Abstract:
The invention proposes a method for signaling various header data ( 5, 10, 20, 25 ) in the transmission of packet data units ( 1 ) in a telecommunications network depending on a type of the respective header data ( 5, 10, 20, 25 ), which requires the lowest possible bandwidth and bit rate. A set of header data ( 5, 10, 20, 25 ) received in a receiver ( 70 ) of the telecommunications network, depending on its signaling ( 30, 35, 40 ), is supplied to one of at least two groups ( 50, 55 ) of algorithms for an evaluation. For a first type of header data ( 5, 10, 20, 25 ), a first algorithm is provided in a first group ( 50 ) of algorithms, and for a second type of header data ( 5, 10, 20, 25 ) a second algorithm is provided in a second group ( 55 ) of algorithms, wherein the first algorithm corresponds to the second algorithm. The signaling ( 30, 35, 40 ) for the first type of header data ( 5, 10, 20, 25 ) and the signaling ( 30, 35, 40 ) for the second type of header data ( 5, 10, 20, 25 ) are combined into a shared signaling.

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/DE01/01115, filed on Mar. 22, 2001 and DE 100 15 640.1, filed Mar. 29, 2000. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention is based on a method for signaling various header data. 
     In packet switched telecommunications networks, payload data are transmitted from a sender to a receiver in packet data units. The packet data units pass through a number of protocol layers in the sender before they are finally sent to the receiver via the telecommunications network. In the process, the individual protocol layers add header data in the form of so-called protocol control data to the actual payload data. These data are also referred to as “headers”. The header data with the protocol control data and the payload data then respectively comprise a packet data unit. In this connection, the protocol control data are used for example to convey the respective packet data unit with the payload data through the telecommunications network to the receiver. As a result, an on the whole relatively large quantity of data can be combined for the protocol control data, which also have to be transported along with the payload data. Particularly in systems with limited bandwidth, as is the case, for example, in mobile radio systems or in telecommunication connections via modems, this especially impedes the bit rate available for the transmission of the payload data. 
     Compression algorithms are used to reduce the data quantity of the protocol control data. These compression algorithms are known, for example, from the documents RFC 1144, Compressing TCP/IP Headers for Low-Speed Serial Links (D 1 ), RFC 2507, IP Header Compression, M. Degermark, B. Nordgren, S. Pink (D 2 ), and RFC 2508, Compressing IP/UDP/RTP Headers for Low-Speed Serial Links (D 3 ). Reference D 2  has disclosed a first group of compression and decompression algorithms of IP headers (Internet Protocol) in combination with TCP headers (Transport Control Protocol) and UDP headers (User Dataframe Protocol). Reference D 3  has disclosed a second group of compression and decompression algorithms, which are based on the compression and decompression algorithms described in reference D 2 , but are only used for IP/UDP/RTP headers (RTP=Real Time Protocol). If packet data units are transmitted from a sender that contains a compressor, to a receiver that contains a decompressor, then the decompressor must be notified as to the nature or type of header data that it is currently receiving. This is usually assured through a corresponding signaling in the form of additional data, as described in the specification “Subnetwork Dependent Convergence Protocol (SNDCP)”, which are sent to the receiver along with the corresponding packet data unit. In this case, for some types of header data with different signaling, a first decompression algorithm is provided in the first group of algorithms and a second decompression algorithm is provided in the second group of algorithms, where the first decompression algorithm and the second decompression algorithm correspond to each other. 
     SUMMARY OF THE INVENTION 
     The method according to the invention has the advantage over the prior art that for the case in which, for a first type of header data, a first algorithm is provided in a first group of algorithms and for a second type of header data, a second algorithm is provided, in a second group of algorithms, where the first algorithm corresponds to the second algorithm, the signaling for the first type of header data and the signaling for the second type of header data are combined into a shared signaling. In this manner, the data quantity to be transmitted in order to send the signaling along with the corresponding packet data unit can be reduced so that the bit rate for the transmission of payload data is impeded as little as possible by the transmission of the signaling. 
     It is particularly advantageous that different types of header data with a shared signaling, depending on their signaling, are supplied to a shared algorithm from the first group and the second group of algorithms. As a result, no additional signaling is required for such header data in order to assign the header data ahead of time to one of the two groups of algorithms in order then, based on the additional signaling, to select from the preselected group the algorithm to be executed so that the above-described savings in data quantity is achieved for the signaling. 
     It is also advantageous that the header data of at least ten different types can be signaled by means of a 3-bit signaling. This is possible through the shared signaling of six of the ten different types and achieves a savings of one bit in comparison to a separate signaling of each different type of header data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention is shown in the drawings and will be explained in detail in the description follows. 
         FIG. 1  shows a packet data unit with header data of a first type, 
         FIG. 2  shows a packet data unit with header data of a second type, 
         FIG. 3  shows a packet data unit with header data of a third type, 
         FIG. 4  shows a packet data unit with a preceding signaling, and 
         FIG. 5  shows a block circuit diagram of a receiver. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In packet switched telecommunications networks, payload data  15  according to  FIG. 1  in the form of packet data units  1  are transmitted from a sender to a receiver  70  according to  FIG. 5 . The packet data units  1  pass through a number of protocol layers in the sender before they are finally sent. In the process, the individual protocol layers add so-called protocol control data in the form of header data, which are also referred to as “headers”, to the payload data  15 . The header data are labeled with the reference numerals  5 ,  10  in  FIG. 1  and, together with the payload data  15 , comprise the packet data unit  1  according to  FIG. 1 . In this connection, the header data  5 ,  10  are used for example to convey the packet data unit  1  with the payload data  15  through the telecommunications network to the receiver  70 . In order to reduce the data quantity of the header data  5 ,  10 , compression algorithms in the sender are used. The header data  5 ,  10  are then compressed with one of these compression algorithms and in this manner, are transmitted via the telecommunication network to the receiver  70  by means of the packet data unit  1 . In the receiver  70 , the header data  5 ,  10  are then decompressed by means of a decompression algorithm, which then reverses the compression of the header data  5 ,  10  executed by the compression algorithm used. 
     The IP protocol layer (Internet Protocol), which is introduced below by way of example, prepends a set of header data in the form of an IP header onto the data from higher protocol layers. If the data are received in the IP protocol layer from a higher TCP protocol layer (Transport Control Protocol), then these data can contain the payload data  15  and a prepended TCP header  10 . The IP protocol layer then also prepends the IP header  5  onto the TCP header  10  so that an IP/TCP header  5 ,  10  is generated, which is prepended onto the payload data  15  according to  FIG. 1 . Correspondingly, an IP/UDP header  5 ,  20  (UDP=User Dataframe Protocol) is prepended onto the payload data  15  of the packet data unit  1  if the data have been received in the IP protocol layer from a UDP protocol layer. 
     Compression algorithms in the sender are used to reduce the data quantity of the header data  5 ,  10 ,  20 . The compression of header data  5 ,  10 ,  20 , which are based on the Internet Protocol (IP), is described in references D 2  and D 3  and will be described briefly below in order to explain the method according to the invention. 
     Reference D 2  describes a method for compressing IP headers  5  in combination with TCP headers  10  or UDP headers  20 . The method is based on the single transmission of a complete combined IP/TCP header  5 ,  10  of this kind or of a complete IP/UDP header  5 ,  20 , which is stored in a compressor of the sender and in a decompressor  45  of the receiver  70 , under a particular identifier CID (Contest Identifier). In this case, the headers are naturally sent along with the corresponding packet data unit  1 . In the subsequent packet data units, those parts of the header data, which do not change or which constantly change, are then no longer transmitted with the header data  5 ,  10 ,  20 . Parts of header data  5 ,  10 ,  20  that change unpredictably are either transmitted to the receiver  70  whole along with the corresponding associated packet data unit  1 , or only the changes in the header data  5 ,  10 ,  20  compared to the last packet data unit sent are transmitted to the receiver  70 . The header data  5 ,  10 ,  20  stored in the decompressor  45  according to  FIG. 5 , under the respectively associated identifier CID, are then updated or refreshed based on the header data  5 ,  10 ,  20  received along with the subsequently transmitted packet data units  1 . In reference D 2 , the following different types of header data  5 ,  10 ,  20  are defined: 
     1. Regular header for uncompressed IP-based header data, for example IP/TCP header data  5 ,  10  according to  FIG. 1  or IP/UDP header data  5 ,  20  according to  FIG. 2 , which contain no other compression-related data (type 1). 
     2. Full header for uncompressed IP/TCP header data  5 ,  10  or uncompressed IP/UDP header data  5 ,  20  with additional compression-related data (type 2). 
     3. Compressed_TCP for compressed IP/TCP header data according to  FIG. 1  (type 3). 
     4. Compressed_TCP_NON_DELTA for header data  5 ,  10 ,  20  in which only the data, which do not change or which constantly change, are omitted, but all other data are transmitted in a complete, compressed format (type 4). 
     5. Compressed_NON-TCP for compressed header data  5 ,  20 , which are not IP/TCP header data  5 ,  10 , but in particular IP/UDP header data  5 ,  20  according to  FIG. 2  (type 5). 
     6. Context_state for header data, which are sent back from the receiver  70  to the sender or from the decompressor  45  to the compressor as an acknowledgment and for the synchronization of header data stored in the decompressor  45  and which do not play any role in the method according to the invention (type 6). 
     Header data of type 1 are not compressed. 
     Header data of type to represent complete header data, which are to be stored in the decompressor  45 , under the associated identifier CID. 
     Header data types 3, 4, and 5 are compressed header data, and header data of type 6 are used for purposes of synchronizing the header data stored in the decompressor  45  and are sent from the decompressor  45  of the receiver to the compressor of the sender. 
     The method described in reference D 3  is based on the method described in D 2 , but is only used for packet data units  1  whose payload data  15  have had a set of RTP header data  25  according to  FIG. 3  prepended onto them in an RTP protocol layer (Real Time Protocol). In the subordinate UDP protocol layer, a UDP header  20  has also been prepended onto the thus generated packet data unit. In the subordinate IP protocol layer, the packet data unit thus generated in the UDP protocol layer has further IP header data  5  prepended onto it, thus generating the packet data unit  1  shown in  FIG. 3 . The header data  5 ,  20 ,  25  shown there can also the referred to as IP/UDP/RTP header data. The following types of IP/UDP/RTP header data  5 ,  20 ,  25  can be differentiated: 
     1. Regular header for uncompressed IP-based header data, for example IP/TCP header data  5 ,  10  according to  FIG. 1  or IP/UDP header data  5 ,  20  according to  FIG. 2 , which contain no other compression-related data (type 7). 
     2. Full header for uncompressed IP/TCP header data  5 ,  10  or uncompressed IP/UDP header data  5 ,  20  with additional compression-related data (type 8). 
     3. Compressed_RTP for compressed IP/UDP/RTP header data  5 ,  20 ,  25  (type 9). 
     4. Compressed_UDP for header data in which only the IP/UDP header  5 ,  20 , but not the RTP header  25  have been compressed (type 10). 
     5. Compressed_NON-TCP for compressed header data, which are not IP/UDP/RTP header data  5 ,  20 ,  25  (type 11). 
     6. Context_state for header data, which are sent back from the receiver  70  to the sender or from the decompressor  45  to the compressor as an acknowledgment and for the synchronization of header data stored in the decompressor  45  and which do not play any role in the method according to the invention (type 12). 
     If packet data units  1  are transmitted from the sender that contains the compressor, to a receiver  70  that contains the decompressor  45 , then the decompressor  45  must be notified as to the nature or type of header data that it is currently receiving. Usually a signaling  30 ,  35 ,  40  is used for this, which is added or prepended onto the packet data unit  1  to be transmitted, as shown in  FIG. 4 . 
     It is now conceivable for packet data units  1  to be transmitted to the receiver  70  with IP/TCP header data  510 , IP/UDP header data  5 ,  20 , or IP/UDP/RTP header data  5 ,  20 ,  25 . In order to permit an evaluation or decompression of header data of all of the types of header data that can be received in the decompressor  45 , these types must be differentiated by means of the signaling  30 ,  35 ,  40 . According to  FIG. 5 , the decompressor  45  contains a first group  50  of algorithms for evaluating or decompressing header data of types 1 to 5 and a second group  55  of algorithms for evaluating or decompressing header data of types 7 to 11. No algorithms need to be provided in the decompressor  45  for header data of type 6 or type 12, since these header data are sent from the decompressor  45  of the receiver  70  to the compressor of the sender. Previously, 4 bits were required in order to be able to explicitly signal the ten types of header data that can be evaluated or decompressed in the decompressor  45 ; one bit was required to select the group  50 ,  55  of algorithms required for the evaluation or decompression of the respective header data. The remaining three bits were used to differentiate among five different algorithms in each of the two groups  50 ,  55 , in order to supply the five types of header data, which could be evaluated or decompressed in the corresponding group of algorithms, to the correspondingly suitable algorithm for the evaluation or decompression. Therefore, up till the present, four bits for the signaling had to be transmitted along with each packet data unit  1 . 
     The invention makes use of the fact that for the evaluation or decompression of header data of types 1, 2, and 5, algorithms in the first group  50  of algorithms are provided, which correspond to the respective algorithm for evaluation or decompression of header data of types 7, 8, and 11 in the second group  55 . This produces a third group  60  in the decompressor  45 , with algorithms, which can be used in a shared fashion for various types of header data, and consequently represents an intersection of the two groups  50 ,  55  of algorithms. Consequently, the third group  60  of shared algorithms includes a first algorithm for evaluating header data of type 1 and type 7, a second algorithm for evaluating header data of type 2 and type 8, and a third algorithm for decompressing header data of type 5 and type 11. In this case, the remaining types of header data to be evaluated or decompressed in the manner described above, either by an algorithm from the first group  50  of algorithms or by an algorithm from the second group  55  of algorithms. In this case, the header data of types 3 and 4 are decompressed by means of a respective algorithm that is only contained in the first group  50  of algorithms, whereas header data of types 9 and 10 are decompressed by means of a respective algorithm that is only contained in the second group  55  of algorithms. 
     In this manner, it is possible to respectively use a shared signaling for the types 1 and 7 of header data, for the types 2 and 8 of header data, and for the types 5 and 11 of header data so that a total of three shared signalings and four additional signalings for the types 3, 4, 9, and 10, or a total of seven different signalings are required, so that three bits are sufficient for the signaling. In  FIGS. 4 and 5 , a first signaling bit is labeled with the reference numeral  30 , a second signaling bit is labeled with the reference numeral  35 , and a third signaling bit is labeled with reference numeral  40 . 
     This is particularly advantageous for telecommunication networks that are embodied as mobile radio networks and in particular are realized using the GSM standard (Global Systems for Mobile communications) or using the UMTS standard (Universal Mobile Telecommunications System) and in which only a limited bandwidth or bit rate is available for the transmission of packet data units. 
     An evaluation of the signaling  30 ,  35 ,  40  takes place in the receiver in a corresponding evaluation unit  65 , which, depending on the signaling detected, sends the received packet data unit  1  to either the first group  50 , the second group  55 , or the third group  60  of algorithms for evaluation or decompression. 
     A table is used below to give an example for the association of the signaling bits  30 ,  35 ,  40  with the individual types of header data: 
     
       
         
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 signaling bits 
                 type 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 30 
                 35 
                 40 
                 type 1, type 7 
               
               
                  0 
                  0 
                  0 
                 type 2, type 8 
               
               
                  0 
                  0 
                  1 
                 type 5, type 11 
               
               
                  0 
                  1 
                  0 
                 type 3 
               
               
                  0 
                  1 
                  1 
                 type 4 
               
               
                  1 
                  0 
                  0 
                 type 9 
               
               
                  1 
                  0 
                  1 
                 type 10