Abstract:
Conventionally, in a system where devices for handling multiple media data such as audio and video are present, there is a problem that the number of audio channels that can be processed at the gateway is limited. In light of this problem, this invention offers a gateway having distributed processing function for a telephone or a data processing system featuring the capability to request address conversion to another terminal within the system to replace the address of stream-type packet data such as audio and video meant for itself, and if the aforementioned terminal to which the request was sent responds that it can handle the requested processing, to notify the address of the terminal processing the address conversion to the terminal transmitting the stream-type packet data.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to gateways and communication terminals that distribute the address conversion process when the traffic of stream-type packet data such as audio and video increases. 
       BACKGROUND 
       [0002]    When handling heavy load stream-type packet data such as audio and video, there is sometimes a gateway installed in the system dedicated for processing stream-type packet data. 
         [0003]    In such a case, processing stream-type packet data for the system entirely at the gateway may reduce the processing load of other devices; however, a new problem arises in which it sets a limit to the maximum traffic load that a gateway can process. 
         [0004]    On the other hand, Patent Document 1 discloses a technology for servers to monitor their processing loads themselves and to distribute the load to other servers when it exceeds a threshold. 
       REFERENCE 
     Patent Document 
       [0000]    
       
         Patent Document 1: Bulletin 2008-040718 (JP) 
       
     
       SUMMARY OF THE INVENTION 
     Problems Solved by the Invention 
       [0006]    However, if the same approach is applied to the aforementioned gateways, it creates problems in implementation, as it requires a backup gateway to be installed in advance. This invention aims to eliminate the need to add new devices by distributing heavy processing loads from stream-type packet data such as audio and video. 
       Means of Solving the Problems 
       [0007]    This invention has been designed to solve the above-stated problems, and its goal is to provide a gateway that configures a telephone or a data system; features the capability to request address conversion to another terminal within the system to replace the address of stream-type packet data such as audio and video meant for itself; and if the aforementioned terminal, to which the request was sent, responds that it can handle the requested processing, notifies the address of the terminal processing the address conversion to the terminal transmitting the stream-type packet data. 
       TECHNICAL ADVANTAGES 
       [0008]    By using this invention, a telephone or a data processing system can distribute the increased load on a particular gateway, caused by an increase in stream-type packet data such as audio and video, thereby effectively eliminating the need for adding a backup gateway. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The invention may be more readily described with references to the accompanying figures: 
           [0010]      FIG. 1  illustrates an overall configuration of the distributed processing gateway and telephone terminals of an embodiment of the invention. 
           [0011]      FIG. 2  is a block diagram showing the configuration of a distributed processing gateway of an embodiment of the invention. 
           [0012]      FIG. 3  is a table showing IP addresses of connection request data of an embodiment of the invention. 
           [0013]      FIG. 4  is a table specifying IP addresses of audio data (No. 1) of an embodiment of the invention. 
           [0014]      FIG. 5  is a table specifying IP addresses of audio data (No. 2) of an embodiment of the invention. 
           [0015]      FIG. 6  is a flow chart showing the operation of the distributed processing gateway of an embodiment of the invention. 
           [0016]      FIG. 7  is a block diagram showing the configuration of telephone terminals of an embodiment of the invention. 
           [0017]      FIG. 8  is a flow chart showing the operation of telephone terminals of an embodiment of the invention. 
           [0018]      FIG. 9  is a sequence chart showing the operation of the distributed processing gateway of an embodiment of the invention. 
           [0019]      FIG. 10  is a sequence chart showing the operation of telephone terminals of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    Assuming that the communication terminals in this invention are telephone terminals, we describe the best way to implement the invention. 
       First Embodiment 
       [0021]      FIG. 1  shows the overall configuration of a telephone system including a gateway with distributed processing function and telephone terminals of an embodiment of the invention. 
         [0022]    As shown in the figure, the telephone system comprises a LAN  70  connected to Telephone Terminals  60  and  61 , an SIP server  40  that controls the overall telephone functions relevant to terminals  60  and  61 , and Gateway  50  that performs address conversion for terminals  60  and  61  to communicate with other terminals on the IP network. 
         [0023]    Furthermore, Router  30  between IP Network  10  and LAN  70  routes the traffic of data packets exchanged between the two. 
         [0024]    There is another Telephone Terminal (hereinafter referred to as “Partner Telephone Terminal  20 ”) connected to the IP Network  10  with which Telephone Terminal  60  communicates. Partner Telephone Terminal  20  can be a telephone system with an SIP server or a telephone terminal that is connected via another network. 
         [0025]    Next, we describe the procedure for establishing communication when Telephone Terminal  60  calls Partner Telephone Terminal  20  across IP Network  10  passing through a conventional Gateway  50 . 
         [0026]    First, Telephone Terminal  60  sends a connection request to SIP Server  40 , which then relays the request to Partner Telephone Terminal  20  via Gateway  50  and Router  30 . 
         [0027]    The connection request is appended with an audio relay IP address at the time it is relayed by SIP Server  40 . Here the audio relay IP address refers to the IP address of relay equipment (hereinafter referred to as the “gateway function”) that converts the IP address for the audio data, i.e., Gateway  50 . 
         [0028]    Upon receipt of the connection request, Partner Telephone Terminal  20  stores the IP address of Gateway  50  and sends a response of “ready for connection (200 OK)” to SIP Server  40  via Router  30  and Gateway  50 . SIP server  40  sends the “ready for connection (200 OK)” to Telephone Terminal  60  that has sent the connection request. 
         [0029]    Then, once Partner Telephone Terminal  20  is in the on-hook state and a call connection request attached with an audio relay IP address is executed, an exchange of audio data between Telephone Terminal  60  and Partner Telephone Terminal  20  will be performed via Gateway  50 . 
         [0030]    In particular, upon receipt of audio data from Telephone Terminal  60 , Gateway  50  performs an audio data or address conversion (hereinafter collectively referred to as “address conversion”) for Partner Telephone Terminal  20  and transmits it to Partner Telephone Terminal  20 . As for audio data received from Partner Telephone Terminal  20  via Router  30 , it performs address conversion for Telephone Terminal  60  and transmits it to the terminal. 
         [0031]    Here in the present system configuration, SIP Server  40 , Gateway  50 , and Telephone Terminals  60  and  61  are independent; however, note that the system may be, for example, a telephone terminal with an SIP server function or a telephone terminal with a gateway function. 
         [0032]      FIG. 2  is a block diagram showing the configuration of each block in Gateway  50 . 
         [0033]    As shown in the diagram, Gateway  50  consists of Line Controller  501 , Gateway Controller  502 , Address Conversion Manager  503 , Address Conversion Request Transmitter  504 , Address Conversion Response Receiver  505 , and Address Conversion Execution Notifier  506 . 
         [0034]    Line Controller  501  transmits and receives IP data in coordination with Gateway Controller  502 . 
         [0035]    Gateway Controller  502  executes conversion between a local area IP address and a global IP address when Telephone Terminal  60  or  61  exchanges data with IP Network  10  via Router  30 . In addition, upon receipt of a connection request from Telephone Terminal  60  or  61 , Gateway Controller  502  stores the audio relay IP address (the IP address of Gateway  50 ) and notifies Address Conversion Manager  503  that it has received a connection request. 
         [0036]    When Address Conversion Manager  503  receives the notification, it sends an address conversion request under the control of the telephone system to a telephone terminal other than Telephone Terminal  60 ; here it is Telephone Terminal  61  in coordination with Address Conversion Request Transmitter  504  to take over the gateway function. 
         [0037]    Although not shown in the illustrated embodiment, Address Conversion Manager  503  specifically monitors the performance of the gateway, and if it determines that the gateway does not have the processing capacity to perform address conversion on its own, it instructs Address Conversion Request Transmitter  504  to substitute the gateway function. 
         [0038]    Upon receipt of the instruction, Address Conversion Request Transmitter  504  generates an address conversion request and sends it to SIP Server  40  through Line Controller  501 . 
         [0039]    Although Telephone Terminal  61  is featured in this embodiment as a terminal with a gateway function, it can also be another gateway or other terminal with a gateway function (e.g., a personal computer with a gateway function). 
         [0040]    Upon receipt of the address conversion request, Telephone Terminal  61  sends back a response to accept the address conversion (hereinafter referred to as “address conversion response”) if it has enough capacity to perform the address conversion. 
         [0041]    Upon receipt of the address conversion response, Address Conversion Response Receiver  505  reports the reception of address conversion response to Address Conversion Manager  503  together with the IP address of the originator of the address conversion response (the IP address of Telephone Terminal  61 ). When Address Conversion Manager  503  receives the notification, it instructs Gateway Controller  502  to replace the audio relay IP address contained in the connection request with the IP address of Telephone Terminal  61 . 
         [0042]    Upon receipt of the instruction, Gateway Controller  502  converts the IP address of Gateway  50  in the connection request, which will be sent to Partner Telephone Terminal  20 , to the address of Telephone Terminal  61  before sending it to Partner Telephone Terminal  20 . 
         [0043]    This allows Gateway Controller  502  to instruct Address Conversion Execution Notifier  506 , via Address Conversion Manager  503 , to send an address conversion notice to Telephone Terminal  60  to notify that the audio relay IP address in the connection request has been converted to the IP address of Telephone Terminal  61 . 
         [0044]    Here the address conversion notice means, when Partner Telephone Terminal  20  sends the connection ready response (200 OK) to Telephone Terminal  60  relayed by the gateway, to convert the audio relay IP address that gave the connection ready response to the IP address of Telephone Terminal  61 . 
         [0045]    As illustrated above, Gateway  50  can exchange data with IP Network  10  using its own IP address conversion function, can monitor the data traffic received and transmitted by Telephone Terminal  60 , and when it receives a connection information, it can request address conversion to another terminal, i.e., Telephone Terminal  61 , enables the gateway function of address conversion for Telephone Terminal  60 , and receives a response from Telephone Terminal  61 , informing that the gateway function has been enabled. 
         [0046]      FIGS. 3 ,  4 , and  5  are tables specifying the IP addresses of the transmission data of an embodiment of the invention. 
         [0047]      FIG. 3  illustrates the transition of connection request (INVITE) between devices when Telephone Terminal  60  calls Partner Telephone Terminal  20 . The request is sent from Telephone Terminal  60  to SIP Server  40 , then through Gateway  50 , Router  30 , and to Partner Telephone Terminal  20 . As shown in  FIG. 3 , for each transmission block field  310 , the IP data field  311  is attached. An IP data field  311  consists of destination IP address field  312 , originator IP address field  313 , and audio relay IP address field  314 . 
         [0048]    Record  315  is the IP data sent from Telephone Terminal  60  to SIP Server  40 . In the illustrated embodiment, the destination IP address field  312  of the IP data block contains the data “LA 3 ,” which is the local IP address of SIP Server  40 ; the originator IP address field  313  contains the data “LA 4 ,” which is the local IP address of Telephone Terminal  60 ; and the audio relay IP address field  314  contains no data. 
         [0049]    Record  316  is the IP data sent from SIP Server  40  to Gateway  50 . In the illustrated embodiment, the destination IP address field  312  of the IP data block contains the data “LA 2 ,” which is the local IP address of Gateway  50 ; the originator IP address field  313  contains the data “LA 3 ,” which is the local IP address of SIP Server  40 ; and the audio relay IP address field  314  contains the data “LA 2 ,” which is the local address of Gateway  50 . 
         [0050]    Record  317  is the IP data sent from Gateway  50  to Router  30 . In the illustrated embodiment, the destination IP address field  312  of the IP data block contains the data “GA 1 ,” which is the global IP address of Partner Telephone Terminal  20 , and the originator IP address field  313  contains the data “LA 2 ,” which is the local IP address of Gateway  50 . The audio relay IP address field  314  in the data to be sent conventionally contains the data “LA 2 ,” which is the local address of Gateway  50 ; however, this invention replaces it with the local address of Telephone Terminal  61 , “LA 5 ,” to distribute the gateway function to Telephone Terminal  61 . 
         [0051]    Record  318  is the IP data sent from Router  30  to Partner Telephone Terminal  20 . Upon receipt of the connection request, Router  30  changes the originator IP address field  313  to “GA 2 ,” which is the global address of Router  30 , before sending the connection request to Partner Telephone Terminal  20 . 
         [0052]      FIG. 4  lists the IP data of audio data sent from Partner Telephone Terminal  20  to Router  30 , which is then passed on to Telephone Terminal  61  and to Telephone Terminal  60 . Partner Telephone Terminal  20  generates the audio data, to be sent to Telephone Terminal  60 , on the basis of the address information contained in the connection request received prior and transmits it. 
         [0053]    Record  319  is the audio data sent from Partner Telephone Terminal  20  to Router  30 . In the illustrated embodiment, the destination IP address field  312  contains the data “GA 2 ,” which is the global IP address of Router  30 ; the originator IP address field  313  contains the data “GA 1 ,” which is the global IP address of Partner Telephone Terminal  20 ; and the audio relay IP address field  314  contains the data “LA 5 ,” which is the local address of Telephone Terminal  61  that performs the address conversion. 
         [0054]    Record  320  is the audio data sent from Router  30  to Telephone Terminal  61 . In this audio data, the destination IP address field  312  contains the local address of Telephone Terminal  61 , “LA 5 ,” and the audio data is sent directly to Telephone Terminal  61  without being forwarded to Gateway  50 . The originator IP address field  313  contains the data “GA 1 ,” which is the global IP address of Partner Telephone Terminal  20 , and the audio relay IP address field  314  contains the data “LA 5 ,” which is the local address of Telephone Terminal  61 . 
         [0055]    Record  321  is the audio data sent from Telephone Terminal  61  to Telephone Terminal  60 . In this audio data, the destination IP address field  312  contains the data “LA 4 ,” which is the local IP address of Telephone Terminal  60 ; the originator IP address field  313  contains the data “LA 5 ,” which is the local IP address of Telephone Terminal  61 , and because the address conversion function has been enabled, the audio relay IP address field  314  is the data “LA 5 ,” which is the local address of Telephone Terminal  61 . 
         [0056]    As illustrated, the audio data from Partner Telephone Terminal  20  is sent to Telephone Terminal  60  using the address conversion function of Telephone Terminal  61  without the intervention of Gateway  50 . 
         [0057]      FIG. 5  shows the IP data of an audio data sent from Telephone Terminal  60  to Telephone Terminal  61 , then passing through Router  30 , and to Partner Telephone Terminal  20 . 
         [0058]    Record  322  is the audio data sent from Telephone Terminal  60  to Telephone Terminal  61 . The destination IP address field  312  contains the data “LA 5 ,” which is the local IP address of Telephone Terminal  61 , and the originator IP address field  313  contains the data “LA 4 ,” which is the local IP address of Telephone Terminal  60 . At that time, the audio relay IP address field  314  contains the data “LA 5 ,” which is the local address of Telephone Terminal  61 . 
         [0059]    Record  323  is the audio data sent from Telephone Terminal  61 , after receiving the previous audio data, to Router  30 . The destination IP address field  312  contains the data “GA 1 ,” which is the global IP address of Partner Telephone Terminal  20 ; the originator IP address field  313  contains the data “LA 5 ,” which is the local IP address of Telephone Terminal  61 ; and the audio relay IP address field  314  contains the data “LA 5 .” 
         [0060]    Record  324  is the audio data sent from Router  30  to Partner Telephone Terminal  20 . The destination IP address field  312  contains the data “GA 1 ,” which is the global IP address of Partner Telephone Terminal  20 ; the originator IP address field  313  contains the data “GA 2 ,” which is the global IP address of Router  30 ; and the audio relay IP address field  314  contains the data “LA 5 .” 
         [0061]      FIG. 6  is a flow chart showing the operation of Gateway  50  of an embodiment of the invention. Gateway  50  monitors the traffic sent and received from IP Network  10  at Gateway Controller  502  and waits for the reception of either a connection request (S 401 ), an address conversion response (S 405 ), a termination notice (S 408 ), a connection ready (S 410 ), or an audio data (S 413 ). 
         [0062]    Upon detection of a connection request (Yes for S 401 ), Address Conversion Manager  503  determines if the gateway has the capacity to execute its address conversion function (gateway function) or not (S 402 ). 
         [0063]    If it is determined to have the capability to execute the address conversion process (Yes for S 402 ), the connection request received is transmitted to Partner Telephone Terminal  20  (S 404 ). 
         [0064]    If it is determined not to have the capacity to execute the address conversion (No for S 402 ), an address conversion request for SIP Server  40  is generated and sent (S 403 ). 
         [0065]    Upon detection of an address conversion response (Yes for S 405 ), the address conversion response is analyzed to extract the originator IP address, which is converted to the audio relay IP address of the connection request (S 406 ). The modified connection request is then transmitted to Partner Telephone Terminal  20  as an address conversion notice (S 407 ). 
         [0066]    Upon detection of a termination notice (Bye) (Yes for S 408 ), Address Conversion Manager  503  instructs Address Conversion Request Transmitter  504  to transmit an address conversion release notice to Telephone Terminal  61  (S 409 ), which performed the distributed address conversion part of the gateway function. 
         [0067]    Upon detection of a connection ready (200 OK) (Yes for S 410 ), Address Conversion Manager  503  instructs Address Conversion Execution Notifier  506  to send an address conversion notice. Address Conversion Execution Notifier  506  converts the audio relay IP address of the connection ready signal (200 OK) to the IP address of Telephone Terminal  61  (S 411 ), and transmits the converted connection ready signal to Telephone Terminal  60  as an address conversion notice (S 412 ). 
         [0068]    Upon receiving the address conversion notice, Telephone Terminal  60  transmits the audio data to Telephone Terminal  61 . 
         [0069]    Upon detection of an audio data (Yes for S 413 ), an address conversion between the local address and the global address is performed as a part of a normal function of a gateway (S 414 ), and the audio data, whose address has been converted, is sent to the destination device (S 415 ). 
         [0070]      FIG. 7  is a block diagram showing the configuration of Telephone Terminal  60  and Telephone Terminal  61  of an embodiment of the invention. 
         [0071]    Telephone Terminal  60  consists of Terminal Controller  602 , which mainly controls the calling function; Keypad  603 , which consists of pushbuttons and a hook switch; Display  604  including LCDs; and Sound Source  605 , which consists of a microphone and a speaker. SIP Section  607  establishes the connection with SIP Server  40 . RTP Processor  606 , which converts audio data from Sound Source  605  into an IP data on the basis of the instruction of SIP Section  607  and transmits the converted data via Line Controller  601 , provides the telephone functionalities of originating/accepting calls. 
         [0072]    In the case of Telephone Terminal  61 , which distributes part of the gateway function, Address Conversion Request Receiver  609  receives the address conversion request data from Gateway  50  and notifies it to Address Conversion Controller  608 . The IP address of Partner Telephone Terminal  20  is attached to the received address conversion request data. If the address conversion process of another terminal is already in progress at the telephone terminal, Address Conversion Controller  608  concludes that the execution of address conversion is not possible, and if not, address conversion is possible. The address conversion response is then transmitted from Address Conversion Response Transmitter  610 . Hereafter, Address Conversion Controller  608  performs address conversion for the multimedia data exchanged between Telephone Terminal  60  and Partner Telephone Terminal  20 . 
         [0073]      FIG. 8  is a flow chart showing the operation of Telephone Terminal  61  of an embodiment of the invention. All communication functions of Telephone Terminal  61  other than the one of gateway are controlled at the Terminal Controller  602 ; therefore, the description of Telephone Terminal  61  is omitted in this flow chart. If an address conversion request from Gateway  50  is received at the Address Conversion Request Receiver  609  (Yes for S 601 ), Address Conversion Controller  608  checks the execution status of the address conversion process of other telephone terminals. If no execution is carried out, i.e., it is possible to perform the task (Yes for S 602 ), Address Conversion Controller  608  sets the IP address of its telephone terminal inside the address conversion response data (S 603 ) and transmits the response to Gateway  50  from Address Conversion Response Transmitter  610  (S 604 ). 
         [0074]    With this operation, Telephone Terminal  61  enables its gateway function and performs distributed processing of address conversion. If an address conversion release is received (Yes for S 605 ) instead of an address conversion request (No for S 601 ), a cancellation of the gateway function (S 606 ) is recognized by Address Conversion Controller  608 . If normal data is received (Yes for S 607 ) instead of an address conversion release (No for S 605 ), the terminal performs an address conversion as a gateway operation (S 608 ). If the data received is not normal (No for S 607 ), it waits for the reception of the next data in the standby mode. 
         [0075]      FIG. 9  is a sequential diagram of the gateway operation of an embodiment of the invention. When Telephone Terminal  60  performs the operation of making an external call (S 701 ), a connection request (INVITE) is sent to SIP Server  40  and the SIP Server then sends the connection request (INVITE) to Gateway  50  to pass it on to IP Network  10  (S 702 ). 
         [0076]    Gateway  50  sends the notice of processing (100 Trying) to Telephone Terminal  60  via SIP Server  40  (S 703 ). Once a connection request (INVITE) is received, Gateway  50  sends an address conversion request to SIP Server  40  to distribute the address conversion part of the gateway function (S 704 ). Here the address conversion request utilizes the INFO message of the SIP protocol and is sent to Telephone Terminal  61  via SIP Server  40  (S 705 ). Telephone Terminal  61  sends an address conversion response to Gateway  50  if it is capable of performing the address conversion (S 706 ). 
         [0077]    Gateway  50  transmits the connection request (INVITE) sent from Telephone Terminal  60  to Partner Telephone Terminal  20  via Router  30  (S 707 ). Here the IP address of Telephone Terminal  61 , where it responded to the gateway distribution, is transmitted as an address conversion execution notice in place of the IP address of Gateway  50 . As a result, Partner Telephone Terminal  20  recognizes Telephone Terminal  61  from the Session Description Protocol (SDP), which specifies the address for the audio data attached to the connection request, and hereafter, transmits all audio data to Telephone Terminal  61 . 
         [0078]    Partner Telephone Terminal  20  will not be requested to respond differently. All it has to do is to use the IP address listed in the SDP section of the audio data attached to the connection request (INVITE) sent by the above SIP server. Normally, the destination IP address for sending audio data of the conversation partner, such as the IP address of a gateway, is specified here. In this invention, IP address of Telephone Terminal  61 , which distributes the gateway function, is used in place of the IP address of the aforementioned gateway. This embodiment defines separately the address conversion notice as the connection request with the aforementioned modified IP. 
         [0079]    Partner Telephone Terminal  20  returns the notice of processing (100 Trying) to Gateway  50  (S 708 ). Next, Partner Telephone Terminal  20  returns the ringing signal (180 Ringing) to Telephone Terminal  60  via Gateway  50  and SIP Server  40  (S 709 ). When Partner Telephone Terminal  20  responds to the call initiated by Telephone Terminal  60  (S 710 ), the successful call signal (200 OK) is sent to Gateway  50  (S 711 ). 
         [0080]    When the successful call signal (200 OK) is sent to Telephone Terminal  60  via SIP Server  40 , Gateway  50  transmits the IP address of Telephone Terminal  61 , which responded to the gateway distribution (address conversion notice) (S 712 ). Telephone Terminal  60  returns the acknowledge signal (ACK) to Partner Telephone Terminal  20  via SIP Server  40  and Gateway  50  (S 713 ). When Telephone Terminal  60  and Partner Telephone Terminal  20  go into conversation (S 714 ), audio data (RTP) are sent to Telephone Terminal  61  that responded to the gateway distribution (S 715 ). 
         [0081]    Telephone Terminal  61  sends the audio data sent from Telephone Terminal  60  to Partner Telephone Terminal  20 . The audio data (RTP) from Partner Telephone Terminal  20  is transmitted to Telephone Terminal  60  via Telephone Terminal  61  (S 716 ). When Telephone Terminal  60  performs the operation of terminating the call (S 717 ), the release signal (Bye) is sent to the gateway via SIP Server  40  (S 718 ). 
         [0082]    Gateway  50  sends an INFO message defined by the IP protocol to SIP Server  40  (S 719 ) to notify Telephone Terminal  61 , which responded to the gateway distribution, of the address conversion release (S 720 ). Gateway  50  sends the shutdown signal (Bye) to Partner Telephone Terminal  20  to cut off the connection (S 721 ). 
         [0083]    Partner Telephone Terminal  20  reports the confirmation (200 OK) to Telephone Terminal  60  via Gateway  50  and SIP Server  40  (S 723 ) once the cutoff operation (S 722 ) is performed. Note that in case of an incoming call, the operation starts with Gateway  50 &#39;s reception of the connection request (INVITE) sent by Partner Telephone Terminal  20  via Router  30 . 
       Second Embodiment 
       [0084]      FIG. 10  is a sequence chart of the telephone terminals of another embodiment of the invention. Although this sequence is basically the same as the one shown in  FIG. 9 , distributed processing of the gateway function is performed by Telephone Terminal  60 , which initiates or accepts telephone calls, rather than Telephone Terminal  61  to reduce the audio data processing load on Gateway  50 . 
         [0085]    Operations that are different from those shown in  FIG. 9  are the ones that are executed when there exists no telephone terminal other than Telephone Terminal  60  that initiates or accepts calls to which Gateway  50  sends the address conversion request for distributed processing (S 805 ). In other words, the address conversion request is sent to Telephone Terminal  60 , which initiated or accepted a call (S 806 ). 
         [0086]    Upon receipt of an address conversion request, Telephone Terminal  60  enables the distributed processing of the gateway function by returning an address conversion response (S 807 ). Next, when Gateway  50  sends a connection request (INVITE) to the telephone service SIP Server  40 , the address of Telephone Terminal  60 , instead of the address of Gateway  50 , is sent as the address conversion execution notice. 
         [0087]    Hereafter, the sequence is same as that shown in  FIG. 9 , and the exchange of audio data between Partner Telephone Terminal  20  and Telephone Terminal  60  is carried out with Telephone Terminal  60  operating as a gateway. The termination of the connection will follow a similar sequence, as shown in  FIG. 9 . 
         [0088]    Although the address conversion request is sent to SIP Server  40 , which selects Telephone Terminal  61  to relay the address conversion request in this embodiment, this application does not restrict the operation to this manner. For example, Gateway  50  may store, in its memory, information of other terminals that also have a gateway function, or even check whether the gateway function is used. 
         [0089]    This invention provides the means for direct control and has the benefit of reducing the load on the SIP server. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
         
           
               10 : IP network 
               20 : Partner telephone terminal 
               30 : Router 
               40 : SIP server 
               50 : Gateway 
               60 : Telephone terminal 
               70 : LAN 
               501 : Line controller 
               502 : Gateway controller 
               503 : Address conversion manager 
               504 : Address conversion request transmitter 
               505 : Address conversion response receiver 
               506 : Address conversion execution notifier 
               601 : Line controller 
               602 : Terminal controller 
               603 : Keypad 
               604 : Display 
               605 : Sound source 
               606 : RTP processor 
               607 : SIP section 
               608 : Address conversion controller 
               609 : Address conversion request receiver 
               610 : Address conversion request transmitter 
             GA 1 : Global IP address of Partner Telephone Terminal  20   
             GA 2 : Global IP address of Router  30   
             LA 1 : Local IP address of Router  30   
             LA 2 : Local IP address of Gateway  50   
           
         
       
     
         [0117]    LA 3 : Local IP address of SIP Server  40 
       LA 4 : Local IP address of Telephone Terminal  60     LA 5 : Local IP address of Telephone Terminal  61