  of a certain hierarchy level may have a link item pointing to an object having a different object ID within a lower hierarchy level as it is illustrated by dotted lines in  FIG. 1   b.    
         [0028]    With additional reference to  FIG. 1   a , processor  34  is configured to assist the user in navigating through the tree  56  of objects. In particular, processor  34  may be configured to monitor a data-carousel signal provided by provider  32  or may look-up in the object cache  42 , to detect an object  14  having a currently selected object ID associated therewith and to render a presentation to the user representing the content of this information object via presentation device  36 . If the currently presented object comprises a link item  24 , the user is prompted to select this or to select one of the link items  24  of the currently presented object. In particular, the user is able to select one of several link items by use of the input device  38 . Upon the selection of a certain link item by the user, processor  34  appoints the object ID referred to by this link item  24  as a newly-selected object ID, whereupon processor  34  monitors, for example, a data-carousel signal provided by provider  32  or a cached version thereof stored in cache  32 , in order to present the textual content of this object to the user and so forth. As outlined before, according to an alternative embodiment, processor  34  requests a newly-selected object ID from provider  32  instead of using a data-carousel signal. 
         [0029]    Processor  34  may use the memory  40  in order to keep track of the recently visited object IDs in their visiting order. In other words, processor  34  may store a path history  58  in memory  40 , the path history  58  comprising a list of traversed object IDs when navigating from the route object  54  to any other object  14 . The path history  58  may be restricted to a certain number of object IDs, with this number being, for example, equal to the maximum number of hierarchy levels or greater than the latter. Processor  34  may use the path history  58  in order to obtain the object ID of the object  50  from where the user reached the currently-displayed object, upon the user requesting returning to this previous object  50  by use of, for example, input device  38 . Processor  34  may be configured to shorten the history path  58  in case a newly-selected object ID is already present in the path history  58 . Further, processor  34  may be configured to remove the oldest or any other object ID from the path history  58  upon the number of different object IDs in the path history exceeding the maximum number. 
         [0030]    The description above was restricted to the application-layer system. That is, the above description was restricted to the structure and the handling of the information object into which the text-based information content is distributed.  FIGS. 2 and 3  show examples for a transmitter and receiver, respectively, which are configured to implement a text-based information service as described above with respect to  FIGS. 1   a  and  1   b , with the transmitter and receiver also comprising components concerning the transport layer. Thus,  FIGS. 2 and 3  also show the interface between application layer on the one hand and transport layer on the other hand. 
         [0031]      FIG. 2  shows an example of a transmitter  70 . The transmitter  70  comprises an application layer unit  72  and a transport layer unit  74 . The application layer unit comprises an object provider  74 , which corresponds to or is functionally identical with provider  32  of  FIG. 1   a . Further, application layer unit  72  comprises a fragmenter  76  and a header adder  78 . Object provider  74 , fragmenter  76  and header adder  78  are connected in series to transport layer unit  74 , in the order mentioned. 
         [0032]    As already described above with respect to  FIG. 1   a , object provider  74  provides objects  14  and outputs them to fragmenter  76 . In the example of  FIG. 2 , each object comprises in addition to object header  16  and object content section  18  additional data, namely an additional header  80  and redundancy data  82 . Object  14  may be, for example, a MSC data group with the additional header  80  being an MSC data group header, the redundancy data  82  being an redundancy code word determined from and enabling error detection or, alternatively, even error correction of MSC data group header  80 , as well as the MSC data group field consisting of object header  16  and object content section  18 . In addition to the information contained in object header  16 , MSC data group header  80  may identify the text-based information service to which the textual content within the object content section  18  belongs, in order to enable to distinguish information object  14  from objects belonging to another service. It should, however, be emphasized that the just-mentioned portions  80  and  82  are merely optional and may be left off. Further, although in  FIG. 2  portions  80  and  82  are described to be included within the information object  14 , it would also be possible to interpret the information object  14  to be restricted to the data group field of an MSC data group only with the reference sign  14  of  FIG. 2  then, denoting an MSC data group. As, however, sections  80  and  82  are merely optional, the units provided by object provider  74  are denoted information objects  14  as a whole. 
         [0033]    Thus, fragmenter  76  receives data from object provider  74  in units of information objects  14 . In particular, fragmenter  76  receives a sequence of information objects  14  from object provider  74 . The fragmenter  76  is responsible for guaranteeing that the transport layer unit  71  is able to handle the transport and packetizing of the information objects  14 . To this end, fragmenter  76  checks as to whether the information object  14  exceeds a predetermined length which, in turn, may be predetermined or may be, in a time-varying manner, prescribed by the transport layer unit  74  depending on physical circumstances such as a current physical channel situation or the like. If the fragmenter  76  determines that the length of a current information object  14  exceeds the threshold length, then fragmenter  76  splits-up the information object into a sequence of fragments  14   a  and  14   b  so as to be, for example, as long as possible as allowed by the threshold length, thus forming a sub-sequence of a sequence of fragment sections at the output of fragmenter  76  for this information object  14 . As just mentioned, the fragments sections belonging to the same object may have different lengths—not only the last one relative to the preceding ones but also the fragment sections preceding the last one, may differ in length among each other. 
         [0034]    Header adder  78  receives the sequence of fragment sections and provides each fragment section with an associated fragment header  84   a  and  84   b , respectively, enabling, by solely relying on the fragment headers  84   a  and  84   b , a de-fragmentation of fragment sections  14   a ,  14   b  to reconstruct the sequence of information objects  14  from the sequence of fragment sections  14   a  and  14   b . In particular, the fragment headers  84   a ,  84   b  may be determined such that same indicate as to whether the fragment section they belong to, is the first fragment section of a sub-sequence of fragment sections forming, together, an information object, as to whether the fragment section it belongs to, is the last fragment section of a sub-sequence of fragment sections forming, together, an information object, and enable to check, solely based on the fragment headers, as to whether the fragment sections completely reconstruct the information object or as to whether a fragment section is missing. 
         [0035]    As shown in  FIG. 2 , each fragment header  84   a ,  84   b  may, for example, comprise a first-flag, a last-flag  88  and a continuity index  90 . The first flag  86  may be enabled if the fragment section  14   a  comprises a first fragment of an information object  14  with, otherwise being disabled. Similarly, the last-flag  88  may be enabled if the fragment section  14   a  associated with fragment header  84   a  comprises a last fragment of an information object, with, otherwise, being disabled. A continuity index  90 , in turn, may comprise a counter that starts from zero at fragment sections  14   a  comprising the first fragment of an information object and is incremented by one for each subsequent fragment section  14   b  comprising a fragment of this information object. The first-flag  86  and last-flag  88  may be one-bit symbols. The continuity index  90  may, for example, be a six-bit counter value. If an information object is fragmented in more than 2 6 =64 fragment sections, the counter may overflow or re-start at zero which could be regarded as normal behaviour at the receiving side as will be described in more detail below. 
         [0036]    In the following, an example for a sequence of fragment headers is listed for the illustrative case that three consecutive information objects are fragmented into one, four and two fragments, respectively. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 First flag 
                 Last flag 
                 Continuity index 
               
               
                   
                   
               
             
             
               
                   
                 1 
                 1 
                 000000 
               
               
                   
                 1 
                 0 
                 000000 
               
               
                   
                 0 
                 0 
                 000001 
               
               
                   
                 0 
                 0 
                 000010 
               
               
                   
                 0 
                 1 
                 000011 
               
               
                   
                 1 
                 0 
                 000000 
               
               
                   
                 0 
                 1 
                 000001 
               
               
                   
                   
               
             
          
         
       
     
         [0037]    The transport layer unit  74  receives the sequence of fragment sections  14   a  and  14   b  each having associated therewith a fragment header  84   a  and  84   b , respectively, and assumes responsibility for the transportation to the receiving side. Due to the fragmentation performed by the fragmenter  76  and header adder  78 , the transport layer unit  74  is not restricted to one being able to cope with the maximum length of the information objects  14 . Rather, a transport layer unit  74  may use any transport layer scheme available. For example, the size limit for the information object  14 , such as in form of MSC data groups, may be 4 kb. Thus, without fragmenter  76  and header adder  78 , a transport layer unit  74  would have to be able to cope with objects of that size. Due to the fragmentation, however, the transport layer unit  74  is not restricted to such a transport layer scheme. For example, the transport layer unit  74  may, in this case, use any of the DAB, DRM, HD radio, Worldspace or any other transport layer system. In fact, the transport layer unit  74  forms a transport signal  92  out of the sequence of fragment sections  14   a ,  14   b  with the associated fragment headers  84   a ,  84   b  in any possible way with, however, logically maintaining the structure of this incoming sequence into the units or fragment section plus fragment header. For example, as shown in  FIG. 4   a , a transport layer unit  74  may packetize each fragment section plus as associated fragment header, i.e. each transport unit, individually into one transport packet content section  94  having, itself, a transport packet header  96  associated therewith. Alternatively, the transport layer unit  92  transports the sequence of fragment sections plus fragment headers as a stream with synchronization headers indicating the borders between consecutive pairs of fragment section and associated fragment header. Even alternatively, the transport layer unit  74  may be able to transport a pair of fragment section plus fragment header distributed to more than one transport packets as illustrated in  FIG. 4   b . The data transfer itself, may be performed in any way such as in form of a terrestrial signal  92  or a satellite signal or the like. Moreover, as already denoted above, the data transmission  92  may be a broadcast signal such as, for example, a wireless transmission broadcast signal, or the transmission aims to specific recipients indicated by a respective address such as, for example, in case of sending the objects on demand. 
         [0038]      FIG. 3  shows a possible receiver for receiving a transport signal  92 . The receiver of  FIG. 3  comprises a transport layer unit  110  and an application layer unit  112  with the latter comprising an extractor  114 , a de-fragmenter  116  and an object handler  118  with the object handler comprising, for example, processor  34  or processor  34  of  FIG. 1   a  and one or more of the elements connected therewith, as shown in  FIG. 1   a.    
         [0039]    The transport layer unit  110  receives a transport signal and reconstructs therefrom a sequence of transport units with each transport unit corresponding or being equal to a pair of fragment headers plus fragment section. The application layer unit  112  of the receiver of  FIG. 3  has the de-fragmenter  116  being connected between the extractor  114  and the object handler  118 . Extractor  114  receives from the transport layer unit  110  the sequence of transport units and extracts therefrom for each transport unit a respective fragment header  120  and fragment section  122 . The de-fragmenter  116 , in turn, de-fragments the forwarded sequence of the fragment sections by use of the fragment headers to obtain the information objects with, at least, for a part of the information objects, composing the respective information object  14  from the respective sub-sequence of fragment sections. The object handler  118 , in turn, uses the thus obtained information objects  14  in the way already discussed above with respect to  FIGS. 1   a  and  1   b.    
         [0040]    In particular, the fragmenter  116  uses the fragment headers in order to check as to whether a fragment of a fragmented information object  14  has become lost somewhere between the transport layer unit  74  of the transmitter and the transport layer unit  110  of the receiver. To this end, the de-fragmenter  116  firstly checks the fragment header of a current fragment section of a current transport unit received from transport layer unit  110  as to whether the associated fragment section comprises a first fragment of an information object. If so, the fragmenter  116  checks the fragment header of the current fragment section as well as the fragment headers associated with a run of fragment sections immediately succeeding the current fragment section as to whether there is a discontinuity indicating that a fragment is missing thereby preventing rebuilding or composing an information object having been fragmented. The afore-mentioned run of consecutive fragment sections is determined to end either at a fragment section preceding a fragment section with a fragment header indicating that its fragment section comprises a first fragment of an information object, or at a fragment section having a fragment header associated therewith which indicates that the respective fragment section comprises a last fragment of an information object, whatever occurs first in the sequence of fragment sections. Both conditions normally apply as can be seen, for example, from the fifth and sixth fragment headers in the above table among which the fifth fragment header belongs to fragment section forming the just-mentioned run end. 
         [0041]    In order to illustrate this in more detail, reference is made to the above exemplified list of fragment headers. Imagine, for example, the current fragment section is the one having the second fragment header in this table. if none of the fragment sections with associated fragment header is lost, the run of consecutive fragment sections extends from the third to fifth fragment header/fragment section pair as the fifth fragment header has the last-flag enabled. If, however, the fifth fragment header plus fragment section would have been lost in transmission, for example, the run of consecutive fragment sections mentioned before would end at the fourth fragment section as this fragment section precedes the immediately following sixth fragment header having the first-flag enabled, and since the first fragment header having the last-flag enabled follows even later. 
         [0042]    If the check reveals that some intermediate fragment section has been lost of the afore-mentioned run or the run ends at a fragment section that immediately precedes a fragment section having a fragment header with the first-flag being enabled, but that has a fragment header the last-flag of which is not enabled, the fragmenter  116  discards the current fragment section plus the run of immediately following fragment sections and resumes the de-fragmentation of the fragment section immediately following the run of fragment sections. 
         [0043]    If, however, the check result is that no fragment is missing, the fragmenter  116  composes the information object from the current fragment section and the run of immediately following fragment sections. Optionally, the fragmenter  116  checks the redundancy information  82  in order to determine as to whether the information object re-composed is correct. 
         [0044]    As a further escape mechanism, the fragmenter  116  may limit the length of run of consecutive fragment sections such that the maximum size for information objects is still fulfilled. If, for example, the fragment section having a fragment header having the first-flag being enabled, is followed by a run of fragment sections ending as defined above, has a sum of the length of these fragment sections exceeding the maximum length for the information objects, it is clear that these fragments belong to different information objects and that any fragment section have been lost. In this case, the fragmenter stops the assembly of fragments at this maximum size, such as at 4 kb, and discards the fragment sections processed so far to resume the processing as denoted above with the next fragment section with a fragment header having the first-flag enabled. 
         [0045]    In particular, when using the type of fragment header having a first-flag, a last-flag and a continuity index  90 , the fragmenter  116  may operate as follows. Firstly, the de-fragmenter  116  may wait for the first-flag being enabled. Then, the fragmenter  116  starts collecting the fragment sections. Continuously, the fragmenter  116  checks the continuity index of the following fragment headers in order to check as to whether there is a discontinuity in the counter indicated by the continuity index  90 . If there is a discontinuity detected, the fragmenter  116  discards all fragments and restarts the operation with the next fragment header having a first-flag enabled. If there is a first-flag detected, the fragmenter  116  knows that a fragment header with the last-flag being enabled has been missed, and therefore, the fragmenter  116  discards the fragment sections collected so far and restarts with the next fragment header having a first-flag being enabled. If, however, the fragmenter  116  reaches the fragment header having a last-flag being enabled before the first occurrence of a fragment header with the first-flag being enabled, the fragmenter  116  passes on the information object  14  composed from the collected fragment sections to the object handler which, in turn, checks, optionally, the redundancy information  82  and, if correct, further processes the information object according to application layer preferences as briefly described above. As indicated above, the collection may be interrupted as soon as the sum of currently collected fragment section lengths exceeds the limit for information objects. 
         [0046]    It is noted that the present invention is neither restricted to carousel based data transmission nor broadcasting. Rather, as was already indicated above, differing from the above outlined description, the embodiments outlined above may also be applied to data transmissions where the data objects are transferred on demand. Similarly, differing from the above outlined description, the above embodiments may be transferred to address-based data transmissions directed to specified addressees which may or may not ordered the transmission by demand. 
         [0047]    In other words, in accordance with an embodiment of the present invention, a receiver for a text-information signal carrying text-based information content being distributed to information objects, may comprise a transport-layer unit for receiving a transport signal so as to obtain a sequence of transport units and an application-layer unit. The application-layer unit comprises an extractor for inspecting each transport unit and extracting a fragment header and a corresponding fragment section therefrom so as to obtain a sequence of fragment sections with associated fragment headers, a de-fragmenter for de-fragmenting the sequence of fragment sections by use of the fragment headers to obtain the information objects with, at least for a part of the information objects, composing the respective information object from a sub-sequence of fragment sections of the sequence of fragment sections, and an information object handler for parsing the information object to obtain an object header and an object content section and processing the information objects according to the object header. Optionally, the transport signal may have each transport unit contained therein in a packetized form distributed to one or more than one transport packet, each transport packet comprising a transport packet header and a transport packet data section, wherein the transport-layer unit may be configured to inspect, for each transport packet, the transport packet header in order to obtain a payload extraction information on a length of the transport content section or on a payload portion within the transport packet section and to extract and forward, by use of the payload extraction information, merely bits of the transport packet to the application-level unit, which concern at least one of the fragment header and the fragment section. 
         [0048]    Similarly, in accordance with an embodiment of the present invention, a transmitter for a text-based information signal carrying text-based information content being distributed to information objects, may comprise an application-layer unit and a transport-layer unit. The application-layer unit may comprise a fragmenter for fragmenting the information objects into a sequence of fragment sections with, at least for a part of the information objects, fragmentising the respective information objects into a sub-sequence of fragment sections of the sequence of fragment sections, and a header adder for providing each fragment section with a fragment header allowing a de-fragmentation of the fragment sections to obtain the information objects, each fragment section and the fragment header the respective fragment section is associated with, forming a transport unit. The transport-layer unit is responsible for transmitting, transport unit-wise, the sequence of transport units within a transport signal. Optionally, the transport-layer unit may be configured to transmit the sequence of transport units within the transport signal such that the transport signal has each transport unit contained therein in a packetized form distributed to one or more than one transport packet, each transport packet comprising a transport packet header and a transport packet data section, the transport packet header comprising a payload extraction information on a length of the transport content section or on a payload portion within the transport packet section indicating the bits of the transport packet which concern at least one of the fragment header and the fragment section. 
         [0049]    Depending on an actual implementation, the inventive broadcast concept can be implemented in hardware or in software. Therefore, the present invention also relates to a computer program, which can be stored on a computer-readable medium such as a CD, a disk, DVD, a memory stick, a memory card or a memory chip. The present invention is, therefore, also a computer program having a program code which, when executed on a computer, performs the inventive method described in connection with the above figures. 
         [0050]    While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention. 
         [0051]    Furthermore, it is noted that all steps indicated in the flow diagrams are implemented by respective means in the receiver, transmitter and units, respectively, and that the implementations may comprise subroutines running on a CPU, circuit parts of an ASIC or the like. 
         [0052]    While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention.