Abstract:
A data transfer management method for effectively reducing collision in data transfer includes the steps of storing a data length (M) of a plurality of packets capable of being transferred in a predetermined transmission time interval, storing the predetermined transmission time interval (t), accumulating the quantity of the packets to be transferred on a communication stream in the predetermined transmission time interval, and limiting the quantity of the packets to be transferred to a value not greater than the data length.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 09/048,120, filed Mar. 26, 1998 entitled “METHOD AND APPARATUS FOR EXECUTING COMMUNICATION IN REAL-TIME AND DATA STRUCTURE FOR REAL-TIME DATA COMMUNICATION”, by T. Nakano, et al, which is a continuation-in-part of application Ser. No. 08/824,338, filed Mar. 26, 1997 now U.S. Pat. No. 5,944,778 entitled “PERIODIC PROCESS SCHEDULING METHOD” by T. Takeuchi et al., the contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to data communication procedures of a network, and more specifically to bandwidth assurance in data communication using a CSMA/CD system. 
     C. Venkatramani, et al, Design, Implementation, and Evaluation of a Software-based Real-Time Ethernet Protocol, SIGCOMM &#39;95 Cambridge, pp. 27-37, and C. Venkatramani, The Design, Implementation, and Evaluation of RETHER: A Real-Time Ethernet Protocol, Dept. of Computer Science, State University of New York at Stony Brook, 1996, pp. 1-125 describe an Ethernet protocol, hardwares and real-time and non-real-time communication. 
     JP-A-3-155241 teaches a LAN system using synchronous and asynchronous communication transfer slots. 
     The communication methods that have been used ordinarily in the LAN include a CSMA/CD system. Data transfer in data communication using this CSMA/CD system is executed in the following procedures. 
     a. A node or a computer requesting data transfer confirms the status of a stream. 
     b. Data transfer is commenced when the stream is empty, and is held on till the stream is empty, when the stream is not empty. 
     c. The node transferring the data compares the transmitted data with the status of the stream, and a plurality of nodes execute simultaneously the data transfer on the same stream and monitor whether or not any data collision occurs. 
     d. When the node transferring the data detects the data collision before the transfer is completed, it stops the transfer and transmits a collision signal representing the occurrence of the data collision to all the nodes on the stream. 
     e. The node transferring the data similarly stops the data transfer when it receives the collision signal before the data transfer is completed. 
     f. When the node transferring the data stops the data transfer in the case of the procedure d or e, a wait time is secured at random and then the data transfer procedure is repeated once again from the beginning. 
     g. When the data transfer is completed successfully by the procedures a to f, normal transfer completion is returned to the transfer request. 
     h. When the data transfer proves failure more than a predetermined number of times due to the data collision by the procedures a to d, the data transfer is stopped and a transfer error is sent back to the transfer request. 
     The node to which the data transfer is generated from the application, or the like, commences the data transfer at any time by the procedures described above. 
     According to this communication method, the stream is not occupied even during the transfer of large quantities of data and the node to which the data transfer request is generated can start the data transfer by interrupting the transfer of large quantities of data. Therefore, this method has been used widely in the conventional data transfer which does not need the real-time feature. 
     In the data transfer of the CSMA/CD system, however, the loss of a packet or a lump of data as the data transfer unit, and delays occur due to the collision with other data transfer. The problem of the loss of the packet, etc. can be solved by detecting time-out and executing re-transfer of the data in the data transfer that does not need the real-time feature. Nonetheless, the existing LAN using the CSMA/CD system cannot easily achieve communication that guarantees the real-time feature because the delay of the packet and the data re-transfer spoil the real-time feature of the communication. 
     A multimedia LAN system as one of the examples of the prior art technologies for solving such a problem is described in JP-A-3-155241. 
     The multimedia LAN system includes a specific apparatus for establishing synchronism as a whole among all the computers constituting the LAN system. To establish this synchronism throughout the whole LAN system, a time-slot for synchronization signal transfer, a time-slot for synchronous data transfer and a time-slot for asynchronous data transfer are disposed so that real-time multimedia data are transferred in a predetermined time interval in the time-slot for synchronization transfer while the time-slot for asynchronous signal transfer makes it possible to execute data transfer not requiring real-time feature by using an access system such as a CSMA/CD system. 
     A video conference system and a video-on-demand system are those applications which process consecutive media generated by digitizing speeches and dynamic images in real-time in a distributed environment using a network. Unless the communication data quantity per unit time is assured in the data communication in these applications, the data transfer cannot meet a playback processing of the consecutive media, so that the playback processing becomes incomplete and the interruption of the speech and disturbance of the images occur. In other words, to accomplish these applications, a data communication assuring the bandwidth, which in turn assures the communication data quantity per unit time, becomes essentially necessary. 
     The multimedia LAN system described above assures the bandwidth by using the time-slot for synchronization signal transfer and the time-slot for asynchronous signal transfer but when compared with the conventional LAN system using the CSMA/CD system, this system involves the problem that a specific apparatus which enables all the computers constituting the LAN system to establish synchronism throughout the whole LAN system must be provided. In other words, the existing LAN apparatus cannot be applied as they are and the change of the LAN specification is unavoidable. 
     SUMMARY OF THE INVENTION 
     To solve the problem described above, it is an object of the present invention to provide a system which can execute data communication assuring the real-time feature on the conventional LAN employing the CSMA/CD system. 
     It is another object of the present invention to provide a method and a system for controlling a transfer bandwidth in such a manner as to reduce packet collision during the data transfer. 
     In accordance with the present invention, there is provided a method of managing data communication comprising: a step of storing a plurality of transfer data lengths (M) that can be transferred within a predetermined transmission time interval, a step of storing said predetermined transfer time interval (t), a step of accumulating the quantity of data to be transferred through a communication stream within said predetermined transmission time interval, and a step of limiting the quantity of said data to be transferred to the value of said data lengths. It is possible to add a step of limiting the quantity of said data to be transferred within said predetermined transmission time interval to a value not greater than the balance obtained by subtracting a predetermined data length margin from the value of said data length. It will be possible to add a step of setting the time under the maximum data blank state, which is inputted by a client and is handled as the time used consecutively, as the time interval in which the transfer of a series of data is to be completed, a step of setting an allowable time determined to a considerably greater time by a server on the basis of said consecutive use time, and a step of detecting that the data received exceeds said consecutive use time. It will be able to provide a step of subtracting a data transfer bandwidth from said data length to cope with a request requesting the use of said data transfer bandwidth from one of a plurality of clients connected to said communication stream, a step of checking whether or not to release said data transfer bandwidth when non-reception of data is detected during said consecutive use time, and a step of adding said data transfer bandwidth to said data length when said data transfer bandwidth is released. It is possible to add a step of accumulating allocated bandwidths when the bandwidths of said communication stream are allocated so as to cope with the request requesting the use of the bandwidths of said data communication bandwidths so as to transmit a series of data from a plurality of clients connected to said communication stream, a step of checking whether or not to release said allocated data communication bandwidths when non-reception of data is detected during a predetermined consecutive use time of a series of data transfer, and subtracting a series of said data communication bandwidths from said accumulated bandwidths when said data communication bandwidths are released. 
     When a plurality of computers transfer simultaneously packets in a network employing a control mechanism for detecting the collision of the packets due to this simultaneous transfer and re-transferring automatically the packets and a computer network system in which these computers are connected by this network, the present invention holds temporarily the execution of the packet transfer request generated from a program operating on each computer, limits the data quantity transferred from each computer per unit time, and executes transfer control so that the traffic of the whole network does not exceed a predetermined value within the unit time. In this way, the present invention reduces the collision probability of the packets due to the simultaneous transfer and assures with a high probability that the relay time required for the packet transfer falls within an allowable value. 
     In the network and the computer network system described above, the present invention provides a traffic control mechanism including bandwidth allocation application means which uses at least one of the computers connected to the network as a global bandwidth reservation management node, and applies a bandwidth allocation request designating the bandwidth or a bandwidth allocation request not designating the bandwidth to the global bandwidth reservation management node before each computer which is to transfer the data starts the data transfer to the computer on the reception side, bandwidth allocation decision means which decides the bandwidth allocated to each computer from the bandwidth that the global bandwidth reservation management node can utilize on the network, the bandwidth allocation request designating the bandwidth applied and the bandwidth allocation request not designating the bandwidth which is applied, bandwidth allocation result report means which reports the allocation bandwidth so decided to the computer which applies the request or all the computers connected to the network, and transfer data quantity change means which sets a transmitting data quantity per unit time when each computer accepts the bandwidth allocation result. Using this traffic control mechanism, the present invention executes the traffic control so that the traffic of the entire network does not exceed a predetermined value within the unit time. 
     Before the data transfer not requiring the real-time feature is started, the bandwidth allocation request not designating the bandwidth is applied to the global bandwidth reservation management node and after this bandwidth allocation is accepted, the data quantity to be transmitted per unit time, which does not require the real-time feature, is set. On the other hand, before the data transfer requiring the real-time feature is started, the bandwidth allocation request designating the bandwidth is applied to the global bandwidth reservation management node and after this bandwidth allocation result is accepted, the data quantity to be transmitted per unit time, which requires the real-time feature, is set. As a result, even when the communication requiring the real-time feature and the communication not requiring the real-time feature exist in mixture, the real-time feature can be guaranteed with a high probability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an explanatory view of constituent elements of a LAN according to the embodiment 1 of the present invention; 
     FIG. 2 is an explanatory view of hardware constituent elements; 
     FIG. 3 is a block diagram of software constituent elements of the embodiment 1; 
     FIG. 4 is a block diagram of the structure of a transfer request; 
     FIG. 5 is a block diagram of the structure of a transfer command; 
     FIG. 6A is an explanatory view of the structure of a communication bandwidth information in the embodiment 1; 
     FIG. 6B is a timing chart showing the relationship between transfer and cycle in a plurality of nodes; 
     FIG. 7 is a flowchart of a transfer request module in the embodiment 1; 
     FIG. 8 is a flowchart of an isochronous transfer module; 
     FIG. 9 is an explanatory view of constituent elements of a LAN in the embodiment 2 of the present invention; 
     FIG. 10 is a block diagram of software constituent elements of ordinary nodes in the embodiment 2; 
     FIG. 11 is a block diagram of software constituent elements of a bandwidth reservation management node in the embodiment 2; 
     FIG. 12 is an explanatory view of a local bandwidth reservation table in the embodiment 2; 
     FIG. 13 is a flowchart of an NRT transfer request module of ordinary nodes in the embodiment 2; 
     FIG. 14 is a flowchart of an RT transfer request module in the embodiment 2; 
     FIG. 15 is a flowchart of an isochronous transfer module in the embodiment 2; 
     FIG. 16 is a flowchart of a bandwidth reservation module of ordinary nodes in the embodiment 2; 
     FIG. 17 is a flowchart of a bandwidth release module of ordinary nodes in the embodiment 2; 
     FIG. 18 is a flowchart of a local bandwidth reservation management module in the embodiment 2; 
     FIG. 19 shows the detail of a consecutive bandwidth reservation check processing in the embodiment 2; 
     FIG. 20 shows the detail of a bandwidth reservation completion processing in the embodiment 2; 
     FIG. 21 shows the detail of a bandwidth release completion processing in the embodiment 2; 
     FIG. 22 shows the detail of a bandwidth consecutive reservation completion processing; 
     FIG. 23 shows the detail of a time-out processing in the embodiment 2; 
     FIG. 24 shows the structure of a global bandwidth reservation table in the embodiment 2; 
     FIG. 25 shows the structure of an NRT global bandwidth reservation table in the embodiment 2; 
     FIG. 26 shows the structure of an RT global bandwidth reservation table in the embodiment 2; 
     FIG. 27 is a flowchart of an NRT transfer request module of a bandwidth reservation management node in the embodiment 2; 
     FIG. 28 is a flowchart of a bandwidth reservation module of a bandwidth reservation management node in the embodiment 2; 
     FIG. 29 is a flowchart of a bandwidth release module of a bandwidth reservation management node in the embodiment 2; 
     FIG. 30 is a flowchart of a global bandwidth reservation management module in the embodiment 2; 
     FIG. 31 is a flowchart of an NRT time-out check in the embodiment 2; 
     FIG. 32 is a flowchart of an RT time-out check in the embodiment 2; 
     FIG. 33 is a flowchart of a bandwidth reservation processing in the embodiment 2; 
     FIG. 34 is a flowchart of a bandwidth release processing in the embodiment 2; 
     FIG. 35 is a flowchart of a bandwidth consecutive reservation processing in the embodiment 2; 
     FIG. 36 is a flowchart of a packet generation processing in the embodiment 2; 
     FIG. 37 shows the structure of a request packet in the embodiment 2; and 
     FIG. 38 shows the structure of an acknowledgement packet in the embodiment 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the first embodiment (embodiment 1) of the present invention will be explained in detail with reference to FIGS. 1 to  8 . Constituent elements relating to the present invention will be first described briefly and then a processing procedure and a data structure will be explained in detail. 
     A network (LAN) dealt with in the present invention and the system constituent elements of both hardwares and softwares will be explained initially. 
     FIG. 1 depicts the connection state of the LAN constituent elements in the present invention. At least two computers (three, in the embodiment shown in FIG. 1)  101   a ,  101   b  and  101   c  are connected in the LAN through an Ethernet  111  which is a CSMA/CD system network having a re-transfer function. 
     FIG. 2 shows the hardware constituent elements in this embodiment. The computer  101  represents the hardware configuration of the computers  101   a ,  101   b  and  101   c  shown in FIG. 1. A processor  103 , a main memory  104 , an external timer  105  and an Ethernet input/output controller  102  are connected to one another in this computer  101  through a bus  106 . The network  111  is connected to the Ethernet input/output controller  102 . 
     The Ethernet input/output controller has a DMA transfer function and transfers the data between the main memory  104  and the Ethernet input/output controller  102  in accordance with a command from the processor  103 . The command from the processor  103  to the Ethernet input/output controller  102  is given as an input/output command on the main memory  104 . The Ethernet input/output controller  102  has a function of collectively processing a command chain formed by connecting a plurality of input/output commands by a pointer. The Ethernet input/output controller  102  has a function of generating an external interrupt to the processor when a processing of a series of input/output commands is completed. 
     The external timer  105  has a function of generating in a predetermined interval an external interrupt to the processor  103 , and this interrupt time interval can be controlled by an operating system OS. 
     FIG. 3 shows several constituent elements associated with a computer software used in this embodiment. The hardwares such as the Ethernet input/output controller  102  and the transfer request module  301  are controlled by the operating system (not shown) lest an application program or a user process is illegally used. The user process indirectly utilizes these hardwares by generating a system call. 
     To process the data input/output or the transfer request generated from the user process, an input/output buffer  312 , control data such as a transfer request queue  311 , a transfer request command queue  313 , and communication bandwidth information  314 , and software modules such as a communication bandwidth information, etc. a transfer request module  301 , an isochronous transfer module  302 , a timer interrupt handler  303 , a scheduler  304 , etc. exist inside the operating system. 
     When the timer interrupt is generated at a predetermined timing, the processor interrupts the program which is presently executed, and activates the timer interrupt handler  303 . This handler  303  activates in turn the isochronous transfer module  302  through the scheduler  304 . 
     When the interrupt is generated from the Ethernet input/output controller  102 , the processor  103  interrupts the program which is executed at present, and activates an input/output interrupt handler  305 . This handler  305  activates in turn the isochronous transfer module  302  through the scheduler  304 . 
     Next, the principal data structures and the processing procedures will be explained with reference to FIGS. 3 to  7 . 
     FIG. 4 shows the structure of a transfer request queue  311  and that of a transfer request command  402 . Transfer request commands  402  and  402 ′ are connected to the transfer request queue  311 . 
     Each transfer request command  402 ,  402 ′ has the following fields. 
     1) pointer  411  for next request: 
     A pointer indicating a next request for chaining a plurality of transfer request commands. 
     2) buffer address  412 : 
     This represents the leading address of a buffer having transfer data. 
     3) transfer data length  413 : 
     This designates the size of the transfer data in a byte unit. 
     FIG. 5 shows the structure of the transfer command queue  313 . The transfer request commands  402  and  402 ′ are connected to the transfer command queue  313 . 
     FIG. 6A shows the structure of the communication bandwidth information  314 . The communication bandwidth information  314  has the following fields. 
     a) communication bandwidth M  601 : 
     This represents the upper limit value of the data length that can be transferred in each cycle of a plurality of packets transferred intermittently by the computer  101 . This value M [byte] is calculated by the formula (1) given below, where C is the number of computers connected to the LAN (sets), V is the physical bandwidth of the LAN [byte/sec], t is the transfer cycle [sec] and R is a margin bandwidth as the data length secured for each transfer cycle  604 : 
     
       
           M= ( V×t−R )/ c   (1) 
       
     
     b) transfer cycle t  604 : 
     This represents the transfer cycle determined primarily by the LAN system of the present invention, and is assumed as 0.04 [sec], for example. 
     FIG. 6B shows the time relationship among the transfer cycle, the margin bandwidth, the communication bandwidth M and the number of modes C=3. 
     Next, the processing flow of the principal software modules shown in FIG. 3 will be explained. 
     FIG. 7 shows the processing flow of the transfer request module  301 . The transfer request module provides means which enables the application to transfer data. The processor  103  generates afresh the transfer request command  402  at the step  701 , stores the address of the transfer buffer in a buffer address field and stores the transfer data length in the byte unit in a transfer data length field  413 . The transfer request command  402  generated at the step  701  is connected to the transfer request queue  311  at the step  702 . 
     FIG. 8 shows the processing flow of the isochronous transfer module  302 . The isochronous transfer module  302  is activated in the interval  604  of the transfer cycle. The value of a local variable sum representing the transfer request data length is cleared to 0 at the step  801 . The address for the leading transfer request command  402  connected to the transfer request queue  311  is substituted for the local variable P representing the pointer for the transfer request at the step  802 . When the value of the local variable P is NULL at the step  803 , the flow proceeds to the step  807  and when the value is other than NULL, the flow proceeds to the step  804 . At this step  804 , the value of the transfer data length filed  413  of the transfer request commend  402  designated by the local variable P is added to the local variable sum. Next whether or not the value of the local variable sum exceeds that communication bandwidth  601  of the communication bandwidth reservation  314  is checked at the step  805 , and when it does not, the flow proceeds to the step  806 . When the value sum exceeds the communication bandwidth  601 , the flow proceeds to the step  807 . At the step  806 , the transfer request  402  designated by the local variable P is shifted from the transfer request queue  311  to the transfer request command queue  313  and the flow proceeds to the step  802 . At the step  807 , on the other hand, after the pointer of the leading transfer command  402  of the transfer request command queue  313  is designated to the Ethernet input/output controller  102  and then activation is effected. 
     When activated by the isochronous transfer module  302 , the Ethernet input/output controller  102  sends the data in accordance with the pointer  412  for the buffer and with the transfer data length field  413  in the connection sequence from the designated transfer request command  402  to the next pointer field  411  to the network  111  through the input/output buffer  312 . 
     Because all the computers  101   a ,  101   b  and  101   c  connected to the network  111  follow the afore-mentioned formula (1), the quantity of the data delivered to the network  111  does not exceed the quantity of the data that can be transferred within the transfer cycle  604 . Further, the delay due to the re-transfer can be absorbed inside the transmission interval time  604  by providing a bandwidth margin. For, the Ethernet  111  is a CSMA/CD system network having a re-transfer function and even when a collision occurs, re-transfer proves successful within the transmission interval time  604  as a margin is provided in such a manner as to secure an empty area for the data transfer within the interval time  604  set in the time in which the re-transfer function operates sufficiently. As a result, the probability of completion of the transfer can be improved. 
     Next, the second embodiment (embodiment 2) of the present invention which can achieve real-time communication by utilizing this operation will be explained in detail with reference to FIGS. 9 to  38 . The constituent elements of this embodiment will be described first and then the processing procedures and the data structure will be explained in detail. 
     FIG. 9 shows the LAN constituent elements of the present invention. In addition to the construction shown in FIG. 1, a computer  901  for globally managing the transfer requests from a plurality of nodes connected to the LAN is shown connected to the LAN. The hardware construction of the computer  901  does not at all alter from the construction of the computer  101  shown in FIG.  2 . 
     FIGS. 10 and 11 show the software constituent and  101   c  as the nodes and FIG. 11 shows the software constituent elements of the computer  901  as the global bandwidth reservation management node. 
     Referring to FIG. 10, in order to process the transfer request of the data generated from the user process, the input/output buffer  312 , the control data such as the local bandwidth reservation table  1011 , the transfer request command queue  313 , the reception command queue  1009 , the traffic control command queue  1008 , etc., and the software modules such as the NRT (Non-Real-Time) transfer request module  1001 , the RT (Real-Time) transfer request module  1002 , the isochronous transfer module  1003 , the bandwidth reservation module  1005 , the bandwidth release module  1006 , the local bandwidth reservation management module  1007 , the timer interrupt handler  303 , the input/output interrupt handler  1004 , the scheduler  304 , etc., are disposed inside the operating system. 
     When the timer interrupt occurs, the processor  103  interrupts the program that is executed at present, and activates the timer interrupt handler  303 . This handler  303  activates in turn the isochronous transfer module  1003  and th local bandwidth reservation management module  1007  through the scheduler  304 . 
     Referring to FIG. 11, in order the process the transfer request of the data generated from the user process, the input/output buffer  312 , the control data such as the local bandwidth reservation table  1011 , the transfer request command queue  313 , the reception command queue  1009 , the traffic control command queue  1008 , the global bandwidth reservation table  1111 , etc., and the software modules such as the NRT (Non-Real-Time) transfer request module  1101 , the RT (Real-Time) transfer request module ( 1002 ), the isochronous transfer module  1003 , the bandwidth reservation module  1105 , the bandwidth release module  1106 , the local bandwidth reservation management table  1007 , the global bandwidth reservation management module  1102 , the timer interrupt handler  303 , the input/output interrupt handler  1104 , the scheduler  304 , etc., are disposed inside the operating system. 
     When the input/output completion interrupt occurs, the processor  103  interrupts the program that is executed at present, and activates the input/output interrupt handler  1104 . This handler  1104  activates in turn the global bandwidth reservation management module  1102  through the scheduler  304 . 
     The nodes  101   a ,  101   b  and  101   c  and the global bandwidth reservation manager  901  exchange the reservation procedure of the bandwidth used for the data transfer before the data is transferred. FIGS. 37 and 38 show the structure of the control packet used for this procedure. 
     FIG. 37 shows the structure of the request packet  3701 . The address which is used for identifying the destination node on the network  111  is stored in a destination address  3711 , and the address used for identifying the source node on the network  111  is stored in a source address  3712 . The value for judging that the data stored in the packet is the request packet when the node receives the packet is stored in a type  3713 . The value for identifying the processing which the request packet requests to the global bandwidth reservation management node is stored in a command  3721 . An identifier for identifying a communication stream as the object of the processing for allocating the communication stream is stored in a stream ID  3722 . A requested bandwidth is stored in a bandwidth  3723 . The address used for identifying a requester node on the network  111  is stored in a requester address  3724 . The value which is primarily set by a requester so as to established correspondence to the acknowledgement packet is set to a request ID  3725 . 
     FIG. 38 shows the structure of an acknowledgement packet  3801 . The address used for identifying a destination node on the network  111  is stored in a destination address  3811 . The address for identifying a source node on the network  111  is stored in a source address  3812 . The value used for judging that the data stored in a packet is an acknowledgement packet when the node receives this packet is stored in a type  3813 . The value used by the receiving node to identify a processing for bandwidth management is stored in a command  3821 . An identifier for identifying a communication stream as the object of processing is stored in a stream ID  3822 . An allocated RT bandwidth is stored in a bandwidth  3823 . The address used for identifying a requester node on the network  111  is stored in a requester address  3824 . The designated request ID  3725  is set to a request ID  3825  when a request packet exists and  0  is set when the corresponding request packet does not exist. 
     Next, the principal data structures shown in FIG. 10 will be explained. 
     The traffic control command queue  1008  and the reception command queue  1009  have exactly the same structure as the transfer request queue shown in FIG.  4 . 
     FIG. 12 shows the structure of the local bandwidth reservation table  1011 . This table  1011  has entries  1211  to  1215  for each stream of the RT transfer and for the NRT transfer. Each entry comprises a stream ID field  1201  representing an identifier of the stream, a bandwidth field  1202  representing an allocated communication bandwidth, a bandwidth updating time field  1203  for storing the time of permission of the allocation or continuation of the bandwidth, a status flag field  1204  representing the status of each entry and a transfer request queue  401  for queuing the transfer requests. The first entry  1211  of the local bandwidth reservation table  1011  is a specific entry which represents the information on the NRT transfer request. 
     Next, each module shown in FIG. 10 will be explained with reference to FIGS. 13 to  23 . 
     FIG. 13 shows the processing flow of the NRT transfer request module  1001 . This is the module which the user of the NRT transfer calls. The processor sets a pointer for the first entry  1211  of the local bandwidth reservation table  1011  to a local variable P representing the pointer to the entries of this table  1011 , at the step  1301 . 
     At the next step  1311 , the value of the stream ID represented by the local variable P is checked. When it is 0, the flow proceeds to the step  1312  so as to secure the NRT bandwidth and when it is not 0, the flow proceeds to the step  1302 . The processor secures the input/output buffer  312  at the step  1312  for the packet request for bandwidth reservation which is the request packet  3701  for the bandwidth reservation. Next, the processor sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth reservation to the command field  3721 , 0 to the bandwidth field  3723  and the values which can be mutually identified to the request ID field  3725 . At the next step  1313 , the processor secures the transfer request command  402  for the traffic control command that requests the transfer of the bandwidth reservation packet  3701 , and sets the address of the bandwidths reservation packet  3701  to the pointer field  412  for the buffer of the transfer request command  402  so secured and the data length of the bandwidth reservation packet  3701  to the transfer data length field  413 . At the step  1 £ 14 , 1 is set to the stream ID represented by the local variable P while 0 is set to the bandwidth represented by the local variable P lest the bandwidth reservation occurs in multiplicity and the bandwidth is used before the bandwidth reservation is confirmed. At the step  1315 , the transfer request command  402  secured at the step  1313  is connected to the traffic control command queue  1008 . 
     At the step  1302 , the transfer request command  402  designated by the user program is connected to the transfer request queue  401  of the entry designated by the local variable P. 
     At the step  1316 , the value representing that the transfer exists is set to the status flag field  1204  designated by the local variable P. 
     The NRT transfer request module  1001  can provide the interface for accepting the NRT data transfer to the user program in the following way. Namely, the user program activates the NRT transfer request module by using the following function. 
     &lt;function name&gt; 
     send_NRT(qh) 
     &lt;argument&gt; 
     qh: pointer for the queue connecting transfer request command 
     &lt;explanation&gt; 
     The module is activated when data transfer is made by using NRT stream. User program uses queue qh chaining transfer requests and accepts a plurality of transfer requests at one time. NRT transfer is executed in the sequence of acceptance. 
     FIG. 14 shows a processing flow of the RT transfer request module  1002 . At the step  1401 , a pointer for the entry of the local bandwidth reservation table  1011  whose argument id coincides with the stream ID of this table  1011  is set to the local variable P representing the pointer to the entries of this table  1011 . 
     At the step  1411 , whether or not the entry of the local bandwidth reservation table  1011  whose argument id coincides with the stream ID of the local bandwidth reservation table  1011  exists is checked, and when it does, the flow proceeds to the step  1402  and when it does not, the flow proceeds to the step  1413 . 
     At the step  1402 , the transfer request command  402  designated by the user program is connected to the transfer request queue  401  of the entry designated by the local variable P. 
     At the step  1412 , the value representing normal completion is set to a return value and a series of processings are completed. The value representing that the argument id is illegal is set to the return value at the step  1413  and a series of processings are completed. 
     The RT transfer request module  1002  provides an interface for accepting the RT data transfer to the user program in the following way. 
     &lt;function name&gt; 
     send_RT(id, qh) 
     &lt;argument&gt; 
     id: stream ID representing stream having secured bandwidth 
     &lt;explanation&gt; 
     RT data transfer is executed by using a stream having stream ID id. User program uses queue qh changing transfer requests and accepts once a plurality of transfer requests. 
     FIG. 15 shows a processing flow of the isochronous transfer module  1003 . The isochronous transfer module  1003  is activated in the interval set to the timer interrupt handler  303 , such as in a 40-msec interval. At the step  1501 , the processor sets the pointer for the first entry  1211  of the local bandwidth reservation table  1011  to the local variable P representing the pointer to the entries of the local bandwidth reservation table  1011 . 
     At the step  1511 , the transfer request command  402  connected to the traffic control command queue  1008  is moved to the transfer command queue  313 . 
     At the step  1502 , the value of the local variable sum representing the transfer request data length is cleared to 0. At the next step  1503 , the address for the leading transfer request command  402  connected to the transfer request queue  401  of the entry designated by the local variable Q is substituted for the local variable P representing the pointer to the transfer request. At the step  1504 , when the value of the local variable P is an invalid value, the flow proceeds to the step  1508  and when it is a value other than the invalid value, the flow proceeds to the step  1505 . At this step  1505 , the value of the transfer data length field  413  of the transfer request  402  designated by the local variable P is added to the local variable sum. Whether or not the value of the local variable sum exceeds the value of the bandwidth field  1202  of the entry designated by the local variable Q is checked at the step  1506 . When it does not, the flow proceeds to the step  1507  and when it does, the flow proceeds to the step  1508 . At the step  1507 , the transfer request  402  designated by the local variable P is moved to the transfer command queue  313  from the transfer request queue  401  of the entry designated by the local variable Q and the flow proceeds to the step  1503 . Whether or not the local variable Q is the last entry of the local bandwidth reservation table  1011  is checked at the step  1508  and when it is the last entry, the flow proceeds to the step  1510  nd when it is not, the flow proceeds to the step  1509 . At this step  1509 , the local variable Q is set to the pointer for the entry next to the entry designated by this local variable Q and then the flow proceeds to the step  1502 . At the step  1510 , the pointer of the leading transfer request command  402  of the transfer request command queue  313  is designated to the Ethernet input/output controller  102  to activate it, and a series of processings are completed. 
     FIG. 16 shows a processing flow of the bandwidth reservation module  1005 . At the step  1601 , the processor secures the input/output buffer  312  for the bandwidth reservation packet as the request packet  3701  for the bandwidth reservation, and sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own to the source address field  3712  and to the requester address field  3712 , the value representing the request packet to the type field  3713 , the value representing the bandwidth reservation to the command field  3721 , the value designated by the argument bw to the bandwidth field  3723 , and a primary value to the request ID field  3725 . At the step  1602 , the processor secures the transfer request command  402  for the traffic control command requesting the transfer of the bandwidth reservation packet  3701  and sets the address of the bandwidth reservation packet  3701  to the pointer field  412  for the buffer of the transfer request command  402  so secured and the data length of the bandwidth reservation packet  3701  to the transfer data length field  413 . At the step  1603 , the processor connects the transfer request command  402  secured at the step  1602  to the traffic control command queue  1008 . The processor waits for the arrival notification of the acknowledgement packet  3801  representing the coincidence of the request ID field of the bandwidth reservation packet  3701  with the request ID field  3825  of the acknowledgement packet  3801  at the step  1604 . When the value of the bandwidth field  3823  of the acknowledgement packet  3801  receiving the arrival notification coincides with the value designated by the argument bw at the step  1605 , the flow proceeds to the step  1606  and when it does not, the flow proceeds to the step  1608 . The value of the identifier field  3822  of the acknowledgement packet  3801  is set to the area designated by the argument id at the step  1606 . At the step  1607 , the value representing normal completion is set at a return value and a series of processings are completed. On the other hand, a value representing the failure of the bandwidth reservation is set as the return value and a series of processings are completed at the step  1608 . 
     The bandwidth reservation module  1005  provides the interface for accepting the bandwidth reservation to the user program in the following way. 
     &lt;function name&gt; 
     reserve_bandwidth (bw, id) 
     &lt;argument&gt; 
     bw: bandwidth requested by user 
     id: pointer to area for storing stream ID representing stream having secured bandwidth 
     &lt;explanation&gt; 
     The stream having the bandwidth bw is secured. When this securing proves successful, the return value representing normal completion is obtained and when securing proves unsuccessful, a return value representing the failure of the bandwidth reservation is obtained. To execute the RT communication, the RT transfer request module is activated by using the stream ID obtained by this function, and the RT communication is thereafter executed. 
     FIG. 17 shows a processing flow of the bandwidth release module  1006 . At the step  1711 , the processor sets the pointer for the entries of the local bandwidth reservation table  1011  in which the argument id coincides with the stream ID of the local bandwidth reservation table  1011  to the local variable P representing the pointer for the entries of the local bandwidth reservation table  1011 . At the step  1712 , whether or not the entry of the local bandwidth reservation table  1011  in which the argument id coincides with the stream ID of the local bandwidth reservation table  1011  exists is checked, and when such an entry exists, the flow proceeds to the step  1701  and when it does not, the flow proceeds to the step  1713 , from the step  1712 . 
     At the step  1701 , the processor secures the input/output buffer  312  for the bandwidth release packet as the request packet  3701  for releasing the bandwidth, and sets the address of the global bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth release to the command field  3721 , the value of the stream ID field  1201  designated by the local variable P to the stream ID field, the value of the bandwidth field  1202  designated by the local variable P to the bandwidth field  3723  and a primary value to the request ID field  3725 . 
     At the step  1702 , the processor secures the transfer request command  402  for the traffic control command requesting the transfer of the bandwidth release packet  3701 , and sets the address of the bandwidth release packet  3701  to the pointer field  412  for the buffer of the transfer request command  402  so secured and the data length of the bandwidth release packet  3701  to the transfer data length field  413 . At the step  1703 , the transfer request command  402  secured at the step  1702  is connected to the traffic control command queue  1008 . At the step  1704 , the processor waits for the arrival notification of the acknowledgement packet  3801  in which the request ID field  3725  of the bandwidth release packet  3701  coincides with the value of the request ID field  3825  of the acknowledgement packet  3801  from the local bandwidth reservation management module  1007 . At the step  1705 , whether or not the value of the bandwidth field  3823  of the acknowledgement packet  3801  receiving the arrival notification is 0 is checked, and when this value is other than 0, the flow proceeds to the step  1706  and when it is 0, the flow proceeds to the step  1707 . At the step  1706 , the processor sets the value representing normal completion as the return value and completes a series of processings. At the step  1706 , the processor sets the value representing the failure of the bandwidth reservation as the return value and completes a series of processings. At the step  1713 , the processor sets the value representing that the argument id is illegal to the return value and completes a series of processings. 
     The bandwidth release module  1006  provides the interface for accepting the bandwidth release to the user program in the following way. 
     &lt;function name&gt; 
     cancel_bandwidth(id) 
     &lt;argument&gt; 
     id: stream ID representing stream having bandwidth to be released 
     &lt;explanation&gt; 
     This module is activated when the stream having the stream ID id is released after completion of the transfer. When this release proves successful, a return value representing normal completion is obtained and when the release proves unsuccessful, a value representing the failure of the bandwidth release is obtained. The stream ID which has succeeded in the release by using this function becomes invalid. 
     FIG. 18 shows a processing flow of the local bandwidth reservation management module  1007 . This local bandwidth reservation management module  1007  is activated in the interval set to the timer interrupt handler  303 , such as 40 msec, for example, through the scheduler  304 . The local bandwidth reservation management module  1007  is also activated through the scheduler  304  whenever the packet to be processed by this module  1007  arrives. At step  1811 , the processor judges whether or not the call of the module results from the timer interrupt and when it does, the flow proceeds to the step  1821  and when it does not, the flow proceeds to the step  1812 . A series of processings for requesting the consecutive bandwidth reservation are executed at the step  1821  before the term of use of the bandwidth shown in FIG. 19 expires. 
     Whether or not the acknowledgement arrives from the global bandwidth reservation manager  901  is checked at the step  1812  and when it does, the flow proceeds to the step  1831  and when it does not, a series of processings are completed. At the step  1831 , whether or not the value of he requester address field  3824  of the arriving acknowledgement packet  3801  coincides with the address of its own node is checked and when it does, the flow proceeds to the step  1813  and when it does not, the flow proceeds to the step  1817 . Whether or not the value of the command field  3821  of the arriving acknowledgement packet  3801  coincides with the value representing the bandwidth reservation acknowledgement is checked, and when it dies, the flow proceeds to the step  1822  and when it does not, the flow proceeds to the step  1814 . A series of processings depending on the result of the bandwidth reservation request shown in FIG. 20 are executed at the step  1182 . At the step  1814 , whether or not the value of the command field  3821  of the arriving acknowledgement packet  3801  coincides with the value representing the bandwidth release acknowledgement is checked, and when it does, the flow proceeds to the step  1823  and when it does not, the flow proceeds to the step  1815 . 
     At the step  1823 , a series of processings depending on the result of the bandwidth release request shown in FIG. 21 are executed. At the step  1815 , whether or not the value of the command field  3821  of the arriving acknowledgement packet  3801  coincides with the value representing the continued bandwidth reservation is checked and when it does, the flow proceeds to the step  1824  and when it does not, the flow proceeds to the step  1816 . A series of processings depending on the result of the continued bandwidth reservation request shown in FIG. 22 are executed at the step  1824 . Whether or not the value of the command field  3821  of the arriving acknowledgement packet  3801  coincides with the value representing the time-out pre-notification is checked at the step  1816  and when it does, the flow proceeds to the step  1825  and when it does not, the flow proceeds to the step  1817 . At the step  1825 , a series of processings by the time-out notification shown in FIG. 23 are executed. At the step  1817 , whether the value of the stream ID  1201  of the first entry  1211  of the local bandwidth reservation table  1011  is 0 or 1 is checked and whether or not the NRT bandwidth is allocated is judged. When the NRT bandwidth is allocated, the flow proceeds to the step  1818  and when it is not, the flow proceeds to the step  1819 . At the step  1818 , the value of the NRT bandwidth field  3826  of the acknowledgement packet  3801  is set to the bandwidth field  1202  of the first entry  1211  of the local bandwidth reservation table  1011 , and at the step  1819 , on the other hand, the input/output buffer  312  allocated to the acknowledgement packet  3801  is released and the flow proceeds to the step  1812 . 
     FIG. 19 shows the detail of a consecutive bandwidth reservation check processing  1821 . At the step  1951 , the processor sets the pointer for the first entry  1211  of the local bandwidth reservation table  1011  to the local variable Q representing the pointer to the entries of this table  1011 . At the step  1952 , it is checked by the client by himself before the generation of the transfer packet whether or not the time inputted by the prediction of the client, such as 9 seconds, has passed after the time marked in the bandwidth updating time field  1203  of the entry designated by the local variable Q, and when it does, the flow proceeds to the step  1953  and when it does not, the flow proceeds to the step  1959 . The time is put into this updating time field at the step  2054  or  2064  in FIG.  20  and at step  2214  is FIG. 22 (as will be later explained). At the step  1953 , whether or not the pointer designated by the local variable Q points the first entry  1211  of the local bandwidth reservation table  1011 , that is, the entry of the NRT bandwidth, is checked, and when it does, the flow proceeds to the step  1954  and when it points the entries other than the NRT bandwidth, the flow proceeds to the step  1955 . At the step  1954 , whether or not the value of the status flag field  1204  of the entry designated by the local variable Q is the value representing that the transfer exists is checked, and when it is that value, the flow proceeds to the step  1955  and when it is not, the flow proceeds to the step  1956 . 
     At the step  1955 , the processor secures the input/output buffer  312  for the bandwidth continued reservation packet as the request packet  3701  for continued bandwidth reservation, and then sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the continued bandwidth reservation to the command field  3712 , the value of the stream ID field  1201  designated by the local variable P to the stream ID field, the value of the bandwidth field  1202  designated by the local variable P to the bandwidth field  3723 , and a primary value to the request ID field  3725 . 
     At the step  1956 , the processor secures the input/output buffer  312  for the bandwidth release packet as the request packet  3701  for the bandwidth release, and then sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth release to the command field  3721 , the value of the stream ID field  1201  designated by the local variable P to the stream ID field, the value of the bandwidth field  1202  designated by the local variable P to the bandwidth field  3723  and a primary value to the request ID field  3725 . 
     At the step  1957 , the processor secures the transfer request packet  402  for the bandwidth release packet or for the traffic control command requesting the transfer of the continued bandwidth reservation packet  3701 , and then sets the address of the band release packet of the continued bandwidth reservation packet  3701  to the pointer field  412  for the buffer of the transfer request command  402  so secured, and the data length of the band release packet or the continued bandwidth reservation packet  3701  to the transfer data length field  413 . At the step  1958 , the transfer request command  402  secured at the step  1957  is connected to the traffic control command queue  1008 . At the next step  1959 , whether or not the entry designated by the local variable Q is the final entry is checked, and when it is, a series of processings are completed and when it is not, the flow proceeds to the step  1960 . At this step  1960 , the pointer for the next entry designated by the local variable Q is set to the local variable Q. 
     FIG. 20 shows the detail of the bandwidth reservation completion processing  1822 . At the step  2051 , the processor checks whether or not the value of the stream ID field  3821  of the acknowledgement packet  3801  is 0, and when it is other than 0, the flow proceeds to the step  2061  and when it is 0, the flow proceeds to the step  2055 . At the step  2061 , whether or not the value of the bandwidth field  3823  of the acknowledgement packet  3801  is 0 is checked, and when it is other than 0, the flow proceeds to the step  2052  and when it is 0, the flow proceeds to the step  2062 . At the step  2052 , a new entry  1215  is generated afresh for the local bandwidth reservation table  1011  and the pointer for this entry  1215  is set to the local variable P designating the entries of the local bandwidth reservation table  1011 . At the step  2053 , the value of the stream ID  3822  of the acknowledgement packet  3801  is set to the stream ID field  1201  designated by the local variable P, and the value of the bandwidth field  3823  of the acknowledgement packet  3801  is set to the bandwidth field  1202  designated by the local variable P. 
     At the step  2054 , the present time is set to the bandwidth updating time field  1203  designated by the local variable P and the status flag  1204  designated by the local variable P is initiated to 0. At the step  2055  the arrival notification is given to the bandwidth reservation module  1005  waiting for the arrival of the acknowledgement packet  3801  having the value of the request ID field  3825 , which coincides with the value set to the request ID field  3725  of the bandwidth reservation packet  3701 , and a series of processings are completed. At the step  2062 , the pointer for the first entry  1211  of the local bandwidth reservation table  1011  is set to the local variable P designating the pointer to the entries of this table  1011 . At the step  2063 , the value of the stream ID  3822  of the acknowledgement packet  3801  is set to the stream ID field  1201  designated by the local variable P, and the value of the NRT bandwidth field  3826  of the acknowledgement packet  3801  is set to the bandwidth field  1202  designated by the local variable P. At the step  2064 , the present time is set to the bandwidth updating time field  1203  designated by the local variable P, the status flag  1204  designated by the local variable P is initialized to 0 and a series of processings are completed. 
     FIG. 21 shows the detail of the bandwidth release completion processing  1823 . At the step  2151 , the processor sets the pointer for the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of this table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  is set to the local variable P designating the pointer for the entries of the local bandwidth reservation table  1011 . Whether or not the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of the table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  exists is checked at the step  2151 , and when it does, the flow proceeds to the step  2153  and when it does not, a series of processings are completed at the step  2152 . At the next step  2153 , whether or not the entry designated by the local variable P coincides with the first entry  1211  of the local bandwidth reservation table  1011  as the NRT bandwidth is checked, and when it does, the flow proceeds to the step  2157  and when it does not, the flow proceeds to the step  2154 . At the step  2154 , the transfer request command  402  of the transfer request queue  401  designated by the local variable P is released. The entry designated by the local variable P is released at the step  2155 . At the step  2156 , the arrival notification given to the bandwidth release module  1006  that waits for the arrival of the acknowledgement packet  3801  having the value of the request ID field  3825 , which is coincident with the value set to the request ID field  3725  of the bandwidth release packet  3701 , and a series of processings are completed. At the step  2157 , 0 is set to the stream ID  1201  designated by the local variable P, and a series of processings are completed. 
     FIG. 22 shows the detail of the continued bandwidth reservation completion processing  1824 . At the step  2211 , the processor sets the pointer for the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of the local bandwidth reservation table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  to the local variable P designating the pointer for the entries of this table  1011 . Whether or not the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of the table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  exists is checked at the step  2211 , and when it does, the flow proceeds to the step  2213  and when it does not, a series of processings are completed at the step  2211 . At the step  2213 , whether or not the value of the bandwidth field  3823  of the acknowledgement packet  3801  coincides with the value of the bandwidth field  1202  designated by the local variable P is checked, and when it does, the flow proceeds to the step  2214  and when it does not, the flow proceeds to the step  2215 . At the step  2214 , the present time is set to the bandwidth updating time field  1203  and a series of processings are completed. At the step  2215 , the transfer request command  402  of the transfer request queue  401  designated by the local variable P is released. The entry designated by the local variable P is released and a series of processings are completed at the step  2216 . 
     FIG. 23 shows the detail of the time-out processing. At the step  2311 , the processor sets the pointer for the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of this table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  to the local variable P designating the pointer for the entries of the table  1011 . At the step  2211 , whether or not the entry of the local bandwidth reservation table  1011  in which the stream ID  1201  of this table  1011  coincides with the stream ID field  3822  of the acknowledgement packet  3801  exists is checked, and when it does, the flow proceeds to the step  2313  and when it does not, a series of processings are completed. 
     At the step  2313 , the processor secures the input/output buffer  312  for the continued bandwidth reservation packet as the request packet  3801  for the continued bandwidth reservation, and then sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the continued bandwidth reservation to the command field  3721 , the value of the stream ID field  1201  designated by the local variable P to the stream ID field, the value of the bandwidth field  1202  designated by the local variable P to the bandwidth field  3723  and a primary value to the request ID field  3725 . At the step  2314 , the processor secures the transfer request command  402  for the traffic control command requesting the transfer of the continued bandwidth reservation packet  3701 , and then sets the address of the bandwidth release packet or the continued bandwidth reservation packet  3701  to the pointer field  412  for the buffer of the transfer request command  402  so secured, and the data length of the bandwidth release packet of the continued bandwidth reservation packet  3701  to the transfer data length field  413 . At the step  2315 , the transfer request command  402  secured at the step  2314  is connected to the traffic control command queue  1008  and a series of processings are completed. 
     In the explanation given above, the address of the bandwidth reservation manager  901  is assumed to be known is advance, but it is easily possible to apply a method which uses broadcast for this address, a method which uses the address detected at the activation of a local bandwidth reservation management  101  or the address detected periodically, by using means for detecting the address of the bandwidth reservation manager  901 , or a method which uses a specific address using the address of the bandwidth reservation manager  901 . 
     Next, the principal data structures shown in FIG. 11 will be explained with reference to FIGS. 24 to  26 . 
     FIG. 24 shows the structure of the global bandwidth reservation table  1111 . The value representing the total of the data quantity that can be transferred by the network  111  per unit time is stored in the physical bandwidth  2451 . The data quantity that is secured as a margin per unit time is secured in the bandwidth margin  2452 . The lower limit value of the quantity of the data allocated to the NRT transfer that can be transferred per unit time is set to the NRT minimum assurance bandwidth  2453 . The quantity of the data allocated to the RT transfer that can be transferred per unit time is stored in the RT allocated bandwidth  2461 . The number of nodes allocating the data quantity for the NRT transfer that can be transferred per unit time is stored in the NRT request node number  2462 . The detailed data for each node to which the data quantity, that can be transferred per unit time for the NRT communication and is allocated to the NRT transfer, is stored in the NRT global bandwidth reservation table  2471  as will be described in detail with reference to FIG.  25 . Further, the detailed data for each node to which the data quantity transferrable per unit time for the RT communication is stored in the RT global bandwidth reservation table  2472  as will be described in detail with reference to FIG.  26 . 
     FIG. 25 shows the structure of the NRT global bandwidth reservation table  2471 . The NRT global bandwidth reservation table  2471  includes the entries  2521  to  2525  for the nodes to which the bandwidth are allocated for the NRT communication. Each entry comprises a stream ID field  2511  representing an identifier of the stream, a requester address field  2512  for storing the address of the node to which the bandwidth is allocated, an acceptance time field  2513  for storing the bandwidth allocation time and the acceptance time of the bandwidth continuation, a status flag field  2514  representing the status of each entry and a request ID field  2515  for primarily recognizing the request when the bandwidth is allocated. 
     FIG. 26 shows the structure of the RT global bandwidth reservation table  2472 . The RT global bandwidth reservation table  2472  includes entries  2621  to  2625  for the streams to which the bandwidth is allocated for the RT communication. Each entry comprises a stream ID field  2611  representing an identifier of the stream, a requester address field  2612  for storing the address of the node to which the bandwidth is allocated, an acceptance time field  2613  for storing the bandwidth allocation time and the acceptance time of the bandwidth continuation, a status flag field  2614  representing the status of each entry, a request ID field  2615  for recognizing primarily the requests when the bandwidth is allocated, and an allocated bandwidth field  2616  for storing the allocated bandwidth. 
     Next, each of the modules shown in FIG. 11 will be explained with reference to FIGS. 27 to  36 . 
     FIG. 27 shows a processing flow of the NRT transfer request module  1101 . At the step  2701 , the processor sets the pointer for the first entry  1211  of the local bandwidth reservation table  1011  to the local variable P representing the entries of the local bandwidth reservation table  1011 . At the step  2702 , the value of the stream ID designated by the local variable P is checked. When it is 0, the flow proceeds to the step  2703  so as to secure the NRT bandwidth and when it is not, the flow proceeds to the step  2706 . At the step  2703 , the processor secures the input/output buffer  312  for the bandwidth reservation packet as the request packet  3701  for reserving the bandwidth, and then sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth reservation to the command field  3721 , 0 to the bandwidth field  3723  and a primary value to the request ID field  3725 . 
     At the step  2704 , 1 is set to the stream ID designated by the local variable P while 0 is set to the bandwidth designated by the local variable P lest the bandwidth reservation occurs in multiplicity and the bandwidth is used before the bandwidth reservation is confirmed. At the step  2705 , the bandwidth reservation packet  3701  secured at the step  2703  is handed over to the global bandwidth reservation management module  1102  and this module  1102  is activated. At the step  2706 , the transfer request command  402  designated by the user program is connected to the transfer request queue  402  of the entry designated by the local variable P. After the value representing that the transfer exists is set to the status flag field  1204  designated by the local variable P, a series of processings are completed at the step  2707 . 
     FIG. 28 shows a processing flow of the bandwidth reservation module  1105 . At the step  2801 , the processor secures the input/output buffer  312  for the bandwidth reservation packet as the request packet  3701  for reserving the bandwidth and then sets the address of the local bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth reservation to the command field  3721 , the value designated by the argument bw to the bandwidth field  3723  and a primary value to the request ID field  3725 . At the step  2802 , the bandwidth reservation packet  3701  secured at the step  3801  is handed over to the global bandwidth reservation management module  1102  and this module  1102  is activated. At the step  2803 , the arrival notification of the acknowledgement packet  3801 , in which the request ID field  3725  of the bandwidth reservation packet coincides with the request ID field  3825  of the acknowledgement packet  380 - 1 , is awaited from the local bandwidth reservation management module  1007 . When the value of the bandwidth field  3823  of the acknowledgement packet  3801  receiving the arrival notification coincides with the value designated by the argument bw, the flow proceeds to the step  2805  and when it does not, the flow proceeds to the step  2807 . At the step  2805 , the value of the identifier field  3822  of the acknowledgement packet  3801  is set to the area designated by the argument id. At the step  2806 , the value representing normal completion is set as the return value and a series of processings are completed. At the step  2807 , the value representing the failure of the bandwidth reservation is set as the return value and a series of processings are completed. 
     FIG. 29 shows a processing flow of the bandwidth release module  1106 . At the step  2901 , the processor sets the pointer for the entries of the local bandwidth reservation table  1011  having the argument id which coincides with the stream ID  1201  of this table  1011  to the local variable P representing the pointer to the entries of the table  1011 . At the step  2902 , whether or not the entry of the local bandwidth reservation table  1011  having the argument id which coincides with the stream ID  1201  of this table  1011  exists is checked, and when it does, the flow proceeds to the step  2903  and when it does not, the flow proceeds to the step  2908 . At the step  2903 , the processor secures the input/output buffer  312  for the bandwidth release packet as the request packet  3701  for releasing the bandwidth, and sets the address of the bandwidth reservation manager  901  to the destination address field  3711  of the request packet  3701  so secured, the address of its own node to the source address field  3712  and to the requester address field  3724 , the value representing the request packet to the type field  3713 , the value representing the bandwidth release to the command field  3712 , the value of the stream ID field  1201  designated by the local variable P to the stream ID, the value of the bandwidth field  1202  designated by the local variable P to the bandwidth field  3723  and a primary value to the request ID field  3725 . 
     At the step  2904 , the processor hands over the bandwidth release packet  3701  secured at the step  2903  to the global bandwidth reservation management module  1102  and activates this module  1102 . At the step  2905 , the processor waits for the arrival notification of the acknowledgement packet  3801  in which the request ID field  3725  of the bandwidth release packet  3701  coincides with the request ID field  3825  of the bandwidth release packet  3701 , from the local bandwidth reservation management module  1007 . At the step  2906 , whether or not the value of the bandwidth field  3823  of the acknowledgement packet  3801  receiving the arrival notification is 0 is checked, and hen it is other than 0, the flow proceeds to the step  2907  and when it is 0, the flow proceeds to the step  2909 . At the step  2907 , the value representing normal completion is set as the return value and a series of processings are completed. At the step  2909 , on the other hand, the value representing the failure of the bandwidth reservation is set as the return value and a series of processings are completed. Further, the value representing that the argument id is illegal is set as the return value and a series of processings are completed at the step  2908 . 
     FIG. 30 shows a processing flow of the global bandwidth reservation management module  1102 . This module  1102  is activated in the interval set to the timer interrupt handler  303  such as 40 msec, for example, through the scheduler  304 . The global bandwidth reservation management module  1102  is also activated by the input/output interrupt handler  1104  through the scheduler  304  whenever the packet to be processed by this module  1102  arrives. At the step  3001 , whether or not the call of the module originates from the timer interrupt is judged, and when it does, the flow proceeds to the step  3021  and when it does not, the flow proceeds to the step  3002 . At the step  3021 , a series of processings due to time-out of the NRT bandwidth are executed. At the step  3002 , whether or not the request packet  3701  arrives is checked, and when it does, the flow proceeds to the step  3003  and when it does not, a series of processings are completed. 
     At the step  3003 , whether or not the value of the command field  3721  of the arriving request packet  3701  coincides with the value representing the bandwidth reservation is checked, and when it does, the flow proceeds to the step  3023  and when it does not, the flow proceeds to the step  3004 . At the step  3023 , a series of processings by the bandwidth reservation request shown in FIG. 33 are executed. At the step  3004 , whether or not the value of the command field  3721  of the arriving request packet  3701  coincides with the value representing the bandwidth release is checked, and when it does, the flow proceeds to the step  3024  and when it does not, the flow proceeds to the step  3005 . Next, a series of processings due to the bandwidth release request shown in FIG. 34 are executed at the step  3023 .. At the step  3005 , whether or not the value of the command field  3721  of the arriving request packet  3701  coincides with the value representing the continued bandwidth reservation is checked, and when it does, the flow proceeds to the step  3025  and when it does not, the flow proceeds to the step  3007 . At the step  3023 , a series of processings due to the continued bandwidth reservation request shown in FIG. 35 are executed. At the step  3006 , the value obtained by subtracting the bandwidth margin  2452  from the physical bandwidth  2451 , the subtracting the RT allocated bandwidth  2461  from the balance and dividing further the balance so obtained by the NRT bandwidth request node number  2462  is set to the NRT bandwidth field  3826  of the acknowledgement packet  3801 . At the step  3026 , a series of processings for generating the packet shown in FIG. 36 are executed. At the step  3007 , the input/output buffer  312  allocated to the request packet  3701  is released and the flow then proceeds to the step  3002 . 
     FIG. 31 shows a processing flow of the NRT time-out check  3021 . At the step  3101 , the processor sets the pointer for the first entry  2521  of the NRT global bandwidth reservation table  2471  to the local variable Q representing the pointer to the entries of this table  2471 . At the step  3102 , whether or not the difference of the value of the acceptance time field  2513  designated by the local variable Q from the present time exceeds the pre-notification time such as 10 seconds is checked, and when it does, the flow proceeds to the step  3110  and when it does not, the flow proceeds to the step  3106 . At the step  3110 , whether or not the difference of the value of the acceptance time field  2513  designated by the local variable Q from the present time exceeds the consecutive bandwidth reservation time such as 12 seconds is checked, and when it does, the flow proceeds to the step  3111  and when it does not, the flow proceeds to the step  3103 . At the step  3111 , the balance obtained by subtracting 1 from the value of the NRT bandwidth request node number  2462  is set to the NRT bandwidth request node number  2462 . 
     At the step  3112 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth release acknowledgement to the command field  3821 , the value of the stream ID field  2511  designated by the local variable Q to the stream ID field  3822 , 0 to the bandwidth field  3823 , the value of the requester address field  2512  designated by the local variable Q to the requester address field  3824  and 0 to the request ID field  3825 . The entry designated by the local variable Q is released at the step  3113 . At the step  3103 , whether or not the value of the status flag  2514  designated by the local variable Q coincides with the value that has been notified is checked, and when it does, the flow proceeds to the step  3106  and when it does not, the flow proceeds to the step  3104 . At the step  3104 , the value representing completion of the notification is set to the status flag  2514  designated by the local variable Q. 
     At the step  3105 , the processor secures the input/output butter  312  for the acknowledgement packet  3801 , and sets the value of the requester address field  2512  designated by the local variable Q to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the time-out pre-notification to the command field  3821 , the value of the stream ID field  2511  designated by the local variable Q to the stream ID field  3822 , 0 to the bandwidth field  3823 , and 0 to the request ID field  3825 . At the step  3026 , a series of processings shown in FIG. 36 are executed. At the step  3106 , whether or not the entry designated by the local variable Q is the last entry is checked and when it is, a series of processings are completed and when it is not, the flow proceeds to the step  3107 . At the step  3107 , the local variable Q is set to the pointer for the next entry and the flow proceeds to the step  3102 . 
     FIG. 32 shows a processing flow of the RT time-out check  3022 . At the step  3201 , the processor sets the pointer for the first entry  2521  of the RT global bandwidth reservation table  2472  to the local variable Q representing the pointer to the entries of the RT global bandwidth reservation table  2472 . At the step  3202 , it is checked whether or not the pre-notification time, which is set by the server by adding a slight time to the consecutive bandwidth reservation time (FIG.  19 ), such as 10 seconds, has passed after the acceptance time held in the field  2613  designated by the local variable Q and when it does, the flow proceeds to the step  3210  and when it does not, the flow proceeds to the step  3206 . The time field  2613  has a time inputted at step  3317  or  3327  (FIG.  33 ), or step  3513  or  3523  (FIG.  35 ). At the step  3210 , whether or not the difference of the value of the acceptance time field  2613  designated by the local variable Q from the present time exceeds the maximum allowable consecutive bandwidth reservation time, which is set by the server by adding a slight time to the pre-notification time, such as 12 seconds, is checked, and when it does, the flow proceeds to the step  3211  and when it does not, the flow proceeds to the step  3203 . At the step  3211 , the value obtained by subtracting the allocation bandwidth  2616  designated by the local variable Q from the RT allocated bandwidth  2461  is set to the RT allocated bandwidth  2461 . 
     At the step  3212 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801  and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth release acknowledgement to the command field  3821 , the value of the stream ID field  2611  designated by the local variable Q to the stream ID field  3822 , the value of the allocation bandwidth field  2616  designated by the local variable Q to the bandwidth field  3823 , the value of the requester address field  2612  designated by the local variable Q to the requester address field  3824  and 0 to the request ID field  3825 . Then, the entry designated by the local variable Q is released at the step  3213 . At the step  3203 , whether or not the value of the status flag  2614  designated by the local variable Q coincides with the value that has been notified, and when it does, the flow proceeds to the step  3206  and when it does not, the flow proceeds to the step  3204 . At this step  3204 , the value representing completion of the notification is set to the status flag  2614  designated by the local variable Q. 
     At the step  3205 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the value of the requester address field  2612  designated by the local variable Q to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  384 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3183 , the value representing the time-out pre-notification to the command field  3821 , the value of the stream ID field  2611  designated by the local variable Q to the bandwidth field  3823  and 0 to the request ID field  3825 . At the step  3026 , a series of processings for generating the packet shown in FIG. 36 are executed. At the step  3206 , whether or not the entry designated by the local variable Q is the last entry is checked, and when it does, a series of processings are completed and when it is not, the flow proceeds to the step  3207 . At this step  3207 , the local variable Q is set to the pointer for the next entry and the flow proceeds to the step  3202 . 
     FIG. 33 shows a processing flow of the bandwidth reservation processing  3023 . At the step  3301 , whether or not the value of the bandwidth field  3723  of the request packet  3701  is 0 is checked, and when it is 0, the flow proceeds to the step  3311  and when it is not, the flow proceeds to the step  3321 . At the step  3311 , the pointer for the entry in which the value of the request ID field  3725  of the request packet  3701  coincides with the value of the request ID field  2515  of the NRT global bandwidth reservation table  2471  is set to the local variable P representing the pointer to the entries of this table  2471 . Whether or not the entry in which the value of the request ID field  3725  of the request packet  3701  coincides with the value of the request ID field  2515  of the NRT global bandwidth reservation table  2471  exists is checked at the step  3311 , and when it does, the flow proceeds to the step  3318  and when it does not, the flow proceeds to the step  3314  from the step  3312 . At the step  1314 , the pointer for the empty entry of the NRT global bandwidth reservation table  2471  is set to the local variable P. At the step  3315 , the value as the sum of 1 and the NRT bandwidth request node number  2462  is set to the NRT bandwidth request number  2462 . At the step  3316 , the processor sets the value of the requester address field  3324  of the request packet  3701  to the requester address field  2512  designated by the local variable P and the value of the request ID field  3725  of the request packet  3701  is set to the request ID field  2515  designated by the local variable P. At the step  3317 , a primary value is set to the stream ID field  2511  designated by the local variable P, the present time is set to the acceptance time field  2513  designated by the local variable P, and 0 is set to the status flag  2514  designated by the local variable P. 
     At the step  3318 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth reservation acknowledgement to the command field  3821 , the value of the stream ID field  2511  designated by the local variable P to the stream ID field  3822 , 0 to the bandwidth field  3823 , the value of the requester address field  2512  designated by the local variable P to the requester address field  3824  and the value of the request ID field  2515  designated by the local variable P to the request ID field  3825 . Thereafter, the processor completes a series of processings. 
     At the step  3321 , the pointer for the entry in which the value of the request ID field  3725  of the request packet  3701  coincides with the value of the request ID field  2615  of the RT global bandwidth reservation table  2472  is set to the local variable P representing the pointer for the entries of the RT global bandwidth reservation table  2472 . Whether or not the entry in which the value of the request ID field  3725  of the request packet  3701  coincides with the value of the request ID field  2615  of the global bandwidth reservation table  2472  exists is checked at the step  3322 , and when it does, the flow proceeds to the step  3328  and when it does not, the flow proceeds to the step  3323 , from the step  3321 . At the step  3323 , whether or not the sum of the value of the RT allocated bandwidth  2461 , the value of the NRT minimum assurance bandwidth  2453 , the value of the bandwidth field  3723  of the request packet  3701  and the value of the bandwidth margin  2452  exceeds the value of the physical bandwidth  2451  is checked, and when it does, the flow proceeds to the step  3331  and when it does not, the flow proceeds to the step  3324 . 
     At the step  3324 , the pointer for the empty entry of the RT global bandwidth reservation table  2472  is set to the local variable P. At the step  3325 , the sum of the RT allocated bandwidth  2461  and the value of the bandwidth field  3723  of the request packet  3701  is set to the RT allocated bandwidth  2461 . At the step  3326 , the processor sets the value of the requester address field  3724  of the request packet  3701  to the requester address field  2612  designated by the local variable P, the value of the request ID field  3725  to the request ID field  2615  designated by the local variable P and the value of the bandwidth field  3723  of the request packet  3701  to the allocation bandwidth field  2616  designated by the local variable P. At the step  3327 , a primary value is set to the stream ID field  2611  designated by the local variable P, the present time is set to the acceptance time field  2613  designated by the local variable P and 0 is set to the status flag field  2614  designated by the local variable P. 
     At the step  3328 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth reservation acknowledgement to the command field  3821 , the value of the stream ID field  2611  designated by the local variable P to the stream ID field  3822 , the value of the bandwidth allocation field  2616  designated by the local variable P to the bandwidth field  3823 , the value of the requester address field  2612  designated by the local variable P to the requester address field  3824  and the value of the request ID  2615  designated by the local variable P to the request ID field  3825 . Thereafter, the processor completes a series of processings. At the step  3331 , the processor secures the input/output buffer  312  for the acknowledge packet  3801 , and sets the value of the requester address field  3724  of the request packet  3701  to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 ; the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth reservation acknowledgement to the command field  3821 , 0 to the stream ID field  3822 , 0 which represents that the RT transfer bandwidth cannot be secured to the bandwidth field  3823  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . Thereafter, the processor completes a series of processings. 
     FIG. 34 shows a processing flow of the bandwidth release processing  3024 . At the step  3401 , whether or not the value of the bandwidth field  3723  of the request packet  3701  is 0 is checked, and when it is 0, the flow proceeds to the step  3411  and when it is not, the flow proceeds to the step  3421 . At the step  3411 , the pointer for the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2511  of the NRT global bandwidth reservation table  2471  is set to the local variable P representing the pointer for the entries of the NRT global bandwidth reservation table  2471 . At the step  3411 , whether or not the entry in which the value of the stream ID  3722  of the request packet  3701  coincides with the value of the stream ID field  2511  of the NRT global bandwidth reservation table  2471  exists is checked, and when it exists, the flow proceeds to the step  3413  and when it does not, the flow proceeds to the step  3431  from the step  3412 . At the step  3413 , the balance obtained by subtracting 1 from the NRT bandwidth request node number  2462  is set to the RT bandwidth request node number  2462 . 
     At the step  3414 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801  and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the source address field  3812 , the value representing the release packet to the type field  3821 , the value representing the bandwidth release acknowledgement to the command field  3821 , the value of the stream ID field  2511  designated by the local variable P to the stream ID field  3822 , 0 to the bandwidth field  3823 , the value of the requester address field  2512  designated by the local variable P to the requester address field  3824  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . At the step  3415 , the processor releases the entry designated by the local variable P and completes a series of processings. 
     At the step  3421 , the pointer for the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2611  of the RT global bandwidth reservation table  2472  is set to the local variable P representing the pointer for the entries of the RT global bandwidth reservation table  2472 . Whether or not the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2611  of the RT global bandwidth reservation table  2427  exists is checked at the step  3421 , and when it does, the flow proceeds to the step  3423  and when it does not, the flow proceeds to the step  3423  and when it does not, the flow proceeds to the step  3431 , from the step  3422 . At the step  3423 , the value obtained by subtracting the value of the allocation bandwidth field  2616  designated by the local variable P from the RT allocated bandwidth  2461  is set to the RT allocated bandwidth  2461 . 
     At the step  3424 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the broadcast address to the destination address field  3811  of the acknowledgement packet  3801  so secured, the address of its own node to the destination address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth release acknowledgement to the command field  3821 , the value of the stream ID field  2611  designated by the local variable P to the stream ID field  3822 , 0 to the bandwidth field  3823 , the value of the requester address field  2612  designated by the local variable P to the requester address field  3824  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . At the step  3425 , the entry designated by the local variable P is released and a series of processings are completed. 
     At the step  3431 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the value of the requester address field  3724  of the request packet  3701  to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the bandwidth release acknowledgement to the command field  3821 , 0 to the stream ID  3822 , 0 to the bandwidth field  3823  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 , and a series of processings are completed. 
     FIG. 35 shows a processing flow of the consecutive bandwidth reservation processing  3025 . At the step  3501 , whether or not the value of the bandwidth field  3723  of the request packet  3701  is 0 is checked, and when it is 0, the flow proceeds to the step  3511  and when it is not, the flow proceeds to the step  3521 . At the step  3511 , the pointer for the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2511  of the NRT global bandwidth reservation table  2471  is set to the local variable P representing the pointer for the entries of the NRT global bandwidth reservation table  2471 . At the step  3511 , whether or not the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID  2511  of the NRT global bandwidth reservation table  2471  exists is checked, and when it does, the flow proceeds to the step  3513  and when it does not, the flow proceeds to the step  3531 , from the step  3512 . At the step  3513 , the present time is set to the acceptance time field  2513  designated by the local variable P. At the step  3514 , 0 is set to the status flag field  2514  designated by the local variable P. 
     At the step  3515 , the processor secures the input/output buffer  312  for the acknowledge packet  3801 , and sets the value of the requester address field  2512  designated by the local variable P to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the consecutive bandwidth reservation acknowledgement to the command field  3821 , the value of the stream ID field  2511  designated by the local variable P to the stream ID field  3822  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . Thereafter, the processor completes a series of processings. 
     At the step  3521 , the pointer for the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2611  of the RT global bandwidth reservation table  2472  is set to the local variable P representing the pointer to the entries of the RT global bandwidth reservation table  2472 . Next, whether or not the entry in which the value of the stream ID field  3722  of the request packet  3701  coincides with the value of the stream ID field  2611  of the RT global bandwidth reservation table  2472  exists is checked at the step  3521 , and when it does, the flow proceeds to the step  3523  and when it does not, the flow proceeds to the step  3531 , from the step  3521 . At the step  3523 , the present time is set to the acceptance time field  2613  designated by the local variable P and at the step  3524 , 0 is set to the status flag field  2614  designated by the local variable P. 
     At the step  3525 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the value of the requester address field  2612  designated by the local variable P to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the consecutive bandwidth reservation acknowledgement to the command field  3821 , the value of the stream ID field  2611  designated by the local variable P to the stream ID field  3822 , the value of the allocation bandwidth field  2616  designated by the local variable P to the bandwidth field  3823  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . Thereafter, the processor completes a series of processings. 
     At the step  3531 , the processor secures the input/output buffer  312  for the acknowledgement packet  3801 , and sets the value of the requester address field  3724  of the request packet  3701  to the destination address field  3811  of the acknowledgement packet  3801  so secured and to the requester address field  3824 , the address of its own node to the source address field  3812 , the value representing the acknowledgement packet to the type field  3813 , the value representing the consecutive bandwidth reservation acknowledgement to the command field  3821 ,  0  to the stream ID field  3822 , 0 to the bandwidth field  3823  and the value of the request ID field  3725  of the request packet  3701  to the request ID field  3825 . Thereafter, the processor completes a series of processings. 
     FIG. 36 shows a processing flow of the packet generation processing  3026 . At the step  3601 , whether or not the destination address field  3811  of the acknowledgement packet  3801  coincides with the address of its own node is checked, and when it does, the flow proceeds to the step  3604  and when it does not, the flow proceeds to the step  3611 . At the step  3604 , the acknowledgement packet  3801  is handed over to the local bandwidth reservation management module  1007 , this module  1007  is activated and a series of processings are completed. At the step  3611 , whether or not the destination address field  3811  of the acknowledgement packet  3801  coincides with the broadcast address is checked, and when it does, the flow proceeds to the step  3612  and when it does not, the flow proceeds to the step  3602 . 
     At the step  3612 , the processor secures the input/output buffer  312  for duplication  3801  of the acknowledgement packet and sets the value of the acknowledgement packet  3801  to each of the fields  3811  to  3813  and  3821  to  3826  of the duplication  3801  of the acknowledgement packet so secured. At the step  3613 , the duplication  3801  of the acknowledgement packet secured at the step  3612  is handed over to the local bandwidth reservation management module  1007 , this module  1007  is actuated and the flow proceeds to the step  3602 . At this step  3602 , the processor secures the transfer request command  402  for the traffic control command requesting the transfer of the acknowledgement packet  3801  and sets the address of the acknowledgement packet  3801  to the pointer field  412  for the buffer of the transfer request command  402  so secured and the data length of the acknowledgement packet  3801  to the transfer data length field  413 . At the step  3603 , the transfer request command  402  secured at the step  3602  is connected to the traffic control command queue  1008  and series of processings are completed. 
     The user process allocates the designated bandwidth to the stream by utilizing the interface provided by the bandwidth reservation module  1005  and transfers the data by utilizing the interface provided by the RT transfer request module  1002  to thereby utilize the real-time communication. After completing the utilization of the real-time communication, the user process releases the bandwidth from the stream by utilizing the interface provided by the bandwidth release module  1006 . Further, the user process transfers the data by utilizing the interface provided by the NRT transfer request module  1001  and utilizes the existing communication which does not require the bandwidth allocation. 
     A bridge system of existing networks and the network according to the present invention can be easily embodied by utilizing a computer having both of the Ethernet input/output controller that utilizes the existing communication method and the Ethernet input/output controller that utilizes the communication method according to the present invention. 
     In the LAN that has gained a wide application, the present invention can provide the real-time communication assuring the bandwidth for the Ethernet that has become wide spread, without changing the existing hardwares. Further, the present invention can accomplish the real-time communication through the internet by disposing a bridge system having the real-time feature between the networks assuring the bandwidth by hardwares such as an ATM (Automatic Teller Machine) and the LAN to which the present invention is applied.