Communication system and control server

摘要

When an IP terminal on the Internet side transmits a name resolution request, which requests to resolve the FQDN of a public server connected to a router, to a SIP/DNS server in which SIP and DNS cooperate to manage the status of the data line of the router and when the data communication line status of the router is a disconnect status, a data communication line connection request instruction is transmitted to the router. The router connects the data communication line and notifies the SIP/DNS server about the result. The SIP/DNS server transmits the IP address of the router to the IP terminal as a response.