A communication system, comprising: a mobile terminal; a base station; an operation/maintenance server; and a gateway that has a deep packet inspection, DPI, function configured to detect whether or not uplink data received from said mobile terminal is illegal traffic, wherein said base station is configured to, if said base station detects that an amount of the traffic of said uplink data exceeds a threshold, transmit an alarm, that denotes that the amount of the traffic of said uplink data exceeds the threshold, to said operation/maintenance server, wherein said operation/maintenance server is configured to, if said operation/maintenance server receives said alarm from said base station, transmit to said gateway an activation command that causes said gateway to activate said DPI function, wherein said gateway is configured to, if said gateway detects that said uplink data is illegal traffic based on said DPI function, transmit to said operation/maintenance server a detection notification that denotes that said uplink data is illegal traffic, wherein said operation/maintenance server is configured to, if said operation/maintenance server receives said detection notification from said gateway, transmit a stop request that requests said base station to stop transmitting said uplink data, and wherein said base station is configured to, once said base station has received said stop request from said operation/maintenance server, even if said base station receives an allocation request that requests uplink resources from said mobile terminal, not allocate the uplink resources to said mobile terminal. a mobile terminal; a base station; an operation/maintenance server; and a gateway that has a deep packet inspection, DPI, function configured to detect whether or not uplink data received from said mobile terminal is illegal traffic, wherein said base station is configured to, if said base station detects that an amount of the traffic of said uplink data exceeds a threshold, transmit an alarm, that denotes that the amount of the traffic of said uplink data exceeds the threshold, to said operation/maintenance server, wherein said operation/maintenance server is configured to, if said operation/maintenance server receives said alarm from said base station, transmit to said gateway an activation command that causes said gateway to activate said DPI function, wherein said gateway is configured to, if said gateway detects that said uplink data is illegal traffic based on said DPI function, transmit to said operation/maintenance server a detection notification that denotes that said uplink data is illegal traffic, wherein said operation/maintenance server is configured to, if said operation/maintenance server receives said detection notification from said gateway, transmit a stop request that requests said base station to stop transmitting said uplink data, and wherein said base station is configured to, once said base station has received said stop request from said operation/maintenance server, even if said base station receives an allocation request that requests uplink resources from said mobile terminal, not allocate the uplink resources to said mobile terminal.