| 摘要 |
<p>PURPOSE:To easily and surely suppress the waste of communication resources by finding that a call established in a public packet switching network via a private packet switching network is allowed to stand uselssly by such a simple and secure method as to detect whether the response of incoming call packet communications to a packet terminal is present or not. CONSTITUTION:A means to verify the validity of the call established at every logical channel is provided. The logical channel having established a call decides whether the packet terminal responds to an incoming call packet transmitted to the packet terminal by the incoming call receiving packet of the same logical channel as that of the incoming call packet, thereby judging that the call established in the logical channel is invalid. Thus a private DSW 104B can detect invalid calls left on a GWS 101 and a PSDN 100, and forms and transmits a restoration request packet CQ by itself, whereby invalid calls are automatically cut and the operation is restored.</p> |
