Patent Publication Number: US-8117305-B2

Title: Communication management system, communication management method, and communication control device

Description:
TECHNICAL FIELD 
     The present invention relates to a communication management technique, and particularly to a communication management system, a communication management method and a communication control apparatus for managing peer to peer (P2P) communication. 
     BACKGROUND ART 
     Due to improved Internet infrastructures and the widespread of communication terminals, such as cellular phone terminals, personal computers, and VoIP (Voice over Internet Protocol) phone sets, the number of Internet users is now exploding. Under such circumstances, security problems such as computer viruses, hacking and spam mails have become apparent, requiring appropriate techniques for communication control. Also, since improved communication environments have enormously increased communication traffic, there are required communication control apparatuses that enable high-speed processing of a large volume of data. 
     [Patent Document 1] Japanese Patent Application Laid-open No. 4-180425. 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In recent years, the number of users of file-sharing networks using P2P communication has been increasing. Such users have rapidly increased because the users can easily obtain desired contents by sharing their contents among each other. On the other hand, a series of problems, such as copyright infringement of contents, distribution of illegal contents, and spread of computer viruses targeting file-sharing networks, have become apparent and are now regarded as social issues. Accordingly, there is an urgent need to develop appropriate techniques for managing P2P communication. 
     The present invention has been made in view of such a situation, and a general purpose thereof is to provide a technique for managing P2P communication appropriately. 
     Means for Solving the Problem 
     One aspect of the present invention relates to a communication management system. The communication management system comprises: a terminal which has a peer to peer connection to communicate with a node conducting peer to peer communication; a node detector which refers to communication data transmitted from or to the terminal so as to detect identification information of the node; and a communication control apparatus which refers to the detected identification information to control peer to peer communication between nodes. 
     The node detector may detect the IP address of the node, and the communication control apparatus may compare the detected IP address with an IP address of a transmission source or a transmission destination of communication data to be controlled, so as to determine if the communication data is derived from the peer to peer communication between nodes. Also, the node detector may further detect the port number of a port through which the node conducts peer to peer communication, and the communication control apparatus may further refer to the detected port number so as to determine if the communication data to be controlled is derived from the peer to peer communication between nodes. 
     The communication control apparatus may comprise: a database which stores identification information of the node detected by the node detector; a search circuit which acquires communication data and searches the database for identification information of the transmission source or transmission destination of the communication data; and a filtering circuit which performs filtering on the communication data in accordance with the search result of the search circuit. 
     The communication management system may further comprise: a node database which stores identification information of the node detected by the node detector; and a database server which refers to the node database to update the database of the communication control apparatus. 
     When the search circuit determines that the transmission source or transmission destination of the communication data is the node, the filtering circuit may discard the communication data. 
     The communication control apparatus may further comprise a detection circuit which determines if the communication data acquired includes a character string that is included in the peer to peer communication and with which the peer to peer communication can be identified, so as to detect communication data derived from the peer to peer communication. When the detection circuit detects communication data derived from the peer to peer communication, the filtering circuit may discard the communication data. Also, the communication control apparatus may further comprise a decoder circuit which decrypts acquired communication data using a decryption key for decrypting communication data encrypted by an application for the peer to peer communication. The detection circuit may determine if communication data decrypted by the decoder circuit includes a character string with which the peer to peer communication can be identified. 
     The communication control apparatus may be configured using FPGA (Field Programmable Gate Array) or may be configured with a wired logic circuit. 
     Another aspect of the present invention relates to a communication management method. The communication management method comprises: referring to communication data transmitted from or to a terminal having a peer to peer connection to communicate with a node conducting peer to peer communication, so as to detect the IP address of the node; and referring to the detected IP address to control peer to peer communication between nodes. 
     Yet another aspect of the present invention relates to a communication control apparatus. The communication control apparatus comprises: a database which stores identification information of a node, the identification information being detected with reference to communication data transmitted between the node and another node through peer to peer communication; a search circuit which acquires communication data and searches the database for identification information of the transmission source or transmission destination of the communication data; and a filtering circuit which performs filtering on the communication data in accordance with the search result of the search circuit. 
     Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, systems, recording mediums and computer programs may also be practiced as additional modes of the present invention. 
     Advantageous Effects 
     The present invention provides a technique for managing P2P communication appropriately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram that shows a configuration of a communication control system according to a base technology. 
         FIG. 2  is a diagram that shows a configuration of a conventional communication control apparatus. 
         FIG. 3  is a diagram that shows a configuration of a communication control apparatus according to the base technology. 
         FIG. 4  is a diagram that shows a configuration of a packet processing circuit. 
         FIG. 5  is a diagram that shows a configuration of a position detection circuit. 
         FIG. 6  is a diagram that shows another example of the position detection circuit. 
         FIG. 7  is a diagram that shows yet another example of the position detection circuit. 
         FIG. 8  is a diagram that shows an example of internal data of a first database. 
         FIG. 9  is a diagram that shows another example of internal data of the first database. 
         FIG. 10  is a diagram that shows yet another example of internal data of the first database. 
         FIG. 11  is a diagram that shows another example of the index circuit. 
         FIG. 12  is a diagram that shows a configuration of a comparison circuit included in a binary search circuit. 
         FIG. 13  is a diagram that shows a configuration of the binary search circuit. 
         FIG. 14  is a diagram that shows still yet another example of internal data of the first database. 
         FIG. 15  is a diagram that shows an example of internal data of a second database. 
         FIG. 16  is a diagram that shows another example of internal data of the second database. 
         FIG. 17  is a diagram that shows another illustrative configuration of the communication control apparatus according to the base technology. 
         FIG. 18  is a diagram that shows a configuration of a communication control apparatus comprising multiple communication control apparatuses. 
         FIG. 19  is a diagram that shows an example of internal data of a management table provided in an operation monitoring server. 
         FIG. 20  is a diagram for describing an operational procedure performed in the event that a communication control apparatus fails. 
         FIGS. 21A ,  21 B and  21 C are diagrams for describing a procedure for updating databases in the communication control apparatuses. 
         FIG. 22  is a diagram that shows a configuration of a communication path control apparatus provided to process packets with multiple communication control apparatuses. 
         FIG. 23  is a diagram that shows a configuration of a communication management system according to an embodiment. 
         FIG. 24  is a diagram that shows another illustrative configuration of the communication management system according to the embodiment. 
         FIG. 25  is a diagram that shows a configuration of the packet processing circuit according to the embodiment. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               10  communication control apparatus 
               20  packet processing circuit 
               30  search circuit 
               32  position detection circuit 
               33  comparison circuit 
               34  index circuit 
               35  comparison circuit 
               36  binary search circuit 
               36 A,  36 B and  36 C comparison circuits 
               36 Z control circuit 
               40  process execution circuit 
               50  first database 
               60  second database 
               100  communication control system 
               110  operation monitoring server 
               120  connection management server 
               130  message output server 
               140  log management server 
               150  database server 
               200  communication path control apparatus 
               300  communication management system 
               310  user terminal 
               320  P2P node 
               322  P2P network 
               330  ISP 
               340  node detector 
               350  P2P node 
               352  P2P node detection network 
               360  P2P node database 
               390  Internet 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First, as a base technology, a communication control system that has no CPU or OS and performs a packet filtering function using a dedicated hardware circuit will be described. Thereafter, there will be described as an embodiment a technique for managing P2P communication using the communication control system of the base technology. 
     (Base Technology) 
       FIG. 1  shows a configuration of a communication control system according to the base technology. A communication control system  100  comprises a communication control apparatus  10  and various peripheral apparatuses provided to support the operation of the communication control apparatus  10 . The communication control apparatus  10  of the base technology performs a packet filtering function provided by an Internet service provider or the like. The communication control apparatus  10  provided on a network path acquires a packet transmitted via the network, analyzes the content, and determines whether or not the packet communication should be permitted. If the communication is permitted, the communication control apparatus  10  will transmit the packet to the network. If the communication is prohibited, the communication control apparatus  10  will discard the packet and return a warning message or the like to the transmission source of the packet if necessary. 
     The communication control system  100  of the base technology includes multiple communication control apparatuses  10   a ,  10   b ,  10   c , etc. and operates them functioning as one communication control apparatus  10 . Hereinafter, each of the communication control apparatuses  10   a ,  10   b ,  10   c , etc. and their collective body will be both referred to as a communication control apparatus  10  with no distinction. 
     In the communication control system  100  of the base technology, each communication control apparatus  10  stores the respective shares of at least part of databases necessary for packet processing; there are provided as many as the number of communication control apparatuses  10  required to share and store such databases, and at least one more apparatus is provided extra. For example, when the number of pieces of data is 300,000 or above but less than 400,000, the number of communication control apparatuses required for operation is four. However, one or more communication control apparatuses  10  should be further provided as standby units in case any of the communication control apparatuses  10  in operation fails or in case a database in any of the communication control apparatuses  10  is updated. Accordingly, at least five communication control apparatuses  10  are provided in total. Conventionally, the entire system has needed to be duplexed considering fault tolerance. According to the technique of the base technology, in contrast, a divided unit of the communication control apparatus  10  may be only provided extra, thereby enabling cost reduction. The operating state of the multiple communication control apparatuses  10   a ,  10   b ,  10   c , etc. is managed by an operation monitoring server  110 . The operation monitoring server  110  of the base technology has a management table for managing the operating state of the communication control apparatuses. 
     The peripheral apparatuses include the operation monitoring server  110 , a connection management server  120 , a message output server  130 , a log management server  140  and a database server  150 . The connection management server  120  manages connection to the communication control apparatus  10 . When the communication control apparatus  10  processes a packet transmitted from a cellular phone terminal, for example, the connection management server  120  authenticates the user as a user entitled to enjoy the service of the communication control system  100 , based on information included in the packet, which uniquely identifies the cellular phone terminal. Once the user is authenticated, packets transmitted from the IP address, which is temporarily provided for the cellular phone terminal, will be transmitted to the communication control apparatus  10  and processed therein, without being authenticated by the connection management server  120  during a certain period. The message output server  130  outputs a message to the destination or the source of packet transmission, according to whether the communication control apparatus  10  has permitted the packet communication. The log management server  140  manages the operating history of the communication control apparatus  10 . The database server  150  acquires the latest database from an external source and provides the database to the communication control apparatus  10 . To update the database without halting the operation of the communication control apparatus  10 , the apparatus may possess a backup database. The operation monitoring server  110  monitors the operating state of the communication control apparatus  10  and its peripheral apparatuses including the connection management server  120 , message output server  130 , log management server  140  and database server  150 . The operation monitoring server  110  has the highest priority in the communication control system  100  and performs supervisory control of the communication control apparatus  10  and all the peripheral apparatuses. Although the communication control apparatus  10  is configured with a dedicated hardware circuit, as will be described later, the operation monitoring server  110  can monitor the operating state even while the communication control apparatus  10  is in operation, by inputting to or outputting from the communication control apparatus  10  the data for monitoring by means of a boundary-scan circuit based on the technique described in Japanese Patent No. 3041340 filed by the present applicant or other techniques. 
     In the communication control system  100  of the base technology, as will be described below, the communication control apparatus  10 , configured with a dedicated hardware circuit for faster operation, is controlled by using a group of peripheral servers connected thereto and having various functions. Accordingly, by suitably replacing the software of the group of servers, a wide variety of functions can be achieved with a similar configuration. Thus, the base technology provides such communication control system having high flexibility. 
       FIG. 2  shows a configuration of a conventional communication control apparatus  1 . The conventional communication control apparatus  1  comprises a communication control unit  2  on the receiving side, a packet processing unit  3 , and a communication control unit  4  on the sending side. The communication control units  2  and  4  include PHY processing units  5   a  and  5   b  for performing physical layer processing of packets, and MAC processing units  6   a  and  6   b  for performing MAC layer processing of packets, respectively. The packet processing unit  3  includes protocol processing units for performing protocol-specific processing, such as an IP processing unit  7  for performing IP (Internet Protocol) processing and a TCP processing unit  8  for performing TCP (Transport Control Protocol) processing. The packet processing unit  3  also includes an AP processing unit  9  for performing application layer processing. The AP processing unit  9  performs filtering or other processing according to data included in a packet. 
     The packet processing unit  3  of the conventional communication control apparatus  1  is implemented by software, using a general-purpose processor, or CPU, and an OS running on the CPU. With such configuration, however, the performance of the communication control apparatus  1  depends on the performance of the CPU, hampering the creation of a communication control apparatus capable of high-speed processing of a large volume of packets. For example, a 64-bit CPU can process only up to 64 bits at a time, and hence, there has existed no communication control apparatus having a higher performance than this. In addition, since the conventional communication control apparatus is predicated on the presence of an OS with versatile functionality, the possibility of security holes cannot be eliminated completely, requiring maintenance work including OS upgrades. 
       FIG. 3  shows a configuration of a communication control apparatus according to the base technology. A communication control apparatus  10  of the base technology comprises a packet processing circuit  20  configured with dedicated hardware employing a wired logic circuit, instead of a packet processing unit that is implemented by software including a CPU and an OS in a conventional communication control apparatus. By providing a dedicated hardware circuit to process communication data, rather than processing it with an OS and software running on a general-purpose processing circuit such as CPU, the performance limitations posed by the CPU or OS can be overcome, enabling a communication control apparatus having high throughput. 
     For example, a case will be considered here in which search is conducted in packet filtering or the like to check if the data in a packet includes reference data, which serves as criteria for filtering. When a CPU is used to compare the communication data with the reference data, there occurs a problem in that, since only 64-bit data can be compared at a time, the processing speed cannot be improved beyond such CPU performance. Since the CPU needs to repeat the process of loading 64 bits of communication data into a memory and comparing it with the reference data, the memory load time becomes a bottleneck that limits the processing speed. 
     In the base technology, by contrast, a dedicated hardware circuit configured with a wired logic circuit is provided to compare communication data with reference data. This circuit includes multiple comparators arranged in parallel, so as to enable the comparison of data having a length greater than 64 bits, such as 1024 bits. By providing dedicated hardware in such manner, bit matching can be simultaneously performed on a large number of bits in parallel. Since 1024-bit data can be processed at a time, while the conventional communication control apparatus  1  using a CPU processes only 64 bits, the processing speed can be improved remarkably. Increasing the number of comparators will improve the throughput, but also increase the cost and size of the apparatus. Accordingly, an optimal hardware circuit may be designed in accordance with the desired performance, cost or size. 
     Since the communication control apparatus  10  of the base technology is configured with dedicated hardware employing a wired logic circuit, it does not require any OS (Operating System). This can eliminate the need for the installation, bug fixes, or version upgrades of an OS, thereby reducing the cost and man-hours required for administration and maintenance. Also, unlike CPUs requiring versatile functionality, the communication control apparatus  10  does not include any unnecessary functions or use needless resources, and hence, reduced cost, a smaller circuit area or improved processing speed can be expected. Furthermore, again unlike conventional OS-based communication control apparatuses, the absence of unnecessary functions decreases the possibility of security holes and thus enhances the tolerance against attacks from malicious third parties over a network. 
     The conventional communication control apparatus  1  processes packets using software predicated on a CPU and an OS. Therefore, all packet data needs to be received before protocol processing is performed, and then the data is passed to an application. In contrast, since packet processing is performed by a dedicated hardware circuit in the communication control apparatus  10  of the base technology, all packet data need not be received before starting the processing; upon reception of necessary data, the processing can be started at any given point in time without waiting for the reception of subsequent data. For example, position detection processing in a position detection circuit, which will be described later, may be started at the time when position identification data for identifying the position of comparison target data is received. Thus, various types of processing can be performed in parallel without waiting for the reception of all data, reducing the time required to process packet data. 
       FIG. 4  shows an internal configuration of the packet processing circuit. The packet processing circuit  20  comprises: first databases  50 A,  50 B and  50 C (hereinafter, they may be collectively referred to as “first databases  50 ”) for storing reference data, which is referred to when processing to be performed on communication data is determined; a search circuit  30  for searching received communication data for the reference data by comparing the two; a second database  60  for storing a search result of the search circuit  30  and a content of processing to be performed on the communication data, which are related to each other; and a process execution circuit  40  for processing the communication data based on the search result of the search circuit  30  and the conditions stored in the second database  60 . 
     The search circuit  30  includes: a position detection circuit  32  for detecting the position of comparison target data, which is to be compared with reference data, in communication data; an index circuit  34  which serves as an example of a determination circuit that determines which range the comparison target data belongs to among three or more ranges, into which the reference data stored in the first database  50  is divided; and a binary search circuit  36  for searching the determined range for the reference data that matches the comparison target data. The reference data may be searched for the comparison target data using any search technique, and a binary search method is used in the base technology. Since an improved binary search method is employed, as will be discussed later, three first databases  50  are provided in the base technology. The first databases  50 A,  50 B and  50 C store the same reference data. 
       FIG. 5  shows an internal configuration of the position detection circuit. The position detection circuit  32  includes multiple comparison circuits  33   a - 33   f  that compare communication data with position identification data for identifying the position of comparison target data. While six comparison circuits  33   a - 33   f  are provided here, the number of comparison circuits may be arbitrary, as will be described later. To the comparison circuits  33   a - 33   f  are input pieces of communication data, with each piece shifted from the preceding one by a predetermined data length, such as 1 byte. These multiple comparison circuits  33   a - 33   f  then simultaneously compare the respective communication data with the position identification data to be detected in parallel. 
     The base technology will be described by way of example for explaining the operation of the communication control apparatus  10 , in which a character string “No. ###” in communication data is detected, the number “###” included in the character string is then compared with reference data, and if the number matches the reference data, the packet will be allowed to pass, while, if they do not match, the packet will be discarded. 
     In the example of  FIG. 5 , communication data “01No.  361  . . . ” is input to the comparison circuits  33   a - 33   f  with a shift of one character each, and position identification data “No.” for identifying the position of the number “###” is sought to be detected in the communication data. More specifically, “01N” is input to the comparison circuit  33   a , “1No” to the comparison circuit  33   b , “No.” to the comparison circuit  33   c , “o.” to the comparison circuit  33   d , “.3” to the comparison circuit  33   e , and “ 36 ” to the comparison circuit  33   f . Then, the comparison circuits  33   a - 33   f  simultaneously perform comparisons with the position identification data “No.”. Consequently, there is found a match with the comparison circuit  33   c , indicating that the character string “No.” exists at the third character from the top of the communication data. Thus, it is found that the numeral data as comparison target data exists subsequent to the position identification data “No.” detected by the position detection circuit  32 . 
     When the same processing is performed by a CPU, since the comparison process needs to be serially performed one by one from the top, such as comparing character strings “01N” and “No.” before comparing “1No” and “No.”, no improvement of detection speed can be expected. In the communication control apparatus  10  of the base technology, in contrast, providing the multiple comparison circuits  33   a - 33   f  in parallel enables simultaneous parallel comparison processing, which could not have been performed with a CPU, improving the processing speed significantly. Providing more comparison circuits will improve the detection speed, as more characters can be compared simultaneously. In consideration of cost or size, a sufficient number of comparison circuits may be provided to achieve a desired detection speed. 
     Aside from detecting position identification data, the position detection circuit  32  may also be used as a circuit for detecting character strings for various purposes. Moreover, the position detection circuit  32  may be configured to detect position identification data in units of bits, not just as a character string. 
       FIG. 6  shows another example of the position detection circuit. In the example shown in  FIG. 6 , when the data length of position identification data is shorter than that prepared in each of the comparison circuits  33   a - 33   f  in the position detection circuit  32 , predetermined data, such as “00H” or “01H”, is padded posterior to the position identification data. Similarly, with regard to communication data to be compared with position identification data, a data length identical with that of the position identification data is extracted from the communication data and input to a comparison circuit, and the same data as padded after the position identification data is also padded posterior thereto. In such case, the communication data may be copied as work, and the copied data may be processed to be input to the comparison circuits  33   a - 33   f , so as not to change the original communication data. Thus, the position detection circuit  32  can be generally used regardless of the length of position identification data. 
       FIG. 7  shows yet another example of the position detection circuit. In the example shown in  FIG. 7 , predetermined data is padded posterior to position identification data in the same way as shown in the example of  FIG. 6 , and, in addition, such data is regarded as a wild card. That is, when data is input as a wild card into the comparison circuits  33   a - 33   f , it is determined that the corresponding part of target data to be compared matches the wild-card data whatever the target data is. Thus, the position detection circuit  32  can be generally used regardless of the length of position identification data. 
       FIG. 8  shows an example of internal data of the first database. The first database  50  stores reference data, which is referred to when processing on packets, such as filtering, routing, switching, or replacement, is determined. The pieces of reference data are sorted according to some sort conditions and stored in ascending or descending order. In the example of  FIG. 8 , 1000 pieces of reference data are stored. 
     The index circuit  34  determines which range comparison target data belongs to among three or more ranges, such as  52   a - 52   d , into which reference data stored in the first database  50  is divided. In the example of  FIG. 8 , the 1000 pieces of reference data are divided into four ranges  52   a - 52   d , i.e., 250 pieces each in a range. The index circuit  34  includes multiple comparison circuits  35   a - 35   c , each of which compares a piece of reference data at the border of the range with the comparison target data. Since the comparison circuits  35   a - 35   c  simultaneously compare the pieces of reference data at the borders with the comparison target data in parallel, which range the comparison target data belongs to can be determined by a single operation of comparison processing. 
     The pieces of reference data at the borders to be input to the comparison circuits  35   a - 35   c  of the index circuit  34  may be set by an apparatus provided outside the communication control apparatus  10 . Alternatively, reference data at predetermined positions in the first database  50  may be set in advance to be automatically input as such. In the latter case, even when the first database  50  is updated, the reference data at the predetermined positions in the first database  50  are automatically input to the comparison circuits  35   a - 35   c . Therefore, the communication control processing can be performed immediately without initialization or the like. 
     As mentioned previously, CPU-based binary search cannot make multiple comparisons at the same time. In the communication control apparatus  10  of the base technology, in contrast, providing the multiple comparison circuits  35   a - 35   c  in parallel enables simultaneous parallel comparison processing, with a significant improvement in the search speed. 
     After the index circuit  34  determines the relevant range, the binary search circuit  36  performs search using a binary search method. The binary search circuit  36  divides the range determined by the index circuit  34  further into 2 n  and subsequently compares the pieces of reference data lying at the borders with the comparison target data, thereby determining which range the comparison target data belongs to. The binary search circuit  36  includes multiple comparators for comparing, bit by bit, reference data with comparison target data. For example, in the base technology are provided 1024 comparators to perform bit matching on 1024 bits simultaneously. When the range to which the comparison target data belongs is determined among the 2 n  split ranges, the determined range is further divided into 2 n . Then, the pieces of reference data lying at the borders are read out to be compared with the comparison target data. Thereafter, this processing is repeated to narrow the range further until reference data that matches the comparison target data is eventually found. 
     The operation will now be described in more detail in conjunction with the foregoing example. Each of the comparison circuits  35   a - 35   c  of the index circuit  34  receives “ 361 ” as comparison target data. As for reference data, the comparison circuit  35   a  receives “ 378 ”, which lies at the border of the ranges  52   a  and  52   b . Similarly, the comparison circuit  35   b  receives reference data “ 704 ” lying at the border of the ranges  52   b  and  52   c , and the comparison circuit  35   c  receives reference data “ 937 ” lying at the border of the ranges  52   c  and  52   d . The comparison circuits  35   a - 35   c  then perform comparisons simultaneously, determining that the comparison target data “ 361 ” belongs to the range  52   a . Subsequently, the binary search circuit  36  searches the reference data for the comparison target data “ 361 ”. 
       FIG. 9  shows another example of internal data of the first database. In the example shown in  FIG. 9 , the number of pieces of reference data is smaller than the number of pieces of data storable in the first database  50 , i.e., 1000 in this case. In such instance, the first database  50  stores the pieces of reference data in descending order, starting with the last data position therein. Then, 0 is stored in the rest of the data positions. The database is loaded with data not from the top but from the bottom of the loading area, and all the vacancies occurring in the front of the loading area, if any, are replaced with zero. Consequently, the database is fully loaded at any time, so that the search time necessary for binary search will be constant. Moreover, if the binary search circuit  36  reads reference data “ 0 ” during a search, the circuit can identify the range without making a comparison, as the comparison result is obvious, and can proceed to the next comparison. Consequently, the search speed can be improved. 
     In CPU-based software processing, the first database  50  stores pieces of reference data in ascending order, from the first data position therein. In the rest of data positions will be stored a maximum value or the like, and in such case, the skip of comparison processing as described above cannot be made during binary search. The comparison technique described above can be implemented by configuring the search circuit  30  with a dedicated hardware circuit. 
       FIG. 10  shows yet another example of internal data of the first database. In the example shown in  FIG. 10 , the reference data is not evenly divided into three or more ranges, but unevenly divided into ranges that accommodate different numbers of pieces of data, such as 500 pieces in the range  52   a  and 100 pieces in the range  52   b . These ranges may be determined depending on the distribution of frequencies with which reference data occurs in communication data. Specifically, the ranges may be determined so that the sums of the frequencies of occurrence of reference data belonging to the respective ranges are almost the same. Accordingly, the search efficiency can be improved. The reference data to be input to the comparison circuits  35   a - 35   c  of the index circuit  34  may be modifiable from the outside. In such case, the ranges can be dynamically set, so that the search efficiency will be optimized. 
       FIG. 11  shows another example of the index circuit. In the examples of  FIGS. 8-10 , the index circuit  34  uses the three comparison circuits  35   a - 35   c  to determine which range comparison target data belongs to among the four ranges of  52   a - 52   d  in the first database  50 . In the example shown in  FIG. 11 , on the other hand, the index circuit  34  is provided with four comparison circuits  35   d - 35   g  for determining whether or not comparison target data is included in each of the four ranges  52   a - 52   d . For example, into the comparison circuit  35   d  are input the 0th and 250th pieces of reference data in the first database  50  and comparison target data. Then, each piece of the reference data is compared to the comparison target data, so as to determine whether or not the reference data is included in the range  52   a . The comparison results provided by the comparison circuits  35   d - 35   g  are input into a determination circuit  35   z , which outputs information providing which range the reference data is included in. Each of the comparison circuits  35   d - 35   g  may output a result indicating whether the reference data is included between the two input pieces of reference data, or may output a result indicating that the reference data is greater than the range, the reference data is included in the range, or the reference data is smaller than the range. When it is determined that the comparison target data is not included in any of the ranges  52   a - 52   d , it can be found that the comparison target data does not exist within the first database  50 . Accordingly, the search can be terminated without performing any further binary search. 
       FIG. 12  shows a configuration of comparison circuits included in the binary search circuit. As mentioned previously, the comparison circuit in the binary search circuit  36  includes 1024 comparators, such as  36   a ,  36   b , . . . . Each of the comparators  36   a ,  36   b , etc. receives 1 bit of reference data  54  and 1 bit of comparison target data  56  to compare the bits in value. The comparison circuits  35   a - 35   c  of the index circuit  34  have similar internal configurations. Since the comparison processing is thus performed by a dedicated hardware circuit, a large number of comparison circuits can be operated in parallel to compare a large number of bits at a time, thereby speeding up the comparison processing. 
       FIG. 13  shows a configuration of the binary search circuit. The binary search circuit  36  includes comparison circuits  36 A,  36 B and  36 C, each of which includes the 1024 comparators  36   a ,  36   b , etc. as shown in  FIG. 12 , and a control circuit  36 Z for controlling the comparison circuits. 
     In a conventional binary search method, a piece of data lying at the one-half position in the search range of a database, in which pieces of data are aligned in ascending or descending order, is read out to be compared with comparison target data in the first search. When the pieces of data are aligned in ascending order and if the comparison target data is smaller than the read out data, it means that the comparison target data might exist within the first half of the search range. Accordingly, in the second search, the search range is newly set to the first half and a piece of data lying at the one-half position in the range, i.e. at the one-quarter position in the original search range, is read out to be compared with the comparison target data. Conversely, if the comparison target data is greater than the read out data, it means that the comparison target data might exist within the second half of the search range. Accordingly, the new search range is set to the second half and a piece of data lying at the one-half position in the range, i.e. at the three-quarter position in the original search range, is read out to be compared with the comparison target data in the second search. In this way, the search range is narrowed by half repeatedly until the target data is reached. 
     In the base technology, in contrast, three comparison circuits are provided for binary search, so that when the data at the one-half position in the search range is compared with comparison target data for the first search, the comparison for the second search between the comparison target data and each of the pieces of data at the one-quarter and three-quarter positions in the search range can be simultaneously performed in parallel. Thus, the first and second searchs can be performed at the same time, thereby reducing the time required to load the data from the database. Also, by operating three comparison circuits in parallel, the number of comparisons can be reduced by half, thereby reducing the search time. 
     In the example of  FIG. 13 , three comparison circuits are provided to perform two searchs simultaneously. When n searchs are to be performed simultaneously, 2 n −1 comparison circuits may be generally provided. The control circuit  36 Z inputs each piece of data at the 1/2 n , 2/2 n , . . . , and (2 n −1)/2 n  positions in the search range into the 2 n −1 comparison circuits respectively, and operates the comparison circuits simultaneously in parallel to allow them to compare the respective pieces of data with comparison target data. The control circuit  36 Z then acquires the comparison results from the comparison circuits and determines if the comparison target data is found. If any of the comparison circuits output a signal indicating that there has been a data match, the control circuit  36 Z will determine that the comparison target data has been found and will terminate the binary search. If there is no such signal output, the process will be shifted to the next search. If the comparison target data exists within the database, the data must lie within a range between points where the comparison results of the 2 n −1 comparison circuits change. In the case where 15 comparison circuits are provided, for example, if the piece of data at the 5/16 position is smaller than comparison target data and if the piece of data at the 6/16 position is greater than the comparison target data, the comparison target data should lie within the range between the 5/16 and 6/16 positions. Thus, the control circuit  36 Z acquires comparison results from the comparison circuits and sets the next search range to a range between points where the comparison results change. The control circuit  36 Z then inputs, into the respective comparison circuits, each piece of data at the 1/2 n , 2/2 n , . . . , and (2 n −1)/2 n  positions in the next search range thus set. 
     There are provided the three first databases  50  in the base technology; the first database  50 A is connected to the comparison circuit  36 A and supplies thereto a piece of data at the one-quarter position in the search range; the first database  50 B is connected to the comparison circuit  36 B and supplies thereto a piece of data at the two-quarter position in the search range; and the first database  50 C is connected to the comparison circuit  36 C and supplies thereto a piece of data at the three-quarter position in the search range. Therefore, pieces of data can be loaded simultaneously into the comparison circuits in parallel, thereby further reducing the time for data loading and enabling high-speed binary search. 
     Providing more comparison circuits will improve the search speed. In consideration of cost or size of the system, a sufficient number of comparison circuits may be provided to achieve a desired search speed. Also, although it is desirable that first databases as many as comparison circuits are provided, some comparison circuits may share a database in consideration of cost or size of the system. 
       FIG. 14  shows still yet another example of internal data of the first database. The first database  50  shown in  FIG. 14  stores URLs of contents to which filtering is applied. The data stored in the first database  50  may include predetermined data recognized as a wild card, such as “00H” or “01H”. In the example shown in  FIG. 14 , “*********” is recognized as a wild card in “http://www.xx.xx/*********”, and, whatever the comparison target data corresponding thereto is, it is determined in the comparators  36   a ,  36   b , etc. that such data matches the wild card. Accordingly, every character string starting with “http://www.xx.xx/” is detected by the binary search circuit  36 . Consequently, processing such as applying filtering to all contents within the domain “http://www.xx.xx/” can be easily performed. 
       FIG. 15  shows an example of internal data of the second database. The second database  60  includes a search result field  62 , which contains a search result of the search circuit  30 , and a processing content field  64 , which contains a processing content to be performed on communication data. The database stores the search results and the processing contents related to each other. In the example of  FIG. 15 , conditions are established such that a packet will be allowed to pass if its communication data contains reference data; if not, the packet will be discarded. The process execution circuit  40  searches the second database  60  for a processing content based on the search result and performs the processing on the communication data. The process execution circuit  40  may also be configured with a wired logic circuit. 
       FIG. 16  shows another example of internal data of the second database. In the example of  FIG. 16 , the processing content is set for each piece of reference data. With regard to packet replacement, replacement data may be stored in the second database  60 . As for packet routing or switching, information on the route may be stored in the second database  60 . The process execution circuit  40  performs processing, such as filtering, routing, switching, or replacement, which is specified in the second database  60 , in accordance with the search result of the search circuit  30 . When the processing content is set for each piece of reference data, as shown in  FIG. 16 , the first database  50  and the second database  60  may be merged with each other. 
     The first database and the second database are configured to be rewritable from the outside. By replacing these databases, various types of data processing and communication control can be achieved using the same communication control apparatus  10 . Also, multistage search processing may be performed by providing two or more databases that store reference data to be searched. In such instance, more complicated conditional branching may be performed by providing two or more databases that store search results and processing contents related to each other. When multiple databases are thus provided to conduct multistage search, a plurality of the position detection circuits  32 , the index circuits  34 , the binary search circuits  36 , etc. may also be provided. 
     The data intended for the foregoing comparison may be compressed by the same compression logic. If both the source data and the target data to be compared are compressed by the same method, the comparison can be performed in the same manner as usual, thus reducing the amount of data to be loaded for comparison. The smaller amount of data to be loaded can reduce the time required to read out the data from the memory, thereby reducing the overall processing time. Moreover, the number of comparators can be also reduced, which contributes to the miniaturization, weight saving, and cost reduction of the apparatus. The data intended for comparison may be stored in a compressed form, or may be read out from the memory and compressed before comparison. 
       FIG. 17  shows another illustrative configuration of the communication control apparatus in the base technology. The communication control apparatus  10  shown in this diagram has two communication control units  12 , each of which has the same configuration as the communication control apparatus  10  shown in  FIG. 4 . There is also provided a switch control unit  14  for controlling the operation of the individual communication control units  12 . Each of the communication control units  12  has two input/output interfaces  16  and is connected to two networks, upstream and downstream, via the respective input/output interfaces  16 . The communication control units  12  receive communication data from either one of the networks and output processed data to the other. The switch control unit  14  switches the inputs and outputs of the input/output interfaces  16  provided for the individual communication control units  12 , thereby switching the directions of the flow of communication data in the communication control units  12 . This allows communication control not only in one direction but also in both directions. 
     The switch control unit  14  may provide control such that: either one of the communication control units  12  processes inbound packets and the other processes outbound packets; both the units process inbound packets; or both the units process outbound packets. Consequently, the directions of communications to control can be changed depending on, for example, the traffic status or intended purpose. 
     The switch control unit  14  may acquire the operating state of the respective communication control units  12  and may switch the direction of communication control according thereto. For example, when one of the communication control units  12  is in a standby state and the other communication control unit  12  is in operation, the unit on standby may be activated as a substitute upon detection of the unit in operation stopping due to a failure or other reasons. This can improve the fault tolerance of the communication control apparatus  10 . Also when one of the communication control units  12  needs maintenance such as a database update, the other communication control unit  12  may be operated as a substitute. Thus, appropriate maintenance can be performed without halting the operation of the communication control apparatus  10 . 
     The communication control apparatus  10  may be provided with three or more communication control units  12 . The switch control unit  14  may, for example, acquire the traffic status to control the direction of communications in the respective communication control units  12  so that more communication control units  12  are allocated for communication control processing in a direction handling higher traffic. This minimizes a drop in the communication speed, even when the traffic increases in one direction. 
       FIG. 18  shows a configuration of a communication control apparatus  10  comprising multiple communication control apparatuses  10   a ,  10   b ,  10   c , etc. Since the first database  50  requires larger capacity in proportion to an increasing number of pieces of data, the database is divided into portions to be stored by the communication control apparatuses  10   a ,  10   b ,  10   c , etc. As will be discussed later, in the communication control system  100  of the base technology, a communication packet to be processed is sent to all the communication control apparatuses  10   a ,  10   b ,  10   c , etc. in operation, and each of the communication control apparatuses  10  then receives and processes the packet. For example, the communication control apparatus  10   a  stores data with data IDs “000001”-“100000”, the communication control apparatus  10   b  stores data with data IDs “100001”-“200000”, and the communication control apparatus  10   c  stores data with data IDs “200001”-“300000”; each of the communication control apparatuses refers to the respective data to process a packet. 
       FIG. 19  shows an example of internal data of a management table  111  provided in the operation monitoring server  110 . The management table  111  includes apparatus ID fields  112 , operating state fields  113  and data ID fields  114 . The apparatus ID fields  112  contain the apparatus IDs of the communication control apparatuses  10   a ,  10   b , etc. The operating state fields  113  contain the operating state of the communication control apparatuses, and the data ID fields  114  contain the ranges of data IDs handled by the communication control apparatuses. The operating state appears as “operating”, “standby”, “failure”, “data updating”, etc. The operating state fields  113  are updated by the operation monitoring server  110  each time the operating state of the communication control apparatuses  10   a ,  10   b , etc. changes. In the example shown in  FIG. 19 , “465183” pieces of data are stored in the first database  50 , so that the five communication control apparatuses  10  having the apparatus IDs “ 1 ”-“ 5 ” are in operation while the communication control apparatus  10  having the apparatus ID “ 6 ” is in a standby state. 
     The operation monitoring server  110  monitors the operating state of multiple communication control apparatuses  10 . When detecting any of the communication control apparatuses  10  being inoperable because of some trouble, the operation monitoring server  110  stores, in the communication control apparatus  10  on standby, the same data as stored in the inoperable apparatus, and places the standby communication control apparatus  10  in operation. For example, when the communication control apparatus  10  with the apparatus ID “ 2 ” halts the operation because of a failure, as shown in  FIG. 20 , the communication control apparatus  10  with the apparatus ID “ 6 ”, which has been on standby, stores the data with data IDs “100001-200000” and starts operating. Thus, even if a communication control apparatus  10  stops because of some trouble, the main operation will be continued properly. The communication control apparatus  10  on standby may store any of the data in advance to be made in a hot standby state, or may be in a cold standby state. 
     Next, the procedure for updating databases stored in the communication control apparatuses  10  will be described. The database server  150  acquires the latest database from an external database at a certain time and retains it therein. In order to reflect, in a communication control apparatus  10 , the latest database retained in the database server  150 , the operation monitoring server  110  transfers the data from the database server  150  and stores it in the communication control apparatus  10  at a certain time. 
       FIGS. 21A ,  21 B and  21 C are diagrams for describing the procedure for updating databases. As with  FIG. 19 ,  FIG. 21A  shows that the communication control apparatuses  10  with the apparatus IDs “ 1 ”-“ 5 ” are in operation while the communication control apparatus  10  with the apparatus ID “ 6 ” is on standby. At the time when a database is to be updated, the operation monitoring server  110  identifies the communication control apparatus  10  in a standby state then and instructs the database server  150  to store the data in the communication control apparatus  10 . In the example shown in  FIG. 21A , the communication control apparatus  10  with the apparatus ID “ 6 ” is on standby, so that the database server  150  stores the data in that apparatus. The operation monitoring server  110  then changes the operating state field  113  for the apparatus ID “ 6 ” to “data updating”. 
       FIG. 21B  shows a state where a database of a communication control apparatus  10  is being updated. The database server  150  stores, in the first database  50  in the communication control apparatus  10  with the apparatus ID “ 6 ” on standby, the data handled by one of the communication control apparatuses  10  in operation. In the example shown in  FIG. 21B , the data with data IDs “000001-100000”, which have been handled by the communication control apparatus  10  with the apparatus ID “ 1 ”, are stored in the communication control apparatus  10  with the apparatus ID “ 6 ”. 
       FIG. 21C  shows a state where the communication control apparatus  10  with the apparatus ID “ 6 ” has had its database updated and is placed in operation, and the communication control apparatus  10  with the apparatus ID “ 1 ” is placed into a standby state instead. Upon completion of storing data in the communication control apparatus  10  with the apparatus ID “ 6 ”, the operation monitoring server  110  starts the operation of the apparatus, which stores the updated database. The operation monitoring server  110  also stops the operation of the communication control apparatus  10  with the apparatus ID “ 1 ”, which stores the database before update, to place the apparatus into a standby state. Thus, the communication control apparatus  10  with an updated database is placed in operation. Then, the data with data IDs “100001-200000” are stored in the communication control apparatus  10  with the apparatus ID “ 1 ” before the apparatus is placed in operation, and, subsequently, the operation of the communication control apparatus  10  with the apparatus ID “ 2 ” is stopped. Thereafter, databases are similarly updated by turns, so that the databases of all the communication control apparatuses  10  can be updated behind the actual operation, without halting the operation of the communication control system  100 . 
     In this way, data stored in each of the communication control apparatuses  10  is not fixed in the base technology, and hence, the communication control apparatus  10  that stores certain data changes with time. If, before a packet is sent to each of the communication control apparatuses  10 , the process of determining which communication control apparatus  10  stores the data of the user is performed, the time for the process will be additionally required. Accordingly, in the present embodiment, a received packet is provided to all the communication control apparatuses  10 , and each of the apparatuses then processes the packet. In the following, a technique for providing such mechanism will be described. 
       FIG. 22  shows a configuration of a communication path control apparatus provided to process packets with multiple communication control apparatuses  10 . A communication path control apparatus  200  comprises a switch  210 , an optical splitter  220 , which is an example of a data supply unit, and a switch  230 . The switch  210  transmits a received packet to the communication control apparatuses  10 . Between the switch  210  and the communication control apparatuses  10 , there is provided the optical splitter  220  that provides the packet to the multiple communication control apparatuses  10   a ,  10   b  and  10   c  in parallel. The switch  210  practically transmits a packet to the optical splitter  220 , which transmits the packet to each of the communication control apparatuses in parallel. 
     If a packet is converted to a broadcast packet so as to be transmitted to the multiple communication control apparatuses  10   a ,  10   b  and  10   c , additional process such as adding a time stamp to the header will be required, which reduces the processing speed. Therefore, a packet is not converted but split by the optical splitter  220  so as to be transmitted as a unicast packet to the multiple communication control apparatuses  10   a ,  10   b  and  10   c . This method will be called “parallelcast” in the present specification. 
     Each of the communication control apparatuses is not set to a mode in which an apparatus receives only packets directed to the MAC address of the apparatus, but set to promiscuous mode in which an apparatus receives all packets regardless of the destination MAC addresses. When receiving a packet sent via parallelcast from the optical splitter  220 , each of the communication control apparatuses omits MAC address matching and acquires every packet to process it. 
     If a packet needs to be returned to the transmission source because, for example, the communication thereof has been prohibited, the communication control apparatus  10   c  will transmit a response packet to the switch  210  bypassing the optical splitter  220 . If the communication control apparatus  10   c  processes the packet and the communication thereof is permitted, the communication control apparatus  10   c  will transmit the packet to a network. Between the communication control apparatuses  10  and the upstream communication line, there is provided the switch  230  by which packets transmitted from the multiple communication control apparatuses  10   a ,  10   b  and  10   c  are aggregated. The communication control apparatus  10   c  will practically transmit the packet to the switch  230 , which transmits the packet to the upstream communication line. 
     When the switch  230  receives a return packet transmitted from the destination of packet transmission and if the return packet need not be processed by the communication control apparatuses  10 , the packet will be transmitted from the port  232  of the switch  230  to the port  212  of the switch  210 , and then transmitted therefrom to the transmission source. On the Internet, the transmission path is generally recorded in the packet to ensure the return path through which a response packet sent in return for the packet can be certainly delivered to the transmission source. In the present embodiment, however, since the return path is already provided within the communication path control apparatus  200 , communication can be performed between apparatuses without recording the path or processing the packet. Consequently, unnecessary process can be eliminated, thereby improving the processing speed. 
     The example in  FIG. 22  shows the case where only a packet transmitted from a transmission source to a transmission destination is processed, but a return packet transmitted from the transmission destination to the transmission source is made to pass through without being processed. Alternatively, the communication path control apparatus  200  may be configured so that the communication control apparatuses  10  process packets transmitted in both directions. In such case, the optical splitters  220  may be provided on both sides of the communication control apparatuses  10 . Also, the bypass path from the switch  230  to switch  210  need not be provided. 
     In such way, by sending a packet via parallelcast to all the communication control apparatuses, the packet can be appropriately processed by the proper communication control apparatus among the multiple communication control apparatuses, without the need to specify, in advance, a communication control apparatus by which the packet is to be processed. 
     Since these communication control apparatuses receive all packets sent via parallelcast from the communication path control apparatus  200  to process or discard them, as stated previously, the apparatuses need not be provided with IP addresses, which uniquely identify apparatuses on the Internet. If the packet processing as discussed above is performed by server apparatuses or the likes, it will be necessary to consider attacks to the server apparatuses. However, since the communication control apparatuses of the present embodiment cannot be directly attacked by malicious third parties via the Internet, communication control can be performed securely. 
     Embodiment 
       FIG. 23  shows a configuration of a communication management system according to the embodiment. A communication management system  300  manages P2P communication, such as blocking or subordinating inappropriate communication between P2P nodes  320 , using the communication control system  100  having a packet filtering function, etc. 
     A user terminal  310 , such as a personal computer, generally connects to an Internet service provider (hereinafter, described as “ISP”)  330  via a public telephone network, a cellular phone network, a LAN or a WAN (not illustrated), and connects to the Internet  390  via the ISP  330 . The P2P nodes  320 , which execute P2P applications including file-sharing software, have P2P connections between each other, forming a P2P network  322 . The “P2P node  320 ” includes an apparatus functioning as a server or a host providing a file search function, etc. in a file-sharing application. 
     In a server-client model, a server stores information while a client acquires information by connecting to the server via the Internet. Accordingly, when distribution of an illegal content is detected, only the server providing the content need be found and stopped. In the P2P network  322 , however, since direct communication is conducted between P2P nodes  320 , distribution of an illegal content therein is difficult to detect; even such distribution can be detected, again it is difficult to identify the P2P node  320  that provides the illegal content. 
     Also, in the case where a file is directly sought among P2P nodes  320  by inquiring for the file, without a file search server for file sharing being not provided in the P2P network  322 , communications will increase at an accelerated pace along with an increasing number of P2P nodes  320 . Accordingly, network congestion may occur, thereby possibly affecting another user terminal  310  using the ISP  330 . 
     In addition, since a P2P node  320  directly communicates with another P2P node  320  in the P2P network  322 , the network is vulnerable to attacks from malicious P2P nodes  320  and could be a breeding ground for spreading viruses. Consequently, users ignorant of or indifferent to computer security use file-sharing applications and get infected with viruses, thereby causing social problems including leakage of important information. 
     Under such circumstances, appropriate techniques for managing P2P communication have been strongly desired, but it has been difficult to regulate data transmission between P2P nodes  320 . The present embodiment proposes a technique for detecting a P2P node  320  and performing appropriate filtering on the communication with the P2P node  320  thus detected. This technique is expected to solve the aforementioned problems, so that the social contribution of the present invention may be considered remarkable. 
     In the present embodiment, the communication control system  100  described in the base technology is provided between the user terminal  310  and a P2P node  320  in the P2P network  322 , as shown in  FIG. 23 . Also, there is provided a P2P node detection network  352  for detecting an IP address, etc. of a P2P node  320 ; the network is used to notify the communication control system  100  of identification information including the IP address of a P2P node  320  detected by a node detector  340  so as to detect communication with the P2P node  320 . The communication control system  100  may be provided at any position in a network, and  FIG. 23  shows an example in which an ISP  330  possesses the communication control system  100 . Since most P2P nodes  320  connect to the Internet  390  via an ISP  330 , P2P communication can be managed more reliably if each ISP  330  employs the communication control system  100 . 
     A P2P node  350  connects to the Internet  390  via a layer  2  switch  344  and a router  342 , and executes a P2P application to have a P2P connection with a P2P node  320  for communication. The node detector  340  is provided between a P2P node  350  and the P2P network  322 , and acquires and analyzes a communication packet transmitted between a P2P node  350  and a P2P node  320  in the P2P network  322  so as to detect identification information including the IP address and the TCP/UDP port number of the P2P node  320 . The node detector  340  does not record the party on the other side of communication when the application used there is other than a P2P application executed by a P2P node  350 , such as one for inquiry to a DNS, and only detects and records the party on the other side of communication using a P2P application. The node detector  340  analyzes a packet transmitted from or to a P2P node  350 , but makes the packet pass through without performing filtering thereon as the detector is layer  2  transparent. The node detector  340  shown in  FIG. 23  may also be provided as a router-type apparatus besides such layer  2  transparent type. In such case, the node detector  340  performs routing as if it were a common router-type apparatus, but also detects and records the party on the other side of communication using a P2P application. The IP address and TCP/UDP port number of a P2P node  320  detected by the node detector  340  are registered in a P2P node database  360 . The data registered in the P2P node database  360  is reflected in the first database  50  of the communication control apparatus  10  at a certain time by the database server  150  of the communication control system  100 , as described in the base technology. 
     The communication control apparatus  10  searches the first database  50  for the IP address and TCP/UDP port number of the transmission source or transmission destination of a packet passing through the ISP  330 , using the index circuit  34  and binary search circuit  36 . If the IP address and TCP/UDP port number are registered in the first database  50 , it means that the packet results from P2P communication with a P2P node  320 . Accordingly, the process execution circuit  40  will discard the packet to block the P2P communication thereof, or will delay the transmission of the packet to subordinate it to other communications. If the IP address and TCP/UDP port number are not registered in the first database  50 , on the other hand, the packet is found to be not from P2P communication, so that the process execution circuit  40  will transmit the packet to the network without discarding it. Thus, P2P communication can be detected and restrained. 
     In the example above, the node detector  340  detects and obtains the IP address and TCP/UDP port number of a P2P node  320 . If another protocol is used in P2P communication, another identification information of a P2P node  320 , with which the P2P communication can be detected, may be obtained depending on the protocol. 
     When the user terminal  310  newly activates a P2P application and communicates with a P2P node  350 , the node detector  340  detects the IP address and TCP/UDP port number of the P2P node, which are registered in the P2P node database  360  thereafter. Therefore, if the time intervals at which the P2P node database  360  is reflected in the communication control system  100  are shortened, the control of P2P communication with a new P2P node  320  can be started in a short time after the first communication with the P2P node  320 . 
     When P2P communication is once conducted with a P2P node  320  and the P2P node  320  is registered in the P2P node database  360 , but if there is no P2P communication with the P2P node  320  in a long time thereafter, the P2P node  320  may be deleted from the P2P node database  360 . For example, in the case where a user uninstalls a P2P application from a user terminal  310  and uses the port number that has been used in communications of the P2P application for another communication, the communication using the port number will be restrained even if it is not P2P communication because the port number is registered together with an IP address in the P2P node database  360 . Accordingly, the dates and times when P2P nodes  320  are detected last time may be recorded in the P2P node database  360 , and when a P2P node  320  has not been detected for a certain period of time after the date and time of its last detection, the information on the P2P node  320  may be deleted from the P2P node database  360 . If the user terminal  310  restarts P2P communication with the P2P node, the P2P node will be detected by the node detector  340  and registered in the P2P node database  360  again, so that P2P communication with the node will be blocked or subordinated. 
       FIG. 24  shows another illustrative configuration of the communication management system. The communication management system  300  shown in  FIG. 24  differs from the communication management system  300  of  FIG. 23  in the configuration of the P2P node detection network  352 . More specifically, the node detector  340  is not provided between the router  342  and layer  2  switch  344  but is connected posterior to the layer  2  switch  344 . In this example, all packets passing through the layer  2  switch  344  are copied and transmitted to the node detector  340 , using the port mirroring function of the layer  2  switch  344 . The node detector  340  analyzes an acquired packet to obtain identification information of a P2P node  320 , and discards the packet. Other configurations and operations are the same as those of the communication management system  300  shown in  FIG. 23 . 
       FIG. 25  shows a configuration of the packet processing circuit  20  of the present embodiment. The packet processing circuit  20  comprises a decoder circuit  70  and a decryption key  72  in addition to the configuration of the packet processing circuit  20  of the base technology shown in  FIG. 4 . 
     In a protocol used for a P2P application, there are often included distinctive character strings. When identification information including the name of a P2P application is provided in the header of a TCP packet, for example, whether or not the packet is derived from P2P communication can be determined by detecting such character strings. Accordingly, in the present embodiment, a character string unique to P2P communication included in a packet is detected using the position detection circuit  32  described in the base technology, so as to determine if it is P2P communication. A packet that includes a character string unique to P2P communication is discarded or subordinated by the process execution circuit  40 , without being subjected to matching with the first database  50  performed by the index circuit  34  and binary search circuit  36 . Accordingly, P2P communication can be detected efficiently to be filtered. 
     With some P2P applications, communication data is encrypted before being transmitted. The decoder circuit  70  decrypts the communication data of an acquired packet, using the decryption key  72  for decrypting communication data encrypted by a P2P application. When communication data is encrypted by a P2P application using common key cryptography, for example, the common key therefor is used as the decryption key  72  to decrypt the communication data thus encrypted. The decoder circuit  70  is provided as a dedicated hardware circuit configured with a wired logic circuit having no CPU or OS, as described in the base technology. The decryption key  72  may be provided to be rewritable from the outside. Accordingly, the packet processing circuit  20  can respond flexibly to the case where the decryption key of a P2P application is changed. Also, the packet processing circuit  20  can be commonly used even when a different P2P application is executed. 
     Also in the case above, the position detection circuit  32  detects a character string unique to P2P communication in the decrypted communication data. If the packet is not derived from P2P communication, decryption process by the decoder circuit  70  leaves a meaningless data string, so that such character string unique to P2P communication will not be detected. Therefore, whether or not a packet is derived from P2P communication can be determined by checking if there is included a character string unique to P2P communication. 
     The present invention has been described with reference to the embodiment. The embodiment is intended to be illustrative only and it will be obvious to those skilled in the art that various modifications to constituting elements or processes could be developed and that such modifications are also within the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a communication management system that manages P2P communication.