Communication Method, Communication Apparatus, and Communication System

Abstract

A network that is to execute transcoding is fixed. IMS networks (SBC 1a and SBC 1b) set an information element that requests either of the IMS networks to execute transcoding into the SDP, and use that information element to select the IMS network (SBC 1a or SBC 1b) that is to execute transcoding between the IMS networks (between SBC 1a and SBC 1b). Then, the selected IMS network executes transcoding of media data.

1 . A communication method executed between a plurality of communication devices, the method comprising, when a certain communication device out of the communication devices is to execute transcoding of media data, causing the certain communication device to perform
 a first step of storing a codec type currently in use that is determined by Session Description Protocol (SDP) negotiation into a codec information storing unit,   a second step of receiving a Session Initiation Protocol (SIP) message containing SDP offer, and   a third step of transmitting the SIP message containing the SDP offer that includes a codec type currently in use in a forwarding destination.   
     
     
         2 . The communication method according to  claim 1 , wherein
 if the SDP offer in the received SIP message includes a codec type currently in use in a forwarding source, the third step involves including the codec type currently in use in the forwarding destination into the SDP offer in the SIP message to be transmitted.   
     
     
         3 . The communication method according to  claim 1 , wherein
 if the SDP offer in the received SIP message does not include a codec type currently in use in a forwarding source and if the certain communication device is capable of transcoding between the codec type included in the SDP offer and the codec type currently in use in the forwarding destination, the third step involves including the codec type currently in use in the forwarding destination into the SDP offer in the SIP message to be transmitted.   
     
     
         4 . A communication method executed between a plurality of communication devices, the method comprising causing a certain communication device of the communication devices to:
 store a codec type currently in use that is determined by Session Description Protocol (SDP) negotiation into a codec information storing unit and   if the certain communication device is determined not to execute transcoding of media data and receives a Session Initiation Protocol (SIP) message containing SDP offer that includes a codec type currently in use in a forwarding source, forward the SIP message without adding the codec type to the SDP offer.   
     
     
         5 . A communication device, comprising:
 a transcoding unit that executes transcoding of media data;   a codec information storing unit that stores a codec type currently in use that is determined by Session Description Protocol (SDP) negotiation; and   an SDP processing unit that, if a Session Initiation Protocol (SIP) message containing SDP offer is received, includes a codec type currently in use in a forwarding destination into the SDP offer when forwarding the SIP message.   
     
     
         6 . A communication device, comprising:
 a codec information storing unit that stores a codec type currently in use that is determined by Session Description Protocol (SDP) negotiation; and   an SDP processing unit that, if the communication device is determined not to execute transcoding of media data and receives a Session Initiation Protocol (SIP) message containing an SDP offer that includes a codec type currently in use in a forwarding source, forwards the SIP message without adding the codec type to the SDP offer.   
     
     
         7 . A communication system, comprising:
 a first communication device; and   a second communication device, wherein   the first communication device includes
 a codec information storing unit that stores a codec type currently in use that is determined by Session Description Protocol (SDP) negotiation and 
 an SDP processing unit that, if the first communication device is determined not to execute transcoding of media data and receives a Session Initiation Protocol (SIP) message containing an SDP offer that includes a codec type currently in use in a forwarding source, forwards the SIP message to the second communication device without adding the codec type into the SDP offer, and 
   the second communication device includes
 a transcoding unit that executes transcoding of media data, 
 a codec information storing unit that stores a codec type currently in use that is determined by the SDP negotiation, and 
   an SDP processing unit that, if the SIP message is received, includes a codec type currently in use in a forwarding destination into the SDP offer when forwarding the SIP message.