Abstract:
A packet buffer management method and system are provided which enable maximum utilization of the hardware resources of the buffer memory, and which are optimum for the number of preset physical ports in use or for the number of service class (CoS) areas. In the buffer memory management method in a packet transmission/reception device, for storing a received packet in the buffer memory and controlling writing and reading of packets to and from the above buffer memory, the control methods are set in units of the service class contained in the header portion of received packets, and areas allocated to each service class in the buffer memory storing received packets are modified according to the set number of the above service classes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method of management of buffer memory which stores packets in a network simulation device which simulates a device for performing packet exchange such as a router, and a buffer memory management system in a network simulation device using this method. 
     2. Description of the Related Art 
     In recent years the amount of traffic of data such as voice and images, which emphasize realtime response, on IP (Internet Protocol) networks has been increasing; and packet states such as packet delays and losses in routers, switches and other devices performing packet exchange in networks have greatly impacted the quality of communication and voice transmission experienced by end users. 
     Hence there has been a need to perform simulations of network quality, using settings to simulate the creation of various packet states in networks. 
     Buffer memory (hereafter called “packet buffers” for convenience) which stores packets is used in routers, switches and other devices performing packet exchange in networks. These packet buffers are used to temporarily store received packets, and to send the packets according to prescribed rules. 
     Hence devices used in the above simulations of network quality must also comprise packet buffers, in order to temporarily store packets and control packet transfer according to preset processing. Through the management of such packet buffers, various packet processing can be simulated. 
     In conventional packet buffer management, packets are stored in a packet buffer in which fixed areas are allocated according to the results of identification of the header portion of packets received from the network, and transfer is performed according to preset packet characteristics. (See for example FIG. 14 in Japanese Patent Laid-open No. 2001-143702.) 
       FIG. 17  is a block diagram of the configuration of a device equivalent to a router, which constitutes a network, employing the packet buffer described in this patent application; the operation of this device is explained below. 
     In the multiplexing portion  1  in the drawing, Ethernet signals of a plurality of n ports are multiplexed. The packet type identification control portion  2  compares the IP address or other identification information in the header portion of a packet multiplexed by the multiplexing portion  1  with registered information, referring to associative memory (CAM: Content-Addressable Memory)  3 . When comparison results in a match, tag information identifying the service class (CoS: Class of Service) as classified by the TCP/UDP port number or similar is read from the SRAM  4  and appended to the packet, which is output. 
     The buffer management control portion  5  manages the writing to and reading from the packet buffer memory  6  of packets to which tag information input from the packet type identification control portion  2  is appended. The packet pointer management memory  7  manages the address pointer specifying address positions at which packets are stored in the packet buffer memory  6 . 
     The above buffer management control portion  5  has a service class (CoS) characteristic table  8 ; in this service class characteristic table  8  are stored, for identified packets, the packet delay, packet loss, packet order inversion, or error insertion or other characteristic content to control operation. 
     The buffer management control portion  5  further has a read/write control portion  9 , which performs read/write control of the packet buffer memory  6 ; a pointer read/write control portion  10 , which specifies the address in the packet buffer memory  6  during read and write operations by the packet read/write control portion  9 , based on the storage address of a packet stored in the packet pointer management memory  7 ; and a packet output control portion  11 , which controls packet output from the packet buffer memory  6  according to the CoS characteristic set in the service class characteristic table  8 . 
     The demultiplexing portion  12  has a function to separate multiplexed packets into n ports. 
       FIG. 18  shows the configuration of the packet buffer memory  6  in  FIG. 17 . The CoS number [of services] ( 1 ) for the output destination physical port numbers  1  to n, and ( 2 ) for each physical port (in the example of the drawing,  8  types) are fixed values. Further, ( 3 ) the CoS number is specified for output destination physical ports, and the amount of memory allocated to each CoS area for all physical ports is uniform and fixed. And, ( 4 ) start addresses and end addresses for each CoS area are fixed. 
     Storage addresses for packets in the packet pointer management memory  7  are stored so as to result in the configuration of packet buffer memory  6  shown in  FIG. 18 . Hence the read/write control portion  9  reads and writes a packet identified by the packet type identification control portion  2  to and from an address position read from the packet pointer management memory  7  and specified by the pointer read/write control portion  10 . 
     Thus as described above, in the conventional configuration shown in  FIG. 17 , storage areas in the packet buffer memory  6  are fixed as shown in  FIG. 18 . 
     Further, in the pointer read/write control portion  10  in the conventional configuration shown in  FIG. 17 , the amount of movement of the management pointer by the packet output control portion  11  according to the service class characteristic table is always fixed, so that no means is provided to enable various packet operations in a simulated network. 
     In conventional packet buffer management as shown in  FIG. 17  and  FIG. 18 , memory areas allocated to each physical port or CoS area are fixed. Consequently when there is a small number of physical ports or CoS areas being used, there occur memory areas in the packet buffer memory  6  which are not used at all. 
     Also, when a delay is added to a transferred packet, the maximum delay time which can be set is determined by the fixed area size regardless of the number of physical ports or the number of CoS areas, and delay times cannot be set making maximum use of memory resources. 
     Further, in the conventional buffer management method the amount of movement of the management pointer-based on settings in the service class characteristic table  8  is fixed, so that it is not possible to perform processing necessary for substitution of the order of transfer of packets in the packet output control portion  11 , for intentional loss of arbitrary packets, or to otherwise simulate network operation. 
     SUMMARY OF THE INVENTION 
     Hence an object of this invention is to provide a packet buffer management method and system which, compared with conventional packet buffer management methods, enable maximum utilization of buffer memory hardware resources, and are optimal for the preset number of physical ports used and number of CoS areas. 
     A further object of this invention is to enable excellent processing performance of various packet operations through comparatively simple hardware. 
     To accomplish the above objects of the present application: 
     a first feature of the invention is a buffer memory management method in a packet transmission/reception device, for storing received packets in a buffer memory and controlling writing and reading of packets to and from said buffer memory, including the steps of: setting in units of the service class included in a header portion of a received packet, a control method for the received packets; and, modifying allocated areas for each service class in said buffer memory storing received packets according to the number of said service classes setting. 
     a second feature of the invention is a buffer memory management method according to the first feature  1 , wherein the control method for the received packets includes delay for the packet, packet loss, packet order inversion, or error insertion, and the service classes are classified by an IP address or TCP/UDP port number comprised by the header portion of the packet. 
     a third feature of the invention is a packet buffer management system, including a buffer memory to store received packets; a control portion to control writing and reading of packets to and from said buffer memory; a service class characteristic table in which are set control methods for packets corresponding to service classes included in header portions of the received packets; and a conversion portion in which are stored allocated areas of the buffer memory corresponding to service classes, wherein the conversion portion modifies the allocated areas of the buffer memory according to the number of service class settings in the service class characteristic table. 
     a fourth feature of the invention is the packet buffer management system according to claim  3 , wherein, in the conversion table, buffer memory allocation areas are in service class units. 
     a fifth feature of the invention is the packet buffer management system according to the third feature, further including a management memory to store transfer pointers indicating the storage position of packets stored in the packet buffer and time stamp values indicating the time at which packets are stored, wherein the control portion performs control of received packets based on packet existence information and the time stamp values within the packet buffer, and based on the control method set in the service class characteristic table. 
     A sixth feature of the invention is the packet buffer management system according to the fifth feature, wherein, as a control method of the control portion, received packet order inversion and router path modification are performed by moving the transfer pointer based on said time stamp value. 
     a seventh feature of the invention according to the third feature, wherein operations to store packets in the buffer memory, packet registration operations, transfer pointer read operations, and packet transfer analysis operations are each performed in parallel. 
     a eighth feature of the invention is the packet buffer management system according to the fifth feature, further including means for storing in said management memory the time of packet storage in the packet buffer as the time stamp, and for judging whether the packet can be transferred by comparing said time stamp with the reference time within the device at the time of packet transfer analysis, wherein when a preset delay time has not elapsed, said time stamp is stored in a time stamp buffer provided in service class units, and in subsequent transfer analysis the time stamp within the time stamp buffer is compared with the reference time. 
     Features of this invention will be further clarified through aspects of the invention, explained with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an aspect of a simulation device to simulate network quality, to which a buffer management method of this invention is applied; 
         FIG. 2  shows the data configuration of CAM and SRAM; 
         FIG. 3  shows the contents of the conversion table  13 ; 
         FIG. 4  shows the configuration of the packet buffer memory  6 ; 
         FIG. 5  shows one example of settings of a service class characteristic table; 
         FIG. 6  shows in detail the configuration of the buffer management control portion  5  in  FIG. 1 , excluding the conversion table  13  and service class characteristic table  8 ; 
         FIG. 7  shows the correspondence relation between each of the packets stored in the packet buffer memory  6  and the packet pointer management memory  7 ; 
         FIG. 8  shows the operation sequence of the buffer management control portion  5 ; 
         FIG. 9  explains the parallel processing in  FIG. 8 ; 
         FIG. 10  is a detailed block diagram of the packet identification control portion  2 ; 
         FIG. 11  shows the data contents of the CAM  3  ( FIG. 11A ) and the SRAM  4  ( FIG. 11B ); 
         FIG. 12  shows the allocation configuration of the packet buffer memory  6 ; 
         FIG. 13  shows the contents of the service class  20 : characteristic table  8 ; 
         FIG. 14  shows the content of the conversion table  13 ; 
         FIG. 15  shows the processing flow when packet delays are caused, as an embodiment of packet operation control; 
         FIG. 16  shows the processing flow when packet order inversion/rerouting is caused, as an embodiment of packet operation control; 
         FIG. 17  is a block diagram of the configuration of a device equivalent to a router comprised by a network employing a packet buffer; and, 
         FIG. 18  shows the configuration of the packet buffer memory  6  in  FIG. 17 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, aspects of the invention are explained. 
       FIG. 1  is a block diagram of an aspect of a simulation device to simulate network quality, to which a buffer management method of the present invention is applied. In comparison with the conventional configuration shown in  FIG. 17 , the simulation device of the present invention has the feature of including a conversion table  13 . 
     In the following explanations, it is assumed that there are  0 th through nth network physical ports,  0  through N IP addresses for CoS identification, and  0  through M types of CoS characteristics. 
     In  FIG. 1 , the multiplexing portion  1  multiplexes the Ethernet signals of a plurality n of ports. The packet type identification control portion  2  has CAM  3  and SRAM  4 , and compares the IP address or other identification information in the header portion of a packet multiplexed by the multiplexing portion  1  with registered information, referring to the associative memory (CAM: Content Addressable Memory)  3 . 
     When comparison results in a match, tag information identifying the service class (CoS: Class of Service), into which the packet is classified by the TCP/UDP port number or similar is read from the SRAM  4  and appended to the packet, which is output. 
     The data configuration of the CAM  3  and SRAM  4  is shown in  FIG. 2 . In the data configuration of the CAM  3  in  FIG. 2A , the (I) IP address and (II) port number which are to be identified are registered in association. 
     In the data configuration of the SRAM  4  shown in  FIG. 2B , the (I) CoS characteristic number, (II) input physical port, (III) output physical port, and (IV) CoS area are associated, corresponding to the order of IP addresses in the CAM  3 . Here (I) the CoS characteristic number is the number of the service class characteristic table in which the characteristic contents are set; (II) the input physical port is the physical port for input; (III) the output physical port is the physical port for output; and (IV) the CoS area is the CoS area (capacity) allocated in the packet buffer memory  6 ; these are registered as a set. 
     Hence the packet type identification control portion  2  judges whether the information in the header portion of a packet input from the multiplexing portion  1  matches an IP address or port number registered in the CAM  3 . If there is a match, the above corresponding information (I) through (IV) from the SRAM  4  is output as tag information and is appended to the input packet, which is sent to the buffer management control portion  5 . 
     The buffer management control portion  5  further has a conversion table  13 , in contrast with the conventional configuration explained in  FIG. 17 . 
     The contents of the conversion table  13  are shown in  FIG. 3 . Output physical ports  0  through M are defined (( 1 )) in the conversion table  13  corresponding to the output physical ports (III) based on the content set in SRAM  4  in  FIG. 2B ; on the basis of this, areas in the packet buffer memory  6  are allocated (( 2 ), ( 3 ), ( 4 )), and combinations with CoS characteristic numbers  0  through M (( 5 )) are created. In allocating the areas of the packet buffer memory  6 , the CoS areas are exchanged with the start addresses (( 3 )) and end addresses (( 4 ), ( 2 )) of the packet buffer memory  6 . 
     By this means, the packet buffer memory  6  is configured as shown in  FIG. 4 . In  FIG. 4 , ( 2 ) CoS numbers are allocated to ( 1 ) output physical port numbers  0  through n. In the example of  FIG. 4 , port  1  has a CoS numbers, port  2  has b CoS numbers, and port n has m CoS numbers. However, each of the CoS numbers corresponds to an IP address for identification, so that in  FIG. 4  the sum of the CoS numbers (a+b+ . . . +m) is N or less. 
     Here, the user performs the following settings in advance for network simulation. 
     First, the characteristic to be applied to the packet is set in the service class characteristic table  8 , as shown in  FIG. 5 . CoS characteristics having  0  to M packet control operations are defined. 
     Second, as previously shown in  FIG. 2A , IP addresses or TCP/UDP port numbers are specified for CoS identification, based on the receiving-side port, in the CAM  3 . 
     Third, as previously shown in  FIG. 2B , for each of  0  through N IP addresses, that is, for each CoS, a CoS characteristic number (I) indicating the characteristic to be applied, an input physical port (II), an output destination physical port number (III), and the amount of buffer area (CoS area) (IV) of the packet buffer memory  9  to be secured, are specified in SRAM  4  (see IV in  FIG. 2B ). 
     On the other hand, as previously indicated in  FIG. 3 , in the conversion table  13  on the side of the buffer management control portion  5 , the contents of the SRAM  4  are rearranged based on the output physical port, and allocation of the packet buffer memory  9  is performed. At this time, the start address and end address of each CoS area are determined. 
       FIG. 6  shows in further detail the configuration of the buffer management control portion  5  in  FIG. 1 , excluding the conversion table  13  and service class characteristic table  8 . 
     In  FIG. 6 , the packet number counter  33  of the pointer read/write control portion  10  indicates, in CoS units, the number of packets stored in the packet buffer memory  6 . The management pointer holding portion  34  indicates the management pointer position of the packet pointer management memory  7 , in CoS units. 
     The transfer control portion  35  of the packet output control portion  11  is provided with a sequencer which controls the transfer of packets read from the packet buffer memory  6 . The transfer analysis portion  36  judges whether packet transfer is possible, according to settings related to packet processing. 
     The management pointer movement amount computation portion  37  computes the amount of pointer movement according to the transfer judgment of the transfer analysis portion  36 . The time stamp holding portion  38  stores the time stamp value read from the packet pointer management memory  7  when a packet delay operation is performed; and the pointer stack portion  39  is used to temporarily store the management pointer value for a stack for transfer later, when packet order inversion/rerouting operations are performed. 
     In  FIG. 6 , the packet read/write control portion  9  has a packet buffer access control portion  31 . When a packet, to which a CoS characteristic has been appended as tag information, is transferred from the packet type identification control portion  2 , the packet is stored in the packet buffer memory  6  by the packet buffer access control portion  31 . 
     After storage in the packet buffer memory  6 , the transfer pointer indicating the storage address is, together with the time stamp, registered in the packet pointer management memory  7  via the management memory access control portion  32 . 
     The number of packets stored in the packet buffer memory  6  in CoS units is recorded in the packet number counter  33 . Based on the value of this packet number counter  33 , the management memory access control portion  32  notifies the transfer analysis portion  36  of the packet output control portion  11  of the fact that there exist transferable packets in the packet buffer memory  6 . 
     Further, the transfer analysis portion  36  determines, based on this notification of the existence of transferable packets and the preset-CoS characteristics, whether packet transfer is possible or not, and the direction and amount of movement of the management pointer held in the management pointer holding portion  34 . 
     As a result of this analysis, control of the transfer of packets in the packet buffer memory  6  and control of movement of the management pointer for the packet pointer management memory  7  are executed. Through these operations, various packet operations can be controlled. 
       FIG. 7  shows the correspondence relations between each of the packets stored in the packet buffer memory  6  and the packet pointer management memory  7 . As shown in  FIG. 7 , each entry (indicated by a time stamp number and transfer pointer number) specified by the management pointer of the packet pointer management memory  7  is associated with a packet within the packet buffer memory  6  in a one-to-one relationship. 
     The following is a summary explanation of packet operation control using the above configuration. 
     Returning to  FIG. 1 , packets input from the network via ports  0  through n are multiplexed by the multiplexing portion  1 . Multiplexed packets are sent to the packet identification control portion  2 . 
     In the packet identification control portion  2 , an IP address or TCP/UDP port number or similar is extracted from the header of a received packet, and a search performed to determine whether there is a match with an IP address or TCP/UDP port number set in advance in the CAM  3 , to judge whether or not the packet currently being received is a CoS packet. 
     When there is a match with an IP address or TCP/UDP port number set in advance in the CAM  3 , the corresponding information in SRAM  4  (see  FIG. 2B ) is read. The information thus read is appended to the beginning of the packet as tag information, and the packet is passed to the buffer management control portion  5 . 
     In the conversion table  13 , as previously explained, the contents of the SRAM  4  shown in  FIG. 2B  are converted, based on the output physical port, into the order CoS number, storage area in the packet buffer memory  6  specified by the start and end addresses, and CoS characteristic number. 
     In the buffer management control portion  5 , an address for writing to packet buffer memory  6  is generated by the packet read/write control portion  9  for a received packet, referring to tag information and the conversion table  13 , and control of writing to the packet buffer memory  6  is performed. 
     When writing is completed, a request for registration in the packet pointer management memory  7  is passed, together with the packet leading address, to the pointer read/write control portion  10 . The pointer read/write control portion  10 , upon receiving the registration request, writes the packet leading address to the packet pointer management memory  7 . 
     In the packet output control portion  11 , in order to execute characteristics set for each CoS according to the contents of the conversion table  13 , the area of the packet stored in the packet buffer memory  6  to be read, the order, time and other management is performed, and a read request is issued to the pointer read/write control portion  10  for the CoS for reading. 
     In the pointer read/write control portion  10 , the CoS transfer pointer for which a read request has been issued is read from the packet pointer management memory  7 , and the packet read request, together with the packet transfer pointer (leading address), is passed to the packet read/write control portion  9 . 
     In the packet read/write control portion  9 , the packet is read from the packet buffer memory  6  at the received transfer pointer, and the packet thus read is sent to the demultiplexing portion  12 . In the demultiplexing portion  12 , the packet is separated into output ports, and output to the network at ports  0  to n. 
     Here detailed operation of the buffer management control portion  5  is explained based on the operation sequence of the buffer management control portion  5  of  FIG. 8 , and referring to the drawing of the configuration of the buffer management control portion  5  in  FIG. 6 . 
     When packet storage in the packet buffer memory  6  is controlled (in process P 1 ) by the packet read/write control portion  9 , a transfer pointer registration request is sent to the pointer read/write control portion  10  (process P 2 ). 
     The transfer pointer is registered in packet pointer management memory  7  (process P 3 ) according to this registration request, and a transfer pointer registration response is returned to the packet read/write control portion  9  (process P 4 ). 
     Here, when there is transfer pointer registration in a plurality of CoS areas, a packet for transfer analysis is determined by a round robin method. Then, notification of packet existence is sent to the transfer analysis portion  36  of the packet output control portion  11  (process P 6 ). The CoS number is contained in the packet existence notification, so that transfer pointers are registered in the pointer stack portion  39  for each Cos. 
     When a packet existence notification is received, a time stamp notification request is sent from the packet output control portion  11  (process P 7 ). The pointer read/write control portion  10 , on receiving the time stamp notification request, reads from the packet pointer management memory  7  the corresponding time stamp registered together with the transfer pointer, as shown in  FIG. 7  (process P 8 ), and sends [the time stamp] to the packet output control portion  11  (process P 9 ). The time stamp sent in this way is held by the time stamp holding portion  38  together with the CoS number appended to the previously sent packet existence notification. 
     In the transfer analysis portion  36  of the packet output control portion  11 , transfer analysis is performed (process P 10 ). In transfer analysis in the transfer analysis portion  36 , the ability or inability to transfer the packet, whether an error is to be inserted or other processing performed, and similar are decided, based on the packet CoS characteristic and the time stamp value. 
     Cases when, as a result of transfer analysis, it is judged that transfer is not possible, are cases in which, in packet delay control, the delay amount between the device internal time and the time stamp is less than a prescribed delay control amount. 
     When transfer is not possible, a transfer inability notification is sent to the pointer read/write control portion  10  (process P 11 ). As the result of transfer analysis at other times (process P 12 ), in the case of packets which can be transferred, a management pointer operation instruction is sent to the pointer read/write control portion  10  (step P 13 ), and a transfer initiation instruction is issued to the packet read/write control portion  9  (process P 14 ). Based on these actions, the packet is read from the packet buffer memory  6  by the packet read/write control portion  9 , and is transferred to the packet output control portion  11  (process P 15 ). 
     The processing of  FIG. 8  is performed in parallel, as shown in  FIG. 9 . Hence the bandwidth of the bus within the device can be used efficiently, and adequate performance can be secured even when packets which impose a heavy load are input from the network. 
     Next, a specific embodiment of this invention is explained. As an embodiment of this invention,  FIG. 10  is a detailed block diagram of the packet identification control portion  2 ,  FIG. 11  shows the data contents of the CAM  3  ( FIG. 11A ) and SRAM  4  ( FIG. 1B ),  FIG. 12  shows the allocation of packet buffer memory  6 ,  FIG. 13  shows a service class characteristic table  8 , and  FIG. 14  shows the contents of a conversion table  13 . 
     In the following explanation of a specific example, the number of physical ports is assumed to be 8 ( 0  to  7 ), the maximum number of CoS identifications is 32, and the maximum number of CoS characteristic numbers is 32. 
     As shown in  FIG. 11 , in this embodiment 18 CoS identifications are performed, out of a maximum 32 CoS identifications. Overall, 16 types (CoS characteristic numbers  0  to  15 ) of CoS characteristics are allocated. In the unused area of SRAM  4  ( FIG. 1B ), by setting EN bits to “0”, [the fact that the area is unused] can be judged. 
     All CoS characteristic numbers  7  are allocated to the input physical port number  3 . Thus in the example shown in  FIG. 11 , the same CoS characteristic is applied to a plurality of IP addresses and TCP/UDP port numbers ( FIG. 11A ). 
     As shown in  FIG. 12A , allocation of the packet buffer memory  6  is performed by dividing the packet buffer memory  6  in advance into 32 fixed areas. Further, these may be the smallest CoS areas, and the CoS areas of the SRAM  4  may be allocated numerically. 
     At this time, by uniquely assigning start addresses and end addresses for the start address and end address of each smallest CoS area (CoS unit), as shown in  FIG. 12A , a CoS area specified by the user and an address in the packet buffer memory  6  can be allocated uniquely. 
     In this embodiment, the configuration of the allocated packet buffer memory  6  is as shown in  FIG. 12B . 
     For example, consider a packet which matches the address  6  (IP address  7 , port number  7 ) in the CAM  3  in  FIG. 11A . From the data contents of the SRAM  4  in  FIG. 11B  and the contents of the service class characteristic table  8  of  FIG. 13 , if the IP address and TCP/UDP port number of the packet input from physical port number  1  are respectively “IP address  7 ” and “port number  7 ”, then the CoS characteristic number  6 , that is, error input with an error occurrence rate of 40% and 300 ms delay insertion are performed simultaneously. 
     The area 3800000h to 3CFFFFFh is allocated to the packet buffer memory  6  (see  FIG. 12 : port number  7 , CoS area  3 ). 
     By securing a broad allocation area for packets with long delay times inserted, as in this embodiment, delay times can be set freely. 
     The operation of this embodiment is explained below. 
     In the detailed block diagram of the packet identification control portion  2  in  FIG. 10 , the CPU IF portion  21  has the functions of an interface with a CPU, not shown. The packet transfer control portion  22  performs packet input and output and generates timing signals. The header extraction portion  23  extracts the IP address or TCP/UDP port number from an input packet. The mask portion  24  masks the IP address and TCP/UDP port number. The CAM  3  has the size of 32 words×288 bits. The SRAM  4  has the size of 32 words×21 bits. The tag latch control portion  25  generates tag information and sends [the tag information] to the tag latch circuit  26 . The selector  27  is a circuit which selects whether to output a tag or to output an input packet. 
     In a packet identification control portion  2  with such a configuration, the IP address is extracted from the input packet data by the IP address extraction portion  23 , mask processing is performed by the mask portion  24 , and together with the TCP/UDP port number and similar, the IP address is input to the CAM  3 . 
     Here, mask processing is processing to apply a filter in order to specify an IP range. In this embodiment, this is achieved by setting the specified bits to “1” according to the settings from the CPU. 
     At this time, bits to be masked must be similarly set to “1” for the CAM  3  also. As with IP address masking, for the CAM  3 , all “1”s are set to for TCP/UDP port numbers, and when TCP/UDP port number searches are not performed the port number is masked with all “1”s and input to the CAM  3 . By this means matches can be detected only for IP addresses, for IP addresses and TCP/UDP port numbers, or for TCP/UDP port numbers only. 
     As a result of a search in the CAM  3 , if a matching IP address and TCP/UDP port number exists, the corresponding data in SRAM  4  is read. If the input physical port set in the read data matches the input physical port of a packet currently being received, and if the EN bit is “1”, then a tag is generated for the packet as a packet to be identified, the tag is appended to the beginning of the packet, and the packet is passed to the buffer management control portion  5 . 
     The input physical port, output physical port, EN information and similar are inserted into the tag, which is used to generate the write address in the packet buffer memory  6  by the buffer management control portion  5 . 
     Here, as embodiments of packet operation control,  FIG. 15  shows the flow of processing when generating a packet delay, and  FIG. 16  shows the flow of processing when causing packet order inversion/rerouting. 
     As shown in  FIG. 15 , when a packet to be delayed is identified as explained (process P 20 ) in  FIG. 6  and the sequence flow of  FIG. 8  (see processes P 10  and P 12 ), a judgment is made as to whether this is the first analysis (process P 21 ). If this is the first analysis (“Yes” in process P 21 ), the time stamp value is read from the packet pointer management memory  7  (process P 22 ); and if it is not the first analysis (“No” in process P 21 ), the time stamp value is read from the time stamp holding portion  38  (process P 23 ). 
     The time stamp value thus read is compared with the device reference time, and a judgment is made as to whether the preset delay time has elapsed (process P 24 ). 
     If the delay time has elapsed, the management-pointer value of the management pointer holding portion  34  is increased by one by the management pointer movement amount computation portion  37  (process P 25 ). By this means, transfer processing moves to the next packet (process P 26 ). 
     If the delay time has not elapsed, the time stamp value read from the packet pointer management memory  7  is stored in the time stamp holding portion  38  (see  FIG. 6 ). During the next transfer analysis, the value in the time stamp holding portion  38  is compared with the reference time. By this means, the load involved in accessing the packet pointer management memory  7  is reduced, and performance is improved. 
       FIG. 16  shows the flow of operation during packet order inversion or rerouting. In  FIG. 16 , the contents of operation control corresponding to the CoS characteristic number identified by the packet type identification control portion  2  are determined, referring to the service class characteristic table  8 . Hence when a packet is identified for which the operation control thus determined is order rearrangement (process P 30 ), the transfer analysis portion  36  (see  FIG. 6 ) judges whether the number of packets received and stored in the packet buffer memory  6  is equal to or greater than the number of packets for order rearrangement (process P 31 ). 
     If the number of packets received and stored is equal to or greater than the number of packets for order rearrangement (“Yes” in process P 31 ), then the pointer movement amount computation portion  37  notifies the management pointer holding portion  34  of the pointer movement amount for n packets for rearrangement, and adds n to the management pointer value (process P 32 ). Next, packet transfer is performed by the transfer control portion  35  (process P 33 ), and when transfer of then packets for packet rearrangement is completed (“Yes” in process P 34 ), the management pointer value in the management pointer holding portion  4  is returned by subtracting n×2 (process P 35 ). 
     Then, the n packets transfer of which was deferred due to the order rearrangement are transferred (process P 36 ). When transfer of the n packets ends (“Yes” in process P 37 ), n is added to the management pointer value of the management pointer holding portion  4 , and subsequently normal transfer is performed (process P 38 ). 
     In this way, by adding and subtracting to the management pointer, packets are transferred in an order different from the received order. This addition and subtraction processing of the management pointer can be realized through simple hardware in the management pointer holding portion  34 , so that high-speed transfer control is possible. 
     As explained above referring to the drawings, through this invention the following advantageous results can be expected. 
     1. When allocating each service class (CoS) area, ranges can be set freely and individually. For example, broad areas can be allocated for packets for which long delay times are applied, and in similar ways maximum use can be made of the physical capacity of the packet buffer in accordance with the [CoS] characteristics. 
     2. With N as the overall number of service classes (CoS) identified, there are no limits on the number of physical ports or the types of characteristics. 
     3. A plurality of IP addresses for CoS identification can be allocated for one type of service class (CoS) characteristic. 
     4. control of packet operations to realize network simulations can be achieved through parallel processing using simple computations, and comparatively simple hardware circuits can be employed in high-performance packet operation control. 
     As explained above, by means of this invention complex operations on packets in a broadband network can be realized with high processing performance through a comparatively simple hardware configuration, and the contents of flexible packet operations can be set and realized in accordance with the desires of users. Hence the quality of communication and voice transmission between end users can be verified or secured, contributing substantially to improving the quality of IP networks.