A subscriber in a communication system for transmitting and receiving data telegrams, wherein a data telegram includes reference data or user data and an identifier. , m1 represents an integer from 1 to 2 and n1 represents an integer from 1 to 3. Before a mobile entity is used to carry the message, a determination is made as to whether the direction of travel of the mobile entity concerned is generally towards either the target receiver or an intermediate staging post suitable for progressing the message towards the target receiver. In response to the search, the processor may find additional information relating to the user stored in the network. The movable portion moves between the first and second substrates due to electrostatic attraction that develops between the movable electrode and the stationary electrode.