Abstract:
A frame transmitting apparatus that transmits a frame via a synchronous digital hierarch network or a synchronous optical network, includes a data-amount detecting unit that detects an amount of data received from other apparatus; and a frame transmitting unit that transmits, when the amount of data detected by the data-amount detecting unit exceeds a predetermined threshold value, a frame in which information pertaining to a frame control is stored in a fixed stuff of a virtual container frame or a synchronous-transport-signal frame.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1) Field of the Invention  
         [0002]     The present invention relates to a frame transmitting apparatus and a frame receiving apparatus that respectively transmits and receives frames transmitted over the synchronous digital hierarch (SDH) network or the synchronous optical network (SONET), and more particularly, to a frame transmitting apparatus and a frame receiving apparatus that efficiently control a data transmission over the SDH/SONET network without lowering efficiency of a transmission process.  
         [0003]     2) Description of the Related Art  
         [0004]     Sending Ethernet (registered Trademark) packets over SDH/SONET network by a technology known as Ethernet (registered Trademark) Over SDH/SONET (EOS), has been gaining ground in recent years.  
         [0005]      FIG. 11  is a drawing for explaining a conventional EOS technology. In the conventional EOS technology, client devices  1   a  to  1   h  send packets over Ethernet (registered Trademark) in the form of a local area network (LAN)  3   a  and  3   b . Transmitting apparatuses  2   a  and  2   b  map the packets to virtual container (VC)/synchronous-transport-signal (STS) frames of SDH/SONET and send the VC/STS frames to the opposing transmitting apparatuses  2   a  and  2   b  over an SDH/SONET network  4 . The client devices  1   a  to  1   h  may be routers, and the like.  
         [0006]     Upon receiving the SDH/SONET frames, the transmitting apparatuses  2   a  and  2   b  convert the SDH/SONET frames into Ethernet (registered Trademark) packets, and send the packets to the client devices  1   a  to  1   h.    
         [0007]     The client devices  1   a  to  1   h  and the transmitting apparatuses  2   a  and  2   b  are provided with oscillators that generate clock signals of a predetermined frequency and carry out data creation and data reading based on the clock signals.  
         [0008]     Large variations in the frequencies of the clock signals generated by the oscillators of different devices lead to erroneous data reading. Therefore, Institute of Electrical and Electronic Engineers (IEEE) has stipulated that the difference of frequencies of the clock signals between different devices shall be limited to no more than ±50 ppm.  
         [0009]     However, even if the difference of the frequencies of the clock signals between different devices is limited to ±50 ppm, problems in effective transmit of packets may still arise if the frequency of the clock signal is far greater than the standard value.  
         [0010]     For instance, let us assume an instance where data is being sent from the client devices  1   a  to  1   d  to the client devices  1   e  to  1   h  via the transmitting apparatuses  2   a  and  2   b . If the frequency of the clock signals of the client devices  1   a  to  1   d  is greater than the frequency of the clock signals of the client devices  1   e  to  1   h , the data sent by the client devices  1   a  to  1   d  slowly builds up in the transmitting apparatus  2   b , resulting in a possible packet loss.  
         [0011]     Further, if there is a limit on the flow rate of data from the client devices  1   a  to  1   d  in the SDH/SONET network  4 , and if the frequency of the clock signals of the client devices  1   a  to  1   d  is large, the data sent from the client devices  1   a  to  1   d  slowly builds up in the transmitting apparatus  2   a , again resulting in a possible packet loss.  
         [0012]     As a countermeasure for packet loss, a range limit method is disclosed in Japanese Patent Laid-Open Publication No. 2002-353979. If the number of packets received from the opposing device exceeds a certain value, a PAUSE packet stipulated by the Ethernet (registered Trademark) standards is sent to the opposing device to control the flow of packets from the device.  
         [0013]     However, in the conventional technology disclosed in the above literature, the efficiency of the transmission process carried out over the SDH/SONET network  4  is compromised.  
         [0014]     Specifically, when a PAUSE packet is to be sent to the transmitting apparatus  2   b  over the SDH/SONET network, the transmitting apparatus  2   b  has to map the PAUSE packet on a VC frame or an STS frame. Consequently, the amount of normal data sent by the transmitting apparatus  2   b  gets limited, resulting in compromised transmission efficiency.  
         [0015]     Again, there is no solution to the problem of accumulating packets sent from the client devices  1   a  to  1   d  in the transmitting apparatus  2   a  arising from the high frequency of the clock signals of the client devices  1   a  to  1   d.    
         [0016]     Thus, effectively controlling the data transmission process without compromising the efficiency of data transmission over the SDH/SONET network  4  has become an important issue that needs tackling.  
       SUMMARY OF THE INVENTION  
       [0017]     It is an object of the present invention to solve at least the above problems in the conventional technology.  
         [0018]     A frame transmitting apparatus according to one aspect of the present invention, which transmits a frame via a synchronous digital hierarch network or a synchronous optical network, includes a data-amount detecting unit that detects an amount of data received from other apparatus; and a frame transmitting unit that transmits, when the amount of data detected by the data-amount detecting unit exceeds a predetermined threshold value, a frame in which information pertaining to a frame control is stored in a fixed stuff of a virtual container frame or a synchronous-transport-signal frame.  
         [0019]     A frame receiving apparatus according to another aspect of the present invention, which receives a frame transmitted via a synchronous digital hierarch network or a synchronous optical network, includes a frame receiving unit that receives a frame in which information pertaining to a frame control is stored in a virtual container frame or a synchronous-transport-signal frame; and a frame control unit that executes the frame control based on the information pertaining to the frame control.  
         [0020]     A method according to still another aspect of the present invention, which is for transmitting and receiving a frame via a synchronous digital hierarch network or a synchronous optical network, includes detecting an amount of data received from other apparatus; transmitting, when the amount of data detected by the data-amount detecting unit exceeds a predetermined threshold value, a frame in which information pertaining to a frame control is stored in a fixed stuff of a virtual container frame or a synchronous-transport-signal frame; and executing, upon receiving the frame transmitted at the transmitting, the frame control based on the information pertaining to the frame control.  
         [0021]     A system according to still another aspect of the present invention, which is for transmitting and receiving a frame via a synchronous digital hierarch network or a synchronous optical network, includes a data-amount detecting unit that detects an amount of data received from other apparatus; a frame transmitting unit that transmits, when the amount of data detected by the data-amount detecting unit exceeds a predetermined threshold value, a frame in which information pertaining to a frame control is stored in a fixed stuff of a virtual container frame or a synchronous-transport-signal frame; and a frame control unit that executes, upon receiving the frame transmitted by the frame transmitting unit, the frame control based on the information pertaining to the frame control.  
         [0022]     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a drawing for explaining a transmission and reception process of a VC-4 frame  10  whose fixed stuff  12  is used as a data storage area;  
         [0024]      FIG. 2  is a drawing for explaining a transmission and reception process of a VC-4 frame  20  whose fixed stuff  22  is used as a storage area;  
         [0025]      FIG. 3  is a drawing for explaining a process of inserting an idle frame  35  between PPP frames  34   a  and  34   b  and storing them in a VC-4 frame  30 ;  
         [0026]      FIG. 4  is a function configuration of a frame transmitting and receiving system according to an embodiment of the present invention;  
         [0027]      FIG. 5  is a detailed functional configuration of a VC-4 mapper  404  shown in  FIG. 4 ;  
         [0028]      FIG. 6  is a detailed functional configuration of a VC-4 terminator  502  shown in  FIG. 4 ;  
         [0029]      FIG. 7  is a flowchart of a transmitting process of the VC-4 frame whose fixed stuff is used as a storage area of PPP frames;  
         [0030]      FIG. 8  is a flowchart of a retrieving process of the PPP frame from the VC-4 frame;  
         [0031]      FIG. 9  is a flowchart of the transmitting process of the VC-4 frame whose fixed stuff includes an idle-frame transmit request;  
         [0032]      FIG. 10  is a flowchart of the transmitting process of the VC-4 frame that includes an idle frame; and  
         [0033]      FIG. 11  is a drawing for explaining a conventional EOS technology. 
     
    
     DETAILED DESCRIPTION  
       [0034]     Exemplary embodiments according to the present invention are explained in detail below with reference to the accompanying drawings.  
         [0035]      FIG. 1  is a drawing for explaining a transmission and reception process of a VC-4 frame  10  whose fixed stuff  12  is used as a data storage area.  
         [0036]     The frame transmission and reception process is carried out under the condition explained with reference to  FIG. 11 , that is, when the frequency of the clock signal of the client devices  1   a  to  1   d  is high and the data sent from the client devices  1   a  to  1   d  has accumulated beyond a predetermined level in the transmitting apparatus  2   a.    
         [0037]     As shown in  FIG. 1 , the VC-4 frame  10  consists of various areas, that is, a Path Overhead (POH)  11 , the fixed stuff  12 , and a payload  13 . The POH  11  is an area that stores control information pertaining to operational management of frame transmission. The fixed stuff  12  is an area where the value of all the bits is set to “1”. The payload  13  is an area that stores Point to Point Protocol (PPP) frames.  
         [0038]     When it is determined that the data sent from the client device has been accumulated beyond a predetermined level in the transmitting apparatus, a fixed-stuff-usage information “55” is stored in the fixed stuff  12 . The fixed-stuff-usage information “55” indicates that the fixed stuff  12  is being used as a PPP frame storage area. The PPP frames are stored in a frame storage area  14  that includes the fixed stuff  12  and the payload  13 , and the VC-4 frame  10  is sent to the transmitting apparatus.  
         [0039]     Upon receiving the VC-4 frame  10 , the transmitting apparatus can determine whether the PPP frames have been sent with the aid of the fixed stuff  12  by checking if the value “55” is stored in the fixed stuff  12  of the VC-4 frame  10 . If the fixed stuff  12  contains the value “55”, the transmitting apparatus retrieves the PPP frames from the frame storage area  14 .  
         [0040]     A transmission error of up to one bit is allowed in the fixed-stuff-usage information. In other words, any value that includes a “5”, such as “54”, “57”, “5D”, “45”, “75”, “15”, “D5”, etc., is treated as “55”. All other values are considered invalid.  
         [0041]     Thus, by storing the fixed-stuff-usage information “55” in the fixed stuff  12 , and using the fixed stuff  12  as a storage area of the PPP frames when data builds up in the transmitting apparatus, the transmit of data is efficiently controlled and the efficiency of data transmission is enhanced.  
         [0042]      FIG. 2  is a drawing for explaining the concept of a transmission and reception process of a VC-4 frame  20  whose fixed stuff  22  is used as a storage area for storing idle-frame-transmit request information. The frame transmission and reception process is carried out under the condition explained with reference to  FIG. 11 , that is, when the frequency of the clock signal of the client devices  1   a  to  1   d  is high and the data sent from the client devices  1   a  to  1   d  has accumulated beyond a predetermined level in the transmitting apparatus  2   b.    
         [0043]     In this process, the transmitting apparatus sends the VC-4 frame  20  that includes the idle-frame transmit request, which is a request to send an idle frame, to a sender transmitting apparatus. Upon receiving the VC-4 frame  20 , the sender transmitting apparatus inserts an idle frame between two PPP frames and stores these frames in the VC-4 frame  20 , thereby controlling the quantity of PPP frames that is transmitted.  
         [0044]     The idle frame is a 4-byte frame having a frame format of generic framing process (GFP) stipulated by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T).  
         [0045]     As shown in  FIG. 2 , idle-frame-transmit request information “AA” is stored the fixed stuff  22  of the VC-4 frame  20 . Control information and PPP frames can still be stored in a POH  21  and a payload  23  of the VC-4 frame  20  even though the idle-frame-transmit request information is stored in the fixed stuff  22 .  
         [0046]     Upon receiving the VC-4 frame  20 , the transmitting apparatus can determine whether there is a request for an idle frame by checking if the value “AA” is stored in the fixed stuff  22  of the VC-4 frame  20 .  
         [0047]     If the value “AA” is stored in the fixed stuff  22 , the transmitting apparatus inserts an idle frame between two PPP frames, stores these frames in the VC-4 frame and sends the VC-4 frame to the transmitting apparatus that made the request for an idle frame.  
         [0048]     A transmission error of up to one bit is allowed in the idle-frame-transmit request information. In other words, any value that includes an “A”, such as “AA”, “AB”, “A8”, “AE”, “A2”, “BA”, “8A”, “EA”, “2A”, etc., is treated as “AA”. All other values are considered invalid.  
         [0049]      FIG. 3  is a drawing for explaining a process of inserting an idle frame  35  between PPP frames  34   a  and  34   b  and storing them in a VC-4 frame  30 . As shown in  FIG. 3 , the transmitting apparatus inserts the idle frame  35  between the PPP frames  34   a  and  34   b  and stores these frames in a payload  33  of the VC-4 frame  30 . The transmitting apparatus also sets control information and a bit value of “1” in a POH  31  and a fixed stuff  32  of the VC-4 frame  30 .  
         [0050]     The transmitting apparatus then sends the VC-4 frame  30  to the transmitting apparatus that requested an idle frame, thereby limiting the quantity of PPP frames transmitted to the transmitting apparatus.  
         [0051]     Thus, by sending to the opposing transmitting apparatus a VC-4 frame that includes an idle-frame insert request when data builds up in the transmitting apparatus, the idle-frame insert request is efficiently sent without compromising the efficiency of data transmission.  
         [0052]     A functional configuration of a frame transmitting and receiving system according to the present embodiment is explained next.  FIG. 4 a  functional configuration of the frame transmitting and receiving system according to the present embodiment. The frame transmitting and receiving system includes a transmitting apparatuses  40  and  50  connected via SDH networks  60   a  and  60   b.    
         [0053]     The transmitting apparatuses  40  and  50  are connected to a clock signal generating device  70 . The clock signal generating device  70  generates clock signals and feeds these clock signals into the transmitting apparatuses  40  and  50  to synchronize the data being sent over the SDH networks  60   a  and  60   b.    
         [0054]     The transmitting apparatuses  40  and  50  receive data from client devices such as routers, and the like, convert the data into frames of VC-4 format that can be sent over the SDH networks  60   a  and  60   b , and send the data to the opposing transmitting apparatuses  50  and  40 .  
         [0055]     The transmitting apparatus  40  includes a data receiver  401 , an elastic storing unit  402 , a PPP mapper  403 , a VC-4 mapper  404 , a data transmitter  405 , a data receiver  406 , a VC-4 terminator  407 , a PPP terminator  408 , an elastic storing unit  409 , a data transmitter  410 , and a clock signal generator  411 .  
         [0056]     The data receiver  401  receives Ethernet (registered Trademark) data from the client device such as a router and separates the clock signal from the data. The elastic storing unit  402  has a memory for storing the data received by the data receiver  401  and keeps track of the data build-up in the memory.  
         [0057]     When the data build-up exceeds a specific threshold value, the elastic storing unit  402  requests the VC-4 mapper  404  to send the data by using the fixed stuff of the VC-4 frame as a storage area of the data, as shown in  FIG. 1 .  
         [0058]     The PPP mapper  403  converts the data received from the client device into PPP frames. The VC-4 mapper  404  takes the data converted to the PPP frames and converts it into a VC-4 frame.  
         [0059]     Further, upon receiving from the elastic storing unit  402  a request to send the data by using the fixed stuff of the VC-4 frame as a data storage area, the VC-4 mapper  404  stores the fixed-stuff-usage information “55” in the fixed stuff of the VC-4 frame. Furthermore, the VC-4 mapper  404  stores the PPP frames fixed stuff and the payload, which together form the frame storage area.  
         [0060]      FIG. 5  is a detailed functional configuration of the VC-4 mapper  404  shown in  FIG. 4 . The VC-4 mapper  404  includes a data buffer  80 , a fixed stuff setting unit  81 , a POH control unit  82 , a control byte setting unit  83 , a multiplexing (MUX) control unit  84 , a 261-ary counter  85 , a nonary counter  86 , and a multiplexer  87 .  
         [0061]     Upon receiving from the elastic storing unit  402  the request to use the fixed stuff of the VC-4 frame as the storage area for PPP frames, the control byte setting unit  83  embeds the fixed-stuff-usage information “55” in the fixed stuff and requests the MUX control unit  84  to store the PPP frames in the frame storage area that includes the fixed stuff and the payload.  
         [0062]     Further, upon receiving from the elastic storing unit  409 , which is described later, idle-frame transmit request to send idle frames to the transmitting apparatus  50 , the control byte setting unit  83  embeds the idle-frame-transmit request information “AA” as shown in  FIG. 2 .  
         [0063]     The MUX control unit  84  controls the multiplexer  87  and creates the VC-4 frame by multiplexing the signals obtained from the data buffer  80 , fixed stuff setting unit  81 , the POH control unit  82 , and the control byte setting unit  83 .  
         [0064]     The 261-ary counter  85  is a counter that counts the columns of the VC-4 frame. The nonary counter  86  is a counter that counts the rows of the VC-4 frame. The multiplexer  87  creates the VC-4 frame by multiplexing the signals obtained from the data buffer  80 , the fixed-stuff setting unit  81 , the POH control unit  82 , and the control byte setting unit  83 .  
         [0065]     To return to  FIG. 4 , the data transmitter  405  converts the VC-4 frame created by the VC-4 mapper  404  into an Administrative Unit (AU) frame, then further converts the AU frame into a synchronous transmit module (STM) frame, and sends the STM frame to the transmitting apparatus  50 .  
         [0066]     The data receiver  406  receives the STM frame sent by the transmitting apparatus  50  via the SDH network  60   b  and carries out an STM frame termination process and an AU frame termination process. The STM frame termination process involves conversion of the STM frame to an AU frame. The AU frame termination process involves conversion of the AU frame into a VC-4 frame.  
         [0067]     The VC-4 terminator  407  carries out a VC-4 frame termination process, which involves retrieving the PPP frames stored in the payload of the VC-4 frame. The PPP terminator  408  carries out a PPP frame termination process, which involves conversion of the PPP frames into Ethernet (registered Trademark) data to be sent to the client device.  
         [0068]     The elastic storing unit  409  has a memory for storing the data obtained from the termination process carried out by the PPP terminator  408  and keeps track of the data build-up in the memory. When the data build-up exceeds a specific threshold value, the elastic storing unit  409  requests the VC-4 mapper  404  to include the idle frames in the VC-4 frame, as shown in  FIG. 2 , and send the VC-4 frame to the transmitting apparatus  50 .  
         [0069]     The data transmitter  410  modulates the data built up in the elastic storing unit  409  and sends the modulated data to the client device. The clock signal generator  411  generates clock signals and feeds the clock signals into the elastic storing unit  409  and the data transmitter  410 .  
         [0070]     The elastic storing unit  402 , the PPP mapper  403 , the VC-4 mapper  404 , the VC-4 terminator  407 , the PPP terminator  408 , and the elastic storing unit  409  generate signals by receiving the clock signals generated by the clock signal generating device  70 .  
         [0071]     The transmitting apparatus  50  includes a data receiver  501 , a VC-4 terminator  502 , a PPP terminator  503 , an elastic storing unit  504 , a data transmitter  505 , a clock signal generator  506 , a data receiver  507 , an elastic storing unit  508 , a PPP mapper  509 , a VC-4 mapper  510 , and a data transmitter  511 .  
         [0072]     The data receiver  501  receives the STM frame sent by the transmitting apparatus  40  via the SDH network  60   a  and carries out the STM frame termination process and the AU frame termination process, respectively involving conversion of the STM frame to an AU frame and conversion of the AU frame to a VC-4 frame.  
         [0073]     The VC-4 terminator  502  carries out the VC-4 frame termination process, involving retrieving the PPP frames stored in the payload of the VC-4 frame. When performing the VC-r frame termination process, the VC-4 terminator  502  determines whether the fixed stuff of the VC-4 frame includes either the fixed-stuff-usage information or the idle-frame-transmit request information.  
         [0074]     If the fixed stuff of the VC-4 frame includes the fixed-stuff-usage information, the VC-4 terminator  502  retrieves the PPP frames stored in the frame storage area, which includes both the areas, namely, the fixed stuff and the payload.  
         [0075]     If the fixed stuff of the VC-4 frame includes the idle-frame-transmit request information, the VC-4 terminator  502  requests the PPP mapper  509  to insert an idle frame between two PPP frames.  
         [0076]      FIG. 6  is a detailed functional configuration of the VC-4 terminator  502  shown in  FIG. 4 . The VC-4 terminator  502  includes a demultiplexer  90 , a POH control unit  91 , a control byte detecting unit  92 , a demultiplexing (DEMUX) control unit  93 , a 261-ary counter  94 , a nonary counter  95 , and a data buffer  96 .  
         [0077]     The demultiplexer  90  retrieves the VC-4 frame from the data receiver  501  and separates the signals of the POH and the fixed stuff from those of the PPP frames. The POH control unit  91  retrieves information pertaining to the POH from the demultiplexer  90  and carries out operational management of frame transmission.  
         [0078]     The control byte detecting unit  92  determines whether the fixed stuff includes either the fixed-stuff-usage information or the idle-frame-transmit request information. If the fixed stuff includes the fixed-stuff-usage information, the control byte detecting unit  92  notifies the DEMUX control unit  93  that the PPP frames are stored in the frame storage area the includes both the areas, namely, the fixed stuff and the payload.  
         [0079]     If the fixed stuff includes the idle-frame-transmit request information, the control byte detecting unit  92  requests the PPP mapper  509  to insert an idle frame between two PPP frames. The DEMUX control unit  93  controls the demultiplexer  90  so as to separate the signals of the POH and the fixed stuff of the VC-4 frame from the signals of the PPP frames.  
         [0080]     Upon receiving the notification from the control byte detecting unit  92  that the PPP frames are stored in the frame storage area, the DEMUX control unit  93  exerts control over the demultiplexer  90  so as to separate the signals of the PPP frames from the frame storage area.  
         [0081]     The 261-ary counter  94  is a counter that counts the columns of the VC-4 frame. The nonary counter  95  is a counter that counts the rows of the VC-4 frame. The data buffer  96  is a buffer where the PPP frames that the demultiplexer  90  separates from the VC-4 frame build up.  
         [0082]     To return to  FIG. 4 , the PPP terminator  503  carries out the PPP frame termination process, which involves conversion of the PPP frames sent to the client device to the Ethernet (registered Trademark) data. The elastic storing unit  504  builds up the data obtained from the PPP frame termination process carried out by the PPP terminator  503 .  
         [0083]     The data transmitter  505  modulates the data built up in the elastic storing unit  504 , and sends the modulated data to the client device. The clock signal generator  506  generates clock signals and feeds the clock signals to the elastic storing unit  504  and the data transmitter  505 .  
         [0084]     The data receiver  507  receives the Ethernet (registered Trademark) data from the client devices such as routers, and separates the clock signals from the received data. The elastic storing unit  508  has a memory for storing data, and builds up the data received by the data receiver  507 .  
         [0085]     The PPP mapper  509  converts the data received from the client devices to PPP frames. Further, upon receiving the request to insert an idle frame between two PPP frames from the VC-4 terminator  502 , the PPP mapper  509  inserts the idle frame between two PPP frames.  
         [0086]     The VC-4 mapper  510  converts the data converted to PPP frames by the PPP mapper  509  to a VC-4 frame. When converting the PPP frames to the VC-4 frame, if idle frames are inserted by the PPP mapper  509 , the VC-4 mapper  510  converts both the PPP frames and the idle frames into a VC-4 frame, as shown in  FIG. 3 .  
         [0087]     The data transmitter  511  converts the VC-4 frame created by the VC-4 mapper  510  to an AU frame and further converts the AU frame into an STM frame, and sends the data in the form of an STM frame to the transmitting apparatus  40 .  
         [0088]     A transmitting process of the VC-4 frame whose fixed stuff is used as a storage area of the PPP frames is explained next.  FIG. 7  is a flowchart of the transmitting process of the VC-4 frame whose fixed stuff is used as a storage area of the PPP frames.  
         [0089]     As shown in  FIG. 7 , the data receiver  401  of the transmitting apparatus  40  receives the data from the client device (Step S 101 ). The elastic storing unit  402  builds up the received data (Step S 102 ) and checks if the data build-up has exceeded a predetermined threshold value (Step S 103 ).  
         [0090]     If the data build-up has exceeded the threshold value (“Yes” at step S 103 ), the control byte setting unit  83  of the VC-4 mapper  404  creates the fixed-stuff-usage information that indicates the fixed stuff is used as a storage area of the PPP frames (Step S 104 ).  
         [0091]     The multiplexer  87  of the VC-4 mapper  404  includes the fixed-stuff-usage information in the fixed stuff and creates a VC-4 frame in which the fixed stuff is used as the frame storage area for storing the PPP frames (Step S 105 ). The data transmitter  405  sends the created VC-4 frame to the transmitting apparatus  50  (Step S 106 ), thus ending the transmitting process of the VC-4 frame.  
         [0092]     If the data build-up has not yet reached the threshold value (“No” at step S 103 ), the multiplexer  87  of the VC-4 mapper  404  creates a VC-4 frame in which the value “1” is set in the entire fixed stuff (Step S 107 ). The process then proceeds to Step S 106  in which the data transmitter  405  sends the created VC-4 frame to the transmitting apparatus  50 , thus ending the transmitting process of the VC-4 frame.  
         [0093]     After the VC-4 frame in which the PPP frames are stored in the fixed stuff is sent, if the data build-up in the elastic storing unit  402  again falls below the threshold value, the VC-4 mapper  404  receives notification to this effect from the elastic storing unit  402 , sets the value “1” in the entire fixed stuff, and creates a normal VC-4 frame in which the PPP frames are stored in the payload.  
         [0094]     A retrieving process of the PPP frames from the VC-4 frame is explained next.  FIG. 8  is a flowchart of the retrieving process of the PPP frames from the VC-4 frame.  
         [0095]     As shown in  FIG. 8 , once the data sent by the transmitting apparatus  40  is received by the data receiver  501  of the transmitting apparatus  50 , the demultiplexer  90  of the VC-4 terminator  502  receives the VC-4 frame from the data receiver  501  (Step S 201 ).  
         [0096]     The demultiplexer  90  separates the VC-4 frame into bytes (Step S 202 ). The control byte detecting unit  92  of the VC-4 terminator  502  determines whether the fixed stuff of the VC-4 frame includes the fixed-stuff-usage information (Step S 203 ).  
         [0097]     If the fixed stuff of the VC-4 frame includes the fixed-stuff-usage information (“Yes” at step S 203 ), the demultiplexer  90  of the VC-4 terminator  502  retrieves the PPP frames from the frame storage area that includes both the fixed stuff and the payload (Step S 204 ).  
         [0098]     The demultiplexer  90  of the VC-4 terminator  502  then outputs the retrieved PPP frames to the PPP terminator  503  via the data buffer  96  (Step S 205 ), thus ending the retrieving process of the PPP frames.  
         [0099]     If the fixed stuff of the VC-4 frame does not include the fixed-stuff-usage information (“No” at step S 203 ), the demultiplexer  90  of the VC-4 terminator  502  retrieves the PPP frames from the payload (Step S 206 ).  
         [0100]     The process then proceeds to Step S 205 , in which the demultiplexer of the VC-4 terminator  502  outputs the retrieved PPP frames to the PPP terminator  503  via the data buffer  96 , thus ending the retrieving process of the PPP frames.  
         [0101]     The transmitting process of the VC-4 frame in which the fixed stuff includes the idle-frame-transmit request information is explained next.  FIG. 9  is a flowchart of the transmitting process of the VC-4 frame whose fixed stuff includes the idle-frame-transmit request information.  
         [0102]     As shown in  FIG. 9 , the data receiver  406  of the transmitting apparatus  40  receives the data from the transmitting apparatus  50  (Step S 301 ). The elastic storing unit  402  builds up the data received by the data receiver  406  and subjected to the VC-4 frame termination process by the VC-4 terminator  407  and the PPP frame termination process by the PPP terminator  408  (Step S 302 ), and determines whether the build-up exceeds a predetermined threshold value (Step S 303 ).  
         [0103]     If the build-up exceeds the threshold value (“Yes” at step S 303 ), the control byte setting unit  83  of the VC-4 mapper  404  receives the control signal from the elastic storing unit  402 , and creates the idle-frame-transmit request information (Step S 304 ).  
         [0104]     The multiplexer  87  of the VC-4 mapper  404  creates a VC-4 frame whose fixed stuff includes the idle-frame-transmit request information (Step S 305 ). The data transmitter  405  sends the created VC-4 frame to the transmitting apparatus  50  (Step S 306 ), thus ending the transmitting process of the VC-4 frame.  
         [0105]     If the build-up has not reached the threshold value (“No” at step S 303 ), the process returns to Step S 301  to continue there onwards.  
         [0106]     After the VC-4 frame which the idle-frame-transmit request information is stored in the fixed stuff is sent, if the data build-up in the elastic storing unit  409  again falls below the threshold value, the VC-4 mapper  404  receives notification to this effect from the elastic storing unit  409 , sets the value “1” in the entire fixed stuff, and creates a normal VC-4 frame in which the PPP frames are stored in the payload.  
         [0107]     Upon receiving the VC-4 frame whose entire fixed frame has the value “1”, the transmitting apparatus  50  can detect that there is no idle-frame-transmit request information in the fixed stuff, and thus stop sending the idle frames.  
         [0108]     Alternatively, the VC-4 mapper  404  may set any value in the fixed stuff of the VC-4 frame other than the value that includes an “A”, such as “AA”, “AB”, “A8”, “AE”, “A2”, “BA”, “8A”, “EA”, “2A”, etc., to request the transmitting apparatus  50  to stop sending the idle frames.  
         [0109]      FIG. 10  is a flowchart of the transmitting process of the VC-4 frame that includes an idle frame.  
         [0110]     As shown in  FIG. 10 , once the data sent by the transmitting apparatus  40  is received by the data receiver  501  of the transmitting apparatus  10 , the demultiplexer  90  of the VC-4 terminator  502  receives the VC-4 frame from the data receiver  501  (Step S 401 ).  
         [0111]     The demultiplexer  90  separates the VC-4 frame into bytes (Step S 402 ). The control byte detecting unit  92  of the VC-4 terminator  502  determines whether the fixed stuff of the VC-4 frame includes the idle-frame-transmit request information (Step S 403 ).  
         [0112]     If the fixed stuff of the VC-4 frame includes the idle-frame-transmit request information (“Yes” at step S 403 ), the PPP mapper  509  receives the idle frame from the VC-4 terminator  502 , and insets the idle frame between the PPP frames (Step S 404 ).  
         [0113]     The VC-4 mapper  510  then creates a VC-4 frame with the idle frame inserted between the PPP frames (Step S 405 ). The data transmitter  511  sends the created VC-4 frame to the transmitting apparatus  40  (Step S 406 ), thus ending the transmitting process of the VC-4 frame that includes idle frames in it.  
         [0114]     If the fixed stuff of the VC-4 frame does not include the idle-frame-transmit request information (“No” at step S 403 ), the process returns to Step S 401  to continue there onwards.  
         [0115]     Thus, according to the present embodiment, the elastic storing unit  402  of the transmitting apparatus  40  or the elastic storing unit  409  of the transmitting apparatus  40  detects the amount of the data received from the client device or the transmitting apparatus  50 . If the amount exceeds a predetermined threshold value, the VC-4 mapper  404  stores either fixed-stuff-usage information or idle-frame-transmit request information in the fixed stuff, and sends the VC-4 frame to the transmitting apparatus  50 . Consequently, even if there is a data build-up in the transmitting apparatus  40 , data transmission over the SDH network  60   a  is efficiently controlled so that there is no compromise in the data transmission efficiency.  
         [0116]     Further, according to the present embodiment, The VC-4 terminator  502  of the transmitting apparatus  50  receives the VC-4 frame whose fixed stuff has either the fixed-stuff-usage information or the idle-frame-transmit request information stored therein, and based on the fixed-stuff-usage information or the idle-frame-transmit request information either retrieves the PPP frames or inserts idle frames between PPP frames. Consequently, data transmission over the SDH network  60   a  is efficiently controlled so that there is no compromise in the data transmission efficiency.  
         [0117]     The present embodiment is explained with an example of VC frame, namely, the VC-4 frame that is transmitted and received over the SDH network. Any frame having a frame format of the VC-4 frame, that is, having a fixed stuff and payload may be used. Examples of such frames are VC frames such as VC-3 frames, STS frames such as Concatenated Synchronous transport signal Level 3 (STS-3c) frame, etc. used in SONET network, and the like.  
         [0118]     All the automatic processes explained according to the present embodiment can be, entirely or in part, carried out manually. Similarly, all the manual processes explained according to the present embodiment can be entirely or in part carried out automatically by a known method.  
         [0119]     The sequence of processes, the sequence of controls, specific names, and data including various parameters can be changed as required unless otherwise specified.  
         [0120]     The constituent elements of the device illustrated are merely conceptual and may not necessarily physically resemble the structures shown in the drawings. For instance, the device need not necessarily have the structure that is illustrated. The device as a whole or in parts can be broken down or integrated either functionally or physically in accordance with the load or how the device is to be used.  
         [0121]     The process function performed by each of the device parts is entirely or partially realized by the CPU or a program executed by the CPU or by a hardware using wired logic.  
         [0122]     According to the present invention, when there is a data build-up in a transmitting apparatus, data transmission is efficiently controlled so that there is no compromise in the data transmission efficiency  
         [0123]     Furthermore, according to the present invention, when there is a data build-up in the transmitting apparatus, data transmission is efficiently controlled as well as the efficiency of data transmission is enhanced.  
         [0124]     Moreover, according to the present invention, when there is a data build-up in the transmitting apparatus, an idle-frame insert request is efficiently sent so that there is no compromise in the efficiency of data transmission over the SDH/SONET network.  
         [0125]     Furthermore, according to the present invention, data transmission is efficiently controlled so that there is no compromise in the efficiency of data transmission over the SDH/SONET network.  
         [0126]     Moreover, according to the present invention, data transmission is efficiently controlled as well as the efficiency of data transmission is enhanced.  
         [0127]     Furthermore, according to the present invention, the idle-frame insert request is efficiently received and the idle frame insertion process is carried out so that there is no compromise in the efficiency of data transmission over the SDH/SONET network.  
         [0128]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set fort h.