Abstract: In IP communication, an authentication code AC1 uniquely generated by a receiving-side communication device 1b is sent to an originating-side communication device 1a (S1, S2), and stored in the originating-side communication device (S3). Packets in which the stored authentication code is embedded are sent to the receiving-side communication device 1b on connection from the originating-side communication device 1a to the receiving-side communication device 1b (S4), and it is determined at the receiving-side communication device whether the originating-side communication device is true or false depending on if the authentication code sent from the receiving-side communication device is contained in the packets received from the originating-side communication device or not (S5).

Abstract: In IP communication, an authentication code AC1 uniquely generated by a receiving-side communication device 1b is sent to an originating-side communication device 1a (S1, S2), and stored in the originating-side communication device (S3). Packets in which the stored authentication code is embedded are sent to the receiving-side communication device 1b on connection from the originating-side communication device 1a to the receiving-side communication device 1b (S4), and it is determined at the receiving-side communication device whether the originating-side communication device is true or false depending on if the authentication code sent from the receiving-side communication device is contained in the packets received from the originating-side communication device or not (S5).

Abstract: A system for determining whether spoofing occurs at an activating communication line under the condition that a connection by three-way handshake can be established between activating and activated communication lines regardless of the spoofing. Authentication units are arranged above communication terminal devices respectively. While a three-way handshake is executed once between the communication terminal devices, a three-way handshake is executed twice between the associated communication lines. One communication line activates the other communication line, and when a connection by a first three-way handshake is established between the communication lines, the connection is disconnected.

Abstract: Communication devices to an IP network through communication lines to each of which a unique identification number is assigned and, in each communication device, the identification numbers of other communication devices allowed to communicate with the each communication device are registered, and the communication lines are uniquely connected for data communication by a three-way handshake based on the identification numbers. A communication line activates another communication line. When a connection is established, the connection is disconnected. It is determined at the activated communication line if a response signal from the activating communication line as a response to a call back signal sent to the activating communication line at a predetermined timing arrives, and it is determined at the activating communication line if a call back signal from the activated communication line arrives. Data communication is performed only when both the activating and activated communication lines are validated.

Abstract: Pulses are produced in accordance with physical quantity changes in order to express the amount of change by count of the pulses produced. The changes are input to a convertor which converts them to corresponding electrical output values which are made available to a sample and hold circuit and to a first input of a comparator. An output value accepted from the convertor is held, as a held value, in the sample and hold circuit and provided therefrom to a second input of the comparator. The comparator produces an output pulse, so as ultimately to provide a trigger pulse and to be counted, only when the first input of the comparator differs from the second input thereof by a preset reference amount. At each trigger pulse, the sample and hold circuit accepts the next available electrical output value from the convertor as the value to be hold and provided to the comparator.