Abstract: In a cable modem system utilizing a DHCP to dynamically allocate an IP address to a subscriber terminal, a DHCP server address notifying portion of a cable modem termination system notifies a cable modem of a DHCP server address, a DHCP relay agent of the cable modem relays DHCP messages as a relay agent, an IP address detector detects the IP address from the DHCP message, an IP address storage stores the IP address, and a packet filtering portion discards a packet having a source IP address other than the IP address stored in the IP address storage when the packet is received from the subscriber terminal.

Abstract: A meter-rate billing system is disclosed in which billing is performed according to an interval while a subscriber uses a network actually, without any exclusive device. The meter-rate billing system on a LAN system for controlling connections to other networks includes a table in which a subscriber information is registered, a LAN controller for retrieving the table according to said subscriber information when a subscriber accesses joining to said LAN system accesses the LAN system, registering the subscriber information in said table if the information has not been registered, updating the registration information if the subscriber information is registered, and deleting the registration information if the registration information is not updated within a predetermined interval, and a billing device for receiving the registration information stored in the table in every predetermined informing interval and judging an interval time during which the registration information is registered in the table.