Abstract:
A packet forwarding device equipped with a statistics collection device and statistics collection method for high speed ports at a low cost while maintaining the required statistical accuracy for each flow. In order to collect a statistic flow with the required accurate statistic information this device contains a high speed flow table, a flow table made up of many flow entries, a search decision table to decide whether to search the high speed flow table or large volume flow table; and the table to be searched is decided when a packet is received. The accuracy of the statistic information for the flow requiring accurate statistic information is guaranteed by the high speed flow table. Further by setting the large volume flow table and sampling rate as needed, statistic information for many flow entries can be collected with a sufficient flow of sampled statistic information, without lowering packet forwarding performance.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese applications JP 2004-016466 filed on Jan. 26, 2004 and JP 2003-195453 filed on Jul. 11, 2003, the contents of which are hereby incorporated by reference into this application.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a statistics collection method for recording information such as the number of packets transmitted and the number of bytes, as well as a statistics collection device containing the statistics collection method and installed in a network.  
       BACKGROUND OF THE INVENTION  
       [0003]     The Internet has become established as an important part of our social infrastructure and besides conventional Best_Effort type data communications, starts to communicate data needed to ensure communication quality such as transaction data for mainstream business operations and audio-video. The volume of data being communicated is also increasing along with the spread of lines for accessing broadband communications by way of technology such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home).  
         [0004]     In order to acquire the communication status on the network in the environment described above, the carrier and ISP (Internet Service Provider) require a network monitoring function for collecting and analyzing statistics on the communication data volume on the network. Among this communication data, there is also a large need for a function for collecting and analyzing statistic information for each data group (hereafter flow) categorized into the data source and address, application and quality level, etc. By utilizing statistic information on each flow, the carrier and ISP can verify the quality assurance status when a communication quality assured service is provided. The carrier and ISP can also use limited network resources effectively to handle increased data volume using Traffic engineering (hereafter abbreviated to TE) technique. The carrier and ISP can also offer provisioning service which provides network resources speedily and timely to meet customer requests (bandwidth, quality of services), and can also detect and analyze network attacks, and can also carry out billing, etc.  
         [0005]     A flow statistics collection method in the technology of the related art for example is the cache method (related technology 1). The related art 1 technology is made up of multiple statistics collection devices distributed within the network and a collector device for collecting statistic information periodically reported from these multiple statistics collection devices and analyzing traffic over the entire network. One example of a statistics collection device is a router that performs packet transfer in the network. Hereafter the processing by the statistics collection device in the related art is described using a router as an example.  
         [0006]     When a packet is received, the router incorporating a statistic collection function searches a flow table in which one or more combinations (hereafter called flow conditions) of packet headers are stored (or registered) for identifying the flow. If the packet matches the stored flow conditions, then a 1 is added to the packet number stored for that matching flow conditions. The byte count of the received packet stored for that matching flow condition is also increased in the same way. If results from the search of the flow table show no matching flow condition, then the received packet header information combination is newly stored in the flow table. A search is made at fixed periodic intervals of each flow condition stored in the flow table and aging processing is performed to delete flow conditions whose statistic information is unchanged from the previous search. To delete a flow condition, a packet with the corresponding statistic information is generated and the packet sent to the collector device.  
         [0007]     The number of bits for the search key in the flow table search is usually large compared to the number of bits of the search key for the destination search made when the router forwards a packet. Therefore, shortening the time needed for the flow table search is difficult compared to the destination search. This fact signifies that flow table search time takes up a large part of the router&#39;s packet processing time. The flow table search process therefore causes packet forwarding performance to deteriorate when flow table search time is larger than the required packet forwarding processing time.  
         [0008]     In the related art technology 2, in order to alleviate the drop in packet forwarding performance due to the flow table search, routers containing high speed lines (ports) perform sampling of packets for flow table searches, according to a predetermined sampling rate and only make a flow table search of the sampled packets.  
         [0009]     Though not a flow table search technology, a technology for making routing table searches was disclosed in JP-A No. 208945/2002 (Related technology 3). The related technology 3 utilizes a stored path table capable of spanning a first memory made up of high speed memories such as a Content Addressable Memory (CAM), and a second memory with a slower search speed than the first memory but possessing a higher degree of entry integration. The related technology 3 is capable of making entry searches requiring a larger number of bits than can be set in the CAM at higher speeds than when utilizing only a RAM (Random Access Memory).  
         [0010]     [Patent document 1] JP-A No. 208945/2002  
         [0011]     The above described related technologies 1 and 2 have the following problems when handing ever-increasingly large amounts of data, and in quality assurance of important data.  
         [0012]     The search key for flow table that is a combination of multiple fields within the packet header has a larger number of bits compared to the search key for destination searches that is made up of only one field within the packet header or combinations of two fields. The number of flow conditions (hereafter, number of flow entries) stored in the flow table must also be several times larger than the number of entries in the destination table.  
         [0013]     One method for searching tables comprised of multiple entries is a method (hereafter, Tree method) for storing flow tables in a tree structure in the memory by utilizing Dynamic Random Access Memory (DRAM) or Static Ram (SRAM) having an inexpensive cost per bit. Using the Tree method has the advantages that only a small number of memory chips are needed when storing information in a table made up of a large number of entries, the device has a low cost, and little installation space is needed in the device. However, multiple memory access lines are usually needed during a search so the search performance falls to only a fraction (less than a fifth or sixth) of that of the CAM method described next. So when search a flow table made up of a large number of entries, a device with a high line (circuit) speed will have a longer flow table search time than the allowable packet transmit time, due to time required for making the flow table search. The related art technology 1 that searches all received packets in a flow table, therefore cannot provide the required packet transmit performance.  
         [0014]     The related art technology 2 provides the required packet transmit performance needed holding lines (port) with a high line speed by lowering the number of times flow table searches are made according to a preset sampling rate. This method performs packet sampling and is capable of finding statistical trends of each packet flow. However this method cannot acquire an accurate number of received packets or a received byte count. This method performs TE and provisioning, network facility planning, and attack detection by finding the statistical flow data size using the sample statistical value. Yet this method has problems because of use of sampling (sample statistical value) in cases for example where utilizing information shown by the network administrator to the network user regarding whether quality assurance is actually being performed on a network for a flow where quality assurance is needed, or when billing, where utilizing an accurate packet count or byte count is important.  
         [0015]     One method for making high speed searches where the search key has a large number of bits is a search method using CAM (hereafter, called the CAM method). The CAM method is capable of high speed searches of search key bit patterns and bit patterns recorded in the memory. However, the cost per bit is high compared to typical memories. Other problems with the CAM method are that the number of CAM chips increases when dealing with large numbers of entries so that the device cost becomes higher, and the available mounting surface area inside the device is inadequate, etc. Yet another problem is that power consumption is high since all bit patterns registered in the memory and the search key bit pattern are compared in parallel.  
         [0016]     The related art technology 3 discloses a method for high speed router searches of routing table. However it does not discuss flow table searches. In methods utilizing CAM and RAM, the time needed for accessing the RAM is added on to the time for the CAM method. Also, the same as with the Tree method when searching flow tables made up of a large number of entries in devices having lines (ports) with a high line speed, the time needed for searching the flow table becomes longer than the allowable packet forwarding processing time. In the related art technology 1 that searches all received packets in a flow table search, achieving the required packet processing performance is difficult  
       SUMMARY OF THE INVENTION  
       [0017]     A first object of the present invention is to provide a packet forwarding method or a packet forwarding device capable of acquiring accurate statistic information on a flow requiring accurate statistic information even when the data size has increased and high speed packet forwarding processing is required. A second object of the present invention is to provide a packet forwarding method or a packet forwarding device capable of collecting statistics on a large number of flows, even when there has been a further increase in the volume of packets to transmit.  
         [0018]     The router of the present invention contains a first table and a means for searching the first table, a second table and a means for searching the second table, and a discrimination means for discriminating between (received) packets requiring collection of all statistic information and packets not requiring collection of all statistic information. To implement the discrimination means, the router of the invention also contains a search discrimination table to decide if the first table or the second table should be searched, and a means to search the search table—discrimination table. The means for searching the first table, the second table and the discrimination table may all be achieved with one search means.  
         [0019]     When the router receives a packet, besides performing the usual routing, the router searches the search table—discrimination table and decides whether to search the first table or the second table. When the router decides to search the first table search, a search is made of the first table and statistics matching the same flow conditions are rewritten.  
         [0020]     The received packets are separated prior to processing so the time required to process the packets is reduced compared to the case of collecting statistic information on all received packets. The accuracy of the collected statistic information is also improved for flows requiring total collection compared to the case of using sampling to collect statistic information from all packets.  
         [0021]     On the other hand, for packets needing a second table search, a decision to search or not search the second table is made according to the sampling rate that was set in the storage means. When decided to search the second table, the second table search processor searches the second table, and statistics for corresponding flow conditions are rewritten.  
         [0022]     Sampling those packets belonging to the same flow conditions stored in the second table, allows increasing the number of flow types capable of collecting statistic information having the same packet forwarding performance. Also, conditions for identifying an adequate flow with sampled statistical values are set in the discrimination table. Further, sampled values from a large number of flows can be collected without lowering the packet forwarding performance, by setting a sampling rate in the storage means at a level that will not lower the packet forwarding performance. Problems other than the above that the present specifications attempt to resolve, and those means to resolve the problems are clarified in the “Detailed Description of the Preferred Embodiments” section and in the drawings.  
         [0023]     By utilizing the statistics collection device of the present invention to set conditions for identifying flows requiring accurate statistic information in the search table-discrimination table, accurate statistic information without sampling can be collected for flows requiring accurate statistic information, without lowering the packet forwarding performance. Further, sampled statistical values from a large number of flow samplings can be collected without lowering the packet forwarding performance, by setting conditions for identifying a sufficient number of flows with sampled statistical values, and by setting a sampling rate in each storage means at a level that will not lower the packet forwarding performance.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a drawing showing the network structure comprised of routers for the statistics collection method of the present invention;  
         [0025]      FIG. 2  is a diagram showing the structure of the packet received in  FIG. 1 ;  
         [0026]      FIG. 3  is a diagram showing the structure of the IPv4 header;  
         [0027]      FIG. 4  is a diagram showing the structure of the IPv6 header;  
         [0028]      FIG. 5  is a diagram showing the structure of the TCP header;  
         [0029]      FIG. 6  is a diagram showing the structure of the UDP header;  
         [0030]      FIG. 7  is a diagram showing an example of the flow condition structure for flow statistics collected by the router R 1  in  FIG. 1 ;  
         [0031]      FIG. 8  is a diagram showing an example of the flow condition structure of flow statistics collected by the router R 1  in  FIG. 1 ;  
         [0032]      FIG. 9  is a block diagram of the structure of the router for the statistics collection method of the present invention;  
         [0033]      FIG. 10  is a block diagram showing the structure of the search processor within the router for the statistics collection method of the present invention;  
         [0034]      FIG. 11  is drawings showing the structure of a high-speed flow table within the router for the statistics collection method of the present invention;  
         [0035]      FIG. 12  is drawings showing the structure of a large scale flow table within the router for the statistics collection method of the present invention;  
         [0036]      FIG. 13  is a block diagram showing the sample discriminator within the router for the statistics collection method of the present invention;  
         [0037]      FIG. 14  is a block diagram showing another sample discriminator within the router for the statistics collection method of the present invention;  
         [0038]      FIG. 15  is a drawing showing a packet number counter table for each input port utilized in the sample discriminator of  FIG. 14 ;  
         [0039]      FIG. 16  is a drawing showing sample period (interval) table for each input port utilized in the sample discriminator of  FIG. 14 ;  
         [0040]      FIG. 17  is a block diagram showing another sample discriminator within the router for the statistics collection method of the present invention;  
         [0041]      FIG. 18  is a drawing showing the structure of a high-speed flow table utilized in the sample discrimination method of the present invention;  
         [0042]      FIG. 19  is a block diagram showing another sample discriminator within the router for the statistics collection method of the present invention;  
         [0043]      FIG. 20  is a block diagram showing another sample discriminator within the router for the statistics collection method of the present invention;  
         [0044]      FIG. 21  is a drawing showing the structure of the random number table for each input port utilized in sample discriminator  FIG. 20 ;  
         [0045]      FIG. 22  is a drawing showing the structure of the threshold table for each input port utilized in sample discriminator  FIG. 20 ;  
         [0046]      FIG. 23  is a block diagram showing another sample discriminator within the router for the statistics collection method of the present invention;  
         [0047]      FIG. 24  is a drawing showing the structure of a high-speed flow table utilized in the sample discrimination method shown in  FIG. 23 ;  
         [0048]      FIG. 25  is a block diagram showing the structure of another router for the statistics collection method of the present invention;  
         [0049]      FIG. 26  is a block diagram showing the structure of another router for the statistics collection method of the present invention;  
         [0050]      FIG. 27  is a block diagram showing the structure of the search processor within the router shown in  FIG. 26 ;  
         [0051]      FIG. 28  is a block diagram of the structure of another router for the statistics collection method of the present invention;  
         [0052]      FIG. 29  is a table showing the structure of statistic information notification packet format utilized in the statistics collection device of the present invention; and  
         [0053]      FIG. 30  is a concept drawing of the control console connected for setting the discriminator table of the statistics collection method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [heading-0054]     First Embodiment  
         [0055]     The flow statistic collection function for the network is described next while referring to  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  and  FIG. 5 . In the present embodiment, “statistic information” signifies processing the router must perform on received packets in order to acquire the specified statistic information as well the type of information the router must collect. The term “statistic information” used here is therefore different from the generally used meaning.  
         [0056]      FIG. 1  is a drawing showing a typical network structure made up of routers having the flow statistic collection function. The network shown in  FIG. 1  is made up of terminals T 1 , T 2 , T 3 , T 4 , servers S 1 , S 2 , and routers R 2 , R 3  each connected with the servers, and a router R 1  connected by way of the ports C_T 1 , C_T 2 , C_T 3 , C_T 4 , C_R 2 , C_R 3  with these terminals and servers. The packet belonging to the flow (hereafter flow  1 ) is sent from the server S 1  to the terminal T 1 . The upper or host protocol within the IP (Internet Protocol) header in flow  1  is TCP (Transmission Control Protocol). The TOS (Type of Service) within the IP header in flow  1  is TOS 1 . The source port number within the TCP header in flow  1  is SPRT 1 . The destination port number within the TCP header in flow  1  is DPRT 1 .  
         [0057]     The packet belonging to the flow (hereafter flow  2 ) is sent from the server S 1  to the terminal T 3 . The upper or host protocol of this packet (flow  2 ) is TCP. The TOS is TOS 1 . The source port number is SPRT 1 . The destination port number is DPRT 3 . The packet belonging to the flow (hereafter called flow x 3 ) is sent from the server S 2  to the terminal T 2 . The upper or host protocol of this flow x 3  is UDP (User Datagram Protocol). The TOS is TOS 2 . The source port number within the UDP header is DPRT 2 . The destination port number within the UDP header is DPRT 2 . The packet belonging to the flow (hereafter flow  4 ) is sent from the server S 2  to the terminal T 4 . The upper or host protocol of this flow 4  is UDP (User Datagram Protocol). The TOS is TOS 2 . The source port number (within the UDP header) is SPRT 2 . The destination port number is DPRT 4 .  
         [0058]      FIG. 2  is a diagram showing the packet being sent or received. The packet here is made up of data and multiple header information for protocols in each layer of the OSI (Open System Interconnection) model. More specifically, the packet is made up of a layer  2  header ( 201 ), a layer  3  header ( 202 ), a layer  4  header ( 203 ), a data ( 204 ). Protocols such as Ethernet (registered trademark), ATM (Asynchronous Transfer Mode), MPLS (Multi_Protocol Label Switching) can be utilized as the layer  2  protocol. Protocols such as IP version 4 (hereafter, IPv4), IP version 6 (hereafter, IPv6) can be utilized as the layer  3  protocol. Protocols such as TCP, UDP can be utilized as the layer  4  protocol.  
         [0059]      FIG. 3  is a diagram showing the structure of an IPv4 header, utilizing the header of the layer  3  protocol as an example. This IPv4 header contains a ToS to indicate the transmit quality of the packet, a protocol showing the layer  4  protocol, an IP address (source IP address) for the source terminal, and an IP address (destination IP address) for the destination terminal. The ToS and the protocol are 8 bits. The source IP address and the destination IP address are both 32 bits.  
         [0060]      FIG. 4  is a diagram showing the structure of an IPv6 header, utilizing the header of the layer  3  protocol as an example. This IPv6 header stores a class indicating the transmit quality of the packet, the following header number for identifying the next header type, source IP address and destination IP address. When the next header is a layer  4  protocol such as TCP or UDP, then a value showing the layer  4  protocol is stored in the next header number. The class is eight bits. The next header number is eight bits, the source IP address and the destination IP address are both 128 bits.  
         [0061]      FIG. 5  is a diagram showing the structure of the TCP header using the header of a layer  4  protocol as an example. The TCP header contains a source port number and a destination port number as a logic port number for identifying the host (upper) application layer. The source port number and the destination port number are both 16 bits.  
         [0062]      FIG. 6  is a diagram showing the structure of the UDP header using the header of a layer  4  protocol as an example. The UDP header contains a source port number and a destination port number, the same as does the TCP header. The source port number and the destination port number are both 16 bits.  
         [0063]      FIG. 7  is a diagram showing flow conditions for flow statistics collected in the router R 1  of  FIG. 1 . The example in  FIG. 7 , shows the source IP address ( 701 ), the destination IP address ( 702 ), the host protocol ( 703 ), the TOS ( 704 ) within the UDP header, and the source port number ( 705 ) and destination port number ( 706 ) as the flow conditions within the TCP or IP header. The combination of header values utilized as the flow conditions here are only a present embodiment and combinations of other values may also be utilized.  
         [0064]      FIG. 8  is an example of statistic information collected for each flow condition. In the example in  FIG. 8 , the statistic information for collection is the number of received packets belonging to each flow (hereafter, called the packet count) ( 801 ), the total sum of the number of bytes for packet belonging to that flow (hereafter called the byte count) ( 802 ), the port number where packets for each flow are input ( 803 ), the port number where packets for each flow are output ( 804 ), and other information ( 805 ). The flow  1  and flow  3  require quality assurance. The flow  1  and flow  3  require quality assurance and are flows requiring accurate statistic information. The flow  2  and flow  3  are flows with adequate statistic sampled values.  
         [0065]     The statistic information shown in  FIG. 8 , is held within the packet forwarding device in a format such as a table. When a packet is received, the received packet is analyzed, the flow conditions extracted, and a search key used to search for flow conditions matching the statistic information held within the device. The received packet is processed as needed based on the hits found in the statistic information. Information acquired from the processing results is stored in the device. The process is described next in detail.  
         [0066]     The structure of the packet forwarding device of the present embodiment is described next while referring to FIG.  9  through  FIG. 24 . The router  900  in  FIG. 9  is comprised of an input port ICn (n=1 through N), an output line OCn (n=1 through N), a packet receive processor  901 , a search processor  1000 , a large scale flow table search processor  902 , a large scale flow table  1200 , a high-speed flow table  1100 , a routing table  903 , a packet transmit processor  904 , and a control section  905 . The control section  905  is connected to the packet receiver processor  901 , a search processor  1000 , a large scale flow table search processor  902 , and packet transmit processor  904  and makes the settings for each of these processors. A method for operating the elements  901  through  905 ,  1000 ,  1100  and  1200  in the router  900  for example is to operate each processor on a single dedicated LSI (device) and connect each processor alternately to the dedicated LSI (device). Another method is to operate multiple processors on a single dedicated LSI, connecting that dedicated LSI alternately to each of the multiple processors.  
         [0067]     Another method is to operate the elements in the router  900  on a general-purpose MPU (Micro Processing Unit) or NP (Network Processor). A CAM (Content Addressable Memory) capable of high-speed searches may be utilized as the memory for storing the high speed flow table  1100 . A DRAM capable of storing multiple flow entries and having a small chip size per bit, as well as an inexpensive cost per bit may be utilized as the memory for storing the large scale flow table  1200 .  
         [0068]     The router  900  shown in  FIG. 9  is a structure with a search table-discrimination table within the high-speed flow table for deciding the high speed flow table processing and large scale flow table processing. In this case, the search processor  1000  searches the search table-discrimination table within the high-speed flow table at the same time as it searches the high-speed flow table, and decides whether or not to search the large scale flow table.  
         [0069]     The router of the present embodiment is comprised of an architecture for searching always first searching the high-speed search table. However the architecture can contain a function for deciding whether to search either the high-speed search table of the large search table. In other words, an architecture can be achieved wherein the packet receive processor  901  decides whether to transmit the packet to the large search processor or the search processor. However, in this case also, the header information for the packet must always be transmitted to the search processor. In order to decide the packet transmission destination, besides a high-speed flow table search, a routing table search must also be made by the search processor.  
         [0070]     A control console can be installed in the router as shown in  FIG. 9  and information stored in the discriminator table can be set there as needed. A concept view of the control console  3000  connection for setting the discrimination table within the router, and the router  900  for the statistic collection function of the present invention are shown in  FIG. 30 . A means for selecting the desired location for displayed contents and changing the displayed contents of the table by way of a display screen  3001  for displaying the contents of the table, and the mouse  3002 , and the keyboard  3000  is installed in the control console  3000 . As shown in  FIG. 31 , this console may also be connected by way of a network to the router  900  for the statistic collection function of the present invention. The function of the console may also be held in a collector device, and that collector device may set information stored in the discrimination table, into the router  900 .  
         [0071]      FIG. 10  shows a typical structure of the search processor  1000  in the router  900  of  FIG. 9 . The search processor  1000  is made up of a header information storage section  1001 , a high-speed flow table search processor  1002 , the routing table search processor  1003 , the sample discrimination section  1300 , the search result generator  1004 , and the flow register-delete processor  1005 .  
         [0072]      FIG. 11  shows the structure of the high-speed flow table  1100  of  FIG. 9  and  FIG. 10 . The flow table  1100  holds one or more entries comprised of a flow entry number field  1101 , a flow condition field  1102 , a search result field  1103 , and a statistic information field  1104 . The flow entry number field  1101  is information relating to a flow condition field  1102 , a search result field  1103 , a statistic information field  1104  and in some cases may be unnecessary depending on the table structure. The flow conditions identical to those shown in  FIG. 7  are one example of the flow condition field  1102 . In other words, the example of the flow condition field  1102  shown in  FIG. 11 , is a combination of the source IP address, the destination IP address, the host (upper layer) protocol, the TOS, the source port number, and the destination source port number.  
         [0073]     The flow  1  and the flow  3  as flows requiring the accurate statistics shown in  FIG. 7 , are respectively set as the flow entry numbers f 1 , f 2  in the high-speed flow table  1100 . In the example in this embodiment, the search table-discrimination table is contained within the high-speed flow table. More specifically, a flow entry number f 3  is set in order to set instructions to search the large search table for flow  2 , and flow  4  adequately sampled for the statistics shown in  FIG. 7 . The “*” shown in the fields for the source IP address field, destination IP address field, host (upper layer) protocol field, TOS field, and destination port number field for flow conditions matching those in the flow entry number f 3 , indicates that the value is not utilized as a flow condition. In other words, the flow condition for flow entry number f 3  indicates that the “Source port number =SPRT2”. By setting the flow entry number (No.) f 3  when making a high-speed flow table search of packets, the entry in the flow entry number f 3  will be a hit when the source port numbers for flow  2  and flow  4  are both SPRT 2 .  
         [0074]     The search result field  1103  is comprised of a sample command flag  1103 _ 1  and sampling rate  1103 _ 2 . The sampling rate here is frequency information as to how often (at what frequency) statistic collection is performed. A “1” setting in the sample command flag  1103 _ 1  indicates sampling and copying of the packet hit into the large table search processor. A setting of “0” indicates no sampling or copying is performed. The sampling rate is set in the sampling rate  1103 _ 2  when copying the packet hit in each flow into the large scale flow table search processor.  
         [0075]     The sampling rate  1103 _ 2  setting is valid when a “1” is set in the sample command flag  1103 _ 1 . In  FIG. 11 , the sample command flag set to “1” and the sampling rate value set to “{fraction (1/1000)}” indicate the search results of the flow entry number (No.) f 3  specifying a large scale flow table search. A sampling rate value of “{fraction (1/1000)}”, indicates a large scale flow table search made for one packet among 1,000 packets that were received. The sampling rate  1103 _ 2  may at times be used for other information according to the formula as described later on.  
         [0076]     The example in the statistic information field  1104  shows the information identical to the statistic information shown in  FIG. 7 . In other words, the example in the statistic information field in  FIG. 11  is comprised of a packet count, a byte count, the input port number, the output port number, and other information. The “_” in the input port number and output port number of the flow entry number f 3  indicate a value with no meaning.  
         [0077]     The flow entry numbers f 1 , f 2  set in  FIG. 11  are not set in particular by the router  900  administrator and may be automatically set in the flow register-delete processor  1005 . The entry for flow entry number f 3  for commanding a large scale flow table search specified in  FIG. 11 , must be set beforehand by the router  900  administrator. The operation for registering and deleting flows by the flow register-delete processor  1005  is described later.  
         [0078]      FIG. 12  is drawings showing the structure of the large scale flow table  1200  of  FIG. 9 . The large scale flow table  1200  is made up of one or more entries comprised of a flow entry number  1201 , a flow condition  1202 , and statistic information  1203 . The flow entry number  1201  is information relating to the flow condition  1202 , a statistic information  1203 , and in some cases may be unnecessary depending on the table structure. The flow conditions identical to those shown in  FIG. 7  are one example of the flow condition  1202 . In other words, the example of the flow condition  1202  shown in  FIG. 12 , is a combination of the source IP address, the destination IP address, the host (upper layer) protocol, the TOS, the source port number, and the destination source port number.  
         [0079]     The flow  2  and flow  4  with adequate sample statistical values shown in  FIG. 7  are respectively set as the flow entry numbers f 4 , f 5  in the large scale flow table  1200 . The statistic information  1203  is shown with statistic information identical to that shown in  FIG. 7 . In other words, the example for statistic information  1203  in  FIG. 12  is comprised of a packet count, a byte count, the input port number, the output port number, and other information.  
         [0080]     The entries for flow entry number f 4 , f 5  set in  FIG. 12  are not set in particular by the router  900  administrator and may be automatically set by the flow register-delete processor (not shown in drawing) within the large scale flow table search processor. The registering and deleting operation of the flow register-delete processor within the large scale flow table search processor  902  is the same processing as the flow register-delete processing of  FIG. 10  and is described later on.  
         [0081]     The operation when the router  900  receives a packet is described next using  FIG. 9 ,  FIG. 10 ,  FIG. 11  and  FIG. 12 .  
         [0082]     The router  900  operation when receiving a packet belonging to the flow  1  shown in  FIG. 7  is described first. In  FIG. 9 , the packet receive processor  901  that received the packet input from the input port, first of all attaches information within the device relating to receive processing such as an input port number (No.) to the packet as a header within the device. The processor  901  then accumulates the packet data and extracts header information such as the header within the device, layer  2  header, layer  3  header, and layer  4  header and sends it to the search processor  1000 . The header information storage section  1001  in  FIG. 10 , temporarily accumulates header information received from the packet receive processor  901  and sends it to the routing table search processor  1003 , high-speed flow table search processor  1002 , and the flow register-delete processor  1005 .  
         [0083]     The routing table search processor  1003  that received the header information, extracts the required information from that header information and generates a search key. The processor  1003  then searches the routing table  903  using that generated search key. The routing table search processor  1003  sends destination information such as the output port number as search results from the routing table  903 , to the high-speed flow table  1002  and search result generator  1004 .  
         [0084]     The high-speed flow table search processor  1002  that received the header information extracts the source IP address, destination IP address, host (upper layer) protocol, TOS, source port number, and destination port number from that header information and generates a search key. The processor  1002  then searches the high speed flow table  1100  using that search key. In the case of the present embodiment, the received packet belongs to the flow  1  so the search key matches the flow entry number f 1  of high speed flow table  1100 . Therefore, the high-speed flow table search processor  1002  acquires the two results of a sample command flag “1” and an invalid sampling rate, and sets the two values in the search results for the flow entry number f 1 . The high-speed flow table search processor  1002  sends these search results to the sample discrimination table  1300 .  
         [0085]     The high-speed flow table search processor  1002  rewrites the statistic information field  1104  for the flow entry number f 1  that matched the search key flow conditions. More specifically, a 1 is added to the packet count for the flow entry number f 1 , the byte count of the received packet is added to the byte count, the input port number within that device header is recorded in the input port number, and the output port number received from the routing table search processor  1003  is recorded in the output port number.  
         [0086]     The sample discrimination table  1300  that received the search results from the high-speed flow table search processor  1002  decides whether or not to generate a copy in the large scale flow table search processor  902  based on those search results, and sends a copy command to the search result generator  1004 . More specifically, a decision not to make a copy is made when the sample command flag in the search results is a “0”. When the sample command flag is a “1”, a decision is made on whether or not to generate a copy utilizing the sampling rate search results. In this example, the sample command flag is “0” so the sample discrimination table  1300  does not issue a copy command to the search result generator  1004 . The detailed embodiment of the sample discrimination table  1300  is described next while referring to  FIG. 13 .  
         [0087]     The search result generator  1004  that received the destination information from the routing table search processor  1003  generates search result information based on the destination information received from the routing table search processor  1003 , and sends the search result information to the packet receive processor  901 . In this example, the search result generator  1004  does not receive that copy command from the sample discrimination table  1300 , so no copy is generated in the large scale flow table search processor  902 .  
         [0088]     The packet receive processor  901  that received the search result information from the search result generator  1004  within the search processor  1000 , attaches the search result information to that accumulated packet data and sends it to the packet transmit processor  904 . The packet transmit processor  904  that received the packet data attached with that search result information, extracts the output port number from the search result information and sends the packet from the corresponding port to that output port number.  
         [0089]     The router  900  operation when a packet belonging to the flow  2  in  FIG. 7  is received is described next. The operation from the time the packet receive processor  901  receives the packet, through the time the high-speed flow table search processor  1002  searches the high speed flow table  1100  is the same as the operation when the packet belong to flow  1  is received.  
         [0090]     In the present embodiment, the search key matches the flow entry number f 3  of high speed flow table  1100  since it is assumed a packet belonging to flow  2  was received. The high-speed flow table search processor  1002  acquires the two results of a sample command flag “1” and a sampling rate of “{fraction (1/1000)}” and these two values are set in the search results for the flow entry number f 3 . The high-speed flow table search processor  1002  sends these search results to the sample discrimination section  1300 . The high-speed flow table search processor  1002  rewrites the statistic information field  1104  for the entry number f 1  that matched the search key for the flow conditions.  
         [0091]     The sample discrimination section  1300  that received the search results from the high-speed flow table search processor  1002 , decides whether or not to copy the search results into the large scale flow table search processor  902 . The discrimination section  1300  notifies the search result generator  1004  of the copy command. In the present embodiment, the sample command flag is “1”, so the sample discrimination section  1300  further decides whether or not to generate a copy at a rate in compliance with the sampling rate of the search results. If  1300  decides not to make a copy according to the sampling rate, then the sample discrimination section  1300  does not notify the search result generator  1004  of the copy command.  
         [0092]     When the sample discrimination section  1300  decides to make a copy according to the sampling rate, the sample discrimination section  1300  informs the search result generator  1004  of the copy command. The following operation for the case where the search result generator  1004  was not informed of the copy command is the same as the operation when the packet belonging to the flow  1  was received and so a description is omitted. Hereafter, the operation is described where the search result generator  1004  is notified of the copy command. A detailed embodiment of the sample discrimination section  1300  is described while referring to  FIG. 13 .  
         [0093]     When the destination information is received from the routing table search processor  1003 , the search result generator  1004  that received the copy command from the discrimination section  1300  generates search result information based on the destination information received from the routing table search processor  1003 . Since the copy command has been received, a flag (Hereafter called a copy flag.) set to a “1 to show there is a copy in the search result information is sent to the packet receive processor  901 . After having sent the search results, the search result generator  1004  adds information identical to the search results, sets a flag (hereafter, large scale flow table search processor flag) to “1” to command sending of a copy to the large scale flow table search processor, and sends it to the packet receive processor  901 . Hereafter, the search result information added to the large scale flow table search processor flag, is called the search result information copy.  
         [0094]     The packet receive processor  901  that received the search result information from the search result generator  1004  inside the search processor  1000 , first of all attaches search result information to that accumulated packet data and then sends it to the packet transmit processor  904 . At this time, a search is made in the search result information for a value of “1” in the copy flag, and a decision made to also use the same packet data for the next search result information copy received. Next, the packet receive processor  901  that received the search result information copy from the search result generator  1004  searches for a “1” value in the large scale flow table search process flag within the search result information copy, attaches a search result information copy to the accumulated packet data used for sending to the packet transmit processor  904 , and transmits it to the large scale flow table search processor  902 . Also the data sent to the large scale flow table search processor  902  may for example be only information extracted from header information required for making a large scale flow table search.  
         [0095]     The packet transmit processor  904  that received the packet data attached with that search result information, extracts the output port number from that search result information, and sends the packet to that output port number from the corresponding port. The large scale flow table search processor  902  that received the packet data attached with that search result information copy, extracts information required for making a large scale flow table search from the packet data and generates a search key. The processor  902  then utilizes that search key to search the large scale flow table  1200 . The search key of the present embodiment is described as identical to the search key generated by the high-speed flow table search processor  1002 . However the search key utilized in the high-speed flow table search processor  1002  may be different from the search key used in the large scale flow table search processor  902 .  
         [0096]     In the present embodiment, the search key matches the flow entry number f 4  of high speed flow table  1200  since it is assumed a packet belonging to flow  2  was received. The large scale flow table search processor  902  rewrites the statistic information  1203  of the flow entry number f 4  that matched the search key flow conditions. More specifically, the search processor  902  adds a 1 to the packet count for the flow entry number f 4 , adds the byte count of the received packet to the byte count, records the input port number within that device header into the input port number, and records the output port number within that search result information into the output port number.  
         [0097]     The operation for registering a new flow entry of the flow register-delete processor  1005  is described next. When searching the high speed flow table  1100  and there are no matches among any of the flow entries, the high-speed flow table search processor  1002  recognizes packets input to the router  900  that belong to new flows, and sends a new flow receive notification to the flow register-delete processor  1005 . The flow register-delete processor  1005  that received that new flow receive notification, extracts information utilized in flow conditions for the high speed flow table, from that received header information, and sends it along with the flow register command to the high-speed flow table search processor  1002 .  
         [0098]     The flow register-delete processor  1005  manages the free memory space stored in the high speed flow table. The processor  1005  also notifies the high-speed flow table search processor  1002  of memory addresses for new flows that should be registered. When there is no free space available to register a new flow in the high speed flow table, a flow deletion process as described next is performed. The high-speed flow table search processor  1002  that receives the memory address that must be registered, information utilized in the flow conditions, and that flow registration command from the flow register-delete processor  1005 , sets the flow conditions in that memory address.  
         [0099]     The operation for deleting the flow entry of flow register-delete processor  1005  is described next. At fixed time intervals, the flow register-delete processor  1005  loads the packet count  801  (or byte count  802 ) from statistic information for each flow entry stored in the high speed flow table  1100  and compares them with the values from the previous time the values were loaded. When the comparison results show the values are different from the previous time, then that time is stored as the new time in the flow entry number. When the comparison results show the values are the same as the previous time, a new time corresponding to the flow entry number is not written, and only a 1 is added to the non-rewrite count for that flow number.  
         [0100]     When the non-rewrite count for the flow entry number matches that preset count, the flow corresponding to that flow entry number is determined to have terminated. The flow register-delete processor  1005  then sends to the high-speed flow table search processor  1002 , a flow delete command and the memory address registered for that flow entry for deletion. The high-speed flow table search processor  1002  that received the memory address of the flow entry for deletion then deletes the flow registered in the memory address.  
         [0101]     When a new flow receive notification is received from the high-speed flow table search processor  1002  and there is no free space for registering the new flow stored in the high speed flow table, the flow register-delete processor  1005  searches all flows for the rewritten time stored in each flow. The flow register-delete processor  1005  deletes the flow having the largest differential between the rewrite time and the current time. The flow register-delete processor  1005  sends the flow delete command, and the memory address registered in the flow entry decided to be deleted, to the high-speed flow table search processor  1002 . The high-speed flow table search processor  1002  that received the flow delete command, and the memory address that the flow entry for deletion is registered, then deletes the flow registered in that memory address.  
         [0102]     The flow register operation in the flow register-delete processor section within the large scale flow table search processor  902  is the same processing as in the flow register-delete processor  1005  described for  FIG. 10 .  
         [0103]     The process for sending statistic information to the collector device after a flow was deleted is described next. The flow register-delete processor  1005  stores statistic information on that deleted flow entry into a memory separate from the memory storing the high speed flow table x 1100  (not shown in  FIG. 9 ). The flow register-delete processor  1005  encapsulates statistic information for that deleted flow entry according to a pre-established packet format for statistic information notification and sends it over the network to the collector.  
         [0104]     Statistic values for the flow deleted by flow register-delete processor  1005  are accurate, non-sampled flow values and so a sampling rate ½ is set as the sampling rate for information within the pre-established packet format. The flow register-delete processor  1005  also handles processing for statistic information after flow registry-deletion within the large scale flow table search processor  902 , to the collector device. However statistic information on flow deleted by the flow registry-deletion section within the large scale flow table search processor  902 , are statistical values sampled according to the sampling rate so the sampling information within the pre-established packet format is set as the sampling rate, as search results within the high speed flow table  1100 .  
         [0105]      FIG. 29  is a drawing showing the structure of the statistic information notification packet format used by the statistics collection device of the present invention. The collector device estimates from the sampling rate, the actual packet count for the flow sent over the network. In the statistics collection device of the present invention, the sampling rate may differ even among flows on the same device so a sampling rate is set for each flow in the packet format. The statistic information notification packet format for the  FIG. 29  is comprised of a header information  2901 , and N (N is a natural number) number of flow information elements (hereafter called flow records). Each flow record is comprised of a flow ID  2911 , a flow sampling rate  2912 , a packet count  2913 , a byte count  2914 , an input port  2916 , and other information  2917 .  
         [0106]     The operation of the sample discriminator  1300  is described next while referring to  FIG. 13 ,  FIG. 14 ,  FIG. 15 ,  FIG. 16 ,  FIG. 17  and  FIG. 18 .  
         [0107]      FIG. 13  is a drawing showing the structure of the sample discriminator  1300 . The method for identifying the sample when comparing the predetermined packet interval (period) and the received packet count in  FIG. 13  and the received packet count equals the packet interval (period) is described. The method for using one type of sampling rate set in the router  900  and not using the sampling rate values set in the entries for the high speed flow table, is described next.  
         [0108]     The sample discriminator of  FIG. 13  is comprised of a  1301  search result accumulator  1301 , packet counter  1302 , sample threshold register  1303 , and comparator  1304 . Here, a 0 is set in the packet counter  1302  when the router  900  starts up. The administrator of the router  900  sets the packet sample interval (or period) in the sample interval register  1303  via the control section  905 . The search result accumulator  1301  receives and accumulates the sample command flags  1303 _ 1  that constitutes the search results of the high speed flow table. The sampling rate  1303 _ 2  is not used in the present embodiment. When the sample command flag is “1”, the search result accumulator  1301  commands the packet counter  1302  to add a “1” to the packet count. The search result accumulator  1301  commands the comparator  1304  to perform the comparison.  
         [0109]     The comparator  1304  that received the compare command, receives the packet count from the packet counter  1302  and compares the sample interval of the packet received from the sample interval register  1303 . When the comparison results show that the condition of packet count value =value of sample interval register, has been fulfilled, the comparator  1304  sends a copy command to the search result generator  1004 , and sends a 0 clear command to the packet counter  1302 . The packet counter  1302  that received the 0 clear command, sets the counter value to 0. If the above conditions have not been fulfilled then the copy command is not conveyed to the search result generator  1004 , or the 0 clear command is not conveyed to the packet counter.  
         [0110]      FIG. 14  is a block diagram showing another structure of the sample discriminator  1300 . In  FIG. 14 , the comparing of the preset packet interval and the received packet count, and the method for deciding to sample when the received packet count is equal to the packet interval is described. The method for using the sampling rate set in each input port of the router  900 , without using the value set in the entry for the high speed flow table is also described.  
         [0111]     The sample discriminator  1300  of  FIG. 14  is comprised of a search result accumulator  1301 , a packet counter table  1305 , a sample threshold table  1306 , a comparator  1304  and an input port number accumulator  1307 . The input port number accumulator  1307  receives the input port number from the header information storage section  1001 .  
         [0112]      FIG. 15  shows the structure of the packet counter table  1305 . The packet counter table  1305  holds the packet count for each input port number and all counters are set to a 0 during startup of the router  900 .  FIG. 16  shows the structure of the sample interval table  1306 . The administrator of the router  900  sets the packet sample interval for each input port number in the sample interval table  1306  by way of the control section  905 . The search result accumulator  1301  receives and accumulates the sample command flag  1103 _ 1  constituting the search results from the high speed flow table from the high speed flow table search processor  1002 . The sampling rate  1103 _ 2  is not used in the case of the present embodiment. When a “1” is set in the sample command flag, the search result accumulator  1301  commands the packet counter to just add a 1 to the packet count corresponding to the input port number.  
         [0113]     The search result accumulator  1301  commands the comparator  1304  to make a comparison. The comparator  1304  that receives the compare command, receives a packet count from the packet counter table  1305  that matches the input port number. The comparator  1304  then compares the sample period of the packet matching that input port number. When the comparison results show that the condition of packet count value=value of sample interval register, has been fulfilled, the comparator  1304  sends a copy command to the search result generator  1004 , and sends a packet counter 0 clear command to the packet counter table  1305  matching the input port number.  
         [0114]     The packet counter  1305  that received the 0 clear command, sets the counter value that matches the input port number to 0. If the above conditions have not been fulfilled, then the comparator  1304  does not convey the copy command to the search result generator  1004 , or the 0 clear command for the corresponding input port number to the packet counter table  1305 .  
         [0115]      FIG. 17  shows another structure of the sample discriminator  1300  different from those in  FIG. 13  and  FIG. 14 . In  FIG. 17 , the comparing of the preset packet interval and the received packet count, and the method for deciding to sample when the received packet count is equal to the packet interval are described. The method for using the value set in the entry for the high speed flow table as the sampling rate is also described.  
         [0116]     The sample discriminator  1300  of  FIG. 17  is comprised of a search result accumulator  1301 , a search result accumulator  1301 , a packet counter accumulator  1308 , a sample interval accumulator  1309 , and a comparator  1304 .  
         [0117]      FIG. 18  shows the structure of the high speed flow table  1100  of the present embodiment. The flow conditions of the present embodiment and the statistic information are the same as shown in  FIG. 11 , so the flow conditions and statistic information are omitted in  FIG. 18 . The search results of  FIG. 18  are made up of a sample command flag  1801 , a packet counter  1802 , and a sample interval  1803 . The packet counter is set to 0 when the router  900  starts up. The administrator of the router  900  sets the sample interval  1803  by way of the control section  905 . The sample interval of the packet for each entry is set to command a large scale flow table search. The flow table  1100  setting may also be made from control console  3000  of  FIG. 30 . The setting may also be made from a control console  3000  connected by way of the network of  FIG. 31 .  
         [0118]     The search result accumulator  1301  receives and accumulates the flow entry number fields  1101  that correspond to the sample command flag  1103 _ 1  search results of the high speed flow table, from the high speed flow table search processor  1002 . The packet counter accumulator  1308  receives and accumulates the packet counts as search results of the high speed flow table from the high speed flow table search processor  1002 . The sample interval accumulator  1309  receives and accumulates sample intervals as search results of the high speed table from the high speed flow table search processor  1002 .  
         [0119]     When the sample flag value is “1”, the search result accumulator  1301  commands the packet counter accumulator  1308  to add only a 1 to the accumulated packet count. The search result accumulator  1301  also commands the comparator  1304  to make a comparison, and send the flow entry numbers that matched. The comparator  1304  that received the compare command, receives the accumulated packet count to which only a 1 was added from the packet counter accumulator  1308  and compares the packet count with the accumulated packet sample interval received from the sample interval accumulator  1307 .  
         [0120]     When the results of the comparison are that the condition of, packet count value=sample interval register value was fulfilled, then the comparator  1304  sends a copy command to the search result generator  1004 , sends matching flow entry numbers, and a packet counter 0 clear command for the corresponding flow entry number, to the high speed flow table search processor  1002  the high speed flow table search processor  1002  that received that 0 clear command, sets a 0 as the packet counter value. However if the above condition was not fulfilled then the comparator  1304  does not send a copy command to the search result generator  1004 .  
         [0121]     The comparator  1304  sends a command (Hereafter called the packet count increment command.) to record the packet counter value incremented only by a 1, in the packet counter corresponding to that flow entry number, and to record that matching flow entry number in the high speed flow table search processor  1002 . The high speed flow table search processor  1002  that received the packet count increment command, and the matching flow number, records a packet counter value added with only a 1, to the packet counter corresponding to the flow number that was a match.  
         [0122]      FIG. 19  shows another structure of the sample discriminator  1300  different from those structures in  FIG. 13 ,  FIG. 14 , and  FIG. 17 . The example in  FIG. 19  describes the method for discriminating the sample when comparing a pseudo-random number with the preset threshold value, and the pseudo-random number is smaller (or larger) than the threshold. Further, the method described here, uses one type of sampling rate set in the router  900  and does not use the value set in the entry for the high speed flow table. In the present embodiment, the sampling rate corresponds to the threshold.  
         [0123]     The discrimination section  1300  of  FIG. 19  is comprised of a search result accumulator  1301 , a random number counter  1310 , a threshold register  1311 , and a comparator  1304 . The random number counter  1302  is comprised for example of a linear feedback shift register using multiple flip-flops. The administrator of the router  900  sets the threshold value in the threshold register  1311  by way of the control section  905 .  
         [0124]     The search result accumulator  1301  receives and accumulates the sample command flag  1103 _ 1  as the search results of the high speed flow table from the high speed flow table search processor  1002 . The sampling rate  1103 _ 2  is not used in the present embodiment. When the sample flag value is “1”, the search result accumulator  1301  commands the random number counter  1310  to generate a new random number based on the random number counter value. The search result accumulator  1301  also commands the comparator  1304  to make a comparison. The comparator  1304  that received the compare command, receives a newly generated random number from the random number counter  1310 , and compares it with the threshold value received from the threshold register  1311 . When the comparison results are that the condition, random number ≧threshold value is established, the comparator  1304  sends a copy command to the search result generator  1004 . If this condition was not established, then the comparator  1304  does not send that copy command to the search result generator  1004 .  
         [0125]      FIG. 20  shows another structure of the sample discriminator  1300  different from those structures in  FIG. 13 ,  FIG. 14 ,  FIG. 17 , and  FIG. 19 . The method in this example describes the method for discriminating the sample by comparing the preset threshold value with the pseudo-random number and that pseudo-random number is smaller (or larger) than that threshold value. In the method described here, the sampling rate type is set in each input port of the router  900 , and does not use values set in entries of the high speed flow table. In the present embodiment, the sampling rate corresponds to the threshold.  
         [0126]     The sample discriminator  1300  of  FIG. 20  is comprised of a search result accumulator  1301 , a random number table  1312 , a threshold table  1313 , a comparator  1304  and an input port number accumulator  1307 . The input port number accumulator  1307  receives an input port number from the header information storage section  1001 . One structure of the random table  1312  is shown in  FIG. 21 . The random number table  1312  holds the random numbers for each input port number. These random number counters are for example comprised of by linear feedback shift registers. One example of the threshold value table  1313  is shown in  FIG. 22 . The threshold value is set in the threshold table  1306 , via the control section  905  in each input port set by the administrator of the router  900 .  
         [0127]     The search result accumulator  1301  receives and accumulates the sample command flag  1103 _ 1  as the search results of the high speed flow table from the high speed flow table search processor  1002 . The sampling rate  1103 _ 2  is not used in the present embodiment. When the sample flag value is “1”, the search result accumulator  1301  commands the random number table  1312  to generate a new random number based on the random number counter value recorded for the corresponding input port number. The search result accumulator  1301  also commands the comparator  1304  to make a comparison. The comparator  1304  that received the compare command, receives a newly generated random number from the random number table  1312  corresponding to the input port number, and compares it with the threshold value received from the threshold table  1313 . When the comparison results are that the condition, random number ≧threshold value is established, the comparator  1304  sends a copy command to the search result generator  1004 . If this condition was not established, then the comparator  1304  does not send that copy command to the search result generator  1004 .  
         [0128]      FIG. 23  shows another structure of the sample discriminator  1300  different from those structures in  FIG. 13 ,  FIG. 14 ,  FIG. 17 ,  FIG. 19  and  FIG. 20 . The example in  FIG. 23  describes the method for discriminating the sample when comparing a pseudo-random number with the preset threshold value, and the pseudo-random number is smaller (or larger) than the threshold. Further, the sampling rate method described here, uses the value set in the entry for the high speed flow table. In the present embodiment, the sampling rate corresponds to the threshold.  
         [0129]     The discrimination section  1300  of  FIG. 23  is comprised of a search result accumulator  1301 , a random number accumulator  1314 , a threshold accumulator  1315  and a comparator  1304 .  FIG. 24  shows the structure of the high speed flow table  1100  of the present embodiment. The flow conditions and statistic information in the case of the present embodiment are the same as shown in  FIG. 11  so the related flow conditions and statistic information in  FIG. 24  are omitted. The search result  2400  of  FIG. 24  is comprised of a sample command flag  2401 , random number  2402  and threshold value  2403 . The random number  2402  of each flow entry is a value generated and stored by a random number generator circuit utilizing a linear feedback shift register. A threshold value for each entry used to command a large scale flow table search is set by the router  900  system administrator in the threshold  2403  via the control section  905 .  
         [0130]     The search result accumulator  1301  receives and accumulates the field  1102  flow entry numbers that match the sample command flag  1103 _ 1  as the search result of the high speed flow table, from the high speed flow table search processor  1002 . The random number accumulator  1314  receives and accumulates random numbers from the high speed flow table search processor  1002  as high speed flow table search results. The threshold accumulator  1315  receives and accumulates threshold values from the high speed flow table search processor  1002  as search results from the high speed flow table. When the sample command flag is “1”, the search result accumulator  1301  commands the random number accumulator  1314  to generate new random numbers based on the accumulated random numbers.  
         [0131]     The search result accumulator  1301  commands the comparator  1304  to make a comparison and to send matching flow entry numbers.  
         [0132]     The comparator  1304  that received the compare command, receives a newly generated random number from the random number accumulator  1314  and compares the packet count with the accumulated packet sample intervals received from the sample interval accumulator  1307 . When the comparison results are that the condition, random number ≧threshold value is established, the comparator  1304  sends a copy command to the search result generator  1004 . If this condition was not established, then the comparator  1304  does not send that copy command to the search result generator  1004 .  
         [0133]     The comparator  1304  sends a command to the high speed flow table search processor  1002  to record the matching flow entry numbers, and the newly generated random number corresponding to the flow entry numbers. The high speed flow table search processor  1002  that received the command to record the random numbers, records the random numbers received from the comparator  1304 , into the corresponding flow entry number.  
         [heading-0134]     Second Embodiment  
         [0135]     A structure different from the packet forwarding device shown in  FIG. 9  is described next while referring to  FIG. 25 . The router  900  of  FIG. 25  contains the input port number ICmn (m=1 through M, n=1 through N), the output port number OCmn (m=1 through M, n=1 through N) The router  900  is comprised of a packet receive processor  901 , a search processor  1000 , a large scale flow table search processor  902 , a large scale flow table  1200 , a routing table  903 , a packet transmit processor  904 , one or more port cards  2501 _m (m=1 through M) made up of the control section  905 , and a crossbar switch  2502  mutually connecting one or more port cards, and an overall controller  2503  to control the entire device.  
         [0136]     The process when receiving the packet is the same as for the router  900  shown in  FIG. 9 . However, the point of difference here is that the packet receive processor  901  that received the statistic information from the search processor  1000  has the crossbar switch  2502  as the destination for sending the packet data attached with the statistic information. The crossbar switch  2502  that received the packet data, extracts the output port number from the search result information, discriminates (or identifies the circuit card storing circuits corresponding to the output port number, and sends the packet data to the packet transmit processor  904  within the identified port card. The remainder of the process is the same as shown in  FIG. 9  for the router  900 .  
         [heading-0137]     Third Embodiment  
         [0138]      FIG. 26  shows a structure different from the packet forwarding device structures shown in  FIG. 9  and  FIG. 25 . The router  900  of  FIG. 26  in this example includes a large search processor in the search processor  2700 . Otherwise, the operation and configuration is identical to the router  900  of  FIG. 25 .  FIG. 27  shows a structure of the search processor  2700  of the router  900  shown in  FIG. 26 . The search processor  2700  differs from the search processor  1000  shown in  FIG. 10  in that is possesses a large scale flow table search processor  2701  for searching a large scale flow table, and a large scale flow register-delete processor  2702  for registering and deleting flows in the large scale flow table.  
         [0139]     When determined that the sample discrimination results of the sample discriminator  1300  and the large scale flow table search were made, instead of sending a copy command from the search discriminator  1300  to the search result generator  1004 , this operation differs in that a command for a large scale flow table search is sent directly to the large scale flow table search processor  2701 . The large scale flow table search processor  2701  that received that search command, generates a search key by extracting information required for making a search key from the header information received from the header information storage section  1001 , searches the large scale flow table  1200 , and collects the statistic information. The operation for the large scale flow registry and deletion processes in the large scale flow register-deletion processor are the same as the flow register process and deletion process in the flow register-delete processor  1005 .  
         [heading-0140]     Fourth Embodiment  
         [0141]      FIG. 28  shows a structure different from the packet forwarding device structures shown in  FIG. 9   FIG. 25  and  FIG. 26 . The router  900  of  FIG. 28  contains a dedicated statistic collection processing card  2800  which is separate from the port card  2501 _m (m=1 through M). This dedicated statistic information processing card is mutually connected with the port card  2501 _m by way of the crossbar switch. The statistic collection processing card  2800  is comprised of a large search processor  902 , a large scale flow table  11200 , and a control section  2801  for controlling the statistic collection processing card  2800 . The crossbar switch  2502  is installed on a dedicated board. This dedicated board contains a card connection means (for example, a mounting slot) for mounting the statistic collection processing card  2800 .  
         [0142]     The processing when a packet is received is the same as that for the router  900  shown in  FIG. 25 . However, the point of difference here is that the packet receive processor  901  that received the search information copy from the search processor  1000 , sends the packet data attached with that search information copy to the statistic collection processing card  2800  via the crossbar switch  2500 . The subsequent large scale flow table search processing is the same as the operation described in  FIG. 9 .  
         [0143]     The router  900  shown in  FIG. 28  possessed only one statistic collection processing card, however the router may possess multiple statistic information collection processing cards. In that case, a card number may be added for identifying one among the multiple statistic information collection processing cards. Setting the card numbers allows dispersing the flow table processing load for multiple flows among multiple statistic information collection processing cards when searching large scale flow tables. The processing load can also be dispersed among multiple statistic information collection processing cards by other methods, without setting card numbers for statistic collection processing cards for each flow. Methods for dispersing the load include calculating a hash value according to an appropriate hash function from the header information in the received packet, and then selecting a dedicated statistic collection processing card based on the hash value, etc.