Abstract: A communication system and a security assurance device are proposed, which are capable of assuring that a target party for communication is implementing security countermeasures. A server 3 transmits information 104 necessary for AC issuance to a security assurance authority 2. The security assurance authority 2 verifies the security of the server 3 during communication based upon this information necessary for AC issuance 104. And, when the security of the server 3 during communication is confirmed, the security assurance authority 2 issues an AC 105 which proves the security of the server 3 during communication, and transmits it to the server 3. Upon receipt of this AC 105, the server 3 transmits the AC 105 to a client 4, according to a connection request from the client 4. And, upon receipt of this AC 105, the client 4 verifies the security during communication of the server 3, based upon the AC 105.

Abstract: An optical communication system is formed by connecting a base station to user stations. Each user station has a transmitting section for upstream communication. The base station has a light source which supplies transmission light used for upstream communication.

Abstract: A communication system and a security assurance device are proposed, which are capable of assuring that a target party for communication is implementing security countermeasures. A server 3 transmits information 104 necessary for AC issuance to a security assurance authority 2. The security assurance authority 2 verifies the security of the server 3 during communication based upon this information necessary for AC issuance 104. And, when the security of the server 3 during communication is confirmed, the security assurance authority 2 issues an AC 105 which proves the security of the server 3 during communication, and transmits it to the server 3. Upon receipt of this AC 105, the server 3 transmits the AC 105 to a client 4, according to a connection request from the client 4. And, upon receipt of this AC 105, the client 4 verifies the security during communication of the server 3, based upon the AC 105.

Abstract: An optical communication system is formed by connecting a base station to user stations. Each user station has a transmitting section for upstream communication. The base station has a light source which supplies transmission light used for upstream communication.

Abstract: An adaptive filter system has a first and a second filter subsystem of like construction, each having a series of delay elements for imparting a unit delay of one sampling interval to successive input samples in order to concurrently obtain a set of input samples of different sampling times. Each set of input samples are multiplied by respective coefficients, and the resulting values are added together for comparison with a reference signal. The coefficients are updated for each new set of input samples. For such updating, the first subsystem uses the step gain that is fixed at one, whereas the step gain used by the second subsystem is varied with time for faster convergence and smaller convergence error.