The present invention relates to the client machine and the server machine and the like which are connected to the communication line, and answers are accurately given to a question of a user of the client machine according to a level of that question. The network apparatus for wireless transmissionreception of data streams includes management information on wireless channels used for the data streams transmitted in a wireless manner among apparatuses in a network. The optical coupling device may include a refractive medium between the first and second conic reflectors. In order to prevent withdrawal of the latching member from the hub a stop in the hub maintains the teeth in engagement with each other thereby maintaining the band in pressure engagement with a circumferential region of a pipe.