Abstract:
The present invention provides a method of performing packet transfer among nodes on a network by a packet transfer node. When the network is divided into a plurality of network areas and routing within an individual network area and between network areas is performed, the method divides packet transfer processing of the packet transfer node into a higher layer and a lower layer, selects one of the higher layer and the lower layer for each packet to be transferred in accordance with information set in the packet transfer node, and performs the packet transfer by the selected hierarchical layer. According to the present invention, an added packet transfer node can be coupled with a network area which is not adjacent to the added packet transfer node to increase flexibility of expanding the network.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to packet transfer technologies on networks, and more particularly, to a packet transfer method in which a network is divided into a plurality of network areas and routing within an individual network area and between network areas is performed. 
     2. Description of the Related Art 
     In recent years, significant increases in the capacity and bandwidth of communication networks typified by the Internet have been made. Thus, the number of communication apparatuses (Network Elements (NEs)) constituting networks and serving as backbones of such communication networks has been increased, and such communication apparatuses have become complicated. 
     In general, such a communication apparatus (hereinafter, referred to as a “node”), which is connected to a network for transmitting a user traffic, is also connected to a monitoring network which transmits packets for monitoring the communication apparatus (node). In this case, the node is often controlled using an OSI network on which routing processing can be performed in accordance with the ISO9542 and ISO10589 standards (hereinafter, referred to as OSI protocols) defined by International Organization for Standardization (ISO). 
     The OSI network adopts a method for dividing the entire network (domain) into a plurality of network areas and managing the plurality of network areas. On the OSI network, packet transfer processing, that is, routing within an individual network area and routing between network areas, is performed individually. Routing within an individual network area is called Level 1 (L1) routing, and routing between network areas is called Level 2 (L2) routing. 
       FIG. 1  shows the concept of a domain and an network area on an OSI network by way of example. 
     In  FIG. 1 , nodes represented by “IS1” are packet transfer nodes having an L1-routing function, and nodes represented by “IS1IS2” are packet transfer nodes having both the L1-routing function and L2-routing function. Nodes represented by “ES” are nodes not having a routing function. 
     In the example shown in  FIG. 1 , a domain  3  is divided into a network area  1  and a network area  2 . 
     In the network area  1 , ES nodes  141  and  142  and an IS1 node  140  communicate with each other on the basis of ES-IS protocol (ISO 9542), IS1 nodes  130  and  140  are L1-connected with each other, and an IS1IS2 node  110  and an IS1 node  120  are L1-connected with each other. An ES node  121  communicate with the IS1 node  120  on the basis of ES-IS protocol (ISO 9542). 
     In the network area  2 , an IS1IS2 node  210 , an IS1 node  220 , and an IS1IS2 node  230  are L1-connected with each other, and an ES node  221  communicate with the IS1 node  220  on the basis of ES-IS protocol (ISO 9542). 
     In addition, the IS1IS2 node  110  in the network area  1  and the IS1IS2 nodes  210  and  230  in the network area  2  are L2-connected with each other (that is, a connection line performing L2 routing is formed). That is, the IS1IS2 nodes within the same network area are L1-connected and L-2 connected with each other. 
     In accordance with the convention of the OSI protocol, a packet transfer node that performs packet transfer within a network area, that is, an IS1 node having an L1-routing function, is required to hold routing information of all the nodes existing within the network area to which the packet transfer node belongs as the routing information table in a memory of the packet transfer node. Thus, when a node is added to a network area, the addition of the node affects the system resources, such as memory resource, address resources and processing performance resources, of all the packet transfer nodes within the network area. Especially in the case that a node includes both functions of transmitting a user traffic and transmitting a monitoring traffic, for example packets transmitted on the OSI network, the system resources of the node tend to be assigned firstly for the processing of the user traffic and the system resources assigned for the processing of the monitoring traffic are often restricted. 
     For example, when nodes are added to a network area, the number of nodes to be added is limited to a range not exceeding the number of nodes a packet transfer node having the least memory resource in the network area can handle (for example, the upper limit of the number of nodes on a network can be set to 300). This is because if more nodes than the limited number of nodes are added, the memory resource of the packet transfer node having the least memory resource in the network area becomes insufficient, and the operation of the entire network including the packet transfer node cannot be ensured. 
     Also, since a node on a network is uniquely identified by a network service access point (NSAP) address and is managed using the NSAP address in accordance with the convention of the OSI protocol, the number of NSAP addresses included within a network area can be limited. 
     Similarly, since a node performing L2 routing is required to have routing information of all the network nodes that perform L2 routing, the number of nodes (or the number of NSAP addresses) having the L2 protocol can be limited (for example, the upper limit of the number of nodes on a network is set to 250). The IS1IS2 nodes having the L1-routing function and the L2-routing function on the OSI network shown in  FIG. 1  are required to hold information on both the L1 routing and L2 routing in the routing information table. 
     Generally, the number of connected nodes continues to increase in accordance with the continued operation of a network. Thus, as shown by the example of the OSI network, the limit of the number of nodes that can be provided in a network area or a domain is an important issue for network architecture. 
     As a technology for adding a node onto an OSI network, a technology for adding a node without consuming an NSAP address and for performing routing is disclosed in Japanese Unexamined Patent Application Publication No. 2005-277893. 
     In known technologies, when a new node is added so as to be adjacent to a network area on a network for which area management is performed, if the network area does not have a memory resource sufficient for adding the node, it is necessary to divide the network area into a plurality of network areas and to cause the new node to be accommodated in one of the divided network areas. Thus, the number of network areas constituting the entire network increases, and managing the entire network becomes complicated. 
     SUMMARY OF THE INVENTION 
     The present invention provides a packet transfer processing composed of a higher layer and a lower layer in a packet transfer node having a routing function, wherein one of the higher layer and the lower layer is selectively performed in accordance with setting of each packet transfer node. 
     A packet transfer method according to an aspect of the present invention for performing packet transfer among nodes on a network includes transmitting a data packet, according to hierarchical packet processing layers composed of a higher layer and a lower layer in a packet transfer node having a routing function to transfer a packet within a network area and/or between network areas of nodes, selecting one of the higher layer and the lower layer for each packet to be transferred by the packet transfer node, and performing, by the packet transfer node, the packet transfer by the selected hierarchical layer. 
     Thus, selection between packet transfer in the higher layer and packet transfer in the lower layer can be performed in accordance with setting of each of the packet transfer nodes. Thus, packet transfer in the lower layer can be performed in parallel with packet transfer in the higher layer without affecting the packet transfer in the higher layer. 
     In the higher layer, the network may be divided into one or more network areas, and routing processing within an individual network area and between network areas may be performed. 
     In the lower layer, bridge processing in which a packet is transferred to a communication link between the packet transfer nodes without going through the routing processing in the higher layer can be performed. 
     Thus, in particular, on a network, which is divided into a plurality of network areas and in which routing processing within an individual network area and between network areas is performed, such as an OSI network, when a node is added, a packet transfer node in a network area that is adjacent to the added node transfers a packet by bridge processing. Thus, packets originating from the added node can be processed by a network area that is not adjacent to the added node and the added node is deemed to be a packet transfer node in the network area. Therefore, network expansion can be achieved while suppressing an increase in the number of network areas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the concept of a domain and a network area on an OSI network by way of example; 
         FIG. 2  shows a case where a node is added onto the OSI network by way of example; 
         FIG. 3  shows a known method for adding a node onto the OSI network by way of example; 
         FIG. 4  shows a method according to a first embodiment of the present invention for adding a node; 
         FIG. 5  shows the functions of the first embodiment; 
         FIG. 6  shows a method according to a second embodiment of the present invention for adding a node; 
         FIG. 7  is a functional block diagram of the second embodiment; 
         FIG. 8  shows an example of the structure of a packet transfer node according to the embodiments of the present invention; 
         FIGS. 9A-9D  each shows an example of the structure of a bridge control table according to the embodiments of the present invention; 
         FIG. 10  shows an example of the structure of packet data according to the second embodiments of the present invention; 
         FIG. 11  is a flowchart showing bridge processing according to the first embodiment of the present invention; and 
         FIG. 12  is a flowchart showing bridge processing according to the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  shows an example of a case where a node is added onto the OSI network shown in  FIG. 1  by way of example. 
     In the example shown in  FIG. 2 , a packet transfer node  150  (IS1 node) located adjacent to the network area  1  and a node  151  (ES node) connected to the packet transfer node  150  are added to the network area  1 . Here, it is assumed that the upper limit of the memory resource of one of the packet transfer nodes in the network area  1  is reached and a packet transfer node in the network area  2  has a sufficient memory resource. 
     Since the packet transfer node  150  to be added is some distance from the network area  2 , it is difficult to directly connect the packet transfer node  150  to the network area  2 . Thus, normally, the packet transfer node  150  should be added by causing the packet transfer node  150  to belong to the network area  1 . However, in the current situation, the network area  1  does not have a sufficient memory resource. Thus, conventionally, after the network area  1  is divided into a plurality of network areas so that the memory resource consumed by each packet transfer node in the divided network areas is reduced, and the packet transfer node  150  is added to one of the network areas obtained by dividing the network area  1 . 
       FIG. 3  shows an example of a known method for adding a node onto the OSI network shown in  FIG. 2 . 
     In the example shown in  FIG. 3 , since a packet transfer node whose memory resource is insufficient exists in the network area  1  that is adjacent to the packet transfer node  150  to be added, the network area  1  is divided into network areas  1   a  and  1   b , and the nodes  150  and  151  are accommodated within the network area  1   b  that is obtained by dividing the network area  1 . That is, the existing nodes  120  and  121  shown in  FIG. 2  and the nodes  150  and  151  form the network area  1   b  in  FIG. 3   
     Thus, conventionally, in order to realize addition of the nodes  150  and  151  as described above, it is necessary to perform routing between the network areas  1   a  and  1   b . In addition, it is necessary to change the existing packet transfer node  120  (the IS1 node that performs only L1 routing) into an IS1IS2 node that is capable of performing routing between network areas (L2 routing). That is, another IS1IS2 node that performs L1 routing and L2 routing is added by dividing the network area  1  into the network areas  1   a  and  1   b.    
     Generally, a disadvantage of the known method is that since network architecture over a plurality of network areas is provided with an L2-routing function, managing the network architecture over a plurality of network areas is more complicated, requires a higher-level management system, and performs a more complicated network operation, compared with managing network architecture within a single network area. 
       FIG. 4  shows an example of node addition according to a first embodiment of the present invention. 
     In this example, although a node cannot be added to the network area  1  that is adjacent to the packet transfer node  150  to be added, since, for example, the network area  1  includes a packet transfer node whose system resources (such as a memory resource or other resources) are insufficient, the network area  2  that is not adjacent to the packet transfer node  150 , has system resources sufficient for adding the node, as in the example of the OSI network shown in  FIG. 2 . 
     In the first embodiment, by connecting the packet transfer node  150  to the packet transfer node  120  (IS1 node) in the network area  1  that is adjacent to the packet transfer node  150 , the packet transfer node  150  is deemed to belong to the network area  2  that is not adjacent to the packet transfer node  150  and without dividing the network area  1 . In the first embodiment, however, for allowing separation from a packet flow based on the known L1 routing or L2 routing, communication links  901   a  and  902   a  are provided in parallel with the existing corresponding communication link  901  between the packet transfer nodes  210  and  110  and the existing corresponding communication link  902  between the packet transfer nodes  110  and  120 . 
     Here, the first embodiment of the present invention is applied to the packet transfer nodes  110  and  120  in the network area  1  and the packet transfer node  210  in the network area  2 , if the packet transfer node  150  is to be added. The packet transfer nodes according to the first embodiment of the present invention, divide packet transfer processing into a higher layer and a lower layer, and a received packet can be selectively processed in the higher layer or the lower layer in accordance with bridge/routing processing setting of each of packet transfer nodes  120 ,  110 . For example, on the OSI network, in the packet transfer processing on the higher layer, the known L1 or L2 routing is performed. In addition, in the packet transfer processing on the lower layer or bridge layer, a packet is switched on the basis of a low layer address such as a MAC (Media Access Control) address between the communication links  904  and  902   a  in the packet transfer node  120 , and between the communication links  902   a  and  901   a  in the packet transfer node  110 , in accordance with setting information set in advance for each node, without performing the routing processing on the higher layer. The bridge layer transfers a packet among the packet transfer nodes, without relation to defined network areas, or without affecting the routing processing of the packet transfer nodes in the defined network areas. Taking the above-mentioned points into consideration, in the following descriptions, packet transfer processing on the higher layer is represented by “routing processing”, and packet transfer processing on the lower layer is represented by “bridge processing”. 
     In  FIG. 4 , a packet P 2  transmitted from the packet transfer node  150  is received at the packet transfer node  120  via the communication link  904 . The packet transfer node  120  transfers to the packet transfer node  110  (the IS1IS2 node) via the newly established communication link  902   a  the packet P 2  received from the packet transfer node  150 . The packet transfer node  110  transfers to the packet transfer node  210  (the IS1IS2 node) via the newly established communication link  901   a  the packet P 2  received via the communication link  902   a . The packet transfer from the packet transfer node  150  to the packet transfer node  210  is performed by packet transfer processing on the lower layer of each of the packet transfer nodes  120 ,  110 , that is, bridge processing at these packet transfer nodes  120 ,  110  with routing functions in the network area  1 . The bridge processing is performed independent of packet transfer processing on the higher layer in which the known L1 or L2 routing, that is, the routing processing, is performed by nodes  120 ,  110 . Thus, the bridge processing is performed without affecting the known packet transfer (for example, the L1 or L2 routing) performed in the network area  1 . 
     The packet transfer node  210  causes the packet received as described above via the communication link  901   a  to be subjected to the routing processing on the higher layer. Thus, the packet is subjected to routing processing (for example, L1 or L2 routing) in the network area  2 , and each node in the network area  2  is capable of dealing with the packet from the packet transfer node  150  as a packet that is equivalent to a packet from a node accommodated within the network area  2 . 
     Similarly, packet transfer from the packet transfer node  210  to the packet transfer node  150  is performed in accordance with a packet flow in a direction that is opposite from the direction of the packet flow from the packet transfer node  150  to the packet transfer node  210 . 
     As described above, according to the first embodiment of the present invention, the packet transfer node  150  can be added, adjacent to the network area  1  whose memory resource is insufficient, to a network as a node belonging to the network area  2  without dividing the network area  1 . 
       FIG. 5  shows the functions of the first embodiment of the present invention for adding a node, by way of an example of the packet transfer nodes  120  and  110  within the network area  1  on the OSI network shown in  FIG. 4 . 
     The packet transfer node  120  receives a packet P 1  via the communication link  903  between the packet transfer node  120  and the ES node  121 . In addition, the packet transfer node  120  receives a packet P 2  from the packet transfer node  150  via the communication link  904 . 
     The received packets P 1  and P 2  are processed by a bridge processing section  21  in the lower layer in accordance with information set in advance in a bridge control table  22  to determine whether the packets read to be bridge processed or routing processed. As shown in  FIG. 9A , reception interface identification information on a packet and transfer destination interface identification information corresponding to the reception interface identification information are set in the bridge control table  22  provided, for example, in the packet transfer node  120 . A packet P 1  received from an interface indicated by reception interface identification information (interface  903  in  FIG. 9A ) whose corresponding transfer destination interface identification information is not set is regarded as not being a target of processing of the bridge processing section  21 , and is delivered to the routing processing section  11  in the higher layer. Then, L1 routing that is similar to known packet transfer processing is performed in accordance with information stored in the known L1 routing table  12 . A packet received from an interface indicated by reception interface identification information that is not set in the bridge control table  22  is also delivered to the routing processing section  11  in the higher layer. 
     In contrast, a packet received from a reception interface (interface  904  in  FIG. 9A ) whose corresponding transfer destination interface identification information is set in the bridge control table  22  of the packet transfer node  120 , is transferred to a communication link indicated by the transfer destination interface identification information (interface  902   a  in  FIG. 9A ) set in the bridge control table  22 . 
     In the example shown in  FIG. 5 , the bridge control table  22  is set, for example, in advance as described below. 
     Since the packet P 1  received via the communication link  903  is a packet received from the node  121  within the network area  1 , transfer destination interface identification information for reception interface identification information corresponding to the communication link  903  is not set or an entry of the reception interface identification information corresponding to the communication link  903  is not registered in the bridge control table  22 , as shown in  FIG. 9A . 
     In contrast, since the packet P 2  received via the communication link  904  is a packet received from the packet transfer node  150 , transfer destination interface identification information for reception interface identification information corresponding to the communication link  904  is set in the bridge control table  22  so as to indicate the communication link  902   a , as shown in  FIG. 9A . 
     In accordance with the bridge control table  22  set as described above, the packet P 1  received from the node  121  belonging to the network area  1  is processed by the routing processing section  11  in the higher layer in accordance with a known procedure, and is transferred to the existing communication link  902 . In contrast, the packet P 2  received from the packet transfer node  150  is processed by the bridge processing section  21  in the lower layer provided in the first embodiment of the present invention, and is transferred to the communication link  902   a  provided for bridge processing, without being processed by the routing processing section  11  in the higher layer. 
     Packet transfer processing of the packet transfer node  110  is performed, as in the processing of the packet transfer node  120 . In the example shown in  FIG. 5 , since the packet transfer node  120  is an IS1 node, the routing processing section  11  in the higher layer performs L1 routing. However, since the packet transfer node  110  is an IS1IS2 node, the routing processing section  11  in the higher layer performs L1 routing and L2 routing. The difference between the processing of the packet transfer node  120  and the processing of the packet transfer node  110  does not affect the principle of the present invention. In addition, since the contents of the routing information table  12  and the bridge control table  22  are individually settable for each packet transfer node, the set contents of the packet transfer node  110  are different from the set contents of the packet transfer node  120 . 
     The packet P 1  received via the communication link  902  between the packet transfer node  120  and the packet transfer node  110  and the packet P 2  received via the communication link  902   a  are processed by the bridge processing section  21  in the lower layer in accordance with information set in advance in the bridge control table  22  of the packet transfer node  110 . Reception interface identification information and transfer destination interface identification information corresponding to the reception interface identification information are set in the bridge control table  22  of the packet transfer node  110 , as shown in  FIG. 9B . If a packet is received from an interface indicated by reception interface identification information (interface  902  in  FIG. 9B ) whose corresponding transfer destination interface identification information is not set, the packet is regarded as not being a target of processing of the bridge processing section  21  in the lower layer. Thus, the packet is delivered to the routing processing section  11  in the higher layer, and L1 routing or L2 routing, which is similar to known packet transfer processing, is performed in accordance with information stored in the routing information table  12 . If a packet is received via a communication link indicated by reception interface identification information that is not set in the bridge control table  22 , the packet is also delivered to the routing processing section  11  in the higher layer. 
     In contrast, if a packet is received from a reception interface (interface  902   a  in  FIG. 9B ) whose corresponding transfer destination interface identification information is set in the bridge control table  22 , the packet is transferred to a communication link indicated by the transfer destination interface identification information (interface  901   a  in  FIG. 9B ) set in the bridge control table  22 . 
     In the example shown in  FIG. 5 , transfer destination interface identification information for reception interface identification information corresponding to the communication link  902  is not set or an entry of the reception interface identification information corresponding to the communication link  902  is not registered in the bridge control table  22 . In contrast, transfer destination interface identification information for reception interface identification information corresponding to the communication link  902   a  is set so as to indicate an interface corresponding to the communication link  901   a.    
     In accordance with the bridge control table  22  of the packet transfer node  120  set as described above, the packet P 1  received at the node  110  from the node  121  belonging to the network area  1  is processed by the routing processing section  11  in the higher layer in accordance with a known procedure, as in the processing of the packet transfer node  120 , and L1 routing and L2 routing are performed in accordance with the contents of the routing information table  12 . Then, the packet P 1  is transferred to the existing communication link  901 . In contrast, the packet P 2  received at the node  110  from the packet transfer node  150  is processed by the bridge processing section  21  in the lower layer provided in the first embodiment of the present invention, and is transferred to the communication link  901   a  provided for bridge processing, as in the processing of the packet transfer node  120 . 
     Although not shown in  FIG. 5 , the packet transfer node  210  in the network area  2  in the first embodiment of the present invention causes the packet received via the communication link  901   a , that is, the packet from the packet transfer node  150 , to be subjected to routing processing in the higher layer. This is realized by not setting transfer destination interface identification information corresponding to reception interface identification information of the communication link  901   a  in the bridge control table  22  of the packet transfer node  210 . 
     As described above, packet transfer of the packet P 2  via the communication links  904 ,  902   a , and  901   a  is performed independent of L1 or L2 routing performed by the packet transfer nodes  120  and  110  in the higher layer. Thus, the packet P 2  can be transferred to the network area  2  without affecting routing processing of each of packet transfer nodes in the network area  1 , and is subjected to the routing processing in the higher layer, that is, L1 routing or L2 routing, by the packet transfer node  210  located at the beginning of the network area  2 . Accordingly, the routing processing is performed as processing in the network area  2 . 
     As described above, the nodes  120  and  110  in the network area  1 , the node  210  in the network area  2 , and the node  150  are provided as packet transfer nodes according to the first embodiment of the present invention, and the contents of the bridge control table  22  used in the bridge processing section  21  in the lower layer of each of the packet transfer nodes are properly set. Thus, the packet P 1  for which routing processing in the higher layer, which is known routing processing, is performed and the packet P 2  for which bridge processing in the lower layer according to the first embodiment of the present invention is performed are capable of passing through the network area  1 , independent of each other. That is, the packet P 2  can be transferred between the added packet transfer node  150  and the packet transfer node  210  in the network area  2  that is adjacent to the network area  1  without affecting a known packet transfer flow in the network area  1 , and routing processing similar to known routing processing can be performed on the packet transfer node  150  as a node belonging to the network area  2 . 
     In the example shown in  FIG. 5 , the principle of the first embodiment of the present invention has been described by way of an example of packet transfer between two nodes. However, the number of nodes via which a packet is transferred is not limited. 
     In addition, the number of communication links is not limited to the number of communication links adopted in the above-described example. 
       FIG. 6  shows an example of node addition according to a second embodiment of the present invention. 
     In this example, although a node cannot be added to the network area  1  that is adjacent to the packet transfer node  150  to be added, since, for example, a packet transfer node whose memory resource is insufficient exists in the network area  1 , the network area  2  that is not adjacent to the packet transfer node  150  has a sufficient memory resource, similarly to the node addition according to the first embodiment shown in  FIG. 4 . 
     In the packet transfer method according to the second embodiment, by connecting the packet transfer node  150  to the packet transfer node  120  in the network area  1  that is adjacent to the packet transfer node  150 , the packet transfer node  150  is deemed to belong to the network area  2  that is not adjacent to the packet transfer node  150 , as in the first embodiment. 
     However, the packet transfer method according to the second embodiment is different from the packet transfer method according to the first embodiment in that it is not necessary to provide a communication link for bridge processing in the lower layer in the network area  1  and in that packet transfer between the packet transfer node  150  and the network area  2  is performed via the existing communication links  902  and  901 . 
     A packet transmitted from the packet transfer node  150  is received at the packet transfer node  120  via the communication link  904 , and the packet transfer node  120  transfers, via the existing communication link  902  by the bridge processing in the lower layer, the packet received from the packet transfer node  150 . The packet transfer node  110  transfers the packet received via the communication link  902  to the packet transfer node  210  in the network area  2  via the existing communication link  901  by the bridge processing in the lower layer. The packet transfer from the packet transfer node  150  to the packet transfer node  210  is performed independent of the known routing processing performed in the higher layer in each of packet transfer nodes (that is, for example, L1 or L2 routing on the OSI network). That is, packet transfer between the packet transfer node  150  and the packet transfer node  210  is performed without affecting the known packet transfer performed in the higher layer in the network area  1 . 
     The packet transfer node  210  in the network area  2  delivers the received packet to the higher layer. Thus, each node in the network area  2  is capable of dealing with the packet received from the packet transfer node  150  as a packet received from a node in the network area  2  without affecting packet transfer in the higher layer in the network area  1 . 
       FIG. 7  shows an example in which the second embodiment of the present invention is applied to the packet transfer nodes  120  and  110  in the network area  1  shown in  FIG. 6 . 
     In the second embodiment, a bridge specification information is set in advance in a packet to be transferred. The bridge specification information can be, for example, flag information in the packet indicating whether the packet is a target of bridge processing. For example, if the bridge specification information indicates “ON”, the packet is regarded as being a target of bridge processing. In contrast, if the bridge specification information indicates “OFF”, the packet is regarded as not being a target of bridge processing. 
     In the example shown in  FIG. 6 , for example, the bridge specification information can be added by processing in the higher layer of the packet transfer node  150 . Thus, each of the packet transfer nodes that relay the packet (in the example shown in  FIG. 6 , the packet transfer nodes  120 ,  110 , and  210 ) is capable of determining whether the packet is a target of bridge processing. Thus, a packet that is to be subjected to bridge processing and a packet that is to be subjected to the known routing processing in the higher layer can be transmitted via the same communication link. Packets P 1  and P 2  received at the packet transfer node  120  are firstly processed in a bridge processing section  21   a  in the lower layer. The bridge processing section  21   a  determines the contents of the extracted bridge specification information. If the bridge specification information indicates “OFF”, the packet is delivered to the routing processing section  11  in the higher layer. 
     If the bridge specification information indicates “ON”, the bridge control table  22  is searched by the bridge processing section  21   a.    
     Reception interface identification information on a packet and transfer destination interface identification information corresponding to the reception interface identification information are set in the bridge control table  22 , as shown in  FIG. 9C . If a packet is received from an interface indicated by reception interface identification information whose corresponding transfer destination interface identification information is not set, the packet is regarded as not being a target of processing of the bridge processing section  21   a  in the lower layer and is delivered to the routing processing section  11  in the higher layer. If a packet is received from an interface indicated by reception interface identification information that is not set in the bridge control table  22 , the packet is also delivered to the routing processing section  11  in the higher layer. 
     If a packet is received from an interface indicated by reception interface identification information (interface  904  in  FIG. 9C ) whose corresponding transfer destination interface identification information (interface  902  in  FIG. 9C ) is set, the packet is regarded as a target of processing of the bridge processing section  21   a  in the lower layer. Then, the packet is transferred to the communication link indicated by the corresponding transfer destination interface identification information (interface  902  in  FIG. 9C ), without performing the routing processing in the higher layer. 
     In the example of the network structure shown in  FIG. 6 , since the packet P 1  received via the communication link  903  is a packet received from the node  121  within the network area  1 , the bridge specification information in the packet P 1  is reset or “OFF”, so the packet P 1  is regarded as not being a target of bridge processing. Therefore, the packet P 1  is delivered to the routing processing section  11  in the higher layer, and is processed in accordance with the known procedure. Then, the packet P 1  is transferred to the existing communication link  902 . 
     If reception interface identification information (interface  903 ) whose corresponding transfer destination interface identification information is not set is registered in the bridge control table  22   a  the bridge control table  22 , the packet P 1  is regarded as not being a target of processing of the bridge processing section  21   a  in the lower layer and is delivered to the routing processing section  11  in the higher layer of the packet transfer node  120 . In this case, the bridge specification information in the packet P 1  can be any. 
     In contrast, since the packet P 2  received via the communication link  904  is a packet received from the added packet transfer node  150 , information indicating the existing communication link  902  is set in the bridge control table  22  as transfer destination interface identification information (interface  902  in  FIG. 9C ) for reception interface identification information (interface  904  in  FIG. 9C ) corresponding to the communication link  904 . Thus, since bridge specification information on the packet P 2  received from the added packet transfer node  150  indicates “ON”, bridge processing in the lower layer is performed on the packet P 2  in accordance with the contents of the bridge control table  22 , and is transferred to the communication link  902  without going through routing processing in the higher layer. 
     Then, the packet transfer node  110  receives the packets P 1  and P 2  via the existing communication link  902  from the packet transfer node  120 . Then the bridge processing section  21  in the lower layer of the packet transfer node  110  searches the bridge control table  22 , which is shown in  FIG. 9D , for reception interface identification information of the communication link  902  and transfer destination interface identification information corresponding to the reception interface identification information. If the reception interface identification information and the transfer destination interface identification information corresponding to the reception interface identification information exist in the bridge control table  22 , the bridge processing section  21  determines bridge specification information on each of the packet P 1  and P 2 . 
     As described above, if the bridge specification information indicates “ON”, the packet is transferred to a communication link indicated by the transfer destination interface identification information. 
     In contrast, if the bridge specification information indicates “OFF” (the bridge specification information is not set), the packet is delivered to the routing processing section  11  in the higher layer. 
     Thus, in the example shown in  FIG. 7 , the packet P 2  whose bridge specification information indicates “ON” is subjected to bridge processing, and then transferred to the communication link  901 . In contrast, the packet P 1  whose bridge specification information is not set or has been reset to “OFF” is subjected to routing processing in the higher layer, and then transferred to the communication link  901 . 
     Although not shown in  FIG. 7 , in the bridge control table  22  in the lower layer of the packet transfer node  210  in the network area  2 , transfer destination interface identification information corresponding to reception interface identification information of the communication link  901  is not set. By this, a packet P 2  received via the communication link  901  is reset by the node  210 . In other words, the packet transfer node  210  resets (sets to “OFF”) bridge specification information on the received packet P 2 , and then delivers the packet P 2  to the higher layer. Thus, the packet P 2  is handled as a target of routing processing in the higher layer in the network area  2 , and the added packet transfer node  150  is processed as a node belonging to the network area  2 . 
     As described above, packet transfer of the packet P 2  via the communication links  904 ,  902 , and  901  is performed by bridge processing in the lower layer, which is independent of L1/L2 routing performed on the packet P 1  in the higher layer of the packet transfer nodes  120  and  110 . Thus, the packet P 2  is transferred to the network area  2  without affecting routing processing on the packet P 1 , which is performed by the higher layer, of each of the packet transfer nodes in the network area  1 , and delivered to the higher layer of the packet transfer node  210 , which is located at the beginning of the network area  2 . Thus, packet transfer between the added packet transfer node  150  and the network area  2  can be performed via the network area  1  without affecting routing processing in the network area  1 , and the added packet transfer node  150  can be processed as a node belonging to the network area  2 . 
     In the example shown in  FIG. 7 , the function of the second embodiment of the present invention has been described by way of an example of packet transfer between two nodes. However, the number of nodes via which a packet is transferred is not limited. 
     In addition, the number of communication links is not limited to the number of communication links adopted in the second embodiment. 
       FIG. 8  shows an example of the structure of a packet transfer node according to the embodiments of the present invention. 
     In this structural example, the higher layer  10  corresponds to a network layer of an OSI reference model, and the lower layer  20  corresponds to a data link layer of the OSI reference model in which the described processes of the present embodiment are implemented in software and/or computing hardware. An implementation example of a packet transfer node on an OSI network is shown in  FIG. 8 . 
     The routing processing section  11  is provided in the higher layer  10 , and L1/L2 routing information is stored in the routing information table  12 . 
     The bridge processing section  21  that performs packet transfer in accordance with information set in the bridge control table  22  without going through routing processing in the higher layer, according to the embodiment of the present invention, is provided in the lower layer  20 . 
     The structural example in  FIG. 8  shows a case where data transfer between nodes is performed in accordance with a Link Access Procedure for the D-channel (LAP-D) in a high-level data link control (HDLC) format. The structural example includes an HDLC LSI  24  that controls an HDLC procedure, a LAP-D driver  23  that controls the LAP-D, and HDLC drivers  24   a ,  24   b , and  24   c  that perform HDCL control for line correspondence. 
     A supervisory controller  40  performs network management. The supervisory controller  40  receives, as command information, a supervisory control operation received from a user terminal  60  (personal computer (PC) or a workstation) provided with monitoring software, such as a simple network management protocol (SNMP) manager, via a user interface processor  50 . Then, the supervisory controller  40  issues an instruction to the routing processing section  11  and performs setting for the bridge control table  22  in accordance with the contents of the command information. 
     Packet data sent from a connected node on the OSI network is terminated at a physical layer  30 , for example, by optical input/output devices  31   a ,  31   b , and  31   c  via an optical fiber  90  serving as a physical communication link, and packet data is extracted. Then, the packet data is delivered to the layer  25 . 
     Then, original datagram is reconstructed by the HDLC LSI  24 , the HDLC drivers  24   a ,  24   b , and  24   c , and the LAPD driver  23 , and the reconstructed datagram is delivered to the bridge processing section  21  as a packet. 
     The bridge processing section  21  performs packet transfer in accordance with information set in the bridge control table  22 . The packet processed by the bridge processing section  21  may or may not be delivered to the higher layer  10  depending on the information set in the bridge control table  22 . 
     Identification information on an interface to which a packet is transferred (transfer destination interface identification information) is stored in association with identification information on an interface by which the packet is received (reception interface identification information) in the bridge control table  22 , as shown in  FIGS. 9A-9D . If transfer destination interface identification information is set in association with identification information on an interface by which the packet is received in the bridge control table  22 , the packet received is switched to the data links  26  of  FIG. 8 , which correspond to communication links  90 , respectively, without delivering the packet to the higher layer  10 . 
     If transfer destination interface identification information is not set or if an entry of reception interface identification information of a communication link via which the packet is received is not registered, processing for the received packet is terminated by the processing in the lower layer  20 . Then, the packet is delivered to the higher layer  10 . 
     In addition, in the second embodiment, also if bridge specification information of a received packet is not set, or the bridge specification information of the packet is reset, the packet is delivered to the higher layer  10 , and processed by the routing processing section  11 . 
     Since as an example three interfaces for the OSI network are provided in the embodiments of the present invention, optical input/output devices  24   a ,  24   b , and  24   c  and the HDLC drivers  24   a ,  24   b , and  24   c  are provided so as to correspond to the three communication links  90 . However, each of the HDLC LSI  24  and the LAPD driver  23  has a function to collectively process input/output data for the three interfaces. 
     In known apparatuses, LAPD driver data output from the LAPD driver  23  is directly input to the routing processing section  11  in the higher layer  10 , and the data is processed in the routing processing section  11 . For example, if the LAPD driver data relates to routing information on the OSI network, the LAPD driver data is properly processed in the routing processing section  11  and used for routing on the OSI network. If the LAPD driver data is user data to be delivered to a further higher layer, for example, the LAPD driver data is transferred to the supervisory controller  40  that performs processing in a higher layer. 
     In the above-mentioned embodiments, a case where three communication links  90  are provided for the bridge processing has been described, for the sake of explanation. However, the number of communication links  90  is not limited to this. 
       FIGS. 9A-9D  show examples of the bridge control table  22 . 
       FIG. 9A  is the bridge control table  22  of the packet transfer node  120 , and  FIG. 9B  is the bridge control table  22  of the packet transfer node  110 , according to the first embodiment of the present invention. 
       FIG. 9C  is the bridge control table  22  of the packet transfer node  120 , and  FIG. 9D  is the bridge control table  22  of the packet transfer node  110 , according to the second embodiment of the present invention. 
     In  FIGS. 9A-9D , reception interface identification information  221  is information for identifying a physical communication link of a received packet, and transfer destination interface identification information  222  is identification information indicating an interface corresponding to a communication link that is a transfer destination of the packet received from the communication link indicated by the reception interface identification information. The reception interface identification information  221  and the transfer destination interface identification information  222  can be any information that can identify a communication link, such as a MAC address and a port number. 
     If the transfer destination interface identification information  222  is not set, bridge processing in the lower layer  20  is not performed, and the packet is delivered to the higher layer  10 . If an entry of the reception interface identification information indicating the communication link via which a packet is received is not registered in the bridge control table  22 , the received packet is also delivered to the higher layer  10 . 
     In the setting example shown in  FIG. 9A , which shows the bridge control table  22  of the node  120  in  FIG. 5  according to the first embodiment, a packet P 1  received via a communication link  903  whose reception interface identification information indicates an interface  903  is not bridge processed by the lower layer  20 , and delivered to the higher layer  10 . Then, for example, for the OSI network, L1/L2 routing is performed. 
     In contrast, a packet P 2  received via the communication link  904  indicated as an interface  904  is transferred to the next transfer node  110  via the communication link  902   a  indicated as an interface  902   a , by the lower layer  20 , without being delivered to the higher layer  10 . That is, bridge processing is performed on the packet. 
       FIG. 9B  shows the setting example of the bridge control table  22  of the node  110  in  FIG. 5 , according to the first embodiment. A packet received via a communication link  902  whose reception interface identification information indicates an interface  902  in  FIG. 9B , is not bridge processed by the lower layer  20 , and delivered to the higher layer  10 . Then, for example, for the OSI network, L1/L2 routing is performed. In contrast, a packet received via the communication link  902   a  indicated as an interface  902   a  in  FIG. 9B , is transferred to the next transfer node  210  via the communication link  901   a  indicated as an interface  901   a  in  FIG. 9B , by the lower layer  20 , without being delivered to the higher layer  10 . That is, bridge processing is performed on the packet. 
     In the second embodiment, if bridge specification information (a bridge flag) stored in a received packet is not set, the received packet is delivered to the higher layer  10  without referring to the bridge control table  22 . 
     If bridge specification information (a bridge flag) stored in a received packet is set, and there is no destination information set in the bridge control table  22 , the received packet is delivered to the higher layer  10 . Otherwise, the bridge control table  22  is searched and the bridge processing is performed on the basis of the bridge control table  22 . 
     In the setting example shown in  FIG. 9C , which shows the bridge control table  22  of the node  120  in  FIG. 7  according to the second embodiment, a packet P 1  received via a communication link  903  is delivered to the higher layer  10  without referring to the bridge control table  22  because the bridge flag included in the received packet is reset. Then, for example, for the OSI network, L1/L2 routing is performed. In contrast, a packet P 2  received via the communication link  904  indicated as an interface  904  in  FIG. 9C , includes the bridge flag set at “ON” and the bridge control table  22  includes the corresponding entry with reception identification information of an interface  904 . Therefore, the received packet is transferred to the next transfer node  110  via the communication link  902  indicated as an interface  902  in  FIG. 9C , by the lower layer  20 , without being delivered to the higher layer  10 . That is, bridge processing is performed on the packet. 
     In the setting example shown in  FIG. 9D , which shows the bridge control table  22  of the node  110  in  FIG. 7  according to the second embodiment, if a bridge flag included in a packet received via a communication link  902  is reset, the received packet is delivered to the higher layer  10 , without referring to the bridge control table  22  and, for example L1/L2 routing is performed. If the bridge flag included in the received packet is “ON”, the bridge control table  22  (as shown in  FIG. 9D ) is referred to. The bridge control table  22  of  FIG. 9D  includes the corresponding entry with reception identification information of an interface  902  and the corresponding transfer destination identification information (interface  901  in  FIG. 9D ) is set. Therefore, the received packet is transferred to the next transfer node  210  via the communication link  901  indicated as an interface  901  in the bridge control table  22 , by the lower layer  20 , without being delivered to the higher layer  10 . That is, bridge processing is performed on the packet. 
     As shown in  FIGS. 9A-9D , it is understood that the size of the information set to the bridge control table  22 ,  22   a  is small and the information is set only to the nodes that perform the bridge processing. Therefore, the influence of the bridge control table  22 ,  22   a  on the memory resources of packet transfer nodes in the network is slight, compared with the influence of the routing table  12  on the memory resources of the packet transfer nodes. 
     A value different depending on the packet transfer node can be set in advance in the bridge control table  22  by various methods such as the supervisory controller  40  shown in the structural example in  FIG. 8 . 
       FIG. 10  shows an example of the structure of packet data according to the embodiments of the present invention. In  FIG. 10 , a structural example of packet data transferred between the LAP-D driver  23  and the bridge processing section  21  in the lower layer  20  in the structural example of the packet transfer node shown in  FIG. 8  is shown. 
     Packet data  800  includes reception interface identification information  810 , a packet size  820 , and a packet body  830 . 
     The reception interface identification information  810  is interface identification information indicating a communication link via which the packet data is transferred, and is set, for example, by the LAP-D driver  23 . The reception interface identification information  810  can be any information that can identify a communication link, such as a MAC address and a port number. 
     In known packet transfer nodes, this interface information is directly delivered to the routing processing section  11  in the higher layer  10  without being used in the lower layer  20 . 
     According to the embodiment, the reception interface identification information  810  is compared with the reception interface identification information  221  set in the bridge control table  22  shown in  FIGS. 9A-9D . If a corresponding entry with the corresponding transfer destination identification information  222  is found in the bridge control table  22 , bridge processing is performed. That is, the packet body  830  is extracted by referring to the packet size  820 , and the packet body  830  is transferred to the communication link indicated by the transfer destination interface identification information  222  without delivering the packet body  830  to the higher layer  10 . 
     In the second embodiment, bridge specification information  831 , or a bridge flag  831 , is stored, for example, in part of the packet body  830 , although the embodiment is not limited to such a configuration and the bridge flag  831  can be set according to any known technique. 
     The packet body  830  includes a header part and a payload part (not shown in  FIG. 10 ), and a bridge flag  831  can be stored in any one of the header part and the payload part. 
     For a packet transfer node according to the second embodiment, when the bridge specification information  831  in the packet data  800  delivered from the LAP-D driver  23  indicates “ON”, the bridge control table  22  in the lower layer  20  is referred to, and if the corresponding transfer destination interface identification information is set bridge processing is performed. If the corresponding transfer destination interface identification information is not set in the bridge control table  22 , “OFF” is set to the bridge specification information  831 , and the packet body  830  is delivered to the higher layer  10 . 
       FIG. 11  is a flowchart showing bridge processing according to the first embodiment. 
     In step S 10 , the reception interface identification information  810  is extracted from the packet data  800  shown in  FIG. 10  by a bridge processing section  21 . 
     In step S 020 , the bridge control table  22  is searched using, as a key, the reception interface identification information  810  extracted in step S 010  by the bridge processing section  21 . 
     In step S 030 , if an entry that corresponds to the reception interface identification information  810  exists in the bridge control table  22  (if the determination in step S 030  is YES), the processing proceeds to step S 040 . If an entry that corresponds to the reception interface identification information  810  does not exist in the bridge control table  22  (if the determination in step S 030  is NO), the processing proceeds to step S 060 . 
     In step S 040 , it is determined, by the bridge processing section  21 , whether transfer destination interface identification information is set corresponding to the reception interface entry found in step S 030 . If the transfer destination interface identification information is set (if the determination in step S 040  is YES), the processing proceeds to step S 050 . If transfer destination interface identification information is not set (if the determination in step S 040  is NO), the processing proceeds to step S 060 . 
     In step S 050 , the packet body  830  is transferred by the bridge processing section  21  to a communication link indicated by the transfer destination interface identification information extracted in step S 040 , and the lower layer  20  processing is terminated without delivering the packet data  800  to the higher layer  10 . That is, bridge processing in the lower layer  20  is performed. 
     In step S 060 , the packet is subjected to routing processing in the higher layer  10 , and the lower layer  20  processing is terminated. 
     As described above, in the first embodiment, a communication link used for bridge processing is provided independent of an existing communication link, and interface identification information on the communication link used for bridge processing is set in advance in the bridge control table  22 . Thus, packet transfer can be performed via the communication link used for bridge processing without affecting the known routing processing performed in the higher layer  10 . 
       FIG. 12  is a flowchart showing bridge processing according to the second embodiment. 
     In the bridge processing shown in  FIG. 12  according to the second embodiment, processing of extracting bridge specification information  831  from a packet and determining the bridge specification information (step S 005 ) and processing of resetting the bridge specification information (step S 055 ) are added to the bridge processing shown in  FIG. 11  according to the first embodiment. 
     In step S 005 , bridge specification information  831  set in a received packet is extracted. If a value indicating that the packet is a target of bridge processing (for example, “ON”) is set (if the determination in step S 005  is YES), the processing proceeds to step S 010 . If a value indicating that the packet is not a target of bridge processing (for example, “OFF”) is set (if the determination in step S 005  is NO), the processing proceeds to step S 060 . 
     In step S 010 , the reception interface identification information  810  is extracted from the packet data  800  shown in  FIG. 10  by a bridge processing section  21 . 
     In step S 020 , the bridge control table  22  is searched using, as a key, the reception interface identification information  810  extracted in step S 010  by the bridge processing section  21 . 
     In step S 030 , if an entry that corresponds to the reception interface identification information  810  exists in the bridge control table  22  (if the determination in step S 030  is YES), the processing proceeds to step S 040 . If an entry that corresponds to the reception interface identification information  810  does not exist in the bridge control table  22  (if the determination in step S 030  is NO), the processing proceeds to step S 055 . 
     In step S 040 , it is determined, by a bridge processing section  21 , whether transfer destination interface identification information is set for the reception interface entry found in step S 030 . If transfer destination interface identification information is set (if the determination in step S 040  is YES), the processing proceeds to step S 050 . If transfer destination interface identification information is not set (if the determination in step S 040  is NO), the processing proceeds to step S 055 . 
     In step S 050 , a packet is transferred to a communication link indicated by the transfer destination interface identification information extracted in step S 040 , and the lower layer  20  processing is terminated without delivering the packet data  800  to the higher layer  10 . 
     In step S 055 , the bridge specification information in the packet is reset (set to “OFF”). 
     In step S 060 , the packet is subjected to routing processing in the higher layer  10 , and the processing is terminated. 
     As described above, in the second embodiment, bridge specification information, which is identification information indicating whether or not a packet is a target of bridge processing, is provided. If the bridge specification information is not set (indicates “OFF”), the packet is subjected to routing processing in the higher layer. If the bridge specification information indicates “ON”, bridge processing in the lower layer can be performed on the basis of the bridge control table  21   a , using a communication link identical to the communication link used for routing processing in the higher layer. Thus, it is unnecessary to provide a communication link used for bridge processing, unlike the first embodiment. 
     The described embodiment processes are implemented in software and/or computing hardware. An apparatus, a method, and computer-readable media according to the embodiment are provided. The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to falling within the scope thereof.