Abstract:
Disclosed is a data transmission device of variable communication capacity that can set bands and set line communication capacities according to users&#39; requests, and can automatically determine usable lines. The data transmission device includes: a transmission device having a transmission unit connected to N (N&gt;1) transmission lines; a reception device having a reception unit connected to N reception lines; and negotiation units connected to both the transmission unit and the reception unit. The transmission unit converts transmission data of parallel bits into a data array with one to N trains that is different in the number of data trains depending on specified transmission capacity. The reception unit synthesizes reception data trains inputted from one to N reception lines determined by specified reception capacity, of the N reception lines. The negotiation unit of the transmission side sends line use/disuse information to the negotiation unit of the reception side so that both the transmission unit and the reception unit select identical lines.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese application JP 2005-064751 filed on Mar. 9, 2005, the content of which is hereby incorporated by reference into this application.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a variable communication capacity data transmission device. More particularly, it relates to a variable communication capacity data transmission device that forms one virtual transmission path by plural transmission lines, and changes transmission rates by automatically negotiating the number of transmission lines between a transmission side and a reception side according to a requested band and a connection state of the transmission lines.  
       BACKGROUND OF THE INVENTION  
       [0003]     Most of long-distance transmission networks adopt serial transmission, and the transmission speed has been increased by raising a transmission clock frequency. However, high-speed serial transmission of 40 Gbps or more has revealed the limits of operation speeds of communication devices and transmission distances, and it has become difficult to achieve higher serial transmission speeds. As a result, a method has been adopted that virtually handles plural serial lines of comparatively low speeds as one transmission path and transmits data in parallel to increase transmission speeds.  
         [0004]     A link aggregation method is known as a communication method of line aggregation type that forms one logical high-speed transmission path by plural transmission lines (IEEE Std 802.3-2002 Edition, “Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications”, Clause 43 “Link Aggregation”, IEEE, 2002.3.8). The link aggregation method allocates data frames to each transmission line on a flow basis. The flow indicates a series of data frames identified by combinations of source addresses of transmission frames, destination addresses, and applications used. No special relationship is required between flows during data transmission (frame transmission). However, a reception side must guarantee the order of data frames within each flow, and the order of frames must not be reversed in a network.  
         [0005]     On the other hand, a device of transmission side assigns sequence numbers to transmission frames and allocates the transmission frames to a transmission buffer containing a small amount of data to be transmitted, and transmits the transmission frames to a line associated with the transmission buffer, while a device of a reception side temporarily stores the received frames in a reception buffer, and then reads the transmission frames in the order of sequence numbers. A communication system of line aggregation type is proposed that prevents the reversal of frame order by the above-mentioned arrangement (see JP-A No. 9866/2002).  
         [0006]     However, in conventional data transmission devices, as a user-selectable communication interface to increase communication speeds, communication speeds are increased with fixed magnifications. For example, in IEEE802.3-compliant communication interfaces, 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps are provided as communication speeds increased in increments of 10 times. In SONET/SDH, 622 Mbps, 2.5 Gbps, 10 Gbps, and 40 Gbps are provided as communication speeds increased in increments of four times.  
         [0007]     However, since an increase in general communication traffic quantities slows in communication speed zones beyond 10 Gbps, most of users using a communication interface of 10 Gbps consider higher communication speeds such as 40 Gbps and 100 Gbps to be unnecessary, presumably from changes in demanded traffic quantities. Even if a band becomes insufficient in 10 Gbps, since making a contract to use with high-speed communication interfaces of 40 Gbps and 100 Gbps yields unnecessary communication costs, most users are satisfied with communication interfaces of 20 Gbps class.  
         [0008]     In the above-mentioned link aggregation, the number of communication interfaces increases in proportion to desired communication capacities. Therefore, users who consider approximately a triple increase in costs to be proper when communication capacity increases 10 times will find this method expensive. The link aggregation, which handles data frames on a flow basis, requires processor operation for flow detection and allocation of transmission frames to specific lines, impeding speedup. Moreover, since data frames belonging to identical flows are transmitted through identical lines to guarantee the order of transmission frames (transmission packets), there is a problem that the occurrence of unused lines reduces transmission efficiency when the number of flows is smaller than the number of lines.  
         [0009]     The method disclosed in JP-A No. 9866/2002 temporarily stores received data frames in a reception device and reads them in the order of sequence numbers. Therefore, even if the data frames are stored in a reception buffer, when a data frame having a next read sequence number specified by an internal counter does not arrive, a read operation must be halted until the data frame arrives. Time for waiting for a target data frame is managed by a timer reset each time a data frame is read from the reception buffer. Accordingly, when a target data frame is lost in the middle of a transmission path, the method described in JP-A No. 9866/2002 completely halts a read operation on received data frames until the timer turns time-out, inevitably causing reduction in transmission efficiency.  
         [0010]     Furthermore, in any of the above-mentioned link aggregation and the method of JP-A No. 9866/2002, an administrator must change the setting of lines in a transmission side and a reception side each time the number of lines is changed, and management is very cumbersome.  
         [0011]     Therefore a need exists to provide a data transmission device of variable communication capacity that can set bands according to users&#39; requests, automatically determine usable lines, and set line communication capacities.  
       SUMMARY OF THE INVENTION  
       [0012]     To satisfy the above mentioned need, a variable communication capacity data transmission device of the present invention has a function that the above-mentioned transmission capacity negotiation unit connected to a transmission side of N lines (N is a natural number satisfying N&gt;1) constituting one virtual transmission path determines the specified transmission capacity and the specified transmission line position, and the above-mentioned reception capacity negotiation unit connected to a reception side of N lines constituting one virtual reception path determines the specified reception capacity and the specified reception line position.  
         [0013]     According to the present invention, since an administrator does not need to set both a transmission side and a reception side to change communication capacity, management costs can be reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts:  
         [0015]      FIG. 1  is a drawing showing an example of a communication system of line aggregation to which the present invention is applied;  
         [0016]      FIG. 2  is a drawing showing a communication device according to an aspect of the present invention;  
         [0017]      FIG. 3  is a drawing showing the transmission unit of  FIG. 2 ;  
         [0018]      FIG. 4A-4D  are drawings showing rate conversion in the transmission unit of  FIG. 2 ;  
         [0019]      FIG. 5  is a drawing showing the reception unit of  FIG. 2 ;  
         [0020]      FIG. 6  is a drawing showing a communication capacity negotiation sequence by a communication device according to an aspect of the present invention;  
         [0021]      FIG. 7  is a drawing showing a communication capacity negotiation sequence by a communication device according to an aspect of the present invention;  
         [0022]      FIG. 8  is a drawing showing the setting of line selectors in the transmission unit of  FIG. 2 ; and  
         [0023]      FIG. 9  is a drawing showing the setting of line selectors in the reception unit of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0024]     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in data transmission devices and methods of transmitting data. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.  
         [0025]      FIG. 1  shows an example of a communication system of line aggregation type to which the present invention is applied.  
         [0026]     A communication system includes plural communication devices  10  ( 10 A- 10 K) and wavelength division multiplexer (WDM)  5 . The communication device  10 A is connected to the WDM  5  through a transmission line LT-A and a reception line LR-A that each include plural serial lines (optical fibers) . Likewise, the communication device  10 K is connected to the WDM  5  through a transmission line LT-K and a reception line LR-K that each including plural optical fibers.  
         [0027]     The WDM  5 , which is connected to an optical fiber  2  serving as part of an optical communication network, wavelength-multiplexes optical signals received from the transmission lines LT-A to LT-K, and transmits them to the optical fiber  2 . It also wavelength-demultiplexes wavelength-multiplexed optical signals received from the optical fiber  2  and outputs the resulting signals to the reception lines LR-A to LR-K.  
         [0028]     The transmission line LT-A and the reception line LR-A, and the transmission line LT-K and the reception line LR-K may, in connection with the WDM  5 , be integrated into one optical fiber through which plural optical signals are wavelength-multiplexed and transmitted. The WDM may be connected with plural optical fibers of the optical communication network.  
         [0029]     Connection by plural optical fibers, even if any path of a line used is disconnected and disabled, can prevent communication from being disabled by using only other usable paths though communication capacity is reduced.  
         [0030]      FIG. 2  shows a communication device according to an aspect of the present invention. A communication device  10 TX (a transmitting side of the communication device  10  or the WDM  5  of  FIG. 1 ) includes a transmission interface  20 , a processor unit  30 , and a storage unit  40 . Likewise, a communication device  10 RX (a receiving side of the communication device  10  or the WDM  5  of  FIG. 1 ), which is connected opposite to the communication device  10 TX, includes a reception interface  25 , a processor unit  30 ′, and a storage unit  40 ′.  
         [0031]     The transmission interface  20  includes a protocol processing unit  50 , a transmission unit  60 , and a negotiation unit  70 . Likewise, the reception interface  25  includes a protocol processing unit  50 ′, a reception unit  80 , and a negotiation unit  70 ′.  
         [0032]     The transmission interface  20  is connected with the processor unit  30  through a bus L 10 . The transmission unit  60  of the transmission interface  20  is connected with the reception unit  80  of the reception interface  25  through plural serial lines LT 1  to LT 4 .  
         [0033]     In the communication device  10 TX, the processor unit  30  executes various application programs stored in the storage unit  40 , and outputs transmission data for other communication devices (or computers) connected through the communication network to the transmission interface  20 .  
         [0034]     The protocol processing unit  50  has part or all of protocol processing functions from the application layer to the data link layer which are shown in the OSI (Open System Interconnection) basic model. However, the processor unit  30  may perform part of processing from the application layer to the data link layer. The protocol processing unit  50  receives transmission data from the processor unit, converts transmission data into a transmission data frame, and outputs the transmission data frame to the transmission data bus L 20  according to a transmission control signal CLl 0  outputted by the transmission unit  60 .  
         [0035]     The transmission unit  60  transmits the transmission data frame outputted by the protocol processing unit  50  to the communication device  10 RX through the serial lines LT 1  to LT 4 .  
         [0036]     In the communication device  10 RX, the reception unit  80  receives the data frame transmitted by the communication device  10 TX and outputs the received data frame by using the reception data bus L 30  and a reception control signal CL 50 . The protocol processing unit  50 ′ has part or all of processing functions from the data link layer to the application layer, converts the received data frame into reception data, and outputs the reception data to the processor unit  30 ′ through the data bus L 10 . The processor unit  30 ′ executes various application programs stored in the storage unit  40 ′, and processes the reception data inputted from the reception interface  25 .  
         [0037]     The following details a method of negotiating the number and position of lines used of the serial lines LT 1  to LT 4  between the communication devices  10 TX and RX.  
         [0038]     The negotiation unit  70  of the communication device  10 TX outputs a control signal for outputting a pattern for inspecting a line state through the output control signal line CL 30 . The transmission unit  60  transmits the inspection pattern to the serial lines LT 1  to LT 4  according to a control signal inputted from the output control signal line CL 30 .  
         [0039]     The reception unit  80  of the communication device  10 RX detects a line state from the inspection pattern received from the serial lines LT 1  to LT 4 , and outputs line state information to the negotiation unit  70 ′ through the signal lines CL 60  and CL 65 . The negotiation unit  70 ′ determines a usable line from the line state information obtained from signal line CL 60  and CL 65 , and outputs usable line information to the communication device  10 TX through notification means CL 80 .  
         [0040]     The negotiation unit  70  of the communication device  10 TX determines a specified transmission capacity and a specified transmission line position from the usable line information received from the notification means CL 80  and a communication capacity request sent through the signal line CL 40  by the processor unit  30 . Furthermore, it outputs to the transmission unit  60  the specified transmission capacity through the signal line CL 20  and the specified transmission line position through the signal line CL 25 , and at the same time notifies the processor unit  30  of the set specified transmission capacity. The transmission unit  60  transmits the line use information to the communication device  10 RX through the serial lines LT 1  to LT 4  according to the specified transmission capacity and the specified transmission line position.  
         [0041]     In the communication device  10 RX, the reception unit  80  detects a line state of the serial lines LT 1  to LT 4 , and outputs line state information to the negotiation unit  70 ′ through the signal lines CL 60  and CL 65 . The negotiation unit  70 ′ determines the specified reception capacity and the specified reception line position based on the line state information obtained from the signal lines CL 60  and CL 65 , outputs to the reception unit  80  the specified reception capacity through the signal line CL 70  and the specified reception line position through the signal line CL 75 , and notifies the processor unit  30 ′ of the set specified reception capacity through the signal line CL 40 ′.  
         [0042]     By the above-mentioned construction, the setting of the transmission interface and the reception interface can be automatically set according to a line connection state between the transmission interface and the reception interface, and a communication capacity request from the processors (or, administrator).  
         [0043]      FIG. 3  shows the transmission unit according to an aspect of the present invention. According to the present aspect of the present invention, the transmission unit  60  includes a buffer memory  100  connected to the transmission data bus L 20  having a width of 4n bits, a buffer control unit  130  connected to the buffer memory  100 , a selector  120  connected to the buffer control unit  130 , a pattern generation unit  155 , a data selector  160  connected to an output line L 21  of the buffer memory  100  and an output line of the pattern generation unit  155 , three rate conversion units  110  ( 110 - 1  to  110 - 3 ) connected to an output line L 22  of the data selector  160  and a rate selector  140 , four line selectors  150  ( 150 - 1  to  150 - 4 ) connected to an output line L 23  of the rate selector  140 , an encoding unit  170 - i  connected to an output line of the line selector  150 - i  (i=1 to 4), a P/S (Parallel/Serial) conversion unit  175 - i  that converts n-bit data outputted from the encoding unit  170 - i  into a serial bit signal, and an electric/optic (E/O) conversion unit  180 - i  that converts an output signal of the P/S conversion unit  175 - i  into an optical signal. Though an example of four lines is shown in the present description, the number of lines is not limited to four.  
         [0044]     The buffer memory  100 , the buffer control unit  130 , the selector  120 , and the rate conversion unit  110  ( 110 - 1  to  110 - 3 ) form a transmission data array conversion unit, and components from the rate selector  140  to the electric/optic (E/O) conversion units  180 - i  form a transmission data output unit.  
         [0045]     The description below assumes that the protocol processing unit  50  outputs a transmission data frame having a width of 4n bits to the transmission data bus L 20 . However, the protocol processing unit  50  may output a transmission data frame having a width of m bits (m is a natural number) to the transmission data bus L 20  and convert it into data having a width of 4n bits by a converter provided in a pre-stage (or a subsequent stage) of the buffer memory  100 . Also, the protocol processing unit  50  may write a transmission data frame having a width of m bits outputted to a transmission data bus L 20  to the buffer memory  100  and convert it into data having a width of 4n bits when reading it from the buffer memory  100 .  
         [0046]     If the width of bits outputted by the protocol processing unit and a bit width of the transmission unit are the same, needless bit width conversion can be avoided. In many cases, they are different. If m is simply an integer multiple of 4n, bit conversion can be easily performed by the latter method. However, if not, like the former, it is necessary to provide a complicated circuit that performs bit conversion and clock conversion.  
         [0047]     A data frame having a width of 4n bits outputted to the transmission data bus L 20  by the protocol processing unit  50  is temporarily stored in the buffer memory  100  by the buffer control unit  130 , and then is read into the output line L 21 . To prevent buffer overflow when an empty area of the buffer memory  100  falls into shortage, the buffer control unit  130  issues a command for commanding the protocol processing unit  50  to halt the output of the data frame through the control signal line CL 10 , and when a sufficient empty area comes into existence, commands the protocol processing unit  50  to transmit the data frame.  
         [0048]     The pattern generation unit  155  prepares continuous inspection patterns as parallel data having a width of 4n bits so that the reception unit  80  constituting the reception interface  25  can inspect the continuity of received data. The data selector  160  is supplied with parallel data having a width of 4n bits outputted to the output line L 21  of the buffer memory  100  and the output line of the pattern generation unit  155 . Either of the parallel data is selected according to the data select signal CL 30  and outputted to the output line L 22 .  
         [0049]     The rate conversion units  110  ( 110 - 1  to  110 - 3 ) are supplied with parallel data having a width of 4n bits outputted to the output line L 22  from the data selector  160 . The first rate conversion unit  110 - 1  operates as a ¾ rate converter that converts parallel input data having a width of 4n bits into parallel data having a width of 3n bits and outputs it. Likewise, the second rate conversion unit  110 - 2  operates as a ½ rate converter that converts parallel input data having a width of 4n bits into parallel data having a width of 2n bits and outputs it. The third rate conversion unit  110 - 3  operates as a ¼ rate converter that converts parallel input data having a width of 4n bits into parallel data having a width of n bits and outputs it.  
         [0050]     The rate selector  140  is supplied with parallel data having a width of 4n bits outputted to the output line L 22 , and the conversion units  110  ( 110 - 1  to  110 - 3 ). The rate selector  140  selects which bit line L 22  the data has been inputted, and with what bit width the data is to be outputted, according to specified of the specified transmission capacity signal CL 20 . The parallel data inputted to the rate selector  140  differs in bit width from n to 4n bits, but is outputted in 4n bits. When the parallel data is inputted with a bit width fewer than 4n (e.g., n-bit width), data of a lacking bit width is filled with null data (e.g., the value 0). The parallel data having a width of 4n bits of the output line L 23  is separated into four trains of data (output lines L 1  to L 4 ) each having a width of n bits.  
         [0051]     In the above-mentioned construction, the buffer control unit  130  adjusts a data amount read from the buffer memory  100  according to a specified transmission capacity signal fed from the control signal line CL 20 . According to an aspect of the present invention, one of data output control signals outputted by the rate conversion units  110 - 1  to  110 - 3  is inputted to the buffer control unit  130  by controlling input selection by the selector  120  by the specified transmission capacity signal CL 20 . However, for first input indicative of full mode time (when the output bus L 21  is selected by the rate selector  140 ) by the selector  120 , a signal indicating always read permission is inputted.  
         [0052]     For example, when the specified transmission capacity signal CL 20  indicates the ¾ rate, the selector  120  outputs the data output control signal outputted by the first rate conversion unit  110 - 1  to the buffer control unit  130 . At this time, the buffer control unit  130  controls the amount of output data to the output bus L 21  by controlling the amount of data to be read from the buffer memory  100 .  
         [0053]      FIGS. 4A  to  4 D show relationships among a state of the specified transmission capacity signal CL 20  according to an aspect of the present invention, data appearing in the output bus L 21 , and data appearing in the output line L 1 -L 4  of the rate selector  140 .  
         [0054]      FIG. 4A  shows a relationship between a data train D 0  appearing in the output bus L 21  and an output data train D 20  appearing in the output lines L 1 -L 4  when the specified transmission capacity signal CL 20  indicates a maximum capacity (full mode) . t 0  to t 7  indicate a power cycle of 4n-bit data, and digits “ 0 ” to “ 31 ” indicate a data number indicating an n-bit data block (alignment order). In the full mode, a data train D 0  having a width of 4n bits is continuously outputted to the output bus L 21  without empty cycles occurring. The output data train D 0  is separated to four data trains each having a width of n bits, and the data trains each having a width of n bits appear in the output lines L 1  to L 4  as a data block array indicated by D 20 .  
         [0055]      FIG. 4B  shows a relationship between a data train D 0  appearing in the output bus L 21  and an output data train D 20  appearing in the output lines L 1 -L 4  when the specified transmission capacity signal CL 20  indicates ¾ mode. In the ¾ mode, a data train D 1  having a width of 4n bits is outputted to the output bus L 21  in a form that contains empty data cycles (t 3 , t 7 , . . . ) at the rate of one to four cycles. Though the output data train D 1  is inputted to the rate conversion units  110 - 1  to  110 - 3 , in the ¾ mode, the output becomes effective in the first rate conversion unit  110 - 1 . The first rate conversion unit  110 - 1  converts a data train (data blocks “ 0 ” to “ 11 ” and “ 12 ” to “ 23 ”) having a width of 4n bits inputted in the period of three consecutive effective data cycles (t 0 -t 2 , t 4 -t 6 , . . . ) into a data train having a width of 3n bits, and outputs it in four cycles.  
         [0056]     The data train having a width of 3n bits outputted from the first rate conversion unit  110 - 1  is separated to three data trains each having a width of n bits, which are supplied as a second input of the rate selector  140 . In this mode, transmission data appears in the output lines L 1 -L 3  as a data block array shown in D 25 - 1 .  
         [0057]      FIG. 4C  shows a relationship between a data train D 0  appearing in the output bus L 21  and an output data train D 25 - 2  appearing in the output lines L 1  to L 4  when the specified transmission capacity signal CL 20  indicates ½ mode. In the ½ mode, a data train D 2  having a width of 4n bits is outputted to the output bus L 21  in a form that contains empty data cycles (t 2 , t 3 , t 6 , t 7 , . . . ) at the rate of two to four cycles. Though the output data train D 2  is inputted to the rate conversion units  110 - 1  to  110 - 3 , in the 1½ mode, the output becomes effective in the second rate conversion unit  110 - 2 . The second rate conversion unit  110 - 2  converts a data train (data blocks “ 0 ” to “ 7 ” and “ 8 ” to “ 15 ”) having a width of 4n bits inputted in the period of two consecutive effective data cycles (t 0 -t 1 , t 4 -t 5 , . . . ) into a data train having a width of 2n bits, and outputs it in four cycles.  
         [0058]     The data train having a width of 2n bits outputted from the second rate conversion unit  110 - 2  is separated to two data trains each having a width of n bits, which are supplied as a third input of the rate selector  140 . In this mode, transmission data appears in the output lines L 1  and L 2  as a data block array shown in D 25 - 2 .  
         [0059]      FIG. 4D  shows a relationship between a data train D 0  appearing in the output bus L 21  and an output data train D 25 - 3  appearing in the output lines L 1  to L 4  when the specified transmission capacity signal CL 20  indicates ¼ mode. In the ¼ mode, a data train D 3  having a width of 4n bits is outputted to the output bus L 21  in a form that contains empty data cycles (t 1 -t 3 , t 5 -t 7 , . . . ) at the rate of three to four cycles. Though the output data train D 3  is inputted to the rate conversion units  110 - 1  to  110 - 3 , in the ¼ mode, the output becomes effective in the third rate conversion unit  110 - 3 . The third rate conversion unit  110 - 3  converts a data train (data blocks “ 0 ” to “ 3 ” and “ 4 ” to “ 7 ”) having a width of 4n bits inputted in the period of consecutive effective data cycles (t 0 , t 4 , . . . ) into a data train having a width of n bits, and outputs it in four cycles.  
         [0060]     The data train having a width of n bits outputted from the third rate conversion unit  110 - 3  is supplied as a fourth input of the rate selector  140 . In this mode, transmission data appears in the output line L 1  as a data block array shown in D 25 - 3 .  
         [0061]     The pattern generation unit  155  generates data in the same data block array as that of parallel data having a width of 4n bits outputted by the buffer memory  100  and the buffer control unit  130 . For example, when the selector  120  selects the ¾ mode (outputs a data output control signal of the rate conversion unit  110 - 1 ), the pattern generation unit  155  generates a continuous inspection pattern in the same block array as that of the data train D 0  of  FIG. 4B .  
         [0062]     Referring again to  FIG. 3 , the line selectors  150  ( 150 - 1  to  150 - 4 ) allocates the output lines LT 1  to LT 4  to any of the lines based on the specified transmission line position signal CL 25 . The line selector  150 - 1  inputs the output line L 1  and a null signal. The line selector  150 - 2  inputs the output lines L 1  and L 2 , and a null signal. The line selector  150 - 3  inputs the output lines L 1  to L 3  and a null signal. The line selector  150 - 4  inputs the output lines L 1  to L 4  and a null signal. The specified transmission line position signal CL 25  feeds selection signals shown in  FIG. 8  to each of the line selectors  150 . In  FIG. 8 , when communication capacity is full mode, there is only one combination to allocate L 1  to L 4  to the data selectors  150 - 1  to  150 - 4 , respectively. When communication capacity is ¾ mode, since L 1  to L 3  are allocated to the four lines, there are four combinations of line allocation. Likewise, there are six combinations for the ½ mode and four combinations. for the ¼ mode.  
         [0063]     L 1  to L 4  may be inputted to all line selectors  150  so that the order of L 1  to L 4  can be interchanged.  
         [0064]     The encoding units  170 - i  (i=1 to 4) convert output data of an i-th line selector  150 - i  into transmission code (e.g., 8B10B code, 64B66B code, scramble, etc.) necessary for transfer on a network transmission path. The transmission codes have the function of averaging the probability of occurrences of “0” and “1” in the case of binary transmission, for example, to assure DC balance in transmission paths. The above-mentioned transmission codes can include communication control information besides user data. The P/S conversion units  175 - i  (i=1 to 4) convert the output data of the encoding units from parallel data having a width of n bits into serial data having a width of 1 bit. The electric/optic (E/O) conversion units  180 - i  (i=1 to 4) convert electrically serial signals outputted from the P/S conversion units  175 - i  into optical signals and outputs them to the transmission lines LTi (i=1 to 4).  
         [0065]      FIG. 5  shows a reception unit of the communication device  10 RX according to an aspect of the present invention. The reception unit  80  includes optic/electric (O/E) conversion units  200 - i  (i=1 to 4) connected to reception lines LRi (i=1 to 4), S/P conversion and code synchronization units  205 - i  (i=1 to 4) connected to the O/E conversion units  200 - i , a code synchronization confirmation unit  210  connected to the S/P conversion and code synchronization units  205 - 1  to  205 - 4 , skew correction units  215 - i  (i=1 to 4) connected to the S/P conversion units  205 - i  and a skew control unit  225 , decoding units  220 - i  (i=1 to 4) connected to the skew correction units  215 - i , a skew control unit  225  connected to the output of the decoding units  220 - 1  to  220 - 4 , line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  connected to the decoding units  220 - i , a rate conversion unit  250 - 3  connected to line selectors  230 - 1  to  230 - 3 , a rate conversion unit  250 - 2  connected to line selectors  235 - 1  and  235 - 2 , a rate conversion unit  250 - 1  connected to a line selector  240 , a rate selector  260  connected to the decoding units  220 - 1  to  220 - 4  and the rate conversion units  250 - 1  to  250 - 3 , a selector  265 ; a reception buffer  275  connected to the rate selector  260 , a buffer control unit  270 , and a continuity inspection unit  280  connected to the rate selector  260 .  
         [0066]     Components from the O/E conversion units  200 - i  to the line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  form a reception data input unit. The rate conversion units  250 - 1  to  250 - 3  form a reception data array conversion unit. The rate selector  260 , the selector  265 , the reception buffer  275 , and the buffer control unit  270  form a reception data output unit.  
         [0067]     The O/E conversion unit  200 - i  convert optical signals received from the reception lines LRi into electrical signals of serial data form. The S/P conversion and code synchronization units  205 - i  converts the serial data outputted from the O/E conversion units  200 - i  into parallel data having a width of n bits, and detects a code separator of transmission code (detects a comma in the case of 8B10B code). The code synchronization confirmation unit  210  confirms a code synchronization state of the S/P conversion and code synchronization units  205 - 1  to  205 - 4 , and sends synchronization state information through the signal line CL 60 . The decoding unit  220 - i  execute conversion reverse to transmission encoding performed by the transmission unit  60  of the communication device  10 TX. The skew control unit  225  detects, from the result of encoding by the decoding units  220 - 1  to  220 - 4 , the difference (skew) between data arrival times that occurred between links of the network during data transmission, and controls the skew correction units  215 - 1  to  215 - 4  to cancel out the skew.  
         [0068]     The line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  select a signal line inputted from one of input lines TR 1  to TR 4  based on the specified reception line position signal CL 75  according to the control signal line CL 70 . The control signal line CL 70  is inputted from the negotiation part  20 ′ so that the line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  select lines shown by  FIG. 9 .  FIG. 9A  shows combinations of selections by the line selectors  230 - 1  to  230 - 3  in the ¾ mode. The line selectors  230 - 1  to  230 - 3  each selectively output parallel data having a width of n bits of one of the signal lines L 1  to L 4  according to line positions  1  to  4  indicated by the specified reception line position signal CL 75 .  FIG. 9B  shows combinations of selections by the line selectors  235 - 1  and  235 - 2  in the ½ mode. The line selectors  235 - 1  to  235 - 2  each selectively output parallel data having a width of n bits of one of the signal lines L 1  to L 4  according to line positions  1  to  4  indicated by the specified reception line position signal CL 75 .  FIG. 9C  shows a combination of selections by the line selector  240  in the 1¼ mode. The line selector  240  selectively outputs parallel data having a width of n bits of one of the signal lines L 1  to L 4  according to line positions  1  to  4  indicated by the specified reception line position signal CL 75 .  
         [0069]     The rate conversion parts  250 - 1  to  250 - 3  perform rate conversion reverse to the rate conversion performed by the transmission unit  60  of the communication device  10 TX. That is, the rate conversion unit  250 - 1  converts a data train having a width of n bits outputted from the line selector  240  into a data train having a width of 4n bits that contains three null data cycles every four cycles4, and supplies it as a fourth input of the rate selector  260 . The rate conversion unit  250 - 2  converts a data train having a width of 2n bit that includes a data train having a width of n bits outputted from the line selector  235 - 1  and a data train having a width of n bits outputted from the line selector  235 - 2  into a data train having a width of 4n bits containing two null data cycles every four cycles, and supplies it as a third input of the rate selector  260 . The rate conversion unit  250 - 3  converts a data train having a width of 3n bits including three data trains each having a width of n bits outputted from the line selectors  230 - 1  to  230 - 3  into a data train having a width of 4n bits containing one null data cycle every four cycles, and supplies it as a second input of the rate selector  260 . The rate selector  260  is supplied, as a first input, with a data train having a width of 4n bits including four data trains each having a width of n bits outputted from the decoding units  220 - 1  to  220 - 4 .  
         [0070]     The rate selector  260  selects any one from among the above-mentioned first input to fourth input according to a specified reception capacity signal specified by the processor  30 ′ through the control signal line CL 70 , and outputs it to the reception buffer  275 . The buffer control unit  270  controls the writing and reading of data to and from the reception buffer  275 . The buffer control unit  270  writes data to the reception buffer  275  in the first half of each cycle and reads data into the reception bus L 30  from the reception buffer  275  in the second half.  
         [0071]     Since a data train having a width of 4n bits outputted by the conversion units  250 - i  (i=1 to 3) contains null data cycles (empty cycles) shown in  FIGS. 4B  to  4 D, the rate conversion units  250 - i  output control signals indicating effective data cycles so that the buffer control unit  270  writes data to the reception buffer  275  in effective data cycles. The control signals are inputted to the selector  265 , and one control signal selected by the selector  265  according to the specified reception capacity signal is supplied to the buffer control unit  270 .  
         [0072]     Therefore, when the specified reception capacity signal from the control signal line CL 70  indicates the ¼ mode described in  FIG. 4 , the rate selector  260  selects a data train from the rate conversion unit  250 - 1  supplied as a fourth input, and the buffer control unit  270 , according to a control signal from the rate conversion unit  250 - 1  selected by the selector  265 , writes data having a width of 4n bits in effective data cycles outputted by the rate conversion unit  250 - 1  to the reception buffer  275 . For the same reason, in the ½ mode, data having a width of 4n bits in effective data cycles outputted by the rate conversion unit  250 - 2  is written to the reception buffer  275 . In the ¾ mode, data having a width of 4n bits in effective data cycles outputted by rate conversion unit  250 - 3  is written to the reception buffer  275 . In ineffective data cycles, null data is outputted to the reception bus L 30 .  
         [0073]     When the specified reception capacity signal from the control signal line CL 70  indicates the full mode, the rate selector  260  selects the first input and the selector  265  selects an enable signal fed as the first input. Accordingly, in this mode, the writing and reading of effective data to and from the reception buffer  275  are performed in all cycles.  
         [0074]     As is apparent from the above-mentioned description, the communication device of the present invention can changeably control the number of lines connected with a communication network. Therefore, when communication data quantity is small, a small number of lines are used, and with an increase in communication data quantity, the number of lines is increased in stages. By doing so, it becomes possible to make a band use contract to meet demands with a communication service provider.  
         [0075]     Referring to  FIG. 6 , a first example of a method of negotiating communication capacity by the communication device according to an aspect of the present invention is shown. The negotiation unit  70  of the communication device  10 TX outputs a control signal for outputting a pattern for inspecting a line state through the output control signal line CL 30 . As a result, since the data selector  160  of the transmission unit  60  selects an inspection pattern outputted by the pattern generation unit  155 , the inspection pattern is outputted to the lines LT 1  to LT 4 .  
         [0076]     The reception unit  80  of the communication device  10 RX detects a line connection state from the inspection pattern received from the serial lines LR 1  to LR 4  of the reception side, and outputs line synchronization information of a usable line with code synchronization established to the negotiation part  70 ′ through the signal line CL 60 . The negotiation unit  70 ′ determines a usable line from the line state information obtained from the signal line CL 60 , and sends usable line information to the communication device  10 TX through notification means CL 80 .  
         [0077]     The negotiation unit  70  of the communication device  10 TX determines a specified transmission capacity and a specified transmission line position according to the usable line information received from the notification means CL 80  and a communication capacity request sent by the processor unit  30  through the signal line CL 40 . Moreover, the negotiation unit  70  outputs the specified transmission capacity through the signal line CL 20  and the specified transmission line position through the signal line CL 25  to the transmission unit  60 , and at the same time notifies the processor unit  30  of the specified transmission capacity.  
         [0078]     The transmission unit  60  determines the lines LT 1  to LT 4  to be used from the specified transmission capacity and the specified transmission line position, and outputs ineffective signals for the lines not to be used. Accordingly, in the reception unit  80  of the communication device  10 RX, the code synchronization confirmation unit  210  detects again a synchronization state of the serial lines LT 1  to LT 4 , and sends line synchronization information to the negotiation unit  70 ′ through the signal line CL 60 . Thereby, the negotiation unit  70 ′ can determine the specified reception capacity and the specified reception line position.  
         [0079]     The transmission unit  60  may, according to the specified transmission capacity and the specified transmission line position, transmit line use information indicating which lines are used (or not used), to the communication device  10 RX through the serial lines LT 1  to LT 4 . Thereby, the reception unit  80  can more correctly determine the specified reception capacity and the specified reception line position. Here, a line use information detecting unit that extracts line use information may be provided in a subsequent stage of the decoding units  220 - i  of the reception unit  80 , and the negotiation unit  70 ′ may determine the specified reception capacity and the specified reception line position from the received line use information. The line use information may be transmitted using control characters of transmission code. Use of control characters of transmission code eliminates the need to provide means for sending line use information to the reception unit except the serial lines LT 1  to LT 4 . Moreover, line use information can be sent also when transmission data is being transmitted from the protocol processing unit, and the specified reception capacity and the specified reception line position can be changed even during data communication.  
         [0080]     The reception unit  80  sets the line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  and the rate selector  260  according to the specified reception capacity and the specified reception line position that are specified in the signal lines CL 70  and CL 75  specified by the negotiation unit  70 ′. Then, in the continuity inspection unit  280 , the reception unit  80  inspects whether parallel data having a width of 4n bits outputted by the rate selector  260  is the same as a content outputted by the transmission unit  60 , and notifies the negotiation unit  70 ′ of the inspection result through the signal line CL 65 . The negotiation unit  70 ′ notifies the negotiation unit  70  of setting completion if the inspection result inputted from the signal line CL 65  is normal. On receipt of notification of setting completion, the transmission interface  20  determines that the setting of the reception interface  25  has been completed, and starts to transmit transmission data from the protocol processing unit.  
         [0081]      FIG. 7  shows a second example of a method of negotiating communication capacity by the communication device according to an aspect of the present invention. According to an aspect of the invention, the inspection of usable lines and setting completion notification from the reception unit  80  that are performed in as described above are omitted.  
         [0082]     The negotiation unit  70  of the communication device  10 TX determines a specified transmission capacity and a specified transmission line position according to a communication capacity request sent by the processor unit  30  through the signal line CL 40 , and outputs the specified transmission capacity through the signal line CL 20  and the specified transmission line position through the signal line CL 25  to the transmission unit  60 , and at the same time notifies the processor unit  30  of the specified transmission capacity.  
         [0083]     The transmission unit  60  determines the lines LT 1  to LT 4  to be used from the specified transmission capacity and the specified transmission line position, and outputs ineffective signals for the lines not to be used. Accordingly, in the reception unit  80  of the communication device  10 RX, the code synchronization confirmation unit  210  detects again a synchronization state of the serial lines LT 1  to. LT 4 , and sends line synchronization information to the negotiation unit  70 ′ through the signal line CL 60 . Thereby, the negotiation unit  70 ′ can determine the specified reception capacity and the specified reception line position.  
         [0084]     The transmission unit  60  may, according to the specified transmission capacity and the specified transmission line position, transmit line use information indicating which lines are used, to the communication device  10 RX through the serial lines LT 1  to LT 4 . Thereby, the reception unit  80  can more correctly determine the specified reception capacity and the specified reception line position. Here, a line use information detecting unit that extracts line use information may be provided in a subsequent stage of the decoding units  220 - i  of the reception unit  80 , and the negotiation unit  70 ′ may determine the specified reception capacity and the specified reception line position from the received line use information. The line use information may be transmitted using control characters of transmission code. Use of control characters of transmission code eliminates the need to provide means for sending line use information to the reception unit except the serial lines LT 1  to LT 4 . Moreover, line use information can be sent also when transmission data is being transmitted from the protocol processing unit, and the specified reception capacity and the specified reception line position can be changed even during data communication.  
         [0085]     The reception unit  80  sets the line selectors  230 - 1  to  230 - 3 ,  235 - 1 ,  235 - 2 , and  240  and the rate selector  260  according to the specified reception capacity and the specified reception line position that are specified in the signal lines CL 70  and CL 75  specified by the negotiation unit  70 ′. Then, in the continuity inspection unit  280 , the reception unit  80  inspects whether parallel data having a width of 4n bits outputted by the rate selector  260  is the same as a content outputted by the transmission unit  60 , and notifies the negotiation unit  70 ′ of the inspection result through the signal line CL 65 .  
         [0086]     The transmission interface  20  first determines a specified transmission capacity and a specified transmission line position. Then, after a certain fixed time has elapsed, it determines that the setting of the reception interface  25  has been completed, and starts to transmit transmission data from the protocol processing unit.  
         [0087]     As is apparent from the present description, the communication device of the present invention enables automatic setting between a transmission interface and a reception interface according to a line connection state between the transmission interface and the reception interface, and a communication capacity request from a processor or administrator.  
         [0088]     According to the present invention, since an administrator does not need to set both a transmission side and a reception side to change communication capacity, management costs can be reduced. Since communication capacity can be changed according to user requests, by making a contract with a communication service provider in a band satisfying demands, unnecessary communication costs can be eliminated. Since the variable communication capacity data transmission device of the present invention performs rate conversion and line allocation in the physical layer, the speed of device operation can be increased in comparison with a link aggregation method that allocates data frames to lines on a flow basis by using processors.  
         [0089]     The present invention relates to a communication interface, and can be used in all devices having a communication interface, such as network devices, including, but not limited to, routers, switches, transmission terminals, media converters, repeaters, and gateways, for example, personal computers, servers, large-scale computers, disk array systems, and network attached storages.  
         [0090]     Those of ordinary skill in the art may recognize that many modifications and variations of the present invention may be implemented without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.