Method and data network for communicating data content, in particular in an elevator system

A data network for communicating data content, the data network comprising:

• a master unit;
• a plurality of slave units connected with the master unit via data communication paths for exchanging data telegrams between one another, wherein the master unit and the slave units are connected in series to form a chain via the data communication paths;
• wherein each of the data telegrams includes a header, a datagram region and a checksum, the datagram region being adapted for serial storage of a plurality of datagrams, each of the datagrams including a piece of data content to be communicated, and wherein the checksum is calculated uniquely on a basis of bits in a remainder of the data telegram;
• wherein the master unit has a master processor unit and at least one data connection and each of the slave units has an associated processor unit and first and second data connections;
• wherein the master unit is adapted to transmit the data telegrams via the at least one data connection to a first slave unit of the slave units on an outward data path up to a last slave unit of the slave units;
• wherein each of the slave units, except the last slave unit, is adapted to forward the data telegrams received at the first data connection from a direction from the master unit in a direction toward the last slave unit via the second data connection, and to forward the data telegrams received at the second data connection from a direction from the last slave unit in a direction toward the master unit via the first data connection;
• wherein the last slave unit is adapted to initiate a data return path by returning the data telegrams received at the first data connection from the direction from the master unit in the direction toward the master unit via the first data connection;
• wherein each of the slave units is adapted to modify the data telegrams exclusively during the data return path;
• and
• wherein the processor unit associated with at least one of the slave units is adapted to read and evaluate the data telegrams on the outward data path and, when any of the data telegrams contains a request to the at least one slave unit to transmit information to the master unit on the data return path, the processor unit associated with the at least one slave unit begins compiling the requested information immediately after receiving and evaluating the corresponding request.