Abstract:
The invention relates to transmitting digital information between the network elements of a frame switched data network. In the present invention, it has surprisingly been discovered that the padding bits of the data field of a minimum sized Ethernet frame can be used for transmitting digital information between the elements of a data network. In that case the frame data field (109) of a minimum sized Ethernet frame contains an information unit (DIU), the size of which in bytes is smaller than the minimum size of a frame data field, as well as other digital information (DI) that is written in an area (107) of the frame data field that corresponds to the padding bits. The invention makes it possible to also utilize the data transmission capacity needed for transmitting the padding bits.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to transmitting digital information between the network elements in a frame switched data network. The object of the invention is a method and system for transmitting digital information in a frame switched data network. 
       BACKGROUND OF THE INVENTION 
       [0002]    Digital information transmitted in frame switched data networks is included in chronologically successive, transmittable data frames. The information contained in a data frame can be coarsely divided into overhead data and payload data. Overhead data includes for example a frame start field, i.e. a synchronizing word by which the starting point of a frame in a transmitted bit flow can be detected. Payload data includes data connected to the utilization of services enabled by the data network, as well as data connected to the operation control and management of the data network. Services enabled by a data network are for instance Internet bank services, electronic shopping services, and electronic data search services. Payload data typically represents an information unit or part of an information unit, produced by a protocol of a higher hierarchy level that uses the transmission service offered by the frame switched data transmission protocol. Said frame switched data transmission protocol can be for example an Ethernet protocol, and said information unit can be for example an IP (Internet Protocol) packet. For instance in a data frame according to the Ethernet protocol, the overhead data is represented by an eight-byte preamble, a six-byte destination address, a six-byte source address, a two-byte frame type detector and a four-byte cyclic redundancy check. In the present document, the term “byte” refers to a group of eight bits, i.e. a bit octet. Payload data carried by an Ethernet frame is placed in a frame data field, the size of which is at least 46 bytes. In case said payload data is less than 46 bytes, the rest of the minimum sized frame data field is filled with padding bits. The Ethernet protocol is described for example in the technical specification IEEE802.3 (Institute of Electrical and Electronics Engineers). In order to be able to utilize the transmission capacity of the data network as effectively as possible, the payload data should be arranged in successive data frames, so that the share of overhead data of all data to be transmitted should be as small as possible, i.e. the share of payload data of all data to be transmitted should be as large as possible. 
       PRIOR ART 
       [0003]    In a prior art arrangement, each digital information unit produced by a protocol of a higher hierarchy level is included in one or several data frames allocated for said information unit. In case the higher hierarchy level protocols produce large quantities of small-size information units, there arises a situation where the share required by said small-size information units of the transmission capacity of the data network is fairly large in comparison with the total data quantity represented by said small-size information units. This kind of situation is created for instance when the frame switched data transmission protocol is an Ethernet protocol, and the higher hierarchy level protocol is an SSM synchronizing protocol (Synchronization Status Messaging in synchronous Ethernet). An SSM protocol is described in the recommendation draft G.8261/Y.1361 of the ITU-T (International Telecommunication Union), in appendix VIII. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is a system for transmitting digital information in a frame switched data network, so that limitations and drawbacks connected to the prior art can be eliminated or alleviated. Another object of the invention is a method for transmitting digital information in a frame switched data network, so that limitations and drawbacks connected to the prior art can be eliminated or alleviated. Yet another object of the invention is a network element, by which limitations and drawbacks connected to the prior art can be eliminated or alleviated. 
         [0005]    In the present invention, it has surprisingly been discovered that the padding bits of a frame data field of a minimum sized Ethernet frame can be used for transmitting digital information between the network elements, such as routers or switches, of a data network. In that case the frame data field of a minimum sized 
         [0006]    Ethernet frame contains a digital information unit, the size of which in bytes is smaller than the minimum size of a frame data field, and also other digital information that is written in an area of the frame data field corresponding to the padding bits. 
         [0007]    By means of the invention, there is achieved a remarkable advantage in that the transmission capacity of the data network can be utilized better than while using the above described prior art arrangement. Now a larger share of the total capacity of the data network is left for utilizing the services enabled by the data network. 
         [0008]    A system according to the invention for transmitting digital information from a first network element to a second network element in an Ethernet frame switched data network is characterized in that the system includes:
       in said first network element a writing unit that is arranged to write said digital information into first padding bits of the frame data field of a minimum sized Ethernet frame, and   in said second network element a reading unit that is arranged to read said digital information from said padding bits,
 
wherein said writing unit is arranged to write flag data into second padding bits of said frame data field of said minimum sized Ethernet frame, said flag data being arranged to indicate whether said first padding bits represent said digital information.
       
 
         [0011]    A method according to the invention for transmitting digital information from a first network element to a second network element in an Ethernet frame switched data network is characterized in that in the method:
       said digital information is written in said first network element into first padding bits of the frame data field of a minimum sized Ethernet frame,   in said first network element, flag data is written into second padding bits of said frame data field of said minimum sized Ethernet frame, said flag data being arranged to indicate whether said first padding bits represent said digital information   said minimum sized Ethernet frame is transmitted from said first network element to said second network element, and   said digital information is read from said first padding bits in said second network element.       
 
         [0016]    A network element according to the invention, which can be for example an IP router or an Ethernet switch, is characterized in that the network element includes a writing unit that is arranged to write said digital information into first padding bits of the frame data field of a minimum sized Ethernet frame, wherein said writing unit is arranged to write flag data into second padding bits of said frame data field of said minimum sized Ethernet frame, said flag data being arranged to indicate whether said first padding bits represent said digital information. 
         [0017]    The various embodiments of the invention are characterized by what is set forth in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]    The invention is described in more detail with reference to the exemplary preferred embodiments and to the appended drawings, where 
           [0019]      FIG. 1  illustrates how digital information is in an embodiment of the invention placed in the padding bits of the frame data field of a minimum sized Ethernet frame in an exemplary situation, 
           [0020]      FIG. 2  illustrates a system according to an embodiment of the invention for transmitting digital information between network elements in an Ethernet frame switched data network, 
           [0021]      FIG. 3  illustrates a system according to an embodiment of the invention for transmitting digital information between network elements in an Ethernet frame switched data network, 
           [0022]      FIG. 4  illustrates a system according to an embodiment of the invention for transmitting digital information between network elements in an Ethernet frame switched data network, 
           [0023]      FIG. 5  illustrates a network element according to an embodiment of the invention, and 
           [0024]      FIG. 6  is a flowchart illustrating a method according to an embodiment of the invention for transmitting digital information from a first network element to a second network element in an Ethernet frame switched data network. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]      FIG. 1  illustrates the placing of digital information according to an embodiment of the invention in the padding bits of the frame data field of a minimum sized Ethernet frame in an exemplary situation. The minimum sized Ethernet frame illustrated in  FIG. 1  contains a preamble  101 , size eight bytes, a destination address  102  (DA), size six bytes, a source address  103  (SA), size six bytes, a frame type detector  104 , size two bytes, a frame data field  109 , size 46 bytes, and a cyclic redundancy check  108 , size four bytes. In  FIG. 1 , the letter “B” refers to bytes. In the exemplary situation illustrated in  FIG. 1 , the share  105  of the frame data field  109  contains a digital information unit DIU that can be for example an IP packet. Now the share  107  of the frame data field  109  contains padding bits. The digital information DI is written in the padding bits contained in the share  106  of the frame data field  109 . In other words, the values of the padding bits contained in the share  106  are selected so that the padding bits contained in the share  106  represent digital information DI. In this embodiment of the invention, in the padding bits placed in the share  110  of the frame data field  109  there is written flag data that indicates whether the padding bits contained in the share  106  represent the digital information DI. Said flag data can be for instance a predetermined bit vector. In an alternative embodiment of the invention, a situation where the padding bits contained in the share  106  of the frame data field  109  do not represent digital information to be utilized, is indicated by giving predetermined values for the padding bits or part of said padding bits. 
         [0026]    In an embodiment of the invention, said flag data contains data that indicates the size of the digital information DI in bytes. 
         [0027]      FIG. 2  illustrates a system according to an embodiment of the invention for transmitting digital information from a first network element  201  to a second network element  202  in an Ethernet frame switched data network  200 , where the other elements of said network, apart from said network elements  201  and  202 , are represented by a cross-hatched ellipse  250 . The network element  201  is a writing unit  203  that is arranged to write digital information DI 1  in the padding bits of the frame data field of a minimum sized Ethernet frame  222 . In this embodiment of the invention, said writing unit  203  is arranged to write digital information DI 1  in an Ethernet frame stored in a buffer memory device  204 . In other words, the writing unit  203  is arranged to write digital information DI 1  in that memory area of said buffer memory device  204  which at the moment of time under observation is storing the padding bits of the frame data field of the Ethernet frame  222 . The dotted line arrow  221  represents said writing. The network element  201  is a transmission unit  205  that is arranged to read Ethernet frames from buffer memory devices  204  and to transmit the read Ethernet frames to a data network element  250 . 
         [0028]    The network element  202  includes a reading unit  206  that is arranged to read digital information DI 2  from the padding bits of the frame data field of the minimum sized Ethernet frame  223 . In this embodiment of the invention, said reading unit  206  is arranged to read digital information DI 2  from an Ethernet frame stored in the buffer memory device  207 . In other words, the reading unit  206  is arranged to read digital information DI 2  from that memory area of said buffer memory device  207  which at the moment of time under observation is storing the padding bits of the frame data field of the Ethernet frame  223 . The dotted line arrow  224  represents said reading. The network element  202  includes a reception unit  208  that is arranged to receive Ethernet frames from the data network element  250  and to write the received Ethernet frames in the buffer memory device  207 . 
         [0029]    For controlling the Ethernet frames stored in the buffer memory devices  204  and  207 , as well as for defining the memory areas to be written and read, there can be used methods and data structures, for example linked lists, that are known as such for men skilled in the art. 
         [0030]    In a system according to an embodiment of the invention, the digital information DI 1  represents time stamp information that indicates the transmission moment of the minimum sized Ethernet frame  222  from the network element  201 . An estimate for said transmission moment can be defined on the basis of the prevailing moment of time, the transmission rate (bits per second) of the transmission unit  205  and on the basis of the quantity of the digital data contained in the buffer memory device  204  that must be transmitted prior to transmitting the Ethernet frame  222 . 
         [0031]    In a system according to an embodiment of the invention, the digital information DI 1  represents the operation control information of an Ethernet frame switched data network  200 . 
         [0032]    In a system according to an embodiment of the invention, the digital information DI 1  represents the management information of an Ethernet frame switched data network  200 . 
         [0033]    The digital information transmitted in padding bits need not represent any of the above enlisted information types, but the above mentioned information types are examples only. In addition to the above mentioned examples, said digital information can represent for instance a random number or some other data to be transmitted from a network element to another network element. 
         [0034]    In a system according to an embodiment of the invention, the writing unit  203  is arranged to define the share represented by the padding bits in the frame data field of the Ethernet frame  222  on the basis of the contents of the information unit placed in said frame data field. Said information unit placed in the frame data field can be for example an IP (Internet Protocol) packet that contains data indicating the size of said IP packet. 
         [0035]    In a system according to an embodiment of the invention, the writing unit  203  is arranged to define the share represented by the padding bits in the frame data field of the Ethernet frame  222  on the basis of the type of the information unit placed in said frame data field, as well as on the basis of a predetermined rule. The information unit placed in said frame data field can be for example an SSM message, and said predetermined rule can represent a known size of the SSM message (Synchronization Status Messaging in synchronous Ethernet). 
         [0036]    In a system according to an embodiment of the invention, the writing unit  203  is arranged to divide the digital information entity that must be transmitted in the network element  202  into at least two parts, each of said parts representing digital information to be written in the padding bits of the frame data field of one minimum sized Ethernet frame. Respectively, the reading unit  206  is arranged to compile the digital information entity of at least two parts, each of said parts representing digital information read from the padding bits of the frame data field of one minimum sized Ethernet frame. 
         [0037]      FIG. 3  illustrates a system according to an embodiment of the invention for transmitting digital information from a first network element  301  to a second network element  302 . The network element  301  is a writing unit  306  that is arranged to write the digital information DI 1  in the padding bits of the frame data field of a minimum sized Ethernet frame E during the transmission of said minimum sized Ethernet frame. In other words, the writing unit is arranged to write the digital information DI 1  in said padding bits while said minimum sized Ethernet frame is being transmitted to a data transmission link  350 . The setting of the value of a single padding bit in a value defined by the digital information DI 1  can be carried out for instance when said padding bit has just been read from the transmission buffer  303 . The dotted line arrow  321  represents said writing. 
         [0038]    The network element  302  includes a reading unit  310  that is arranged to read the digital information DI 2  from the padding bits of the frame data field of a minimum sized Ethernet frame E during the reception of said minimum sized Ethernet frame. In other words, the reading unit is arranged to read the digital information DI 2  from said padding bits while said minimum sized Ethernet frame is being received from the data transmission link  350 . The reading of the value of a single padding bit can be carried out for instance when said padding bit is being written in the reception buffer  307 . The dotted line arrow  322  represents said reading. 
         [0039]    The embodiment illustrated in  FIG. 3  is advantageous particularly when the transmission time of the digital information DI 1  from the network element  301  to the network element  302  must be as short as possible, and/or when the fluctuation of said transmission time between separate transmissions must be as slight as possible. This kind of situation is at hand for example when the digital information DI 1  represents the timing information that is used for synchronizing the operations of the network elements  301  and  302 . 
         [0040]      FIG. 4  illustrates a system according to an embodiment of the invention for transmitting digital information between the network elements  401  and  402  in an Ethernet frame switched data network. The system illustrated in  FIG. 4  enables a two-directional transmission of digital information between the network elements  401  and  402 . Other parts of the data network, apart from said network elements  401  and  402 , are represented by a cross-hatched ellipse  450 . 
         [0041]    The network element  401  includes a writing unit  403  that is arranged to write digital information in the padding bits of the frame data field of a minimum sized Ethernet frame E. The network element  401  includes a reading unit  404  that is arranged to read digital information from the padding bits of the frame data field of another minimum sized Ethernet frame E. 
         [0042]    The network element  402  is a writing unit  406  that is arranged to write digital information in the padding bits of the frame data field of a minimum sized Ethernet frame E. The network element  402  is a reading unit  405  that is arranged to read digital information from the padding bits of the frame data field of another minimum sized Ethernet frame E. 
         [0043]      FIG. 5  illustrates a network element  500  according to an embodiment of the invention. The network element includes a writing unit  501  that is arranged to write the digital information DI 1  to be transmitted in the padding bits of the frame data field of a first minimum sized Ethernet frame E. The network element includes a transmission unit  502  that is arranged to transmit Ethernet frames E in the transmission port  550 . 
         [0044]    A network element according to an embodiment of the invention includes a reading unit  503  that is arranged to read the received digital information DI 2  from the padding bits of the frame data field of a second minimum sized Ethernet frame E. The network element includes a reception unit  504  that is arranged to receive Ethernet frames E from the reception port  551 . 
         [0045]    In a network element according to an embodiment of the invention, the writing unit  501  is arranged to write the digital information DI 1  to be transmitted in the padding bits of the frame data field of said first minimum sized Ethernet frame during the transmission of said first minimum sized Ethernet frame. 
         [0046]    In a network element according to an embodiment of the invention, the reading unit  503  is arranged to read the received digital information DI 2  from the padding bits of the frame data field of said second minimum sized Ethernet frame during the reception of said second minimum sized Ethernet frame. 
         [0047]    In a network element according to an embodiment of the invention, the digital information DI 1  to be transmitted represents time stamp information that indicates the transmission moment of said first minimum sized Ethernet frame. 
         [0048]    The network element illustrated in  FIG. 5  can be for example an IP router or an Ethernet switch, and it can serve for instance as a base station in a mobile phone network. 
         [0049]    The blocks  510  and  511  illustrated in  FIG. 5  represent such elements of the network element that are not significant with respect to the present invention. 
         [0050]      FIG. 6  is a flowchart illustrating a method according to an embodiment of the invention for transmitting digital information from a first network element to a second network element in an Ethernet frame switched data network. In step  601 , said digital information is written in said first network element in the padding bits of the frame data field of a minimum sized Ethernet frame. In step  602 , said minimum sized Ethernet frame is transmitted from said first network element to said second network element. In step  603 , said digital information is read from said padding bits in said second network element. 
         [0051]    In a method according to an embodiment of the invention, said digital information is written in said padding bits while the minimum sized Ethernet frame is being transmitted from said first network element, and said digital information is read from said padding bits while the minimum sized Ethernet frame is being received in said second network element. 
         [0052]    In a method according to an embodiment of the invention, said digital information represents time stamp information that indicates the transmission moment of said minimum sized Ethernet frame from said first network element. 
         [0053]    In a method according to an embodiment of the invention, said digital information represents the operation control information of said Ethernet frame switched data network. 
         [0054]    In a method according to an embodiment of the invention, said digital information represents the management information of said Ethernet frame switched data network. 
         [0055]    In a method according to an embodiment of the invention, the share of the frame data field corresponding to said padding bits is defined on the basis of the contents of the information unit placed in said frame data field. The information unit placed in said frame data field can be for example an IP packet that contains data indicating the size of said IP packet. 
         [0056]    In a method according to an embodiment of the invention, the share of the frame data field corresponding to said padding bits is defined on the basis of the type of the information unit placed in the frame data field, and on the basis of a predetermined rule. The information unit placed in said frame data field can be for example an SSM message, and said predetermined rule can be for example information of the size of the SSM message (Synchronization Status Messaging in synchronous Ethernet). 
         [0057]    In a method according to an embodiment of the invention, the digital information entity is in said first network element divided into at least two parts, each of said parts representing digital information to be written in the padding bits of the frame data field of one minimum sized Ethernet frame. Respectively, said digital information entity is compiled in said second network element of at least two parts, each of said parts representing the digital information read from the padding bits of the frame data field of one minimum sized Ethernet frame. In other words, the digital information entity can be transmitted from the first network element to the second network element by using the padding bits of the frame data fields of several minimum sized Ethernet frames. 
         [0058]    As is obvious for a man skilled in the art, the invention and its various embodiments are not restricted to the above described exemplary embodiments, but the invention and its embodiments can be modified within the scope of the independent claim.