Abstract:
To implement a calling party number anonymous service in an IP telephone service. An IP telephone terminal adds the setting of requesting a Pool IP address along with a normal IP address to a REGISTER message directed from the IP telephone terminal to an SIP server and requests the assignment of a temporary IP address if receiving an anonymous call incoming request message. The SIP server makes the temporary assignment of the Pool IP address and notifies the temporary IP address to a called party IP telephone terminal by adding it to an INVITE message, if the called IP address of the anonymous call incoming request INVITE message is the IP telephone terminal. The called IP telephone terminal receiving the assignment of the temporary IP address can make the connection, communication and disconnection processes employing the temporary IP address as the self IP address in the following dialog.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese patent application JP 2009-133709 filed on Jun. 3, 2009, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a communication system, a session control management server and a session control method, and more particularly to a communication system, a session control management server and a session control method for performing a response process in the case of receiving an anonymous call incoming request, with the session control in the internet. 
         [0004]    2. Description of the Related Art 
         [0005]    At present, with the spread of the internet, an IP telephone service using the internet is provided by each carrier and an Internet Service Provider (ISP). Also, in the IP telephone service, a Voice over IP (VoIP) communication for transferring voice data with an Real Time Transport Protocol (RTP) packet is performed by establishing a channel (session) between the terminals before starting the communication. 
         [0006]    As a main session control protocol for making the session establishment and disconnection between the terminals, an Session Initiation Protocol (SIP) is specified for controlling the session between the terminals via an SIP server. 
         [0007]    An SIP message is composed of a start line part and a header part for carrying the request or response information and a message body part for describing the session content, in which an Session Description Protocol (SDP), for example, is employed to describe the session content, and the other party of communication is identified by a request Uniform Resource Identifier (URI) described in the start line part. Also, in a process of establishing the session, the RTP packet communication conditions between the terminals, such as calling the receiver, each protocol for voice or video, and the bit rate, are decided. 
       SUMMARY OF THE INVENTION 
       [0008]    In the IP telephone service, the session establishment between the terminals is basically made, employing the URI information such as the telephone numbers of the calling party and the called party, but since it has a calling party number anonymous service (hereinafter referred to as anonymous) in the same way as a telephone exchange service, the called party receiving an anonymous call can confirm the calling party by speech. 
         [0009]    However, the IP telephone service, unlike the telephone exchange service, is specified to notify an IP address and so on for use in the RTP packet communication in establishing the session with an SIP message, so that the IP address of the called party is unconditionally notified to the calling party. Therefore, there is a problem that the IP address of the called party is known before confirming the calling party by speech. 
         [0010]    Further, in the case of the malicious calling party, there is a possibility of causing a damage such as a Denial of Service (DOS) attack of flowing a large number of packets to the IP terminal after acquiring the IP address of the called party. 
         [0011]    In Japanese Patent No. 2004-228829, a method for protecting the IP address of the calling party was described but the receiver side was not described. 
         [0012]    In the light of the above-mentioned problems, an object of this invention is to provide a communication system, a session control management server and a session control method for implementing a calling party number anonymous service in the IP telephone service. 
         [0013]    According to the invention, in an IP telephone network in which a plurality of IP telephone terminals having a function of making the communication employing a temporary IP address in receiving an anonymous call incoming request message, for example, are connected to an SIP server for assigning the temporary IP address from a Pool IP address, and adding the assigned temporary IP address to an INVITE message to be transferred in receiving an anonymous call incoming request INVITE message directed to an IP telephone terminal receiving a temporary IP address request message, the IP telephone terminal adds the setting of requesting the Pool IP address along with the normal IP address to a Contact field of a REGISTER message in registering the information with the SIP server, and requests the assignment of the temporary IP address if receiving the anonymous call incoming request message. 
         [0014]    The SIP server, upon detecting the request setting in the REGISTER message, can register the information regarding the normal IP address and the information for assigning the Pool IP address at the anonymous call incoming request in a subscriber management table. 
         [0015]    Also, the SIP server makes the temporary assignment of the Pool IP address and notifies the temporary IP address to the called party IP telephone terminal by adding it to a From field of the INVITE message, if the called party IP telephone terminal for the anonymous call incoming request INVITE message is the IP telephone terminal. 
         [0016]    The called party IP telephone terminal receiving the assignment of the temporary IP address can make the connection, communication and disconnection processes employing the temporary IP address for the self IP address in the following dialog. Under the above session control, the called party IP telephone terminal that communicates with a calling party IP telephone terminal for the anonymous call incoming request can make the communication without the self IP address known to the anonymous party. 
         [0017]    The session control protocol is not the SIP, but the session control protocol such as an MGCP, H.248 may be employed in the same way as the SIP. 
         [0018]    Though the method for assigning the Pool IP address from the SIP server has been described above, another method may be applied in which the called party IP telephone terminal requests a DHCP server for the temporary IP address if recognizing an anonymous call incoming request (Anonymous). 
         [0019]    According to the first solving means of the present invention, there is provided a communication system in which a plurality of IP terminals are connected to a session control management server, the session control management server comprising: 
         [0020]    a connection management table storing a status indicating talking or disconnected, calling party information and called party information; and 
         [0021]    a subscriber management table storing a telephone number, an identifier and an IP address for each subscriber; 
         [0022]    wherein 
         [0023]    the session control management server extracts the calling party information and the called party information from a first connection request message received from an IP terminal, and registers a calling party address as the calling party information and a called terminal identifier as the called party information in the connection management table; 
         [0024]    the session control management server sends a second connection request message including the called terminal identifier and a temporary IP address assigned to a called IP terminal in the called party information to the called IP terminal; 
         [0025]    the called IP terminal extracts the called party information from the received second connection request message and sends a response message using the temporary IP address as a self IP address to the session control management server if the temporary IP address is included; and 
         [0026]    the session control management server makes the communication between a calling IP terminal and the called IP terminal under the session connection establishment control by referring to the connection management table with the temporary IP address. 
         [0027]    According to the second solving means of the present invention, there is provided a session control management server in a communication system in which a plurality of IP terminals are connected to the session control management server, the session control management server comprising: 
         [0028]    a connection management table storing a status indicating talking or disconnected, calling party information and called party information; and 
         [0029]    a subscriber management table storing a telephone number, an identifier and an IP address for each subscriber; 
         [0030]    wherein 
         [0031]    the session control management server extracts the calling party information and the called party information from a first connection request message received from an IP terminal, and registers a calling party address as the calling party information and a called terminal identifier as the called party information in the connection management table; 
         [0032]    the session control management server sends a second connection request message including the called terminal identifier and a temporary IP address assigned to a called IP terminal in the called party information to the called IP terminal; 
         [0033]    the session control management server receives a response message employing the temporary IP address as the self IP address from the called IP terminal, and 
         [0034]    the session control management server makes a communication between the calling IP terminal and the called IP terminal under the session connection establishment control by referring to the connection management table with the temporary IP address. 
         [0035]    According to the third solving means of the present invention, there is provided a session control method using a communication system in which a plurality of IP terminals are connected to a session control management server, the session control management server comprising: 
         [0036]    a connection management table storing a status indicating talking or disconnected, calling party information and called party information; and 
         [0037]    a subscriber management table storing a telephone number, an identifier and an IP address for each subscriber; 
         [0038]    wherein 
         [0039]    the session control management server extracts the calling party information and the called party information from a first connection request message received from an IP terminal, and registers a calling party address as the calling party information and a called terminal identifier as the called party information in the connection management table; 
         [0040]    the session control management server sends a second connection request message including the called terminal identifier and a temporary IP address assigned to a called IP terminal in the called party information to the called IP terminal; 
         [0041]    the called IP terminal extracts the called party information from the received second connection request message and sends a response message using the temporary IP address as a self IP address to the session control management server if the temporary IP address is included; and 
         [0042]    the session control management server makes the communication between a calling IP terminal and the called IP terminal under the session connection establishment control by referring to the connection management table with the temporary IP address. 
         [0043]    With this invention, there can be provided a communication system and a session control method for implementing a calling party number anonymous service in the IP telephone service. For example, with this invention, it is possible to increase the security of the receiver side by notifying the temporary address as the IP address of the receiver under the session control. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a diagram showing an IP telephone network configuration example. 
           [0045]      FIG. 2  is a block diagram showing the configuration of a main part of an IP telephone terminal. 
           [0046]      FIG. 3  is a block diagram showing the configuration of a main part of an SIP server. 
           [0047]      FIGS. 4A and 4B  are views showing the organization of a subscriber management table. 
           [0048]      FIGS. 5A ,  5 B and  5 C are views showing the organization of a connection management table. 
           [0049]      FIGS. 6A and 6B  are views showing the organization of a Pool address management table. 
           [0050]      FIG. 7  is a chart showing a sequence example for registering the IP telephone terminal information with the SIP server. 
           [0051]      FIG. 8  is a view showing a description example of a REGISTER message (including a request example at the time of Anonymous). 
           [0052]      FIG. 9  is a chart showing a connection, speech and disconnection sequence example between the IP telephone terminals. 
           [0053]      FIG. 10  is a view showing a description example of an INVITE message (at the time of calling party Anonymous) from the calling party IP telephone terminal. 
           [0054]      FIG. 11  is a view showing a description example of an INVITE message (at the time of calling party Anonymous and Pool IP address assignment) from the SIP server. 
           [0055]      FIG. 12  is a view showing a description example of a  180  Ringing message (at the time of setting the called party IP address=Pool IP address) from the called party IP telephone terminal. 
           [0056]      FIG. 13  is a flowchart showing a registration process flow at the IP telephone terminal. 
           [0057]      FIG. 14  is a flowchart showing a REGISTER process flow in the SIP server. 
           [0058]      FIG. 15  is a flowchart showing an INVITE process flow in the SIP server. 
           [0059]      FIG. 16  is a flowchart showing an INVITE receiving process flow at the IP telephone terminal. 
           [0060]      FIG. 17  is a flowchart showing a connection registration process flow in the SIP server. 
           [0061]      FIG. 18  is a flowchart showing a disconnection registration process flow in the SIP server. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    The security on the receiver side can be increased by notifying a temporary address as the IP address of a receiver to the calling party under the session control as will be described in the following. An embodiment will be described below in detail with reference to the drawings. 
       A. System 
       [0063]      FIG. 1  is a diagram showing a configuration example of an IP telephone network using an SIP as the session control protocol. 
         [0064]    The network comprises a plurality of IP telephone terminals  1  ( 1 - 1 A to  1 - 1   n ,  1 - 2 A to  1 - 2   m ), an SIP server  2 , an L2SW  3  ( 3 - 1 ,  3 - 2 ) for connecting each IP telephone terminal  1  to the routers (R)  4  ( 4 - 1  to  4 - 3 ) and the DHCP servers  5  ( 5 - 1 ,  5 - 2 ) for dynamically assigning the IP address. When the communication is made between each IP telephone terminal  1 , first of all, an IP telephone terminal  1  registers with the SIP server  2 . Next, for the SIP server  2 , the connection control to communicate with the other party of communication is made via the SIP server  2  with an SIP message, and after the completion of session connection, the communication is made between the IP telephone terminals  1 . 
         [0065]      FIG. 2  is a block diagram showing the configuration of a main part of the IP telephone terminal  1 . 
         [0066]    The IP telephone terminal  1  mainly comprises a line IF (interface)  11 , a processor  12 , an SIP processing section  13 , a protocol processing section  14 , a speaker  15  of user interface, a microphone  16  and a key  17 . The SIP processing section  13  mainly performs a registration process (F 1 ), an INVITE receiving process (F 102 ) and a connection/disconnection process  131  in accordance with the information inputted by the key  17 . The protocol processing section  14  performs a decode process for an RTP packet received from the line IF  11 . The decoded voice is outputted from the speaker  15 . Also, it performs an encode process for the voice inputted from the microphone  16 , and sends an RTP packet from the line IF  11 . 
         [0067]      FIG. 3  is a block diagram showing the configuration of a main part of the SIP server  2 . 
         [0068]    The SIP server  2  mainly comprises a line IF  21 , a processor  22 , an SIP processing section  23 , a connection management table  24 , a subscriber management table  25  and a Pool address management table  26 . The SIP processing section  23  mainly performs a REGISTER process (F 2 ), an INVITE process (F 101 ), a connection registration process (F 103 ) and a disconnection registration process (F 104 ). 
         [0069]      FIGS. 4A and 4B  are views showing the table organization of the subscriber management table  25  for managing each subscriber information registered with the SIP server  2  through the REGISTER process (F 2 ). 
         [0070]    The subscriber management table  25  includes a subscriber telephone number  251 , an SIP URI  252 , an IP address  253  and an option  254 . 
         [0071]      FIGS. 5A ,  5 B and  5 C are views showing the table organization of the connection management table  24  for management on the SIP server  2  through each of the INVITE process (F 101 ), the connection registration process (F 103 ) and the disconnection registration process (F 104 ) under the session control. 
         [0072]    The connection management table  24  includes a connection start time  241 , a disconnection time  242 , a status  243 , the calling party information  244 , the called party information  245  and the remarks  246 . 
         [0073]      FIGS. 6A and 6B  are views showing the table organization of the Pool address management table  26 . 
         [0074]    The Pool address management table  26  includes an IP address  261 , a start time  262  and a user  263 . 
         [0075]    In the drawings, each table has a reference number (#). 
       B. Operation 
       [0076]    A session control processing operation via the SIP server  2  to communicate between user- 1 @A( 1 - 1 A) and user- 2 @B( 1 - 2 B) according to the embodiment  1  will be described below with reference to the sequence charts of  FIGS. 7 and 9 , the SIP message views of  FIGS. 10 to 12  and the flowcharts of  FIGS. 13 to 18 . 
       1. Registration 
       [0077]      FIG. 7  is a chart showing a sequence example for registering the IP telephone terminal information with the SIP server. 
         [0078]      FIG. 13  is a flowchart showing a registration process flow at the IP telephone terminal. 
         [0079]    The SIP processing section  13  performs the registration process (F 1 ) for the SIP server  2  to enable the communication, when the power of the user- 2 @B ( 1 - 2 B) is turned on, as shown in the sequence chart of  FIG. 7 . In the registration process (F 1 ) as shown in  FIG. 13 , a determination is made (F 11 ) whether a Pool IP address is requested or not if there is an anonymous call incoming request. If the Pool IP address is not requested (N), a REGISTER message is sent (F 13 ) with the basic information set in the REGISTER message. On the other hand, if the Pool IP address is requested (Y), in addition to the basic information, a Pool IP address request is additionally set in a Contact field of the REGISTER message (F 12 ) to request the assignment of the pool IP address from the SIP serve  2  at the time of anonymous call incoming and the REGISTER message is sent (F 13 ). 
         [0080]      FIG. 8  is a view showing a description example of the REGISTER message (including a request example at the time of Anonymous). 
         [0081]    REGISTER (Anonymous: Pool (SQ 1 )) with the setting of Contact:&lt;sip:user- 2 @anonymous-pool&gt;(M 11 ) added through the registration process (F 1 ) for the REGISTER message (M 1 ) as shown in  FIG. 8  is transferred from the user- 2 @B ( 1 - 2 B) to the SIP server  2 . 
         [0082]      FIG. 14  is a flowchart showing a REGISTER process flow in the SIP server. 
         [0083]    If the SIP server  2  receives the REGISTER (SQ 1 ), the SIP processing section  23  performs the REGISTER process (F 2 ). In the REGISTER process (F 2 ) as shown in  FIG. 14 , a determination is made (F 21 ) whether or not there is a Pool IP address request in the Contact field of the received REGISTER message (M 1 ). Herein, if there is a setting of Contact:&lt;sip:user- 2 @anonymous-pool&gt;(M 11 ), for example, (Y), the SIP processing section  23  registers 03-5000-2222 for the telephone number ( 251 ) and user- 2 @B for the SIP URI ( 252 ) from the From field and registers IPv 4 =11.0.0.2 for the IP address ( 253 ) from the Contact field, for example, as the basic information in #s( 255 ) of the subscriber management table  25 , as shown in  FIG. 4B . Also, the SIP processing section  23  registers 03-5000-2222 for the telephone number ( 251 ), user- 2 @B for the SIP URI( 252 ) and IPv 4 =Pool for the IP address ( 253 ), for example, in #t( 256 ), further registers (F 22 ) the option ( 254 ) for assigning the Pool IP address at the time of anonymous call incoming, and then sends the  200  OK message (F 23 ). 
         [0084]    Also, if there is no setting for the Pool IP address request at step F 21  (N), the SIP processing section  23  registers only the #s( 255 ), without registering the #t( 256 ), and sends the  200  OK message (F 23 ). The OK message is transferred as the  200  OK (SQ 2 ) message from the SIP server  2  to the user- 2 @B( 1 - 2 B). 
       2. Anonymous Call Incoming 
       [0085]      FIG. 9  is a chart showing a connection, speech and disconnection sequence example between the IP telephone terminals. 
         [0086]      FIG. 10  is a view showing a description example of an INVITE message (at the time of calling party Anonymous) from the calling party IP telephone terminal. 
         [0087]    Each process for making the anonymous call incoming request between user- 1 @A( 1 - 1 A) and user- 2 @B( 1 - 2 B) via the SIP server  2  in the sequence of  FIG. 9  will be described below. 
         [0088]    Calling 
         [0089]    The user- 1 @A( 1 - 2 A) transfers the INVITE message (M 101 ) as shown in  FIG. 10  to the SIP server  2  with the INVITE (Anonymous) (SQ 101 ). The user- 1 @A( 1 - 2 A) sets From:anonymous&lt;sip:anonymous@A&gt;;tag=qqqqqq (M 1011 ) indicating to be anonymous, for example, as the value of From header in the INVITE message (M 101 ) for the calling party number anonymous request. 
         [0090]    INVITE Process 
         [0091]    If the SIP server  2  receives the INVITE (SQ 101 ), the SIP processing section  23  performs an INVITE process (F 101 ). 
         [0092]      FIG. 15  is a flowchart showing an INVITE process flow in the SIP server. 
         [0093]    In the INVITE process (F 101 ) as shown in  FIG. 15 , when the INVITE message (M 101 ) is received, the connection start time ( 241 )=2009/1/10 11: 58:28 for the INVITE message (M 101 ) receiving time and the status ( 243 )=INVITE process  200  OK wait are set, for example, in # 2  ( 247 ) of the connection management table ( 24 ), as shown in  FIG. 5A . 
         [0094]    For the calling party information ( 244 ), anonymous, anonymous@A and IP 4 =10.0.0.1 for C=IN are set as the information from the From field value “anonymous&lt;sip:anonymous@A &gt; ;tag=qqqqqq” (M 1011 ) and the Contact field value “&lt;sip:anonymous@10.0.0.1&gt;” M 1013 ) in the header part, for example, and the anonymous connection request is set for the remarks ( 246 ). 
         [0095]    For the called party information ( 245 ), 03-5000-2222 and user- 2 @B are set as the information from the To field value “03-5000-2222&lt;sip:user- 2 @B&gt;” (M 1012 ) in the header part, for example, (F 1011 ). 
         [0096]    Also, the subscriber management table ( 25 ) is searched with the value of called party information ( 245 ) (telephone number “03-5000-2222” or SIP URI “user- 2 @B”) as the search key information to extract the IP address information on the called party side, and IP 4 =11.0.0.2 and pool are additionally set as the called party information ( 245 ) in the connection management table ( 24 ) (F 1012 ). 
         [0097]    Next, the SIP processing section  23  determines (F 1013 ) whether or not there is the unknown (anonymous) connection request in the calling party information by referring to the connection management table ( 24 ), or from the INVITE message (M 101 ). If there is no unknown (anonymous) connection request (N), the SIP processing section  23  sends the INVITE message (F 1018 ). On the other hand, if there is the unknown (anonymous) connection request (Y), the SIP processing section  23  searches the subscriber management table ( 25 ) with the value of calling party information ( 244 ) (IP address “IP 4 =10.0.0.1”) as the search key information to extract the calling party telephone number and the SIP URI information, and additionally sets the telephone number=045-111-1111 and SIP URI=user- 1 @A as the calling party information ( 244 ) in the connection management table ( 24 ) (F 1014 ). 
         [0098]    Also, the SIP processing section  23  determines whether or not there is the pool request as the called party IP address (F 1015 ). For example, the SIP processing section  23  refers to the subscriber management table ( 25 ) based on the called party telephone number or SIP URI, in which if the IP address=Pool is set at the corresponding IP address ( 253 ), or the information of assigning the Pool IP address at the time of anonymous call incoming is set in the corresponding option ( 254 ), the SIP processing section  23  can determine that there is the pool request. 
         [0099]    If there is no pool request (N) at step F 1015 , the SIP processing section  23  sends the INVITE message to the user- 2 @B (F 1018 ). On the other hand, if there is the pool request (Y), the SIP processing section  23  selects the empty addresses in the Pool address management table ( 26 ) in the prescribed order or rule, assigns the IP address ( 261 )=11.0.0.202 in #3( 264 ), for example, with the settings of the start time ( 262 )=2009/1/10 11:58:28 and the user ( 263 )=user- 2 @B from the To field, and adds Pool=11.0. 0.202 as the called party information ( 245 ) in the connection management table ( 24 ) (F 1016 ), as shown in  FIG. 6B . 
         [0100]    Next, the SIP processing section  23  adds the Pool address to the INVITE message to notify the assigned Pool address to the user- 2 @B( 1 - 2 B) (F 1017 ). 
         [0101]      FIG. 11  is a view showing a description example of the INVITE message (at the time of calling party Anonymous and Pool IP address assignment) from the SIP server. 
         [0102]    For the addition of the Pool address, the assigned Pool address=11.0.0.202 is added to the INVITE message as “;pool=IN IP 4  11.0.0.202 in To:03-5000-2222&lt;sip:user- 2 @B&gt;;pool=IN IP 4  11.0.0.202 (M 1021 ) in the INVITE message (M 102 ), for example, as shown in  FIG. 11 . 
         [0103]    Thereafter, the SIP processing section  23  sends the INVITE message to the user- 2 @B (F 1018 ). The INVITE message is transferred as the INVITE (SQ 102 ) from the SIP server  2  to the user- 2 @B( 1 - 2 B). 
         [0104]    INVITE Receiving Process 
         [0105]      FIG. 16  is a flowchart showing an INVITE receiving process flow at the IP telephone terminal. 
         [0106]    In the user- 2 @B( 1 - 2 B), the SIP processing section  13  performs the INVITE receiving process (F 102 ). In the INVITE receiving process (F 102 ) as shown in  FIG. 16 , the To field value in the received INVITE message (M 102 ) is extracted (F 1021 ), and a determination is made whether or not the Pool IP address is assigned (F 1022 ). 
         [0107]    For example, if there is the setting of To:03-5000-2222&lt;sip:user- 2 @B&gt;;pool=IN IP 4  11.0.0.202 (M 1021 ) (Y), the user- 2 @B( 1 - 2 B) employs the Pool IP address (11.0.0.202) assigned in the SIP server  2 , instead of the formal IP address (11.0.0.2), as the self IP address for use in the SIP message in this dialog and the RTP packet (F 1023 ). Thereafter, the SIP processing section  13  sends the  180  Ringing message to the SIP server  2  (F 1024 ). 
         [0108]    On the other hand, if there is no setting at step F 1022  (N), the SIP processing section  13  sends the  180  Ringing message, the user- 2 @B( 1 - 2 B) employs the formal IP address (11.0.0.2) as the self IP address for use in the SIP message in this dialog and the RTP packet (F 1024 ). 
         [0109]    The SIP processing section  13  sends the  180  Ringing (SQ 103 ) from the user- 2 @B( 1 - 2 B) to the SIP server  2 . 
         [0110]      FIG. 12  is a view showing a description example of the  180  Ringing message (at the time of setting called party IP address=Pool IP address) from the called party IP telephone terminal. 
         [0111]    The user- 2 @B( 1 - 2 B) sets the Pool IP address as &lt;sip:user- 2 @11.0.0.202&gt;(M 1031 ) to the Contact field in the  180  Ringing (M 103 ) as shown in  FIG. 12 , with the  180  Ringing (SQ 103 ) through the INVITE receiving process (F 102 ). 
         [0112]    Response 
         [0113]    Also, the SIP server  2  receives the  180  Ringing (SQ 103 ) from the user- 2 @B( 1 - 2 B), and transfers the  180  Ringing to the user- 1 @A( 1 - 1 A) (SQ 104 ). 
         [0114]    The user- 2 @B( 1 - 2 B) transiting to an off-hook state sends the  200  OK (SQ 105 ) from the user- 2 @B ( 1 - 2 B) to the SIP server  2 , which then transfers it to the user- 1 @A( 1 - 1 A) (SQ 106 ). 
         [0115]    The user- 1 @A( 1 - 1 A) receiving the  200  OK (SQ 106 ) sends it as an ACK (SQ 107 ) to the SIP server  2  from the user- 1 @A( 1 - 1 A). 
         [0116]    Connection Registration Process 
         [0117]      FIG. 17  is a flowchart showing a connection registration process flow in the SIP server. 
         [0118]    In the SIP server  2 , the SIP processing section  23  performs a connection registration process (F 103 ). In the connection registration process (F 103 ) as shown in  FIG. 17 , the ACK message is received (F 1031 ), the connection start time ( 241 ) is updated to 2009/1/10 11:58:29, and the status ( 243 ) is changed to the talking (F 1032 ), as indicated at # 2  in  FIG. 5B . Thereafter, the SIP processing section  23  sends the ACK message (F 1033 ). The SIP processing section  23  transfers the ACK (SQ 108 ) from the SIP server  2  to the user- 2 @B( 1 - 2 B). 
         [0119]    In this way, the RTP (VoIP) communication (SQ 109 ) is performed between user- 1 @A( 1 - 1 A) and user- 2 @B( 1 - 2 B) under the session connection establishment control from the INVITE (SQ 101 ) to the ACK (SQ 108 ). 
         [0120]    Disconnection Registration Process 
         [0121]    After the completion of speech, in disconnecting from the user- 1 @A( 1 - 1 A), for example, BYE(SQ 110 ) is transmitted to the SIP server  2 , and transferred from the SIP server  2  to the user- 2 @B ( 1 - 23 ) (SQ 111 ). The user- 2 @B( 1 - 2 B) receiving the BYE(SQ 111 ) sends the  200  OK (SQ 112 ) to the SIP server  2 . 
         [0122]      FIG. 18  is a flowchart showing a disconnection registration process flow in the SIP server. 
         [0123]    In the SIP server  2 , the SIP processing section  23  performs a disconnection registration process (F 104 ). In the disconnection registration process (F 104 ) as shown in  FIG. 18 , the  200  OK message for the BYE message is received (F 1041 ), and the disconnection time ( 242 ) is updated to 2009/1/10 12:4:12 and the status ( 243 ) is changed to disconnect (F 1042 ), as indicated at # 2  in  FIG. 5C . Thereafter, the  200  OK message is sent (F 1043 ). The SIP processing section  23  transfers the  200  OK message (SQ 113 ) from the SIP server  2  to the user- 1 @A( 1 - 1 A). 
         [0124]    In this way, the disconnection of the RTP (VoIP) communication (SQ 109 ) between user-l@A( 1 - 1 A) and user- 2 @B( 1 - 2 B) is completed under the session disconnection control from the BYE (SQ 110 ) to the  200  OK (SQ 113 ). 
         [0125]    Though in this embodiment, the SIP is used as the session control protocol and the Pool IP address is used for the called party IP address in the anonymous call incoming request (Anonymous), the session control protocol such as an MGCP, H.248 may be also used in the same way as the SIP. 
         [0126]    Also, though the method of assigning the Pool IP address from the SIP server has been described above, the called party IP telephone terminal may request the DHCP server for the temporary IP address, if it recognizes the anonymous call incoming request (Anonymous).