Packet transmission node device realizing packet transfer scheme and control information transfer scheme using multiple virtual connections

A packet transmission node which realizes a packet transfer scheme in which a plurality of virtual connections for different qualities of service are set up in correspondence to a multicast destination address, and output virtual connection identifiers are stored in correspondence to destination addresses in a routing table, so that a packet is transferred to output virtual connections determined by referring to the routing table according to a destination address of a packet. A packet transmission node also realizes a control information transfer scheme in which different output virtual connections are set up for a user data packet and a control packet having an identical destination address, and output virtual connection identifiers are stored in correspondence to destination addresses and upper layer protocol identifiers in a routing table, so that a packet is transferred to an output virtual connection determined by referring to the routing table according to a destination address and an upper layer protocol identifier of a packet.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a packet transmission node device which 
functions as a router or a host for transmitting and receiving packets by 
being connected to a virtual connection oriented network, and a packet 
transfer scheme and a control information transfer scheme used in a packet 
transmission node device. 
2. Description of the Background Art 
A virtual connection oriented network is a network based on techniques such 
as ATM (Asynchronous Transfer Mode), frame relay, fiber channel, HIPPI 
(High Performance Parallel Interface), etc. 
On such a network, it is possible to realize a multicast in which a packet 
sent by a sender to a destination address for multicast (a multicast 
address) in a network layer is distributed to a plurality of receivers by 
the network. In the following, for the sake of simplicity, a case of an IP 
(Internet Protocol) multicast communication on an ATM network which uses 
IP as the network layer will be described. 
FIG. 1 shows a conventional scheme for transferring a packet destined to a 
multicast address G in an IP multicast communication system. In FIG. 1, H0 
to H9 are hosts, where H0 is a sender, and H1, H2, H4, H5, H6, H7 and H8 
are receivers. R is a router for transferring a packet, which is connected 
with the hosts H0 to H9 through ATM connections. 
When the network layer is IP, each node (host or router) belongs to a 
logical group called IP subnet. The communication within the same IP 
subnet is realized by the direct transfer without passing through a 
router, while the communication between different IP subnets is realized 
by utilizing a packet transfer at a router. In FIG. 1, H0, H8 and R belong 
to an IP subnet A, H1, H2, H3 and R belong to an IP subnet B, H4, H5, H6, 
H7 and R belong to an IP subnet C, and H9 and R belong to an IP subnet D. 
The direct transfer within the same IP subnet can be realized by using 
either a point-to-multipoint ATM connection or a multicast server (MCS) 
for carrying out a transfer by duplicating a packet. 
In such an IP multicast communication system, a conventional procedure for 
transferring a packet sent to the multicast address G from a host H0 is as 
follows. 
First, the host H0 transfers a packet destined to G to the host H8 and the 
router R by using a point-to-multipoint ATM connection. The host H8 then 
receives this packet and processes the received packet suitably, while the 
router R transfers this packet to the other subnets (subnets B and C) 
which have hosts participating in this multicast address G. 
In the subnet B, the packet is transferred from the router R to the 
multicast server MCS by using a point-to-point ATM connection, and the 
multicast server MCS transfers this packet to the hosts H1 and H2 by using 
a point-to-multipoint ATM connection. On the other hand, in the subnet C, 
the packet is transferred from the router R to the hosts H4, H5, H6 and H7 
by using a point-to-multipoint ATM connection. The subnet D has no host 
which is participating in this multicast address G, so that the packet is 
not transferred to the subnet D. 
In this manner, a conventional multicast communication scheme uses one 
point-to-multipoint connection or one point-to-point connection to a 
multicast server in transferring the packet between nodes, so that only 
one and the same quality of service can be provided with respect to one 
multicast address, and it has been impossible to realize a multicast in 
which different qualities of service can be provided with respect to 
different receivers participating in one and the same multicast address. 
Now, at a time of transferring a packet to a next hop node from a packet 
transmission node such as a router or a host connected to the virtual 
connection oriented network, a virtual connection to that next hop node is 
set up according to a prescribed connection set up protocol, and a packet 
transfer is carried out by using a set up virtual connection. 
The packets exchanged between transmitting and receiving terminal nodes 
include actual data between terminal applications as well as various types 
of control messages, such as a message for a resource reservation for the 
purpose of requesting a desired communication quality. 
In a currently available router connected to the virtual connection 
oriented network, the identical transfer processing is applied to all the 
packets which have the identical destination node address, regardless of 
whether each packet is carrying the user data or the control message. 
Namely, in a case of the transfer to the virtual connection oriented 
network, a routing table is referred according to the destination node 
address of each packet, and then each packet is transmitted to the 
identical virtual connection according to the routing table, regardless of 
whether each packet is carrying the user data or the control message. 
However, when the control information and the actual communication 
information are transferred through the same virtual connection, the 
following problems arise. 
(1) In a case of adopting the expansion of the router architecture as 
described in the Internet Draft "draft-katsube-router-atm-overview-00.txt" 
(which realizes a faster transfer processing by directly connecting an 
input virtual connection and an output virtual connection inside a router, 
without carrying out a network layer processing), it becomes impossible to 
recognize the control message at a router. 
In this case, there is a need to provide a mechanism for extracting only 
those frames (or cells) received from one virtual connection which 
correspond to the control message packets, and carrying out an appropriate 
processing to the extracted control message packets, so as to be able to 
transfer the other user data frames (or cells) without carrying out the 
packet level processing. However, an incorporation of such a mechanism 
causes an increase of a cost for the packet transmission node. 
(2) When a problem occurs in the virtual connection which is transferring 
the user data, the transfer of both the user data and the control message 
will be stopped, so that there is a possibility for a case in which a 
handling such as a substitute route selection required at a time of the 
problem in the virtual connection cannot be carried out properly. 
(3) It is impossible to control a plurality of related virtual connections 
by using a single virtual connection. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a packet 
transmission node device and a packet transfer scheme capable of realizing 
a multicast in which different qualities of service can be provided with 
respect to different receivers participating in one and the same multicast 
address. 
It is another object of the present invention to provide a packet 
transmission node device and a control information transfer scheme in 
which it becomes possible to recognize the control message at a router 
even when an expanded router architecture is used. 
It is another object of the present invention to provide a packet 
transmission node device and a control information transfer scheme in 
which a handling such as a substitute route selection required at a time 
of a problem in the virtual connection can be carried out properly. 
It is another object of the present invention to provide a packet 
transmission node device and a control information transfer scheme in 
which it is possible to control a plurality of related virtual connections 
by using a single virtual connection. 
According to one aspect of the present invention, there is provided a 
packet transmission node device, comprising: a routing table for storing 
output virtual connection identifiers in correspondence to destination 
addresses, including identifiers of a plurality of virtual connections for 
different qualities of service in correspondence to a multicast 
destination address; and transfer means for transferring a packet to 
output virtual connections determined by referring to the routing table 
according to a destination address of said packet. 
According to another aspect of the present invention, there is provided a 
method of packet transmission from a packet transmission node, comprising 
the steps of: setting up a plurality of virtual connections for different 
qualities of service in correspondence to a multicast destination address; 
storing output virtual connection identifiers in correspondence to 
destination addresses, including identifiers of said plurality of virtual 
connections for different qualities of service set up in correspondence to 
the multicast destination address, in a routing table of the packet 
transmission node; and transferring a packet from the packet transmission 
node to output virtual connections determined by referring to the routing 
table according to a destination address of said packet. 
According to another aspect of the present invention there is provided a 
packet transmission node device, comprising: a routing table for storing 
output virtual connection identifiers in correspondence to destination 
addresses and upper layer protocol identifiers, including identifiers of 
different output virtual connections for a user data packet and a control 
packet having an identical destination address; and transfer means for 
transferring a packet to an output virtual connection determined by 
referring to the routing table according to a destination address and an 
upper layer protocol identifier of said packet. 
According to another aspect of the present invention there is provided a 
method of packet transmission from a packet transmission node, comprising 
the steps of: setting up different output virtual connections for a user 
data packet and a control packet having an identical destination address; 
storing output virtual connection identifiers in correspondence to 
destination addresses and upper layer protocol identifiers, including 
identifiers of said different output virtual connections set up for a user 
data packet and a control packet having an identical destination address, 
in a routing table of the packet transmission node; and transferring a 
packet to an output virtual connection determined by referring to the 
routing table according to a destination address and an upper layer 
protocol identifier of said packet. 
Other features and advantages of the present invention will become apparent 
from the following description taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 2 to FIG. 5, the first embodiment of a packet 
transmission node device for realizing a packet transfer scheme according 
to the present invention will be described in detail. 
In short, in this first embodiment, a node device connected with at least 
one virtual connection oriented network has a memory means for storing 
information including a source address, a destination address, an output 
interface, an output virtual connection identifier, and a quality of 
service. This node device also has a transfer means for transferring a 
packet by referring to the memory means according to a destination address 
or a pair of a source address and a destination address of a transmitting 
packet, determining an output interface and an output virtual connection, 
and controlling a packet transmission means of the determined output 
interface to transmit the packet through the determined output virtual 
connection. 
The memory means stores a plurality of output virtual connection 
identifiers in correspondence to a plurality of qualities of service with 
respect to a destination group address or a pair of a source address and a 
destination group address, so that a plurality of point-to-multipoint 
connections are used with respect to one group address. Consequently, it 
becomes possible to provide different qualities of service with respect to 
different output virtual connections, i.e., with respect to different 
receivers participating in this group address. 
In addition, the above described mechanism of the node device of this first 
embodiment can be used along with the conventional multicast delivery 
mechanism, such that the conventional mechanism can be utilized when all 
the hosts participating in the same multicast address are requesting the 
identical quality of service, while the mechanism of this first embodiment 
can be utilized when there are hosts which request different qualities of 
service. 
Now, the multicast packet transfer scheme at the node device (a host or a 
router) in this first embodiment will be described in further detail. In 
the following, the overview of the packet flow in this multicast packet 
transfer scheme will be described first, and then the node device 
configuration and the packet transmission procedure in this first 
embodiment will be described. 
FIG. 2 shows an exemplary overview of the packet flow in this multicast 
packet transfer scheme. In FIG. 2, H0 to H9 are hosts, where H0 is a 
sender, R0 and R1 are routers for transferring packets, and H1, H2, H4, 
H5, H6, H7 and H8 are receivers which correspond to the group address G. 
The router R0 is connected with the hosts H0 to H9 except for H7 and the 
router R1 through ATM connections, and #1, #2 and #3 depicted around the 
router R0 indicate output interface numbers of this router R0. 
When the network layer is IP, each node (host or router) belongs to a 
logical group called IP subnet. The communication within the same IP 
subnet is realized by the direct transfer without passing through a 
router, while the communication between different IP subnets is realized 
by utilizing a packet forwarding at a router. In FIG. 2, H0, H8 and R0 
belong to an IP subnet A, H1, H2, H3 and R0 belong to an IP subnet B, R0, 
H4, H5, H6 and R1 belong to an IP subnet C, and H9 and R0 belong to an IP 
subnet D. The IP subnet B has a multicast server (MCS) for carrying out a 
transfer by duplicating a packet. 
In FIG. 2, a procedure for transferring a packet sent to the multicast 
address G from a host H0 is as follows. 
First, the host H0 transfers a packet destined to G to the host H8 and the 
router R0 by using a point-to-multipoint ATM connection. The host H8 then 
receives this packet and processes the received packet suitably, while the 
router R0 transfers this packet to the other subnets (subnets B and C) 
which have hosts participating in this multicast group G. 
In the subnet B, the packet is transferred from the router R0 to the 
multicast server MCS though the output interface #2 by using a 
point-to-point ATM connection with the identifier VPI/VCI=10/105 at the 
output interface corresponding to QOS=1, and the multicast server MCS 
transfers this packet to the hosts H1 and H2 by using a 
point-to-multipoint ATM connection. 
On the other hand, in the subnet C, the packet is transferred from the 
router R0 to the hosts H4 to H6 and the router R1 through the output 
interface #3 by using two point-to-multipoint ATM connections with the 
identifiers VPI/VCI=10/100 and VPI/VCI=10/101 at the output interface 
corresponding to QOS=1 and QOS=2, respectively, as indicated in FIG. 2. 
The subnet D has no host which is participating in this multicast group G, 
so that the packet is not transferred to the subnet D. 
In order to transfer the packet of the identical destination to two ATM 
connections by duplicating the packet at the router in the above described 
manner, the router R0 carries out the following packet transmission 
procedure. Note that FIG. 2 shows an exemplary case in which this packet 
transfer is carried out by the router R0, but the similar packet transfer 
can also be carried out by a host for transmitting a packet, so that the 
packet transmission procedure will be described below for a node in 
general, which can be either a router or a host. 
First, FIG. 3 shows a node device configuration in this first embodiment, 
where solid lines indicate the packet flow, while a dashed line indicates 
the control information flow related to a table referring. In this 
configuration of FIG. 3, a node device 100 comprises a packet reception 
unit 101, a packet analysis and transfer unit 102 connected with the 
packet reception unit 100, a packet transmission unit 103 connected with 
the packet analysis and transfer unit 102, upper layers 104 connected with 
the packet analysis and transfer unit 102, and a routing table 105 which 
is referred to by the packet analysis and transfer unit 102. 
The packet reception unit 101 is connected with a LAN (Local Area Network) 
such as ATM, and functions to assemble a network layer packet from 
datalink layer frames received from the LAN according to a protocol of the 
LAN. Here, the datalink layer frames are given by ATM cells, and the 
network layer packet is given by an IP packet. 
The packet analysis and transfer unit 102 judges whether a packet received 
at the packet reception unit 101 is a packet destined to this node 100 or 
not. When the received packet is destined to this node 100, this packet 
will be given to the upper layers 104, whereas when the received packet is 
not destined to this node 100, the packet analysis and transfer unit 102 
carries out the network layer processing, refers to the packet header, and 
determines an output interface and a next hop node or an output connection 
identifier according to the routing table 105. In a case of ATM, the 
output connection is a VC (Virtual Channel) and the output connection 
identifier is VPI/VCI. The packet analysis and transfer unit 102 also 
handles a packet given from the upper layers 104 similarly by carrying out 
the network layer processing, and determining an output interface and a 
next hop node or an output connection identifier according to the routing 
table 105. 
The packet transmission unit 103 converts the packet given from the packet 
analysis and transfer unit 102 into the datalink layer frames of the 
connected LAN, and transmits the converted datalink layer frames to the 
LAN according to the next hop node or the output connection identifier 
given by the packet analysis and transfer unit 102. 
The upper layers 104 are protocols above the network layer such as TCP 
(Transmission Control Protocol), or UDP (User Datagram Protocol). More 
specifically, the upper layers 104 can be a routing protocol for 
exchanging routing information, an application software, an RSVP (Resource 
Reservation Protocol) message, etc. 
The routing table 105 is a table to be referred by the packet analysis and 
transfer unit 102. This routing table 105 is set up either statically in 
advance, or dynamically by the routing protocol. 
For an exemplary case shown in FIG. 2, this routing table 105 has a content 
as shown in FIG. 4. In this routing table of FIG. 4, the output VPI/VCI 
and the quality of service (QOS) can be searched out by using the source 
address and the destination address of the packet to be transferred as a 
search key. It is also possible to use the destination address alone as a 
search key, without using the transmission source. 
When the packet is assigned with an importance level according to a scheme 
such as a hierarchical coding to be described below such that which packet 
is to be transmitted is determined according to this importance level, the 
multicast packet is transferred or transmitted by referring to the quality 
of service in the routing table, but when the packet is not assigned with 
an importance level or when all the packets are to be transmitted, there 
is no need to refer to the quality of service in the routing table at a 
time of actually transferring or transmitting the multicast packet. 
In this first embodiment, there is a possibility for transmitting one 
packet to a plurality of interfaces and a plurality of output virtual 
connections, so that it is necessary for the routing table 105 to have a 
plurality of output I/Fs and a plurality of output VPI/VCIs with respect 
to a single destination address or a single pair of the source address and 
the destination address. For this reason, the routing table shown in FIG. 
4 is formed by a linked list in which a plurality of output routes are 
linked by pointers. 
In FIG. 4, the routing table has such a setting that, when the source H0 
receives a packet with the destination address G, this packet will be 
transferred to an ATM connection (A) with the output I/F=#3, the output 
VPI/VCI=10/100, and QOS=1; an ATM connection (B) with the output I/F=#3, 
the output VPI/VCI=10/101, and QOS=2; and an ATM connection (C) with the 
output I/F=#2, the output VPI/VCI=10/105, and QOS=1. 
Here, for the node group of H1, H2, H4, H5, H6, and R1 corresponding to the 
multicast group G, the ATM connection (A) is a point-to-multipoint 
connection terminated at the hosts H4 and H5, the ATM connection (B) is a 
point-to-multipoint connection terminated at the host H6 and the router 
R1, and the ATM connection (C) is a point-to-point connection to the 
multicast server MCS, which is connected with the point-to-multipoint 
connection from the multicast server MCS to the hosts H1 and H2. 
Note that it is possible to make various modifications to this setting, 
such as a modification to change the above described ATM connection (A) 
into a point-to-point connection to a multicast server for making 
connection with the point-to-multipoint connection to the hosts H4 and H5, 
for example. 
When the receivers (H4, H5, H6, and R1, for example) request the respective 
qualities of service (a bandwidth requested by H4 and H5 is larger than a 
bandwidth requested by H6 and R1, for example), the setting of the ATM 
connections and the routing table is made by setting up the ATM 
connections (a VC of QOS=1 terminated at H4 and H5, and a VC of QOS=2 
terminated at H6 and R1) to satisfy the requested qualities of service, 
and registering information on these connections in the routing table 105. 
The packet transmission procedure in this first embodiment is carried out 
according to the flow chart of FIG. 5 as follows. This procedure is to be 
carried out when a router receives the multicast packet at the packet 
reception unit 101 and transfers this packet to the next hop node, or when 
a host transmits a packet from the upper layers 104. 
The packet given to the packet analysis and transfer unit 102 is analyzed, 
and the routing table 105 is searched by using the source and the 
destination address of that packet (step S1). Here, it is also possible to 
carry out the search by using the destination address alone. As long as 
the output route is registered in the routing table 105, the registered 
output route is referred and the packet is transmitted to the registered 
output I/F and output VPI/VCI according to the quality of service 
specified for each connection (step S2). Here, the packet transmission 
according to the quality of service implies the packet transmission while 
dropping packets according to the quality of service. For example, an 
importance level assigned to each packet can be registered within each 
packet according to the hierarchical coding scheme, such that the packets 
to be transmitted can be selected according to this importance level and 
the quality of service specified for each connection. 
This processing is repeated as many times as necessary, and when the 
processing to transmit one packet is completed for all the output 
connections registered in the routing table 105, this packet transmission 
procedure is terminated. In this manner, it is possible to transfer the 
packet of the identical destination to a plurality of ATM connections by 
duplicating the packet. 
In an exemplary case shown in FIG. 2, when the packet with the source 
address H0 and the destination address G is received at the router R0, the 
routing table 105 is searched, and this packet is transferred to the ATM 
connection (A) with the output I/F=#3, the output VPI/VCI=10/100, and the 
QOS=1 first. Then, by searching the routing table 105 further, this packet 
is also transferred to the ATM connection (B) with the output I/F=#3, the 
output VPI/VCI=10/101, and the QOS=2. Finally, by searching the routing 
table 105 further, this packet is also transferred to the ATM connection 
(C) with the output I/F=#2, the output VPI/VCI=10/105, and the QOS=1, so 
as to complete the packet transfer. 
As described, according to this first embodiment, a plurality of output 
virtual connections including point-to-multipoint connections are made 
available with respect to one multicast address, so that it becomes 
possible to provide different qualities of service with respect to 
different output virtual connections, i.e., with respect to different 
receivers participating in this multicast group. 
Referring now to FIG. 6 to FIG. 15, the second to sixth embodiments of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In the following, it is to be understood that a virtual connection oriented 
network is a network based on techniques such as ATM (Asynchronous 
Transfer Mode), frame relay, fiber channel, HIPPI (High Performance 
Parallel Interface), etc. 
It is also to be understood that a packet transmission node is either a 
packet switching device such as a router or a packet 
transmission/reception terminal. 
It is also to be understood that a node address is given by an IP address, 
a MAC address, an address of IPX, an address of AppleTalk, etc. 
It is also to be understood that a control packet is a packet used for a 
resource reservation protocol such as STII (Stream Protocol II) and RSVP 
(Resource Reservation Protocol), which is to be exchanged between 
transmission and reception terminals through a packet transmission node, 
for example. 
In short, in the control information transfer scheme according to the 
present invention, when a packet transmission node transmits a packet to a 
next hop node by using a virtual connection, the virtual connection to 
which the packet is to be transmitted is determined by referring the 
routing table according to both a destination node address field and a 
protocol identifier in the packet header at the packet analysis and 
transfer unit. Namely, the routing table is formed such that an output 
interface and an output virtual connection can be obtained by using both 
the destination address field and the protocol identifier as a search key. 
Here, it is also possible to use a source address as a search key in 
addition. 
In one aspect of the control information transfer scheme according to the 
present invention, two types of virtual connections for control packets 
and for user data packets are separately provided, even for those control 
packets and user data packets which have the same destination node address 
(unicast or multicast) and which are to be transferred (transmitted) to 
the same next hop node (the same next hop node group in a case of 
multicast). Then the control packets and the user packets are transferred 
(transmitted) by using the respective virtual connections according to the 
setting in the routing table. 
In another aspect of the control information transfer scheme according to 
the present invention, among those packets which have the same destination 
group address, the user data packets are transferred (transmitted) by 
using a virtual connection for transferring (transmitting) to a next hop 
node group which should receive/transfer the packets having the above 
noted group address. On the other hand, for the control packets, a virtual 
connection for transferring (transmitting) the control packets altogether 
to a packet transmission node group including a next hop node group which 
should receive/transfer the packets having the above noted group address 
as well as a next hop node group which should receive/transfer the packets 
having other group address different from the above noted group address. 
Then, the control packets are transferred (transmitted) altogether by 
using that virtual connection. 
Now, with references to FIG. 6 and FIG. 7, the second embodiment of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In this second embodiment, the configuration of the packet transmission 
node device is basically the same as that of FIG. 3 in the first 
embodiment described above. 
In a case where the packet transmission node device 100 is a router, when a 
packet is received from the packet reception unit 101, a network layer 
packet (an IP datagram in a case of IP) is assembled from the datalink 
layer frames (cells in a case of ATM), and given to the packet analysis 
and transfer unit 102. 
At the packet analysis and transfer unit 102, an output interface and an 
output virtual connection for transmitting this packet are determined by 
searching the routing table 105 according to the header information of the 
received packet, and this packet is sent to the packet transmission unit 
103 corresponding to the determined output interface. 
At the packet transmission unit 103, this packet is converted into the 
datalink layer frames (cells in a case of ATM), and the converted datalink 
layer frames are transmitted to the output virtual connection determined 
by the packet analysis and transfer unit 102. 
Now, with references to FIG. 6 and FIG. 7, the control information transfer 
scheme in this second embodiment will be described for an exemplary case 
in which the packet transmission node device is a router. 
FIG. 6 shows an exemplary network system configuration in this second 
embodiment. In FIG. 6, routers R1, R2 and R3 are connected to a virtual 
connection oriented network N, and the other routers R and hosts H 
connected with these routers R1, R2 and R3 are connected to 
connection-less networks such as Ethernets. 
In this exemplary configuration, the content of the routing table at the 
router R1 is as shown in FIG. 7, which is to be referred in a case of 
transferring packets which have destination addresses "a.b.c.d", "p.q.x.y" 
and "e.f.g.h" of the hosts. 
The search key to be used in searching this routing table of FIG. 7 is the 
destination IP address and the protocol identifier in the packet header. 
The protocol identifier indicates whether the upper layer protocol of that 
packet is TCP or UDP (which also indicates that it is a user data packet), 
or if it is a control message for RSVP, etc. (which also indicates that it 
is a control packet). As a result of searching this routing table, the 
information such as the output interface indicating an interface port to 
which the packet should be outputted, the next hop node address indicating 
an IP address of the next hop node, and the identifier of the virtual 
connection to which the packet should be outputted (an identifier VPI/VCI 
of a VC (Virtual Channel) of an ATM connection is used in FIG. 7 as an 
example) can be obtained. 
In a case of searching by using the destination IP address alone as a 
search key as in a case of a conventional routing table, the packets are 
going to be outputted to the same virtual connection regardless of whether 
the upper layer protocol is TCP or UDP, or whether it is a control message 
for RSVP, etc. or not. In contrast, in this second embodiment, as shown in 
FIG. 7, the packets are outputted to different virtual connections when 
the upper layer protocols are different even when the destination IP 
address is the same. 
Namely, for the packet with the destination IP address "a.b.c.d", the IP 
address of the next hop router is "p.q.r.s", and as the virtual connection 
up to that next hop router, the virtual connection with VPI/VCI=100/200 is 
provided for data transfer (user data packet transfer), while the virtual 
connection with VPI/VCI=100/201 is provided for RSVP control message (path 
message) transfer (control packet transfer). 
Also, for the packet with the destination IP address "p.q.x.y", the IP 
address of the next hop router is "p.q.r.s", and as the virtual connection 
up to that next hop router, the virtual connection with VPI/VCI=100/100 is 
provided for data transfer, while the virtual connection with 
VPI/VCI=100/201 is also used for RSVP control message transfer. In this 
manner, the control packets having different destination IP addresses and 
the same next hop node can be transferred by using the same virtual 
connection. 
Also, for the packet with the destination IP address "e.f.g.h", the IP 
address of the next hop router is "p.q.r.t", and as the virtual connection 
up to that next hop router, the virtual connection with VPI/VCI=500/888 is 
provided for data transfer, while the virtual connection with 
VPI/VCI=500/777 is provided for RSVP control message transfer. 
Here, the set up of each virtual connection can be realized by the ATM 
signaling procedure or the management procedure. 
Next, with references to FIG. 8 and FIG. 9, the third embodiment of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In this third embodiment, the configuration of the packet transmission node 
device is basically the same as that of FIG. 3 in the first embodiment 
described above. 
FIG. 8 shows an exemplary network system configuration in this third 
embodiment. In FIG. 8, routers R1, R2, R3 and R4 are connected to a 
virtual connection oriented network N. This third embodiment is directed 
to a case of the multicast communication using the IP group address. 
In this exemplary configuration, the content of the routing table at the 
router R1 is as shown in FIG. 9, which is to be referred in a case of 
transferring packets which have the group addresses "225.0.0.100" and 
"230.10.10.0" as the destination addresses. 
The search key to be used in searching this routing table of FIG. 9 is the 
destination group address (multicast address) and the protocol identifier 
in the packet header (and possibly the source address). As a result of 
searching this routing table, the information such as the output interface 
Indicating an interface port to which the packet should be output, and the 
identifier of the virtual connection to which the packet should be output 
(an identifier VPI/VCI of a VC (Virtual Channel) of an ATM connection is 
used in FIG. 9 as an example) can be obtained. 
FIG. 8 shows an exemplary case in which the routers R2 and R3 are 
participating in the group address "225.0.0.100", while the routers R3 and 
R4 are participating in the group address "230.10.10.0". In other words, 
the hosts participating in the group address "225.0.0.100" exist on a 
downstream side of the routers R2 and R3, while the hosts participating in 
the group address "230.10.10.0" exist on a downstream side of the routers 
R3 and R4. 
In this third embodiment, as shown in FIG. 9, the packets are output to 
different virtual connections when the upper layer protocols are different 
even when the destination group address is the same. 
Namely, for the packet with the destination group address "225.0.0.100", 
the point-to-multipoint virtual connection with VPI/VCI=50/100 connected 
to R2 and R3 is provided for data transfer, while the point-to-multipoint 
virtual connection with VPI/VCI=50/200 connected to R2 and R3 is provided 
for RSVP control message transfer. 
Also, for the packet with the destination group address "230.10.10.0", the 
point-to-multipoint virtual connection with VPI/VCI=100/10 connected to R3 
and R4 is provided for data transfer, while the point-to-multipoint 
virtual connection with VPI/VCI=100/11 connected to R3 and R4 is provided 
for RSVP control message transfer. 
Here, the set up of each virtual connection is going to be realized by the 
ATM signaling procedure or the management procedure. 
Next, with references to FIG. 10 and FIG. 11, the fourth embodiment of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In this fourth embodiment, the configuration of the packet transmission 
node device is basically the same as that of FIG. 3 in the first 
embodiment described above. 
FIG. 10 shows an exemplary network system configuration in this fourth 
embodiment. In FIG. 10, the third embodiment of FIG. 8 is modified by 
incorporating a multicast server (MCS) in order to provide the multicast 
communications of a plurality of senders efficiently. 
In this fourth embodiment, the manner of utilizing virtual connections for 
data transfer is the same as in the third embodiment described above. On 
the other hand, as a virtual connection for RSVP control message transfer 
to the destination group address "225.0.0.100", a virtual connection with 
VPI/VCI=25/888 connected to the MCS is utilized, and the MCS which 
received the control message through this virtual connection then 
transfers the control messages to the routers R2 and R3 on the downstream 
side by using a point-to-multipoint virtual connection with VPI/VCI=20/444 
connected to the routers R2 and R3. 
In this case, it is not necessary for every transmission node to have a 
point-to-multipoint virtual connection for control message transfer to the 
multicast address "225.0.0.100", and it suffices for each transmission 
node to have a point-to-point virtual connection to the MCS, so that it is 
possible to expect a reduction of a number of virtual connections compared 
with a case of having as many point-to-multipoint virtual connections as a 
number of senders as in the third embodiment described above. 
In this exemplary configuration, the content of the routing table at the 
router R1 is as shown in FIG. 11. 
In this fourth embodiment, as shown in FIG. 11, the packets are output to 
different virtual connections when the upper layer protocols are different 
even when the destination group address is the same. 
Namely, for the packet with the destination group address "225.0.0.100", 
the point-to-multipoint virtual connection with VPI/VCI=50/100 connected 
to R2 and R3 is used for data transfer when the upper layer protocol is 
TCP (user data packet), while the point-to-point virtual connection with 
VPI/VCI=25/888 connected to the MCS is used for RSVP control message 
transfer when the upper layer protocol is RSVP (control packet). This 
virtual connection with VPI/VCI=25/888 is a point-to-point virtual 
connection from which packets are forwarded by the MCS to a 
point-to-multipoint virtual connection with VPI/VCI=20/444 connected to R2 
and R3. 
Here, the set up of each virtual connection is going to be realized by the 
ATM signaling procedure or the management procedure. 
Note that the MCS can determine the output interface and the output virtual 
connection according to VPI/VCI of the received cell. In a case of the 
configuration of FIG. 10, the MCS has such a setting that the 
point-to-multipoint virtual connection with VPI/VCI=20/444 is determined 
according to VPI/VCI of the received cell. Here, in order to avoid the 
interleaving at the cell level in a case where the control messages from a 
plurality of senders (which are received through different virtual 
connections) are to be transmitted to the same point-to-multipoint virtual 
connection, it is preferable to assemble the cell up to the AAL (ATM 
Adaptation Layer) frame. Alternatively, it is also possible to assemble a 
packet from the received cell at the MCS, and determine the output VPI/VCI 
by referring to the destination group address as in a usual router. 
Note also that the above described fourth embodiment is directed to an 
exemplary case in which only the control packets are transferred by using 
the MCS, but it is also possible to transfer the user data packets by 
using the MCS as well. In such a case, however, the virtual connection for 
data transfer and the virtual connection for control message transfer are 
to be provided separately in accordance with the present invention. 
Next, with references to FIG. 12 and FIG. 13, the fifth embodiment of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In this fifth embodiment, the configuration of the packet transmission node 
device is basically the same as that of FIG. 3 in the first embodiment 
described above. 
FIG. 12 shows an exemplary network system configuration in this fifth 
embodiment. In this fifth embodiment, the manner of utilizing virtual 
connections for data transfer is the same as in the third embodiment 
described above. On the other hand, as a virtual connection for RSVP 
control message transfer, a virtual connection with VPI/VCI=50/333 
connected to all of R2, R3 and R4 is utilized. This virtual connection is 
provided in correspondence to an IP address "224.0.0.1" which means all 
local nodes participating in the multicast communication. 
In this exemplary configuration, the content of the routing table at the 
router R1 is as shown in FIG. 13. 
The search key to be used in searching this routing table of FIG. 13 is the 
destination group address (multicast address) and the protocol identifier 
in the packet header (and possibly the source address). 
In this fifth embodiment, as shown in FIG. 13, the packets are output to 
different virtual connections when the upper layer protocols are different 
even when the destination group address is the same. 
Namely, for the packet with the destination group address "225.0.0.100", 
the point-to-multipoint virtual connection with VPI/VCI=50/100 connected 
to R2 and R3 is used for data transfer when the upper layer protocol is 
TCP (user data packet), while the point-to-multipoint virtual connection 
with VPI/VCI=50/333 connected to all of R2, R3 and R4 is used for RSVP 
control message transfer when the upper layer protocol is RSVP (control 
packet). 
Also, for the packet with the destination group address "230.10.10.0", the 
point-to-multipoint virtual connection with VPI/VCI=100/10 connected to R3 
and R4 is used for data transfer, while the point-to-multipoint virtual 
connection with VPI/VCI=50/333 is also used for RSVP control message 
transfer. 
In addition, the packets with the destination group address "224.0.0.1" are 
also transferred by the point-to-multipoint virtual connection with 
VPI/VCI=50/333. This IP address "224.0.0.1" is used for the packet 
communication in which the upper layer protocol is IGMP (Internet Group 
Management Protocol) for example. 
The virtual connection with VPI/VCI=50/333 is a point-to-multipoint virtual 
connection destined to R2, R3 and R4 which is set up with respect to the 
IP address "224.0.0.1". 
Here, the set up of each virtual connection is going to be realized by the 
ATM signaling procedure or the management procedure. 
In this fifth embodiment, all the multicast participating nodes are members 
of the address "224.0.0.1" so that when the control messages are 
transmitted to the point-to-multipoint virtual connection destined to this 
address "224.0.0.1", each downstream side node is going to receive the 
messages not relevant to that node, but it suffices to discard such 
messages not relevant to each node at the receiving side. 
Note that the above described fifth embodiment is directed to an exemplary 
case in which the control packets are transmitted to the virtual 
connection which is set up to be destined to all the local nodes 
participating in the multicast communication, but using the configuration 
similar to that of FIG. 12, it is also possible to specify some multicast 
groups among a plurality of existing multicast groups, and transmit the 
control packets to a point-to-multipoint virtual connection which is set 
up to be destined to the local nodes participating in any of the specified 
multicast groups (nodes for which the hosts participating in the specified 
multicast group exist on their downstream sides). 
Next, with references to FIG. 14 and FIG. 15, the sixth embodiment of a 
packet transmission node device for realizing a control information 
transfer scheme according to the present invention will be described in 
detail. 
In this sixth embodiment, the configuration of the packet transmission node 
device is basically the same as that of FIG. 3 in the first embodiment 
described above. 
FIG. 14 shows an exemplary network system configuration in this sixth 
embodiment. In FIG. 14, the fifth embodiment of FIG. 12 is modified by 
incorporating a multicast server (MCS) in order to provide the multicast 
communications of a plurality of senders efficiently. 
In this sixth embodiment, the manner of utilizing virtual connections for 
data transfer is the same as in the fifth embodiment described above. On 
the other hand, as a virtual connection for RSVP control message transfer 
to the destination group address "224.0.0.1" described above, a virtual 
connection with VPI/VCI=25/888 connected to the MCS is utilized, and the 
MCS which received the control message through this virtual connection 
then transfers the control messages to the routers R2, R3 and R4 on the 
downstream side by using a point-to-multipoint virtual connection with 
VPI/VCI=10/555 connected to the routers R2, R3 and R4 and destined to the 
address "224.0.0.1". 
In this case, it is not necessary for every transmission node to have a 
point-to-multipoint virtual connection for control message transfer to the 
multicast address "224.0.0.1", and it suffices for each transmission node 
to have a point-to-point virtual connection to the MCS, so that it is 
possible to expect a reduction of a number of virtual connections compared 
with a case of having as many point-to-multipoint virtual connections as a 
number of senders as in the fifth embodiment described above. 
In this exemplary configuration, the content of the routing table at the 
router R1 is as shown in FIG. 15. 
In this sixth embodiment, as shown in FIG. 15, the packets are output to 
different virtual connections when the upper layer protocols are different 
even when the destination group address is the same. 
Namely, for the packet with the destination group address "225.0.0.100", 
the point-to-multipoint virtual connection with VPI/VCI=50/100 connected 
to R2 and R3 is used for data transfer when the upper layer protocol is 
TCP (user data packet), while the point-to-point virtual connection with 
VPI/VCI=25/888 connected to the MCS is used for RSVP control message 
transfer when the upper layer protocol is RSVP (control packet). 
Also, for the packet with the destination group address "230.10.10.0", the 
point-to-multipoint virtual connection with VPI/VCI=100/10 connected to R3 
and R4 is used for data transfer, while the point-to-point virtual 
connection with VPI/VCI=25/888 is also used for RSVP control message 
transfer. 
In addition, the packets with the destination group address "224.0.0.1" are 
also transferred by the point-to-point virtual connection with 
VPI/VCI=25/888. 
The virtual connection with VPI/VCI=25/888 is a point-to-point virtual 
connection from which packets are forwarded by the MCS to a 
point-to-multipoint virtual connection with VPI/VCI=10/555 connected to 
R2, R3 and R4. 
Here, the set up of each virtual connection is going to be realized by the 
ATM signaling procedure or the management procedure. 
Note that the MCS can determine the output interface and the output virtual 
connection according to VPI/VCI of the received cell. In a case of the 
configuration of FIG. 14, the MCS has such a setting that the 
point-to-multipoint virtual connection with VPI/VCI=10/555 is determined 
according to VPI/VCI of the received cell. Here, in order to avoid the 
interleaving at the cell level in a case where the control messages from a 
plurality of senders (which are received through different virtual 
connections) are to be transmitted to the same point-to-multipoint virtual 
connection, it is preferable to assemble the cell up to the AAL (ATM 
Adaptation Layer) frame. Alternatively, it is also possible to assemble a 
packet from the received cell at the MCS, and determine the output VPI/VCI 
by referring to the destination group address as in a usual router. 
Note also that this sixth embodiment is directed to an exemplary case in 
which only the control packets are transferred by using the MCS, but it is 
also possible to transfer the user data packets by using the MCS as well. 
In such a case, however, the virtual connection for data transfer and the 
virtual connection for control message transfer are to be provided 
separately in accordance with the present invention. 
As described, according to the second to sixth embodiments, it becomes 
possible to separate the virtual connection to be used for the user data 
packet transmission and the virtual connection to be used for the control 
packet transmission, by using the information other than the destination 
address in determining the output virtual connection for each packet. 
Consequently, when this control information transfer scheme is applied to a 
router within which the input virtual connection and the output virtual 
connection are directly connected, it becomes possible to recognize and 
handle the control message at the router by concatenating the input and 
output virtual connections used for the user data packet transmission, 
while carrying out the network layer processing for the virtual connection 
to be used for the control message packet transmission. 
Also, even when a problem occurs in the virtual connection which is 
transferring the user data packets, it is still possible to transfer the 
control packets. 
In addition, it becomes possible to control a plurality of related virtual 
connections simultaneously, by means of a single virtual connection. 
Thus, according to the control information transfer scheme of the present 
invention, it becomes possible to recognize the control message at a 
router even when an expanded router architecture is used, a handling such 
as a substitute route selection required at a time of trouble in the 
virtual connection can be carried out properly, and it is possible to 
control a plurality of related virtual connections by using a single 
virtual connection. 
It is to be noted that the packet transfer scheme of the first embodiment 
described above and the control information transfer scheme of any of the 
second to sixth embodiment described above can be realized simultaneously 
by the same packet transmission node device. 
For instance, as shown in FIG. 16, the packet transfer scheme of FIG. 2 
described above may be modified by incorporating an additional virtual 
connection with VPI/VCI=10/444 connected to the hosts H4 to H6 and the 
router R1, which is to be used for control message packet transfer 
according to the control information transfer scheme of the present 
invention. 
In this case, the routing table of the packet transmission node device has 
a content as shown in FIG. 17, which effectively combines a content 
similar to that of FIG. 4 for user data packet transfer and a content 
similar to that of FIGS. 7, 9, 11, 13 or 15 for control packet transfer. 
It is also to be noted that, besides those already mentioned above, many 
modifications and variations of the above embodiments may be made without 
departing from the novel and advantageous features of the present 
invention. Accordingly, all such modifications and variations are intended 
to be included within the scope of the appended claims.