Router device and datagram transfer method for data communication network system

Abstract

A router device realizing a datagram transfer method for improving the datagram transfer efficiency by ascertaining the transfer target and/or the requested quality of service without referring to the datagram content. The router device has network interfaces connected with networks including at least one virtual connection oriented network, a table for registering a correspondence between a virtual connection identifier and a transfer target network interface and/or a quality of service, a connection identifier analysis unit for determining a transfer target network interface and/or a quality of service for a datagram entered from one virtual connection, by referring to the table according to a virtual connection identifier of that one virtual connection. The datagram can be transferred to the determined transfer target network interface, while applying a priority control for datagrams to be transferred by the router device according to the determined quality of service.

1. A router device for transferring datagrams among networks comprising:
 network interfaces connected with networks including at least one virtual connection oriented network;    a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;    connection identifier analysis means for determining a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transfer means for transferring the datagram to the transfer target network interface determined by the connection identifier analysis means.    
     
     
       2. The router device of  claim 1 , further comprising reception means for receiving a datalink frame from the virtual connection and assembling the datalink frame into the datagram. 
     
     
       3. The router device of  claim 1 , wherein the memory also stores a correspondence between a virtual connection identifier and an output virtual connection identifier to be used in a case where a network connected with the transfer target network interface is a virtual connection oriented network. 
     
     
       4. The router device of  claim 3 , wherein the connection identifier analysis means also notifies an output virtual connection identifier for the datagram to the transfer target network interface. 
     
     
       5. The  A router device of  claim 1   for transferring datagrams among networks comprising:
   network interfaces connected with networks including at least one virtual connection oriented network;    
   a memory configured to store a correspondence between a virtual connection identifier and a transfer target network interface;    
   a connection identifier analysis unit configured to determine a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    
   a transfer unit configured to transfer the datagram to the transfer target network interface determined by the connection identifier analysis unit ,  
 wherein the memory also stores a correspondence between a  the virtual connection identifier and a next hop network layer address to be used in a case where network connected with the transfer target network interface is a non-virtual connection oriented network.  
 
     
     
       6. The router device of  claim 5 , wherein the connection identifier analysis means  unit also notifies a next hop network layer address for the datagram to the transfer target network interface. 
     
     
       7. The  A router device of  claim 1 , further comprising:  for transferring datagrams among networks comprising:
   network interfaces connected with networks including at least one virtual connection oriented network;    
   a memory configured to store a correspondence between a virtual connection identifier and a transfer target network interface;    
   a connection identifier analysis unit configured to determine a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;    
   a transfer unit configured to transfer the datagram to the transfer target network interface determined by the connection identifier analysis unit; and    
 a datagram analysis means for registeringunit configured to register in advance a correspondence between a datagram content and a transfer target network interface, and determiningto determine a transfer target network interface for the datagram according to a datagram content of the datagram when the memory does not store the transfer target network interface in correspondence to the virtual connection identifier of the virtual connection; ,  
 wherein the transfer means  unit transfers the datagram to the transfer target network interface determined by the datagram analysis means  unit when the memory does not store the transfer target network interface in correspondence to the virtual connection identifier of the virtual connection.  
 
     
     
       8. The  A router device of  claim 1   for transferring datagrams among networks comprising:
   network interfaces connected with networks including at least one virtual connection oriented network;    
   a memory configured to store a correspondence between a virtual connection identifier and a transfer target network interface;    
   a connection identifier analysis unit configured to determine a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    
   a transfer unit configured to transfer the datagram to the transfer target network interface determined by the connection identifier analysis unit,  wherein: 
 the memory also stores a correspondence between a virtual connection identifier and a quality of service;    the connection identifier analysis means  unit also determines a quality of service for the datagram by referring to the memory according to a virtual connection identifier of the virtual connection; and    the router device further comprises: 
 a scheduler means for applyingconfigured to apply a priority control for datagrams to be transferred by the router device according to the quality of service determined by the connection identifier analysis meansunit, such that the transfer meansunit transfers the datagram to which the priority control is applied by the scheduler means .  
   
 
     
     
       9. The router device of  claim 8 , further comprising:
 a datagram analysis means for registeringunit configured to register in advance a correspondence between a datagram content and a transfer target network interface, and determiningto determine a transfer target network interface for the datagram to which the priority control is applied by the scheduler means  according to a datagram content of the datagram;  
 wherein the scheduler means  makes the priority control of orders in which datagrams are given to the datagram analysis means  unit.  
 
     
     
       10. The router device of  claim 8 , further comprising:
 processing means for determininga processor configured to determine a transfer target network interface and/or next hop network layer address and to applyingapply a network layer processing for the datagram to be transferred by the router device;,  
 wherein the scheduler means  makes the priority control of orders in which datagrams are given to the processing means  processor.  
 
     
     
       11. The router device of  claim 1 , further comprising
 datagram processing means for applying a network layer processing to the datagram to be transferred by the router device.    
     
     
       12. The  A router device of  claim 11   for transferring datagrams among networks comprising:
   network interfaces connected with networks including at least one virtual connection oriented network;    
   a memory configured to store a correspondence between a virtual connection identifier and a transfer target network interface;    
   a connection identifier analysis unit configured to determine a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    
   a transfer unit configured to transfer the datagram to the transfer target network interface determined by the connection identifier analysis unit; and    
   a datagram processing unit configured to apply network layer processing to the datagram to be transferred by the router device , wherein the datagram processing meansunit is separately provided for each network interface.  
 
     
     
       13. A router device for transferring datagrams among networks, comprising:
 at least one network interface connected with at least one virtual connection oriented network;    a memory for storing a correspondence between a virtual connection identifier and an output virtual connection identifier;    connection identifier analysis means for determining an output virtual connection identifier for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transfer means for transferring the datagram such that the datagram is outputted to a virtual connection having the output virtual connection identifier determined by the connection identifier analysis means.    
     
     
       14. The router device of  claim 13 , further comprising reception means for receiving a datalink frame from the virtual connection and assembling the datalink frame into the datagram. 
     
     
       15. A router device for transferring datagrams among networks, comprising:
 at least one network interface connected with at least one virtual connection oriented network;  
 a memory for storing  configured to store a correspondence between a virtual connection identifier and a quality of service;  
 a connection identifier analysis means for determiningunit configured to determine a quality of service for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;  
 a scheduler means for applyingconfigured to apply a priority control for datagrams to be transferred by the router device according to the quality of service determined by the connection identifier analysis meansunit; and  
 a transfer means for transferringunit configured to transfer the datagram to which the priority control is applied by the scheduler means .  
 
     
     
       16. The router device of  claim 15 , further comprising:
 a datagram analysis means for registeringunit configured to register in advance a correspondence between a datagram content and a transfer target network interface, and determiningto determine a transfer target network interface for the datagram to which the priority control is applied by the scheduler means  according to a datagram content of the datagram; ,  
 wherein the scheduler means  makes the priority control of orders in which datagrams are given to the datagram analysis means  unit.  
 
     
     
       17. The router device of  claim 15 , further comprising:
 processing means for determininga processor configured to determine a transfer target network interface and/or next hop network layer address and to applying a  network layer processing for the datagram to be transferred by the router device; ,  
 wherein the scheduler means  makes the priority control of orders in which datagrams are given to the processing means  processor.  
 
     
     
       18. A router device for transferring AAL frames from an ATM network through network interfaces connected with networks including at least one ATM network, each network interface connected with said at least one ATM network including reception means for receiving ATM cells from an ATM network and assembling an AAL frame from the received ATM cells, and transmission means for forming ATM cells from an AAL frame and transmitting the formed ATM cells to an ATM network, the router device comprising:
 a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;    connection identifier analysis means for determining a transfer target network interface for an AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;    processing means for determining a transfer target network interface for the AAL frame by assembling datagram from the AAL frame and analyzing the assembled datagram, when the memory does not store the transfer target network interface in correspondence to the virtual connection identifier of the virtual connection; and    transfer means for transferring the AAL frame to the transfer target network interface determined by one of the connection identifier analysis means and the processing means.    
     
     
       19. An ATM network interface card device for interfacing an ATM network and a bus for connecting other network interfaces connected with other networks, the ATM network interface card device comprising:
 reception means for receiving ATM cells from the ATM network and assembling an AAL frame from the received ATM cells;    a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;    connection identifier analysis means for determining a transfer target network interface for an AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transfer means for transferring the AAL frame through the bus to the transfer target network interface determined by the connection identifier analysis means.    
     
     
       20. A router device for transferring datagrams among networks, comprising:
 at least one network interface connected with at least one virtual connection oriented network;  
 a memory for storing  configured to store a correspondence between a virtual connection identifier and a protocol type information indicating a type and/or a version of a protocol;  
 a connection identifier analysis means for determiningunit configured to determine a protocol type information for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;  
 a datagram analysis means for determiningunit configured to determine a transfer target network interface/next hop network layer address for the datagram according to a datagram content of the datagram, the datagram analysis meansunit having a plurality of processors in correspondence to different protocols, and the datagram is entered into one of said plurality of processors which corresponds to a protocol of a type and/or a version indicated by the protocol type information determined by the connection identifier analysis meansunit; and  
 a transfer means for transferringunit configured to determine the datagram to the transfer target network interface/next hop network layer address determined by the datagram analysis meansunit.  
 
     
     
       21. A method for transferring datagrams among networks, using a router device having network interfaces connected with networks including at least one virtual connection oriented network, the method comprising the steps of:
 storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory provided at the router device;    determining a transfer target network interface for a datagram entered from a virtual connection at the router device, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transferring the datagram to the transfer target network interface determined by the determining step.    
     
     
       22. A method for transferring datagrams among networks, using a router device having at least one network interface connected with at least one virtual connection oriented network, the method comprising the steps of:
 storing a correspondence between a virtual connection identifier and an output virtual connection identifier in a memory provided at the router device;    determining an output virtual connection identifier for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transferring the datagram such that the datagram is outputted to a virtual connection having the output virtual connection identifier determined by the determining step.    
     
     
       23. A method for transferring datagrams among networks, using a router device having at least one network interface connected with at least one virtual connection oriented network, the method comprising the steps of:
 storing a correspondence between a virtual connection identifier and a quality of service in a memory provided at the router device;  
 determining a quality of service for a datagram entered from a virtual connection at the router device, by referring to the memory according to a virtual connection identifier of the virtual connection;  
 applying a priority control for datagrams to be transferred by the router device according to the quality of service determined by the determining step; and  
 transferring the datagram to which the priority control is applied by the applying step.  
 
     
     
       24. A method for transferring AAL frames from an ATM network, using a router device having network interfaces connected with networks including at least one ATM network, each network interface connected with said at least one ATM network including reception means for receiving ATM cells from an ATM network and assembling an AAL frame from the received ATM cells, and transmission means for forming ATM cells from an AAL frame and transmitting the formed ATM cells to an ATM network, the method comprising the steps of:
 storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory provided at the router device;    determining a transfer target network interface for an AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;    processing the AAL frame to determine a transfer target network interface for the AAL frame by assembling datagram from the AAL frame and analyzing the assembled datagram, when the memory does not store the transfer target network interface in correspondence to the virtual connection identifier of the virtual connection; and    transferring the AAL frame to the transfer target network interface determined by one of the determining step and the processing step.    
     
     
       25. A method for interfacing an ATM network and a bus for connecting other network interfaces connected with other networks, the method comprising the steps of:
 receiving ATM cells from the ATM network and assembling an AAL frame from the received ATM cells;    storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory;    determining a transfer target network interface for an AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and    transferring the AAL frame through the bus to the transfer target network interface determined by the determining step.    
     
     
       26. A method for transferring datagrams among networks, using a router device having at least one network interface connected with at least one virtual connection oriented network, the method comprising the steps of:
 storing a correspondence between a virtual connection identifier and a protocol type information indicating a type and/or a version of a protocol in a memory provided at the router device;  
 determining a protocol type information for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;  
 determining a transfer target network interface/next hop network layer address for the datagram according to a datagram content of the datagram, wherein a plurality of processors are provided at the router device in correspondence to different protocols, and the datagram is entered into one of said plurality of processors which corresponds to a protocol of a type and/or a version indicated by the protocol type information determined by the determining step; and  
 transferring the datagram to the determined transfer target network interface/next hop network layer address.  
 
     
     
       27. A data communication network system, comprising:
 networks including at least one virtual connection oriented network;    a transmission node provided in each network for transmitting datagrams such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection; and    a router device for connecting at least two of the networks, the router device including: 
 network interfaces connected with said at least two of the networks;  
 a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;  
 connection identifier analysis means for determining a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and  
 transfer means for transferring the datagram to the transfer target network interface determined by the connection identifier analysis means.  
   
     
     
       28. A data communication network system, comprising:
 networks including at least one virtual connection oriented network;    a transmission node provided in each network for transmitting datagrams such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection; and    a router device for connecting at least two of the networks, the router device including: 
 at least one network interface connected with said at least two of the networks;  
 a memory for storing a correspondence between a virtual connection identifier and an output virtual connection identifier;  
 connection identifier analysis means for determining an output virtual connection identifier for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and  
 transfer means for transferring the datagram such that the datagram is outputted to a virtual connection having the output virtual connection identifier determined by the connection identifier analysis means.  
   
     
     
       29. A data communication network system, comprising:
 networks including at least one virtual connection oriented network;  
 a transmission node provided in each network for transmitting  configured to transmit datagrams such that datagrams with an identical quality of service are transmitted through at least one specific virtual connection; and  
 a router device for connecting  configured to connect at least two of the networks, the router device including: , 
 at least one network interface connected with said at least two of the networks; ,  
 a memory for storing  configured to store a correspondence between a virtual connection identifier and a quality of service; ,  
 a connection identifier analysis unit means for determiningconfigured to determine a quality of service for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;,  
 a scheduler means for applyingconfigured to apply a priority control for datagrams to be transferred by the router device according to the quality of service determined by the connection identifier analysis means;, and  
 a transfer means for transferringunit configured to transfer the datagram to which the priority control is applied by the schedulermeans .  
 
 
     
     
       30. A data communication network system, comprising:
 networks including at least one ATM network;    a transmission node provided in each network for transmitting datagrams such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection; and    a router device for connecting at least two of the networks, and for transferring AAL frames from an ATM network through network interfaces connected with the networks, each network interface connected with said at least one ATM network including reception means for receiving ATM cells from an ATM network and assembling an AAL frame from the received ATM cells, and    transmission means for forming ATM cells from an AAL frame and transmitting the formed ATM cells to an ATM network, the router device including: 
 a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;  
 connection identifier analysis means for determining a transfer target network interface for an AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;  
 processing means for determining a transfer target network interface for the AAL frame by assembling datagram from the AAL frame and analyzing the assembled datagram, when the memory does not store the transfer target network interface in correspondence to the virtual connection identifier of the virtual connection; and  
 transfer means for transferring the AAL frame to the transfer target network interface determined by one of the connection identifier analysis means and the processing means.  
   
     
     
       31. A data communication network system, comprising:
 networks including at least one ATM network;    a transmission node provided in each network for transmitting datagrams such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection; and    a router device for connecting at least two of the networks including an ATM network; and    an ATM network interface card device for interfacing an ATM network and a bus for connecting other network interfaces connected with other networks, the ATM network interface card device including: 
 reception means for receiving ATM cells from the ATM network and assembling an AAL frame from the received ATM cells;  
 a memory for storing a correspondence between a virtual connection identifier and a transfer target network interface;  
 connection identifier analysis means for determining a transfer target network interface for a AAL frame assembled from ATM cells entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; and  
 transfer means for transferring the AAL frame through the bus to the transfer target network interface determined by the connection identifier analysis means.  
   
     
     
       32. A data communication network system, comprising:
 networks including at least one virtual connection oriented network;  
 a transmission node provided in each network for transmitting  configured to transmit datagrams such that datagrams of an identical protocol type and/or version are transmitted through at least one specific virtual connection; and  
 a router device for connecting  configured to connect at least two of the networks, the router device including: , 
 at least one network interface connected with said at least two of the networks; ,  
 a memory for storing  configured to store a correspondence between a virtual connection identifier and a protocol type information indicating a type and/or a version of a protocol; ,  
 a connection identifier analysis means for determiningunit configured to determine a protocol type information for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection; ,  
 a datagram analysis unit means for determiningconfigured to determine a transfer target network interface/next hop network layer address for the datagram according to a datagram content of the datagram, the datagram analysis meansunit having a plurality of processors in correspondence to different protocols, and the datagram is entered into one of said plurality of processors which corresponds to a protocol of a type and/or a version indicated by the protocol type information determined by the connection identifier analysis means;unit, and  
 a transfer means for transferringunit configured to transfer the datagram to the transfer target network interface/next hop network layer address determined by the datagram analysis meansunit.  
 
 
     
     
       33. A transmission node device for transmitting datagrams to a router device, comprising:
 a memory for storing a correspondence between a destination and an output virtual connection identifier, the correspondence being known to the router device;    datagram analysis means for determining an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a destination of the datagram; and    transmission means for transmitting the datagram to a virtual connection having the output virtual connection identifier determined by the datagram analysis means, such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection.    
     
     
       34. A transmission node device for transmitting datagrams to a router device, comprising:
 a memory for storing  configured to store a correspondence between a quality of service specifying information indicating a quality of service and an output virtual connection identifier, the correspondence being known to the router device;  
 a datagram analysis means for determiningunit configured to determine an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a quality of service specifying information of the datagram; and  
 a transmission means for transmittingunit configured to transfer the datagram to a virtual connection having a virtual connection identifier identical to the output virtual connection identifier determined by the datagram analysis meansunit, such that datagrams with an identical quality of service specifying information are transmitted through at least one specific virtual connection.  
 
     
     
       35. A transmission node device for transmitting datagrams to a router device, comprising:
 a memory for storing  configured to store a correspondence between a protocol type information indicating a type and/or a version of a protocol and an output virtual connection identifier, the correspondence being known to the router device;  
 a datagram analysis means for determiningunit configured to determine an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a type and/or a version of a protocol of the datagram; and  
 a transmission means for transmittingunit configured to transmit the datagram to a virtual connection having a virtual connection identifier identical to the output virtual connection identifier determined by the datagram analysis meansunit, such that datagrams of an identical protocol type and/or version are transmitted through at least one specific virtual connection.  
 
     
     
       36. A method for transmitting datagrams to a router device, comprising the steps of:
 storing in a memory a correspondence between a destination and an output virtual connection identifier, the correspondence being known to the router device;    determining an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a destination of the datagram; and    transmitting the datagram to a virtual connection having the output virtual connection identifier determined by the determining step, such that datagrams destined to an identical destination are transmitted through at least one specific virtual connection.    
     
     
       37. A method for transmitting datagrams to a router device, comprising the steps of:
 storing in a memory a correspondence between a quality of service specifying information indicating a quality of service and an output virtual connection identifier, the correspondence being known to the router device;  
 determining an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a quality of service specifying information of the datagram; and  
 transmitting the datagram to a virtual connection having a virtual connection identifier identical to the output virtual connection identifier determined by the determining step, such that datagrams with an identical quality of service specifying information are transmitted through at least one specific virtual connection.  
 
     
     
       38. A method for transmitting datagrams to a router device, comprising the steps of:
 storing in a memory a correspondence between a protocol type information indicating a type and/or a version of a protocol and an output virtual connection identifier, the correspondence being known to the router device;  
 determining an output virtual connection identifier for a datagram to be transmitted, by referring to the memory according to a type and/or a version of a protocol of the datagram; and  
 transmitting the datagram to a virtual connection having a virtual connection identifier identical to the output virtual connection identifier determined by the determining step, such that datagrams of an identical protocol type and/or version are transmitted through at least one specific virtual connection.  
 
     
     
       39. A router device for transferring datagrams among networks comprising:
   network interfaces connected with networks including at least one virtual connection oriented network and at least one non - virtual connection oriented network;        a memory configured to store a correspondence between a virtual connection identifier and a transfer target network interface, and also to store a correspondence between the virtual connection identifier and a network layer address;        a first connection identifier analysis unit configured to determine a transfer target network interface for a datagram entered from a virtual connection, by referring to the memory according to a virtual connection identifier of the virtual connection;        a second connection identifier analysis unit configured to determine a transfer target network layer address for the datagram entered from the virtual connection, by referring to the memory according to the virtual connection identifier of the virtual connection;        a first transfer unit configured to transfer the datagram to the transfer target network interface connected with another virtual connection oriented network, when the transfer target network interface is determined by the first connection identifier analysis unit; and        a second transfer unit configured to transfer the datagram to the transfer target network interface connected with the at least one non - virtual connection oriented network toward the transfer target network layer address, when the transfer target network layer address is determined by the second connection identifier analysis unit.     
     
     
       40. A router device according to  claim 39 , wherein:
   the transfer target network interface is configured to transfer the datagrams toward a datalink address determined using the transfer target network layer address.     
     
     
       41. A router device according to  claim 39 , wherein:
   a transfer target of the datagram is determined without referring to the datagram content.     
     
     
       42. A method for transferring datagrams among networks, using a router device having network interfaces connected with networks including at least one virtual connection oriented network and at least one non- virtual connection oriented network, the method comprising the steps of:      storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory provided at the router device, and also storing a correspondence between the virtual connection identifier and a network layer address        first determining a transfer target network interface for a datagram entered from a virtual connection at the router device, by referring to the memory according to a virtual connection identifier of the virtual connection;        second determining a transfer target network layer address for the datagram entered from the virtual connection, by referring to the memory according to the virtual connection identifier of the virtual connection;        first transferring the datagram to the transfer target network interface connected with another virtual connection oriented network, when the transfer target network interface is determined by the first determining step; and        second transferring the datagram to the transfer target network interface connected with the at least one non - virtual connection oriented network toward the transfer target network layer address, when the transfer target network layer address is determined by the second determining step.     
     
     
       43. A method according to  claim 42 , wherein:
   the step of second transferring transmits the datagrams from the transfer target network interface toward a datalink address determined using the transfer target network layer address.     
     
     
       44. A method according to  claim 42 , wherein:
   the step of determining the transfer target network layer address is performed without referring to the datagram content.     
     
     
       45. A method for transferring datagrams among networks, using at least two router devices having network interfaces connected with networks including at least one virtual connection oriented network, the method comprising the steps of:
   storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory provided at a router device;        determining transfer target network interface for a datagram entered from a virtual connection at the router device, by referring to the memory according to a virtual connection identifier of the virtual connection on which the datagram is received;        transferring the datagram to the transfer target network interface determined by the determining step;        first transmitting the datagram along with another virtual connection identifier from the transfer target network interface over a second virtual connection to another router device;        receiving the datagram, at said another router device, from the transfer target network interface at the router device over the second virtual connection;        removing said another virtual connection identifier from the datagram at said another router device; and        second transmitting said datagram, at said another router device, away from said another router device without said another virtual connection identifier, and without adding another virtual connection identifier.     
     
     
       46. A method according to  claim 45 , wherein said step of second transmitting said datagram away from said another router device comprises transmitting said datagram over a non- virtual connection oriented network.   
     
     
       47. A method according to  claim 46 , wherein said step of second transmitting said datagram way from said another router device comprises transmitting said datagram to a location using a network layer address associated with the datagram. 
     
     
       48. A method according to  claim 45 , wherein said step of second transmitting said datagram way from said another router device comprises transmitting said datagram to a location using a network layer address associated with the datagram. 
     
     
       49. A method according to  claim 48 , wherein said step of second transmitting said datagram way from said another router device comprises transmitting said datagram without referring to the datagram content to a location using a network layer address associated with the datagram. 
     
     
       50. A method for transferring datagrams among networks, using a router device having network interfaces connected with networks including at least one virtual connection oriented network, the method comprising the steps of:
   storing a correspondence between a virtual connection identifier and a transfer target network interface in a memory provided at the router device;        determining a transfer target network interface for a datagram entered from a virtual connection at the router device, by referring to the memory according to a virtual connection identifier of the virtual connection on which the datagram is received;        transferring the datagram to the transfer target network interface determined by the determining step; and        transmitting said datagram from the router device without said virtual connection identifier, and without adding another virtual connection identifier.     
     
     
       51. A plurality of router devices for transferring datagrams among networks, comprising:
   a first router device including,      a first set of network interfaces connected to at least a first virtual connection oriented network,        a first memory configured to store a first correspondence between a first input virtual connection identifier and a first transfer target network interface,        a first connection identifier analysis unit configured to determine the first transfer target network interface for a first datagram entered from a first input virtual connection, by referring to the first memory according to the first input virtual connection identifier of the first virtual connection, and        a first transfer unit configured to transfer the first datagram to the first transfer target network interface determined by the first connection identifier analysis unit; and          a second router device including,      a second set of network interfaces connected to at least a second virtual connection oriented network,        a second memory configured to store a second correspondence between a second input virtual connection identifier and a next hop layer address to be used in a case where the second set of network interfaces is connected to at least a non - virtual connection oriented network,        a second connection identifier analysis unit configured to determine a second transfer target network interface for a second datagram entered from a second input virtual connection, by referring to the second memory according to the second input virtual connection identifier of the second virtual connection, and        a second transfer unit configured to transfer the second datagram to the second transfer target network interface determined by the second connection identifier analysis unit.       
     
     
       52. A method for transferring datagrams among networks, using a first router device and a second router device having network interfaces connected with networks including at least one virtual connection oriented network, the method comprising the steps of:
   storing a correspondence between a first virtual connection identifier and a first transfer target network interface in a memory provided at the first router device;        determining a first transfer target network interface for a datagram entered from a first virtual connection at the first router, by referring to the memory provided at the first router device according to a virtual connection identifier of the first virtual connection;        transferring the datagram entered from the first virtual connection to the first transfer target network interface determined by the determining step;        storing a correspondence between a second virtual connection identifier and a second transfer target network interface in a memory provided at the second router device, said second transfer target network interface being connected to a next hop network layer address to be used in a case where the network interfaces of the second router is connected to at least a non - virtual connection oriented network;        determining a second transfer target network interface for a datagram entered from a second virtual connection at the second router, by referring to the memory provided at the second router device according to a virtual connection identifier of the second virtual connection;        transferring the datagram entered at the second virtual connection to the second transfer target network interface determined by the determining step.     
     
     
       53. A plurality of router devices for transferring datagrams among networks, comprising:
   a first router device including,        a first set of network interfaces connected to at least a first virtual connection oriented network,        a first memory configured to store a first correspondence between a first input virtual connection identifier and a first output virtual connection identifier,        a first connection identifier analysis unit configured to determine the first transfer target network interface for a first datagram entered from a first input virtual connection, by referring to the first memory according to the first input virtual connection identifier of the first virtual connection, and        a first transfer unit configured to transfer the first datagram to the first transfer target network interface determined by the first connection identifier analysis unit        a second router device including,        a second set of network interfaces connected to at least a second virtual connection oriented network,        a second memory configured to store a second correspondence between a second input virtual connection identifier, a second transfer target network interface, and a second output virtual connection identifier,        a second connection identifier analysis unit configured to determine the second transfer target network interface for a second datagram entered from a second input virtual connection, by referring to the second memory according to the second input virtual connection identifier of the second virtual connection, and        a second transfer unit configured to transfer the second datagram to the second transfer target network interface determined by the second connection identifier analysis unit without attaching said second output virtual connection identifier to said second datagram.     
     
     
       54. A method for transferring datagrams among networks, using a first router device and a second router device having network interfaces connected with networks including at least one virtual connection oriented network, the method comprising the steps of:
   storing a correspondence between a first virtual connection identifier and a first transfer target network interface in a memory provided at the first router device;        determining a first transfer target network interface for a datagram entered from a first virtual connection at the first router, by referring to the memory provided at the first router device according to a virtual connection identifier of the first virtual connection;        transferring the datagram entered from the first virtual connection to the first transfer target network interface determined by the determining step;        storing a correspondence between a second virtual connection identifier and a second transfer target network interface in a memory provided at the second router device;        determining a second transfer target network interface for a datagram entered from a second virtual connection at the second router, by referring to the memory provided at the second router device according to a virtual connection identifier of the second virtual connection; and        transferring the datagram entered at the second virtual connection to the second transfer target network interface determined by the determining step without attaching an output virtual connection identifier to said datagram entered from the second virtual connection.