Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the peer-to-peer communication of one-to-one type, or in particular to a session relay apparatus in which the network operation policy for the relay nodes on the network can be set and canceled with the start or the end of the peer-to-peer communication as a motive.  
           [0002]    The network operated and managed by a network provider such as a communication carrier or ISP (Internet Service Provider) is configured of a plurality of relay nodes interconnected for relay the user packets. In the network configured of the relay nodes, the network operation policy for controlling the route and the communication quality of the user packets is called simply as the policy. This policy is set for each application or each user in accordance with the priority or security of the packet relay operation. The relay nodes making up the network perform the process of relay the packets in accordance with the policy thus set.  
           [0003]    The network has arranged therein a policy server for uniquely managing the policy, and this policy server reflects the policy in the network by distributing the policy to a multiplicity of relay nodes constituting the network. A well-known protocol for distributing the policy from the policy server is COPS (Common Open Policy Service) defined in the standard recommendation RFC (Request for Comments) prepared by IETF (Internet Engineering Task Force) and issued by IAB (Internet Architecture Board).  
           [0004]    The network provider can set in a network, for example, a policy for priority control in which the packet of a specific user is repeated preferentially over the packets of the other users. In this case, the policy server classifies specific influent packets in the network into a plurality of priority control classes for the relay node called the edge node arranged in the network boundary, and distributes the policy for setting in the packet header the value called DSCP (Diffserv Code Point) corresponding to each priority control class. The edge node with this policy set therein determines whether the packets flowing into the network configured of the relay nodes meet the conditions set by the policy, and in the presence of a packet meeting the particular conditions, the DSCP value is set in the header of the packet in accordance with the priority control class assigned to the particular packet. Each relay node making up the network performs the priority control of the packets in accordance with the DSCP value set by the edge node.  
           [0005]    An example of priority control of the packets with the DSCP value set by the edge node is described in JP-A-2000-253047. In the technique called Diffserv (Differentiated Services) described in this publication, the relay node called the core node arranged in the network transfers packets by priority control in accordance with the order of priority set in the DSCP value under the rules predetermined based on the DSCP value in the header of the received packet. This technique called Diffserv is used, as in the IP (Internet Protocol) telephone, to reduce the transfer delay in transmitting/receiving, on the IP network, the packets requiring the real time property such as audio packets and video packets.  
           [0006]    In the peer-to-peer communication of one-to-one type like the IP telephone, on the other hand, a session is established between two communication terminals by a session control protocol typically including SIP (Session Initiation Protocol) defined in the standard recommendation RFC 3261, and the peer-to-peer communication conducted with real time data such as voice and image on the session thus established. The term “session” is defined as the period from the start to the end of the logical connection for communication executed between two communication terminals. Also, the term “peer-to-peer communication” is defined as a form of direct communication established between communication terminals without any server therebetween. In SIP, a session relay apparatus for relay the session control message searches for the terminal of the other party of communication, holds the information required for the peer-to-peer communication including the address of the communication terminal, the port number and the data number or otherwise executes the session management. The “session control message” repeated by the session control message is defined as a message transmitted or received prior to the start or end of the session between communication terminals.  
           [0007]    In this peer-to-peer communication, the contents of the data transmitted and received between the communication terminals for each session may be different, include audio data or dynamic image data even in the communication between the same terminals. In such a case, packets are required to be repeated with the proper policy in accordance with the contents of the data, i.e. the contents of the communication. In the case where the network policy is controlled by the policy server as described above, the start and end of the peer-to-peer communication cannot be detected by the policy server, and therefore, the operator of the policy server is required to set the proper policy in accordance with the contents of the communication for the edge nodes in accordance with the start and end of the peer-to-peer communication. In this method, however, an increased network size requires frequent policy setting process, and therefore the setting by the operator may fail to meet the requirements.  
           [0008]    In the method for setting in the edge nodes all the policies on the communication terminal for the peer-to-peer communication, on the other hand, the search process for the conditions of classification of the policy control in the edge nodes increases with the increase in the network scale. The increased search process imposes a processing burden on the edge nodes, resulting in an increased packet relay delay for real-time packets.  
         SUMMARY OF THE INVENTION  
         [0009]    Accordingly, an object of the present invention is to provide a policy settable peer-to-peer session relay apparatus, which detects the start and end of the peer-to-peer communication between communication terminals, and and sets or cancels the policy for the edge node containing each communication terminal. As a result, the operator is not required to perform the policy setting operation, and the packet relay delay at the edge nodes otherwise caused by the unrequired policy setting process is prevented.  
           [0010]    Specifically, there is provided a session relay apparatus, wherein each relay node includes a mechanism for establishing a session between communication terminals, a mechanism for generating a policy and a mechanism for distributing the policy generated, thereby making it possible to generate and distribute a policy in accordance with the establishment of a session.  
           [0011]    The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a block diagram showing a configuration of a session relay apparatus according to the invention.  
         [0013]    [0013]FIG. 2 is a diagram showing an example of a mesh configuration of a communication network using a session relay apparatus according to the invention.  
         [0014]    [0014]FIG. 3 shows a sequence of the communication steps for starting the peer-to-peer communication.  
         [0015]    [0015]FIG. 4 is a diagram for explaining an example of the session information and the peer-to-peer communication information in the INVITE message.  
         [0016]    [0016]FIG. 5 shows a table structure representing an example configuration of a policy storage unit.  
         [0017]    [0017]FIG. 6 shows a table structure representing an example configuration of a communication terminal-relay node correspondence storage unit.  
         [0018]    [0018]FIG. 7 is a diagram for explaining the contents of the policy generated by the policy generating unit.  
         [0019]    [0019]FIG. 8 is a sequence diagram showing the communication steps to end the peer-to-peer communication.  
         [0020]    [0020]FIG. 9 is a flowchart for explaining the operation of the policy generating unit.  
         [0021]    [0021]FIG. 10 shows a mesh configuration as another configuration of the communication network using the session relay apparatus according to the invention.  
         [0022]    [0022]FIG. 11 is a diagram for explaining an example of the session information and the peer-to-peer communication information in the OK message. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]    An embodiment of the invention is explained below with reference to a case in which SIP is used as a peer-to-peer communication session control protocol and COPS as a policy distribution protocol. In embodying the invention, the session control protocol is not limited to SIP, and the policy distribution protocol other than COPS may be used.  
         [0024]    [0024]FIG. 1 is a block diagram showing a block configuration of a session relay apparatus according to the invention. A session relay apparatus  10  according to the invention comprises a packet transmitter/receiver  100  for transmitting/receiving IP packets, a session control unit  110  for controlling the peer-to-peer communication session, a session storage unit  120  for holding the session status, a policy distribution unit  200  for distributing a policy to edge nodes, a policy generating unit  210  for generating a policy, a policy storage unit  220  for storing the policy generated, and a communication terminal-relay node correspondence storage unit  230  for holding the correspondence between each communication terminal and a corresponding edge node for accommodating the particular communication terminal. In this configuration, the session relay apparatus  10  receives a peer-to-peer communication session control message transmitted from the peer-to-peer communication terminal  15  on the IP network and transfers the peer-to-peer communication session control message to the session relay apparatus  10  for managing a destination communication terminal. The session relay apparatus  10  distributes the policy to the edge node  20  accommodating the communication terminal at the start and end of the session.  
         [0025]    [0025]FIG. 2 is a diagram showing a mesh network configuration in which the session relay apparatus according to the invention is used with the IP network of Diffserv as a QoS-controllable IP network. The policy used for the network is not limited to the priority control using the DSCP value based on Diffserv but may be other policies for embodying the invention.  
         [0026]    More specifically, a mesh configuration configured of an edge node  20  providing a relay node and a core node  30  and the operation are shown for the peer-to-peer communication with a QoS policy set by the DSCP value between a peer-to-peer communication terminal  15   a  having an IP address of 192.168.10.1 and a destination communication terminal  15   b  having an IP address of 192.168.20.1 through an IP network capable of QoS control based on the DSCP value.  
         [0027]    In starting the peer-to-peer communication with the communication terminal  15   b , the first step is for the communication terminal  15   a  to transfer a peer-to-peer communication session control message requesting the session relay apparatus  10   a  having the IP addresses 192.168.100.10 to start the peer-to-peer communication with the communication terminal  15   b . The peer-to-peer communication session control message from the communication terminal  15   a  is transmitted to the communication terminal  15   b  through the relay apparatus  10   a  according to the invention and the relay apparatus  10   b  having the IP address 192.168.100.20 for managing the communication terminal  15   b . In the process, the relays apparatus  10   a  and  10   b  analyze the peer-to-peer communication session control message individually, and extracting the QoS classification conditions for the peer-to-peer communication, generate a QoS policy for communication between the communication terminals  15   a  and  15   b . The term “the QoS classification conditions”, as described later with reference to FIG. 7, is defined as the conditions including the information for identifying a packet determined by the address value and the port number of the packet, and a packet satisfying the conditions is assigned a DSCP value adapted for the particular conditions. The QoS policy generated is set in the edge node  20   a  of IP address 192.168.100.1 accommodating the communication terminal  15   a  and the edge node  20   b  of IP address 192.168.100.2 accommodating the communication terminal  15   b . By doing so, these edge nodes are governed by the policy for setting the DSCP value predetermined for the packets meeting the QoS classification conditions.  
         [0028]    The session relays apparatus according to the invention and an example of the operation of a communication network (the QoS-controlled peer-to-peer communication operation between the terminals) using the same session relays apparatus is explained below with reference to FIGS.  3  to  9 .  
         [0029]    [0029]FIG. 3 is a sequence diagram showing the communication process for the communication terminal A ( 15   a ) to start the peer-to-peer communication with the communication terminal B ( 15   b ).  
         [0030]    First, the communication terminal A ( 15   a ) sends an INVITE message  501  providing a session control message requesting the session relay apparatus A ( 10   a ) to start the peer-to-peer communication with the communication terminal B. FIG. 4 shows the contents of the INVITE message sent from the communication terminal A ( 10   a ). The header of the control message provides the session information  800 , and the portion stored in the payload of the control message and described by SDP (Session Description Protocol) provides the peer-to-peer communication information  801 . As described above, the session information contains information required to uniquely identify the session such as ID information for the communication terminal, and the peer-to-peer communication information contains information required to specify the contents of the peer-to-peer communication such as the communication data type and the protocol used for communication of the particular data type. It is seen from FIG. 4 that the transmitter IP address is 192.168.10.1 ( 810 ), the destination port number is 49170 ( 820 ), the communication data is audio, and RTP (Realtime Transport Protocol) is used as a communication protocol.  
         [0031]    The session relay apparatus A ( 10   a ) that has received the INVITE message analyzes the contents of the INVITE message through the session control unit  110 , and transfers the INVITE message  503  to the session relay apparatus B ( 10   b ), while at the same time responding to the communication terminal A ( 15   a ) with a trying message  504  indicating the transfer of the INVITE message. The session control unit  110  also delivers to the policy generating unit  210  the session information  800  and the peer-to-peer communication information  801  stored in the INVITE message. The policy generating unit  210  holds the session information  800  and the peer-to-peer communication information  801  thus delivered ( 502 ). In this case, the policy generating unit  210  may hold either the whole or at least the required part of the session information  800  or the peer-to-peer communication information  801 . Also, the session control unit  110  may deliver only at least the required part of the session information  800  and the peer-to-peer communication information  801  to the policy generating unit  210 .  
         [0032]    The session relay apparatus B ( 10   b ) that has received the INVITE message from the session relay apparatus A ( 10   a ) transfers the INVITE message  505  to the communication terminal B ( 15   b ) and responds to the session relay apparatus A ( 10   a ) with the trying message  506 .  
         [0033]    In the case where a ringing message  507  indicating that the communication terminal B ( 15   b ) that has received the INVITE message  505  is in preparation for communication is transmitted to the session relay apparatus B ( 10   b ) as a response, the session relay apparatus B ( 10   b ) transmits a ringing message  508  to the relay apparatus A ( 10   a ). The relay apparatus A ( 10   a ) that has received this ringing message  508  similarly transmits a ringing message  509  to the communication terminal A ( 15   a ).  
         [0034]    Once the preparation for the peer-to-peer communication is over and the communication becomes possible, the communication terminal B ( 15   b ) transfers an OK message  510  to the session relay apparatus B ( 10   b ). FIG. 11 shows the contents of the OK message  510  transmitted from the communication terminal B ( 15   b ). Like the INVITE message shown in FIG. 4, the header of the OK message constituting the session control message based on SIP constitutes the session information  900 , under which the portion described by SDP (Session Description Protocol) provides the peer-to-peer communication information  901 . FIG. 11 indicates that the destination IP address is 192.168.20.1.820 ( 910 ), the transmitter port number is 49171, the communication data is audio, and RTP ( 920 ) is used as a communication protocol.  
         [0035]    The session relay apparatus B ( 10   b ) that has received this OK message  510  extracts, through the session control unit  110 , the session information  900  and the peer-to-peer communication information  901  stored in the OK message and delivers them to the policy generating unit  210 . The session control unit  110  transfers the OK message  512  to the session relay apparatus A ( 10   a ) through the packet transmitter/receiver  100 . The policy generating unit  210  that has received the session information  900  and the peer-to-peer communication information  901  from the session control unit  110  holds the same information ( 511 ). In the process, the policy generating unit  210  may hold either the whole or at least the required part of the session information  900  or the peer-to-peer communication information  901 . Also, the session control unit  110  may deliver either the whole or at least the required part of the session information  900  and the peer-to-peer communication information  901  to the policy generating unit  210 .  
         [0036]    Upon similar transfer of the OK message  513  to the communication terminal A ( 15   a ) from the session relay apparatus A ( 10   a ) that has received the OK message  512 , the communication terminal A ( 15   a ) that has received the OK message transmits an ACK message  514  indicating the start of the peer-to-peer communication to the session relay apparatus A ( 10   a ).  
         [0037]    Upon receipt of the ACK message  514 , the establishment of the session is notified from the session control unit  110  to the policy generating unit  210  in the session relay apparatus A ( 10   a ). The policy generating unit  210  that has received this notification registers in the policy management table  220  the session information and the peer-to-peer communication information held therein, while at the same time generating and delivering a QoS policy to a QoS policy distribution unit  200  ( 515 ).  
         [0038]    [0038]FIG. 5 is a diagram showing a table configuration as an example table configuration of the policy storage unit  220  of the session relay apparatus. Each entry is produced for each peer-to-peer communication, i.e. each time the session is established. The policy storage unit  220  shown in FIG. 5 stores “Call-ID”, “To tag” and “From tag” of the session information  800  shown in FIG. 4 for uniquely identifying the session in SIP. Also, the policy storage unit  220  stores the address and the port number of the transmitter and the address and the port number of the destination contained in the peer-to-peer communication information  801  shown in FIG. 4, and further the DSCP value indicating the priority relay control level of packets and the address of the next relay node for selecting a relay network.  
         [0039]    [0039]FIG. 7 is a diagram for explaining an example of the policy generated by the policy generating unit  210  of the session relay apparatus. The policy is described in PIB (Policy Information Base) format indicating the rules of the conditional operation type according to SPPI (Structure of Policy Provisioning Information). PIB for Diffserv, for example, is laid down in RFC3317. According to the embodiment shown in FIG. 7, the operation ( 1001 ) of rewriting the DSCP value as 0×001010 is used for the packet meeting the conditions including the transmitter IP address of 192.168.10.1, the transmitter port number of 49170, the destination IP address of 192.168.20.1 and the destination port number of 49171. In this way, the QoS generated includes the QoS control classification conditions  1001  and the packet processing  1001  under the same conditions. Thus, the DSCP value of the packet with the edge node  20  meeting the conditions is rewritten and the core node  30  executes the packet priority control based on the DSCP value.  
         [0040]    The policy distribution unit  200  executes the process of setting the QoS policy generated by the policy generating unit  210 , in the edge node  20   a  using the COPS protocol. For this purpose, the policy distribution unit  200  produces a decision message  516  in accordance with the COPS protocol using the QoS policy delivered from the policy generating unit, searches the communication terminal-relay node correspondence storage unit  230  by way of the transmitter IP address contained in the QoS policy, and transmits the produced decision message  516  to the edge node A ( 20   a ) accommodating the communication terminal A ( 15   a ). The policy in PIB format is encoded by BER (Basic Encoding Rules) of ASN.1 (Abstract Syntax Notation one) defined in ISO (International Organization for Standardization), and transmitted to the edge node as a decision message.  
         [0041]    [0041]FIG. 6 is a diagram showing a table configuration representing an example configuration of the communication terminal-relay node correspondence storage unit  230  of the session relay apparatus. In this example, each entry corresponds to one communication terminal. The communication terminal-relay node correspondence storage unit  230  shown in FIG. 6 includes the IP address of a communication terminal, and the IP address of the edge node accommodating the particular communication terminal. The communication terminal-relay node correspondence storage unit is set manually by the network manager or automatically by communication between the session relay apparatus, the edge node and the communication terminal.  
         [0042]    The edge node A ( 20   a ) registers by retrieving the QoS control classification conditions and the packet processing from the QoS policy stored in the decision message  516  received on the one hand, and transmits a report message  517  indicating the complete registration as a response to the session relay apparatus A ( 10   a ). The session relays apparatus A ( 10   a ) that has received the report message  517  transmits an ACK message  519  to the session relay apparatus B ( 10   b ) ( 518 ).  
         [0043]    In the session relay apparatus B ( 10   b ) that has received the ACK message, the session control unit  110  notifies the policy generating unit  210  that the session has been established. The policy generating unit  210  that has received this notification registers in the policy storage unit  220  the session information  900  and the peer-to-peer communication information  901  stored therein ( 520 ), and in accordance with the COPS protocol, generates and transmits the decision message  521  to the edge node B ( 20   b ) accommodating the communication terminal B ( 10   b ) through the policy distribution unit  210 .  
         [0044]    The edge node B ( 20   b ) that has received the decision message  521  similarly registers the QoS control classification conditions and the packet processing and transmits a report message  522  to the session relay apparatus B ( 10   b ). The session relay apparatus B ( 10   b ) that has received this report message transmits an ACK message  524  to the communication terminal B ( 15   b ) ( 523 ). The receipt of this ACK message by the communication terminal B ( 15   b ) indicates that the session is established between the communication terminal A ( 15   a ) and the communication terminal B ( 15   b ).  
         [0045]    By the operation described above, the session is established between the communication terminals and the QoS policy is completely set in the relay network. The communication terminal A ( 15   a ) transmits the peer-to-peer communication packet  525 , and the edge node A ( 20   a ) sets the QoS control class, i.e. the DSCP value of the particular packet ( 526 ). In similar fashion, the edge node B ( 20   b ) sets the QoS control class for the peer-to-peer communication packet  528  sent from the communication terminal B ( 15   b ) ( 527 ). In the network  40 , the core node  30  executes the packet relay process by priority control in accordance with the order of priority set in the packet.  
         [0046]    [0046]FIG. 8 is a sequence diagram showing the communication process executed in the case where the communication terminal B ( 15   b ) terminates the peer-to-peer communication with the communication terminal A ( 15   a ). The communication terminal B ( 15   b ) transmits a BYE message  601  indicating the end of the session to the session relay apparatus B ( 10   b ). The session relay apparatus B ( 10   b ) that has received this BYE message further transfers a BYE message  602  to the session relay apparatus A ( 10   a ). The session relay apparatus A ( 10   a ) that has received this BYE message similarly transfers a BYE message  603  to the communication terminal A ( 15   a ). The communication terminal A ( 15   a ) that has received the BYE message transmits an OK message  604  to the session relay apparatus A ( 10   a ).  
         [0047]    In the session relay apparatus A ( 10   a ) that has received the OK message, the session control unit notifies the policy generating unit that the session has ended. The policy generating unit  210  that has received this notification searches the policy management table  220  using “Call-ID”, “To tag” and “From tag” stored in the OK message, deletes the corresponding entry from the policy storage unit  220 , generates the QoS policy indicating the cancellation of the QoS control and delivers the QoS policy to the policy distribution unit  200 .  
         [0048]    The policy distribution unit  200 , using the COPS protocol, executes the process of setting in the edge node  20   a  the QoS policy generated by the policy generating unit  210 . The policy distribution unit  200  that has received the QoS policy indicating the cancellation of the QoS control generates a decision message  606  in accordance with the COPS protocol, searches the communication terminal-edge node correspondence table  230  for the edge node A ( 20   a ) accommodating the communication terminal A ( 15   a ) and distributes a decision message  606  to the edge node A ( 20   a ).  
         [0049]    The edge node A ( 20   a ) that has received the decision message  606  deletes the corresponding QoS policy setting ( 608 ), and sends a report message  607  indicating the complete deletion as a response to the session relay apparatus A ( 15   a ).  
         [0050]    The session relay apparatus A ( 10   a ) that has received the report message  607  transmits an OK message  609  to the session relay apparatus B ( 10   b ). In the session relay apparatus B ( 10   b ) that has received the OK message, the end of the session is notified from the session control unit  110  to the policy generating unit  210 . The policy generating unit  210  that has received this notification deletes the corresponding entry of the policy from the internal policy storage unit  220  based on the information contained in the OK message. The policy distribution unit  200 , in order to instruct the edge node  20   b  to cancel the policy setting, prepares a decision message  611  in accordance with the COPS protocol and sends it to the edge node B ( 20   b ) ( 610 ).  
         [0051]    The edge node B ( 20   b ) that has received the decision message  611  deletes the QoS policy setting and transmits a report message  612  to the session relay apparatus B ( 10   b ). The session relay apparatus B ( 10   b ) that has received this report message transmits an OK message  614  to the communication terminal B ( 20   b ) ( 613 ). Through these steps, the peer-to-peer communication is terminated and the corresponding QoS control is canceled.  
         [0052]    [0052]FIG. 9 is an operation flowchart showing the process executed by the policy generating unit  210  included in the session relay apparatus  10  according to the invention. The policy generating unit  210  initializes the policy storage unit  220  at the time of starting and then repeatedly executes the following-described process.  
         [0053]    The policy generating unit  210  first checks whether the establishment of a session has been detected or not. One method of detecting the session establishment consists in the notification from the session control unit  110 . Upon detection of the session establishment, the policy generating unit  210  generates a policy for setting the DSCP value, from the session information and the peer-to-peer communication information in the INVITE message providing the session control message. The policy generating unit  210  registers the generated policy in the policy storage unit  220 , and through the policy distribution unit  200 , sets a policy in the edge node  20  according to the COPS protocol.  
         [0054]    In the case where the session is not established or after the aforementioned process is executed upon detection of the session establishment, the policy generating unit  210  checks whether the end of the session has been detected or not. One method of detecting the end of a session consists in the notification from the session control unit  110 . Upon detection of the end of a session, the policy generating unit  210  searches the policy storage unit  220  with the session information in the OK message providing the session control message as a key. The policy generating unit  210  generates a policy for clearing the DSCP value using the entry of the search result, and through the policy distribution unit  210 , cancels the policy setting in the edge node  20  according to the COPS protocol. The corresponding entry of the policy storage unit  220  is deleted subsequently by the policy generating unit  210 .  
         [0055]    [0055]FIG. 10 shows a mesh configuration of the network using the session relay apparatus  10  according to the invention as a communication network with a selectable relay network. Networks  40   a ,  40   b ,  40   c  exist as relay networks. The band of each network can be secured by selecting a relay network in accordance with the type of the peer-to-peer communication data. In the case where the relay network designated by numeral  40   a  is selected by policy setting, for example, the address of the relay node  30   aa  connected to the relay network  40   a  is registered in the “relay network” item of the policy storage unit  220  shown in FIG. 5. As a result, the session relay apparatus  10   a  transfers to the relay node  30   aa  those packets received from the communication terminal  15   a  which meet the required conditions, and transmits them through the relay network  40   a  to the communication terminal  15   b . This embodiment is effectively applicable to a case in which with different policies preset in the networks  40   a ,  40   b  and  40   c , for example, a network using a policy conforming with the packet transmitted from the communication terminal A  15   a  to the communication terminal B  15   b  is selected.  
         [0056]    It will thus be understood from the foregoing description that according to this invention, the start and end of the policy settable peer-to-peer communication are detected by a session relay apparatus, so that a policy can be set in each edge node accommodating a communication terminal at the start of communication, while the policy setting can be canceled at the end of communication. Also, the need of the policy-setting operation by the operator is eliminated, thereby making it possible to prevent the packet relay delay which otherwise might occur in an edge node by the unrequited policy setting.  
         [0057]    Embodiments of the invention are described above. Nevertheless, this invention is not limited to these embodiments, but as obvious to those skilled in the art, can be variously modifiable within the scope of the appended claims without departing from the spirit of the invention.

Technology Category: 5